Method for manufacturing electromagnetic steel sheet, and cold-rolled sheet

Abstract

A method for manufacturing an electromagnetic steel sheet by heating a billet to a temperature of 1300 DEG C or less, hot-rolling the billet to obtain a hot-rolled sheet, annealing the hot-rolled sheet, then cold-rolling the hot-rolled sheet to obtain a cold-rolled steel sheet having a final sheet thickness, and finally annealing the cold-rolled sheet, a method for manufacturing an electromagnetic steel sheet having excellent magnetic characteristics by preferentially appearing crystal grains having a specific orientation without impairing the grain growth properties of recrystallized crystal grains by setting the difference between the vicinity of the grain boundaries in the processed crystal grains of the cold-rolled steel sheet and the amount of strain in the crystal grains to a predetermined value or more; and a cold-rolled sheet used in this production method, the steel sheet containing, in mass%, 0 to 0.100% of C, 1.00 to 5.00% of Si, 0 to 1.00% of Mn, 0 to 0.02% of P, 0 to 2.00% of Al, 0 to 0.010% of N, 0 to 0.010% of S, 0 to 0.010% of Se, 0 to 0.100% of Ti, 0 to 0.100% of Nb, and 0 to 0.100% of V, and further containing at least one of Sn and Sb in a total of 0 to 0.200%.

Description

Technical Field

[0001] The present invention relates to a method for producing an electromagnetic steel sheet having excellent magnetic properties and mainly used for an iron core of a motor, a transformer, etc., and a cold-rolled sheet cold-rolled to a final sheet thickness used in the method. Background Art

[0002] In recent years, from the perspective of protecting the earth's environment and reducing costs, energy consumption reduction is required in many technical fields. Along with this, there is also a strong demand for low iron loss and high magnetic flux density for electromagnetic steel plates used in the cores of motors, transformers, etc. In order to reduce iron loss, it is effective to increase the content of components such as Si and Al that increase the resistivity of steel. This is because if the resistivity increases, the eddy current loss generated by the magnetization of the steel plate decreases. However, the large addition of Si, Al, etc. will lead to a decrease in magnetic flux density, causing new problems such as reduced torque and increased copper loss in the motor.

[0003] Therefore, research has been actively conducted to improve the texture of steel sheets to increase the magnetic flux density. The magnetization behavior of iron is dependent on the crystal orientation, so in order to increase the magnetic flux density, the easy magnetization axis is increased in the direction parallel to the sheet surface. <001> Orientation, that is, the development of a texture in which a large number of {100} planes parallel to the plate surface exist, is effective.

[0004] As a method for developing the above-mentioned texture, for example, Patent Document 1 proposes a method of performing warm rolling while reducing the Al content as much as possible, and Patent Document 2 proposes a method of adding P to steel and performing low-temperature and long-term intermittent annealing before cold rolling.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2002-003944

[0008] Patent Document 2: Japanese Patent Application Publication No. 2005-200756 Summary of the invention

[0009] Problems to be solved by the invention

[0010] As mentioned above, since the magnetization behavior of iron is orientation-dependent, the ideal crystal orientation for obtaining good magnetic properties is determined to a certain extent. However, according to the research of the inventors, it has been found that if you want to make grains with the same crystal orientation appear first, there is a tendency for the grain growth to decrease during recrystallization annealing. In order to obtain good magnetic properties, the grains need to have a certain size, so the reduction in grain growth is also a reason for the reduction in magnetic properties.

[0011] However, in the prior art including the above-mentioned Patent Document 1 and Patent Document 2, the actual situation is that no research has been conducted on the above-mentioned problems and their solutions.

[0012] The present invention is completed in view of the above-mentioned problems of the prior art, and its purpose is to propose a manufacturing method for an electromagnetic steel sheet that can preferentially allow grains of a specific orientation to appear without damaging the grain growth properties of recrystallized grains, and to provide a cold-rolled sheet that is cold-rolled to a final sheet thickness for use in the manufacturing method.

[0013] Means for solving problems

[0014] The inventors have repeatedly conducted intensive studies on solutions to the above-mentioned problems. As a result, they have found that by excluding as much as possible the elements that form fine precipitates contained in the steel raw material used for the production of the electromagnetic steel sheet, and giving a difference in the amount of strain in the rolled structure (processed grains) formed by cold rolling to the final sheet thickness near the grain boundary and in the grain, it is possible to effectively suppress the deterioration of the grain growth during recrystallization, and ultimately improve the magnetic properties of the finished sheet, thereby developing the present invention.

[0015] That is, the present invention provides a method for manufacturing an electromagnetic steel sheet, characterized in that it comprises the following steps: heating a steel slab to a temperature of 1300° C. or less, hot rolling to produce a hot-rolled sheet, subjecting the hot-rolled sheet to hot-rolled sheet annealing, cold rolling to produce a cold-rolled sheet of a final sheet thickness, and subjecting the cold-rolled sheet to final annealing, wherein the steel slab has the following component composition, the component composition comprising C: 0 to 0.100 mass %, Si: 1.00 to 5.00 mass %, Mn: 0 to 1.00 mass %, P: :0~0.02 mass %, Al: 0~2.00 mass %, N: 0~0.010 mass %, S: 0~0.010 mass %, Se: 0~0.010 mass %, Ti: 0~0.100 mass %, Nb: 0~0.100 mass % and V: 0~0.100 mass %, and further contains at least one of Sn and Sb in a total amount of 0~0.200 mass %, and the balance is Fe and inevitable impurities. In the above-mentioned method for manufacturing an electromagnetic steel sheet, G b With G g The ratio (G b / G g ) becomes 1.03 or more, wherein the orientation difference between an arbitrary measurement point and a first close measurement point when the crystal orientation of the processed grains existing in the plate thickness cross section of the cold-rolled plate having the above-mentioned final plate thickness is measured by the EBSD method is set as K1(°), the orientation difference between the same arbitrary measurement point and a second close measurement point is set as K2(°), the difference between the above K1 and K2 (K2-K1) is set as G(°), and the above G near the grain boundary is set as the above G b (°), the above G in the grain is set to the above Gg (°). The processed grains are grains that are flattened by cold rolling and are elongated in the rolling direction. The vicinity of the grain boundary refers to an area of ​​the processed grains in the plate thickness section of the cold-rolled plate that is 2.5 μm in the direction perpendicular to the surface of the steel plate and 50 μm in the direction parallel to the surface of the steel plate starting from the grain boundary parallel to the surface of the steel plate. In addition, the inside of the grain refers to an area that includes the center point of the processed grains and is 5 μm in the direction perpendicular to the surface of the steel plate and 50 μm in the direction parallel to the surface of the steel plate.

[0016] The method for producing the electromagnetic steel sheet of the present invention is characterized in that cold rolling to the final sheet thickness is performed by combining unidirectional rolling and reverse rolling.

[0017] The method for producing the electromagnetic steel sheet of the present invention is characterized in that cold rolling to the final sheet thickness is performed in combination with reverse rolling and aging treatment in a temperature range of 20 to 300°C.

[0018] The present invention is also directed to a cold-rolled sheet that is cold-rolled to a final sheet thickness and is used in the manufacture of an electromagnetic steel sheet. The cold-rolled sheet is characterized in that: b With G g The ratio (G b / G g ) is 1.03 or more, wherein the orientation difference between an arbitrary measurement point and its first close measurement point when the crystal orientation of the processed grains existing in the plate thickness cross section is measured by the EBSD method is set to K1 (°), the orientation difference between the same arbitrary measurement point and its second close measurement point is set to K2 (°), the difference between the above K1 and K2 (K2-K1) is set to G (°), and the above G near the grain boundary is set to the above G b (°), the above G in the grain is set to the above G g (°). The processed grains are grains that are flattened by cold rolling and are elongated in the rolling direction. The vicinity of the grain boundary refers to an area of ​​the processed grains in the plate thickness section of the cold-rolled plate that is 2.5 μm in the direction perpendicular to the surface of the steel plate and 50 μm in the direction parallel to the surface of the steel plate starting from the grain boundary parallel to the surface of the steel plate. In addition, the inside of the grain refers to an area that includes the center point of the processed grains and is 5 μm in the direction perpendicular to the surface of the steel plate and 50 μm in the direction parallel to the surface of the steel plate.

[0019] Effects of the Invention

[0020] According to the present invention, precipitate-forming elements in the steel raw material used for manufacturing the electromagnetic steel sheet can be eliminated as much as possible, and a large difference can be given between the grain boundary vicinity of the grains present in the steel sheet after cold rolling and the corresponding variables in the grains, so that the reduction in grain growth during recrystallization can be effectively suppressed. Therefore, according to the present invention, an electromagnetic steel sheet with excellent magnetic properties can be stably provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] [ Figure 1 ] shows the relationship between cold rolling conditions and iron loss W of the finished steel sheet. 15 / 50 Graph of the relationship.

[0022] [ Figure 2 ] is a graph showing the cold rolling conditions and the G of the cold rolled sheet b / G g and the relationship between the particle size of the finished sheet.

[0023] [ Figure 3 ] is a schematic diagram illustrating the processed grains near the grain boundary and inside the grains. DETAILED DESCRIPTION

[0024] First, the experiment that led to the development of the present invention will be described.

[0025] A steel slab having a composition containing 0.002 mass % C, 3.02 mass % Si and 0.10 mass % Mn and the balance being Fe and inevitable impurities was heated to a temperature of 1100°C and hot rolled to form a hot rolled plate with a plate thickness of 2.3 mm. Next, the hot rolled plate was pickled and descaled, and then hot rolled plate annealing was performed at 1100°C × 10s. The steel plate structure after the hot rolled plate annealing was a recrystallized structure formed by equiaxed grains, and the average grain size was about 400μm. Next, the steel plate after the hot rolled plate annealing was cold rolled for 15 passes using a Sendzimir rolling mill to form a cold rolled plate with a final plate thickness of 0.30mm. At this time, as shown in Table 1, the cold rolling was performed under four conditions of A to D, and the same reduction ratio was adjusted for 1 to 15 passes under any condition. Then, the cold rolled plate with the final plate thickness was subjected to a final annealing of 1000°C × 20s. It should be noted that the "unidirectional rolling" shown in Table 1 refers to a rolling method in which the rolling direction of each pass is in the same direction. In addition, "reverse rolling" refers to a rolling method in which the rolling direction of each pass is set to the opposite direction for each pass (the same below).

[0026] [Table 1]

[0027]

[0028] A test piece for magnetic measurement was collected from the steel sheet after the final annealing obtained in this way, and the iron loss W was measured by the method described in JIS C2550-1 (2011). 15 / 50 (Iron loss under the conditions of magnetic flux density 1.5T excitation and frequency 50Hz).

[0029] Figure 1 The results of the iron loss measurement are shown in FIG. According to the figure, among the cold rolling conditions A to D, conditions C and D show low iron loss values. Therefore, the RD-TD surface (steel plate surface) of the obtained product plate was etched with a 3% by mass nitric acid ethanol solution, and the steel plate structure was photographed with an optical microscope, and the image was analyzed to determine the average crystal grain size of the equivalent circle diameter. As a result, Figure 2 As shown, it can be seen that the average crystal grain size of the product sheets obtained by cold rolling under conditions C and D is relatively large, being 110 μm or more.

[0030] Generally, it is known that the steel sheet before cold rolling is a recrystallized structure of equiaxed grains, and the steel sheet after cold rolling becomes a processed structure in which the grains are flattened and stretched in the RD direction due to rolling. The recrystallized grains generated in the final annealing are generated from the region with a large amount of strain in the steel sheet after cold rolling. Therefore, in order to investigate the cause of the difference in grain size of the finished sheet as described above, the inventors conducted an investigation focusing on the strain distribution in the crystal grains flattened by cold rolling. It should be noted that in the present invention, the above-mentioned flat grains stretched in the rolling direction are also referred to as "processed grains".

[0031] Specifically, the inventors used the EBSD method to perform local orientation analysis on the cold-rolled sheet after final cold rolling and before final annealing, and compared the strain near the grain boundary of the processed grain and the strain in the grain. The above local orientation analysis was performed on the RD-ND section (plate thickness section in the rolling direction) at the center of the plate width of the cold-rolled sheet, and the measurement area was RD direction: 1000μm×ND direction: 300μm (total plate thickness), and the step length (measurement interval) was 0.5μm (hexagonal grid). The device used in the local orientation analysis was a scanning electron microscope JEOL JSM-7001F, and the software of the EBSD measurement system was OIMAnalysis8.6 manufactured by TSL.

[0032] Next, based on the results of the above local orientation analysis, in order to compare the strain near the grain boundary and in the grain of the processed grain, the orientation difference between an arbitrary measurement point and its first closest measurement point measured by the EBSD method is defined as K1(°), the orientation difference between the same arbitrary measurement point and its second closest measurement point is defined as K2(°), and the difference K2-K1 between the above K1 and K2 is defined as G(°). For more than 5 processed grains in each region, G near the grain boundary and in the grain are respectively calculated, and the average value of G near the grain boundary is set as G. b, the average value in the grain is set to G g In addition, in the above OIMAnalysis software, K1 is called KAM1st and K2 is called KAM2nd. Therefore, G is equivalent to the difference between KAM2nd and KAM1st. Figure 3 As shown in the figure, the vicinity of the grain boundary is a region of 2.5 μm in the ND direction and 50 μm in the RD direction starting from the grain boundary of the processed grain that is roughly parallel to the TD direction. In addition, the region within the grain is a region of 5 μm in the ND direction and 50 μm in the RD direction, including the center of the processed grain. It should be noted that in this analysis, the plate thickness section measured by the EBSD method is Figure 3 As shown, the cross section is set as the RD direction parallel to the surface of the steel plate (RD-ND cross section, the plate thickness cross section in the rolling direction), but it can also be set as the TD direction parallel to the surface of the steel plate (TD-ND cross section, the plate thickness cross section in the plate width direction).

[0033] Next, the G near the grain boundary measured as described above was evaluated according to the rolling conditions. b With the G g The ratio of G b / G g , and the results are shown in Figure 2 From this figure, it can be seen that under cold rolling conditions A and B, the ratio of the grain boundary to the grain is b / G g Close to 1.00, i.e. G b With G g The difference is small, but under cold rolling conditions C and D, the grain boundary is higher than G b / G g It is above 1.03.

[0034] The reason why the crystal grain size is large and the magnetic properties are good under the cold rolling conditions C and D as described above is not entirely clear, but the inventors believe it to be as follows.

[0035] Assuming that the origin of the recrystallized grains (recrystallized nuclei) is located in the processed structure after cold rolling, that is, in the processed grains, when one processed grain is uniformly deformed by cold rolling, it is believed that the recrystallized nuclei with the same crystal orientation are generated therefrom. That is, the possibility of generating recrystallized grains with almost the same orientation from one processed grain is high. However, for these recrystallized grains, the grain boundary orientation difference between them and the adjacent recrystallized grains is small, so it is believed that the grain boundary energy is low and the driving force for grain growth is low.

[0036] Here, the difference between K1 and K2 (K2-K1), i.e., the value of G, in the vicinity of the grain boundary and in the grain is different, which means that the orientation difference between the first approach measurement point and the second approach measurement point in the two regions is different, that is, the deformation behavior of the two regions is different, and the accumulated strain amount is also different. That is, as in the cold rolling conditions C and D in Table 1, the ratio G of G near the grain boundary and in the grain is b / G g The large value indicates that the deformation behavior is different near the grain boundary of the processed grain and inside the grain, and the accumulated strain (strain energy) near the grain boundary is larger than that inside the grain. As a result, it is believed that the recrystallized grains generated near the grain boundary can promote grain growth.

[0037] It should be noted that the value of G is largely dependent on the step size (measurement interval) of EBSD measurement, so G b , G g The value of G varies greatly depending on the measurement conditions. Therefore, in the present invention, G is not used in the evaluation of the difference in strain amount. b , G g The value of G b / G g As described above, since the step length affects the G value, it is preferably in the range of 0.05 to 0.5 μm, and more preferably in the range of 0.10 to 0.25 μm.

[0038] It should be noted that the present invention is to increase the above ratio G b / G g , improve the grain growth in the final annealing to increase the grain size of the finished sheet, thereby ensuring good magnetic properties. Therefore, from the perspective of further improving the above-mentioned effects of the present invention, in addition to the above-mentioned ratio G b / G g In addition to the appropriateness of the steel raw material, it is also preferred to reduce the elements contained in the steel raw material that form fine precipitates and hinder grain growth as much as possible. Elements that form the above-mentioned fine precipitates include C, Al, N, S, Se, Ti, Nb and V. It should be noted that the average crystal grain size of the steel plate (product plate) of the present invention in the RD-TD plane is preferably 110 μm or more, and more preferably 120 μm or more.

[0039] Next, the component composition of the steel material used for manufacturing the electromagnetic steel sheet of the present invention will be described.

[0040] C: 0 to 0.100 mass%

[0041] As shown above, C is a harmful element that forms carbides, and it is desirable to reduce it as much as possible. However, excessive reduction of C at the stage of steel raw material (slab) will increase manufacturing costs. Therefore, in the case where it can be reduced to less than 0.005 mass% through the manufacturing process of electromagnetic steel sheet, such as decarburization annealing, a certain amount may be contained in the steel raw material. Therefore, considering the decarburization property, the C content is set to the range of 0 to 0.100 mass%. The preferred C content is in the range of 0 to 0.005 mass% where decarburization annealing is not required.

[0042] Si: 1.00 to 5.00 mass%

[0043] Si is an element effective in increasing the resistivity of steel and reducing iron loss. However, when the Si content is less than 1.00 mass%, the above effect is insufficient. On the other hand, if it is greater than 5.00 mass%, the workability of the steel deteriorates and cold rolling becomes difficult. Therefore, the Si content is set in the range of 1.00 to 5.00 mass%. The preferred Si content is in the range of 2.00 to 4.00 mass%.

[0044] Mn: 0 to 0.50 mass%

[0045] Mn is an element that forms sulfide and selenide precipitates, so it is desirable to reduce it as much as possible. However, Mn has the effect of improving hot workability, so it can be contained up to 0.50 mass% without hindering grain growth. The preferred Mn content is in the range of 0 to 0.25 mass%.

[0046] P: 0 to 0.02 mass%

[0047] P is an element that makes steel embrittled and significantly deteriorates manufacturability, so it is desirable to reduce it as much as possible. However, it has the effect of improving the texture after recrystallization, so it can be contained up to 0.02 mass% without hindering grain growth. The preferred range is 0 to 0.01 mass%.

[0048] Al: 0 to 2.00 mass%, N: 0 to 0.010 mass%, S: 0 to 0.010 mass%, Se: 0 to 0.010 mass%, Ti: 0 to 0.100 mass%, Nb: 0 to 0.100 mass%, and V: 0 to 0.100 mass%

[0049] As mentioned above, the above elements are harmful elements that form fine precipitates, and it is hoped that they will be reduced as much as possible. Excessive reduction of the above elements will lead to an increase in refining costs. However, as described later, by lowering the slab heating temperature and coarsening the precipitates, the adverse effects on grain growth can be reduced. Therefore, if the above elements are below the above upper limit values, it is permissible even if they are contained. It should be noted that, in terms of the preferred content, Al is in the range of 0 to 1.20 mass % and other elements are in the range of 0 to 0.003 mass %.

[0050] Sn and Sb: at least one of 0 to 0.200 mass % in total

[0051] Sn and Sb are elements that segregate at grain boundaries and inhibit grain growth, and it is desirable to reduce them as much as possible. However, Sn and Sb have the effect of improving recrystallization texture, so they can be contained up to 0.200 mass% without showing the effect of inhibiting grain growth. The total is preferably in the range of 0 to 0.100 mass%.

[0052] In addition, in the steel raw material used for this invention, the balance other than the above-mentioned components is substantially Fe and inevitable impurities.

[0053] Next, the method for producing the electromagnetic steel sheet of the present invention will be described.

[0054] The steel raw material (slab) used in the manufacture of the electromagnetic steel sheet of the present invention can be manufactured by a conventional continuous casting method or an ingot-blowing rolling method after melting the steel adjusted to the above-mentioned component composition by a commonly known refining process using a converter, an electric furnace, a vacuum degassing treatment device, etc. In addition, a thin cast sheet with a thickness of 100 mm or less can be manufactured from the above-mentioned smelted steel by a direct casting method. These slabs and thin cast sheets are usually heated to a specified temperature and then hot-rolled to form hot-rolled sheets of a specified thickness, but they can also be directly hot-rolled without reheating after casting. The heating temperature when heating the slab before hot rolling is preferably 1100°C or less. This is because, without decomposing and dissolving the precipitates present in the steel raw material, coarse and harmless precipitates and inclusions remain, which can inhibit the subsequent generation of fine precipitates. However, when the content of the precipitate-forming element is small, it can also be heated to about 1300°C. It should be noted that the hot rolling subsequent to the above-mentioned slab heating can be carried out according to the conditions known in the past, and there is no particular restriction.

[0055] As required, the steel plate (hot-rolled plate) obtained by the above hot rolling is preferably subjected to hot-rolled plate annealing. In the case of hot-rolled plate annealing, it is preferably carried out under the condition of maintaining the temperature range of 800°C to 1300°C for more than 5s. When the annealing temperature is lower than 800°C, the rolling structure (banded structure) generated during hot rolling will not recrystallize and remain, which may hinder the recrystallization in the final annealing after cold rolling. On the other hand, if the annealing temperature exceeds 1300°C, the oxide scale on the surface of the steel plate begins to melt, which may deteriorate the manufacturability.

[0056] It should be noted that, for the hot rolled sheet after hot rolling or after hot rolled sheet annealing, it is desirable to remove the scale formed on the surface of the steel sheet during hot rolling. The removal method may be any of the following methods: a method of chemically removing the scale by pickling with an acid heated to a high temperature, a method of mechanically removing the scale, a method of combining these methods, and the like.

[0057] Next, the hot rolled sheet after descaling is subjected to one cold rolling or two or more cold rollings with intermediate annealing to obtain a cold rolled sheet of the final sheet thickness. Here, in the present invention, it is important to provide a difference in the corresponding variables near the grain boundary and in the grain in the cold rolling (final cold rolling) to obtain the above-mentioned final sheet thickness for the grains (processed grains) extending in the rolling direction in the processed structure generated by rolling.

[0058] As a method for giving a difference between the strain near the grain boundary and the strain in the grain, there is a method of combining unidirectional rolling and reverse rolling as used in the above-mentioned experiment. The combination of unidirectional rolling and reverse rolling can be performed once or more, and the order and the direction of the final pass can be whatever.

[0059] In addition, a method of combining the reverse rolling used in the later-described embodiments with one or more aging treatments performed between the passes of the reverse rolling may also be used. The above-mentioned aging treatment is preferably maintained at a temperature range of 20 to 300°C for more than 1 hr (hour). This is because, by performing the aging treatment within the above-mentioned temperature range, light elements such as C and N are segregated at the grain boundaries, the deformation behavior near the grain boundaries and within the grains changes, and the strain amounts between the above-mentioned regions are prone to differences. When the temperature is below 20°C, the diffusion rates of C and N decrease, and the aging treatment time becomes longer. On the other hand, if it exceeds 300°C, recovery may occur. The preferred aging treatment temperature is in the range of 25 to 250°C.

[0060] It should be noted that, of course, methods other than the above may be used as a method for imparting strain to the vicinity of the grain boundary of the processed grain and within the grain.

[0061] In addition, in the aforementioned experiments and the examples described below, the rolling reduction ratios in each pass of the unidirectional rolling and the reverse rolling were set to be the same, but they do not necessarily have to be the same.

[0062] The cold-rolled steel sheet (cold-rolled sheet) having the above-mentioned final sheet thickness is subjected to final annealing after cleaning the steel sheet surface by degreasing, pickling, etc. as required to obtain a finished sheet. The final annealing is preferably carried out under the condition of maintaining the temperature in the range of 750°C to 1100°C for more than 5 seconds. The temperature range of 800°C to 1050°C is more preferred.

[0063] It should be noted that electromagnetic steel sheets are mostly used in the form of stacked steel sheets, but from the perspective of ensuring the insulation between the steel sheets in this case, it is preferred to cover the surface of the steel sheet after final annealing with an insulating film. From the perspective of improving punchability, the insulating film preferably uses an organic film. In addition, in order to reduce iron loss, it is preferred to use a tension-imparting insulating film that imparts tension to the surface of the steel sheet. The method of covering the insulating film may be any of roller coating, electrostatic coating, etc., without particular limitation.

[0064] Example 1

[0065] After heating a steel billet having a composition containing C: 0.004 mass%, Si: 3.54 mass% and Mn: 0.05 mass%, and the balance being Fe and inevitable impurities to a temperature of 1250°C, hot rolling is performed to produce a hot rolled plate with a plate thickness of 2.5 mm. Next, the oxide scale on the surface of the hot rolled plate is pickled and removed, and then the hot rolled plate is annealed at 1050°C × 20s. Next, the steel plate after the hot rolled plate annealing is cold rolled for 12 passes using a Sendzimir rolling mill to produce a cold rolled plate with a final plate thickness of 0.25 mm. At this time, the cold rolling conditions are changed to three conditions of E to G as shown in Table 2. It should be noted that in all conditions, the reduction ratios of each pass from 1 to 12 are all the same. Next, the cold rolled plate is subjected to a final annealing of 1025°C × 10s in a dry atmosphere of 10vol% H2 + 90vol% N2 to obtain a finished plate.

[0066] [Table 2]

[0067]

[0068] The steel sheets after the final annealing (product sheets) and the steel sheets before the final annealing (after the final cold rolling) obtained in this way were subjected to the following evaluation tests.

[0069] (1)Magnetic properties

[0070] A test piece for magnetic measurement was collected from the above-mentioned product steel sheet, and the iron loss W was measured according to the method described in JIS C2550-1 (2011). 15 / 50 (Iron loss under the conditions of magnetic flux density 1.5T excitation and frequency 50Hz).

[0071] (2) Average particle size

[0072] A test piece for investigating the crystal grain size was collected from the above-mentioned product plate, and the surface of the steel plate (RD-TD surface) was etched with a 3 mass % nitric acid ethanol solution. After the crystal grains appeared, an image was taken with an optical microscope, and the image was analyzed to determine the average grain size of the equivalent circle diameter.

[0073] (3) Ratio G b / Gg

[0074] For the cold-rolled sheet after final cold rolling and before final annealing, local orientation analysis was performed using the EBSD method. The local orientation analysis was performed on the RD-ND section (sheet thickness section in the rolling direction) at the center of the sheet width, and the measurement area was RD direction: 1000μm × ND direction: 250μm (total sheet thickness), and the step length (measurement interval) was 0.50μm (regular hexagonal grid). The device used in the local orientation analysis was a scanning electron microscope JEOL JSM-7001F, and the software of the EBSD measurement system was OIM Analysis 8.6 manufactured by TSL.

[0075] Next, based on the results of the above local orientation analysis, in order to compare the strain near the grain boundary and in the grain of the processed grain, the orientation difference between an arbitrary measurement point measured by the EBSD method and its first closest measurement point is set as K1 (°), the orientation difference between the same arbitrary measurement point and its second closest measurement point is set as K2 (°), and the difference K2-K1 between the above K1 and K2 is set as G (°) for evaluation. For more than 5 processed grains in each area, G near the grain boundary and in the grain are respectively calculated, and the average value of the above G near the grain boundary is set as G b , the average value in the grain is set to G g , find the ratio G b / G g It should be noted that if Figure 3 As shown, the vicinity of the grain boundary is a region of the processed grain that is within 2.5 μm in the ND direction and 50 μm in the RD direction starting from the grain boundary that is roughly parallel to the TD direction. In addition, the inside of the grain is a region that includes the center of the processed grain and is 5 μm in the ND direction × 50 μm in the RD direction.

[0076] The results of the above evaluation tests are shown in Table 2. From the results, it can be seen that the ratio Gb / Gg of the cold-rolled sheets cold-rolled under the conditions satisfying the present invention was 1.03 or more, the average grain size was large, and the iron loss characteristics were good.

[0077] Example 2

[0078] A steel slab having the composition described in Table 3 and the balance being Fe and inevitable impurities was heated to a temperature of 1050°C and hot rolled to form a hot rolled plate with a plate thickness of 2.2 mm. Next, the oxide scale on the surface of the hot rolled plate was pickled and removed, and after hot rolled plate annealing at 1050°C×20s, a Sendzimir rolling mill was used to perform 7 passes of cold rolling to form a cold rolled plate with a final plate thickness of 0.25 mm. At this time, in the above cold rolling, 4 passes of unidirectional rolling were performed to form an intermediate plate thickness of 1.5 mm, and then, after aging treatment at room temperature (20°C) for 240 hours, 7 passes of reverse rolling were further performed. At this time, the reduction ratios of each pass of unidirectional rolling and reverse rolling were adjusted to be the same.

[0079] Then, the cold rolled sheet was subjected to final annealing at 950°C × 30s in a humid atmosphere of 45 vol% H2 + 55 vol% N2 and a dew point of 55°C. The magnetic properties and average grain size of the steel sheet (product sheet) obtained after final annealing were measured in the same manner as in Example 1. In addition, for the cold rolled sheet after final cold rolling and before final annealing, the measurement area was set to RD direction: 500 μm × ND direction: 250 μm (total sheet thickness) and the step size was 0.25 μm (regular hexagonal grid). In addition, the local orientation analysis was performed by the EBSD method in the same manner as in Example 1 to determine the ratio Gb / Gg.

[0080] The results of the above measurements are shown in Table 3. From the results, it can be seen that the steel sheets using raw materials having a component composition satisfying the present invention and cold-rolled under the conditions satisfying the present invention have a ratio Gb / Gg of 1.03 or more, a large average grain size, and good iron loss characteristics.

[0081] [Table 3]

[0082]

[0083] Industrial Applicability

[0084] The technology of the present invention can be applied to the production of both non-oriented electromagnetic steel sheets and oriented electromagnetic steel sheets, and can also be applied to the production of thin steel sheets for automobiles.

Claims

1. A method for manufacturing an electromagnetic steel sheet, characterized in that: The method comprises the following steps: heating a steel slab to a temperature of 1300° C. or less, hot rolling the steel slab to form a hot-rolled sheet, annealing the hot-rolled sheet, cold rolling the hot-rolled sheet to form a cold-rolled sheet having a final sheet thickness, and finally annealing the cold-rolled sheet. The steel billet has a composition comprising 0 to 0.100 mass % of C, 1.00 to 5.00 mass % of Si, 0 to 1.00 mass % of Mn, 0 to 0.02 mass % of P, 0 to 2.00 mass % of Al, 0 to 0.010 mass % of N, 0 to 0.010 mass % of S, 0 to 0.010 mass % of Se, 0 to 0.010 mass % of Ti, 0 to 0.100 mass % of Nb, and 0 to 0.100 mass % of V, and further comprising 0 to 0.200 mass % of at least one of Sn and Sb, and the balance being Fe and unavoidable impurities. In the method for manufacturing the electromagnetic steel sheet, G b With G g The ratio (G b / G g ) becomes 1.03 or more, wherein the orientation difference between an arbitrary measurement point and a first close measurement point when the crystal orientation of the processed grains existing in the plate thickness cross section of the cold-rolled plate having the final plate thickness is measured by the EBSD method is set to K1(°), the orientation difference between the same arbitrary measurement point and a second close measurement point is set to K2(°), the difference between K1 and K2 (K2-K1) is set to G(°), and the G near the grain boundary is set to G b (°), the G in the grain is set to the G g (°), Among them, the processed grains refer to grains that are flattened by cold rolling and elongated in the rolling direction, the vicinity of the grain boundary refers to the area of ​​the processed grains in the plate thickness section of the cold-rolled plate, which is 2.5μm in the direction perpendicular to the steel plate surface × 50μm in the direction parallel to the steel plate surface as the starting point, and the inside of the grain refers to the area containing the center point of the processed grains, which is 5μm in the direction perpendicular to the steel plate surface × 50μm in the direction parallel to the steel plate surface.

2. The method for manufacturing an electromagnetic steel sheet according to claim 1, wherein: The cold rolling to obtain the final sheet thickness is performed by combining unidirectional rolling and reverse rolling.

3. The method for manufacturing an electromagnetic steel sheet according to claim 1, wherein: Cold rolling to the final sheet thickness is performed by combining reverse rolling and aging treatment in a temperature range of 20 to 300°C.

4. A cold-rolled sheet, which is a cold-rolled sheet cold-rolled to a final sheet thickness for use in the manufacture of an electromagnetic steel sheet, wherein: G b With G g The ratio (G b / G g ) is 1.03 or more, among which, The orientation difference between an arbitrary measurement point and its first closest measurement point when measuring the crystal orientation of processed grains existing in the plate thickness cross section by the EBSD method is set as K1(°), the orientation difference between the same arbitrary measurement point and its second closest measurement point is set as K2(°), the difference between K1 and K2 (K2-K1) is set as G(°), and the G near the grain boundary is set as G b (°), the G in the grain is set to the G g (°), Among them, the processed grains refer to grains that are flattened by cold rolling and elongated in the rolling direction, the vicinity of the grain boundary refers to the area of ​​the processed grains in the plate thickness section of the cold-rolled plate, which is 2.5μm in the direction perpendicular to the steel plate surface × 50μm in the direction parallel to the steel plate surface as the starting point, and the inside of the grain refers to the area containing the center point of the processed grains, which is 5μm in the direction perpendicular to the steel plate surface × 50μm in the direction parallel to the steel plate surface.

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