JP2016089198A - Manufacturing method of oriented electromagnetic steel sheet excellent in magnetic properties - Google Patents

Abstract

PROBLEM TO BE SOLVED: To propose a method for stably manufacturing an oriented electromagnetic steel sheet having high magnetic flux density and low iron loss.SOLUTION: There is provided a manufacturing method of an oriented electromagnetic steel sheet by hot rolling a steel slab containing, by mass%, C:0.002 to 0.10%, Si:2.5 to 6.0%, Mn:0.01 to 0.8%, Al:0.010 to 0.050%, N:0.003 to 0.020%, burning the hot rolled sheet, cold rolling, burning a primary crystal and finishing burning, where the finish cold rolling in the cold rolling is conducted with 2 paths or more and total rolling reduction of 80 to 95%, rolling at 20% or more is conducted after conducting an aging treatment with at least 1 path with the total rolling reduction in a range of less than 60% at 150 to 250°C×1 minute, rolling at 20% or more with a biting temperature of 150°C or more after conducting an aging treatment with at least 1 path with total rolling reduction in a range of 60% or more at 250 to 300°C×1 minute or more and average rate of temperature rise between 500 to 700°C of the burning primary crystal is set at 50°C/s or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet that is excellent in magnetic characteristics suitable for use in an iron core or the like of a transformer.

  Electrical steel sheets are soft magnetic materials that are widely used as transformers and motor iron cores. Above all, grain oriented electrical steel sheets have excellent magnetic properties such as high magnetic flux density and low iron loss because the crystal orientation is highly integrated in the {110} <001> orientation called Goss orientation. Used in the iron core of containers.

  As a method for highly accumulating the crystal orientation in the Goss orientation, a technique using a precipitate called an inhibitor is known. In the finish annealing process, the inhibitor is finely dispersed and precipitated in the steel, suppresses crystal grain growth, and selectively grows only crystal grains having Goss orientation (hereinafter referred to as “secondary recrystallization”). ").

  There are several substances that act as inhibitors, but AlN is most widely used industrially. For example, Patent Document 1 discloses a technique for increasing the magnetic flux density by adding a small amount of Al to a steel slab and precipitating AlN to form an inhibitor. This technique of using AlN as an inhibitor is extremely effective for obtaining a high magnetic flux density. However, in order to further increase the magnetic flux density, it is necessary to optimize the texture before the secondary recrystallization is caused by finish annealing. That is, it is important to optimize the primary recrystallization texture before finish annealing and to form a sufficient amount of Goss orientation grains that cause secondary recrystallization in the primary recrystallization texture.

  In the technique of using AlN as an inhibitor, as a method of promoting the formation of Goss orientation grains, the steel sheet is rolled in a cold rolling process, or the steel sheet is heated and held between rolling passes to perform an aging treatment. The so-called “warm rolling technique” is known. For example, in Patent Document 2, aging is performed for 1 minute or more in a temperature range of 50 to 350 ° C. with respect to a steel sheet between a plurality of passes in the final cold rolling with a reduction ratio of 81 to 95% consisting of a plurality of passes. A technique for performing the treatment at least once is disclosed. Further, in Patent Document 3, in the final cold rolling, an aging treatment at a temperature of 200 to 300 ° C. is performed at least two passes, and at a stage where the total rolling reduction is 55% or more, the biting temperature (at the time of biting) The steel plate temperature) is 110 to 190 ° C. and 20 to 30% rolling is disclosed.

  The reason why the above-described warm rolling technique is effective is that the transition introduced by rolling is fixed by solute C or carbide, and the activity of slip surfaces other than the normal slip surface is induced to form a shear band. This is because it is promoted and nuclei of Goss-oriented grains are formed inside the shear zone. The Goss nuclei formed in this way are recrystallized in the primary recrystallization annealing and become the nuclei of secondary recrystallization, so that the secondary recrystallized grains after the finish annealing are refined and the iron loss is a constituent factor. One of the abnormal eddy current losses is reduced.

  As a technique for reducing the iron loss by refining the secondary recrystallized grains, a technique for rapidly heating the heating process of the primary recrystallization annealing is known in addition to the above-described warm rolling technique. For example, in Patent Document 4, the steel sheet after the final cold rolling is rapidly heated to a temperature range of 700 ° C. or higher at a rate of temperature increase of 80 ° C./s or more, thereby refining secondary recrystallized grains and iron loss. A technique for reducing the above is disclosed. In addition, this document discloses that a grain-oriented electrical steel sheet having more excellent iron loss characteristics can be manufactured by combining a rapid heating technique of primary recrystallization annealing and a warm rolling technique.

  The technique of rapid heating by the above primary recrystallization annealing is to recrystallize ND // <111> oriented grains that start recrystallization at a temperature lower than the Goss orientation by heating to a temperature higher than the recrystallization temperature in a short time. By suppressing this, recrystallization of Goss oriented grains is promoted.

Japanese Examined Patent Publication No. 46-023820 Japanese Patent Publication No. 54-013846 JP 2013-139629 A Japanese Patent No. 3392579

  By applying the above-described technique, it is possible to produce a grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss. However, demands for energy saving in recent years have become more severe, and it has become difficult to stably provide a grain-oriented electrical steel sheet that can meet the above demands with the above-described conventional technology.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to propose a method for stably producing a grain-oriented electrical steel sheet having a higher magnetic flux density and a lower iron loss than before.

  As described above, both the warm rolling technology in cold rolling and the rapid heating technology in primary recrystallization annealing promote the formation of Goss orientation nuclei and their recrystallization. There is a big one. However, the above two technologies are technologies mainly aimed at miniaturization of secondary recrystallized grains, and in order to achieve further higher magnetic flux density and lower iron loss, the orientation of secondary recrystallized grains must be further increased. It is considered effective to increase and reduce the hysteresis loss.

  In order to achieve the above-mentioned problem from the viewpoint of the texture, it is important to improve the degree of integration of the ND // <111> orientation or the ND // <411> orientation in the primary recrystallization texture. Since these orientations become a matrix in which the Goss orientation grains are phagocytosed during secondary recrystallization, the priority of growth of the Goss orientation grains in the secondary recrystallization is increased, and the secondary recrystallization highly accumulated in the Goss orientation. This is because it is important to obtain a texture.

  In the primary recrystallization texture, as a technique for improving the degree of integration of the ND // <111> orientation or the ND // <411> orientation, as disclosed in Patent Documents 3 and 4 described above, By controlling the cooling rate, ND // <111 in the primary recrystallized texture using a method of reducing the solute C and N in the steel sheet before cold rolling and finely precipitated carbides. > There is a technique for increasing the strength of the orientation. However, these technologies have strong implications as countermeasures against the decrease in the ND // <111> orientation when applying warm rolling technology or rapid heating technology, and basically improve the texture. It is not intended to improve the magnetic characteristics.

  Therefore, the inventors repeated detailed examinations paying attention to the warm rolling conditions in the final cold rolling. As a result, the final cold rolling pass consisting of multiple passes is divided into a first half pass and a second half pass that is close to the final plate thickness, an aging treatment is performed at an appropriate temperature before each pass, and the biting temperature of the second half pass is set. It has been found that by optimizing, the Goss orientation strength in the primary recrystallization texture can be increased, and the strength of the ND // <411> orientation can be enhanced, and the present invention has been developed.

  That is, the present invention is C: 0.002-0.10 mass%, Si: 2.5-6.0 mass%, Mn: 0.01-0.8 mass%, Al: 0.010-0.050 mass%, N: 0.003 to 0.020 mass%, with the balance being Fe and inevitable impurities, hot-rolled steel slab, hot-rolled sheet annealed, cold once more than two times sandwiching intermediate or intermediate annealing In the method for producing a grain-oriented electrical steel sheet comprising a series of steps of rolling, primary recrystallization annealing also serving as decarburization annealing, applying an annealing separator mainly composed of MgO to the steel sheet surface, and finishing annealing, the cold The final cold rolling in the rolling is performed at a total reduction rate of 80 to 95% at 2 passes or more, and at least one pass is aging treatment at 150 to 250 ° C. for 1 minute or more in a range where the total reduction rate is less than 60%. 20% or more after applying After rolling at a rate of at least one pass in the range where the total rolling reduction is 60% or more, 250-300 ° C x 1 minute or more, and the biting temperature is 150 ° C or more, the rolling reduction is 20% or more. And a method for producing a grain-oriented electrical steel sheet, characterized in that an average rate of temperature increase between 500 and 700 ° C. in the heating process of primary recrystallization annealing is 50 ° C./s or more.

  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 0.03 mass% and Se: 0.002 to 0.03% 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: 0.01-0.50mass%, Cu: 0.01-0.50mass%, P : 0.005-0.50 mass%, Ni: 0.01-1.50 mass%, Sb: 0.005-0.50 mass%, Sn: 0.005-0.50 mass%, Mo: 0.005-0 100% by mass, B: 0.0002 to 0.0025 mass%, Nb: 0.0010 to 0.0100 mass% and V: 0.001 to 0.01 mass%, or one or more selected from It is characterized by that.

  According to the present invention, a grain-oriented electrical steel sheet having a high magnetic flux density and a low iron loss can be stably provided.

It is a figure which shows the relationship between the aging treatment temperature in the first half of the last cold rolling, and a magnetic characteristic. It is a figure which shows the relationship between the aging treatment temperature in the last half of final cold rolling, and a magnetic characteristic.

First, the experiment that led to the development of the present invention will be described.
A steel slab containing C: 0.07 mass%, Si: 3.3 mass%, Mn: 0.06 mass%, Al: 0.024 mass% and N: 0.0080 mass% is reheated to 1400 ° C, and then hot. After rolling to a sheet thickness of 2.2 mm and hot-rolled sheet annealing at 1100 ° C. for 60 seconds, cold-rolled to a sheet thickness of 1.5 mm and after intermediate annealing at 1120 ° C. for 80 seconds A cold rolled sheet having a final sheet thickness of 0.23 mm was obtained by the second cold rolling.
Here, the second cold rolling (final cold rolling) was 6 passes, and rolling was performed according to the pass schedule shown in Table 1. Further, before rolling in the second pass and the fifth pass, an aging treatment is performed in which the steel sheet is heated to various temperatures and held for 10 minutes, and before rolling in the first pass, the third pass, and the fourth pass, 100 ° C. And an aging treatment for 10 minutes. Further, the biting temperature (steel plate temperature at the time of biting) was 180 ° C. only in the fifth pass, and the plate was passed after cooling to 100 ° C. or lower in the other passes.

Next, the cold-rolled sheet is heated to 700 ° C. with an average rate of temperature increase between 500 ° C. and 700 ° C. being 100 ° C./s, and then mixed with hydrogen and nitrogen with an oxidation potential of P _H2O / P _H2 = 0.40. After performing primary recrystallization annealing, which also serves as decarburization annealing that keeps soaking at 850 ° C for 120 seconds in a humid atmosphere, an annealing separator mainly composed of MgO is applied to the surface of the test piece and held at 1150 ° C for 5 hours Finish annealing was performed.
With respect to the test piece after finish annealing thus obtained, the magnetic flux density is 1.7 T, the iron loss W _{17/50 at} an excitation frequency of 50 Hz, and the magnetic flux density at an excitation magnetic field of 800 A / m and an excitation frequency of 50 Hz in accordance with JIS C2550. the B ₈ were measured.

Regarding the results obtained in the above experiment, the iron loss W _17/50 and the magnetic flux density B ₈ when the aging treatment temperature before the second pass was fixed at 260 ° C. and the aging treatment temperature before the second pass was changed were as _follows . The change is shown in FIG. From this figure, when the aging treatment temperature before the second pass is gradually increased from around room temperature, the magnetic flux density is also improved, but the iron loss is greatly improved, particularly in the range of 150 to 250 ° C. It can be seen that iron loss is obtained. And the steel plate that has been subjected to the aging treatment at the temperature showing the above good iron loss is confirmed to be refined in the secondary recrystallized grain size. This is thought to be due to the reduction of

Next, FIG. 2 shows changes in the iron loss W _17/50 and the magnetic flux density B ₈ when the aging treatment temperature before the second pass is fixed at 200 ° C. and the aging treatment temperature before the fifth pass is changed. . From this figure, when the aging treatment temperature before the fifth pass is increased, the magnetic flux density is improved, and the iron loss is improved accordingly. Especially, the iron loss is most in the range of 250 to 300 ° C. It can be seen that the magnetic flux density is good. Therefore, it can be seen that not only the iron loss but also the magnetic flux density can be improved by appropriately controlling the aging treatment temperature of the latter half pass in the final cold rolling.

  Based on the above experimental results, the secondary recrystallized grains were refined by dividing the multiple passes in the final cold rolling into a first half pass and a second half pass, and applying an aging treatment under the optimum conditions at each stage pass. It was found that the magnetic flux density and the iron loss can be improved at the same time.

Although the reason for the above has not been clarified yet, the inventors consider as follows.
Goss nuclei after cold rolling are formed in shear bands formed during rolling. The shear band is formed in the latter half of the cold rolling when the total rolling reduction is high, but the shear band in the latter half of the cold rolling is fixed by warm rolling from the first half of the cold rolling and fixing the dislocation. Formation is promoted and Goss nuclei increase. On the other hand, in order to reliably form a shear band even in the latter half of the cold rolling, warm rolling is required. However, according to the investigation by the inventors, by adopting warm rolling, ND // <411. > It was found that the formation of orientation nuclei was also promoted.

  The reason why the ND // <111> orientation is increased is that the slip plane matching theory described in the report of Imamura et al. (Metall. Mater. Trans. A., Vol. 32A, pp. 403-408), ie, adjacent Even if the Schmid factor is not the maximum, the deformation band is formed by the preferential activity of the grooving system that shares the grooving surface with the adjacent grains. This can be explained by the idea that crystal rotation occurs and becomes the core of recrystallization in the subsequent primary recrystallization annealing. That is, ND // <411> oriented nuclei exist inside the deformation zone formed by Slip plane matching, but since the formation of the deformation zone occurs mainly in the latter half of the cold rolling, Aging treatment is required. In addition, it is estimated that the formation of ND // <411> orientation nuclei by Slip plane matching and the generation of Goss orientation nuclei by the formation of shear bands compete with each other or coexist in the latter half of cold rolling. It is considered that the warm plane is set to a relatively high temperature of 250 ° C. or higher so that the slip plane matching mechanism works preferentially and the ND // <411> orientation is increased.

For the above reasons, when the aging treatment is performed only in the first half of the cold rolling or only in the second half of the cold rolling, the effect of the warm rolling cannot be sufficiently obtained. Therefore, in the present invention, it is an indispensable requirement to perform aging treatment in both the first half pass where the total reduction rate is lower and the latter half pass where the total reduction rate is higher than that at the total reduction rate of 60%. To do.
Further, in order to sufficiently obtain the effect of the aging treatment, the rolling (pass) after the aging treatment needs to be performed at a rolling reduction of 20% or more.

  Further, there is an appropriate temperature for the aging treatment temperature in each of the first half pass and the second half pass of cold rolling, the aging treatment temperature in the first half of cold rolling is in the range of 150 to 250 ° C., and the aging treatment temperature in the second half of cold rolling is 250. It is necessary to make it into the range of -300 degreeC. When the aging treatment temperature in the first half of the cold rolling is less than 150 ° C., the formation of Goss orientation nuclei becomes insufficient. When the temperature exceeds 250 ° C., formation of Goss orientation nuclei is promoted, but ND // <411> orientation nuclei decrease. As a result, a good magnetic flux density cannot be obtained. On the other hand, if the aging treatment temperature in the latter half of the cold rolling is less than 250 ° C., the formation of ND // <411> oriented grains becomes insufficient, and if the aging treatment temperature exceeds 300 ° C., strain recovery starts. Can not get enough.

Further, in the rolling (pass) after the aging treatment in the second half of the cold rolling, it is necessary to set the biting temperature to 150 ° C. or higher in order to promote the formation of the Goss orientation due to the dynamic aging effect. The upper limit of the biting temperature is preferably about 300 ° C. in order to prevent an excessive increase in aging temperature due to heat generated by processing.
The present invention has been developed based on the above novel findings.

Next, the component composition of the steel material (slab) used for manufacture of the grain-oriented electrical steel sheet of the present invention will be described.
C: 0.002-0.10 mass%
C is a component necessary for generating Goss-oriented crystal grains. In order to exhibit such an effect, it is necessary to contain 0.002 mass% or more. However, when the C content exceeds 0.10 mass%, decarburization annealing is insufficient even if decarburization annealing is performed, causing magnetic aging. Therefore, C is in the range of 0.002 to 0.10 mass%. Preferably it is the range of 0.01-0.08 mass%.

Si: 2.5-6.0 mass%
Si is an element necessary for increasing the specific resistance of steel and reducing iron loss. If the amount is less than 2.5 mass%, the above effect is not sufficient. On the other hand, if the amount exceeds 6.0 mass%, the workability of the steel is lowered and it becomes difficult to roll. Therefore, Si is set to a range of 2.5 to 6.0 mass%. Preferably, it is in the range of 2.9 to 5.0 mass%.

Mn: 0.01 to 0.8 mass%
Mn is an element necessary for improving hot workability. If it is less than 0.01 mass%, the above effect is not sufficient. On the other hand, if it exceeds 0.8 mass%, the magnetic flux density after secondary recrystallization decreases. Therefore, Mn is set to a range of 0.01 to 0.8 mass%. Preferably it is the range of 0.05-0.5 mass%.

Al: 0.010-0.050 mass%, N: 0.003-0.020 mass%
Both Al and N are elements necessary for inhibitor formation. If the content of Al and N is less than the above lower limit value, the inhibitor effect cannot be sufficiently obtained. On the other hand, if the content exceeds the upper limit value, the temperature for dissolving AlN becomes too high, and the slab is heated at a high temperature. Also remains undissolved and deteriorates the magnetic properties. Therefore, the contents of Al and N are within the above range. Preferably, Al: 0.015-0.040 mass%, N: 0.005-0.015 mass%.

  Note that the steel material (slab) used in the present invention is an inhibitor forming element, in addition to the above Al and N, further S: 0.002-0.03 mass% and / or Se: 0.002-0.03 mass%. Can be contained. If the respective contents are less than the above lower limit value, the inhibitor effect cannot be sufficiently obtained. On the other hand, if the above upper limit value is exceeded, the solid solution temperature of the inhibitor w becomes too high, and the slab is reheated to a high temperature. Also remain undissolved and degrade the magnetic properties. Therefore, the content of S and Se is preferably within the above range. More preferably, it is the range of S: 0.005-0.02mass%, Se: 0.01-0.02mass%.

  Moreover, the steel raw material used for this invention is Cr: 0.01-0.50mass%, Cu: 0.01-0.50mass%, and P: for the purpose of reducing an iron loss further in addition to the said component composition. For the purpose of improving the magnetic flux density, one or more selected from 0.005 to 0.50 mass%, and Ni: 0.01 to 1.50 mass%, Sb: 0.005 to 0.00. 50 mass%, Sn: 0.005-0.50 mass%, Mo: 0.005-0.100 mass%, B: 0.0002-0.0025 mass%, Nb: 0.0010-0.0100 mass%, and V: 0 One or two or more selected from 0.001 to 0.01 mass% may be contained. When the content of each element is less than the lower limit, the effect of improving the magnetic properties is small, whereas when the upper limit is exceeded, secondary recrystallization is destabilized and the growth of secondary recrystallized grains is suppressed, On the other hand, the magnetic properties are degraded.

  The balance other than the above components is Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the inclusion of components other than those described above is not rejected.

Next, the manufacturing method of the grain-oriented electrical steel sheet of this invention is demonstrated.
The steel material (slab) used in the method for producing a grain-oriented electrical steel sheet according to the present invention is obtained by melting a steel having the above component composition by a generally known refining process, and then performing continuous casting or ingot-bundling rolling. Although it can manufacture, it is preferable to manufacture by the continuous casting method with the favorable uniformity of a component composition.

  In order to sufficiently dissolve the inhibitor-forming component, the slab is reheated to a temperature of about 1400 ° C., and then hot-rolled under ordinary conditions to obtain a hot-rolled sheet.

  The hot-rolled sheet needs to be subjected to hot-rolled sheet annealing in order to obtain good magnetic properties. The temperature of this hot-rolled sheet annealing is preferably in the range of 800 to 1150 ° C. If it is less than 800 degreeC, the band structure formed by hot rolling will remain, it will become difficult to obtain the primary recrystallized structure of a sized particle, and the development of secondary recrystallization will be inhibited. On the other hand, when the temperature exceeds 1150 ° C., the crystal grains after the hot-rolled sheet annealing are excessively coarsened, so that it becomes difficult to obtain a primary recrystallized structure of sized grains.

  The steel sheet after the hot-rolled sheet annealing is then cold-rolled with a final thickness by performing cold rolling twice or more times with one or intermediate annealing. The annealing temperature when performing the intermediate annealing is preferably in the range of 900 to 1200 ° C. If it is less than 900 ° C., the recrystallized grains become finer, the Goss orientation nuclei in the primary recrystallized structure are reduced, and the magnetic properties are lowered. On the other hand, when the temperature exceeds 1200 ° C., the crystal grains become too coarse as in the hot-rolled sheet annealing, and it becomes difficult to obtain a primary recrystallized structure of the sized grains.

  In addition, the final cold rolling for rolling to the final plate thickness increases the ND // <111> structure and the ND // <411> structure of the primary recrystallization texture to obtain a good magnetic flux density. It is necessary to make it 80 to 95% of range. If the total rolling reduction is less than 80%, the ND // <111> structure and ND // <411> structure of the primary recrystallization texture are not sufficiently sharpened, so that a high magnetic flux density cannot be obtained. This is because when the rate exceeds 95%, secondary recrystallization hardly occurs. A preferred total rolling reduction is in the range of 85-92%.

  In the final cold rolling, the total rolling reduction is in the range of less than 60%, and at least one pass is subjected to an aging treatment at a temperature of 150 to 250 ° C. for 1 minute or more, and then the rolling reduction of 20% or more. It is necessary to carry out rolling. If the aging treatment is not performed at all, or if the aging treatment temperature is less than 150 ° C. or the aging time is less than 1 minute, the Goss orientation nucleus after cold rolling is not sufficiently formed, and iron loss is improved by refining secondary recrystallized grains. The effect cannot be obtained sufficiently. On the other hand, when the aging treatment temperature is higher than 250 ° C., formation of Goss orientation nuclei is promoted, but ND // <411> orientation nuclei are reduced, and a good magnetic flux density cannot be obtained.

  Also, if the pass reduction ratio immediately after the aging treatment is lower than 20%, the effect of improving the texture by the aging treatment cannot be sufficiently obtained, and both the refinement of secondary recrystallized grains and a good magnetic flux density are obtained. I can't. In addition, it is preferable to hold | maintain said aging treatment in the temperature range of 170-230 degreeC for 5 minutes or more preferably, and it is preferable to make the rolling reduction of the pass after an aging treatment into the range of 25-50%.

  Furthermore, even when the total rolling reduction of the final cold rolling is in the range of 60% or more, at least one pass is subjected to an aging treatment for holding for 1 minute or more at a temperature of 250 to 300 ° C, and then the biting temperature is 150 ° C or more. It is necessary to perform rolling at a rolling reduction of 20% or more. If the aging treatment is not performed or the aging treatment temperature is less than 150 ° C. or the treatment temperature is less than 1 minute, the Goss orientation nucleus and the ND // <411> structure after cold rolling are not sufficiently developed, and secondary recrystallization is performed. Grain refinement and high magnetic flux density cannot be realized. On the other hand, when the aging treatment temperature exceeds 300 ° C., recovery proceeds, so that the effect of warm rolling cannot be obtained.

  Further, in the pass immediately after the aging treatment, if the biting temperature is less than 150 ° C., the Goss orientation nucleus due to dynamic aging is not sufficiently formed, and if the rolling reduction is lower than 20%, the texture by the aging treatment Since the improvement effect cannot be obtained sufficiently, neither the refinement of secondary recrystallized grains nor a good magnetic flux density can be obtained. The above aging treatment is preferably held at a temperature of 270 to 300 ° C. for 5 minutes or more, and the pass immediately after the aging treatment has a biting temperature of 170 ° C. or more and a rolling reduction of 25 to 50%. The range is preferable.

  In addition, since the final cold rolling of this invention needs to give an aging treatment twice at least, it is necessary to roll by two or more passes. The upper limit number of rolling is not particularly limited, but it is preferable to stop at 8 passes or less from the viewpoint of securing a reduction ratio (20% or more) necessary for rolling after the aging treatment and ensuring high productivity. .

  The rolling mill for performing the final cold rolling may be either a tandem rolling mill or a reverse rolling mill. However, since a aging treatment of 1 minute or more is required between passes, it is preferably performed by a reverse rolling mill. Furthermore, the method for performing the aging treatment may be any method as long as the aging conditions (temperature, time) described above can be ensured. For example, if the aging treatment is not performed before the first pass, the processing heat generated by rolling is generated. It may be used, and after heating the steel plate to a predetermined temperature by heater heating or induction heating, it is wound around a coil and held at the above temperature and time, or the rolled steel plate is wound around the coil and then a heating furnace is used. Alternatively, a heating method may be used.

  The cold-rolled sheet rolled to the final sheet thickness is then subjected to primary recrystallization annealing with a soaking temperature of 700 to 900 ° C. Under the present circumstances, in the heating process of the said primary recrystallization annealing, in order to acquire a favorable magnetic characteristic, it is necessary to make the average temperature increase rate between 500-700 degreeC into 50 degrees C / s or more. When the heating rate is less than 50 ° C./s, recrystallization of Goss orientation nuclei and ND // <411> orientation nuclei is not promoted, and secondary recrystallized grains are refined and magnetic flux density is increased. I can't. A preferable temperature increase rate is 100 ° C./s or more. The upper limit of the temperature increase rate is not particularly limited, but is preferably about 600 ° C./s from the viewpoint of controllability of the temperature increase rate.

  In addition, although the steel raw material used for the manufacturing method of the grain-oriented electrical steel sheet according to the present invention has an essential requirement to contain C in an amount of 0.002 mass% or more, C remains in the product plate in excess of 0.005 mass%. If this is the case, magnetic aging is caused and the magnetic properties are deteriorated. Therefore, it is necessary to perform decarburization annealing to reduce C. This decarburization annealing is desirably performed at a temperature of 700 to 900 ° C. in a wet atmosphere of a hydrogen-nitrogen mixture, and may be performed in combination with the soaking process of the primary recrystallization annealing. What is primary recrystallization annealing? You may carry out as another process.

  The steel sheet after the decarburization annealing is then applied and dried with an annealing separator mainly composed of MgO on the steel sheet surface, and then subjected to finish annealing to develop a secondary recrystallized structure. In addition, although application | coating of the annealing separation agent to a steel plate surface is normally apply | coated as a slurry, you may carry out using electrostatic application | coating which does not bring in a water | moisture content. The finish annealing is performed at a temperature of 800 ° C. or higher in order to develop secondary recrystallization, and is held at a temperature of 800 ° C. or higher for 20 hours or longer in order to complete the secondary recrystallization. Is desirable. A preferable temperature for developing secondary recrystallization is in the range of 850 to 950 ° C.

If emphasis is placed on the punching workability and the glassy forsterite (Mg ₂ SiO ₄ ) film is not formed on the steel plate surface, it is sufficient that the secondary recrystallization is completed, so the finish annealing is finished as it is. It is also possible to do.
On the other hand, when a forsterite film is formed or a purification treatment is performed to remove the inhibitor-forming component, it is preferable to heat to a temperature of about 1200 ° C. in a hydrogen atmosphere after the completion of secondary recrystallization. .

After the finish annealing, the steel loss is reduced by removing the unreacted annealing separator remaining on the steel sheet surface by washing, brushing, pickling, etc., and then performing flattening annealing to correct the shape. It is effective for.
In addition, when the steel sheet after the finish annealing is used by being laminated, an insulating film is applied to the steel sheet surface before or after the flattening annealing or at the time of the flattening annealing in order to provide insulation. Preferably.
The insulating coating is preferably of a tension imparting type that imparts tension to the surface of the steel plate in order to further reduce iron loss. When applying the above tension-imparting film, the film adhesion can be achieved by applying a film through a binder or by applying a film after depositing an inorganic substance on the steel sheet surface by physical vapor deposition or chemical vapor deposition. It is more preferable because a coating film having excellent iron loss reduction effect can be obtained.

  Furthermore, in order to further reduce the iron loss of the product steel plate, it is preferable to perform a magnetic domain refinement treatment. As a method for performing magnetic domain subdivision treatment, there are conventionally known methods such as forming a linear groove or strain region on a product steel plate by roller processing or the like, or irradiating an electron beam, laser, plasma jet, etc. Or a method of introducing grooves on the surface of the cold-rolled sheet having the final thickness by etching or the like.

A steel slab containing C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.10 mass%, Al: 0.023 mass%, and N: 0.008 mass% is reheated to 1400 ° C and then hot. Rolled to a hot-rolled sheet with a thickness of 2.2 mm, subjected to hot-rolled sheet annealing at 1100 ° C. × 60 seconds, and then cold-rolled to a thickness of 1.8 mm, intermediate annealing at 1120 ° C. × 60 seconds After that, a cold rolled sheet having a final sheet thickness of 0.23 mm was obtained by the second cold rolling.
The second cold rolling (final cold rolling) was performed by a reverse mill with a 7-pass schedule shown in Table 2. At this time, an aging treatment is performed by changing the heating temperature for 15 minutes before rolling in the third and sixth passes of the final cold rolling, and aging for 15 minutes at 100 ° C. before the other passes. Treated. Further, the biting temperature was changed to 120 ° C. or 180 ° C. only in the fifth pass, and cooled to 100 ° C. or lower in the other passes.
Next, the cold rolled sheet was heated to 700 ° C. by changing the average temperature rising rate between 500 ° C. and 700 ° C. to 20 ° C./s or 80 ° _C./s , and then the oxidation potential P _H2O / P _H2 = 0.39. After performing primary recrystallization annealing that also serves as decarburization annealing at 850 ° C. for 120 seconds in a mixed wet atmosphere of hydrogen and nitrogen, an annealing separator mainly composed of MgO is applied to the surface of the test piece at 1200 ° C. Finish annealing was performed for 5 hours.
About the test piece after the finish annealing thus obtained, the magnetic flux density 1.7T, the iron loss W _17/50 at an excitation frequency of 50 Hz, and the magnetic flux density B at an excitation magnetic field of 800 A / m and an excitation frequency of 50 Hz in accordance with JIS C2550. ₈ was measured and the results are shown in Table 3. From Table 3, the aging treatment temperature before 3 passes is in the range of 150 to 250 ° C, the aging treatment temperature before 6 passes is in the range of 250 to 300 ° C, and the biting temperature in the 6th pass is 150 ° C or higher. This shows that the magnetic flux density and iron loss are greatly improved. Moreover, it turns out that iron loss is further improved by raising the temperature increase rate in primary recrystallization annealing to 50 degrees C / s or more.

Steel slabs having various component compositions shown in Table 4 were reheated to 1400 ° C., and then hot-rolled to obtain a hot-rolled sheet having a thickness of 2.2 mm, and subjected to hot-rolled sheet annealing at 1100 ° C. × 60 seconds. Thereafter, it was cold-rolled to a thickness of 1.8 mm, subjected to intermediate annealing at 1120 ° C. for 60 seconds, and then cold-rolled to a final thickness of 0.23 mm by the second cold rolling.
The second cold rolling (final cold rolling) was performed in 7 passes using a reverse mill, and the rolling was performed according to the pass schedule shown in Table 2 as in Example 1. In this case, an aging treatment is performed for 20 minutes at 200 ° C. before each of the 2, 3, and 4 passes of cold rolling, and 270 ° C. before each of the 5, 6, and 7 passes. The aging treatment was performed for 20 minutes, and the biting temperature of all passes was controlled in the range of 160 ° C to 200 ° C.
Next, the cold-rolled sheet is heated to 700 ° C. with an average rate of temperature increase between 500 ° C. and 700 ° C. being 120 ° C./s, and then mixed with hydrogen and nitrogen at an oxidation potential of P _H2O / P _H2 = 0.42. Finished by applying a primary recrystallization annealing that also serves as a decarburization annealing at 850 ° C. for 120 seconds in a humid atmosphere, and then applying an annealing separator mainly composed of MgO to the surface of the test piece and holding at 1200 ° C. for 5 hours. Annealed.
About the test piece of finish annealing obtained in this way, the magnetic flux density 1.7 T, the iron loss W _17/50 at an excitation frequency of 50 Hz, and the magnetic flux density B _{8 at an} excitation magnetic field of 800 A / m and an excitation frequency of 50 Hz in accordance with JIS C2550. Was measured and listed in Table 4. It can be seen from Table 4 that a grain-oriented electrical steel sheet excellent in magnetic flux density and iron loss can be produced by using a steel material containing a composition component suitable for the present invention.

A steel slab containing C: 0.07 mass%, Si: 3.2 mass%, Mn: 0.09 mass%, Al: 0.025 mass%, and N: 0.009 mass% is reheated to 1400 ° C. and then hot. Rolled to a hot-rolled sheet having a thickness of 2.2 mm, subjected to hot-rolled sheet annealing at 1100 ° C. × 60 seconds, then cold-rolled to a sheet thickness of 1.5 mm, and subjected to intermediate annealing at 1100 ° C. × 60 seconds. After the application, a cold rolled sheet having a final sheet thickness of 0.23 mm was obtained by the second cold rolling.
Here, the second cold rolling (final cold rolling) is performed in 6 passes using a reverse mill, rolled in accordance with the pass schedule shown in Table 5, and before the 2 passes shown in Table 6. In the first, an aging treatment was performed at 200 ° C. × 10 minutes for the first time and 250 ° C. × 10 minutes for the second time. Further, in the pass after the second aging treatment, the biting temperature was 150 ° C., and in the other passes, the aging treatment was performed at 80 ° C. for 10 minutes, and then the rolling was performed at the temperature of 80 ° C.
Subsequently, after heating the said cold rolled sheet to 700 degreeC by making the average temperature increase rate between 500-700 degreeC into 120 degreeC / s, the mixing wet atmosphere of the oxidation potential _PH2O / _PH2 = 0.39. After performing primary recrystallization annealing that also serves as decarburization annealing at 850 ° C. for 120 seconds below, finish annealing is performed by applying an annealing separator mainly composed of MgO to the test piece surface and holding at 1200 ° C. for 5 hours. gave.
About the test piece after the finish annealing thus obtained, the magnetic flux density 1.7T, the iron loss W _17/50 at an excitation frequency of 50 Hz, and the magnetic flux density B at an excitation magnetic field of 800 A / m and an excitation frequency of 50 Hz in accordance with JIS C2550. ₈ was measured and the result is shown in Table 6. From Table 6, the magnetic properties are greatly improved by applying the first aging treatment in a range where the total reduction ratio is less than 60% and applying the second aging treatment in a range where the total reduction ratio is 60% or more. I understand that.

Claims (3)

C: 0.002-0.10 mass%, Si: 2.5-6.0 mass%, Mn: 0.01-0.8 mass%, Al: 0.010-0.050 mass%, N: 0.003- A steel slab containing 0.020 mass%, the balance being Fe and inevitable impurities, is hot-rolled, hot-rolled sheet annealed, cold-rolled twice or more sandwiching intermediate or intermediate annealing, and decarburized annealing In the method for producing a grain-oriented electrical steel sheet comprising a series of steps in which the primary recrystallization annealing also serves as a coating, applying an annealing separator mainly composed of MgO to the steel sheet surface, and finishing annealing,
The final cold rolling in the cold rolling is performed at 2 or more passes with a total rolling reduction of 80 to 95%, and
At least one pass in a range where the total rolling reduction is less than 60%, after aging treatment at 150 to 250 ° C. for 1 minute or more, rolling at a rolling reduction of 20% or more,
At least one pass in a range where the total rolling reduction is 60% or more, after aging treatment of 250 to 300 ° C. × 1 minute or more, rolling at a rolling reduction of 20% or more with a biting temperature of 150 ° C. or more,
A method for producing a grain-oriented electrical steel sheet, wherein an average rate of temperature increase between 500 and 700 ° C. in the heating process of the primary recrystallization annealing is 50 ° C./s or more. The steel slab contains one or two selected from S: 0.002 to 0.03 mass% and Se: 0.002 to 0.03% in addition to the 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: 0.01 to 0.50 mass%, Cu: 0.01 to 0.50 mass%, P: 0.005 to 0.50 mass%, Ni: 0.00. 01 to 1.50 mass%, Sb: 0.005 to 0.50 mass%, Sn: 0.005 to 0.50 mass%, Mo: 0.005 to 0.100 mass%, B: 0.0002 to 0.0025 mass% Nb: 0.0010-0.0100 mass% and V: 0.001-0.01 mass% It contains 1 type, or 2 or more types chosen from Claim 1 or 2 directions characterized by the above-mentioned. Method for producing an electrical steel sheet.

Images