JP2018184654A - Method for producing grain-oriented electrical steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To propose a method for producing a grain-oriented magnetic steel sheet that is stably secondary recrystallized and has good iron loss characteristics even with high content of Si.SOLUTION: The grain-oriented magnetic steel sheet comprises 0.002 to 0.2% of C, 2.8 to 4.6% of Si, 0.01 to 0.8% of Mn, 0.010 to 0.050% of Al and 0.003 to 0.020% of N in mass%. A steel slab having a maximum percentage of γ phase of 30 vol% or more as determined by thermodynamic calculation from the composition is produced by hot rolling, hot-rolling and annealing, cold rolling, decarburization annealing and finish annealing. At a temperature Ts between 800 and 950°C in the course of heating process of finish annealing, the atmosphere is controlled to have an amount of hydrogen Vof 10 vol% or less. At a temperature of Ts or higher and 1150°C or lower, the atmosphere of a mixture of nitrogen and hydrogen is controlled so that the nitrogen content V(vol%) satisfies 12.5×[Si]-35≤V≤12.5×[Si]+35.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet, and more specifically to a method for producing a grain-oriented electrical steel sheet having low iron loss.

  The electrical steel sheet is a soft magnetic material widely used as a core material for transformers and motors, and there are non-oriented electrical steel sheets and directional electrical steel sheets. In particular, grain-oriented electrical steel sheets are used mainly as iron core materials for large transformers because they exhibit excellent magnetic properties by highly accumulating crystal orientation in the {110} <001> orientation called the Goss orientation. Yes. Therefore, this grain-oriented electrical steel sheet is required to have low loss due to excitation, that is, iron loss, in order to reduce energy loss that occurs when the transformer is excited.

  The iron loss of the grain-oriented electrical steel sheet can be separated into hysteresis loss and eddy current loss. The hysteresis loss can be reduced by increasing the degree of integration of the crystal orientation in the Goss orientation. Therefore, for example, in Patent Document 1, AlN is finely precipitated in the manufacturing process, and this is used as an inhibitor for pinning the grain boundary during finish annealing, whereby the Goss orientation is preferentially recrystallized, A technique for manufacturing a grain-oriented electrical steel sheet having a high degree of integration is disclosed.

  On the other hand, as a method of reducing eddy current loss, a method of adding Si to increase the specific resistance of steel and reducing eddy current generated when a product is excited is known. However, when Si in the steel is increased, there is a problem that secondary recrystallization in the Goss orientation in finish annealing becomes difficult, secondary recrystallization failure occurs, and the magnetic properties are greatly deteriorated. Therefore, the Si content of the grain-oriented electrical steel sheet is generally stopped at about 3 mass%.

In order to solve the above-mentioned problem, for example, Non-Patent Document 1 discloses a technique for stably producing secondary recrystallization even when the Si content is increased to 3.8 mass% by adding Sn. Yes. In Non-Patent Document 1, the magnetic flux density of a product plate having a thickness of 0.285 mm with Si added to 3.8 mass% and Sn added to 0.1 mass% is 1.7 T, and the iron when excited at a frequency of 50 Hz is used. It is stated that the loss W _17/50 was 0.94 W / kg.

  As a method for reducing the eddy current loss of the grain-oriented electrical steel sheet, a method of reducing the plate thickness is known in addition to a method of increasing the Si amount. However, it is known that when the plate thickness is decreased, the secondary recrystallization becomes unstable as in the case where the Si amount is increased. As a technique for solving this problem, for example, in Patent Document 2, after performing primary recrystallization annealing, by applying an electrostatic separator with an annealing separator mainly composed of magnesia, moisture contained in magnesia is at the time of final annealing. A technique for suppressing the degradation of the inhibitor and stabilizing secondary recrystallization is disclosed.

Japanese Patent Publication No. 40-15644 Japanese Patent No. 2530521

Shozaburo Nakajima et al., “Effect of Sn addition on secondary recrystallization of 3.8 mass% Si unidirectional electrical steel sheet”, 1991, Journal of the Japan Institute of Metals, Vol. 55, No. 11, p. 1274-1281

  However, when the grain-oriented electrical steel sheet is industrially produced, even if magnesia is electrostatically applied, the applied magnesia absorbs moisture in the air, so that the instability of secondary recrystallization cannot be completely eliminated. Furthermore, in recent years, the demand for energy saving has increased further, and further reduction in iron loss has been demanded.

  The present invention has been made in view of the above-described problems of the prior art, and its purpose is to stably develop secondary recrystallization even when the Si content is high, and to have good iron loss characteristics. Is to propose a method of manufacturing a grain-oriented electrical steel sheet capable of obtaining the above.

  In order to solve the above-mentioned problems, the inventors have conducted intensive studies on measures for stabilizing secondary recrystallization of grain-oriented electrical steel sheets having high Si without adding excessive Sn. As a result, the maximum fraction of the γ phase calculated from the component composition of the steel slab is increased, the annealing atmosphere in the heating process of finish annealing is switched during the heating, and the hydrogen content in the annealing atmosphere is lowered on the low temperature side. On the high temperature side, the inventors have found that secondary recrystallization can be stably expressed by increasing the nitrogen content in the annealing atmosphere in accordance with the Si content, leading to the development of the present invention.

That is, the present invention includes C: 0.002 to 0.2 mass%, Si: 2.8 to 4.6 mass%, Mn: 0.01 to 0.8 mass%, Al: 0.010 to 0.050 mass%, and N: 0.003 to 0.020 mass%, and the remainder is heated with a steel slab having a composition composed of Fe and inevitable impurities, and hot-rolled into a hot-rolled sheet. After performing plate annealing, cold rolling is performed once or two or more times with intermediate annealing to obtain a cold-rolled sheet having a final thickness, and after the cold-rolled sheet is decarburized and annealed, the directional electromagnetic wave is subjected to finish annealing. In the steel sheet manufacturing method, the maximum fraction of the γ phase obtained from the above component composition by thermodynamic calculation is 30% or more in terms of molar fraction (mol%), and any of the 800 to 950 ° C. in the heating process of the finish annealing is performed. An annealing atmosphere below the temperature Ts, The content _{V H2} of the unit is a mixed atmosphere of a single or a nitrogen and argon 10 vol% or less of nitrogen or argon, the annealing atmosphere of Ts exceeds 1150 ° C. temperature below, the content of nitrogen _V N2 (vol%) satisfies the following ( 1) Formula;
12.5 × [Si] −35 ≦ V _N2 ≦ 12.5 × [Si] +35 (1)
Here, the above [Si] is the Si content (mass%).
We propose a method for producing grain-oriented electrical steel sheets characterized by having a mixed atmosphere of hydrogen and nitrogen satisfying the above.

  The steel slab used in the method for producing a grain-oriented electrical steel sheet of the present invention is selected from S: 0.002 to 0.030 mass% and Se: 0.002 to 0.100 mass% in addition to the above component composition. It is characterized by containing 1 type or 2 types.

  Moreover, in addition to the said component composition, the said steel slab used for the manufacturing method of the grain-oriented electrical steel sheet of this invention is further Cr: 0.010-0.500 mass%, Ni: 0.010-1.500 mass%, Sn : 0.005 to 0.500 mass%, Sb: 0.005 to 0.500 mass%, P: 0.005 to 0.500 mass%, Cu: 0.010 to 0.500 mass%, Mo: 0.005 to 0 100% by mass, B: 0.0002 to 0.0025 mass%, Nb: 0.0010 to 0.0100 mass%, and V: 0.0010 to 0.0100 mass%, or one or more types selected from It is characterized by that.

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that the maximum fraction of the γ phase obtained from the above component composition by thermodynamic calculation is 40% or more in terms of mole fraction (mol%).

  Moreover, the manufacturing method of the grain-oriented electrical steel sheet according to the present invention is characterized in that the final cold rolling reduction ratio of the cold rolling is 85% or more.

  According to the present invention, since secondary recrystallization can be stably expressed even when Si is high, it is possible to stably provide a grain-oriented electrical steel sheet with low iron loss.

The content V _N2 of nitrogen in the atmosphere at a high temperature region of the Si content and final annealing Atsushi Nobori process is a graph showing the effect on the iron loss W _17/50. Ambient switching temperature T _S at the final annealing heating process is a graph showing the effect on the iron loss W _17/50. It is a graph which shows the influence which the maximum fraction of (gamma) phase has on the iron loss _{W17 / 50} .

Hereinafter, experiments that have led to the development of the present invention will be described.
(Experiment 1)
Si: 2.8 to 4.6 mass%, Mn: 0.07 mass%, Al: 0.02 mass%, and N: 0.010 mass%, and further, the content of C is 0.03 to 0.2 mass% The steel slab varied in the range of 1) was reheated to a temperature of 1400 ° C. and hot-rolled to obtain a hot-rolled sheet having a thickness of 2.4 mm, and subjected to hot-rolled sheet annealing at 1100 ° C. × 60 seconds. Under the present circumstances, C content of the said steel slab was made into the quantity from which the maximum fraction of (gamma) phase calculated | required by thermodynamic calculation will be 35% in a molar fraction (mol%). Here, the thermodynamic calculation was performed on a computer using Thermo-Calc 3.1, and the database used for the calculation was SSOL4 (version 4.9) (hereinafter the same). Moreover, the rolling start temperature (entrance side temperature) of the 1st pass in the finish rolling of the said hot rolling was 1050 degreeC or more.
Thereafter, the hot-rolled sheet after the hot-rolled sheet annealing is cold-rolled to an intermediate thickness of 1.7 mm, subjected to an intermediate annealing of 1100 ° C. × 80 s, and finally cold-rolled to a final sheet thickness of 0.23 mm. The cold-rolled sheet was used.

Next, the above cold-rolled sheet is subjected to decarburization annealing at 850 ° C. × 120 s, and after applying an annealing separator mainly composed of MgO to the steel sheet surface, secondary recrystallization annealing and purification annealing held at 1200 ° C. for 6 hours are performed. Finish annealing was performed.
At this time, the annealing atmosphere in the heating process of the finish annealing is 100 vol% nitrogen from room temperature to 850 ° C., and a mixed atmosphere of nitrogen and hydrogen from 850 ° C. to 1150 ° C., and the nitrogen content V _N2 in the atmosphere is Various changes were made in the range of 0 to 100 vol%. Further, the annealing atmosphere from 1150 ° C. to 1200 ° C. leading to the purification annealing and during the purification annealing was set to 100 vol% hydrogen.

A test piece was collected from the steel plate after finish annealing thus obtained, and the iron loss W _17/50 at an excitation frequency of 50 Hz was measured in _accordance with _JISC2550 .
FIG. 1 shows the relationship between the Si content and the nitrogen content V _N2 in the annealing atmosphere in the range of 850 ° C. to 1150 ° C. and the iron loss W _{17/50 in} the heating process of finish annealing. From this figure, when the Si content in the steel slab is less than 2.8 mass%, the specific resistance of the steel is low and the eddy current loss is not sufficiently reduced. _Therefore , W _17/50 ≦ 0.85 W / kg in any condition. It is not possible to obtain a good iron loss that satisfies the above. Moreover, even if Si content exceeds 4.6 mass%, secondary recrystallization does not express normally and a favorable iron loss characteristic cannot be obtained. However, when the Si content is in the range of 2.8 to 4.6 mass%, the nitrogen content V _{N2 in} the atmosphere from 850 ° C. to 1150 ° C. when the Si content (mass%) is expressed as [Si]. (Vol%) the following formula (1);
12.5 × [Si] −35 ≦ V _N2 ≦ 12.5 × [Si] +35 (1)
It was found that good iron loss can be obtained within the range satisfying above.

As shown in the above formula (1), in the high temperature region of the finish annealing heating process, the reason why the iron loss improves as the nitrogen content V _N2 in the annealing atmosphere increases as the Si content increases. The inventors consider as follows.
In the finish annealing, the decomposition of AlN in the steel, which is an inhibitor, starts from the steel sheet surface layer, and recrystallized grains become coarse from the steel sheet surface layer. In high-Si steel, where secondary recrystallization is difficult to occur, when the inhibitor's inhibitory power is weak, the coarsening of the crystal grains proceeds from the surface layer of the steel sheet. As a result, secondary recrystallization does not occur and good iron loss cannot be obtained.
However, if there is more than a certain amount of nitrogen in the annealing atmosphere of finish annealing, nitrogen is absorbed by the steel sheet surface layer during annealing, and AlN decomposition is suppressed to the high temperature range of finish annealing, so secondary recrystallization occurs. It will be easier.
However, if the nitrogen content V _N2 in the annealing atmosphere is too high, absorption of nitrogen into the steel sheet surface layer becomes excessive, preventing AlN from decomposing at an appropriate temperature. It becomes difficult to express.
Therefore, there are a lower limit and an upper limit for the nitrogen content V _N2 in the atmosphere of the heating process of finish annealing.

Based on the above experimental results, the inventors further developed an annealing atmosphere having the appropriate nitrogen content V _N2 in order to stabilize the secondary recrystallization in the grain-oriented electrical steel sheet having a high Si content. An experiment was conducted to check the switching temperature.
(Experiment 2)
After reheating a steel slab containing C: 0.085 mass%, Si: 3.5 mass%, Mn: 0.07 mass%, Al: 0.02 mass% and N: 0.01 mass% to a temperature of 1400 ° C Then, it was hot-rolled to obtain a hot-rolled sheet having a thickness of 2.6 mm, and subjected to hot-rolled sheet annealing at 1100 ° C. for 60 seconds. The maximum fraction of the γ phase obtained from the above component composition by thermodynamic calculation was 34.5% in terms of mole fraction (mol%). Moreover, the rolling start temperature (entrance side temperature) of the 1st pass in the finish rolling of the said hot rolling was 1050 degreeC or more.
Thereafter, the hot-rolled sheet after the hot-rolled sheet annealing is cold-rolled to an intermediate thickness of 1.8 mm, subjected to an intermediate annealing of 1100 ° C. × 80 s, and finally cold-rolled to have a sheet thickness of 0.23 mm Cold-rolled sheet was used.

Next, the above cold-rolled sheet is subjected to decarburization annealing at 850 ° C. × 120 s, and after applying an annealing separator mainly composed of MgO to the steel sheet surface, secondary recrystallization annealing and purification annealing held at 1200 ° C. for 6 hours are performed. Finish annealing was performed. At this time, the annealing atmosphere was switched at various different temperatures Ts between 740 and 1050 ° C. in the heating process of the finish annealing. Specifically, from room temperature to the above temperature Ts, an annealing atmosphere of 100 vol% nitrogen was used, and from the temperature Ts to 1150 ° C., a nitrogen and hydrogen mixed atmosphere having a nitrogen content V _N2 of 30 vol% was used. Further, the annealing atmosphere from 1150 ° C. to 1200 ° C. and during the purification annealing was set to 100 vol% hydrogen.

A test piece was collected from the steel plate after finish annealing thus obtained, and the iron loss W _17/50 at an excitation frequency of 50 Hz was measured in _accordance with _JISC2550 .
FIG. 2 shows the relationship between the temperature Ts at which the annealing atmosphere is switched and the iron loss W _17/50 . From this figure, it was found that when Ts was less than 800 ° C. or higher than 950 ° C., good iron loss was not obtained, and good iron loss was obtained when Ts was in the range of 800 ° C. to 950 ° C.

As described above, the inventors consider the reason why good iron loss can be obtained by setting the atmosphere switching temperature Ts in the range of 800 ° C. or more and 950 ° C. or less.
As shown in Experiment 1, by using a mixed atmosphere of nitrogen and hydrogen in which the nitrogen content V _N2 is controlled according to the Si content, as the annealing atmosphere in the high temperature region of the finishing annealing heating process, it is appropriate. Secondary recrystallization can be developed at temperature.

The inventors consider the reason as follows.
Hydrogen has a role of promoting the decomposition of the inhibitor on the surface layer of the steel sheet and initiating secondary recrystallization. For this reason, when the content of hydrogen in the low temperature region is high, the decomposition of the inhibitor proceeds excessively and secondary recrystallization failure occurs. On the other hand, maintaining an atmosphere with a low hydrogen content up to a high temperature prevents AlN from decomposing at an appropriate temperature, making it difficult for secondary recrystallization to occur. Therefore, it is considered that an upper limit and a lower limit exist in the atmosphere switching temperature Ts.

The inventors further conducted an experiment to investigate the influence of the structural change accompanying the change in the Si content on the iron loss characteristics.
(Experiment 3)
Contains Mn: 0.07 mass%, Al: 0.02 mass%, N: 0.01 mass%, and changes Si in 4 steps of 2.8 mass%, 3.6 mass%, 4.0 mass%, and 4.6 mass% Further, the steel slab whose C content was adjusted so that the maximum fraction of the γ phase obtained by thermodynamic calculation was 0 to 100% in terms of mole fraction (mol%) was returned to a temperature of 1400 ° C. After heating, it was hot-rolled to obtain a hot-rolled sheet having a thickness of 2.6 mm. Moreover, the rolling start temperature (entrance side temperature) of the 1st pass in the finish rolling of the said hot rolling was 1000 degreeC or more. Next, after hot-rolled sheet annealing at 1100 ° C. × 60 seconds, the hot-rolled sheet after the hot-rolled sheet annealing is cold-rolled to an intermediate thickness of 1.8 mm and subjected to intermediate annealing at 1100 ° C. × 80 s. After that, final cold rolling was performed to obtain a cold-rolled sheet having a final sheet thickness of 0.23 mm.

Next, the above cold-rolled sheet is subjected to decarburization annealing at 850 ° C. × 120 s, and after applying an annealing separator mainly composed of MgO to the steel sheet surface, secondary recrystallization annealing and purification annealing held at 1200 ° C. for 6 hours are performed. Finish annealing was performed. Here, the annealing atmosphere from room temperature to 850 ° C. in the heating process in the finish annealing is 100 vol% nitrogen, and the annealing atmosphere from 850 ° C. to 1150 ° C. is a mixed atmosphere of hydrogen and nitrogen having a nitrogen content V _N2 of 35 vol%. It was. Further, the annealing atmosphere from 1150 ° C. to 1200 ° C. and during the purification annealing was set to 100 vol% hydrogen.

A test piece was collected from the steel plate after finish annealing thus obtained, and the iron loss W _17/50 at an excitation frequency of 50 Hz was measured in _accordance with _JISC2550 .
FIG. 3 shows the relationship between the maximum fraction of the γ phase obtained from the component composition of the steel slab, the iron loss W _17/50, and the Si content. From this figure, it can be seen that good iron loss can be obtained by setting the maximum fraction of the γ phase to 30 vol% or more.

As shown in FIG. 3 above, the inventors have found that the reason why a good iron loss can be obtained by setting the maximum fraction of the γ phase to 30 vol% or more even in a steel having a Si content higher than 2.8 mass%. Thinks as follows.
In the manufacture of grain-oriented electrical steel sheets, the inhibitor contained in the slab is solid-dissolved and finely precipitated in the subsequent process, so that the slab is heated to a temperature of about 1200 to 1400 ° C. before hot rolling. The steel structure becomes coarse. Since Si is a ferrite-forming element, at high Si, depending on the component composition, it becomes a ferrite single phase, but when hot rolling a slab having a coarse steel structure of such a ferrite single phase, the structure of a hot-rolled sheet Becomes non-uniform and the crystal grain size in the primary recrystallized structure after decarburization annealing becomes non-uniform. If the crystal grain size is non-uniform, the driving force for grain growth is also non-uniform, so that the secondary recrystallization in the finish annealing becomes unstable and causes the iron loss characteristics to deteriorate.
On the other hand, if the composition is such that even a high Si has a predetermined amount or more of an austenite phase generated in a high temperature range, the structure is refined by the austenite transformation, so the crystal grain size after the primary recrystallization becomes uniform and secondary. It is thought that recrystallization stabilizes.
However, since the fraction of the austenite phase decreases as the Si content increases, the secondary recrystallization is stabilized by controlling the component composition and securing the maximum fraction of the γ phase to 30 vol% or more. Good iron loss can be obtained.
The present invention has been completed by further studying the above experimental results.

Next, the component composition of the steel slab used for the manufacturing method of the grain-oriented electrical steel sheet according to the present invention will be described.
C: 0.002-0.2 mass%
If C is less than 0.002 mass%, the grain boundary strengthening effect due to C is lost, and the slab is cracked. Further, C is an austenite forming element, and is an element necessary for increasing the maximum fraction of the γ phase and refining the steel structure of the slab. On the other hand, when it exceeds 0.2 mass%, it becomes difficult to reduce C to 0.005 mass% or less at which magnetic aging does not occur by decarburization annealing. Therefore, C is in the range of 0.002 to 0.2 mass%. Preferably it is the range of 0.01-0.1 mass%.

Si: 2.8 to 4.6 mass%
Si is an element necessary for increasing the specific resistance of steel and reducing eddy current loss. If the effect is less than 2.8 mass%, the effect is not sufficient. On the other hand, if it exceeds 4.6 mass%, secondary recrystallization becomes difficult, workability is lowered, and rolling becomes difficult. Therefore, Si is set to a range of 2.8 to 4.6 mass%. Preferably it is the range of 3.0-4.0 mass%.

Mn: 0.01-0.80 mass%
Mn is an element necessary for improving the hot workability of steel. If the effect is less than 0.01 mass%, the effect is not sufficiently obtained. On the other hand, if it exceeds 0.80 mass%, the magnetic flux density of the product plate is lowered. Therefore, Mn is set to a range of 0.01 to 0.80 mass%. Preferably it is the range of 0.02-0.50 mass%.

Al: 0.010-0.050 mass% and N: 0.003-0.020 mass%
Both Al and N are components necessary as an inhibitor-forming element. If the amount is less than the lower limit value, the inhibitor effect cannot be sufficiently obtained. On the other hand, if the upper limit value is exceeded, the solid solution temperature during slab reheating is low. It becomes too high, and even after reheating the slab, it remains in an undissolved state, causing a decrease in magnetic properties. Therefore, Al is set in the range of 0.010 to 0.050 mass%, and N is in the range of 0.003 to 0.020 mass%, respectively. Preferably, Al ranges from 0.015 to 0.035 mass%, and N ranges from 0.005 to 0.015 mass%, respectively.

In addition to satisfying the above component composition, the steel slab used in the present invention has a maximum value when plotting the mole fraction (mol%) of the γ phase obtained thermodynamically from the component composition of the steel for each temperature ( The maximum fraction) needs to be 30 vol% or more. When the maximum fraction of the γ phase is less than 30 vol%, the effect of refining the steel structure due to the austenite transformation during hot rolling becomes insufficient, and a uniform primary recrystallized structure cannot be obtained after decarburization annealing. Secondary recrystallization becomes unstable. Since Si is a ferrite-forming element, increasing the Si content decreases the maximum fraction of the γ phase. Therefore, by adding another austenite-forming component, for example, C, the maximum fraction of the γ phase is increased to 30 vol. It is necessary to secure at least%. A preferable maximum fraction of the γ phase is 40 vol% or more.
As described above, in the present invention, the thermodynamic calculation of the maximum fraction of the γ phase is performed using Thermo-Calc 3.1 and the database is SSOL4 (version 4.9).

The steel slab, which is the raw material of the grain-oriented electrical steel sheet of the present invention, can contain the following elements, although the balance other than the basic components described above is Fe and inevitable impurities.
S: One or two selected from 0.002 to 0.030 mass% and Se: 0.002 to 0.100 mass% S and Se combine with Mn to form an inhibitor, but each contains If the amount is less than the lower limit, the inhibitor effect cannot be sufficiently obtained.On the other hand, if the amount exceeds the upper limit, the solid solution temperature becomes too high at the time of slab reheating, and remains undissolved even after slab reheating. As a result, the magnetic characteristics are degraded. Therefore, when adding S and Se, it is preferable to set it as the range of S: 0.002-0.030 mass% and Se: 0.002-0.100 mass%, respectively. More preferably, it is the range of S: 0.005-0.020 mass% and Se: 0.010-0.050 mass%, respectively.

Cr: 0.010-0.500 mass%
Cr is a useful element that stabilizes the formation of a forsterite film in finish annealing and reduces film defects. However, if the content is less than 0.010 mass%, the above effect is poor, while if it exceeds 0.500 mass%, the magnetic flux density decreases. Therefore, when adding Cr, it is preferable to set it as the range of 0.010-0.500 mass%. More preferably, it is the range of 0.050-0.400 mass%.

Ni: 0.010 to 1.500 mass%
Since Ni is an austenite forming element, Ni is a useful element for increasing the maximum γ phase fraction of the slab. However, when the content is less than 0.010 mass%, the above effect is small. On the other hand, when the content exceeds 1.500 mass%, the workability deteriorates and the plate-through property deteriorates, and secondary recrystallization becomes unstable. Magnetic properties deteriorate. Therefore, when adding Ni, it is preferable to set it as the range of 0.010-1.500 mass%. More preferably, it is the range of 0.100 to 1.000 mass%.

Sn: 0.005-0.500 mass%, Sb: 0.005-0.500 mass%, P: 0.005-0.500 mass%, Cu: 0.010-0.500 mass%, and Mo: 0.005- One or more selected from 0.100 mass% Sn, Sb, P, Cu and Mo are effective elements for improving magnetic properties, but their respective contents satisfy the lower limit of the above range. Otherwise, the effect of improving the magnetic properties is poor. On the other hand, if the respective contents exceed the upper limit of the above range, the secondary recrystallization becomes unstable and the magnetic properties are deteriorated. Therefore, when adding the said element, it is preferable to add in the said range, respectively. More preferably, Sn: 0.01 to 0.10 mass%, Sb: 0.01 to 0.10 mass%, P: 0.01 to 0.10 mass%, Cu: 0.05 to 0.300 mass%, and Mo, respectively. : It is the range of 0.01-0.05 mass%.

B: 0.0002 to 0.0025 mass%, Nb: 0.0010 to 0.0100 mass% and V: 0.0010 to 0.0100 mass%, or one or more selected from B10, Nb and V are All of them are useful elements for improving the magnetic flux density because they precipitate as fine nitrides or carbides and play a role as inhibitors. However, if each content is less than the lower limit of the above range, the effect of improving the magnetic properties is poor, whereas if each content exceeds the above range, purification in finish annealing becomes difficult and iron loss deteriorates. To do. Therefore, when adding the said element, it is preferable to add in the said range, respectively. More preferably, the ranges are B: 0.0002 to 0.0015 mass%, Nb: 0.0010 to 0.0060 mass%, and V: 0.0010 to 0.0060 mass%, respectively.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
Steel slab The steel material (slab) used in the method for producing the grain-oriented electrical steel sheet according to the present invention is obtained by melting steel having the above-described component composition by a conventional refining process using a converter, a vacuum degassing apparatus, or the like. It may be produced by a conventional continuous casting method or ingot-bundling rolling method, or may be a thin cast piece having a thickness of 100 mm or less by a direct casting method, and is not particularly limited.

Slab Reheating and Hot Rolling Prior to hot rolling, the steel slab is reheated to a temperature of about 1200 to 1400 ° C. in accordance with a conventional method to dissolve the inhibitor-forming element, and then hot rolled. Use hot-rolled sheet. As for the conditions of this hot rolling, when rough rolling is performed, it is preferable that the end temperature of rough rolling is 1100 ° C. or higher and the finish temperature of finish rolling is 900 ° C. or higher. In addition, it is preferable that the entrance side temperature of the 1st pass in the finish rolling of hot rolling, ie, rolling start temperature, shall be 1000 degreeC or more from a viewpoint of ensuring a high (gamma) phase fraction. More preferably, it is 1050 degreeC or more.

Hot-rolled sheet annealing The steel sheet after the hot rolling is then subjected to hot-rolled sheet annealing. The soaking temperature of this hot-rolled sheet annealing is preferably in the range of 800 to 1150 ° C. in order to obtain good magnetic properties. If it is less than 800 degreeC, the band structure formed by hot rolling will remain, it will be difficult to obtain the primary recrystallized structure of a sized particle, and there exists a possibility that the growth of a secondary recrystallized grain may be inhibited. On the other hand, if the temperature exceeds 1150 ° C., the grain size after hot-rolled sheet annealing becomes too coarse, and on the contrary, it becomes difficult to obtain a primary recrystallized structure of sized particles. The soaking time for hot-rolled sheet annealing is preferably about 10 to 600 seconds.

Cold Rolling The steel sheet after hot-rolled sheet annealing is then made into a cold-rolled sheet having a final thickness by cold rolling at least once with intermediate or intermediate annealing. The soaking temperature in the case of performing the intermediate annealing is preferably in the range of 900 to 1200 ° C. When the temperature is lower than 900 ° C., the recrystallized grains after the intermediate annealing become fine, and the Goss nuclei in the primary recrystallized structure may be reduced to deteriorate the magnetic properties of the product plate. On the other hand, when it exceeds 1200 ° C., the crystal grains become too coarse as in the case of hot-rolled sheet annealing, and it becomes difficult to obtain a primary recrystallized structure of sized grains. The soaking time for the intermediate annealing is preferably about 10 to 600 seconds.

  Moreover, it is preferable that the reduction rate in the final cold rolling of the cold rolling is 85% or more. By setting the reduction ratio to 85%, the primary recrystallization texture becomes advantageous for the secondary recrystallization in the Goss orientation, the magnetic flux density is improved, and the hysteresis loss is improved. A more preferable rolling reduction is 87% or more. Note that the upper limit of the cold rolling reduction is preferably about 95%.

Decarburization annealing The cold-rolled sheet having the final thickness is then subjected to decarburization annealing that also serves as primary recrystallization annealing at a soaking temperature of 700 to 1000 ° C. When the soaking temperature is less than 700 ° C., primary recrystallization and decarburization do not proceed sufficiently, and a desired primary recrystallization texture cannot be obtained. On the other hand, when the temperature exceeds 1000 ° C., the primary recrystallized grains become too coarse, and the driving force for secondary recrystallization of Goss orientation grains in the subsequent finish annealing may be lost, and secondary recrystallization may not easily occur. Therefore, it is preferable that the soaking temperature of the decarburization annealing is in the range of 700 to 1000 ° C. The soaking time for decarburization annealing is preferably about 10 to 600 seconds.

Finish annealing After decarburization annealing, the steel separator is coated with an annealing separator mainly composed of MgO, dried, and then subjected to finish annealing consisting of secondary recrystallization annealing and purification annealing. The secondary recrystallized structure accumulated in the film is developed and a forsterite film is formed. In the finish annealing, it is preferable to raise the temperature to about 1200 ° C. for purification treatment and for the formation of a forsterite film.

Here, the most important thing in the method of manufacturing the grain-oriented electrical steel sheet according to the present invention is that the annealing atmosphere from the room temperature to the initial heating stage is a single atmosphere of nitrogen or argon or a mixed atmosphere of nitrogen and argon in the heating process of finish annealing. In addition, the hydrogen content V _H2 contained in the atmosphere is set to 10 vol% or less, and an annealing atmosphere in a stage from any temperature Ts to 1150 ° C. between 800 to 950 ° C. in the heating process of the finish annealing is performed. , Consisting of hydrogen and nitrogen, and the nitrogen content V _N2 (vol%) is the following formula (1):
12.5 × [Si] −35 ≦ V _N2 ≦ 12.5 × [Si] +35 (1)
It is necessary to switch to a mixed atmosphere that satisfies the above.

The reason why the hydrogen content V _H2 in the initial stage of the heating process is set to 10 vol% or less is that when V _H2 exceeds 10 vol%, the decomposition of the inhibitor proceeds and the suppression power is weakened, so secondary recrystallization is normal. This is because the iron loss deteriorates. Preferred V _H2 is 5 vol% or less.
The reason for switching the annealing atmosphere in the heating process in the high temperature range is that, in the high temperature range of the finish annealing, the decomposition of the inhibitor occurs and secondary recrystallization occurs, but in steel with a high Si content, Since the inhibitory power is weak, the inhibitor is easily decomposed and secondary recrystallization tends to become unstable. Therefore, the nitrogen content V _N2 in the annealing atmosphere is increased, and nitrogen is absorbed into the steel to suppress the decomposition of the inhibitor and stabilize the secondary recrystallization.
Moreover, the reason why the switching temperature Ts of the atmosphere is set to any temperature in the range of 800 to 950 ° C. is that when the switching temperature is lower than 800 ° C., the decomposition of the inhibitor proceeds early, so that secondary recrystallization is unstable. On the other hand, if the temperature is higher than 950 ° C., the absorption of nitrogen becomes excessive and secondary recrystallization is difficult to develop. A preferable switching temperature Ts is in the range of 800 to 900 ° C.
The annealing atmosphere after heating to 1150 ° C. may be in accordance with conventional conditions and is not particularly limited. However, for the purpose of purifying steel, it is desirable that the atmosphere has a high hydrogen content.

  The steel sheet after the above-mentioned finish annealing is iron loss by removing the unreacted annealing separator adhering to the steel sheet surface by water washing, brushing, pickling, etc., and then performing flattening annealing to correct the shape. It is effective in reducing the above. This is because the finish annealing is normally performed in the state of a coil, so that the characteristics are prevented from deteriorating when measuring the iron loss due to the winding habit of the coil.

  Further, when the steel plates of the present invention are laminated and used, it is effective to form an insulating coating on the steel plate surface in the flattening annealing or before and after that. In particular, in order to reduce iron loss, it is preferable to apply a tension-imparting film that imparts tension to the steel sheet as the insulating film. For the formation of the tension-imparting film, a method of applying a tension film through a binder or a method of depositing an inorganic substance on the surface of a steel sheet by a physical vapor deposition method or a chemical vapor deposition method has excellent film adhesion and remarkably iron. Since an insulating film having a large loss reducing effect can be formed, it is more preferable.

Moreover, in order to further reduce the iron loss, it is preferable to perform a magnetic domain fragmentation process. As a processing method, a method of generally forming a groove in the final product plate, introducing a thermal strain or an impact strain in a linear or dotted manner by electron beam irradiation, laser irradiation, plasma irradiation, or the like, For example, a method of forming a groove by etching the steel sheet surface in an intermediate process such as a steel sheet cold-rolled to the final thickness can be used.
In addition, what is necessary is just to follow the general manufacturing method of a grain-oriented electrical steel sheet other than the above-mentioned manufacturing conditions.

As shown in Table 1, the Si content was varied in the range of 2.8 to 4.6 mass%, Mn: 0.01 to 0.8 mass%, Al: 0.010 to 0.050 mass%, and A steel slab containing 1400 in the range of N: 0.003 to 0.020 mass% and containing C so that the maximum fraction of the γ phase obtained by thermodynamic calculation is a value shown in Table 1. After reheating to a temperature of ° C., it was hot-rolled to obtain a hot-rolled sheet having a thickness of 2.4 mm and subjected to hot-rolled sheet annealing at 1100 ° C. for 30 seconds. Moreover, the rolling start temperature (entrance side temperature) of the 1st pass in the finish rolling of the said hot rolling was 1000 degreeC or more.
Thereafter, the hot-rolled sheet after the above-mentioned hot-rolled sheet annealing is cold-rolled to an intermediate thickness of 1.5 mm, subjected to an intermediate annealing of 1100 ° C. × 40 s, and finally cold-rolled to a final sheet thickness of 0.23 mm. The cold-rolled sheet was used. Next, after performing decarburization annealing also serving as primary recrystallization annealing at 850 ° C. × 120 s, an annealing separator mainly composed of MgO is applied, and then secondary recrystallization annealing is performed and held at 1200 ° C. for 5 hours. Finish annealing consisting of purification annealing was performed.
At this time, the atmosphere from the room temperature in the heating process in the finish annealing to the temperature of Ts shown in Table 1 is a mixed atmosphere of nitrogen and hydrogen, and the volume fraction V _H2 of hydrogen in the atmosphere is a numerical value shown in Table 1. In addition, the annealing atmosphere from the Ts temperature to 1150 ° C. was a mixed atmosphere of nitrogen and hydrogen, and the nitrogen content V _N2 in the atmosphere was varied as shown in Table 1. Further, the annealing atmosphere from 1150 ° C. to 1200 ° C. and during the purification annealing was set to 100 vol% hydrogen.
Test pieces were collected from the steel sheet after finish annealing thus obtained, and the iron loss W _17/50 at an excitation frequency of 50 Hz was measured in _accordance with _JISC2550 . The results are shown in Table 1.
From this result, it can be seen that all the steel plates manufactured under conditions suitable for the manufacturing conditions of the present invention are excellent in iron loss characteristics.

Steel slabs having various component compositions shown in Table 2 were reheated to a temperature of 1410 ° C., and then hot-rolled to obtain a hot-rolled sheet having a thickness of 2.2 mm, and hot-rolled sheet annealing at 1080 ° C. for 60 seconds. Was given. Moreover, the rolling start temperature (entrance side temperature) of the 1st pass in the finish rolling of the said hot rolling was 1050 degreeC or more.
Thereafter, the hot-rolled sheet after the hot-rolled sheet annealing is cold-rolled to an intermediate thickness of 1.6 mm, subjected to an intermediate annealing of 1100 ° C. × 40 s, and finally cold-rolled to a final sheet thickness of 0.23 mm. The cold-rolled sheet was used. Next, after performing decarburization annealing also serving as primary recrystallization annealing at 840 ° C. × 100 s, an annealing separator mainly composed of MgO is applied, and then, secondary recrystallization annealing and holding at 1180 ° C. for 8 hours. Finish annealing consisting of purification annealing was performed.
Under the present circumstances, the annealing atmosphere of the heating process in the said finish annealing was made into 100 vol% of nitrogen from room temperature to Ts: 900 degreeC, and was made into the mixed atmosphere of 50 vol% of nitrogen and 50 vol% of hydrogen from Ts: 900 degreeC to 1150 degreeC. Further, the annealing atmosphere from 1150 ° C. to 1180 ° C. leading to the purification annealing and during the purification annealing was set to 100 vol% hydrogen.
A test piece was collected from the steel sheet after finish annealing thus obtained, and the iron loss W _17/50 at an excitation frequency of 50 Hz was measured in _accordance with _JISC2550 .
The measurement results are shown in Table 2. From this result, it can be seen that the steel sheets manufactured under the conditions suitable for the present invention using the steel material having the component composition suitable for the present invention all have excellent iron loss characteristics.

Claims (5)

C: 0.002 to 0.2 mass%, Si: 2.8 to 4.6 mass%, Mn: 0.01 to 0.8 mass%, Al: 0.010 to 0.050 mass%, and N: 0.003 After heating a steel slab containing 0.020 mass%, the balance being composed of Fe and inevitable impurities, hot-rolled into a hot-rolled sheet, and hot-rolled sheet subjected to hot-rolled sheet annealing In the method for producing a grain-oriented electrical steel sheet that is subjected to finish annealing after cold rolling of the final sheet thickness by cold rolling twice or more times sandwiching one time or intermediate annealing, and decarburizing annealing of the cold rolled sheet,
The maximum fraction of γ phase obtained from the above component composition by thermodynamic calculation is 30% or more in terms of mole fraction (mol%),
An annealing atmosphere at a temperature Ts of 800 to 950 ° C. or less in the heating process of the finish annealing is a nitrogen or argon simple substance or a mixed atmosphere of nitrogen and argon with a hydrogen content V _H2 of 10 vol% or less,
A method for producing a grain-oriented electrical steel sheet, characterized in that an annealing atmosphere having a temperature exceeding Ts and not higher than 1150 ° C. is a mixed atmosphere of hydrogen and nitrogen in which the nitrogen content V _N2 (vol%) satisfies the following formula (1): .
12.5 × [Si] −35 ≦ V _N2 ≦ 12.5 × [Si] +35 (1)
Here, the above [Si] is the Si content (mass%). The steel slab contains one or two selected from S: 0.002 to 0.030 mass% and Se: 0.002 to 0.100 mass% in addition to the above component composition. The manufacturing method of the grain-oriented electrical steel sheet according to claim 1. In addition to the above component composition, the steel slab further includes Cr: 0.010 to 0.500 mass%, Ni: 0.010 to 1.500 mass%, Sn: 0.005 to 0.500 mass%, and Sb: 0.00. 005 to 0.500 mass%, P: 0.005 to 0.500 mass%, Cu: 0.010 to 0.500 mass%, Mo: 0.005 to 0.100 mass%, B: 0.0002 to 0.0025 mass% Nb: 0.0010-0.0100 mass% and V: 0.0010-0.0100 mass% It contains 1 type, or 2 or more types chosen from mass%, The direction of Claim 1 or 2 characterized by the above-mentioned. Method for producing an electrical steel sheet. The directionality according to any one of claims 1 to 3, wherein the maximum fraction of the γ phase obtained by thermodynamic calculation from the component composition is 40% or more in terms of mole fraction (mol%). A method for producing electrical steel sheets. The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein a final cold rolling reduction ratio of the cold rolling is 85% or more.