RU2849989C2 - Electrotechnical steel sheet with oriented grain structure and method for its manufacture - Google Patents

Abstract

FIELD: electrical steel.

SUBSTANCE: the present invention relates to an electrical steel sheet with an oriented grain structure and a method for its manufacture, and can be used as a material for the iron core of a transformer. An electrical steel sheet with an oriented grain structure is proposed. The base steel sheet has a chemical composition containing, by mass %: si 2.5-4.5, Mn 0.01-1.00, N≤ 0.01, C≤ 0.01, solution.Al≤ 0.01, S≤ 0.01, Se≤ 0.01, P 0.00-0.05, Sb 0.00-0.50, Sn 0.00-0.30, Cr 0.00-0.50, Cu 0.00-0.50, Ni 0.00-0.50 and Bi 0.0000-0.0100, the remainder being Fe and impurities. The density B8 of the magnetic flux in the rolling direction of the sheet is greater than or equal to 1.93 T, the deformed area extending across the entire width of the sheet is periodically formed at intervals L of 3-30 mm in a direction crossing the rolling direction, this area has a width W of 0.2-30.6 mm; a protruding part having a maximum height D(_protrusion)of 1-5 μm is formed on one surface of this area, and a recessed part having a maximum depth D(_{recess) of} 1-4 μm is formed on the opposite surface.

EFFECT: material for the iron core of a transformer.

7 cl, 1 dwg, 6 tbl, 6 ex

Description

Field of technology to which the invention relates

[0001] The present invention relates to a grain-oriented electrical steel sheet and to a method for producing the same.

This application claims priority from Japanese Patent Application No. 2022-060901, filed in Japan on March 31, 2022, the contents of which are incorporated herein by reference.

Description of the prior art

[0002] Grain-oriented electrical steel sheet is a soft magnetic material and is mainly used as the material for transformer iron cores. Therefore, grain-oriented electrical steel sheet must have magnetic properties, such as high magnetization properties and low iron loss.

[0003] Iron loss is the power loss due to consumption in the form of thermal energy that occurs when the iron core is excited by an AC magnetic field, and the iron loss should be as low as possible from the viewpoint of energy conservation. The largest dominant factor in the iron loss characteristics is the magnetic flux density (for example, the magnetic flux density in a B8 magnetic field: 800 A/m), and the higher the value of the magnetic flux density, the lower the iron loss. In the grain-oriented electrical steel sheet, in order to increase the magnetic flux density, the crystal orientation is generally developed, during the manufacturing process, into the Goss orientation (in the {110}<001> orientation), which has excellent magnetic characteristics (the degree of development of the orientation increases). By refining the magnetic domain structure of the grain-oriented electrical steel sheet having a high magnetic flux density, low iron loss is realized. To increase the degree of orientation development according to the Goss orientation, high-temperature, long-term finish annealing is typically performed. Through finish annealing, grains in which the {110}<001> orientation develops, i.e., "Goss-oriented grains," grow to sizes on the order of cm by absorbing surrounding grains (during secondary recrystallization), so that the crystal orientations are aligned (the degree of orientation development increases).

[0004] In order to improve the degree of development of the orientation described above, in the technology described in Patent Documents 1 to 3, rapid heating is performed in the temperature increasing step during the decarburization annealing step to increase the number of Goss-oriented grains as the core of secondary recrystallization in the steel sheet. Subsequently, after secondary recrystallization, a large number of grains with crystal orientations having a small deviation from the Goss orientation are formed. The crystal structure with such a configuration achieves a high magnetic flux density.

List of bibliographic references

Patent documents

[0005] Patent Document 1

Unexamined Patent Application (Japan), First Publication Number H07-62436

Patent Document 2

Unexamined Patent Application (Japan), First Publication Number H10-280040

Patent Document 3

Unexamined Patent Application (Japan), First Publication No. 2003-096520

The essence of the invention

Problems solved by the invention

[0006] As a specific method for rapidly heating a steel sheet, methods such as high-power heating and induction heating are provided. However, in order to further reduce the iron loss by the above-described prior art, it is necessary to increase the temperature increase rate compared to the conventional approach. Therefore, it is necessary to increase the size of the equipment, which leads to an increase in the equipment cost and manufacturing cost. In addition, there is a possibility that the temperature non-uniformity in the steel sheet becomes large, and there is a possibility that deterioration in the shape of the steel sheet and variation in magnetic characteristics occur in the final product. In addition, when the temperature increase rate is increased compared to the conventional approach, Goss-oriented grains as secondary recrystallization nuclei are enriched, but {111}<112>-oriented grains, which promote the growth of Goss-oriented grains in the secondary recrystallization process, are reduced. As described above, there is a limit to increasing the degree of orientation development and realizing a high magnetic flux density only by simply increasing the temperature increase rate. When using grain-oriented electrical steel sheets as transformer core material, it is also important to increase the space factor. Here, the space factor schematically represents, in a stacked body formed by stacking multiple grain-oriented electrical steel sheets, the ratio of the total volume of the grain-oriented electrical steel sheets to the total volume (including voids) of the stacked body.

[0007] The present invention is made to solve the above-mentioned problems, and an object of the present invention is to provide a grain-oriented electrical steel sheet from which an iron core having a high magnetic flux density and a high space coefficient can be produced, and a method for producing the grain-oriented electrical steel sheet.

Solution to the problem

[0008] In order to solve the above-described problems, according to an aspect of the present invention, there is provided a grain-oriented electrical steel sheet, which is characterized in that the base steel sheet has a chemical composition containing, in mass%: Si: 2.5-4.5%, Mn: 0.01-1.00%, N: 0.01% or less, C: 0.01% or less, solution.Al: 0.01% or less, S: 0.01% or less, Se: 0.01% or less, P: 0.00-0.05%, Sb: 0.00-0.50%, Sn: 0.00-0.30%, Cr: 0.00-0.50%, Cu: 0.00-0.50%, Ni: 0.00-0.50% and Bi: 0.0000-0.0100%, wherein the remainder includes Fe and impurities, the magnetic flux density B8 in the rolling direction of the grain-oriented electrical steel sheet is 1.93 T or more, the deformed region extending across the entire width of the grain-oriented electrical steel sheet is periodically formed at an interval L of 3 mm or more and 30 mm or less in the direction intersecting the rolling direction of the grain-oriented electrical steel sheet, the deformed region has a width W of 0.2 mm or more and 30.6 mm or less, a protrusion having a maximum height D _protrusion of 1 μm or more and 5 μm or less is formed on one surface of the deformed region, and a recessed portion having a maximum depth D _recess of 1 μm or more and 4 μm or less is formed on the opposite surface.

[0009] According to another aspect of the present invention, there is provided a grain-oriented electrical steel sheet, which is characterized in that the base steel sheet has a chemical composition comprising, in mass%: Si: 2.5-4.5%, Mn: 0.01-1.00%, N: 0.01% or less, C: 0.01% or less, solution.Al: 0.01% or less, S: 0.01% or less, Se: 0.01% or less, P: 0.00-0.05%, Sb: 0.00-0.50%, Sn: 0.00-0.30%, Cr: 0.00-0.50%, Cu: 0.00-0.50%, Ni: 0.00-0.50% and Bi: 0.0000-0.0100%, wherein the residue includes Fe and impurities, the magnetic flux density B8 in the rolling direction of the grain-oriented electrical steel sheet is 1.93 T or more, the deformed region extending across the entire width of the grain-oriented electrical steel sheet is periodically formed at an interval L of 3 mm or more and 30 mm or less in the direction intersecting the rolling direction of the grain-oriented electrical steel sheet, the deformed region has a width W of 0.2 mm or more and 30.6 mm or less, a protrusion having a maximum height _{Dprotrusion of} 1 μm or more and 8 μm or less is formed on one surface of the deformed region, a recessed portion having a maximum depth _{Drecess of} 1 μm or more and 8 μm or less is formed on the opposite surface, and the protrusion has a steepness _2Dprotrusion /W of 0.0001 or more and less than 0.0050.

[0010] In the deformed region, the ratio of the area of grains whose crystal orientation deviates from the Goss orientation by 15° or more to the total area of the deformed region may be 5% or less.

[0011] The chemical composition of the base steel sheet may contain, in wt.%, one or more selected from the group consisting of: P: 0.01-0.05%, Sb: 0.01-0.50%, Sn: 0.01-0.30%, Cr: 0.01-0.50%, Cu: 0.01-0.50%, Ni: 0.01-0.50% and Bi: 0.0001-0.0100%.

[0012] According to another aspect of the present invention, there is provided a method for producing a grain-oriented electrical steel sheet, which is characterized in that the method includes a hot rolling step for heating a slab having a chemical composition comprising, in wt.%: Si: 2.5-4.5%, Mn: 0.01-1.00%, N: 0.01-0.02%, C: 0.02-0.10%, sol.Al: 0.01-0.05%, in total one or two of S and Se: 0.01-0.05%, P: 0.00-0.05%, Sn: 0.00-0.30%, Sb: 0.00-0.50%, Cr: 0.00-0.50%, Cu: 0.00-0.50%, Ni: 0.00-0.50% and Bi: 0.0000-0.0100%, wherein the remainder includes Fe and impurities, and for hot rolling the heated slab to form a hot-rolled steel sheet; a hot strip annealing step for annealing the hot-rolled steel sheet; a cold rolling step for performing cold rolling on the hot-rolled steel sheet after the hot strip annealing step to form a cold-rolled steel sheet; a decarburization annealing step for subjecting the cold-rolled steel sheet to decarburization annealing to form a decarburization annealed steel sheet; a finish annealing step for applying an annealing separator to the decarburization annealed steel sheet and then performing finish annealing that forms a glass film on the surface of the decarburization annealed steel sheet to form a finish annealed sheet; and an insulating film forming step of applying an insulating film forming liquid to the finish annealed sheet and then performing heat treatment so as to form an insulating film on the surface of the finish annealed sheet, the decarburization annealing step includes a partial rapid heating step of heating the cold rolled steel sheet to a temperature of 200°C or more and 550°C or less in a non-oxidizing atmosphere and under a tension of 0.2 kg/ ^mm2 or more and 1.2 kg/ ^mm2 or less and partially rapidly heating the surface of the cold rolled steel sheet over the entire width of the cold rolled steel sheet, at an interval L within the range represented by expression (1), in a direction intersecting the rolling direction; and a temperature raising step of raising the temperature of the cold-rolled steel sheet after the partial rapid heating step from a temperature range of 550°C or lower to a temperature range of 750-950°C at an average heating rate of 5°C/s or more and 2000°C/s or less in a non-oxidizing atmosphere; and the expressions (2) to (4) are satisfied when the average intensity applied to the portion to be partially and rapidly heated, which is subjected to partial rapid heating, is denoted as P (W), the diameter in the rolling direction of the portion to be partially and rapidly heated is denoted as Dl (mm), the diameter in the sheet width direction of the portion to be partially and rapidly heated is denoted as Dc (mm), the scanning speed in the sheet width direction of the portion to be partially and rapidly heated is denoted as Vc (mm/s), the irradiation energy density is denoted as Up=4/π x P/(Dl x Vc), and the instantaneous power density is denoted as Ip=4/π x P/(Dl x Dc).

3 mm ≤ L ≤ 30 mm (1)

L/50 ≤ Dl ≤ L/2 (2)

5 J/ ^mm2 ≤ Up ≤ 48 J/ ^mm2 (3)

0.05 kW/mm ² ≤ Ip ≤ 4.99 kW/mm ² (4)

[0013] Here, the irradiation energy density Up can additionally satisfy expression (5).

5 J/mm ² ≤ Up < 62.5 x Dl J/mm ² (5)

[0014] The chemical composition of the slab may comprise, in wt.%, one or more selected from the group consisting of: P: 0.01-0.05%, Sn: 0.01-0.30%, Sb: 0.01-0.50%, Cr: 0.01-0.50%, Cu: 0.01-0.50%, Ni: 0.01-0.50% and Bi: 0.0001-0.0100%.

Advantages of the invention

[0015] According to the above aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet from which an iron core having a high magnetic flux density and a high space coefficient can be produced, and a method for producing the grain-oriented electrical steel sheet.

Brief description of the drawing

[0016] Fig. 1 is an explanatory view illustrating the appearance of a grain-oriented electrical steel sheet according to the present embodiment.

Embodiments of the invention

[0017] 1. Research by the authors of the present invention

Embodiments of the present invention will now be explained. First, the investigations conducted by the inventors of the present invention will be described. The inventors of the present invention conducted investigations into rapid heating technology using a new method to solve the above-described problems. As a result, the inventors of the present invention discovered that the Goss orientation can be effectively enriched in a steel sheet by applying various heating methods, such as a laser beam, electron beam, infrared heating, dielectric heating, microwave heating, arc heating, plasma heating, induction heating, or electric resistance heating, to a portion of the steel sheet, in particular, by instantaneously heating the surface layer (from the outermost surface to a layer approximately 1/5 t (t: sheet thickness)) from the outermost surface of the steel sheet. Furthermore, when the annealing temperature increase rate of a region other than the partially heated region of the present method is appropriately set, it is possible to realize a state in which {111}<112>, which is the lattice orientation of the coincident sites, is enriched in a region (including the region from the surface layer of the steel sheet to the rear surface of the heated surface) other than the partially heated region. As a result, it is possible to realize a grain-oriented electrical steel sheet having excellent magnetic properties.

[0018] However, in the method for producing the grain-oriented electrical steel sheet described above, since the steel sheet is partially heated rapidly, there is a problem in that the shape of the heated portion becomes poorer in quality (i.e., it is significantly deformed), and the fill factor decreases. In other words, when this grain-oriented electrical steel sheet is used in a transformer, there is a problem in that it does not sufficiently contribute to improving the efficiency of the transformer.

[0019] Thus, the present inventors have extensively conducted studies on a method for producing a grain-oriented electrical steel sheet capable of achieving both preferable magnetic characteristics and a preferable sheet shape even when the steel sheet is subjected to partial rapid heating, and as a result, have arrived at the following conclusions.

[0020] 2. Method for manufacturing a sheet of electrical steel with an oriented grain structure

The method for producing a grain-oriented electrical steel sheet according to the present embodiment includes the following steps.

(1) A hot rolling step for heating a slab having a predetermined composition and hot rolling the heated slab so as to form a hot rolled steel sheet;

(2) hot strip annealing step for annealing the hot rolled steel sheet;

(3) a cold rolling step for performing cold rolling on the hot rolled steel sheet after the hot strip annealing step, so as to form a cold rolled steel sheet;

(4) a decarburization annealing step of subjecting the cold rolled steel sheet to decarburization annealing so as to form a decarburized annealed steel sheet;

(5) a finish annealing step of applying an annealing separator to the decarburized annealed steel sheet and then performing finish annealing that forms a glass film on the surface of the decarburized annealed steel sheet so as to form a finish annealed sheet; and

(6) an insulating film forming step of applying an insulating film forming liquid to the finish annealed sheet and then performing heat treatment so as to form an insulating film on the surface of the finish annealed sheet.

Each step is described below. For steps or conditions not described, known steps and conditions may apply.

[0021] 2-1. Hot rolling stage

In the hot rolling step, a slab having a predetermined composition is heated, and the heated slab is hot rolled to form a hot-rolled steel sheet. The heating temperature is not particularly limited, but is preferably 1100°C or higher. When the heating temperature is lower than 1100°C, the inclusion formed in the slab cannot be dissolved, and there is a risk that the inhibitors are not sufficiently formed during the hot rolling step or the hot strip annealing step described later. Therefore, the heating temperature of the slab is preferably 1100°C or higher. The upper limit of the heating temperature of the slab is not limited, but heating above 1450°C may melt the slab, making hot rolling difficult. Therefore, the heating temperature of the slab is preferably 1450°C or lower.

[0022] The hot rolling conditions are not particularly limited and can be appropriately set based on the required characteristics. The thickness of the hot rolled steel sheet obtained by hot rolling is preferably, for example, in the range of 1.0 mm or more and 4.0 mm or less.

[0023] 2-2. Chemical composition of the slab

To achieve the desired magnetic properties as grain-oriented electrical steel sheet, the chemical composition of the hot-rolled slab is within the following range. In the description below, unless otherwise specified, "%" represents "wt.%" relative to the total slab weight.

[0024] Si: 2.5-4.5%

Silicon (Si) is an extremely effective element for increasing the electrical resistance (resistivity) of steel, thereby reducing eddy current losses, which constitute a portion of iron losses. When the Si content of a slab is less than 2.5%, the resistivity is low, and eddy current losses cannot be reduced sufficiently. Furthermore, since the steel undergoes a phase transformation during finish annealing, secondary recrystallization does not proceed sufficiently, and the desired magnetic flux density and low iron losses cannot be achieved. Therefore, the Si content of a slab is 2.5% or more. The Si content of a slab is preferably 2.6% or more, and more preferably 2.7% or more.

[0025] On the other hand, when the Si content exceeds 4.5%, the steel sheet becomes brittle, and the passability of the sheet during the manufacturing stage is noticeably deteriorated. Therefore, the Si content of the slab is 4.5% or less. The Si content of the slab is preferably 4.4% or less, more preferably 4.2% or less.

[0026] Mn: 0.01-1.00%

Manganese (Mn) is an important element that forms MnS or MnSe, which are among the main moderators. When the Mn content of the slab is less than 0.01%, the absolute amount of MnS or MnSe required to induce secondary recrystallization is insufficient. Therefore, the Mn content of the slab is 0.01% or greater. The Mn content is preferably 0.03% or greater, more preferably 0.06% or greater.

[0027] On the other hand, when the Mn content of the slab exceeds 1.00%, the steel undergoes phase transformation during finish annealing, secondary recrystallization does not proceed sufficiently, and the preferred magnetic flux density and low iron loss cannot be achieved. Therefore, the Mn content of the slab is 1.00% or less. The Mn content is preferably 0.98% or less, more preferably 0.96% or less.

[0028] N: 0.01-0.02%

Nitrogen (N) is an element that reacts with Al (acid-soluble aluminum), described below, to form AlN, which functions as a moderator. To form AlN sufficiently to function as a moderator, the N content is 0.01% or greater.

[0029] On the other hand, when the N content exceeds 0.02%, pores are formed in the steel sheet during cold rolling, the strength of the steel sheet increases, and the passability of the sheet during manufacturing deteriorates. Therefore, the N content of the slab is 0.020% or less.

[0030] C: 0.02-0.10%

Carbon (C) is an element that exhibits the effect of improving magnetic flux density, but when the C content of the slab exceeds 0.10%, the performance in the decarburization annealing step decreases. In addition, when the C content of the slab is large and decarburization is insufficient, the steel undergoes phase transformation during secondary recrystallization annealing (i.e., finish annealing), and secondary recrystallization does not continue sufficiently, resulting in the failure to achieve the desired magnetic flux density and low iron loss, or the magnetic performance deteriorates due to magnetic aging. Therefore, the C content of the slab is 0.10% or less. The lower the C content, the better for performance and iron loss reduction. From the perspective of performance and iron loss reduction, the C content is preferably 0.09% or less, and more preferably 0.08% or less.

[0031] On the other hand, when the C content of the slab is less than 0.02%, the effect of improving the magnetic flux density cannot be achieved. Therefore, the C content of the slab is 0.02% or more. The C content is preferably 0.04% or more, more preferably 0.06% or more.

[0032] solution.Al: 0.01-0.05%

Acid-soluble aluminum (sol.Al) is a constituent element of the main moderator among chemical compounds called "moderators"/inhibitors that affect secondary recrystallization in a grain-oriented electrical steel sheet, and is an essential element in terms of developing secondary recrystallization in the base steel sheet according to the present embodiment. When the content of sol.Al in the slab is less than 0.01%, AlN, which functions as a moderator, is not sufficiently formed, and secondary recrystallization becomes insufficient. Therefore, the content of sol.Al is 0.01% or more. The content of sol.Al is preferably 0.02% or more.

[0033] On the other hand, when the solution Al content exceeds 0.05%, AlN, which functions as a moderator, is not formed sufficiently, and secondary recrystallization becomes insufficient. Therefore, the solution Al content is 0.05% or less. The solution Al content is preferably 0.04% or less, and more preferably 0.03% or less.

[0034] In total, one or two of S and Se: 0.01-0.05%

Sulfur (S) and selenium (Se) are important elements that react with Mn to form the moderators MnS and MnSe. Since MnS or MnSe must be formed as a moderator, the slab may contain one of S and Se, or two of S and Se. When the sum of one or two of S and Se is less than 0.01%, a sufficient moderator is not formed. Therefore, the sum of one or two of S and Se is 0.01% or more. The sum of one or two of S and Se is preferably 0.02% or more.

[0035] On the other hand, when the total of one or two of S and Se exceeds 0.05%, hot embrittlement is caused, and hot rolling is very difficult. Therefore, the total of one or two of S and Se is 0.05% or less. The total of one or two of S and Se is preferably 0.04% or less, and more preferably is 0.03% or less.

[0036] The slab may contain one or more optional additional elements listed below, in addition to the elements described above.

[0037] P: 0.00-0.05%

Phosphorus (P) is an element that reduces machinability during rolling. By setting the P content to 0.05% or less, it is possible to suppress excessive reduction in machinability during rolling and suppress fracture during manufacturing. Therefore, the P content is 0.05% or less. The P content is preferably 0.04% or less, and more preferably 0.03% or less.

[0038] The lower limit of the P content is not limited and may include 0.00%, but P is also an element having the effect of improving texture and enhancing magnetic characteristics. To obtain this effect, the P content may be 0.005% or more or 0.01% or more.

[0039] Sn: 0.00-0.30%

Tin (Sn) is an element that improves magnetic properties. Therefore, Sn may be contained in the slab. When Sn is contained, the Sn content is preferably 0.01% or more to achieve the desired magnetic property improvement. The Sn content is preferably 0.03% or more, and more preferably 0.05% or more, taking into account both magnetic properties and film adhesion.

[0040] On the other hand, when the Sn content exceeds 0.30%, the glass film is noticeably deteriorated, and tension sufficient for refining magnetic domains cannot be obtained, resulting in deterioration of the iron loss characteristics. Therefore, the Sn content is 0.30% or less. The Sn content is preferably 0.20% or less, more preferably 0.10% or less.

[0041] Sb: 0.00-0.50%

Antimony (Sb) is an element that enhances magnetic properties. Therefore, it can be contained in the slab. When Sb is contained, the Sb content is preferably 0.01% or more to achieve the desired magnetic property enhancement effect. The Sb content is more preferably 0.02% or more.

On the other hand, when the Sb content exceeds 0.50%, the adhesion of the glass film deteriorates. Therefore, the Sb content is 0.50% or less. The Sb content is preferably 0.40% or less.

[0042] Cr: 0.00-0.50%

Chromium (Cr) is an element that promotes the occupancy rate of the Goss orientation in the secondary recrystallization structure, improves magnetic properties, and promotes glass film adhesion, similar to Sn and Cu described below. Therefore, it can be contained in the slab. To achieve the above effect, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.

[0043] On the other hand, when the Cr content exceeds 0.50%, Cr oxide is formed and the magnetic properties deteriorate. Therefore, the Cr content is 0.50% or less. The Cr content is preferably 0.30% or less, more preferably 0.10% or less.

[0044] Cu: 0.00-0.50%

Copper (Cu) is an element that promotes the occupancy rate of the Goss orientation in the secondary recrystallization structure and improves the adhesion of the glass film. Therefore, it can be contained. To achieve the above effect, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more.

[0045] On the other hand, when the Cu content exceeds 0.50%, the steel sheet becomes brittle during hot rolling. Therefore, the Cu content of the slab is 0.50% or less. The Cu content is preferably 0.30% or less, more preferably 0.10% or less.

[0046] Ni: 0.00-0.50%

Nickel (Ni) is an element effective in increasing electrical resistance and reducing iron loss. Ni is also effective in controlling the metallographic structure of hot-rolled steel sheets to improve magnetic properties. Therefore, Ni can be contained. To achieve the above effect, the Ni content is preferably 0.01% or more. A Ni content of 0.02% or more is more preferable.

[0047] On the other hand, when the Ni content exceeds 0.50%, secondary recrystallization may become unstable. Therefore, the Ni content is 0.50% or less. The Ni content is preferably 0.30% or less.

[0048] Bi: 0.0000-0.0100%

Bi has the effect of improving the retarder function and magnetic characteristics. However, when the Bi content exceeds 0.0100%, Bi has a negative impact on the formation of the glass film, and therefore the Bi content is preferably 0.0100% or less. The Bi content is preferably 0.0050% or less, and more preferably 0.0030% or less. The lower limit of the Bi content can be 0%, but since the above-described effect can be expected, the Bi content can be 0.0001% or more or 0.0005% or more.

[0049] Residue: Fe and impurities

The chemical composition of the slab used in the method for producing the grain-oriented electrical steel sheet according to the present embodiment may contain the above-described elements, and the remainder may be Fe and impurities. Here, the impurity is an element that is a contaminant extracted from ore or scrap as raw material, the production environment, etc., when the base steel sheet is industrially produced, and means an element that can be contained in an amount that does not adversely affect the performance of the grain-oriented electrical steel sheet according to the present embodiment.

[0050] The chemical composition of the slab described above can be measured by a general analytical method. For example, the components of steel can be measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). C and S can be measured by a combustion infrared absorption method, N can be measured by an inert gas melting method by thermal conductivity, and O can be measured by a non-dispersive infrared absorption method after inert gas melting.

[0051] 2-3. Hot strip annealing stage

Hot strip annealing is the annealing step for hot-rolled steel sheet produced during the hot rolling process. This annealing process induces recrystallization in the metallographic structure, allowing for the development of favorable magnetic properties.

[0052] In the hot strip annealing step of the present embodiment, the hot-rolled steel sheet produced in the hot rolling step can be annealed according to a known method. Methods for heating the hot-rolled steel sheet during annealing are not particularly limited, and a known heating method can be used. The annealing conditions are also not particularly limited, but, for example, the hot-rolled steel sheet can be annealed in a temperature range of 900-1200°C for 10 seconds to 5 minutes.

[0053] 2-4. Cold rolling stage

In the cold rolling stage, the hot-rolled steel sheet, following the hot strip annealing step, undergoes a multi-pass cold rolling process to form a cold-rolled steel sheet. Cold rolling can be a single-pass process, or it can be a multi-pass process that includes intermediate annealing between passes. This process can be accomplished by interrupting cold rolling and performing at least one or two intermediate annealings before the final cold rolling stage. Furthermore, the type of rolling equipment used in cold rolling is not limited and can include a tandem rolling mill, a reversible rolling mill, or a rolling method combining the two.

[0054] When performing intermediate annealing, it is preferable to maintain the intermediate annealing at a temperature of 1000-1200°C for 5-180 seconds. The annealing atmosphere is not particularly limited. The number of intermediate annealings is preferably three or less, taking into account the manufacturing cost. Before the cold rolling step, the surface of the hot-rolled steel sheet can be pickled under known conditions.

[0055] 2-5. Decarburizing annealing stage

In the decarburization annealing step, cold-rolled steel sheet undergoes decarburization annealing to form decarburized annealed steel sheet. During decarburization annealing, the cold-rolled steel sheet undergoes primary recrystallization, and C, which negatively affects magnetic properties, is removed from the steel sheet. The details of the decarburization annealing step are described below.

[0056] 2-6. Final annealing stage

In the finish annealing step, a predetermined annealing separator is applied to one or both surfaces of the decarburized annealed steel sheet obtained in the decarburization annealing step, and then finish annealing is performed. In this way, a finish annealed sheet is produced. Through finish annealing, grains in which the {110}<001> orientation develops, i.e., "Goss-oriented grains," grow to a size of about cm by absorbing surrounding grains (during secondary recrystallization) so that the crystal orientations are aligned (the degree of orientation development increases). Finish annealing is generally performed for a long time in a state in which the steel sheet is wound in the form of a coil. Therefore, before the finish annealing, an annealing separator is applied to the decarburized annealed steel sheet and dried to prevent jamming inside and outside the coil winding.

[0057] An annealing separator containing MgO as a main component (for example, containing 80% or more in terms of weight fraction) is used as an annealing separator to be applied. By using an annealing separator containing MgO as a main component, a glass film can be formed on the surface of the base steel sheet. When MgO is not the main component, the glass film is not formed. This is because the glass film is obtained from the chemical _{compound Mg2SiO4} or _{MgAl2O4 ,} and Mg required for the formation reaction is insufficient when MgO is not the main component. The glass film may or may not be formed.

[0058] The finishing annealing may be performed, for example, under conditions in which the temperature is raised to 1150-1250°C in an atmospheric gas containing hydrogen and nitrogen, and the annealing is performed in the temperature range for 10-60 hours.

[0059] 2-7. Stage of forming an insulating film

In the insulating film formation step, an insulating film-forming liquid is applied to the finish-annealed sheet, followed by heat treatment to form an insulating film on the surface of the finish-annealed sheet. This heat treatment forms an insulating film on the surface of the finish-annealed steel sheet. For example, the insulating film-forming liquid may contain colloidal silicon dioxide and phosphate. The insulating film-forming liquid may also contain chromium. Furthermore, to reduce iron loss, magnetic domain refinement treatment can be performed after the insulating film formation. For example, mechanical tension, such as a groove, can be applied using a roller, or linear thermal deformation can be applied using a laser, etc.

[0060] 2-8. Details of the decarburization annealing step

The decarburization annealing step is described in detail below. The decarburization annealing step includes a partial rapid heating step and a temperature increase step.

2-8-1. Partial rapid heating stage

In the partial rapid heating step, the cold-rolled steel sheet is heated to a temperature of 200°C or more and 550°C or less in a non-oxidizing atmosphere and under a tension of 0.2 kg/ ^mm2 or more and 1.2 kg/ ^mm2 or less, and the surface of the cold-rolled steel sheet is partially and rapidly heated over the entire width of the cold-rolled steel sheet, at an interval L within the range represented by expression (1), in a direction intersecting the rolling direction (for example, in a direction of 30-150 degrees, preferably 60-120 degrees, more preferably 80-100 degrees relative to the rolling direction, even more preferably approximately perpendicular to the rolling direction (90 degrees)).

3 mm ≤ L ≤ 30 mm (1)

[0061] A non-oxidizing atmosphere is, for example, a nitrogen atmosphere. When the hydrogen gas in the atmosphere is less than 4% by volume, the oxygen content may be 100 ppm or less. When the atmosphere in the partial rapid heating step is not a non-oxidizing atmosphere, deterioration in magnetic properties may occur due to oxidation of the portion (partially and rapidly heated portion) irradiated with the laser described below, and deterioration in magnetic properties may occur due to oxidation during heating of the cold-rolled steel sheet.

[0062] The heating temperature of the cold-rolled steel sheet is 200°C or more and less than 550°C. When the heating temperature of the cold-rolled steel sheet is lower than 200°C, the shape of the cold-rolled steel sheet may deteriorate due to insufficient temperature. When the heating temperature of the cold-rolled steel sheet exceeds 550°C, deterioration of magnetic properties may occur due to relaxation. The heating temperature of the cold-rolled steel sheet is preferably 250°C or more, and more preferably 300°C or more. The heating temperature of the cold-rolled steel sheet is preferably 500°C or less, and more preferably 450°C or less.

[0063] The tension applied to the cold-rolled steel sheet is 0.2 kg/ ^mm2 or more and 1.2 kg/ ^mm2 or less in the rolling direction (in the direction of sheet passage). When the tension is less than 0.2 kg/ ^mm2 , deterioration in the shape of the cold-rolled steel sheet may occur due to insufficient tension. When the tension exceeds 1.2 kg/ ^mm2 , deterioration in magnetic properties may occur. The tension is preferably 0.3 kg/ ^mm2 or more, more preferably 0.4 kg/ ^mm2 or more. The tension is preferably 1.1 kg/ ^mm2 , more preferably 1.0 kg/ ^mm2 .

[0064] Specific methods for partially rapidly heating a cold-rolled steel sheet include irradiation with a laser beam or an electron beam (hereinafter collectively referred to as "beams"), infrared heating, dielectric heating, microwave heating, arc heating, plasma heating, induction heating, electric resistance heating, and the like. In the present embodiment, the surface of the cold-rolled steel sheet is partially rapidly heated by irradiating the entire width of the cold-rolled steel sheet with a beam at an interval of L. Here, the interval of L is 3 mm or more and 30 mm or less. When the interval of L is less than 3 mm, the effect of the present embodiment cannot be achieved. When the interval of L exceeds 30 mm, the effect of the present embodiment is reduced.

[0065] The interval L is preferably 5 mm or more, and more preferably 7 mm or more. The interval L is preferably 25 mm or less, and more preferably 20 mm or less.

[0066] Additionally, the expressions (2) to (4) are satisfied when the intensity applied to the portion to be partially and quickly heated, which is subjected to partial rapid heating (for example, the focused portion of the laser), is denoted as P (W), the diameter in the rolling direction of the portion to be partially and quickly heated (for example, the diameter in the rolling direction of the focused diameter of the laser), is denoted as Dl (mm), the diameter in the sheet width direction of the portion to be partially and quickly heated (for example, the diameter in the sheet width direction of the focused diameter of the laser), is denoted as Dc (mm), the scanning speed in the sheet width direction of the portion to be partially and quickly heated (for example, the scanning speed of the laser), is denoted as Vc (mm/s), the irradiation energy density is denoted as Up=4/π x P/(Dl x Vc), and the instantaneous power density is denoted as Ip=4/π x P/(Dl x Dc).

L/50 ≤ Dl ≤ L/2 (2)

5 J/ ^mm2 ≤ Up ≤ 48 J/ ^mm2 (3)

0.05 kW/mm ² ≤ Ip ≤ 4.99 kW/mm ² (4)

[0067] The focused diameter Dl is L/50 or more and L/2 or less. When the focused diameter Dl is less than L/50, the partially and rapidly heated portion is insufficient, the secondary recrystallization nuclei become insufficient, and a problem occurs in secondary recrystallization. When the focused diameter Dl exceeds 2/L, the partially and rapidly heated portion becomes excessive, the lattice orientation of the coincident sites for promoting the growth of secondary recrystallization nuclei becomes insufficient, and the orientation of secondary recrystallization deteriorates.

[0068] The focused diameter Dl is preferably L/25 or more, and more preferably 3L/50 or more. The focused diameter Dl is preferably 9L/20 or less, and more preferably 2L/5 or less.

[0069] The irradiation energy density Up is represented by 4/π x P/(Dl x Vc) and is 5 J/mm ² or more and 48 J/mm ² or less. When the irradiation energy density Up is less than 5 J/mm ² , the recrystallization/grain growth of the surface layer of the steel sheet does not continue sufficiently, and the effect by rapid heating cannot be achieved. When the irradiation energy density Up exceeds 48 J/mm ² , the microstructure of the surface layer of the steel sheet is significantly coarsened due to excessive heat input, and a problem occurs in secondary recrystallization. In addition, since the shape of the steel sheet is also poor in quality, the irradiation energy density Up is limited to 48 J/mm ² or less.

[0070] The irradiation energy density Up is preferably 45 J/mm ² or less, more preferably 40 J/mm ² or less, and still more preferably less than 62.5 x Dl J/mm ² . In other words, the irradiation energy density Up preferably further satisfies expression (5).

5 J/mm ² ≤ Up < 62.5 x Dl J/mm ² (5)

[0071] The irradiation energy density Up is preferably 7 J/mm ² or more, and more preferably 9 J/mm ² or more.

[0072] The instantaneous power density is represented by Ip=4/π x P/(Dl x Dc) and is 0.05 kW/ ^mm2 or more and 4.99 kW/ ^mm2 or less. When the instantaneous power density is less than 0.05 kW/ ^mm2 , the rapid heating effect cannot be achieved, and the magnetic properties become poor in quality. When the instantaneous power density exceeds 4.99 kW/ ^mm2 , defects are formed in the steel sheet.

[0073] The instantaneous power density is preferably 0.07 kW/ ^mm2 or more, and more preferably 0.09 kW/ ^mm2 or more. The instantaneous power density is preferably 4.0 kW/ ^mm2 or less, and more preferably 3.0 kW/ ^mm2 or less.

[0074] 2-8-2. Temperature increase stage

In the temperature raising step, the cold-rolled steel sheet is heated from a temperature range of 550°C or lower after the partial rapid heating step to a temperature range of 750-950°C at an average heating rate of 5°C/sec or higher and 2000°C/sec or lower in a non-oxidizing atmosphere. When the temperature of the cold-rolled steel sheet after the partial rapid heating step is higher than the temperature at the beginning of the temperature raising step, the cold-rolled steel sheet is immediately cooled. The average here is the time average. When the temperature raising rate is less than 5°C/sec, the lattice orientation of the coincident sites for promoting the growth of secondary recrystallization nuclei is excessive, and the magnetic properties become poor. When the temperature raising rate exceeds 2000°C/sec, the lattice orientation of the coincident sites decreases, and the magnetic properties become poor.

[0075] By means of the decarburization annealing step, C, which has a negative influence on the magnetic characteristics, can be removed from the steel sheet, and the Goss orientation can be enriched in the surface layer of the laser-irradiated portion. In addition, {111}<112>, which is the lattice orientation of coincident sites, can be enriched in the crystal orientations of the peripheral region. Furthermore, the deformation of the laser-irradiated portion can be suppressed, and the space coefficient can be increased. Therefore, according to the present embodiment, it is possible to provide a method for producing a grain-oriented electrical steel sheet that can achieve both preferable magnetic characteristics and a preferable sheet shape, even when the steel sheet is subjected to partial rapid heating with a laser beam, an electron beam, etc.

[0076] 2-9. Nitriding treatment

In addition to the above treatments, nitriding treatment can be performed. Nitriding treatment can be performed, for example, after decarburization is completed during the decarburization annealing step. Nitriding treatment can be performed under certain conditions. Preferred nitriding conditions, for example, are as follows.

Nitriding treatment temperature: 700-850°C

Nitriding treatment furnace atmosphere (nitriding treatment atmosphere): An atmosphere containing hydrogen, nitrogen and a gas having nitriding ability such as ammonia.

[0077] When the nitriding treatment temperature is 700°C or higher, or the nitriding treatment temperature is 850°C or lower, nitrogen readily enters the steel sheet during the nitriding treatment. When the nitriding treatment is performed in this temperature range, a preferable amount of nitrogen can be provided in the steel sheet. Therefore, fine AlN is preferentially formed in the steel sheet before secondary recrystallization. As a result, secondary recrystallization preferentially develops during finish annealing. The time for maintaining the steel sheet at the nitriding treatment temperature is not particularly limited and may be, for example, 10 to 60 seconds.

[0078] 3. Configuration of grain-oriented electrical steel sheet

3-1. Chemical composition

The configuration of the grain-oriented electrical steel sheet produced by the above-described method for producing grain-oriented electrical steel sheet is described below. First, the chemical composition of the grain-oriented electrical steel sheet is described. In the following description, unless otherwise specified, the symbol "%" represents "weight %" relative to the total weight of the base steel sheet. The base steel sheet refers to a section of the steel sheet for the grain-oriented electrical steel sheet.

[0079] Si: 2.5-4.5%

Silicon (Si) is an extremely effective element for increasing the electrical resistance (resistivity) of steel and reducing eddy current losses, which constitute a portion of iron loss. When the Si content of the base steel sheet is less than 2.5%, the resistivity is low and eddy current losses cannot be reduced sufficiently. Furthermore, since the steel undergoes a phase transformation during secondary recrystallization annealing, secondary recrystallization does not continue sufficiently, and the desired magnetic flux density and low iron loss cannot be achieved. Therefore, the Si content of the base steel sheet is 2.5% or more. The Si content of the slab is preferably 2.6% or more, and more preferably 2.7% or more.

[0080] On the other hand, when the Si content exceeds 4.5%, the steel sheet becomes brittle, and the passability of the sheet in the manufacturing stage is noticeably deteriorated. Therefore, the Si content of the base steel sheet is 4.5% or less. The Si content of the base steel sheet is preferably 4.4% or less, and more preferably 4.2% or less.

[0081] Mn: 0.01-1.00%

In grain-oriented electrical steel sheets, Mn is present in the form of solid-solution Mn. Since solid-solution Mn increases resistivity, it can reduce iron loss. Therefore, it can be present at a content of 0.01-1.00% in grain-oriented electrical steel sheets. Since solid-solution Mn has a lesser effect on increasing resistivity than Si, and its content is lower than Si, the effect is limited.

[0082] N: 0.01% or less

N is the starting material for AlN as a moderator, as described above, but the content is preferably as low as possible because N is an element that has a negative effect on the magnetic properties of grain-oriented electrical steel sheets. In the present embodiment, the N content is 0.01% or less. The lower limit includes 0, but it is difficult to completely reduce the content to 0 on an industrial scale, and therefore approximately 0.0005% represents a significant lower limit.

[0083] C: 0.01% or less

Because C is an element that negatively affects the magnetic properties of grain-oriented electrical steel sheets, the C content is preferably as low as possible. In the present embodiment, the C content is 0.01% or less. The lower limit includes 0, but it is difficult to completely reduce the content to 0 on an industrial scale, and therefore approximately 0.0005% represents a significant lower limit.

[0084] Al solution: 0.01% or less

As described above, Al is the starting material for AlN as a moderator, but the content is preferably as low as possible because Al is an element that has a negative impact on the magnetic properties of grain-oriented electrical steel sheets. In the present embodiment, the Al content is 0.01% or less. The lower limit includes 0, but it is difficult to completely reduce the content to 0 on an industrial scale, and therefore approximately 0.0005% represents a significant lower limit.

[0085] S: 0.01% or less, Se: 0.01% or less

S and Se are the starting materials for MnS and MnSe as moderators, but the content is preferably as low as possible because S and Se are elements that have a negative impact on the magnetic properties of grain-oriented electrical steel sheets. In the present embodiment, the content of S and Se is 0.01% or less. The lower limit includes 0, but it is difficult to completely reduce the content to 0 on an industrial scale, and therefore approximately 0.0005% represents a significant lower limit.

[0086] The grain-oriented electrical steel sheet may further contain any one or more selected from the group consisting of: P: 0.00-0.05%, Sb: 0.00-0.50%, Sn: 0.00-0.30%, Cr: 0.00-0.50%, Cu: 0.00-0.50%, Ni: 0.00-0.50% and Bi: 0.0000-0.0100% as optional additional elements. This preferred content and characteristics are as described above. In the grain-oriented electrical steel sheet, the remainder is iron and impurities. The definition of impurities is as described above.

[0087] The chemical composition of the base steel sheet described above can be measured by a general analytical method. For example, the components of the steel can be measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). C and S can be measured by an infrared absorption method after combustion, N can be measured by an inert gas melting method by thermal conductivity, and O can be measured by a non-dispersive infrared absorption method after inert gas melting.

[0088] 3-2. Characteristics of grain-oriented electrical steel sheet

The magnetic flux density B8 in the rolling direction of the grain-oriented electrical steel sheet is 1.93 T or more. As described above, the grain-oriented electrical steel sheet according to the present embodiment has high magnetic characteristics. The magnetic flux density B8 in the rolling direction of the grain-oriented electrical steel sheet is preferably 1.94 T or more, and more preferably 1.95 T or more. In order to obtain a magnetic flux density B8 of 1.94 T or more, for example, the irradiation energy density Up can be set to 5 to 41 J/mm ² , and the temperature rise rate in the temperature rise step can be set to 20 to 1500°C/sec.

[0089] A deformed region extending across the entire width of the grain-oriented electrical steel sheet is periodically formed at an interval L of 3 mm or more and 30 mm or less in a direction intersecting the rolling direction of the grain-oriented electrical steel sheet (for example, 30-150 degrees relative to the rolling direction). Such a deformed region is formed by the decarburization annealing step described above. The deformed region has a width W of 0.2 mm or more and 30.6 mm or less. A projection having a maximum height _{Dprotrusion of} 5 μm or less is formed on one surface of the deformed region, and a recessed portion having a maximum depth _{Drecess of} 4 μm or less is formed on the opposite surface. Alternatively, a protrusion having a maximum height _{Dprotrusion of} 8 μm or less is formed on one surface of the deformed region, a recessed portion having a maximum depth _{Drecess of} 8 μm or less is formed on the opposite surface, and the protrusion has a steepness _2Dprotrusion /W of 0.0001 or more and less than 0.0050. As described above, since the degree of deformation of the deformed region, which is the region irradiated with a laser, is suppressed such that it is low, the space coefficient can be increased. The appearance of the grain-oriented electrical steel sheet is shown in Fig. 1(a) and 1(b). Fig. 1(a) is a top view of the grain-oriented electrical steel sheet, and Fig. 1(b) is a cross-sectional side view of the deformed region (a cross-sectional view perpendicular to the surface of the grain-oriented electrical steel sheet). The lower limits of the maximum height D _protrusion and the maximum depth D _recess are approximately 1 μm, since the steel sheet deforms slightly when partial rapid heating is applied. In Fig. 1(b), the reference value T represents the sheet thickness for grain-oriented electrical steel sheet.

[0090] Here, when a protrusion having a maximum height _Dprotrusion of 8 μm or less is formed on one surface of the deformed region, and a recessed portion having a maximum depth _{Drecess of} 8 μm or less is formed on the opposite surface, the protrusion has a steepness _2Dprotrusion /W of preferably 0.0001 or more and less than 0.0050. In this case, the spatial coefficient may be further increased. Here, in order to obtain a steepness _2Dprotrusion /W of 0.0001 or more and less than 0.0050, for example, in the decarburization annealing step described above, Up may be set to less than 62.5 x Dl J/mm ² . When a protrusion having a maximum height _Dprotrusion of 5 μm or less is formed on one surface of the deformed region, and a recessed portion having a maximum depth _{Drecess of} 4 μm or less is formed on the opposite surface, the absolute value of the steepness _2Dprotrusion /W is not particularly limited. In other words, according to the above-described method for producing a grain-oriented electrical steel sheet, the maximum height Dprotrusion of the _protrusion is at least 8 μm or less, and the maximum depth _Drecess of the recessed portion is 8 μm or less. When the maximum height Dprotrusion of the _protrusion exceeds 5 μm, or when the maximum depth _Drecess of the recessed portion exceeds 4 μm, the steepness _2Dprotrusion /W is preferably 0.0001 or more and less than 0.0050. When the steepness is calculated, the unit of the maximum height Dprotrusion of the _protrusion is converted into mm so that it coincides with the unit of width W of the deformed region before calculating the steepness.

[0091] Furthermore, in the deformed region, the ratio (area fraction) of the area of grains (abnormal grains) whose crystal orientation deviates from the Goss orientation by 15° or more to the total area of the deformed region is preferably 5% or less. This makes it possible to further improve the magnetic properties of the grain-oriented electrical steel sheet. In order to obtain such a crystal orientation, for example, in the decarburization annealing step described above, Up can be set to 48 J/ ^mm2 or less.

[0092] Therefore, the grain-oriented electrical steel sheet according to the present embodiment can achieve both the preferred magnetic characteristics and the preferred sheet shape. In other words, an iron core having a high magnetic flux density and a high space coefficient can be produced from the grain-oriented electrical steel sheet according to the present embodiment.

Examples

[0093] 1. Example 1

The advantages of one aspect of the present invention are described in more detail below with reference to examples, but the conditions in the examples represent one example of conditions adapted to confirm the feasibility and advantages of the present invention, and the present invention is not limited to this one example of conditions. The present invention can use various conditions as long as the objective of the present invention is achieved, without departing from the essence of the present invention.

[0094] A slab is prepared in which the chemical composition comprises, in wt.%: C: 0.08%, Si: 3.3%, Mn: 0.08%, S: 0.02%, Al: 0.03% and N: 0.01%, with the remainder being Fe and impurities.

[0095] This slab is heated to 1350°C in a heating furnace. A hot rolling step is performed on the heated slab to produce a hot-rolled steel sheet having a sheet thickness of 2.3 mm. The hot-rolled steel sheet is subjected to a hot annealing step in a hot annealing strip and then cold rolling to produce a cold-rolled steel sheet having a thickness of 0.22 mm. A decarburization annealing step is performed on the cold-rolled steel sheet after the cold rolling step. In this decarburization annealing step, partial rapid heating with a laser beam is performed on one surface of the steel sheet under the conditions shown in Tables 1A-C before the temperature is increased. In Example 1, the focused diameter Dl in the rolling direction and the laser irradiation interval L are varied. The scanning direction of the laser is set to 90 degrees relative to the rolling direction. At this time, the focused diameter Dc in the width direction and the scanning speed Vc are adjusted so that the irradiation energy density Up and the instantaneous power density Ip do not vary.

[0096] After partial rapid heating, the steel sheet is primarily recrystallized by heating in a non-oxidizing atmosphere containing hydrogen and nitrogen at a temperature increase rate shown in Tables 1D-F, then the decarburization annealing temperature is set to 830°C, and the steel sheet is held for 60 seconds. At this time, the atmosphere in the heat treatment furnace for performing the decarburization annealing treatment is a humid atmosphere containing hydrogen and nitrogen. An annealing separator (water slurry) containing MgO as the main component is applied to the surface of the steel sheet after the decarburization annealing, and then the steel sheet is wound into a coil form. The steel sheet wound into a coil is subjected to finish annealing.

[0097] For the steel sheet, after the finish annealing step, a step of forming an insulating film is performed. In the step of forming an insulating film, an insulating coating agent, mainly consisting of colloidal silica and phosphate, is applied to the surface (glass film) of the grain-oriented electrical steel sheet after the finish annealing step, and then annealed. In this way, an insulating film as a highly tensioned insulating film is formed on the glass film. The grain-oriented electrical steel sheet for each test number is produced through the above-mentioned manufacturing steps.

[0098] 1-1. Removing the film

The chemical composition of the base steel sheet can be measured by a known component analytical method. First, the primary film (glass film) and secondary film (insulating film) are removed from the base steel sheet by the following method. Specifically, a grain-oriented electrical steel sheet containing the secondary film is immersed in a high-temperature alkaline solution to remove the secondary film. The composition and temperature of the alkaline solution and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet containing the secondary film is immersed in an aqueous sodium hydroxide solution of NaOH: 30-50 wt% + _H2O : 50-70 wt% at 80-90°C for 5-10 minutes and, after immersion, washed with water and dried. Through this step, the secondary film is removed from the grain-oriented electrical steel sheet.

[0099] Additionally, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in high-temperature hydrochloric acid to remove the primary film. The concentration and temperature of the hydrochloric acid and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in 30-40% by weight hydrochloric acid at 80-90°C for 1-5 minutes and, after immersion, is washed with water and dried. In the above steps, a base steel sheet from which the secondary film and the primary film are removed is obtained.

[0100] 1-2. Experiment with measuring the chemical composition of the base steel sheet

The chemical composition of the base steel sheet for grain-oriented electrical steel sheet for each test number is measured using the following method. First, the primary film and secondary film of the grain-oriented electrical steel sheet are removed using the above-described method to extract the base steel sheet. Using the base steel sheet, the chemical composition of the base steel sheet is analyzed using the following method (measuring the chemical composition of steel sheet).

Chips are collected from the obtained base steel sheet. The collected chips are dissolved in acid to form a solution. The solution is subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES) for elemental analysis. The C and S contents are determined using the known high-frequency combustion method (infrared absorption after combustion). The N content is determined using the known inert gas fusion method by thermal conductivity. Specifically, the measurement is performed using a component analyzer (trade name: ICPS-8000) manufactured by Shimadzu Corporation.

[0101] The analysis results show that the chemical composition of the base steel sheet in any of the test numbers in Example 1 contains, in mass%: C: 0.01% or less, Si: 3.3%, Mn: 0.08%, S: 0.01% or less, sol.Al: 0.01% or less, and N: 0.01% or less, with the remainder being Fe and impurities.

[0102] The magnetic characteristic (B8 magnetic flux density value) of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2556 (2015). The obtained B8 magnetic flux density is shown in Tables 1D to F.

[0103] The shape of the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, using a commercially available surface roughness measuring device (SE3500, manufactured by Kosaka Laboratory Ltd.) and SE2555N (apex curvature radius: 2 μm) as the stylus of the detection unit, with the measurement length in the rolling direction set to 15 mm per measurement, the measurement is continuously performed 5 times, whereby the surface roughness is measured along a length of 75 mm in total. The measurement is performed on both the front side and the back side. W, D _protrusion , and D _recess at each of the five points in the measurement areas of the front side and the back side are measured and evaluated using their average value. The width W of the resulting deformed region, the maximum depth D _recess of the recessed portion on one side of the surface of the deformed region, and the maximum height D _protrusion of the protrusion on the side of the rear surface of the deformed region are shown in Tables 1D-F.

[0104] In addition, the spatial coefficient of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2550-5 (2020). The obtained spatial coefficient is shown in Tables 1D to F.

[0105] In addition, the area ratio of abnormal grains in the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, the crystal orientation of the region with the width W of the deformed region is carried out at a pitch of 2 mm in the width direction of the grain-oriented electrical steel sheet along the centerline in the longitudinal direction of the deformed region using a Laue diffractometer. Then, from the crystal orientation of each measurement point, the number of measurement points indicating abnormal grains having a deviation angle of 15° or more from the Goss orientation is extracted, and the ratio of the number of these measurement points to the total number of measurement points is considered as the area ratio of abnormal grains. However, for the steel number with poor quality magnetism of less than 1.93 T, when measuring the magnetic characteristics described above, the area ratio of abnormal grains is not measured using the Laue diffractometer. The area fraction of the obtained abnormal grains is shown in Tables 1D-F.

[0106] Referring to Tables 1A-F, in steel No. 1-10, the laser irradiation interval L is small, the laser effect is excessive, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0107] In steel No. 61-70, since the laser irradiation interval L is large, the laser irradiation effect is small, and the magnetic characteristic is less than 1.93 T, which is poor in quality.

[0108] In steel No. 11, 21, 31, 41 and 51, since the focused diameter Dl in the rolling direction is small relative to the laser irradiation interval L, the size of the rapidly heated portion is insufficient, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0109] In steel No. 20, 30, 40, 50 and 60, since the focused diameter Dl in the rolling direction is large relative to the laser irradiation interval L, the rapidly heated portion is excessive, and the magnetic flux density is less than 1.93 T, which is poor in quality.

In the steel number other than the above, since all the conditions of the manufacturing stage are proper, the magnetic flux density is 1.93 T or more, which is excellent, and the space coefficient is also up to 96% or more.

[0110] Table 1A

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 1 Nitrogen 400 0.8 0.01 29.00 45 700.0 8 0.20 1 2 Nitrogen 400 0.8 0.02 14:00 45 360.0 8 0.20 1 3 Nitrogen 400 0.8 0.04 7.00 45 180.0 8 0.20 1 4 Nitrogen 400 0.8 0.06 5.00 45 120.0 8 0.19 1 5 Nitrogen 400 0.8 0.10 3.00 45 70.0 8 0.19 1 6 Nitrogen 400 0.8 0.20 1.50 45 35.0 8 0.19 1 7 Nitrogen 400 0.8 0.40 0.80 45 18.0 8 0.18 1 8 Nitrogen 400 0.8 0.45 0.60 45 16.0 8 0.21 1 9 Nitrogen 400 0.8 0.50 0.60 45 14.0 8 0.19 1 10 Nitrogen 400 0.8 0.60 0.50 45 12.0 8 0.19 1 11 Nitrogen 400 0.8 0.05 6.00 45 143.0 8 0.19 3 12 Nitrogen 400 0.8 0.06 5.00 45 120.0 8 0.19 3 13 Nitrogen 400 0.8 0.12 2.50 45 60.0 8 0.19 3 14 Nitrogen 400 0.8 0.18 1.50 45 40.0 8 0.21 3 15 Nitrogen 400 0.8 0.30 1.00 45 24.0 8 0.19 3 16 Nitrogen 400 0.8 0.60 0.50 45 12.0 8 0.19 3 17 Nitrogen 400 0.8 1.20 0.25 45 6.0 8 0.19 3 18 Nitrogen 400 0.8 1.35 0.22 45 5.0 8 0.19 3 19 Nitrogen 400 0.8 1.50 0.20 45 5.0 8 0.19 3 20 Nitrogen 400 0.8 1.60 0.18 45 4.5 8 0.20 3

[0111] Table 1B

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm ` Nitrogen 400 0.8 0.08 4.00 45 90.0 8 0.18 5 22 Nitrogen 400 0.8 0.10 3.00 45 70.0 8 0.19 5 23 Nitrogen 400 0.8 0.20 1.50 45 36.0 8 0.19 5 24 Nitrogen 400 0.8 0.30 1.00 46 24.0 8 0.20 5 25 Nitrogen 400 0.8 0.50 0.60 47 15.0 8 0.20 5 26 Nitrogen 400 0.8 1.00 0.30 48 8.0 8 0.20 5 27 Nitrogen 400 0.8 2.00 0.15 49 4.0 8 0.21 5 28 Nitrogen 400 0.8 2.30 0.13 45 3.0 8 0.19 5 29 Nitrogen 400 0.8 2.50 0.12 45 3.0 8 0.19 5 30 Nitrogen 400 0.8 2.60 0.11 45 2.8 8 0.20 5 31 Nitrogen 400 0.8 0.18 1.50 45 40.0 8 0.21 10 32 Nitrogen 400 0.8 0.20 1.50 45 36.0 8 0.19 10 33 Nitrogen 400 0.8 0.40 0.70 45 18.0 8 0.20 10 34 Nitrogen 400 0.8 0.60 0.50 45 12.0 8 0.19 10 35 Nitrogen 400 0.8 1.00 0.30 45 7.0 8 0.19 10 36 Nitrogen 400 0.8 2.50 0.12 45 3.0 8 0.19 10 37 Nitrogen 400 0.8 3.80 0.08 45 2.0 8 0.19 10 38 Nitrogen 400 0.8 4.50 0.07 45 1.5 8 0.18 10 39 Nitrogen 400 0.8 5.00 0.06 45 1.5 8 0.19 10 40 Nitrogen 400 0.8 5.20 0.05 45 1.3 8 0.22 10

[0112] Table 1C

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 41 Nitrogen 400 0.8 0.20 1.40 45 36.0 8 0.20 20 42 Nitrogen 400 0.8 0.40 0.70 45 18.0 8 0.20 20 43 Nitrogen 400 0.8 0.80 0.40 45 9.0 8 0.18 20 44 Nitrogen 400 0.8 1.20 0.25 45 6.0 8 0.19 20 45 Nitrogen 400 0.8 2.40 0.13 45 3.0 8 0.18 20 46 Nitrogen 400 0.8 4.00 0.07 45 1.8 8 0.20 20 47 Nitrogen 400 0.8 8.00 0.04 45 0.9 8 0.18 20 48 Nitrogen 400 0.8 9:00 0.03 45 0.8 8 0.21 20 49 Nitrogen 400 0.8 10.00 0.03 45 0.7 8 0.19 20 50 Nitrogen 400 0.8 10.50 0.03 45 0.7 8 0.18 20 51 Nitrogen 400 0.8 0.50 0.60 45 14.0 8 0.19 30 52 Nitrogen 400 0.8 0.60 0.50 45 12.0 8 0.19 30 53 Nitrogen 400 0.8 1.20 0.25 45 6.0 8 0.19 30 54 Nitrogen 400 0.8 1.80 0.15 45 4.0 8 0.21 30 55 Nitrogen 400 0.8 3.00 0.10 45 2.4 8 0.19 30 56 Nitrogen 400 0.8 6.00 0.05 45 1.2 8 0.19 30 57 Nitrogen 400 0.8 12:00 0.03 45 0.6 8 0.16 30 58 Nitrogen 400 0.8 13.50 0.02 45 0.5 8 0.21 30 59 Nitrogen 400 0.8 15.00 0.02 45 0.5 8 0.19 30 60 Nitrogen 400 0.8 17:00 0.02 45 0.4 8 0.17 30 61 Nitrogen 400 0.8 0.50 0.60 45 14.0 8 0.19 35 62 Nitrogen 400 0.8 0.70 0.40 45 10.0 8 0.20 35 63 Nitrogen 400 0.8 1.40 0.20 45 5.0 8 0.20 35 64 Nitrogen 400 0.8 2.10 0.15 45 3.5 8 0.18 35 65 Nitrogen 400 0.8 3.50 0.10 45 2.0 8 0.16 35 66 Nitrogen 400 0.8 7.00 0.04 45 1.0 8 0.20 35 67 Nitrogen 400 0.8 14:00 0.02 45 0.5 8 0.20 35 68 Nitrogen 400 0.8 17:00 0.02 45 0.4 8 0.17 35 69 Nitrogen 400 0.8 17.50 0.02 45 0.4 8 0.16 35 70 Nitrogen 400 0.8 18:00 0.02 45 0.4 8 0.16 35

[0113] Table 1D

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 1 1000 0.1 0.001 0.003 0.0600 - 1.84 97 Comparative example 2 1000 0.1 0.001 0.002 0.0400 - 1.90 97 Comparative example 3 1000 0.2 0.001 0.002 0.0200 - 1.91 97 Comparative example 4 1000 0.3 0.001 0.002 0.0133 - 1.92 97 Comparative example 5 1000 0.4 0.001 0.001 0.0050 - 1.92 97 Comparative example 6 1000 0.8 0.001 0.001 0.0025 - 1.92 98 Comparative example 7 1000 1.0 0.001 0.001 0.0020 - 1.92 98 Comparative example 8 1000 1.0 0.001 0.002 0.0040 - 1.91 98 Comparative example 9 1000 0.9 0.001 0.001 0.0022 - 1.90 98 Comparative example 10 1000 1.0 0.001 0.001 0.0020 - 1.88 98 Comparative example 11 1000 0.2 0.001 0.002 0.0200 - 1.89 97 Comparative example 12 1000 0.2 0.001 0.002 0.0200 0 1.93 97 Example of invention 13 1000 0.4 0.001 0.001 0.0050 0 1.93 97 Example of invention 14 1000 0.7 0.001 0.001 0.0029 0 1.94 98 Example of invention 15 1000 1.1 0.001 0.001 0.0018 0 1.94 98 Example of invention 16 1000 2.8 0.001 0.002 0.0014 0 1.94 98 Example of invention 17 1000 3.0 0.001 0.001 0.0007 0 1.94 98 Example of invention 18 1000 2.9 0.001 0.001 0.0007 0 1.93 98 Example of invention 19 1000 2.7 0.001 0.001 0.0007 0 1.93 98 Example of invention 20 1000 2.9 0.001 0.001 0.0007 - 1.91 98 Comparative example

[0114] Table 1E

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 21 1000 0.3 0.001 0.002 0.0133 - 1.88 97 Comparative example 22 1000 0.5 0.001 0.002 0.0080 0 1.93 97 Example of invention 23 1000 0.8 0.001 0.001 0.0025 0 1.93 98 Example of invention 24 1000 1.1 0.001 0.001 0.0018 0 1.94 98 Example of invention 25 1000 2.0 0.001 0.001 0.0010 0 1.94 98 Example of invention 26 1000 4.2 0.001 0.002 0.0010 0 1.94 98 Example of invention 27 1000 5.0 0.001 0.001 0.0004 0 1.94 98 Example of invention 28 1000 5.0 0.001 0.001 0.0004 0 1.93 98 Example of invention 29 1000 5.0 0.001 0.002 0.0008 0 1.93 98 Example of invention 30 1000 5.0 0.001 0.001 0.0004 - 1.91 98 Comparative example 31 1000 0.7 0.001 0.001 0.0029 0 1.89 98 Comparative example 32 1000 0.9 0.001 0.001 0.0022 0 1.94 98 Example of invention 33 1000 1.8 0.001 0.001 0.0011 0 1.94 98 Example of invention 34 1000 2.2 0.001 0.001 0.0009 0 1.95 98 Example of invention 35 1000 4.3 0.001 0.001 0.0005 0 1.95 98 Example of invention 36 1000 7.8 0.001 0.001 0.0003 0 1.95 98 Example of invention 37 1000 9.8 0.001 0.002 0.0004 0 1.95 98 Example of invention 38 1000 9.9 0.001 0.001 0.0002 0 1.94 98 Example of invention 39 1000 9.8 0.001 0.001 0.0002 0 1.94 98 Example of invention 40 1000 10.0 0.001 0.001 0.0002 - 1.92 98 Comparative example

[0115] Table 1F

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 41 1000 1.1 0.001 0.002 0.0036 - 1.90 98 Comparative example 42 1000 1.7 0.001 0.001 0.0012 0 1.94 98 Example of invention 43 1000 3.3 0.001 0.001 0.0006 0 1.94 98 Example of invention 44 1000 4.6 0.001 0.002 0.0009 0 1.95 98 Example of invention 45 1000 7.7 0.001 0.001 0.0003 0 1.95 98 Example of invention 46 1000 15.8 0.001 0.001 0.0001 0 1.95 98 Example of invention 47 1000 19.8 0.001 0.002 0.0002 0 1.95 98 Example of invention 48 1000 21.0 0.001 0.001 0.0001 0 1.94 98 Example of invention 49 1000 20.6 0.001 0.001 0.0001 0 1.94 98 Example of invention 50 1000 19.7 0.001 0.001 0.0001 - 1.92 98 Comparative example 51 1000 2.0 0.001 0.001 0.0010 - 1.88 98 Comparative example 52 1000 2.2 0.001 0.001 0.0009 0 1.93 98 Example of invention 53 1000 4.6 0.001 0.002 0.0009 0 1.93 98 Example of invention 54 1000 7.1 0.001 0.001 0.0003 0 1.94 98 Example of invention 55 1000 12.4 0.001 0.001 0.0002 0 1.94 98 Example of invention 56 1000 22.9 0.001 0.002 0.0002 0 1.94 98 Example of invention 57 1000 29.6 0.001 0.002 0.0001 0 1.94 98 Example of invention 58 1000 30.0 0.001 0.001 0.0001 0 1.93 98 Example of invention 59 1000 30.6 0.001 0.001 0.0001 0 1.93 98 Example of invention 60 1000 29.9 0.001 0.001 0.0001 - 1.91 98 Comparative example 61 1000 1.8 0.001 0.001 0.0011 - 1.76 98 Comparative example 62 1000 2.9 0.001 0.001 0.0007 - 1.87 98 Comparative example 63 1000 5.6 0.001 0.001 0.0004 - 1.88 98 Comparative example 64 1000 8.0 0.001 0.001 0.0003 - 1.89 98 Comparative example 65 1000 13.8 0.001 0.001 0.0001 - 1.89 98 Comparative example 66 1000 28.2 0.001 0.001 0.0001 - 1.89 98 Comparative example 67 1000 34.8 0.001 0.002 0.0001 - 1.89 98 Comparative example 68 1000 35.0 0.001 0.001 0.0001 - 1.89 98 Comparative example 69 1000 35.0 0.001 0.001 0.0001 - 1.90 98 Comparative example 70 1000 35.3 0.001 0.001 0.0001 - 1.90 98 Comparative example

[0116] 2. Example 2

A slab is prepared in which the chemical composition is, in wt.%: C: 0.08%, Si: 3.3%, Mn: 0.08%, S: 0.02%, Al: 0.03% and N: 0.01%, with the remainder being Fe and impurities.

[0117] This slab is heated to 1350°C in a heating furnace. A hot rolling step is performed on the heated slab to produce a hot-rolled steel sheet having a sheet thickness of 2.3 mm. The hot-rolled steel sheet is subjected to a hot annealing step in a hot annealing strip and then cold rolling to produce a cold-rolled steel sheet having a thickness of 0.22 mm. A decarburization annealing step is performed on the cold-rolled steel sheet after the cold rolling step. In this decarburization annealing step, partial rapid heating with a laser beam is performed on one surface of the steel sheet under the conditions shown in Tables 2A-C before the temperature is increased. The scanning direction of the laser is set to 90 degrees relative to the rolling direction. At this time, the focused diameter Dc in the width direction and the scanning speed Vc vary so that the irradiation energy density Up and the instantaneous power density Ip vary.

[0118] After partial rapid heating, the steel sheet is primarily recrystallized by heating in a non-oxidizing atmosphere containing hydrogen and nitrogen at a temperature increase rate shown in Tables 2D-F, then the decarburization annealing temperature is set to 830°C, and the steel sheet is held for 60 seconds. At this time, the atmosphere in the heat treatment furnace for performing the decarburization annealing treatment is a humid atmosphere containing hydrogen and nitrogen. An annealing separator (water slurry) containing MgO as the main component is applied to the surface of the steel sheet after the decarburization annealing, and then the steel sheet is wound into a coil form. The steel sheet wound into a coil is subjected to finish annealing.

[0119] For the steel sheet, after the finish annealing step, a step of forming an insulating film is performed. In the step of forming an insulating film, an insulating coating agent, mainly consisting of colloidal silica and phosphate, is applied to the surface (glass film) of the grain-oriented electrical steel sheet after the finish annealing step, and then annealed. In this way, an insulating film as a highly tensioned insulating film is formed on the glass film. The grain-oriented electrical steel sheet for each test number is produced through the above-mentioned manufacturing steps.

[0120] 2-1. Removing the film

The chemical composition of the base steel sheet can be measured by a known component analytical method. First, the primary film and secondary film are removed from the base steel sheet by the following method. Specifically, a grain-oriented electrical steel sheet containing a secondary film is immersed in a high-temperature alkaline solution to remove the secondary film. The composition and temperature of the alkaline solution and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet containing a secondary film is immersed in an aqueous sodium hydroxide solution of NaOH: 30-50 wt% + _H2O : 50-70 wt% at 80-90°C for 5-10 minutes and, after immersion, washed with water and dried. Through this step, the secondary film is removed from the grain-oriented electrical steel sheet.

Additionally, the grain-oriented electrical steel sheet from which the secondary film is removed and the primary film remains is immersed in high-temperature hydrochloric acid to remove the primary film. The concentration and temperature of the hydrochloric acid and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet from which the secondary film is removed and the primary film remains is immersed in 30-40 wt% hydrochloric acid at 80-90°C for 1-5 minutes and, after immersion, rinsed with water and dried. This produces a base steel sheet from which both the secondary and primary films have been removed.

2-2. Experiment with measuring the chemical composition of the base steel sheet

The chemical composition of the base steel sheet for grain-oriented electrical steel sheet for each test number is measured using the following method. First, the primary film and secondary film of the grain-oriented electrical steel sheet are removed using the above-described method to extract the base steel sheet. Using the base steel sheet, the chemical composition of the base steel sheet is analyzed using the following method (measuring the chemical composition of steel sheet).

Chips are collected from the obtained base steel sheet. The collected chips are dissolved in acid to form a solution. The solution is subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES) for elemental analysis. The C and S contents are determined using the known high-frequency combustion method (infrared absorption after combustion). The N content is determined using the known inert gas fusion method by thermal conductivity. Specifically, the measurement is performed using a component analyzer (trade name: ICPS-8000) manufactured by Shimadzu Corporation.

[0121] The analysis results show that the chemical composition of the base steel sheet in any of the test numbers in Example 2 contains, in mass%: C: 0.01% or less, Si: 3.3%, Mn: 0.08%, S: 0.01% or less, sol.Al: 0.01% or less, and N: 0.01% or less, with the remainder being Fe and impurities.

[0122] The magnetic characteristic (B8 magnetic flux density value) of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2556 (2015). The obtained B8 magnetic flux density is shown in Tables 2D to F.

[0123] The shape of the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, using a commercially available surface roughness measuring device (SE3500, manufactured by Kosaka Laboratory Ltd.) and SE2555N (apex curvature radius: 2 μm) as the stylus of the detection unit, with the measurement length in the rolling direction set to 15 mm per measurement, the measurement is continuously performed 5 times, whereby the surface roughness is measured along a length of 75 mm in total. The measurement is performed on both the front side and the back side. W, D _protrusion , and D _recess at each of the five points in the measurement areas of the front side and the back side are measured and evaluated using their average value. However, for a steel grade in which Ip is excessive and defects are clearly formed in the laser-irradiated area, roughness testing is not performed. The width W of the resulting deformed region, the maximum depth D _recessed of the recessed portion on one side of the deformed region's surface, and the maximum height D _protrusion of the protrusion on the flank side of the deformed region are shown in Tables 2D-F.

[0124] In addition, the spatial coefficient of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2550-5 (2020). The obtained spatial coefficient is shown in Tables 2D-F.

[0125] Additionally, the area ratio of abnormal grains in the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, the crystal orientation of the region with the width W of the deformed region is measured at a pitch of 2 mm in the width direction of the grain-oriented electrical steel sheet along the centerline in the longitudinal direction of the deformed region using a Laue diffractometer. Then, from the crystal orientation of each measurement point, the number of measurement points indicating abnormal grains having a deviation angle of 15° or more from the Goss orientation is extracted, and the ratio of the number of these measurement points to the total number of measurement points is considered as the area ratio of abnormal grains. However, for the steel number with poor quality magnetism of less than 1.93 T, when measuring the magnetic characteristics described above, the area ratio of abnormal grains is not measured using the Laue diffractometer. The area fraction of the obtained abnormal grains is shown in Tables 2D-F.

[0126] Referring to Tables 2A-F, in steel No. 1-10, the instantaneous power density Ip is low, the rapid heating effect by laser heating is small, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0127] In steel No. 61-70, the instantaneous power density Ip is high, and defects due to laser heating are generated to a large extent, due to which the magnetic flux density is deteriorated, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0128] In steel No. 11, 21, 31, 41 and 51, the irradiation energy density Up is low, the rapid heating effect by laser heating is small, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0129] In steel numbers 10, 20, 30, 40, 50 and 60, the irradiation energy density Up is high, the heat supplied by laser heating is excessive, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0130] In steel numbers 7-9, 17-19, 27-29, 37-39, 47-49 and 57-59, the irradiation energy density Up is large relative to the focused diameter Dl, and the steepness is large. The protrusion D is also large, the spatial coefficient is significantly deteriorated, and the spatial coefficient is less than 96%, which is poor in quality. In steel numbers other than the above, since all the conditions of the manufacturing step are proper, the magnetic flux density is 1.93 T or more, which is excellent, and the spatial coefficient is also up to 96% or more.

Table 2A

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 1 Nitrogen 400 0.8 0.60 2.50 45 32.0 3 0.04 10 2 Nitrogen 400 0.8 0.60 2.50 45 19.0 5 0.04 10 3 Nitrogen 400 0.8 0.60 2.50 45 14.0 7 0.04 10 4 Nitrogen 400 0.8 0.60 2.50 45 11.0 9 0.04 10 5 Nitrogen 400 0.8 0.60 2.50 45 6.4 15 0.04 10 6 Nitrogen 400 0.8 0.60 2.50 45 3.2 30 0.04 10 7 Nitrogen 400 0.8 0.60 2.50 45 2.4 40 0.04 10 8 Nitrogen 400 0.8 0.60 2.50 45 2.1 45 0.04 10 9 Nitrogen 400 0.8 0.60 2.50 45 1.9 50 0.04 10 10 Nitrogen 400 0.8 0.60 2.50 45 1.7 56 0.04 10 11 Nitrogen 400 0.8 0.60 2.00 45 31.8 3 0.05 10 12 Nitrogen 400 0.8 0.60 2.00 45 19.1 5 0.05 10 13 Nitrogen 400 0.8 0.60 2.00 45 13.6 7 0.05 10 14 Nitrogen 400 0.8 0.60 2.00 45 10.6 9 0.05 10 15 Nitrogen 400 0.8 0.60 2.00 45 6.4 15 0.05 10 16 Nitrogen 400 0.8 0.60 2.00 45 3.2 30 0.05 10 17 Nitrogen 400 0.8 0.60 2.00 45 2.4 40 0.05 10 18 Nitrogen 400 0.8 0.60 2.00 45 2.1 45 0.05 10 19 Nitrogen 400 0.8 0.60 2.00 45 1.9 50 0.05 10 20 Nitrogen 400 0.8 0.60 2.00 45 1.7 55 0.05 10

[0131] Table 2B

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 21 Nitrogen 400 0.8 0.60 0.50 45 31.8 3 0.19 10 22 Nitrogen 400 0.8 0.60 0.50 45 19.1 5 0.19 10 23 Nitrogen 400 0.8 0.60 0.50 45 13.6 7 0.19 10 24 Nitrogen 400 0.8 0.60 0.50 45 10.6 9 0.19 10 25 Nitrogen 400 0.8 0.60 0.50 45 6.4 15 0.19 10 26 Nitrogen 400 0.8 0.60 0.50 45 3.2 30 0.19 10 27 Nitrogen 400 0.8 0.60 0.50 45 2.4 40 0.19 10 28 Nitrogen 400 0.8 0.60 0.50 45 2.1 45 0.19 10 29 Nitrogen 400 0.8 0.60 0.50 45 1.9 50 0.19 10 30 Nitrogen 400 0.8 0.60 0.50 45 1.7 55 0.19 10 31 Nitrogen 400 0.8 0.60 0.10 45 31.8 3 0.95 10 32 Nitrogen 400 0.8 0.60 0.10 45 19.1 5 0.95 10 33 Nitrogen 400 0.8 0.60 0.10 45 13.6 7 0.95 10 34 Nitrogen 400 0.8 0.60 0.10 45 10.6 9 0.95 10 35 Nitrogen 400 0.8 0.60 0.10 45 6.4 15 0.95 10 36 Nitrogen 400 0.8 0.60 0.10 45 3.2 30 0.95 10 37 Nitrogen 400 0.8 0.60 0.10 45 2.4 40 0.95 10 38 Nitrogen 400 0.8 0.60 0.10 45 2.1 45 0.95 10 39 Nitrogen 400 0.8 0.60 0.10 45 1.9 50 0.95 10 40 Nitrogen 400 0.8 0.60 0.10 45 1.7 55 0.95 10

[0132] Table 2C

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 41 Nitrogen 400 0.8 0.60 0.02 45 31.8 3 4.77 10 42 Nitrogen 400 0.8 0.60 0.02 45 19.1 5 4.77 10 43 Nitrogen 400 0.8 0.60 0.02 45 13.6 7 4.77 10 44 Nitrogen 400 0.8 0.60 0.02 45 10.6 9 4.77 10 45 Nitrogen 400 0.8 0.60 0.02 45 6.4 15 4.77 10 46 Nitrogen 400 0.8 0.60 0.02 45 3.2 30 4.77 10 47 Nitrogen 400 0.8 0.60 0.02 45 2.4 40 4.77 10 48 Nitrogen 400 0.8 0.60 0.02 45 2.1 45 4.77 10 49 Nitrogen 400 0.8 0.60 0.02 45 1.9 50 4.77 10 50 Nitrogen 400 0.8 0.60 0.02 45 1.7 55 4.77 10 51 Nitrogen 400 0.8 0.60 0.02 47 33.5 3 4.99 10 52 Nitrogen 400 0.8 0.60 0.02 47 20.0 5 4.99 10 53 Nitrogen 400 0.8 0.60 0.02 47 14.0 7 4.99 10 54 Nitrogen 400 0.8 0.60 0.02 47 11.0 9 4.99 10 55 Nitrogen 400 0.8 0.60 0.02 47 7.0 14 4.99 10 56 Nitrogen 400 0.8 0.60 0.02 47 4.0 25 4.99 10 57 Nitrogen 400 0.8 0.60 0.02 47 2.5 40 4.99 10 58 Nitrogen 400 0.8 0.60 0.02 47 2.2 45 4.99 10 59 Nitrogen 400 0.8 0.60 0.02 47 2.0 50 4.99 10 60 Nitrogen 400 0.8 0.60 0.02 47 1.9 52 4.99 10 61 Nitrogen 400 0.8 0.60 0.02 48 34.0 3 5.09 10 62 Nitrogen 400 0.8 0.60 0.02 48 20.0 5 5.09 10 63 Nitrogen 400 0.8 0.60 0.02 48 15.0 7 5.09 10 64 Nitrogen 400 0.8 0.60 0.02 48 11.0 9 5.09 10 65 Nitrogen 400 0.8 0.60 0.02 48 7.0 15 5.09 10 66 Nitrogen 400 0.8 0.60 0.02 48 4.0 25 5.09 10 67 Nitrogen 400 0.8 0.60 0.02 48 2.5 41 5.09 10 68 Nitrogen 400 0.8 0.60 0.02 48 2.3 44 5.09 10 69 Nitrogen 400 0.8 0.60 0.02 48 2.1 49 5.09 10 70 Nitrogen 400 0.8 0.60 0.02 48 1.9 55 5.09 10

[0133] Table 2D

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 1 1000 2.4 0,000 0,000 0.0000 - 1.92 98 Comparative example 2 1000 2.2 0.001 0.001 0.0009 - 1.92 98 Comparative example 3 1000 2.2 0.001 0.001 0.0009 - 1.92 98 Comparative example 4 1000 2.3 0.002 0.002 0.0017 - 1.92 98 Comparative example 5 1000 2.4 0.002 0.002 0.0017 - 1.92 97 Comparative example 6 1000 2.6 0.004 0.005 0.0038 - 1.92 97 Comparative example 7 1000 2.2 0.006 0.006 0.0055 - 1.91 95 Comparative example 8 1000 2.3 0.007 0.007 0.0061 - 1.90 95 Comparative example 9 1000 2.4 0.008 0.008 0.0067 - 1.90 95 Comparative example 10 1000 2.4 0.010 0.010 0.0083 - 1.89 94 Comparative example 11 1000 2.2 0,000 0,000 0.0000 - 1.92 98 Comparative example 12 1000 2.2 0.001 0.001 0.0009 0 1.93 98 Example of invention 13 1000 2.6 0.001 0.001 0.0008 0 1.93 98 Example of invention 14 1000 2.4 0.001 0.001 0.0008 1 1.94 98 Example of invention 15 1000 2.3 0.002 0.002 0.0017 1 1.94 97 Example of invention 16 1000 2.4 0.004 0.004 0.0033 1 1.94 97 Example of invention 17 1000 2.2 0.007 0.006 0.0055 3 1.93 95 Comparative example 18 1000 2.5 0.007 0.007 0.0056 2 1.93 95 Comparative example 19 1000 2.4 0.008 0.008 0.0067 3 1.93 95 Comparative example 20 1000 2.3 0.009 0.009 0.0078 - 1.91 94 Comparative example

[0134] Table 2E

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 21 1000 2.3 0,000 0,000 0.0000 - 1.92 98 Comparative example 22 1000 2.6 0.001 0.001 0.0008 0 1.93 98 Example of invention 23 1000 1.9 0.001 0.001 0.0011 0 1.94 98 Example of invention 24 1000 2.0 0.002 0.002 0.0020 0 1.95 98 Example of invention 25 1000 2.0 0.002 0.003 0.0030 0 1.95 97 Example of invention 26 1000 2.5 0.004 0.006 0.0048 0 1.95 97 Example of invention 27 1000 2.4 0.006 0.007 0.0058 1 1.94 95 Comparative example 28 1000 2.4 0.006 0.008 0.0067 2 1.93 95 Comparative example 29 1000 2.4 0.007 0.008 0.0067 4 1.93 95 Comparative example 30 1000 2.3 0.009 0.009 0.0078 - 1.91 94 Comparative example 31 1000 2.2 0,000 0,000 0.0000 - 1.92 98 Comparative example 32 1000 2.2 0.001 0.001 0.0009 0 1.93 98 Example of invention 33 1000 2.8 0.001 0.001 0.0007 0 1.94 98 Example of invention 34 1000 2.4 0.001 0.002 0.0017 0 1.95 98 Example of invention 35 1000 2.6 0.002 0.004 0.0031 0 1.95 97 Example of invention 36 1000 2.7 0.005 0.005 0.0037 0 1.95 97 Example of invention 37 1000 2.1 0.006 0.007 0.0067 1 1.94 95 Comparative example 38 1000 2.4 0.007 0.008 0.0067 3 1.93 95 Comparative example 39 1000 2.4 0.008 0.008 0.0067 4 1.93 95 Comparative example 40 1000 2.4 0.009 0.010 0.0083 - 1.91 94 Comparative example

[0135] Table 2F

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 41 1000 2.1 0,000 0.001 0.0010 0 1.92 98 Comparative example 42 1000 2.0 0.001 0.001 0.0010 0 1.93 98 Example of invention 43 1000 2.0 0.001 0.002 0.0020 0 1.94 98 Example of invention 44 1000 1.9 0.001 0.001 0.0011 0 1.95 98 Example of invention 45 1000 1.9 0.002 0.003 0.0032 0 1.95 97 Example of invention 46 1000 2.4 0.003 0.005 0.0042 0 1.95 97 Example of invention 47 1000 2.4 0.005 0.006 0.0050 1 1.94 95 Comparative example 48 1000 1.8 0.007 0.007 0.0078 2 1.93 95 Comparative example 49 1000 2.3 0.008 0.008 0.0070 2 1.93 95 Comparative example 50 1000 2.4 0.009 0.010 0.0083 - 1.91 94 Comparative example 51 1000 2.3 0,000 0.001 0.0009 - 1.92 98 Comparative example 52 1000 2.4 0.001 0.001 0.0008 0 1.93 98 Example of invention 53 1000 2.3 0.001 0.001 0.0009 0 1.93 98 Example of invention 54 1000 2.6 0.001 0.002 0.0015 0 1.94 98 Example of invention 55 1000 2.5 0.002 0.002 0.0016 0 1.94 97 Example of invention 56 1000 2.6 0.004 0.004 0.0031 1 1.94 97 Example of invention 57 1000 2.4 0.005 0.007 0.0058 1 1.93 95 Comparative example 58 1000 2.4 0.006 0.008 0.0067 2 1.93 95 Comparative example 59 1000 2.2 0.007 0.008 0.0073 4 1.93 95 Comparative example 60 1000 2.4 0.009 0.012 0.0100 - 1.90 94 Comparative example 61 1000 - - - - - 1.88 97 Comparative example 62 1000 - - - - - 1.89 97 Comparative example 63 1000 - - - - - 1.90 97 Comparative example 64 1000 - - - - - 1.91 97 Comparative example 65 1000 - - - - - 1.91 96 Comparative example 66 1000 - - - - - 1.91 96 Comparative example 67 1000 - - - - - 1.90 94 Comparative example 68 1000 - - - - - 1.89 94 Comparative example 69 1000 - - - - - 1.88 94 Comparative example 70 1000 - - - - - 1.86 93 Comparative example

[0136] 3. Example 3

A slab is prepared in which the chemical composition is, in wt.%: C: 0.08%, Si: 3.3%, Mn: 0.08%, S: 0.02%, Al: 0.03% and N: 0.01%, with the remainder being Fe and impurities.

[0137] This slab is heated to 1350°C in a heating furnace. A hot rolling step is performed on the heated slab to produce a hot-rolled steel sheet having a sheet thickness of 2.3 mm. The hot-rolled steel sheet is subjected to a hot annealing step in a hot annealing strip and then cold rolling to produce a cold-rolled steel sheet having a thickness of 0.22 mm. A decarburization annealing step is performed on the cold-rolled steel sheet after the cold rolling step. In this decarburization annealing step, partial rapid heating with a laser beam is performed on one surface of the steel sheet under the conditions shown in Tables 3A-C before the temperature is increased. The scanning direction of the laser is set to 90 degrees relative to the rolling direction. During this time, the focused diameter Dc in the width direction and the scanning speed Vc vary, resulting in variations in the irradiation energy density Up and the instantaneous power density Ip. The difference from Example 2 lies in the values of the focused diameter Dl in the rolling direction and the scanning speed Vc.

[0138] After partial rapid heating, the steel sheet is primarily recrystallized by heating in a non-oxidizing atmosphere containing hydrogen and nitrogen at a temperature increase rate shown in Tables 3D-F, then the decarburization annealing temperature is set to 830°C, and the steel sheet is held for 60 seconds. At this time, the atmosphere in the heat treatment furnace for performing the decarburization annealing treatment is a humid atmosphere containing hydrogen and nitrogen. An annealing separator (water slurry) containing MgO as the main component is applied to the surface of the steel sheet after the decarburization annealing, and then the steel sheet is wound into a coil form. The steel sheet wound into a coil is subjected to finish annealing.

[0139] For the steel sheet, after the finish annealing step, a step of forming an insulating film is performed. In the step of forming an insulating film, an insulating coating agent mainly consisting of colloidal silica and phosphate is applied to the surface (glass film) of the grain-oriented electrical steel sheet after the finish annealing step, and then annealing is performed. In this way, an insulating film as a highly tensioned insulating film is formed on the glass film. The grain-oriented electrical steel sheet for each test number is produced through the above-mentioned manufacturing steps.

[0140] 3-1. Removing the film

The chemical composition of the base steel sheet can be measured by a known component analytical method. First, the primary film and secondary film are removed from the base steel sheet by the following method. Specifically, a grain-oriented electrical steel sheet containing a secondary film is immersed in a high-temperature alkaline solution to remove the secondary film. The composition and temperature of the alkaline solution and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet containing a secondary film is immersed in an aqueous sodium hydroxide solution of NaOH: 30-50 wt% + _H2O : 50-70 wt% at 80-90°C for 5-10 minutes and, after immersion, washed with water and dried. Through this step, the secondary film is removed from the grain-oriented electrical steel sheet.

[0141] Additionally, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in high-temperature hydrochloric acid to remove the primary film. The concentration and temperature of the hydrochloric acid and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in 30-40% by weight of hydrochloric acid at 80-90°C for 1-5 minutes and, after immersion, is washed with water and dried. In this way, a base steel sheet from which the secondary and primary films are removed is obtained.

[0142] 3-2. Experiment with measuring the chemical composition of the base steel sheet

The chemical composition of the base steel sheet for grain-oriented electrical steel sheet for each test number is measured using the following method. First, the primary film and secondary film of the grain-oriented electrical steel sheet are removed using the above-described method to extract the base steel sheet. Using the base steel sheet, the chemical composition of the base steel sheet is analyzed using the following method (measuring the chemical composition of steel sheet).

Chips are collected from the obtained base steel sheet. The collected chips are dissolved in acid to form a solution. The solution is subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES) for elemental analysis. The C and S contents are determined using the known high-frequency combustion method (infrared absorption after combustion). The N content is determined using the known inert gas fusion method by thermal conductivity. Specifically, the measurement is performed using a component analyzer (trade name: ICPS-8000) manufactured by Shimadzu Corporation.

[0143] The analysis results show that the chemical composition of the base steel sheet in any of the test numbers in Example 3 contains, in mass%: C: 0.01% or less, Si: 3.3%, Mn: 0.08%, S: 0.01% or less, sol.Al: 0.01% or less, and N: 0.01% or less, with the remainder being Fe and impurities.

[0144] The magnetic characteristic (B8 magnetic flux density value) of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2556 (2015). The obtained B8 magnetic flux density is shown in Tables 3D-F.

[0145] The shape of the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, using a commercially available surface roughness measuring device (SE3500, manufactured by Kosaka Laboratory Ltd.) and SE2555N (apex curvature radius: 2 μm) as the stylus of the detection unit, with the measurement length in the rolling direction set to 15 mm per measurement, the measurement is continuously performed 5 times, whereby the surface roughness along a length of 75 mm in total is measured. The measurement is performed on both the front side and the back side. W, D _protrusion , and D _recess at each of the five points in the measurement areas of the front side and the back side are measured and evaluated using their average value. However, for a steel grade in which Ip is excessive and defects obviously form in the deformed region, roughness testing is not performed. The width W of the resulting deformed region, the maximum depth D _{of the} recessed portion on one side of the deformed region's surface, and the maximum height D _{of the protrusion} on the back surface side of the deformed region are shown in Tables 3D-F.

[0146] In addition, the spatial coefficient of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2550-5 (2020). The obtained spatial coefficient is shown in Tables 3D-F.

[0147] Additionally, the area ratio of abnormal grains in the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, the crystal orientation of the region with the width W of the deformed region is measured at a pitch of 2 mm in the width direction of the grain-oriented electrical steel sheet along the centerline in the longitudinal direction of the deformed region using a Laue diffractometer. Then, from the crystal orientation of each measurement point, the number of measurement points indicating abnormal grains having a deviation angle of 15° or more from the Goss orientation is extracted, and the ratio of the number of these measurement points to the total number of measurement points is considered as the area ratio of abnormal grains. However, for the steel number with poor quality magnetism of less than 1.93 T, when measuring the magnetic characteristics described above, the area ratio of abnormal grains is not measured using the Laue diffractometer. The area fraction of the obtained abnormal grains is shown in Tables 3D-F.

[0148] Referring to Tables 3A-F, in steel No. 1-10, the instantaneous power density Ip is low, the rapid heating effect by laser heating is small, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0149] In steel No. 61-70, the instantaneous power density Ip is high, and defects due to laser heating are generated to a large extent, due to which the magnetic flux density is deteriorated, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0150] In steel No. 11, 21, 31, 41 and 51, the irradiation energy density Up is low, the rapid heating effect by laser heating is small, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0151] In steel numbers 10, 20, 30, 40, 50 and 60, the irradiation energy density Up is high, the heat supplied by laser heating is excessive, the magnetic flux density is deteriorated and is less than 1.93 T.

[0152] In a steel number other than the above, since all the conditions of the manufacturing step are proper, the magnetic flux density is 1.93 T or more, which is excellent, and the space coefficient is also up to 96% or more.

[0153] Table 3A

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 1 Nitrogen 400 0.8 2.00 0.70 45 10.0 3 0.04 10 2 Nitrogen 400 0.8 2.00 0.70 45 6.0 5 0.04 10 3 Nitrogen 400 0.8 2.00 0.70 45 4.0 7 0.04 10 4 Nitrogen 400 0.8 2.00 0.70 45 3.0 10 0.04 10 5 Nitrogen 400 0.8 2.00 0.70 45 2.0 14 0.04 10 6 Nitrogen 400 0.8 2.00 0.70 45 1.0 29 0.04 10 7 Nitrogen 400 0.8 2.00 0.70 45 0.8 36 0.04 10 8 Nitrogen 400 0.8 2.00 0.70 45 0.7 41 0.04 10 9 Nitrogen 400 0.8 2.00 0.70 45 0.6 48 0.04 10 10 Nitrogen 400 0.8 2.00 0.70 45 0.5 55 0.04 10 11 Nitrogen 400 0.8 2.00 0.60 45 10.0 3 0.05 10 12 Nitrogen 400 0.8 2.00 0.60 45 6.0 5 0.05 10 13 Nitrogen 400 0.8 2.00 0.60 45 4.0 7 0.05 10 14 Nitrogen 400 0.8 2.00 0.60 45 3.0 10 0.05 10 15 Nitrogen 400 0.8 2.00 0.60 45 2.0 14 0.05 10 16 Nitrogen 400 0.8 2.00 0.60 45 1.0 29 0.05 10 17 Nitrogen 400 0.8 2.00 0.60 45 0.8 36 0.05 10 18 Nitrogen 400 0.8 2.00 0.60 45 0.7 41 0.05 10 19 Nitrogen 400 0.8 2.00 0.60 45 0.6 48 0.05 10 20 Nitrogen 400 0.8 2.00 0.60 45 0.5 57 0.05 10

[0154] Table 3B

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 21 Nitrogen 400 0.8 2.00 0.15 45 10.0 3 0.19 10 22 Nitrogen 400 0.8 2.00 0.15 45 6.0 5 0.19 10 23 Nitrogen 400 0.8 2.00 0.15 45 4.0 7 0.19 10 24 Nitrogen 400 0.8 2.00 0.15 45 3.0 10 0.19 10 25 Nitrogen 400 0.8 2.00 0.15 45 2.0 14 0.19 10 26 Nitrogen 400 0.8 2.00 0.15 45 1.0 29 0.19 10 27 Nitrogen 400 0.8 2.00 0.15 45 0.8 36 0.19 10 28 Nitrogen 400 0.8 2.00 0.15 45 0.7 41 0.19 10 29 Nitrogen 400 0.8 2.00 0.15 45 0.6 48 0.19 10 30 Nitrogen 400 0.8 2.00 0.15 45 0.5 57 0.19 10 31 Nitrogen 400 0.8 2.00 0.03 45 10.0 3 0.95 10 32 Nitrogen 400 0.8 2.00 0.03 45 6.0 5 0.95 10 33 Nitrogen 400 0.8 2.00 0.03 45 4.0 7 0.95 10 34 Nitrogen 400 0.8 2.00 0.03 45 3.0 10 0.95 10 35 Nitrogen 400 0.8 2.00 0.03 45 2.0 14 0.95 10 36 Nitrogen 400 0.8 2.00 0.03 45 1.0 29 0.95 10 37 Nitrogen 400 0.8 2.00 0.03 45 0.8 36 0.95 10 38 Nitrogen 400 0.8 2.00 0.03 45 0.7 41 0.95 10 39 Nitrogen 400 0.8 2.00 0.03 45 0.6 48 0.95 10 40 Nitrogen 400 0.8 2.00 0.03 45 0.5 57 0.95 10

[0155] Table 3C

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 41 Nitrogen 400 0.8 2.00 0.01 45 10.0 3 2.86 10 42 Nitrogen 400 0.8 2.00 0.01 45 6.0 5 2.86 10 43 Nitrogen 400 0.8 2.00 0.01 45 4.0 7 2.86 10 44 Nitrogen 400 0.8 2.00 0.01 45 3.0 10 2.86 10 45 Nitrogen 400 0.8 2.00 0.01 45 2.0 14 2.86 10 46 Nitrogen 400 0.8 2.00 0.01 45 1.0 29 2.86 10 47 Nitrogen 400 0.8 2.00 0.01 45 0.8 36 2.86 10 48 Nitrogen 400 0.8 2.00 0.01 45 0.7 41 2.86 10 49 Nitrogen 400 0.8 2.00 0.01 45 0.6 48 2.86 10 50 Nitrogen 400 0.8 2.00 0.01 45 0.5 57 2.86 10 51 Nitrogen 400 0.8 2.00 0.01 75 17.0 3 4.77 10 52 Nitrogen 400 0.8 2.00 0.01 75 10.0 5 4.77 10 53 Nitrogen 400 0.8 2.00 0.01 75 7.0 7 4.77 10 54 Nitrogen 400 0.8 2.00 0.01 75 6.0 8 4.77 10 55 Nitrogen 400 0.8 2.00 0.01 75 3.0 16 4.77 10 56 Nitrogen 400 0.8 2.00 0.01 75 1.5 32 4.77 10 57 Nitrogen 400 0.8 2.00 0.01 75 1.3 37 4.77 10 58 Nitrogen 400 0.8 2.00 0.01 75 1.2 40 4.77 10 59 Nitrogen 400 0.8 2.00 0.01 75 1.1 43 4.77 10 60 Nitrogen 400 0.8 2.00 0.01 75 0.9 53 4.77 10 61 Nitrogen 400 0.8 2.00 0.01 90 19.0 3 5.73 10 62 Nitrogen 400 0.8 2.00 0.01 90 12.0 5 5.73 10 63 Nitrogen 400 0.8 2.00 0.01 90 8.0 7 5.73 10 64 Nitrogen 400 0.8 2.00 0.01 90 6.0 10 5.73 10 65 Nitrogen 400 0.8 2.00 0.01 90 4.0 14 5.73 10 66 Nitrogen 400 0.8 2.00 0.01 90 2.0 29 5.73 10 67 Nitrogen 400 0.8 2.00 0.01 90 1.5 38 5.73 10 68 Nitrogen 400 0.8 2.00 0.01 90 1.3 44 5.73 10 69 Nitrogen 400 0.8 2.00 0.01 90 1.2 48 5.73 10 70 Nitrogen 400 0.8 2.00 0.01 90 1.1 52 5.73 10

[0156] Table 3D

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 1 1000 7.8 0,000 0,000 0.0000 - 1.91 98 Comparative example 2 1000 8.2 0.001 0.001 0.0002 - 1.91 98 Comparative example 3 1000 8.1 0.001 0.001 0.0002 - 1.91 98 Comparative example 4 1000 8.3 0.001 0.002 0.0005 - 1.92 98 Comparative example 5 1000 7.6 0.002 0.003 0.0008 - 1.92 97 Comparative example 6 1000 7.5 0.005 0.005 0.0013 - 1.92 97 Comparative example 7 1000 7.6 0.007 0.006 0.0016 - 1.91 97 Comparative example 8 1000 8.1 0.007 0.007 0.0017 - 1.90 96 Comparative example 9 1000 8.0 0.008 0.008 0.0020 - 1.89 96 Comparative example 10 1000 8.0 0.009 0.009 0.0023 - 1.88 95 Comparative example 11 1000 8.0 0,000 0,000 0.0000 - 1.92 98 Comparative example 12 1000 7.9 0.001 0.001 0.0003 0 1.93 98 Example of invention 13 1000 7.9 0.001 0.001 0.0003 0 1.93 98 Example of invention 14 1000 8.0 0.001 0.002 0.0005 0 1.94 98 Example of invention 15 1000 7.6 0.002 0.002 0.0005 1 1.94 97 Example of invention 16 1000 7.5 0.005 0.005 0.0013 2 1.93 97 Example of invention 17 1000 8.3 0.006 0.007 0.0017 2 1.93 97 Example of invention 18 1000 8.3 0.007 0.007 0.0017 3 1.93 96 Example of invention 19 1000 8.6 0.008 0.008 0.0019 4 1.93 96 Example of invention 20 1000 8.4 0.009 0.009 0.0021 - 1.87 95 Comparative example

[0157] Table 3E

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 21 1000 8.1 0,000 0,000 0.0000 - 1.91 98 Comparative example 22 1000 8.3 0.001 0.001 0.0002 0 1.93 98 Example of invention 23 1000 8.2 0.001 0.001 0.0002 0 1.94 98 Example of invention 24 1000 8.6 0.001 0.002 0.0005 0 1.95 98 Example of invention 25 1000 8.1 0.001 0.002 0.0005 0 1.95 97 Example of invention 26 1000 8.2 0.004 0.004 0.0010 0 1.95 97 Example of invention 27 1000 8.1 0.007 0.007 0.0017 1 1.94 97 Example of invention 28 1000 8.3 0.007 0.007 0.0017 1 1.94 96 Example of invention 29 1000 8.2 0.008 0.008 0.0020 2 1.93 96 Example of invention 30 1000 8.6 0.009 0.009 0.0021 - 1.87 95 Comparative example 31 1000 8.4 0,000 0,000 0.0000 0 1.92 98 Comparative example 32 1000 8.1 0.001 0.001 0.0002 0 1.93 98 Example of invention 33 1000 8.2 0.001 0.001 0.0002 0 1.94 98 Example of invention 34 1000 7.9 0.001 0.001 0.0003 0 1.95 98 Example of invention 35 1000 7.8 0.002 0.002 0.0005 0 1.95 97 Example of invention 36 1000 7.9 0.005 0.004 0.0010 0 1.94 97 Example of invention 37 1000 8.1 0.006 0.007 0.0017 1 1.94 97 Example of invention 38 1000 8.1 0.007 0.007 0.0017 2 1.93 96 Example of invention 39 1000 8.1 0.008 0.008 0.0020 4 1.93 96 Example of invention 40 1000 8.3 0.009 0.009 0.0022 - 1.85 95 Comparative example

[0158] Table 3F

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 41 1000 8.4 0,000 0,000 0.0000 - 1.91 98 Comparative example 42 1000 8.1 0.001 0.001 0.0002 0 1.93 98 Example of invention 43 1000 8.3 0.001 0.001 0.0002 0 1.94 98 Example of invention 44 1000 7.5 0.001 0.001 0.0003 0 1.95 98 Example of invention 45 1000 7.6 0.002 0.003 0.0008 0 1.96 97 Example of invention 46 1000 7.8 0.004 0.005 0.0013 0 1.95 97 Example of invention 47 1000 8.0 0.006 0.006 0.0015 1 1.94 97 Example of invention 48 1000 7.9 0.007 0.007 0.0018 2 1.93 96 Example of invention 49 1000 8.0 0.008 0.008 0.0020 3 1.93 96 Example of invention 50 1000 8.8 0.009 0.009 0.0020 - 1.84 95 Comparative example 51 1000 7.9 0,000 0,000 0.0000 - 1.91 98 Comparative example 52 1000 7.9 0.001 0.001 0.0003 0 1.93 98 Example of invention 53 1000 8.6 0.001 0.001 0.0002 0 1.93 98 Example of invention 54 1000 8.0 0.001 0.001 0.0003 0 1.94 98 Example of invention 55 1000 8.1 0.002 0.002 0.0005 0 1.95 97 Example of invention 56 1000 8.3 0.004 0.005 0.0012 0 1.94 97 Example of invention 57 1000 8.1 0.005 0.006 0.0015 1 1.93 97 Example of invention 58 1000 8.5 0.006 0.007 0.0016 3 1.93 96 Example of invention 59 1000 8.6 0.008 0.008 0.0019 4 1.93 96 Example of invention 60 1000 8.0 0.009 0.009 0.0023 - 1.83 95 Comparative example 61 1000 - - - - - 1.88 97 Comparative example 62 1000 - - - - - 1.87 97 Example of invention 63 1000 - - - - - 1.89 97 Example of invention 64 1000 - - - - - 1.90 97 Example of invention 65 1000 - - - - - 1.91 96 Example of invention 66 1000 - - - - - 1.89 96 Example of invention 67 1000 - - - - - 1.87 96 Example of invention 68 1000 - - - - - 1.87 95 Example of invention 69 1000 - - - - - 1.86 95 Example of invention 70 1000 - - - - - 1.67 95 Comparative example

[0159] 4. Example 4

A slab is prepared in which the chemical composition is, in wt.%: C: 0.08%, Si: 3.3%, Mn: 0.08%, S: 0.02%, Al: 0.03% and N: 0.01%, with the remainder being Fe and impurities.

[0160] This slab is heated to 1350°C in a heating furnace. A hot rolling step is performed on the heated slab to produce a hot-rolled steel sheet having a sheet thickness of 2.3 mm. The hot-rolled steel sheet is subjected to a hot annealing step in a hot annealing strip and then cold rolling to produce a cold-rolled steel sheet having a thickness of 0.22 mm. A decarburization annealing step is performed on the cold-rolled steel sheet after the cold rolling step. In this decarburization annealing step, partial rapid heating with a laser beam is performed on one surface of the steel sheet under the conditions shown in Table 4A before the temperature is increased. The scanning direction of the laser is set to 90 degrees relative to the rolling direction.

[0161] After partial rapid heating, the steel sheet is primarily recrystallized by heating in a non-oxidizing atmosphere containing hydrogen and nitrogen at a temperature increase rate shown in Table 4B, then the decarburization annealing temperature is set to 830°C, and the steel sheet is held for 60 seconds. In Example 4, the temperature increase rate is varied. At this time, the atmosphere in the heat treatment furnace for performing the decarburization annealing treatment is a humid atmosphere containing hydrogen and nitrogen. An annealing separator (water slurry) containing MgO as the main component is applied to the surface of the steel sheet after the decarburization annealing, and then the steel sheet is wound into a coil form. The steel sheet wound into a coil is subjected to finish annealing.

[0162] For the steel sheet, after the finish annealing step, a step of forming an insulating film is performed. In the step of forming an insulating film, an insulating coating agent, mainly consisting of colloidal silica and phosphate, is applied to the surface (glass film) of the grain-oriented electrical steel sheet after the finish annealing step, and then annealing is performed. In this way, an insulating film as a highly tensioned insulating film is formed on the glass film. The grain-oriented electrical steel sheet for each test number is produced through the above-mentioned manufacturing steps.

[0163] 4-1. Removing the film

The chemical composition of the base steel sheet can be measured by a known component analytical method. First, the primary film and secondary film are removed from the base steel sheet by the following method. Specifically, a grain-oriented electrical steel sheet containing a secondary film is immersed in a high-temperature alkaline solution to remove the secondary film. The composition and temperature of the alkaline solution and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet containing a secondary film is immersed in an aqueous sodium hydroxide solution of NaOH: 30-50 wt% + _H2O : 50-70 wt% at 80-90°C for 5-10 minutes and, after immersion, washed with water and dried. Through this step, the secondary film is removed from the grain-oriented electrical steel sheet.

[0164] Additionally, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in high-temperature hydrochloric acid to remove the primary film. The concentration and temperature of the hydrochloric acid and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in 30-40 mass% hydrochloric acid at 80-90°C for 1-5 minutes and, after immersion, is washed with water and dried. In this way, a base steel sheet from which the secondary and primary films are removed is obtained.

[0165] 4-2. Experiment with measuring the chemical composition of the base steel sheet

The chemical composition of the base steel sheet for grain-oriented electrical steel sheet for each test number is measured using the following method. First, the primary film and secondary film of the grain-oriented electrical steel sheet are removed using the above-described method to extract the base steel sheet. Using the base steel sheet, the chemical composition of the base steel sheet is analyzed using the following method (measuring the chemical composition of steel sheet).

Chips are collected from the obtained base steel sheet. The collected chips are dissolved in acid to form a solution. The solution is subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES) for elemental analysis. The C and S contents are determined using the known high-frequency combustion method (infrared absorption after combustion). The N content is determined using the known inert gas fusion method by thermal conductivity. Specifically, the measurement is performed using a component analyzer (trade name: ICPS-8000) manufactured by Shimadzu Corporation.

[0166] The analysis results show that the chemical composition of the base steel sheet in any of the test numbers in Example 4 contains, in mass%: C: 0.01% or less, Si: 3.3%, Mn: 0.08%, S: 0.01% or less, sol.Al: 0.01% or less, and N: 0.01% or less, with the remainder being Fe and impurities.

[0167] The magnetic characteristic (B8 magnetic flux density value) of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2556 (2015). The obtained B8 magnetic flux density is shown in Table 4B.

[0168] The shape of the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, using a commercially available surface roughness measuring device (SE3500, manufactured by Kosaka Laboratory Ltd.) and SE2555N (apex curvature radius: 2 μm) as the stylus of the detection unit, with the measurement length in the rolling direction set to 15 mm per measurement, the measurement is continuously performed 5 times, whereby the surface roughness along a length of 75 mm in total is measured. The measurement is performed on both the front side and the back side. W, D _protrusion , and D _recess at each of the five points in the measurement areas of the front side and the back side are measured and evaluated using their average value. The width W of the obtained deformed region, the maximum depth D _recess of the recessed portion on one side of the surface of the deformed region, and the maximum height D _protrusion of the protrusion on the side of the rear surface of the deformed region are shown in Table 4B.

[0169] In addition, the spatial coefficient of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2550-5 (2020). The obtained spatial coefficient is shown in Table 4B.

[0170] Additionally, the area ratio of abnormal grains in the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, the crystal orientation of the region with the width W of the deformed region is measured at a pitch of 2 mm in the width direction of the grain-oriented electrical steel sheet along the centerline in the longitudinal direction of the deformed region using a Laue diffractometer. Then, from the crystal orientation of each measurement point, the number of measurement points indicating abnormal grains having a deviation angle of 15° or more from the Goss orientation is extracted, and the ratio of the number of these measurement points to the total number of measurement points is considered as the area ratio of abnormal grains. However, for the steel number with poor quality magnetism of less than 1.93 T, when measuring the magnetic characteristics described above, the area ratio of abnormal grains is not measured using the Laue diffractometer. The area fraction of the obtained abnormal grains is shown in Table 4B.

[0171] Referring to Tables 4A and B, in steel No. 1, 14 and 27, the temperature rise rate is slow, the effect of providing secondary recrystallization nuclei only depending on the rapid heating effect by laser heating is insufficient, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0172] In steel No. 13, 26 and 39, the temperature rise rate is high, the lattice orientation of the matching sites to promote the growth of secondary recrystallization nuclei is reduced, and the magnetic flux density is less than 1.93 T, which is poor in quality.

[0173] In a steel number other than the above, since all the conditions of the manufacturing step are proper, the magnetic flux density is 1.93 T or more, which is excellent, and the space coefficient is also up to 96% or more.

[0174] Table 4A

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 1 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 2 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 3 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 4 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 5 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 6 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 7 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 8 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 9 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 10 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 11 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 12 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 13 Nitrogen 400 0.8 0.60 1.00 45 10.0 10 0.10 10 14 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 15 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 16 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 17 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 18 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 19 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 20 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 21 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 22 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 23 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 24 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 25 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 26 Nitrogen 400 0.8 2.00 0.30 45 3.0 10 0.10 10 27 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 28 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 29 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 30 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 31 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 32 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 33 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 34 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 35 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 36 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 37 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 38 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10 39 Nitrogen 400 0.8 5.00 0.11 45 1.1 10 0.10 10

[0175] Table 4B

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 1 1 2.2 0.002 0.002 0.0018 - 1.76 98 Comparative example 2 5 2.2 0.001 0.001 0.0009 0 1.93 98 Example of invention 3 20 2.1 0.001 0.002 0.0019 0 1.94 98 Example of invention 4 50 2.3 0.002 0.002 0.0017 0 1.94 98 Example of invention 5 100 2.4 0.001 0.002 0.0017 0 1.96 98 Example of invention 6 200 2.3 0.002 0.002 0.0017 0 1.96 98 Example of invention 7 400 2.3 0.001 0.001 0.0009 0 1.96 98 Example of invention 8 600 1.9 0.002 0.002 0.0021 0 1.95 98 Example of invention 9 800 2.2 0.002 0.002 0.0018 0 1.95 98 Example of invention 10 1000 2.4 0.002 0.002 0.0017 0 1.95 98 Example of invention 11 1500 2.4 0.002 0.002 0.0017 0 1.94 98 Example of invention 12 2000 2.3 0.001 0.002 0.0017 0 1.93 98 Example of invention 13 2500 2.4 0.002 0.002 0.0017 - 1.92 98 Comparative example 14 1 7.5 0.002 0.002 0.0005 - 1.83 98 Comparative example 15 5 7.8 0.001 0.002 0.0005 0 1.93 98 Example of invention 16 20 8.0 0.001 0.001 0.0003 0 1.95 98 Example of invention 17 50 7.5 0.002 0.002 0.0005 0 1.94 98 Example of invention 18 100 7.6 0.001 0.001 0.0003 0 1.96 98 Example of invention 19 200 7.8 0.002 0.002 0.0005 0 1.96 98 Example of invention 20 400 7.5 0.001 0.002 0.0005 0 1.95 98 Example of invention 21 600 7.8 0.002 0.002 0.0005 0 1.94 98 Example of invention 22 800 7.9 0.002 0.002 0.0005 0 1.94 98 Example of invention 23 1000 8.0 0.001 0.002 0.0005 0 1.94 98 Example of invention 24 1500 8.0 0.002 0.002 0.0005 0 1.93 98 Example of invention 25 2000 7.9 0.001 0.001 0.0003 0 1.93 98 Example of invention 26 2500 7.9 0.002 0.002 0.0005 - 1.91 98 Comparative example 27 1 9.2 0.001 0.001 0.0002 - 1.84 98 Comparative example 28 5 10.1 0.002 0.002 0.0004 0 1.93 98 Example of invention 29 20 10.6 0.002 0.002 0.0004 0 1.95 98 Example of invention 30 50 9.8 0.001 0.001 0.0002 0 1.95 98 Example of invention 31 100 9.9 0.001 0.002 0.0004 0 1.96 98 Example of invention 32 200 9.9 0.001 0.001 0.0002 0 1.95 98 Example of invention 33 400 10.0 0.001 0.001 0.0002 0 1.95 98 Example of invention 34 600 10.2 0.001 0.001 0.0002 0 1.94 98 Example of invention 35 800 9.9 0.001 0.002 0.0004 0 1.94 98 Example of invention 36 1000 10.2 0.001 0.001 0.0002 0 1.93 98 Example of invention 37 1500 9.2 0.001 0.001 0.0002 0 1.93 98 Example of invention 38 2000 9.6 0.001 0.001 0.0002 0 1.93 98 Example of invention 39 2500 9.4 0.001 0.002 0.0004 - 1.92 98 Comparative example

[0176] 5. Example 5

A slab is prepared in which the chemical composition is, in wt.%: C: 0.08%, Si: 3.3%, Mn: 0.08%, S: 0.02%, Al: 0.03% and N: 0.01%, with the remainder being Fe and impurities.

[0177] This slab is heated to 1350°C in a heating furnace. A hot rolling step is performed on the heated slab to produce a hot-rolled steel sheet having a sheet thickness of 2.3 mm. The hot-rolled steel sheet is subjected to a hot annealing step in a hot annealing strip and then cold rolling to produce a cold-rolled steel sheet having a thickness of 0.22 mm. A decarburization annealing step is performed on the cold-rolled steel sheet after the cold rolling step. In this decarburization annealing step, partial rapid heating with a laser beam is performed on one surface of the steel sheet under the conditions shown in Table 5A before the temperature is increased. The scanning direction of the laser is set to 90 degrees relative to the rolling direction. In Example 5, the tension applied to the cold-rolled steel sheet during laser beam irradiation and the temperature of the cold-rolled steel sheet are varied.

[0178] After partial rapid heating, the steel sheet is primarily recrystallized by heating in a non-oxidizing atmosphere containing hydrogen and nitrogen at a temperature increase rate shown in Table 5B, then the decarburization annealing temperature is set to 830°C, and the steel sheet is held for 60 seconds. At this time, the atmosphere in the heat treatment furnace for performing the decarburization annealing treatment is a humid atmosphere containing hydrogen and nitrogen. An annealing separator (water slurry) containing MgO as the main component is applied to the surface of the steel sheet after the decarburization annealing, and then the steel sheet is wound into a coil form. The steel sheet wound into a coil is subjected to finish annealing.

[0179] For the steel sheet, after the finish annealing step, a step of forming an insulating film is performed. In the step of forming an insulating film, an insulating coating agent, mainly consisting of colloidal silica and phosphate, is applied to the surface (glass film) of the grain-oriented electrical steel sheet after the finish annealing step, and then annealing is performed. In this way, an insulating film as a highly tensioned insulating film is formed on the glass film. The grain-oriented electrical steel sheet for each test number is produced through the above-mentioned manufacturing steps.

[0180] 5-1. Removing the film

The chemical composition of the base steel sheet can be measured by a known component analytical method. First, the primary film and secondary film are removed from the base steel sheet by the following method. Specifically, a grain-oriented electrical steel sheet containing a secondary film is immersed in a high-temperature alkaline solution to remove the secondary film. The composition and temperature of the alkaline solution and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet containing a secondary film is immersed in an aqueous sodium hydroxide solution of NaOH: 30-50 wt% + _H2O : 50-70 wt% at 80-90°C for 5-10 minutes and, after immersion, washed with water and dried. Through this step, the secondary film is removed from the grain-oriented electrical steel sheet.

[0181] Additionally, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in high-temperature hydrochloric acid to remove the primary film. The concentration and temperature of the hydrochloric acid and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in 30-40% by weight hydrochloric acid at 80-90°C for 1-5 minutes and, after immersion, is washed with water and dried. In this way, a base steel sheet from which the secondary and primary films are removed is obtained.

[0182] 5-2. Experiment with measuring the chemical composition of the base steel sheet

The chemical composition of the base steel sheet for grain-oriented electrical steel sheet for each test number is measured using the following method. First, the primary film and secondary film of the grain-oriented electrical steel sheet are removed using the above-described method to extract the base steel sheet. Using the base steel sheet, the chemical composition of the base steel sheet is analyzed using the following method (measuring the chemical composition of steel sheet).

Chips are collected from the obtained base steel sheet. The collected chips are dissolved in acid to form a solution. The solution is subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES) for elemental analysis. The C and S contents are determined using the known high-frequency combustion method (infrared absorption after combustion). The N content is determined using the known inert gas fusion method by thermal conductivity. Specifically, the measurement is performed using a component analyzer (trade name: ICPS-8000) manufactured by Shimadzu Corporation.

[0183] The analysis results show that the chemical composition of the base steel sheet in any of the test numbers in Example 5 contains, in mass%: C: 0.01% or less, Si: 3.3%, Mn: 0.08%, S: 0.01% or less, sol.Al: 0.01% or less, and N: 0.01% or less, with the remainder being Fe and impurities.

[0184] The magnetic characteristic (B8 magnetic flux density value) of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2556 (2015). The obtained B8 magnetic flux density is shown in Table 5B.

[0185] The shape of the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, using a commercially available surface roughness measuring device (SE3500, manufactured by Kosaka Laboratory Ltd.) and SE2555N (apex curvature radius: 2 μm) as the stylus of the detection unit, with the measurement length in the rolling direction set to 15 mm per measurement, the measurement is continuously performed 5 times, whereby the surface roughness along a length of 75 mm in total is measured. The measurement is performed on both the front side and the back side. W, D _protrusion , and D _recess at each of the five points in the measurement areas of the front side and the back side are measured and evaluated using their average value. The width W of the obtained deformed region, the maximum depth D _recess of the recessed portion on one side of the surface of the deformed region, and the maximum height D _protrusion of the protrusion on the side of the rear surface of the deformed region are shown in Table 5B.

[0186] In addition, the spatial coefficient of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2550-5 (2020). The obtained spatial coefficient is shown in Table 5B.

[0187] Additionally, the area ratio of abnormal grains in the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, the crystal orientation of the region with the width W of the deformed region is measured at a pitch of 2 mm in the width direction of the grain-oriented electrical steel sheet along the centerline in the longitudinal direction of the deformed region using a Laue diffractometer. Then, from the crystal orientation of each measurement point, the number of measurement points indicating abnormal grains having a deviation angle of 15° or more from the Goss orientation is extracted, and the ratio of the number of these measurement points to the total number of measurement points is considered as the area ratio of abnormal grains. However, for the steel number with poor quality magnetism of less than 1.93 T, when measuring the magnetic characteristics described above, the area ratio of abnormal grains is not measured using the Laue diffractometer. The area fraction of the obtained abnormal grains is shown in Table 5B.

[0188] Referring to Tables 5A and 5B, in steel No. 1-5, the tension during laser heating is low, the groove and projection in the deformed region are large, the steepness is 0.01 or more, and the space coefficient is less than 96%.

[0189] In steel No. 21-25, the tension during laser heating is high, causing deterioration of the primary recrystallization texture, the magnetic properties are inferior in quality, and the B8 magnetic flux density is less than 1.93 T.

[0190] In steel numbers 6, 11 and 16, the temperature during laser heating is low, the shape deterioration associated with the rapid temperature change in the deformed region is significant, the groove and projection in the deformed region are large, the steepness is 0.01 or more, and the space factor is less than 96%.

[0191] In steel numbers 10, 15 and 20, the temperature during laser heating is high, recrystallization continues before laser heating, and the partial rapid heating effect is not obtained, due to which the magnetic flux density is inferior in quality and less than 1.93 T.

[0192] In a steel number other than the above, since all the conditions of the manufacturing step are proper, the magnetic flux density is 1.93 T or more, which is excellent, and the space coefficient is also up to 96% or more.

[0193] Table 5A

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 1 Nitrogen 150 0.1 0.60 0.40 45 15.0 6 0.24 10 2 Nitrogen 200 0.1 0.60 0.40 45 15.0 6 0.24 10 3 Nitrogen 400 0.1 0.60 0.40 45 15.0 6 0.24 10 4 Nitrogen 550 0.1 0.60 0.40 45 15.0 6 0.24 10 5 Nitrogen 600 0.1 0.60 0.40 45 15.0 6 0.24 10 6 Nitrogen 150 0.2 0.60 0.40 45 15.0 6 0.24 10 7 Nitrogen 200 0.2 0.60 0.40 45 15.0 6 0.24 10 8 Nitrogen 400 0.2 0.60 0.40 45 15.0 6 0.24 10 9 Nitrogen 550 0.2 0.60 0.40 45 15.0 6 0.24 10 10 Nitrogen 600 0.2 0.60 0.40 45 15.0 6 0.24 10 11 Nitrogen 150 0.5 0.60 0.40 45 15.0 6 0.24 10 12 Nitrogen 200 0.5 0.60 0.40 45 15.0 6 0.24 10 13 Nitrogen 400 0.5 0.60 0.40 45 15.0 6 0.24 10 14 Nitrogen 550 0.5 0.60 0.40 45 15.0 6 0.24 10 15 Nitrogen 600 0.5 0.60 0.40 45 15.0 6 0.24 10 16 Nitrogen 150 1.2 0.60 0.40 45 15.0 6 0.24 10 17 Nitrogen 200 1.2 0.60 0.40 45 15.0 6 0.24 10 18 Nitrogen 400 1.2 0.60 0.40 45 15.0 6 0.24 10 19 Nitrogen 550 1.2 0.60 0.40 45 15.0 6 0.24 10 20 Nitrogen 600 1.2 0.60 0.40 45 15.0 6 0.24 10 21 Nitrogen 150 1.4 0.60 0.40 45 15.0 6 0.24 10 22 Nitrogen 200 1.4 0.60 0.40 45 15.0 6 0.24 10 23 Nitrogen 400 1.4 0.60 0.40 45 15.0 6 0.24 10 24 Nitrogen 550 1.4 0.60 0.40 45 15.0 6 0.24 10 25 Nitrogen 600 1.4 0.60 0.40 45 15.0 6 0.24 10

[0194] Table 5B

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 1 1000 2.5 0.010 0.011 0.0088 0 1.95 93 Comparative example 2 1000 2.6 0.009 0.009 0.0069 0 1.95 94 Comparative example 3 1000 2.4 0.007 0.008 0.0067 0 1.95 95 Comparative example 4 1000 2.2 0.006 0.006 0.0055 0 1.95 95 Comparative example 5 1000 2.4 0.006 0.006 0.0050 - 1.91 95 Comparative example 6 1000 2.4 0.006 0.007 0.0058 0 1.95 95 Comparative example 7 1000 2.4 0.004 0.004 0.0033 0 1.95 97 Example of invention 8 1000 2.2 0.002 0.002 0.0018 0 1.95 98 Example of invention 9 1000 2.5 0.001 0.001 0.0008 0 1.95 98 Example of invention 10 1000 2.6 0.001 0.001 0.0008 - 1.91 98 Comparative example 11 1000 2.4 0.006 0.006 0.0050 0 1.94 95 Comparative example 12 1000 2.4 0.003 0.004 0.0033 0 1.94 97 Example of invention 13 1000 2.3 0.003 0.003 0.0026 0 1.94 97 Example of invention 14 1000 2.3 0.002 0.002 0.0017 0 1.94 98 Example of invention 15 1000 2.6 0.001 0.001 0.0008 - 1.91 98 Comparative example 16 1000 2.2 0.006 0.007 0.0064 0 1.93 95 Comparative example 17 1000 2.4 0.004 0.004 0.0033 0 1.93 97 Example of invention 18 1000 2.8 0.003 0.003 0.0021 0 1.93 97 Example of invention 19 1000 2.9 0.002 0.003 0.0021 0 1.93 97 Example of invention 20 1000 2.4 0.002 0.002 0.0017 - 1.91 98 Comparative example 21 1000 2.3 0.008 0.008 0.0070 - 1.89 95 Comparative example 22 1000 2.4 0.005 0.005 0.0042 - 1.92 97 Comparative example 23 1000 2.3 0.005 0.005 0.0043 - 1.92 97 Comparative example 24 1000 2.4 0.004 0.004 0.0033 - 1.92 97 Comparative example 25 1000 2.4 0.003 0.003 0.0025 - 1.89 97 Comparative example

[0195] 6. Example 6

A slab with the chemical composition shown in Table 6A, with the remainder being Fe and impurities, is prepared. This slab is heated to 1350°C in a reheating furnace. The heated slab undergoes hot rolling to produce a hot-rolled steel sheet with a sheet thickness of 2.3 mm. The hot-rolled steel sheet undergoes annealing in a hot annealing strip and then cold rolling to produce a cold-rolled steel sheet with a thickness of 0.22 mm. A decarburization annealing step is performed on the cold-rolled steel sheet after the cold rolling step. In this decarburization annealing step, partial rapid heating with a laser beam is performed on one surface of the steel sheet under the conditions shown in Table 6B before the temperature is increased. The laser scanning direction is set at 90 degrees relative to the rolling direction.

[0196] After partial rapid heating, the steel sheet is primarily recrystallized by heating in a non-oxidizing atmosphere containing hydrogen and nitrogen at a temperature increase rate shown in Table 6C, then the decarburization annealing temperature is set to 830°C, and the steel sheet is held for 60 seconds. At this time, the atmosphere in the heat treatment furnace for performing the decarburization annealing treatment is a humid atmosphere containing hydrogen and nitrogen. An annealing separator (water slurry) containing MgO as the main component is applied to the surface of the steel sheet after the decarburization annealing, and then the steel sheet is wound into a coil form. The steel sheet wound into a coil is subjected to finish annealing.

[0197] For the steel sheet, after the finish annealing step, a step of forming an insulating film is performed. In the insulating film forming step, an insulating coating agent, mainly consisting of colloidal silica and phosphate, is applied to the surface (glass film) of the grain-oriented electrical steel sheet after the finish annealing step, and then annealing is performed. In this way, an insulating film as a highly tensioned insulating film is formed on the glass film. The grain-oriented electrical steel sheet for each test number is produced through the above-mentioned manufacturing steps.

[0198] 6-1. Removing the film

The chemical composition of the base steel sheet can be measured by a known component analytical method. First, the primary film and secondary film are removed from the base steel sheet by the following method. Specifically, a grain-oriented electrical steel sheet containing a secondary film is immersed in a high-temperature alkaline solution to remove the secondary film. The composition and temperature of the alkaline solution and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet containing a secondary film is immersed in an aqueous sodium hydroxide solution of NaOH: 30-50 wt% + _H2O : 50-70 wt% at 80-90°C for 5-10 minutes and, after immersion, washed with water and dried. Through this step, the secondary film is removed from the grain-oriented electrical steel sheet.

[0199] Additionally, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in high-temperature hydrochloric acid to remove the primary film. The concentration and temperature of the hydrochloric acid and the immersion time can be appropriately adjusted. For example, the grain-oriented electrical steel sheet from which the secondary film is removed and on which the primary film remains is immersed in 30-40% by weight hydrochloric acid at 80-90°C for 1-5 minutes and, after immersion, is washed with water and dried. In this way, a base steel sheet from which the secondary and primary films are removed is obtained.

[0200] 6-2. Experiment with measuring the chemical composition of the base steel sheet

The chemical composition of the base steel sheet for grain-oriented electrical steel sheet for each test number is measured using the following method. First, the primary film and secondary film of the grain-oriented electrical steel sheet are removed using the above-described method to extract the base steel sheet. Using the base steel sheet, the chemical composition of the base steel sheet is analyzed using the following method (measuring the chemical composition of steel sheet).

Chips are collected from the obtained base steel sheet. The collected chips are dissolved in acid to form a solution. The solution is subjected to inductively coupled plasma atomic emission spectrometry (ICP-AES) for elemental analysis. The C and S contents are determined using the known high-frequency combustion method (infrared absorption after combustion). The N content is determined using the known inert gas fusion method by thermal conductivity. Specifically, the measurement is performed using a component analyzer (trade name: ICPS-8000) manufactured by Shimadzu Corporation.

[0201] The analysis results show that the chemical composition of the base steel sheet in Example 6 contains the components described in Table 6A, with the remainder being Fe and impurities.

[0202] The magnetic characteristic (B8 magnetic flux density value) of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2556 (2015). The obtained B8 magnetic flux density is shown in Table 6C.

[0203] The shape of the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, using a commercially available surface roughness measuring device (SE3500, manufactured by Kosaka Laboratory Ltd.) and SE2555N (apex curvature radius: 2 μm) as the stylus of the detection unit, with the measurement length in the rolling direction set to 15 mm per measurement, the measurement is continuously performed 5 times, thereby measuring the surface roughness over a length of 75 mm in total. The measurement is performed on both the front side and the back side. W, D _protrusion , and D _recess at each of the five points in the measurement areas of the front side and the back side are measured and evaluated using their average value. The width W of the obtained deformed region, the maximum depth D _recess of the recessed portion on one side of the surface of the deformed region, and the maximum height D _protrusion of the protrusion on the side of the rear surface of the deformed region are shown in Table 6C.

[0204] In addition, the spatial coefficient of the grain-oriented electrical steel sheet for each test number is evaluated in accordance with JIS C2550-5 (2020). The obtained spatial coefficient is shown in Table 6C.

[0205] In addition, the area ratio of abnormal grains in the deformed region of the grain-oriented electrical steel sheet for each test number is measured by the following method. That is, the crystal orientation of the region with the width W of the deformed region is measured at a pitch of 2 mm in the width direction of the grain-oriented electrical steel sheet along the centerline in the longitudinal direction of the deformed region using a Laue diffractometer. Then, from the crystal orientation of each measurement point, the number of measurement points indicating abnormal grains having a deviation angle of 15° or more from the Goss orientation is extracted, and the ratio of the number of these measurement points to the total number of measurement points is considered as the area ratio of abnormal grains. However, for the steel number with poor quality magnetism of less than 1.93 T, when measuring the magnetic characteristics described above, the area ratio of abnormal grains is not measured using the Laue diffractometer. The area fraction of the obtained abnormal grains is shown in Table 6C.

[0206] Referring to Tables 6A-C, in steel Nos. 1-19, since the chemical composition of the slab is proper and all the conditions of the manufacturing step are proper, the magnetic flux density is 1.93 T or more, which is excellent, and the space coefficient is also up to 96% or more.

[0207] Table 6A

Steel number Chemical composition of the slab (wt.%) Chemical composition of steel sheet (wt.%) C Si Sol-Al Mn N S Other C Si Sol-Al Mn N S Other 1 0.08 3.3 0.03 0.08 0.01 0.02 0.00 3.3 0.00 0.08 0.00 0.00 2 0.08 3.5 0.03 0.06 0.01 0.01 0.00 3.5 0.00 0.06 0.00 0.00 3 0.06 2.6 0.02 0.10 0.02 0.02 0.00 2.6 0.00 0.10 0.01 0.00 4 0.07 2.9 0.02 0.04 0.01 0.01 0.00 2.9 0.00 0.04 0.00 0.00 5 0.09 3.6 0.03 0.12 0.01 0.03 0.01 3.6 0.01 0.12 0.00 0.01 6 0.08 3.2 0.03 0.08 0.01 0.02 0.03 P 0.00 3.3 0.00 0.08 0.00 0.00 0.03 P 7 0.08 3.4 0.02 0.08 0.01 0.02 0.01 Sb 0.00 3.4 0.00 0.08 0.00 0.00 0.01 Sb 8 0.05 2.9 0.01 0.14 0.01 0.01 0.08 Sn 0.00 2.9 0.00 0.14 0.00 0.00 0.08 Sn 9 0.08 3.3 0.03 0.08 0.01 0.02 0.05 Cr 0.00 3.3 0.00 0.08 0.00 0.00 0.05 Cr 10 0.08 3.3 0.03 0.08 0.01 0.02 0.05 Cu 0.00 3.3 0.00 0.08 0.00 0.00 0.05 Cu 11 0.08 3.4 0.03 0.08 0.01 0.02 0.04 Ni 0.00 3.4 0.00 0.08 0.00 0.00 0.04 Ni 12 0.08 3.3 0.03 0.08 0.01 0.02 0.0020 Bi 0.00 3.3 0.00 0.08 0.00 0.00 0.0020 Bi 13 0.09 3.4 0.03 0.08 0.01 0.02 0.01 P, 0.10 Sn 0.00 3.4 0.00 0.08 0.00 0.00 0.01 P, 0.10 Sn 14 0.08 3.3 0.03 0.08 0.01 0.02 0.01 P, 0.05 Cu 0.00 3.3 0.00 0.08 0.00 0.00 0.01 P, 0.05 Cu 15 0.08 3.2 0.03 0.08 0.02 0.02 0.10 Sn, 0.0012 Bi 0.00 3.2 0.00 0.08 0.01 0.00 0.10 Sn, 0.0012 Bi 16 0.08 3.2 0.02 0.08 0.01 0.02 0.03 Cr, 0.05 Ni, 0.01 Sb 0.00 3.2 0.00 0.08 0.00 0.00 0.03 Cr, 0.05 Ni, 0.01 Sb 17 0.08 3.4 0.03 0.08 0.01 0.02 0.20 Sn, 0.01 P, 0.03 Ni 0.00 3.4 0.00 0.08 0.00 0.00 0.20 Sn, 0.01 P, 0.03 Ni 18 0.08 3.3 0.03 0.06 0.01 0.01 0.01 Se 0.00 3.3 0.01 0.06 0.00 0.00 0.01 Se 19 0.08 3.3 0.03 0.07 0.01 0.01 0.01 Se, 0.06 Sn, 0.05 P 0.00 3.3 0.00 0.07 0.00 0.00 0.01 Se, 0.06 Sn, 0.05 P

[0208] Table 6B

Steel number Laser irradiation conditions Atmosphere Temperature of steel sheet, °C Tension of steel sheet, kg/ ^mm2 Focused diameter Dl in the rolling direction, mm Focused diameter Dc in the width direction, mm Output power P, W Speed Vc, mm/s Energy density Up of irradiation, J/mm ² Instantaneous power density Ip, kW/mm ² Laser irradiation interval L, mm 1 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 2 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 3 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 4 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 5 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 6 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 7 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 8 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 9 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 10 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 11 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 12 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 13 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 14 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 15 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 16 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 17 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 18 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10 19 Nitrogen 400 1.0 0.60 0.50 45 12 8 0.19 10

[0209] Table 6C

Steel number Rate V of temperature increase at the stage of decarburizing annealing, °C/s Width W of the deformed region, mm Maximum depth D _{of the} recessed part on the laser-irradiated surface, mm Maximum height D _{of the protrusion} on the rear surface of the laser-irradiated area, mm 2D _slope /W Abnormal grain coefficient,% Magnetic flux density B8, T Spatial coefficient,% Notes 1 1000 2.0 0.001 0.001 0.0010 0 1.93 97 Example of invention 2 1000 2.4 0.002 0.002 0.0017 0 1.93 97 Example of invention 3 1000 2.2 0.002 0.002 0.0018 0 1.94 97 Example of invention 4 1000 1.8 0.001 0.002 0.0022 0 1.94 97 Example of invention 5 1000 2.6 0.001 0.002 0.0015 0 1.93 97 Example of invention 6 1000 2.0 0.001 0.002 0.0020 0 1.93 97 Example of invention 7 1000 2.2 0.002 0.002 0.0018 0 1.93 97 Example of invention 8 1000 2.4 0.001 0.002 0.0017 0 1.94 97 Example of invention 9 1000 2.4 0.001 0.002 0.0017 0 1.93 98 Example of invention 10 1000 2.2 0.001 0.001 0.0009 0 1.94 97 Example of invention 11 1000 2.6 0.001 0.002 0.0015 0 1.93 97 Example of invention 12 1000 2.4 0.001 0.002 0.0017 0 1.95 98 Example of invention 13 1000 2.4 0.001 0.001 0.0008 0 1.94 98 Example of invention 14 1000 2.3 0.001 0.001 0.0009 0 1.94 98 Example of invention 15 1000 2.4 0.001 0.001 0.0008 0 1.96 98 Example of invention 16 1000 2.5 0.002 0.001 0.0008 0 1.93 98 Example of invention 17 1000 2.4 0.001 0.001 0.0008 0 1.94 98 Example of invention 18 1000 2.4 0.001 0.002 0.0017 0 1.93 97 Example of invention 19 1000 2.9 0.002 0.002 0.0014 0 1.93 97 Example of invention

[0210] Although preferred embodiments of the present invention are described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is obvious that those skilled in the art to which the present invention belongs may conceive of various changes or modifications within the scope of the technical idea described in the claims, and it should naturally be understood that they also belong to the scope of the present invention.

Claims (95)

1. A sheet of grain-oriented electrical steel containing: base steel sheet having a chemical composition containing, wt.%: Si: 2.5-4.5, Mn: 0.01-1.00, N: 0.01 or less, C: 0.01 or less, solution.Al: 0.01 or less, S and/or Se: 0.01 or less, optionally, one or more of: P: up to 0.05, Sb: up to 0.50, Sn: up to 0.30, Cr: up to 0.50, Cu: up to 0.50, Ni: up to 0.50 and Bi: up to 0.0100, the rest is Fe and impurities, wherein the magnetic flux density B8 in the rolling direction of the grain-oriented electrical steel sheet is 1.93 T or more, the deformed region extending across the entire width of the grain-oriented electrical steel sheet is periodically formed at an interval L of 3 mm or more and 30 mm or less in the direction intersecting the rolling direction of the grain-oriented electrical steel sheet, the deformed region has a width W of 0.2 mm or more and 30.6 mm or less, a protrusion having a maximum height D _protrusion of 1 μm or more and 5 μm or less is formed on one surface of the deformed region and a recessed portion having a maximum depth D _{recessed of} 1 μm or more and 4 μm or less is formed on the opposite surface. 2. A sheet of electrical steel with an oriented grain structure, containing: base steel sheet having a chemical composition containing, wt.%: Si: 2.5-4.5, Mn: 0.01-1.00, N: 0.01 or less, C: 0.01 or less, solution.Al: 0.01 or less, S and/or Se: 0.01 or less, optionally, one or more of: P: up to 0.05, Sb: up to 0.50, Sn: up to 0.30, Cr: up to 0.50, Cu: up to 0.50, Ni: up to 0.50 and Bi: up to 0.0100, the rest is Fe and impurities, wherein the magnetic flux density B8 in the rolling direction of the grain-oriented electrical steel sheet is 1.93 T or more, the deformed region extending across the entire width of the grain-oriented electrical steel sheet is periodically formed at an interval L of 3 mm or more and 30 mm or less in the direction intersecting the rolling direction of the grain-oriented electrical steel sheet, the deformed region has a width W of 0.2 mm or more and 30.6 mm or less, a protrusion having a maximum height D _protrusion of 1 μm or more and 8 μm or less is formed on one surface of the deformed region, a recessed portion having a maximum depth D _{recessed of} 1 μm or more and 8 μm or less is formed on the opposite surface, and the protrusion has a steepness 2D _protrusion /W of 0.0001 or more and less than 0.0050. 3. A grain-oriented electrical steel sheet according to claim 1 or 2, wherein in the deformed region the ratio of the area of grains whose crystal orientation deviates from the Goss orientation by 15° or more to the total area of the deformed region is 5% or less. 4. A grain-oriented electrical steel sheet according to claim 1 or 2, wherein the base steel sheet has a chemical composition containing, by weight, one or more of: P: 0.01-0.05, Sb: 0.01-0.50, Sn: 0.01-0.30, Cr: 0.01-0.50, Cu: 0.01-0.50, Ni: 0.01-0.50 and Bi: 0.0001-0.0100. 5. A method for producing a sheet of electrical steel with an oriented grain structure according to paragraph 1 or 2, wherein the method includes: - a stage of hot rolling, in which a slab is heated, having a chemical composition containing, by weight %: Si: 2.5-4.5, Mn: 0.01-1.00, N: 0.002-0.020, C: 0.02-0.10, solution.Al: 0.01-0.05, S and/or Se: 0.01-0.05, optionally, one or more of: P: up to 0.05, Sn: up to 0.30, Sb: up to 0.50, Cr: up to 0.50, Cu: up to 0.50, Ni: up to 0.50 and Bi: up to 0.0100, the rest is Fe and impurities, and hot rolling of the slab is performed, which is heated to form a hot rolled steel sheet; - the stage of annealing hot-rolled steel sheet, at which the hot-rolled steel sheet is annealed; - a cold rolling step in which cold rolling is performed on the hot rolled steel sheet after the annealing step on the hot rolled steel sheet to form the cold rolled steel sheet; - a decarburization annealing step in which the cold-rolled steel sheet is subjected to decarburization annealing to form a decarburized annealed steel sheet; - a finish annealing step of applying an annealing separator to the decarburized annealed steel sheet and then performing finish annealing to form a glass film on the surface of the decarburized annealed steel sheet to form a finish annealed sheet; and - a stage of forming an insulating film, in which a liquid forming an insulating film is applied to the finish annealed sheet and then heat treatment is performed to form an insulating film on the surface of the finish annealed sheet, wherein the decarburization annealing step comprises a heating step by laser beam irradiation or electron beam irradiation of heating the cold-rolled steel sheet to a temperature of 200°C or more and 550°C or less in a non-oxidizing atmosphere and under a tension of 0.2 kg/ ^mm2 or more and 1.2 kg/ ^mm2 or less, and heating by laser beam irradiation or electron beam irradiation the surface of the cold-rolled steel sheet over the entire width of the cold-rolled steel sheet at an interval L within the range represented by expression (1) in a direction intersecting the rolling direction; and - a temperature raising step after said heating step of raising the temperature of the cold-rolled steel sheet in a furnace having a non-oxidizing atmosphere from a temperature range of 550°C or lower to a temperature range of 750-950°C at an average heating rate of 5°C/s or more and 2000°C/s or less; and where expressions (2)-(4) are satisfied: 3 mm ≤ L ≤ 30 mm, (1) L/50 ≤ Dl ≤ L/2, (2) 5 J/mm ² ≤ Up ≤ 48 J/mm ² , (3) 0.05 kW/mm ² ≤ Ip ≤ 4.99 kW/mm ² , (4), where P (W) - average intensity applied to the area heated by the beam; Dl (mm) – focused beam diameter in the rolling direction of the section of steel sheet that is being heated; Dc (mm) – focused beam diameter in the direction of the sheet width of the section of steel sheet that is being heated; Vc (mm/s) – scanning speed in the direction of the sheet width of the section that is being heated; Up is the irradiation energy density (J/mm ² ), where Up=4/π × P/(Dl × Vc); and Ip is the instantaneous power density, where Ip=4/π × P/(Dl × Dc). 6. A method for manufacturing a sheet of electrical steel with an oriented grain structure according to claim 5, in which the irradiation energy density Up additionally satisfies expression (5): 5 (J/mm ² ) ≤ Up < 62.5 × Dl (J/mm ² ) (5). 7. A method for manufacturing a sheet of electrical steel with an oriented grain structure according to paragraph 5 or 6, in which, at the hot rolling stage, a slab is heated having a chemical composition containing, by weight %, one or more of: P: 0.01-0.05, Sn: 0.01-0.30, Sb: 0.01-0.50, Cr: 0.01-0.50, Cu: 0.01-0.50, Ni: 0.01-0.50 and Bi: 0.0001-0.0100.