JPH0649654A - Silicon steel sheet having excellent magnetism after magnetic domain control and its production - Google Patents

Abstract

PURPOSE:To produce the grain-oriented steel sheet having excellent magnetism after magnetic domain control by specifying at the temp. and atmosphere conditions at the time of recrystallization annealing the time of producing the silicon steel sheet by hot rolling, cold rolling and recrystallization annealing of a silicon steel slab having a specific compsn. CONSTITUTION:The silicon steel slab having the compsn. regulated in contents to 1 to 7% Si, <=0.015% S and <=0.013% Mn is hot rolled to a hot coil and in succession, oxides are removed from the surfaces thereof by pickling the surfaces; thereafter the stab is cold rolled to a final sheet thickness. The steel sheet is subjected to primary recrystallization annealing and thereafter the surfaces are coated with an MgO-contg. slurry of a sepn. agent for annealing and the coatings are dried, by which secondary recrystallization annealing is executed N2 is enriched during the primary recrystallization annealing during this stage, and the compsn. of an atmosphere gas is so adjusted between 800 to 1000 deg.C at the time of heating up of the secondary recrystallization annealing that the partial pressure of hydrogen attains <=60%. The steel sheet is thus so formed that the oxides sized >=0.7mum exist just at cumulative <=60% between 10mum lengths of the arbitrary position in the sheet thickness direction on the inner side of the sheet thickness direction separately from the forsterite layer on the front surfaces of the steel sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain-oriented silicon steel sheet having excellent magnetic properties after controlling magnetic domains and a method for producing the same.

[0002]

2. Description of the Related Art 1-7 excellent magnetic properties for transformers, etc.
%, A primary coating that secures insulating properties when applying a silicon steel sheet containing Si and applies tension to the surface of the steel sheet to improve the magnetic characteristics necessary for improving the performance of the transformer and that has good adhesion to the steel sheet. In the prior art, the formation of slag was one of the important problems of grain-oriented silicon steel sheets. That is, in the usual technique, after the primary annealing accompanied by decarburization, a steel sheet is coated with a slurry of magnesium oxide (MgO) fine powder called magnesia dissolved in water, dried if necessary, and then subjected to secondary recrystallization. It burned in the annealing step, forsterite reaction with SiO ₂ and Si in the steel sheet (Mg ₂
A ceramic-like insulating primary coating called SiO ₄ ) is formed. This is effective for giving tension to the steel sheet and improving the magnetic characteristics, especially the characteristic value called iron loss, which governs the efficiency of the transformer. Moreover, this state of forsterite formation is referred to as the GOSS orientation of the steel sheet in the secondary recrystallization, and is {11 with respect to the steel sheet longitudinal direction (rolling direction) which is essential for improving the magnetic permeability and the magnetic flux density.
It is well known that it also plays an important role in growing slightly coarse secondary recrystallized grains having a crystal orientation of 0} <001>. On the other hand, during the secondary recrystallization annealing temperature rising process, even if an attempt is made to carry out secondary recrystallization without forming a sufficiently dense film, fine nitrides and sulfides called inhibitors in the steel sheet remain as they are. Or, it decomposes and quickly escapes to the outside of the steel sheet, so that the GOSS oriented grains are preferentially grown during the temperature rise and the inhibitor effect of the role of suppressing the growth of other oriented grains cannot be exhibited. The secondary recrystallized grains of GOSS oriented grains are not partially or entirely grown, resulting in a steel sheet having extremely poor magnetic properties. It should be noted that titanium oxide (TiO ₂ or the like) or another compound may be added to this MgO to form a more dense primary coating.

However, as seen in the advent of amorphous materials in recent years, there is a great demand for iron loss reduction of magnetic steel sheets, which greatly affects the energy conversion efficiency of transformers for energy saving, and the above-mentioned prior art extension meets this demand. It has become difficult to respond. In the prior art, in addition to the above method, a so-called product steel plate surface after secondary recrystallization is mechanically or energy-irradiated with a laser or the like to intentionally give a groove or some kind of scratch to subdivide the magnetic domain, A so-called magnetic domain control method is used to improve the loss. However, even with this method, it was still difficult to realize a low iron loss that can counter amorphous.

[0004]

In view of the problems of the prior art, the present invention aims to obtain a grain-oriented silicon steel sheet having an extremely high magnetic flux density and a low iron loss based on the following technical knowledge. A new product development technology was found. The contents will be described below.

[0005]

The gist of the present invention is as follows.
The items are as follows. (1) Forste of the surface of the steel sheet containing Si 1 to 7%
Light (Mg₂SiO _Four) Layers and partially or wholly
Separated and oxidized to a thickness of 0.7 μm or more inside the plate thickness direction
The object accumulates within the length of 10 μm at any position in the plate thickness direction.
After magnetic domain control characterized by the presence of less than 60%
Grain-oriented silicon steel sheet with excellent magnetism.

(2) Si 1 to 7%, S ≦ 0.015%
Containing forsterite (Mg ₂ SiO
₄ ) Partly or wholly separated from the layer, oxide with a thickness of 0.7 μm or more inside the plate thickness direction is accumulated 60% or less within a length of 10 μm at any position in the plate thickness direction. A grain-oriented silicon steel sheet excellent in magnetism after control of magnetic domains, characterized in that it exists only.

(3) Si 1 to 7%, Mn ≦ 0.013
% Of forsterite (Mg ₂ Si
O ₄ ) layer is partially or wholly separated, and oxides with a thickness of 0.7 μm or more are accumulated on the inner side in the plate thickness direction and accumulated at a position of 10 μm at any position in the plate thickness direction at a cumulative rate of 60%. A grain-oriented silicon steel sheet excellent in magnetism after control of magnetic domains, characterized in that only the following exist.

(4) Si 1 to 7%, Mn ≦ 0.013
%, S ≦ 0.015%, partially or wholly separated from the forsterite (Mg ₂ SiO ₄ ) layer on the surface of the steel sheet, and oxidized to a thickness of 0.7 μm or more inside the sheet thickness direction. A grain-oriented silicon steel sheet excellent in magnetism after magnetic domain control, characterized in that a cumulative amount of 60% or less is present within a length of 10 μm at an arbitrary position in the plate thickness direction.

(5) Smelting steel containing 1 to 7% Si,
Hot rolling, cold rolling, primary recrystallization annealing and secondary recrystallization annealing are the basic steps, and a method for producing a grain-oriented silicon steel sheet that enriches nitrogen between the start of temperature increase and the end of cooling during primary recrystallization At 800 to 100 at the time of temperature rise in the secondary recrystallization annealing
The magnetic composition after controlling the magnetic domain is characterized in that the atmosphere gas composition at at least one point of any temperature interval of 30 ° C. when dividing 0 ° C. at 10 ° C. intervals is 60% or less of hydrogen partial pressure. Of excellent manufacturing method of silicon steel sheet.

(6) Si 1 to 7%, S ≦ 0.015%
Of steel containing slag, and hot rolling, cold rolling, primary recrystallization annealing and secondary recrystallization annealing are the basic steps, and nitrogen is enriched from the start of temperature rise to the end of cooling during primary recrystallization. In the method for producing a grain-oriented silicon steel sheet, an atmosphere at at least one or more points at arbitrary temperature intervals of 30 ° C. when the temperature range of 800 to 1000 ° C. during the secondary recrystallization annealing temperature rise is divided at 10 ° C. intervals. A method for producing a silicon steel sheet having excellent magnetic properties after controlling magnetic domains, characterized in that a gas composition is set to a hydrogen partial pressure of 60% or less.

(7) Si 1 to 7%, Mn ≦ 0.013
% Of steel, with hot rolling, cold rolling, primary recrystallization annealing and secondary recrystallization annealing as the basic steps, and nitrogen enrichment between the start of temperature increase and the end of cooling during primary recrystallization. In the method for producing a grain-oriented silicon steel sheet, the temperature at which the secondary recrystallization annealing temperature rise is 800 to 1000 ° C. is divided at intervals of 10 ° C. at at least one or more points at arbitrary temperature intervals of 30 ° C. A method for producing a silicon steel sheet having excellent magnetism after magnetic domain control, characterized in that an atmospheric gas composition is set to a hydrogen partial pressure of 60% or less.

(8) Si 1 to 7%, Mn ≦ 0.013
%, S ≦ 0.015%, and hot-rolling, cold-rolling, primary recrystallization annealing and secondary recrystallization annealing are the basic steps. From the start of temperature rise during primary recrystallization to the end of cooling. In the method for producing a grain-oriented silicon steel sheet that is enriched with nitrogen, the temperature range of 800 ° C to 1000 ° C during the secondary recrystallization annealing is divided into 10 ° C intervals at arbitrary temperature intervals of 30 ° C. A method for producing a silicon steel sheet having excellent magnetic properties after magnetic domain control, characterized in that an atmospheric gas composition at at least one point is at a hydrogen partial pressure of 60% or less.

The present invention will be described in detail below. Secondary recrystallization of grain-oriented silicon steel sheet is called Goss orientation {11
It is essential that grains having a 0} <001> orientation are sufficiently grown during secondary recrystallization annealing (also called finish annealing). This is to coarsely recrystallize only certain grains in the primary recrystallization annealing (hereinafter referred to as primary annealing). At this time, fine precipitates such as AlN called an inhibitor are sufficiently formed before the finish annealing. It is well known that it is technically necessary to keep. Then, nitrogen necessary for this purpose is added during steel melting, after primary annealing, or during other steps. When adding nitrogen during steel melting, it is necessary to raise the slab heating temperature during hot rolling,
Therefore, various loads on the heating furnace are large, and avoiding this is also an industrial problem.

From this point of view, it is clear that the method of adding nitrogen in the subsequent step is rather advantageous. It has also been clarified in the present invention that the most suitable method for adding nitrogen is from the start of temperature increase of the primary annealing to the cooling. if,
When nitrogen is added during or immediately after the primary annealing, the equipment for nitriding reaction is installed inside or close to a part of the equipment for the primary annealing that also normally functions for decarburization, and after the primary annealing or in parallel with it, nitriding is performed. A method of reacting is also effective. In the case of steel having sufficiently low carbonization during steel melting, it is more important than the decarburizing function to change the oxide layer of the surface layer after the primary annealing so as to make it advantageous for the coating reaction.

In the present invention, the following points were found as important technical knowledge in such a manufacturing method. During so-called secondary recrystallization annealing (also referred to as finish annealing), forsterite formation up to 1000 ° C., especially at a temperature rise of annealing in order to form a primary coating film having the above-mentioned characteristics of insulation, tension, interlayer resistance, etc. In order to make the atmosphere sufficiently oxidizing in the temperature range up to, some means for increasing the oxygen potential in the atmosphere, for example, a method for increasing the dew point temperature, a method for increasing the ratio of the partial pressure of water vapor and the partial pressure of hydrogen, etc. Further, as described above, a method of adding a special additive is often adopted in order to lower the melting point of MgO powder. However, if this method is excessively performed, a very thick primary coating is formed, which is also called a normal so-called plain material,
In the grain-oriented silicon steel sheet used without performing the magnetic domain control, the iron loss is sufficiently low and is an effective method, but it is rather not preferable for the purpose of improving the iron loss after the magnetic domain control which is the object of the present invention. Can also be considered. As is clear from the present invention, this is because the oxidation progresses too much and the internal oxide grains directly under forsterite grow too much, and the magnetic domain refinement effect by the treatment on the steel plate surface performed by a laser or a mechanical method is performed. Because it will not be enough.

The horizontal axis of FIG. 1 is a partial forsterite (Mg ₂ SiO ₄ ) layer on the surface of the steel sheet (0.23 mm thick) after secondary recrystallization annealing of the steel having the components shown in Table 1 Or, as a whole, the oxides having a size of 0.7 μm or more in the plate thickness direction are accumulated inside the plate thickness direction in a cumulative percentage of 10 μm at any position in the plate surface direction. The vertical axis indicates the magnetic flux density B ₈ (T, Tesla) and the iron loss W _17/50 (watt
t / kg). Further, FIG. 2 is a schematic view of a SEM photograph of the symbols a, b, and c of FIG. 1 at 10000 times. As is clear from FIG. 1, the size is 0.7 in the plate thickness direction.
Oxide with a size of μm or more is 10
It can be seen that the magnetic characteristics deteriorate when more than 60% exists in the range of μm. It is considered that this is because the large oxide directly under forsterite hinders the magnetic domain control effect of laser irradiation as described above. This tendency is remarkable especially in the case of low Mn.

[0017]

[Table 1]

A more important point in the present invention is to find a manufacturing method for controlling the size of this oxide. That is, the formation of this oxide is due to the absorption of oxygen from the surface of the steel sheet during the temperature rise process of the secondary recrystallization annealing, which is also determined by the optimum conditions in relation to the formation time of forsterite. come. That is, once the forsterite is sufficiently formed, this oxide no longer grows coarsely and does not reach a harmful state. However, since forsterite itself is a kind of oxide composed of Mg, Si, and O, an oxidizing atmosphere is necessary in the formation process. It is necessary that the ratio of the steam partial pressure in the atmosphere to make the atmosphere of oxidizing (P _H20) and a hydrogen partial pressure (P _H2) is increased, the hydrogen partial pressure to indirectly To this Must be small.

According to the present invention, when the temperature between 800 and 1000 ° C. is divided at intervals of 10 ° C., the atmospheric gas composition at at least one point at any temperature interval of 30 ° C. has a hydrogen partial pressure of 60% or less. When forsterite is sufficiently formed, the forsterite (Mg
₂ SiO ₄ ) is partially or wholly separated, and an oxide having a size of 0.7 μm or more in the plate thickness direction in the plate thickness direction (plate thickness center direction) is formed in the plate surface direction. It is satisfied that there is less than 60% cumulative for a length of 10 μm at any position. The reason for this is not always clear, but once the forsterite is formed efficiently in this temperature range, the oxide directly below is no longer exposed to the oxidizing atmosphere and does not grow so much, so the secondary recrystallization annealing does not occur. I believe that the purpose of will be achieved. It is not always clear why the 30 ° C. interval is necessary, but it is considered that if the temperature is lower than 30 ° C., sufficient heat retention of the plate is not performed in that temperature range. Therefore, it suffices that the temperature is maintained in the atmosphere more than an arbitrary 30 ° C. interval in the temperature range. The reason for setting the length of 10 μm at an arbitrary position in the plate surface direction is that it is easy to obtain a statistically average representative value if the length is 10 μm in relation to the length of inclusions.

Further, important points in the manufacturing method of the present invention are as follows. If the amount of Mn is too large, the growth of this oxide is remarkable especially in an oxidizing atmosphere. The reason for this is not clear, but one is that in the process of oxide formation, M
It is considered that n is present. This is because it is possible that Mn is also a mediator in Al-based oxides.

Next, the amount of S is also important. If there is a large amount of S, Mn
Easy to form S. If MnS is too much, it tends to act as an inhibitor, which is not a bad thing in itself. However, in the present invention, nitrogen is not enriched at the time of steel melting, but it is heated in hot rolling for nitriding in the vicinity of the primary annealing step. The temperature can be kept low. For this reason, if the amount of S is too large, the amount of undissolved MnS will increase, which not only causes frequent ear cracking, but also Al
MnS even on the control as an inhibitor of N
It is essential that there are not too many.

Further, in order to lower the melting point of MgO and more stably form forsterite, Ti is preferably Ti.
Additives such as O ₂ , Na ₂ B ₄ O ₇ and Sb ₂ (SO ₄ ) ₃ are preferably added to MgO. Especially Sb ₂ (SO
₄ ) ₃ is effective in lowering the melting point of magnesia (MgO) and forming forsterite stably at lower temperatures.
It is effective in suppressing the growth of the oxide.

Since the atmosphere of the secondary recrystallization annealing usually uses decomposition gas of ammonia (NH ₃ ) in many cases,
In this case, the partial pressure ratio of nitrogen and hydrogen is 1: 3, that is, the hydrogen partial pressure is 75% and the nitrogen partial pressure is 25%. In the present invention, 80
The hydrogen partial pressure at a temperature interval of 0 to 1000 ° C. is 60
%, So that if most of the rest is considered to be nitrogen partial pressure, it means that it should be approximately 40% or more. If the temperature is below 800 ° C, the nitrogen partial pressure is 60%.
Further, when adding Sb ₂ (SO ₄ ) ₃ , forsterite is more likely to be stably formed if the nitrogen partial pressure is 40% or less. Any atmosphere may be used above 1000 ° C, but industrially it is convenient to continue the atmosphere up to 1000 ° C. Even in this case, in soaking retention at the highest temperature, for example, 1200 ° C., hydrogen is often used mainly for the purpose of purification.

Next, a method for manufacturing a silicon steel sheet to which the present invention is applied will be described. As described above, the silicon steel sheet to which the present invention can be applied contains Al as necessary in addition to Si, and Si
₃ N ₄ or AlN, and M when there is a large amount of S in steel
Limited to steels with nS as the primary inhibitor. Of course, in addition to Si and Al, Sn, Se, Sb, Cu, B, N
The addition of other additive elements such as b, Ti, and V to improve the magnetic characteristics does not change the basis of the present invention.

Silicon steel using AlN, Si ₃ N ₄ or MnS as an inhibitor is known, and the technique of the present invention can be applied to any of them.
However, in order to exert the characteristics of the present invention further, the silicon steel sheet obtained by the following manufacturing method is most suitable. That is, a steel containing Si of 1 to 7% is used as a starting material, Al is contained in an amount of 0.1% or less when the steel is melted, and cooling is performed from the start of temperature rise during primary recrystallization annealing in the silicon steel sheet manufacturing process. A manufacturing method is used in which N is contained in an amount of 30 to 600 ppm before secondary recrystallization annealing by forcibly adding N to the steel sheet through a direct nitriding reaction until the end. Ammonia may be used as a specific means.

In the present invention, Si is used as the source as described above.
At least 1% is required to form rusterite, but 7
%, The workability is extremely deteriorated and it is not suitable for industrial production.
Yes. Al is effective in forming an AlN inhibitor. Only
If it exceeds 0.1%, Al ₂O₃The amount produced is large,
It impairs the cleanliness of all steels and thus adversely affects the magnetic properties.
Bring

N is indispensable for forming Si ₃ N ₄ and AlN inhibitor, and in the present invention, at least 30 ppm is required after primary annealing, that is, before finish annealing.
On the other hand, when Al is intentionally used in a large amount, 60 ppm or more is necessary to secure the amount of AlN. However, 600
If it exceeds ppm, it reacts with Al or Si to form a compound that does not function as an inhibitor, which is not preferable.

When S is positively utilized, at least 0.01% is necessary for effectively using MnS as an inhibitor, but in the present invention, N is added in a large amount during steel melting. Since it is not used as an inhibitor, the hot rolling heating temperature can be lowered. In order to make full use of this feature, steel containing a large amount of S is not melted and causes damage such as melting and ear cracking, so the maximum S content is preferably 0.015%.

The regulation of Mn is important in the present invention. This is because, as described above, if Mn is too much, the growth of the oxide is particularly remarkable in the oxidizing atmosphere, which is not preferable as the magnetic domain control material. If it exceeds 0.13%, the growth of oxides is particularly remarkable. To further reduce the oxide, 0.10% or less is preferable. The other elements are not particularly characteristic in the present invention as compared with the conventional steel, but the following restrictions are preferable.

C must be sufficiently low during steel melting or sufficiently low during decarburization annealing of primary annealing, and is preferably 0.03% or less at the start of secondary recrystallization annealing. O is Al ₂ O ₃ if it is 0.05% or less after the steel is melted.
It is preferable for cleanliness without making too much. Next, the production method of the present invention other than the chemical components will be described.

Molten steel obtained by tapping the steel in a converter or an electric furnace and adjusting the composition by adding a refining step as necessary is subjected to a continuous casting method, an ingot slabbing method, or a hot rolling step omitted. By thin slab continuous casting method for thickness of 30-400mm
The slab is (50 mm or less in the thin slab continuous casting method). Here, 30 mm is the lower limit of productivity, 400 mm
Is an upper limit for preventing abnormal distribution of Al ₂ O ₃ etc. due to center segregation. In the thin slab continuous casting method, 50
mm is the upper limit for suppressing the generation of coarse particles due to the low cooling rate.

The slab is reheated to 1000 to 1400 ° C. by gas heating, electric heating, etc., and then hot rolled to obtain a hot coil having a thickness of 10 mm or less.
Here, 1000 ° C. is the lower limit of AlN melting,
C is the upper limit of surface roughness and material deterioration. Also 10 mm
Is the upper limit for obtaining a cooling rate that produces a proper precipitate.
In the thin slab continuous casting method, it is also possible to directly form a coil, and for that purpose, 10 mm or less is preferable.

The hot coil thus produced is often annealed again at 800 to 1250 ° C. to improve the magnetism. Here, 800 ° C. is the lower limit for remelting AlN, and 1250 ° C. is the upper limit for preventing AlN coarsening.
After such a treatment step, the hot coil is pickled directly or batchwise and then cold rolled. Cold rolling is 60 to 9
5%, 60% is the limit of recrystallization in the present invention, and preferably 70% or more by primary annealing {111} <1
12> GOSS with a large number of oriented grains during secondary recrystallization annealing
This is the lower limit for accelerating the generation of oriented grains, while if it exceeds 95%, GOSS referred to as swinging GOSS grains in secondary recrystallization annealing.
When the oriented grains rotate in the plane of the plate, grains which are not favorable for the magnetic properties are generated. The above is the case of manufacturing by the so-called single cold rolling method, but when cold rolling-annealing-cold rolling is performed by calling the double cold rolling method, the first reduction rate is 10 to 80%, and the second reduction rate. Is 50 to 95%. Here, 10% is the minimum reduction ratio necessary for recrystallization, 80% and 95% are the upper limit reduction ratios for producing proper GOSS-oriented grains during secondary recrystallization, respectively, and 50% in the double cold rolling method. Is {11 at the time of primary annealing
1} <112> It is the lower limit of the reduction ratio that appropriately leaves grains.

It is also commonly called "interpass aging", and heating the steel sheet in the range of 100 to 400 ° C by an appropriate method during the cold rolling is also effective for improving the magnetic properties. 10
If it is less than 0 ° C, the effect of aging is not obtained, while if it exceeds 400 ° C, dislocations are recovered. Next, primary recrystallization annealing is performed, but the primary annealing temperature is preferably 700 to 950 ° C. Here, 700 ° C. is the lower limit temperature at which recrystallization is possible,
950 ° C. is an upper limit temperature for suppressing the generation of coarse grains in primary recrystallization. Although the primary annealing is performed in both the single cold rolling method and the double cold rolling method, decarburization is effective in this annealing. As described above, C is not preferable for the growth of secondary recrystallized grains, and if it remains as an impurity, it causes deterioration of iron loss. It is preferable that C be lowered during the melting of steel because not only the decarburization step can be shortened but also {111} <112> oriented grains can be increased. By setting an appropriate dew point in this decarburization annealing step, an oxide layer necessary for subsequent primary film formation is secured.

Further, in the present invention in which AlN or N of Si ₃ N ₄ inhibitor is forcibly added by the nitriding method or the like during the primary annealing, in the period from the start of the temperature increase of the primary annealing to the end of the cooling, specifically, the primary During or immediately after annealing, nitriding is performed with ammonia (NH ₃ ) or the like by a nitriding method. In this case, the nitriding temperature is preferably 600 to 950 ° C. Here, 600 ° C. is the lower limit of the nitriding reaction,
On the other hand, 950 ° C. is the upper limit for suppressing the generation of coarse particles.

In the present invention, the nitriding is preferably carried out after the primary recrystallization annealing, but industrially, a partition is provided on the rear surface of the same furnace and the atmosphere is slightly changed as necessary, and NH ₃
Nitrogen is often nitrided in parallel with primary recrystallization because a gas is passed or it is carried out in close proximity. At this time, as described above, the lower the N ₂ partial pressure is, the larger the nitriding amount is, and the partial pressure ratio P _N2 / P _H2 of nitrogen and hydrogen is preferably 0.5 or less.

After performing the primary annealing and the above nitriding method, after that,
Magnesium oxide (MgO is the main component.
Powder) is dissolved in water or an aqueous solution containing water as a main component to form a slurry, which is applied to a steel sheet. At this time, a trace amount of an appropriate compound may be added for the purpose of facilitating the melting of the MgO powder during the subsequent secondary recrystallization annealing and accelerating the forsterite formation reaction. When TiO ₂ is added, 1 to 15% is preferable, but 1% here is the lower limit for exerting the forsterite reaction promoting effect,
If it exceeds 15%, the amount of MgO decreases and the forsterite reaction does not proceed. An antimony-based compound such as Sb ₂ (SO ₄ ) ₃ is effective in melting MgO at a relatively low temperature, and if added, 0.05 to 5% is preferable. Here, 0.05% is the lower limit for causing the above-mentioned low-temperature melting, while on the other hand, when it exceeds 5%, it is too much to inactivate the original reaction of MgO forsterite. Na ₂ B ₄ O
Boron-based compounds such as ₇ and strontium / barium-based, carbon / nitride-based, sulfide-based compounds that have similar effects
Chloride compounds are relatively hotter than Ms.
It has the effect of melting gO, and when added, the content of O.
05-5% is preferable. Here, 0.05% is the lower limit for exerting the above-mentioned effect, while if over 5%, MgO is still present.
It is not preferable because it inactivates the original reaction of forsterite. It should be noted that these compounds may be added in combination with each other.

The percentage of the compound added here is MgO.
The weight ratio is shown in% when the weight of is 100%. Secondary recrystallization annealing has a maximum temperature of 1100 to 130
It is preferably carried out at 0 ° C. 1100 ° C. is the lower limit temperature at which the secondary recrystallization is performed, while if it exceeds 1300 ° C., the crystal grains become excessively large and iron loss is deteriorated.

The above is an important part of the method for producing a silicon steel sheet according to the present invention, but industrially, the steel sheet after secondary recrystallization is insulated with an organic or inorganic material for the purpose of further improving the insulation characteristics and magnetic characteristics. It is particularly important to apply a high-strength coating (coating) having a coating in combination with heat treatment or the like, and that step is also performed. The reason for this is that the primary coating having high tensile properties such as forsterite and the above-mentioned insulating coating can effectively reduce iron loss not only by the insulating property but also by the tension effect. Furthermore, called magnetic domain control, the magnetic domain subdivision of steel sheet by mechanical, optical, chemical treatment or various energy irradiation methods such as laser and plasma or non-destructive energy application to the steel sheet surface reduces iron loss. It is extremely effective and is also the main object of the present invention.

[0040]

EXAMPLE Steels having chemical compositions as shown in Table 2 were melted in a converter, and Table 3 (continued 1 in Table 2) and Table 4 (continued 2 in Table 2)
It was manufactured under the conditions shown in. The hot-rolled sheet was partially annealed under the condition of 1120 ° C. × 30 seconds. In addition, aging between passes during cold rolling was performed except for A-4 and A-8, but the condition is 250 ° C.

In the nitriding subsequent to the primary recrystallization annealing which is particularly important in the present invention, the atmosphere is dried with the same gas composition in the inside of the furnace where the partition is provided in the same furnace, and NH
It was performed by flowing a fixed amount of ₃ gases. The nitriding amount (nitrogen amount) after such primary annealing is shown in the same table. In addition, A-6,
Only A-7 was subjected to nitrogen addition during finish annealing, and the value in parentheses in Table 3 is the amount of nitriding after finish annealing. Also B-1
B-3 are those enriched with nitrogen during the melting of steel. Further, a powder was applied to this steel plate, and the powder was dissolved in water to form a slurry, which was then dried at 350 ° C. Here,% is the weight ratio when the weight of MgO is 100%. After that, secondary recrystallization annealing was performed while changing the average heating rate from 800 ° C. to the highest reached temperature variously.
The highest temperature reached for finish annealing is 1200 ° C (however, A-1
0 to A-12 is 1250 ° C, A-13 to A-15 is 11
It was performed at 70 ° C., but the atmosphere in this soaking is 100% hydrogen for purification. Although Table 4 shows the atmospheric gas composition of the finish annealing, this ratio shows the ratio of the main components, and some mixed gases are not described. Further, a phosphoric acid-based high-strength insulating coating (secondary coating) is applied by heating, then the plate is removed and strain relief annealing is performed at 850 ° C. for 4 hours (N
₂ 90% -H ₂ 10%, were carried out in the Dry). Table 5
The magnetic domain control of each product was performed by the method shown in (Continued 3 of Table 2). Further, a magnetic measurement test was conducted. Table 5 shows the results. In Table 5, the “cumulative length ratio (%) of product inclusions in 10 μm” means that the layer of forsterite (Mg ₂ SiO ₄ ) on the surface of the steel sheet is partially or wholly separated. Shows the cumulative percentage of oxides having a size of 0.7 μm or more in the plate thickness direction in the plate thickness direction in a 10 μm length at an arbitrary position in the plate surface direction. . Magnetic measurement is 60 x 300 mm single plate SS
Measured by T test method, B ₈ (800 A / m magnetic flux density, unit is Tesla) and W _17/50 (iron loss at 50 Tesla at 1.7 Tesla, unit is watt / kg), W _13/50 (50
The iron loss at 1.3 Tesla in Hz) was measured.

As shown in Table 5, those falling within the range of the present invention have a sufficiently low iron loss and are within the target range of the present invention.

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Table 5]

[0047]

According to the present invention, it is possible to obtain a grain-oriented silicon steel sheet having excellent magnetic properties after magnetic domain control.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a cumulative ratio of oxides having a thickness of 0.7 μm or more existing for a length of 10 μm at an arbitrary position in a plate surface direction and magnetic characteristics after magnetic domain control.

2 is a symbol a in FIG. 1 (cumulative ratio of oxides having a thickness of 0.7 μm or more existing within a length of 10 μm at an arbitrary position in the plate surface direction: 83%), and b (also 40%). FIG. 3 is a schematic view of a SEM photograph of a product of C, C (also 3%) at a magnification of 10,000 in the plate thickness direction.

[Explanation of symbols]

 1: Forsterite 2: Oxide 3: Ferrite

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsutomu Haraya 1-1 1-1 Tobata-cho, Tobata-ku, Kitakyushu, Kitakyushu, Fukuoka Inside the Nippon Steel Co., Ltd. Yawata Works (72) Inventor Hodaka Hodaka, Tobata-ku, Kitakyushu, Kitakyushu, Fukuoka No. 1 No. 1 within Yawata Works, Nippon Steel Co., Ltd. (72) Nozomi Ishibashi, No. 1 No. 1 Tobita-cho, Tobata-ku, Kitakyushu City, Fukuoka Prefecture Inside the Yawata Works, Nippon Steel

Claims (8)

[Claims] 1. A phosphor on the surface of a steel sheet containing 1 to 7% of Si.
Rosterite (Mg ₂SiO_Four) Layers and partial or full
Physically separate and have a thickness of 0.7 μm or more inside the plate thickness direction
Oxide of 10μm length at any position in the plate thickness direction
Magnetic domains characterized by a cumulative total of less than 60%
A grain oriented silicon steel sheet with excellent magnetic properties after control. 2. Forsterite (Mg ₂ SiO ₄ ) on the surface of a steel sheet, containing 1 to 7% Si and S ≦ 0.015%.
The oxide having a thickness of 0.7 μm or more is present inside the plate thickness direction partially or wholly separated from the above layer, and the accumulated amount is 60% or less in a 10 μm length at any position in the plate thickness direction. A grain-oriented silicon steel sheet excellent in magnetism after domain control, characterized by not performing. 3. Forsterite (Mg ₂ SiO ₄ ) on the surface of a steel sheet, containing 1 to 7% Si and Mn ≦ 0.013%.
The oxide having a thickness of 0.7 μm or more is present inside the plate thickness direction partially or wholly separated from the above layer, and the accumulated amount is 60% or less in a 10 μm length at any position in the plate thickness direction. A grain-oriented silicon steel sheet excellent in magnetism after domain control, characterized by not performing. 4. Si 1 to 7%, Mn ≦ 0.013%, S
≦ 0.015%, and partially or wholly separated from the forsterite (Mg ₂ SiO ₄ ) layer on the surface of the steel sheet, and an oxide having a thickness of 0.7 μm or more inside the sheet thickness direction,
Cumulative 60% during 10 μm length at any position in the plate thickness direction
A grain-oriented silicon steel sheet excellent in magnetism after control of magnetic domains, characterized in that only the following exist. 5. A steel containing 1 to 7% Si is melted, and hot rolling, cold rolling, primary recrystallization annealing and secondary recrystallization annealing are the basic steps, and cooling is started from the start of temperature rise during primary recrystallization. In the method for producing a grain-oriented silicon steel sheet that is enriched with nitrogen until the end, a temperature interval of 30 ° C is arbitrarily set when the interval between 800 ° C and 1000 ° C during secondary recrystallization annealing is divided by 10 ° C intervals. In the method for producing a silicon steel sheet having excellent magnetic properties after magnetic domain control, the atmospheric gas composition at at least one or more points is set to a hydrogen partial pressure of 60% or less. 6. A steel containing 1 to 7% Si and S ≦ 0.015% is smelted, and hot rolling, cold rolling, primary recrystallization annealing and secondary recrystallization annealing are the basic steps, and primary recrystallization is performed. In the method for producing a grain-oriented silicon steel sheet in which nitrogen is enriched from the start of temperature increase to the end of cooling, the
A magnetic domain control characterized in that the atmospheric gas composition at at least one point of any temperature interval of 30 ° C. when dividing between 0 ° C. and 1000 ° C. at 10 ° C. intervals is set to 60% or less of hydrogen partial pressure. A method for manufacturing a silicon steel sheet having excellent post magnetism. 7. A steel containing 1 to 7% Si and Mn ≦ 0.013% is smelted, and hot rolling, cold rolling, primary recrystallization annealing and secondary recrystallization annealing are the basic steps, and primary recrystallization is performed. In the method for producing a grain-oriented silicon steel sheet in which nitrogen is enriched from the start of temperature rise to the end of cooling, when 800 to 1000 ° C. during the secondary recrystallization annealing temperature rise is divided at 10 ° C. intervals. A method for producing a silicon steel sheet having excellent magnetic properties after magnetic domain control, characterized in that an atmospheric gas composition at at least one point at arbitrary temperature intervals of 30 ° C. is set to a hydrogen partial pressure of 60% or less. 8. Si 1-7%, Mn ≦ 0.013%, S
Steel containing ≤ 0.015% is smelted, hot rolling, cold rolling, primary recrystallization annealing and secondary recrystallization annealing are the basic steps, from the start of temperature rise to the end of cooling during primary recrystallization. In the method for producing a grain-oriented silicon steel sheet that enriches nitrogen with
The temperature between 800 and 1000 ° C during the secondary recrystallization annealing temperature rise is 10
A silicon steel sheet excellent in magnetism after magnetic domain control, characterized in that the atmospheric gas composition at at least one point in an arbitrary temperature interval of 30 ° C. when divided at intervals of 0 ° C. is set to a hydrogen partial pressure of 60% or less. Production method.