Grain-oriented electrical steel sheet and method for manufacturing the same

Abstract

This grain-oriented electromagnetic steel sheet comprises, on the surface thereof: a plurality of magnetic domain control processing lines extending in a direction intersecting the rolling direction; a magnetic domain control region that is a region within 10 mm from each of the magnetic domain control processing lines; and a non-magnetic domain control region that is a region separated by more than 10 mm from all of the magnetic domain control processing lines. The average value |βNDr| of the absolute value of the β angle in the non-magnetic domain control region and the average value |βDr| of the absolute value of the β angle in the magnetic domain control region satisfy |βDr|-|βNDr| ≤ -0.1°.

Description

[Technical Field]

[0001] This invention relates to grain-oriented electrical steel sheets and methods for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2023-166178, filed in Japan on September 27, 2023, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets contain 7% by mass or less of Si, and the secondary recrystallized grains have an easy magnetization axis in the rolling direction. <001> oriented {110} <001> This is a steel sheet with a secondary recrystallized texture concentrated in a specific orientation (Goss orientation). Grain-oriented electrical steel sheets are mainly used as cores for power transformers. A reduction in energy loss (iron loss) is required for grain-oriented electrical steel sheets.

[0003] To reduce iron loss, techniques for narrowing the magnetic domain width of grain-oriented electrical steel sheets (magnetic domain subdivision technology by magnetic domain control processing) have been known for some time. The magnetic domain width can be narrowed by introducing thermal strain by irradiating the surface of the grain-oriented electrical steel sheet with a laser or electron beam in a direction intersecting the rolling direction. Alternatively, the magnetic domain width can also be narrowed by forming grooves on the surface of the grain-oriented electrical steel sheet in a direction intersecting the rolling direction. Methods for forming grooves include irradiating with a laser or electron beam, mechanical processing such as gears, and chemical processing such as etching.

[0004] In recent years, various improvement techniques related to magnetic domain subdivision have been proposed to provide grain-oriented electrical steel sheets with good iron loss characteristics (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2012-57219 [Patent Document 2] Japanese Patent Application Publication No. 2012-12664 [Patent Document 3] Japanese Patent Application Publication No. 2012-57218 [Overview of the project] [Problems that the invention aims to solve]

[0006] When magnetic domain control processing is applied to grain-oriented electrical steel sheets, the magnetostrictive properties of the sheet change due to the return-flowing magnetic domains. This worsens the noise characteristics of the grain-oriented electrical steel sheets. Noise characteristics refer to the degree of noise generated by electrical products (e.g., transformers and motors) manufactured using grain-oriented electrical steel sheets as a material. Magnetostriction is the phenomenon in which the external shape of a ferromagnetic material is slightly deformed when it is magnetized. When grain-oriented electrical steel sheets are excited with alternating current, vibration occurs as the magnitude of the magnetostriction changes in accordance with the change in the strength of the magnetization. The magnitude of this magnetostriction is 10 -6 Although the magnitude is very small, this magnetostriction generates vibrations in the iron core, which propagate to external structures such as the transformer tank, resulting in noise. In other words, while magnetic domain control is effective in reducing iron loss in grain-oriented electrical steel sheets, it worsens the noise characteristics of grain-oriented electrical steel sheets. In recent years, there has been an increasing demand for not only reduced iron loss but also reduced noise in grain-oriented electrical steel sheets. However, no magnetic domain subdivision technology has been proposed to date that can adequately achieve both reduced noise and reduced iron loss.

[0007] This disclosure aims to provide grain-oriented electrical steel sheets that have low iron loss and low noise characteristics when used in electrical products, and a method for manufacturing the same. [Means for solving the problem]

[0008] The inventors of this invention investigated grain-oriented electrical steel sheets that exhibit low iron loss and excellent noise characteristics. As a result, they found that while magnetic domain control is effective in reducing iron loss in grain-oriented electrical steel sheets, it also worsens the noise characteristics of the grain-oriented electrical steel sheets. Therefore, they found that the deterioration of noise characteristics can be suppressed by providing a non-magnetic domain control region. As a result of further investigation, the inventors analyzed the changes in magnetic domains before and after magnetic domain control of grain-oriented electrical steel sheets and found that there are parts where the magnetic domain width becomes finer due to magnetic domain control and parts where it hardly becomes finer.

[0009] This disclosure was made in light of the above findings. [1] A grain-oriented electrical steel sheet according to one aspect of the present disclosure has a plurality of magnetic domain control processing lines extending in a direction intersecting the rolling direction on its surface, a magnetic domain control region which is a region within 10 mm from the magnetic domain control processing lines, and a non-magnetic domain control region which is a region more than 10 mm away from all of the magnetic domain control processing lines, wherein the average value of the absolute values ​​of the β angles in the non-magnetic domain control region |βNDr| and the average value of the absolute values ​​of the β angles in the magnetic domain control region |βDr| satisfy the following equation (5) Furthermore, the β angle is the angle of deviation of the crystal grain from the Goss orientation around the axis perpendicular to the rolling direction TD. . |βDr|-|βNDr|≦-0.1° (5) The grain-oriented electrical steel sheet described in [2][1] may have an average value of 500 μm or less for the magnetic domain width of the non-magnetic domain control region. The grain-oriented electrical steel sheet described in [3] [1] or [2] may have a maximum value of 1000 μm or less for the magnetic domain width of the non-magnetic domain control region. In the grain-oriented electrical steel sheet described in any of [4][1] to [3], the plurality of magnetic domain control processing lines may be grooves. In the grain-oriented electrical steel sheet described in [5][4], the maximum value of the groove depth in the magnetic domain control processing line may be non-uniform at each measurement point of the groove depth. In the grain-oriented electrical steel sheet described in [6][5], an evaluation area is set on the surface of a square with a side length of 50 mm and one side parallel to the rolling direction, and within the evaluation area, imaginary lines parallel to the rolling direction and with a length of 50 mm are set at 5 mm intervals perpendicular to the rolling direction, and each of the multiple intersections between the imaginary lines and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the maximum value of the depth of the groove in units of μm, measured at each of the magnetic domain subdivision points, is defined as D m , the aforementioned D m The variance of σ(D) m ) 2When σ(D m ) 2 > 3.0 may be satisfied. [7][5] or the grain-oriented electrical steel sheet according to [6] sets a square evaluation region on the surface with a side length of 50 mm and one side parallel to the rolling direction. Further, inside the evaluation region, when virtual lines parallel to the rolling direction and with a length of 50 mm are set at intervals of 5 mm in a direction perpendicular to the rolling direction, each of the plurality of intersection points of the virtual lines and the plurality of magnetic domain control processing lines is taken as a magnetic domain subdivision point. Among the magnetic domain subdivision points, the arithmetic mean value of the maximum value of the depth of the groove in units of μm measured at each magnetic domain subdivision point where the β angle is less than 2° is D m(β<2) And, among the magnetic domain subdivision points, the arithmetic mean value of the maximum value of the depth of the groove in units of μm measured at each magnetic domain subdivision point where the β angle is 2° or more is D m(β≧2) When, D m(β<2) > D m(β≧2) May be satisfied. [8][1] to [3] Any of the described grain-oriented electrical steel sheets may be a thermal strain in which a tensile stress of 40 MPa or more is introduced in the plurality of magnetic domain control processing lines. [9][8] The grain-oriented electrical steel sheet described may have a non-uniform maximum value of the tensile stress introduced into the thermal strain in the magnetic domain control processing line for each measurement point of the tensile stress.

[10] [9] The grain-oriented electrical steel sheet described sets a square evaluation region on the surface with a side length of 50 mm and one side parallel to the rolling direction. Further, inside the evaluation region, when virtual lines parallel to the rolling direction and with a length of 50 mm are set at intervals of 5 mm in a direction perpendicular to the rolling direction, each of the plurality of intersection points of the virtual lines and the plurality of magnetic domain control processing lines is taken as a magnetic domain subdivision point. The maximum value of the tensile stress in units of MPa introduced into the thermal strain measured at each magnetic domain subdivision point is TS m The variance of the TS m Is σ(TS m ) 2 When, σ(TS m ) 2 > 5.0 may be satisfied. In the grain-oriented electrical steel sheet described in

[11] [9] or

[10] , an evaluation area is set on the surface of a square with a side length of 50 mm and one side parallel to the rolling direction, and within the evaluation area, imaginary lines parallel to the rolling direction and with a length of 50 mm are set at 5 mm intervals perpendicular to the rolling direction, and each of the multiple intersections of the imaginary lines and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the arithmetic mean of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain subdivision points where the β angle is less than 2°, is defined as TS m(β<2) The arithmetic mean of the maximum tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or more, is taken as TS m(β≧2) In that case, TS m(β<2) >TS m(β≧2) It may satisfy the requirement.

[12] A method for manufacturing a grain-oriented electrical steel sheet according to another aspect of the present disclosure comprises: a magnetic domain image acquisition step of acquiring a magnetic domain image of the surface of the grain-oriented electrical steel sheet; a region identification step of identifying a region in the grain-oriented electrical steel sheet where the magnetic domain width is greater than 500 μm based on the magnetic domain image obtained in the magnetic domain image acquisition step; and a magnetic domain control line formation step of forming magnetic domain control lines on the surface of the grain-oriented electrical steel sheet, wherein the magnetic domain control line formation step comprises a magnetic domain control region which is a region within 10 mm of the magnetic domain control lines and a non-magnetic domain control region which is a region which is more than 10 mm away from all of the magnetic domain control lines, and the magnetic domain control lines are formed in the region where the magnetic domain width is greater than 500 μm such that the average value of the absolute values ​​of the β angles in the non-magnetic domain control region |βNDr| and the average value of the absolute values ​​of the β angles in the magnetic domain control region |βDr| are |βDr|-|βNDr|≦-0.1° Furthermore, the β angle is the angle of deviation of the crystal grain from the Goss orientation around the axis perpendicular to the rolling direction TD. . In the method for manufacturing grain-oriented electrical steel sheets described in

[13] and

[12] , the magnetic domain control processing lines may be formed by irradiation with a laser or electron beam in the magnetic domain control processing line formation step. [Effects of the Invention]

[0010] According to the above embodiments of this disclosure, it is possible to provide grain-oriented electrical steel sheets that have low iron loss and low noise when used in electrical products (excellent noise characteristics), and a method for manufacturing the same. [Brief explanation of the drawing]

[0011] [Figure 1A] This is a schematic diagram showing an example of a grain-oriented electrical steel sheet according to this embodiment. [Figure 1B] This is a schematic diagram showing an example of a grain-oriented electrical steel sheet according to this embodiment. [Figure 1C] This is a schematic diagram showing an example of a grain-oriented electrical steel sheet according to this embodiment. [Figure 2] This graph shows the relationship between the magnetic domain width before laser irradiation and the magnetic domain width after laser irradiation. [Figure 3A] This graph shows an example of the distribution of magnetic domain widths in grain-oriented electrical steel sheets before magnetic domain subdivision processing. [Figure 3B] This graph shows an example of the distribution of magnetic domain widths in grain-oriented electrical steel sheets after magnetic domain refinement treatment. [Figure 3C] This figure shows an example of a magnetic domain image acquired by an image acquisition device. [Figure 3D] This figure schematically illustrates Figure 3C. [Figure 4] This block shows an example of the hardware configuration of an image acquisition device. [Figure 5] This is a block diagram showing an example of the hardware configuration of an analysis device. [Figure 6] This is a schematic diagram showing an example of the configuration of a laser irradiation device. [Figure 7] This is a schematic diagram illustrating a method for extracting multiple subregions from a magnetic domain image of grain-oriented electrical steel sheets. [Figure 8] This is an example of multiple partial Fourier images obtained by applying a two-dimensional Fourier transform to each of several subregions extracted from a magnetic domain image of a grain-oriented electrical steel sheet. [Figure 9] This graph schematically shows the relationship between the size of the magnetic domain width and the magnetic domain control saturation strength. [Figure 10]This graph schematically shows the relationship between the magnitude of the β angle and the magnetic domain control saturation intensity. [Figure 11] This is a schematic cross-sectional view of a grain-oriented electrical steel sheet, where the magnetic domain control processing lines represent thermal strain. [Figure 12] This is a schematic cross-sectional view of a grain-oriented electrical steel sheet, where the magnetic domain control processing lines are grooves. [Figure 13] This is a schematic planar diagram illustrating a method for measuring the magnetic domain control strength at the intersection of a magnetic domain control processing line and a virtual line when the magnetic domain control processing line is thermal strain. [Figure 14] This is a schematic plan view illustrating a method for measuring the magnetic domain control strength at the intersection of a magnetic domain control processing line and a virtual line when the magnetic domain control processing line is a groove. [Modes for carrying out the invention]

[0012] A grain-oriented electrical steel sheet (a grain-oriented electrical steel sheet according to this embodiment) and a method for manufacturing the same, according to one embodiment of this disclosure, will be described. As shown in Figure 1A, the grain-oriented electrical steel sheet 1 according to this embodiment has a plurality of magnetic domain control processing lines 11 extending in a direction intersecting the rolling direction RD on its surface, a magnetic domain control region 12 which is an area within 10 mm from the magnetic domain control processing lines, and a non-magnetic domain control region 13 which is an area more than 10 mm away from all of the magnetic domain control processing lines. As described later, the grain-oriented electrical steel sheet according to this embodiment may have a forsterite coating and / or an insulating coating on the surface of the base steel sheet. The following will explain each of these points. However, if the grain-oriented electrical steel sheet has a base steel sheet and a forsterite coating and / or insulating coating, the following provisions regarding chemical composition, magnetic domain control lines, magnetic domain control regions, and non-magnetic domain control lines apply to the base steel sheet. However, the provisions regarding sheet thickness apply to the entire grain-oriented electrical steel sheet, including the base steel sheet and the forsterite coating and / or insulating coating.

[0013] [Grain-oriented electrical steel sheet] (chemical composition) The chemical composition of grain-oriented electrical steel sheet 1 is not limited and may be equivalent to that of known grain-oriented electrical steel sheet 1. For example, grain-oriented electrical steel sheet 1 may have a chemical composition of the following in mass%, in mass%,: Si: 2.50~7.00%, Mn: 0~1.00%, C: 0~0.085%, acid-soluble Al: 0~0.065%, N: 0~0.012%, Cr: 0~0.300%, Cu: 0~0.400%, P: 0~0.500%, Sn: 0~0.300%, Sb: 0~0. It may contain 300%, Ni: 0-1.000%, S: 0-0.015%, Se: 0-0.015%, Bi: 0-0.020%, Nb: 0-0.030%, V: 0-0.030%, Mo: 0-0.030%, Ta: 0-0.030%, W: 0-0.030%, B: 0-0.080%, and Ti: 0-0.015%. The remainder of the chemical composition includes Fe and impurities.

[0014] The chemical composition of grain-oriented electrical steel sheet 1 can be measured using general analytical methods for steel. For example, the chemical composition can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, a test piece is taken from the center of the sample in the thickness direction, and the chemical composition of grain-oriented electrical steel sheet 1 can be measured using a Shimadzu ICPS-8100 or similar (measuring device) under conditions based on a pre-established calibration curve. The C and S content, which is difficult to measure with ICP-AES, can be measured using the combustion-infrared absorption method. The N content can be measured using the inert gas fusion-thermal conductivity method.

[0015] If a forsterite coating and / or insulating coating is formed on the grain-oriented electrical steel sheet 1, the forsterite coating and / or insulating coating should be removed from the grain-oriented electrical steel sheet 1 before analyzing the chemical composition of the grain-oriented electrical steel sheet 1 (i.e., the chemical composition of the base steel sheet). The insulating coating can be removed, for example, by immersing the sample in a sodium hydroxide solution, followed by immersion in dilute sulfuric acid and then nitric acid. The temperature and concentration of the sodium hydroxide, dilute sulfuric acid, and nitric acid solutions, as well as the immersion time, should be adjusted as appropriate to prevent excessive dissolution of the sample's base metal. An example of the conditions for removing the insulating coating is as follows: First, immerse the sample in a 20% sodium hydroxide solution at 80°C for 15 minutes. Then, dry the sample. Next, immerse the sample in a 10% dilute sulfuric acid solution at 80°C for 4 minutes. After that, remove any sludge adhering to the surface of the sample with a cloth or the like. Finally, immerse the sample in a 10% nitric acid solution at room temperature for about 10 seconds while stirring. Forsterite coatings can be removed, for example, by immersing the sample in sulfuric acid followed by immersion in nitric acid. The temperature, concentration, and immersion time of the sulfuric acid and nitric acid should be adjusted as appropriate to prevent excessive dissolution of the sample's base metal. An example of the conditions for removing forsterite coatings is as follows: First, immerse the sample in 10% sulfuric acid at 80°C for 3 minutes. Then, wash the surface of the sample with water using a cloth or similar to remove any sludge adhering to the surface. After that, dry the sample. Furthermore, immerse the sample in 10% nitric acid at room temperature for about 5 seconds while stirring.

[0016] The thickness of the grain-oriented electrical steel sheet 1 is not limited, but is preferably, for example, 0.15 mm to 0.30 mm. By setting the thickness to 0.30 mm or less, classical eddy current losses can be suppressed and iron losses can be further improved. On the other hand, by setting the thickness to 0.15 mm or more, rolling efficiency can be improved and productivity can be improved.

[0017] (Magnetic domain control processing line 11) Multiple magnetic domain control processing lines 11 provided on the surface of the grain-oriented electrical steel sheet 1 have the function of subdividing the 180° magnetic domains. By subdividing the magnetic domains, the iron loss of the grain-oriented electrical steel sheet 1 can be reduced. A magnetic domain is a collection of magnetic dipoles existing inside a ferromagnetic material, and is a small region in which the magnetic moment is aligned in one direction. A 180° magnetic domain is a region in which the magnetization direction is aligned with that of the crystal. <100> A 180° magnetic domain is a magnetic domain that is situated between two 180° magnetic domain walls that are oriented and approximately parallel to the rolling direction (RD). The distance between adjacent magnetic domain walls within a 180° magnetic domain (domain wall spacing) is called the width of the 180° magnetic domain. Hereafter, unless otherwise specified, the width of a 180° magnetic domain will simply be referred to as "domain width."

[0018] The direction of extension of the magnetic domain control processing line 11 is not particularly limited, as long as it intersects with the rolling direction (i.e., is not parallel to the rolling direction). As shown in Figure 1A, the magnetic domain control processing line 11 and the rolling direction RD may be approximately perpendicular (approximately parallel to the rolling perpendicular direction TD). That is, the angle between the magnetic domain control processing line 11 and the rolling perpendicular direction TD may be substantially 0°. On the other hand, the angle between the magnetic domain control processing line 11 and the rolling perpendicular direction TD may be greater than 0°. For example, the angle between the magnetic domain control processing line 11 and the rolling perpendicular direction TD may be any value within the range of 0° to 45°. The angle between the magnetic domain control processing line 11 and the rolling perpendicular direction TD may be 1° or more, 3° or more, or 5° or more. The angle between the magnetic domain control processing line 11 and the rolling perpendicular direction TD may be 40° or less, 35° or less, or 30° or less.

[0019] As illustrated in Figure 1A, the angle between all magnetic domain control lines 11 and the rolling perpendicular direction TD may be the same. That is, all magnetic domain control lines 11 may extend parallel to each other. On the other hand, the angles between the magnetic domain control lines 11 and the rolling perpendicular direction TD may vary. That is, some or all of the multiple magnetic domain control lines 11 may extend non-parallel to each other. The average value of the angle between the magnetic domain control lines 11 and the rolling perpendicular direction TD may be 1° or more, 3° or more, or 5° or more. The average value of the angle between the magnetic domain control lines 11 and the rolling perpendicular direction TD may be 40° or less, 35° or less, or 30° or less. The average angle can be calculated by measuring the angle between a single magnetic domain control line and the rolling perpendicular direction (TD) at multiple locations, or by measuring the angles between multiple magnetic domain control lines and the rolling perpendicular direction (TD) at one or more locations and calculating the average value. Furthermore, as shown in Figure 1B, the magnetic domain control processing lines 11 do not have to be interrupted midway (i.e., all magnetic domain control processing lines are formed over the entire width of the steel plate), and the magnetic domain control processing lines 11 may include curved portions (i.e., they do not have to be composed solely of straight lines).

[0020] The type of magnetic domain control processing line 11 is not particularly limited, but preferred examples are thermal strain and / or grooves. If the magnetic domain control processing line 11 is a groove, the magnetic domain control processing line 11 can be identified visually. If the grain-oriented electrical steel sheet 1 has an insulating coating, the magnetic domain control processing line 11 can be identified visually by removing the insulating coating using a known stripping agent.

[0021] If the magnetic domain control processing line 11 is thermal strain, the magnetic domain control processing line 11 may not be visible. In this case, for example, an image acquisition device 30 with a configuration as illustrated in Figure 4 can be used to capture a magnetic domain image, and the location of the thermal strain can be identified by observing the captured magnetic domain image. When capturing the image, a DC magnetic field is applied along the direction ND, which is the normal direction to the rolling surface of the grain-oriented electrical steel sheet 1, as needed, while capturing the magnetic domain image.

[0022] (Spacing of magnetic domain control processing lines 11 along the rolling direction RD) In multiple magnetic domain control processing lines 11, the spacing along the rolling direction RD of adjacent magnetic domain control processing lines 11 is not particularly limited. A smaller spacing enhances the effect of improving iron loss. On the other hand, a larger spacing improves noise characteristics. The spacing can be appropriately selected according to the characteristics required for the grain-oriented electrical steel sheet 1. For example, the spacing along the rolling direction RD of adjacent magnetic domain control processing lines 11 may be 1.0 mm or more, 2.0 mm or more, 3.0 mm or more, or 5.0 mm or more. The spacing along the rolling direction RD of adjacent magnetic domain control processing lines 11 may be 10.0 mm or less, 9.0 mm or less, 8.0 mm or less, or 7.0 mm or less. The spacing between adjacent magnetic domain control processing lines 11 along the rolling direction RD may be constant or it may vary (fluctuate). If it varies, for example, the average value of the spacing between adjacent magnetic domain control processing lines 11 along the rolling direction RD may be 1.0 mm or more, 2.0 mm or more, 3.0 mm or more, or 5.0 mm or more. The average value of the spacing between adjacent magnetic domain control processing lines 11 along the rolling direction RD may be 10.0 mm or less, 9.0 mm or less, 8.0 mm or less, or 7.0 mm or less. The spacing can be determined by drawing one or more straight lines L along the rolling direction RD and measuring the distance between two adjacent points LP at the intersection of the straight lines L and the magnetic domain control processing lines. When calculating the average value of the spacing, multiple distances between two adjacent points LP can be measured and averaged.

[0023] The angle between the magnetic domain control processing line 11 and the rolling perpendicular direction TD can be measured using known angle measuring means after identifying the magnetic domain control processing line 11 and the rolling perpendicular direction TD using the procedures described above and below.

[0024] The spacing of the magnetic domain control processing lines 11 along the rolling direction RD can be measured using known length measuring means after identifying the magnetic domain control processing lines 11 and the rolling direction RD using the procedures described above and below. Here, the spacing of the magnetic domain control processing lines 11 along the rolling direction RD is the distance from the center of the width of the rolling direction RD of one magnetic domain control processing line to the center of the width of the rolling direction RD of the adjacent magnetic domain control processing line.

[0025] As described above, the magnetic domain control processing lines 11 are, for example, thermal strains or grooves. Thermal strains can be formed using means such as laser irradiation, electron beam irradiation, and ion implantation. Grooves can be formed using means such as laser irradiation, electron beam irradiation, and machining, etching, etc.

[0026] Thermal distortion is eliminated by distortion-relieving annealing or a similar heat treatment. Therefore, when the grain-oriented electrical steel sheet 1 is heat-treated, it is preferable to make the magnetic domain control treatment lines 11 grooves. On the other hand, since thermal distortion can be easily formed, it is preferable to make the magnetic domain control treatment lines 11 thermal distortion when simplification of the manufacturing process is required. The grain-oriented electrical steel sheet 1 may have both thermal distortion and grooves.

[0027] Furthermore, if the magnetic domain control processing line 11 is thermal strain, it is preferable that tensile stress is introduced in the thermal strain. The greater the tensile stress, the greater the effect of improving iron loss. On the other hand, the smaller the tensile stress, the better the noise characteristics. The tensile stress can be appropriately selected according to the characteristics required for the grain-oriented electrical steel sheet 1. The magnitude of the tensile stress is not particularly limited, but it is preferable that, for example, in at least a portion of the magnetic domain control processing line 11, the tensile stress in any direction is 40 MPa or more, 60 MPa or more, or 80 MPa or more. If the tensile stress in at least one direction is 40 MPa or more, the requirement that "the tensile stress in any direction is 40 MPa or more" is considered to be met. Also, for example, it is preferable that, in at least a portion of the magnetic domain control processing line 11, the tensile stress in any direction is 300 MPa or less, 200 MPa or less, 180 MPa or less, or 150 MPa or less. The tensile stress in any direction in the magnetic domain control processing line 11 may be uniform or may vary.

[0028] The magnitude of the tensile stress introduced by thermal strain is measured using the EBSD Wilkinson method and the Cross Court manufactured by BLG Vantage. The EBSD Wilkinson method is described in detail in AJ Wilkinson, et al., "High-resolution elastic strain measurement from electron backscatter diffraction patterns: New levels of sensitivity," Ultramicroscopy Vol 106, No.4-5, March 2006, pp. 307-313. When measuring the magnitude of tensile stress introduced by thermal strain using the EBSD Wilkinson method and BLG Vantage's Cross Court, first, the magnetic domain control processing lines 11 are identified using the procedure described above. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control processing lines 11 and perpendicular to them. This cut surface is used as the measurement surface. The cross section of the magnetic domain control processing lines 11 included in the measurement surface is analyzed using the EBSD Wilkinson method and BLG Vantage's Cross Court to extract tensile stress components in any direction and measure their magnitude. For example, tensile stress components can be extracted in the direction normal to the rolling surface ND, in the direction parallel to the magnetic domain control processing lines 11, and in the direction perpendicular to both the rolling surface normal to the rolling surface ND and the magnetic domain control processing lines 11. The number of measurement points is, for example, 10. If the tensile stress in any direction is 40 MPa or more at at least one location on the grain-oriented electrical steel sheet 1 (i.e., the tensile stress in at least one direction is 40 MPa or more), then it is determined that the maximum value of the tensile stress in any direction in the magnetic domain control processing lines of the grain-oriented electrical steel sheet 1 is 40 MPa or more. Therefore, for the purpose of determining whether the maximum value of the tensile stress is 40 MPa or more, the measurement of tensile stress may be stopped as soon as a measurement point where the tensile stress in any direction is 40 MPa or more is found. However, the σ(TS) described later... m ) 2 , TS m(β<2) , or TS m(β≧2)To determine the tensile stress, do not stop the measurement, but determine the tensile stress at each measurement point.

[0029] When the magnetic domain control processing line 11 is a groove, the greater the groove depth and width, the greater the effect of improving iron loss. On the other hand, the smaller the groove depth and width, the better the noise characteristics. The groove shape can be appropriately selected according to the characteristics required for the grain-oriented electrical steel sheet 1. The groove depth is not particularly limited, but is preferably, for example, 5 μm to 50 μm. The groove depth may be 6 μm or more, 7 μm or more, or 10 μm or more. The groove depth may be 48 μm or less, 45 μm or less, or 40 μm or less. The groove width (width at the opening) is not particularly limited, but is preferably, for example, 10 μm to 300 μm. The groove width may also be specified as 20 μm or more, 30 μm or more, or 50 μm or more. The groove width may also be specified as 280 μm or less, 250 μm or less, or 200 μm or less. The groove depth and width may be uniform or variable. If they vary, it is preferable that the average of the depth and width of multiple grooves is within the above range.

[0030] The depth and width of the grooves can be measured by determining the surface shape of the sample using a known three-dimensional measuring machine. If the grain-oriented electrical steel sheet 1 has an insulating coating, the insulating coating is removed using the procedure described above before performing three-dimensional measurement of the sample surface.

[0031] (Method for determining the rolling direction RD and the direction perpendicular to the rolling direction TD) The rolling direction RD and the direction perpendicular to the rolling direction TD of the grain-oriented electrical steel sheet 1 are determined by the following means. (1) If the sample is cut from a coiled grain-oriented electrical steel sheet 1, the width direction of the coil is considered to be the rolling direction TD. Also, the direction perpendicular to the rolling direction TD and the rolling surface normal direction ND is considered to be the rolling direction RD. (2) If the sample is cut from a component of an electrical product, the rolling direction RD and the direction perpendicular to the rolling direction TD are determined from the rolling defects on the surface of the grain-oriented electrical steel sheet 1. The direction in which the rolling defects extend is considered to be the rolling direction RD. The direction perpendicular to the rolling direction RD and the direction normal to the rolling surface ND is considered to be the direction perpendicular to the rolling direction TD. (3) If it is difficult to determine the rolling direction RD and the direction perpendicular to rolling TD from the rolling defects on the surface of the grain-oriented electrical steel sheet 1, the rolling direction RD and the direction perpendicular to rolling TD shall be determined from the crystal orientation of the grain-oriented electrical steel sheet 1. Specifically, the crystal orientation of the grain-oriented electrical steel sheet 1 to be evaluated shall be measured at multiple points. The easy magnetization axis whose angle with respect to the crystal orientation at the measurement point is closest to a right angle with respect to the rolling surface normal direction ND (thickness direction) shall be determined. <001> The direction in which the deviation angle from the rolling plane is minimized is considered the rolling direction RD, and the direction perpendicular to the rolling direction RD and the direction normal to the rolling plane ND is considered the direction perpendicular to the rolling plane TD.

[0032] (Magnetic domain control region 12) (Non-magnetic domain control region 13) As described above, the magnetic domain control processing lines 11 provided on the surface of the grain-oriented electrical steel sheet 1 have the function of subdividing the 180° magnetic domains. Furthermore, the smaller the spacing between the magnetic domain control processing lines, the greater the effect of improving iron loss. For this reason, in general magnetic domain control processing, the spacing between the magnetic domain control processing lines does not exceed 20 mm; in other words, the regions (magnetic domain control processing regions) within 10 mm of the magnetic domain control processing lines 11 are formed to be in contact with each other or partially overlap. This is also true in the width direction, and the magnetic domain control processing lines 11 are formed so that the spacing between them does not exceed 20 mm in the scanning direction of the magnetic domain control processing lines 11. Therefore, in a grain-oriented electrical steel sheet that has undergone normal magnetic domain control processing, there is no non-magnetic domain control region, which is a region that is more than 10 mm away from all of the multiple magnetic domain control processing lines. In contrast, the grain-oriented electrical steel sheet 1 according to this embodiment is characterized by providing a non-magnetic domain control region 13 by interrupting the magnetic domain control processing lines 11 in the extending direction or by widening the spacing in the rolling direction. As mentioned above, while magnetic domain control is effective in reducing iron loss in grain-oriented electrical steel sheets, it also worsens the noise characteristics of grain-oriented electrical steel sheets. Therefore, by providing a non-magnetic domain control region, the deterioration of noise characteristics can be suppressed. In other words, both noise reduction and iron loss reduction can be achieved in a balanced manner.

[0033] Further investigations by the inventors revealed that the changes in magnetic domains before and after magnetic domain control of grain-oriented electrical steel sheets revealed that there are areas where the magnetic domain width becomes finer due to magnetic domain control and areas where it hardly becomes finer. In other words, they found that the effect of magnetic domain refinement when magnetic domain control is performed differs depending on the magnetic domain width before magnetic domain control. More specifically, it was found that the effect of magnetic domain refinement by magnetic domain control is less apparent in regions where the magnetic domain width is narrow.

[0034] Based on the above findings, it is clear that preferentially applying magnetic domain control processing to regions with wide magnetic domain widths is extremely effective in achieving both low iron loss and low noise. Magnetic domain control processing in regions with wide magnetic domain widths can reduce iron loss. Since magnetic domain control processing lines formed in regions with narrow magnetic domain widths are thought to cause deterioration of noise characteristics due to recirculating magnetic domains, minimizing magnetic domain control processing in regions with narrow magnetic domain widths can prevent deterioration of noise characteristics. Therefore, in order to minimize the deterioration of noise characteristics while obtaining the effect of reducing iron loss, magnetic domain control processing is mainly performed in regions with wide magnetic domain widths where the effect of magnetic domain subdivision is large. It is preferable to perform magnetic domain control processing only in regions with wide magnetic domain widths, but it is permissible to perform magnetic domain control processing in regions with narrow magnetic domain widths if the proportion is small, as the deterioration of noise characteristics will also be small. Furthermore, it is preferable to perform magnetic domain control processing in all regions with wide magnetic domain widths, but regions where magnetic domain control processing is not performed may be included as long as they satisfy equation (5) described later. The region in which magnetic domain control is performed will be described later, but in grain-oriented electrical steel sheets in which a sufficient reduction in iron loss can be obtained even if magnetic domain control is mainly performed in such specific regions in order to suppress deterioration of noise characteristics, it was found that after magnetic domain control treatment, the average value of the absolute values ​​of the β angle in the non-magnetic domain control region |βNDr| and the average value of the absolute values ​​of the β angle in the magnetic domain control region |βDr| satisfy the following equation (5). |βDr|-|βNDr|≦-0.1° (5) Therefore, in the grain-oriented electrical steel sheet according to this embodiment, the average value of the absolute values ​​of the β angle in the non-magnetic domain control region |βNDr| and the average value of the absolute values ​​of the β angle in the magnetic domain control region |βDr| are controlled to satisfy the above equation (5).

[0035] The reason why grain-oriented electrical steel sheets satisfying equation (5) exhibit low iron loss is presumed to be as follows: To reduce iron loss, magnetic domain subdivision is performed by magnetic domain control processing. However, in regions with narrow magnetic domain widths, the effect of reducing iron loss is small even if magnetic domain control processing is performed in those regions. The β angle shown in equation (5) is the angle of deviation of the crystal grain from the Goss orientation around the axis perpendicular to the rolling direction TD. In the grain-oriented electrical steel sheet 1 before magnetic domain control processing, there is a close relationship between the β angle and the magnetic domain width. In the grain-oriented electrical steel sheet 1 before magnetic domain control processing, the smaller the β angle, the wider the magnetic domain width. This β angle does not change with magnetic domain control processing. In other words, satisfying equation (5) indicates that domain control processing is performed in regions with relatively wide domain widths (small β angles), and not in regions with narrow domain widths (large β angles). In other words, by selecting regions with a large domain subdivision effect and performing domain control processing, it can be said that the greatest possible reduction in iron loss is achieved while suppressing the deterioration of noise characteristics.

[0036] Furthermore, our investigations revealed that the domain refinement effect is small in regions with narrow domain widths. As shown in Figure 2, in regions with a domain width of approximately 500 μm or less, the domain width is approximately the same before and after the domain control process. This suggests that the domain refinement effect of domain control is almost negligible in regions with a domain width of approximately 500 μm or less. Therefore, it is preferable not to perform domain control in these regions, and as a result, the average domain width in the non-domain-controlled region is preferably 500 μm or less. It is also preferable that the maximum domain width in the non-domain-controlled region is 1000 μm or less.

[0037] The average of the absolute values ​​of the β angles in the magnetic domain-controlled region and the non-magnetic domain-controlled region is calculated using the following method. For example, a sample with a side length of 100 mm (or more) can be cut from the grain-oriented electrical steel sheet 1 and used for measurement. If the grain-oriented electrical steel sheet 1 is a coil, a sample can be taken from any point on the coil. Similarly, if the grain-oriented electrical steel sheet 1 is a component incorporated into an electrical product such as a transformer or motor, a sample can be taken from any point on the component. If the size of the component is small, the side length of the sample may be less than 100 mm. In this case, the total sample area should be 10,000 mm². 2 The above should be achieved. In this process, it is desirable to collect the sample using methods such as wire cutting to minimize the effects of mechanical distortion on the sample. On the surface of this sample, draw a virtual line VL1 parallel to the width direction (TD) perpendicular to the rolling direction, and a virtual line VL2 parallel to the rolling direction (RD). The distance between virtual lines VL1 and VL2 is 5 mm. The intersection of these virtual lines VL1 and VL2 is defined as VP1, and the absolute value of the β angle at VP1 is measured. The average of these absolute values ​​of the β angle is taken as the average value of the absolute values ​​of the β angle. However, the β angle is the value obtained by rounding the measured value to the second decimal place. That is, the significant figures of the β angle are to the first decimal place. The β angle is measured by the side reflection Laue method. The side reflection Laue method is a widely known method for measuring crystal orientation.

[0038] The average and maximum values ​​of the magnetic domain width in the non-magnetic domain control region are determined by the following method. From grain-oriented electrical steel sheets, a sample with a side length of 100 mm (or 100 mm or more) or a total sample area of ​​10,000 mm², including the non-magnetic domain control region. 2 Samples are collected in the manner described above. A magnetic domain image is acquired from this sample using an image acquisition device that includes a light source, a magneto-optical sensor (MO sensor), an image sensor, and a signal processing unit. This magnetic domain image is output via cable or wireless communication to an analysis device, which is a computer device such as a personal computer (PC) equipped with a calculation unit, memory, display unit, input unit, and communication interface. The calculation unit analyzes the magnetic domain structure from the magnetic domain image using the line segment method. An example of measurement using the line segment method is described below. Figure 3C is a magnetic domain image acquired by Matesy GmbH's CMOS-MagView. Figure 3D is a schematic representation of Figure 3C to illustrate the measurement process. In the line segment method, line segments Ls perpendicular to the magnetic domains are drawn for evaluation. The line segments are drawn at intervals of 3 per 1 cm in the rolling direction RD. The domain width is derived based on the interval w of the intersection points Ip between the 180° domain wall and the line segment Ls. However, if there are recirculating domains 301 or noise 302, these are not counted as domain walls. Also, when calculating the average domain width, the average interval is determined from the length of each line segment Ls and the number of intersection points Ip.

[0039] All of the parameters described above are measured on a sample of a predetermined size taken from the grain-oriented electrical steel sheet 1. If the grain-oriented electrical steel sheet 1 is a coil, the sample can be taken from any point on the coil. Similarly, if the grain-oriented electrical steel sheet 1 is a component incorporated into electrical products such as transformers or motors, the sample can be taken from any point on the component. If the size of the component is small, the length of one side of the sample may be reduced, but the total sample area should remain the same. When taking the sample, it is desirable to use a method such as wire cutting to minimize the effects of mechanical strain on the sample.

[0040] In the grain-oriented electrical steel sheet according to this disclosure, it is preferable that the maximum value of the tensile stress introduced into the groove depth or thermal strain, which is an indicator of the strength of magnetic domain control in the magnetic domain control processed line, is non-uniform at each measurement point of the groove depth or tensile stress. While a higher magnetic domain control strength enhances the effect of magnetic domain subdivision, it also tends to increase hysteresis loss and worsen noise characteristics. According to the inventors' new findings, the magnetic domain control saturation strength is not uniform in grain-oriented electrical steel sheets. Therefore, it is preferable to make the magnetic domain control strength non-uniform according to the magnetic domain control saturation strength. The magnetic domain control saturation strength is the magnetic domain control strength at which the effect of magnetic domain subdivision processing substantially saturates. When the magnetic domain control strength is below the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the reduction in iron loss. However, when the magnetic domain control strength exceeds the magnetic domain control saturation strength, increasing the magnetic domain control strength does not significantly improve the effect of reducing iron loss. On the other hand, even when the magnetic domain control strength exceeds the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the hysteresis loss and the worse the noise characteristics. Therefore, it is extremely preferable to keep the magnetic domain control strength within a range that does not exceed the magnetic domain control saturation strength.

[0041] When the magnetic domain control processing line is thermal strain, each of the multiple intersections between the virtual line and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the maximum value of the tensile stress per unit MPa introduced into the thermal strain, measured at each of the magnetic domain subdivision points, is defined as TS m , TS m The variance of σ(TS) m ) 2 In that case, σ(TS m ) 2 It is more preferable to satisfy a score of >5.0.

[0042] The "maximum tensile stress introduced into the thermal strain" is the maximum tensile stress measured in a single arbitrary measurement cross-section. Since the tensile stress varies within a single measurement cross-section, a single "maximum tensile stress introduced into the thermal strain" can be identified for each measurement cross-section. As schematically shown in Figure 11, the thermal strain 541 has a certain extent of spread across the cross-section. The tensile stress is highest in the area directly irradiated by the laser, and lower in areas further away. That is, the measured tensile stress differs for each measurement location in the cross-section. According to the tensile stress measurement method described later, the distribution and maximum value of tensile stress in the cross-section can be derived.

[0043] When the magnetic domain control strength is uniform, the maximum value of tensile stress introduced into the thermal strain 541 is constant throughout the entire magnetic domain control processing line 11. On the other hand, when the magnetic domain control strength is non-uniform, the maximum value of tensile stress introduced into the thermal strain along the magnetic domain control processing line is non-uniform at each tensile stress measurement point. Hereinafter, the maximum value of tensile stress introduced into the thermal strain may simply be referred to as "tensile stress".

[0044] Furthermore, the inventors have found that the magnetic domain control saturation strength has a strong correlation with the β angle. The β angle is the angle of deviation of the crystal grain from the Goss orientation around the axis perpendicular to the rolling direction (TD). Where the β angle is small, the magnetic domain control saturation strength is large. In addition, there is a correlation between the β angle and the magnetic domain width in grain-oriented electrical steel sheets before magnetic domain control treatment. In grain-oriented electrical steel sheets before magnetic domain control treatment, the larger the β angle, the narrower the magnetic domain width. However, in grain-oriented electrical steel sheets after magnetic domain control treatment, the correlation between the magnetic domain width and the β angle becomes smaller. This is because the magnetic domain control treatment changes the magnetic domain width but does not change the β angle.

[0045] Therefore, it is preferable to select the optimal domain control strength according to the size of the magnetic domain width or β angle. For example, it is preferable to perform a domain subdivision process with a high domain control strength in areas where the magnetic domain width is wide and the β angle is small, and to perform a domain subdivision process with a low domain control strength in areas where the magnetic domain width is narrow and the β angle is large. Also, as mentioned above, the domain subdivision process is not performed in areas where the original magnetic domain width is narrow. Specifically, the arithmetic mean of the maximum tensile stress per unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is less than 2°, is calculated as TS. m(β<2) The arithmetic mean of the maximum tensile stress per unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or greater, is defined as TS m(β≧2) In that case, TS m(β<2) >TS m(β≧2) It is preferable that the following conditions be met. In this case, the iron loss of the grain-oriented electrical steel sheet after magnetic domain control is further reduced. On the other hand, the increase in hysteresis loss and deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0046] TS m and σ(TS m ) 2 An example of the measurement method is explained using Figure 13. In Figure 13, the dashed lines are multiple virtual lines VL set parallel to the rolling direction RD of the grain-oriented electrical steel sheet at 5 mm intervals. The X and O marks in Figure 13 are the intersections of the virtual lines VL and the thermal strain 541, which is the magnetic domain control processing line. The β angle at the locations marked with X is 2° or more, and the β angle at the locations marked with O is less than 2°. However, σ(TS) m ) 2 When calculating this, the β angle at the intersection does not need to be considered.

[0047] First, the rolling direction RD of the grain-oriented electrical steel sheet is identified. The rolling direction RD can be identified by the method described later. Next, virtual lines VL are set parallel to the rolling direction RD of the grain-oriented electrical steel sheet at 5 mm intervals. Then, the intersection points of the virtual lines VL and the thermal strain 541, which is a magnetic domain control processing line, are identified. If the thermal strain 541 is not visible to the naked eye, the thermal strain 541 is identified based on the magnetic domain image. The shape of the measurement sample is preferably a rectangle with a size of 100 mm or more along the rolling direction RD and a size of 100 mm or more along the direction perpendicular to the rolling direction TD. It is preferable that one side of the rectangle be parallel to the rolling direction RD.

[0048] Then, an evaluation area is set as a square with a side length of 50 mm and one side parallel to the rolling direction, and the TS is measured at all intersections of the measurement area. m Measure and TS m Variance σ(TS) m ) 2 The tensile stress TS introduced in thermal strain is calculated. m This is measured using the EBSD Wilkinson method and CrossCourt, manufactured by BLG Vantage.

[0049] When measuring the magnitude of tensile stress introduced by thermal strain using the EBSD Wilkinson method and BLG Vantage's Cross Court, first, the thermal strain 541, which is the magnetic domain control processing line, is identified using the procedure described above. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control processing line and perpendicular to it. This cut surface is used as the measurement surface. The cross section of the magnetic domain control processing line included in the measurement surface is analyzed using the EBSD Wilkinson method and BLG Vantage's Cross Court to extract tensile stress components in any direction and measure their magnitude. For example, tensile stress components can be extracted in the direction normal to the rolling surface, in the direction parallel to the magnetic domain control processing line, and in the direction perpendicular to both the rolling surface normal and the magnetic domain control processing line. The maximum value of tensile stress TS identified at each of multiple measurement points. M Variance σ(TS) M ) 2This is derived according to the method for deriving the population variance described in paragraph 2.36 of JIS Z 8101-1:2015 "Statistics - Terminology and symbols - Part 1: General statistical terms and terms used in probability".

[0050] Also, TS m(β<2) and TS m(β≧2) It is measured using the following method. First, by measuring the β angle at each intersection, we identify intersections where the β angle is 2° or greater, and intersections where the β angle is less than 2°. In grain-oriented electrical steel sheets, the β angle is measured using the side reflection Laue method. The side reflection Laue method is a widely known method for measuring crystal orientation. Next, at each intersection where the β angle is 2° or greater, the maximum value of the tensile stress TS m Identify these values ​​and calculate their arithmetic mean. This value is then used as the TS. m(β≧2) It will be considered as such. Furthermore, at each intersection where the β angle is less than 2°, the maximum tensile stress TS m Identify these values ​​and calculate their arithmetic mean. This value is then used as the TS. m(β<2) It is considered that the maximum tensile stress TS introduced into the thermal strain 541 at the intersection is... m The measurement method is as described above.

[0051] When the magnetic domain control processing line is a groove, a square evaluation area is set on the surface with a side length of 50 mm and one side parallel to the rolling direction. Furthermore, within the evaluation area, imaginary lines parallel to the rolling direction and with a length of 50 mm are set at 5 mm intervals perpendicular to the rolling direction. Each of the multiple intersections between the imaginary lines and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the maximum value of the groove depth in units of μm measured at each magnetic domain subdivision point is defined as D. m , the aforementioned D m The variance of σ(D) m ) 2 In that case, σ(D m ) 2 It is more preferable to satisfy >3.0. In this case, the magnetic domain control strength is changed based on the magnitude of the magnetic domain width or the magnitude of the β angle, and the increase in hysteresis loss and deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0052] Furthermore, the arithmetic mean of the maximum groove depth in units of μm, measured at each of the magnetic domain refinement points where the β angle is less than 2°, is D m(β<2) D is the arithmetic mean of the maximum groove depth in units of μm measured at each of the magnetic domain subdivision points where the β angle is 2° or greater. m(β≧2) In that case, D m(β<2) >D m(β≧2) It is even more preferable to satisfy the following conditions. In this case, in the magnetic domain control processing line, the magnetic domain control intensity is high where the β angle is small, and low where the β angle is large. Consequently, the iron loss of the grain-oriented electrical steel sheet after magnetic domain control is further reduced. On the other hand, the increase in hysteresis loss and deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0053] D m and σ(D m ) 2 An example of the measurement method is shown in Figure 14. The dashed lines in Figure 14 are multiple virtual lines VL set at 5 mm intervals parallel to the rolling direction RD of the grain-oriented electrical steel sheet. The X and O marks in Figure 14 are the intersections of the virtual lines VL and the groove 542, which is the magnetic domain control processing line. The β angle at the locations marked with X is 2° or more, and the β angle at the locations marked with O is less than 2°. However, σ(D m ) 2 When calculating this, the β angle at the intersection does not need to be considered.

[0054] First, the rolling direction of the grain-oriented electrical steel sheet is determined. Next, virtual lines VL are set parallel to the rolling direction RD of the grain-oriented electrical steel sheet at 5 mm intervals. Then, the intersection points of the virtual lines VL and the magnetic domain control processing lines are determined. If the magnetic domain control processing lines are grooves 542, the magnetic domain control processing lines are easily visible to the naked eye. The shape of the measurement area is preferably a rectangle with a size of 100 mm or more along the rolling direction RD and a size of 100 mm or more along the direction perpendicular to the rolling direction TD. It is preferable that one side of the rectangle be parallel to the rolling direction RD.

[0055] Then, a square evaluation area is set with a side length of 50 mm and one side parallel to the rolling direction, and the maximum value D of the groove depth at all intersections in the measurement area is measured. m Measure the maximum depth D of the groove. m Variance σ(D m ) 2 Calculate the maximum groove depth D. m The measurement method is as follows: Measurements are performed using a Bruker Control GT-I white light interference microscope. The lenses used are a 5x objective lens (numerical aperture 0.12, optical resolution 2.2 μm) and a 1x internal lens. The light source is a white LED, and the camera is a monochrome CCD (1200 × 1000 pixels). The pixel size is 1.37 μm. Using the analysis software Vision64 Map Premium 9.2, tilt correction is performed by fitting to the least-squares plane, and then long-wavelength undulations are removed using a Gaussian filter with a cutoff value of 2.5 mm for analysis. The pixel size may be resampled to 10 μm if necessary during analysis. Also, parts that are clearly judged to be abnormal points may be excluded from the analysis. Depending on the properties of the sample, the type of lens, filter value, and correction method may be changed. If grooves are formed in the grain-oriented electrical steel sheet, but the surface irregularities cannot be measured due to an insulating coating, etc., the insulating coating, etc. should be removed using a known method, and the above measurement should be performed.

[0056] First, by measuring the β angle at each intersection, we identify intersections where the β angle is 2° or greater, and intersections where the β angle is less than 2°. Next, we measure the D at all intersections where the β angle is 2° or greater. mCalculate the arithmetic mean of and use this as D m(β≧2) It is assumed that the β angle is D at all intersections less than 2°. m Calculate the arithmetic mean of and use this as D m(β<2) It is assumed that the maximum depth D of the groove at the intersection is... m The measurement method is as described above.

[0057] (film) The grain-oriented electrical steel sheet 1 may have a forsterite coating on its surface (i.e., the grain-oriented electrical steel sheet may consist of a base steel sheet and a forsterite coating formed on the surface of the base steel sheet). The grain-oriented electrical steel sheet 1 may also have an insulating coating on the surface of the base steel sheet or on the surface of the forsterite coating (i.e., the grain-oriented electrical steel sheet may consist of a base steel sheet and a forsterite coating formed on the surface of the base steel sheet and an insulating coating formed on the surface of the forsterite coating, or it may consist of a base steel sheet and an insulating coating formed on the surface of the base steel sheet). The forsterite coating and the insulating coating may be formed on one side or on both sides of the grain-oriented electrical steel sheet 1.

[0058] Forsterite coatings are inorganic coatings, for example, those primarily composed of magnesium silicate. Forsterite coatings are formed, for example, during finish annealing, by a reaction between an annealing separation agent containing magnesia (MgO) applied to the surface of the base steel sheet and the components of the base steel sheet surface. Forsterite coatings have a composition derived from, for example, the annealing separation agent and the components of the base steel sheet (more specifically, a composition primarily composed of Mg2SiO4). On the other hand, if an annealing separation agent mainly composed of Al2O3 is used in finish annealing, forsterite coatings may not be formed.

[0059] The insulating coating has the function of imparting electrical insulation and tension to the grain-oriented electrical steel sheet 1. By imparting tension to the grain-oriented electrical steel sheet 1 and facilitating magnetic domain wall movement in the grain-oriented electrical steel sheet 1, iron loss in the grain-oriented electrical steel sheet 1 can be reduced. Furthermore, the insulating coating can impart various properties such as corrosion resistance, heat resistance, and slipperiness to the grain-oriented electrical steel sheet 1. The insulating coating may be a known coating formed, for example, by applying a coating solution mainly composed of phosphate and colloidal silica to the surface of a forsterite coating and baking it.

[0060] [Manufacturing method] The grain-oriented electrical steel sheet according to this embodiment can achieve the above-described effects regardless of the manufacturing method, as long as it possesses the above-described characteristics. However, the following method is preferable because it allows for stable manufacturing. In other words, the grain-oriented electrical steel sheet according to this embodiment can be manufactured by a manufacturing method including the following steps (I) to (III). If the distribution of magnetic domain widths is clear, steps (I) and (II) may be omitted. (I) Magnetic domain image acquisition process for acquiring magnetic domain images of grain-oriented electrical steel sheets. (II) A region identification step that identifies regions in the grain-oriented electrical steel sheet where the magnetic domain width exceeds 500 μm, based on the magnetic domain image obtained in the magnetic domain image acquisition step. (III) A process for forming magnetic domain control lines on the surface of a grain-oriented electrical steel sheet. Let me explain each step.

[0061] The grain-oriented electrical steel sheet (raw material) used in the magnetic domain image acquisition process, or in the magnetic domain control processing line formation process if the magnetic domain image acquisition process or the region identification process is not performed, may be any known grain-oriented electrical steel sheet. For example, the raw material has a chemical composition in mass percent of: Si: 2.50-7.00%, Mn: 0-1.00%, C: 0-0.085%, acid-soluble Al: 0-0.065%, N: 0-0.012%, Cr: 0-0.300%, Cu: 0-0.400%, P: 0-0.500%, Sn: 0-0.300%, Sb: 0-0.300%. It may contain %, Ni: 0-1.000%, S: 0-0.015%, Se: 0-0.015%, Bi: 0-0.020%, Nb: 0-0.030%, V: 0-0.030%, Mo: 0-0.030%, Ta: 0-0.030%, W: 0-0.030%, B: 0-0.080%, and Ti: 0-0.015%. The remainder of the chemical composition includes Fe and impurities. The grain-oriented electrical steel sheet used as the base material may have a forsterite coating formed on its surface.

[0062] (Magnetic domain image acquisition process) (Area identification process) In the magnetic domain image acquisition process, a magnetic domain image of the surface of the grain-oriented electrical steel sheet is acquired before the magnetic domain control processing line formation process. In the region identification process, based on the magnetic domain image obtained in the magnetic domain image acquisition process, regions in the grain-oriented electrical steel sheet where the magnetic domain width exceeds 500 μm are identified. As mentioned above, the effect of magnetic domain refinement is small in regions with narrow magnetic domain widths, and it is considered that almost no effect of magnetic domain refinement by magnetic domain control can be obtained in regions with magnetic domain widths of approximately 500 μm or less. Therefore, it is preferable not to perform magnetic domain control in this region. In the subsequent magnetic domain processing line formation process, magnetic domain control processing lines are formed on the surface of the grain-oriented electrical steel sheet 1 such that non-magnetic domain control regions 13 are formed. By identifying regions where the magnetic domain width exceeds 500 μm and mainly performing magnetic domain control processing on those regions, the number of magnetic domain control processing lines can be reduced, thereby reducing iron loss while suppressing deterioration of noise characteristics.

[0063] (Magnetic domain control processing line formation process) In the magnetic domain control processing line formation process, magnetic domain control processing lines are mainly formed in the regions where the magnetic domain width exceeds 500 μm, as identified in the region identification process (it is preferable not to form magnetic domain control processing lines in regions where the magnetic domain width is 500 μm or less, but this is permissible if the proportion is small), thereby forming multiple magnetic domain control processing lines extending in a direction intersecting the rolling direction on the surface of the grain-oriented electrical steel sheet. At that time, the magnetic domain control processing lines are formed so that a magnetic domain control region 12 and a non-magnetic domain control region 13 are formed. Furthermore, the magnetic domain control processing lines are formed so that the average value of the absolute values ​​of the β angles in the non-magnetic domain control region |βNDr| and the average value of the absolute values ​​of the β angles in the magnetic domain control region |βDr| satisfy the following equation (5). |βDr|-|βNDr|≦-0.1° (5) Since the β angle does not change due to the magnetic domain control process, by examining the β angle at each position of the grain-oriented electrical steel sheet before the magnetic domain control line formation process, it is possible to form magnetic domain control lines that satisfy equation (5).

[0064] Preferably, the magnetic domain control strength is determined according to the magnetic domain width of the grain-oriented electrical steel sheet before the magnetic domain subdivision process. The magnetic domain control strength is the amount of thermal strain if the means of magnetic domain control is thermal strain, and the depth of the groove if the means of magnetic domain control is a groove. In this case, the maximum value of the tensile strength introduced into the thermal strain or the groove depth in the magnetic domain control processing line will be non-uniform at each measurement point of the tensile strength or groove depth.

[0065] The greater the strength of magnetic domain control, the greater the effect of magnetic domain subdivision. On the other hand, the greater the strength of magnetic domain control, the more likely it is to lead to increased hysteresis loss and deterioration of noise characteristics. Furthermore, according to the inventors' new findings, the magnetic domain control saturation strength is not uniform in grain-oriented electrical steel sheets.

[0066] The magnetic domain control saturation strength is the magnetic domain control strength at which the effect of magnetic domain subdivision processing saturates. When the magnetic domain control strength is below the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the reduction in iron loss. However, when the magnetic domain control strength exceeds the magnetic domain control saturation strength, increasing the magnetic domain control strength does not further enhance the effect of reducing iron loss. However, even when the magnetic domain control strength exceeds the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the hysteresis loss and the worse the noise characteristics. Therefore, it is extremely preferable to keep the magnetic domain control strength within a range that does not exceed the magnetic domain control saturation strength.

[0067] Specifically, it is preferable to perform a magnetic domain refinement process with a high magnetic domain control intensity in areas where the magnetic domain width is wide and the β angle is small, and to perform a magnetic domain refinement process with a low magnetic domain control intensity in areas where the magnetic domain width is narrow and the β angle is large. In regions where the β angle is large, the effect of magnetic domain control is not obtained, so the magnetic domain control saturation intensity is 0. In regions where the β angle is below a predetermined value, the effect of magnetic domain control is obtained. For example, it is estimated that the effect of magnetic domain control is obtained when the β angle is 2° or less. Furthermore, in regions where the β angle is below a predetermined value, the magnetic domain control saturation intensity increases as the β angle increases. And in regions where the β angle is even smaller, the magnetic domain control saturation intensity becomes approximately constant.

[0068] Figure 9 shows a schematic graph illustrating the method for determining the magnetic domain control strength based on the magnetic domain width. In Figure 9, the vertical axis represents the magnetic domain control strength, and the horizontal axis represents the magnitude of the magnetic domain width. The solid line in Figure 9 represents the magnetic domain control saturation strength. In regions with narrow magnetic domain widths, no effect of magnetic domain control is obtained, so the magnetic domain control saturation strength is 0. In regions where the magnetic domain width exceeds 500 μm, the effect of magnetic domain control is obtained. Furthermore, in regions where the magnetic domain width exceeds 500 μm, the magnetic domain control saturation strength increases as the magnetic domain width increases. Finally, in regions where the magnetic domain width exceeds approximately 1200 μm, the magnetic domain control saturation strength becomes approximately constant.

[0069] Figure 10 shows a schematic graph illustrating the method for determining the magnetic domain control strength based on the β angle. In Figure 10, the vertical axis represents the magnetic domain control strength, and the horizontal axis represents the magnitude of the β angle. The solid line in Figure 10 represents the magnetic domain control saturation strength. In the region where the β angle is large, no effect of magnetic domain control is obtained, so the magnetic domain control saturation strength is 0. In the region where the β angle is below a predetermined value, the effect of magnetic domain control is obtained. For example, it is estimated that the effect of magnetic domain control is obtained when the β angle is 2° or less. Furthermore, in the region where the β angle is below a predetermined value, the magnetic domain control saturation strength increases as the β angle increases. And in the region where the β angle is even smaller, the magnetic domain control saturation strength becomes approximately constant.

[0070] It is most preferable that the relationship between the magnetic domain width at the location where magnetic domain control is performed and the magnetic domain control intensity lies on the solid line graph in Figure 9. Alternatively, it is most preferable that the relationship between the β angle at the location where magnetic domain control is performed and the magnetic domain control intensity lies on the solid line graph in Figure 10. The magnetic domain control saturation intensity can be used as the target value for the magnetic domain control intensity.

[0071] Furthermore, there exists a minimum magnetic domain control intensity, which is the minimum intensity at which the magnetic domain control effect manifests. When performing magnetic domain control, it is even more preferable that the magnetic domain control intensity is equal to or greater than the minimum magnetic domain control intensity.

[0072] However, the magnetic domain control strength may vary slightly from the target value, the magnetic domain control saturation strength. In Figures 9 and 10, the region that is greater than or equal to the minimum magnetic domain control strength and within a certain range from the graph of magnetic domain control saturation strength is referred to as the target range for magnetic domain control strength. The magnetic domain control strength and the magnetic domain width of the area to be controlled are preferably located within the shaded area enclosed by the dashed lines in Figures 9 and 10.

[0073] The magnetic domain control lines may be thermal strains or grooves. When thermal strains are used, the magnetic domain control lines are formed by irradiation with a laser or electron beam. The irradiation conditions may be within a known range. When the magnetic domain control lines are thermal strains, the magnetic domain control intensity can be varied by the irradiation conditions of the laser or electron beam. Specifically, the power of the laser or electron beam, irradiation time, irradiation interval, etc., can be changed to increase the average irradiation energy density Ua (mJ / mm²) per unit area. 2 You just need to change ). Methods for creating grooves include irradiating with a laser or electron beam, mechanical processing such as gears, and chemical processing such as etching. The depth of the grooves formed in the grain-oriented electrical steel sheet can be changed by adjusting the time, intensity, shape, etc.

[0074] The formation direction of the magnetic domain control processing lines (scanning direction in the case of a laser, etc.), the spacing of the magnetic domain control processing lines in the rolling direction RD, and the width and depth of the grooves in the magnetic domain control processing lines can be controlled by known methods so as to fall within the range of the grain-oriented electrical steel sheet according to the embodiment described above.

[0075] (Specific methods in the magnetic domain image acquisition process and the magnetic domain control line formation process) The acquisition of magnetic domain images and the identification of regions with a magnetic domain width exceeding 500 μm can be performed using the following method. Surface magnetic domain images can be acquired, for example, by an image acquisition device. Next, the distribution of 180° domain widths (domain widths) is derived from the magnetic domain images. The distribution of magnetic domain widths on the original plate can be derived, for example, by using an analysis device. Regions where the magnetic domain width is greater than or equal to a predetermined value (for example, more than approximately 500 μm) are determined as regions where magnetic domain control processing should be performed (hereinafter sometimes simply referred to as processing regions).

[0076] The processing area may be determined by the operator visually observing the magnetic domain image displayed on the display unit of the analysis device.

[0077] Figure 4 shows an example of the hardware configuration of an image acquisition device 30 that acquires magnetic domain images of a raw plate (grain-oriented electrical steel sheet 1 before magnetic domain control processing). The image acquisition device 30 comprises a light source unit 31, a magneto-optical sensor (MO sensor 33), an image sensor 35, and a signal processing unit 37.

[0078] The light source unit 31 has a light source consisting of light-emitting diodes (LEDs) and irradiates the MO sensor 33 with light that has a aligned plane of polarization.

[0079] The MO sensor 33 is a device for measuring the magnetic domain structure of a magnetic material. The MO sensor 33 has an observation surface on which the magnetic material sample to be measured is placed. Light emitted from the light source unit 31 passes through the inside of the MO sensor 33 and is reflected by the reflective layer. The reflected light passes through the inside of the MO sensor 33 again and is output to the outside of the MO sensor 33. When the original plate, which is the magnetic material sample, is placed on the observation surface of the MO sensor 33, a leakage magnetic field is generated inside the MO sensor 33 according to the direction of the spontaneous magnetization of the original plate. This leakage magnetic field rotates the polarization plane of the reflected light.

[0080] The image sensor 35 is a Complementary Metal-Oxide-Semiconductor (CMOS) image sensor. The image sensor 35 forms an image of the reflected light from the MO sensor 33 on its light-receiving surface, performs photoelectric conversion, and outputs the resulting analog signal to the signal processing unit 37. By detecting the reflected light with a rotated plane of polarization using the image sensor 35, the distribution of the stray magnetic field can be obtained, revealing the magnetic domain structure of the original plate.

[0081] The signal processing unit 37 includes an amplifier, an AD converter, a Digital Signal Processor (DSP), etc. The analog signal output from the image sensor 35 is amplified by the amplifier. The analog signal is then converted into a digital signal by the AD converter. By applying predetermined digital processing using the DSP to this digital signal, an image signal is generated. The image signal generated by the signal processing unit 37 is output to the analysis device 40 (see Figure 5) via cable or wireless communication.

[0082] Figure 5 shows the hardware configuration of the analysis device 40 for analyzing the magnetic domain structure of the original plate. The analysis device 40 is a computer device such as a personal computer (PC). The analysis device 40 comprises a calculation unit 41, a memory 43, a display unit 45, an input unit 47, and a communication interface 49.

[0083] The arithmetic unit 41 has a Central Processing Unit (CPU). The arithmetic unit 41 analyzes the magnetic domain structure from the magnetic domain image of the original plate according to the program stored in the memory 43. The arithmetic unit 41 then determines the processing area to which magnetic domain control processing will be applied. The processing performed by the arithmetic unit 41 will be described in detail later.

[0084] Memory 43 includes Read Only Memory (ROM) and Random Access Memory (RAM). ROM stores programs executed by the CPU of the arithmetic unit 41, and data necessary for the execution of these programs. Programs and data stored in ROM are loaded into RAM and executed.

[0085] The memory 43 may have magnetic memory such as a hard disk drive (HDD), or optical memory such as an optical disc. Alternatively, the memory 43 may store programs and data on a computer-readable recording medium that is detachable from the analysis device 40. Alternatively, the memory 43 may receive programs executed by the arithmetic unit 41 from a network via a communication interface 49.

[0086] The display unit 45 has a display such as a liquid crystal display (LCD), a plasma display, or an organic electroluminescent (EL) display. The display unit 45 displays an image based on the image signal output from the image acquisition device 30. The display unit 45 also displays the results of the magnetic domain structure analysis performed by the calculation unit 41.

[0087] The input unit 47 has input devices such as a mouse and keyboard. The communication interface 49 is an interface for sending and receiving data with external devices via a network such as a Local Area Network (LAN), Wide Area Network (WAN), or the Internet.

[0088] Instead of general-purpose hardware such as a CPU, the arithmetic unit 41 may employ dedicated hardware such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA) specifically designed for analyzing magnetic domain structures.

[0089] Figures 4 and 5 show cases where the image acquisition device 30 and the analysis device 40 are separate devices, but a system in which the image acquisition device 30 and the analysis device 40 are integrated may also be used.

[0090] Known methods such as laser irradiation, electron beam irradiation, and ion implantation can be used to introduce thermal strain to the surface of the original plate. Known methods such as laser irradiation, electron beam irradiation, and machining can be used to form grooves on the surface of the original plate. The configuration of the laser irradiation device 500 that introduces thermal strain by laser irradiation will be described below.

[0091] Figure 6 shows the configuration of the laser irradiation device 500. The laser irradiation device 500 comprises a polygon mirror 501, a light source device 503, a collimator 505, a focusing lens 507, a motor 509, a sensor 511, a control unit 513, and a plate feeding device 515.

[0092] The sheet feeding device 515 feeds the raw sheet in the rolling direction RD.

[0093] The polygon mirror 501 is, for example, shaped like a regular polygonal prism. Multiple plane mirrors are provided on each of the multiple sides that make up the regular polygonal prism-shaped polygon mirror 501. The laser beam LB is incident on the plane mirrors of the polygon mirror 501 in one direction (horizontally) from the light source device 503 via the collimator 505 and is reflected by the plane mirrors.

[0094] The polygon mirror 501 is rotatable around the rotation axis O1 by drive from the motor 509. The incident angle of the laser beam LB on the plane mirror changes sequentially according to the rotation angle of the polygon mirror 501. This sequentially changes the reflection direction of the laser beam LB, allowing scanning of the surface of the original plate. In Figure 6, the symbol P represents the spacing between adjacent magnetic domain control processing lines 11, i.e., the irradiation pitch of the laser beam LB.

[0095] The light source device 503 outputs a laser beam LB in a predetermined irradiation method (for example, a continuous irradiation method or a pulsed irradiation method) under the control of the control unit 513.

[0096] The focusing lens 507 is positioned in the optical path of the laser beam LB reflected from the polygon mirror 501. The focusing lens 507 constitutes a focusing optical system with a predetermined focal length. The laser beam LB reflected from the polygon mirror 501 is focused onto the surface of the original plate via the focusing lens 507, thereby introducing thermal strain to the surface of the original plate.

[0097] Motor 509 is connected to the polygon mirror 501. Under the control of the control unit 513, motor 509 rotates the polygon mirror 501.

[0098] Sensor 511 is connected to the drive shaft of motor 509. Sensor 511 detects the rotation angle of the polygon mirror 501, which is rotated by motor 509. Furthermore, sensor 511 outputs a signal indicating the detected rotation angle (hereinafter referred to as the rotation angle signal) to control unit 513.

[0099] The control unit 513 consists of a processor. The control unit 513 is connected to the light source device 503, the motor 509, the sensor 511, and the sheet feed device 515. The control unit 513 receives a speed signal input from the sheet feed device 515. Furthermore, the control unit 513 outputs a signal to the motor 509 instructing it to rotate the polygon mirror 501.

[0100] Furthermore, the control unit 513 controls the on / off state of the laser beam LB output by the light source device 503 based on the stress introduction signal representing the processing area and the rotation angle signal output from the sensor 511. If the laser irradiation device 500 is electrically connected to the analysis device 40, the stress introduction signal is input from the analysis device 40 to the laser irradiation device 500. The stress introduction signal may also be input to the laser irradiation device 500 by an operator.

[0101] Next, an example of a method for determining the processing area will be described in detail. The process for identifying the processing area is performed, for example, by the calculation unit 41 of the analysis device 40.

[0102] The calculation unit 41 derives the distribution of magnetic domain widths of the original plate, for example, using the line segment method. The calculation unit 41 then determines that regions where the magnetic domain width is greater than or equal to a predetermined value (for example, more than approximately 500 μm) are areas where magnetic domain control processing should be preferentially applied.

[0103] In the line segment method, the magnetic domain is evaluated by drawing line segments perpendicular to the domain. The line segments are drawn so that there are three segments per centimeter in the direction parallel to the magnetic domain. The domain width is derived based on the spacing of the intersection points between the 180° magnetic domain wall and the line segments.

[0104] Figure 3A shows an example of the distribution of magnetic domain widths of grain-oriented electrical steel sheet 1 before magnetic domain control processing, obtained by analyzing the magnetic domain image acquired by Matesy GmbH's CMOS-MagView using a two-dimensional Fourier transform. Figure 3B shows the distribution of magnetic domain widths after applying magnetic domain control processing to the surface of grain-oriented electrical steel sheet 1 in Figure 3A, obtained in the same manner as in Figure 3A. The magnetic domain control processing here was performed by irradiating with a continuous wave laser in a direction approximately perpendicular to the rolling direction RD. In Figures 3A and 3B, the unit of the numerical values ​​is μm. As an example of analysis using the two-dimensional Fourier transform, we will explain how to derive the distribution of magnetic domain widths using the short-interval two-dimensional Fourier transform (hereinafter referred to as "ST2DFT"), which is an extension of the short-interval Fourier transform, one of the signal processing methods that has long been used for time-frequency analysis of audio signals, to a two-dimensional domain.

[0105] The image (magnetic domain image) represented by the image signal acquired by the image acquisition device 30 is denoted as x(k,l) as a data sequence in two-dimensional coordinates (kl coordinates). In this embodiment, the magnetic domain image to be analyzed is an image binarized with two colors, or an image represented with three or more gradations (multi-gradation), such as grayscale.

[0106] To derive the distribution of magnetic domain widths of the original plate 2, the calculation unit 41 performs the following processes (A-1), (A-2), and (A-3). (A-1) Processing to extract multiple subregions from a magnetic domain image; (A-2) Process to perform ST2DFT; (A-3) Process for deriving the distribution of magnetic domain widths. The following provides a detailed explanation of the processes described in A-1 to A-3.

[0107] (A-1) Process of extracting multiple subregions from a magnetic domain image To extract multiple subregions from a magnetic domain image and analyze their respective frequency structures, the range in the k-direction is defined as 0 ≤ k ≤ N k Set to -1, and define the range in the l direction as 0 ≤ l ≤ N lUse the window function Wa(k, l) of a rectangular window with -1 (N k and N l are natural numbers). As the window function Wa(k, l), a Hamming window, a Hanning window, a Blackman window, etc. can be applied.

[0108] Express the observation position in the data sequence x(k, l) of the magnetic domain image by the index (n, m), and let the shift amounts of the window function Wa(k, l) in the k - direction and the l - direction be S k and S l respectively. Then (n, m, S k , S l are integers), as shown in Equation (1), the data sequence x k nS ≤ k ≤ nS k +N k -1, mS l ≤ l ≤ mS l +N l -1 of the partial region cut out from the magnetic domain image is obtained. nm (k - nS k , l - mS l ).

[0109]

Number

[0110] Fig. 8 shows an example in which partial regions corresponding to observation positions (n, m) = (1, 1), (2, 2), (3, 3),..., (P, Q) (P and Q are natural numbers) are cut out from the magnetic domain image G.

[0111] In this embodiment, N k and N l defining the range of the window function Wa(k, l) are parameters corresponding to the number of pixels in the k - direction and the number of pixels in the l - direction in the partial region, respectively.

[0112] (A - 2) Process of performing ST2DFT Let the data sequence of the partial region be x nm (n´, m´)=x nm (k - nS k , l - mS l) defined as x nm When a two-dimensional Fourier transform is applied to (n', m'), a partial Fourier image X(f) corresponding to the subregion of the observation position (n, m) is obtained, as shown in equation (2). k ,f l ,n,m) is obtained.

[0113]

number

[0114] spatial frequency f k The resolution of Δf k , spatial frequency f l The resolution of Δf l When written as, Δf k and Δf l It is defined as shown in equation (3).

[0115]

number

[0116] For example, the data column x of each subregion shown in Figure 7 nm (k-nS k ,l-mS l When a two-dimensional Fourier transform is applied to ), as shown in Figure 8, a partial Fourier image X(f k ,f l ,n,m) is obtained.

[0117] (A-3) Process for deriving the distribution of magnetic domain widths Partial Fourier image X(f k ,f l When a partial Fourier image X(f, n, m) is obtained, k ,f l Coordinates of the peak position of the spot (k component f) kmax (n,m) and l component f l max (n,m) is determined. Regarding the derivation of the peak position, the region near k=0 and l=0 is excluded because it is highly dependent on the image contrast.

[0118] Then, from the spatial frequency resolution defined in equation (3) and the peak position of the spot in the partial Fourier image, the distribution of magnetic domain width L(n,m) is derived as shown in equation (4).

[0119]

number

[0120] Thus, by using ST2DFT, it becomes possible to quantitatively derive the distribution L(n,m) of the magnetic domain width while preserving the positional information of the magnetic domain image.

[0121] Once the calculation unit 41 derives the distribution of magnetic domain widths, it determines the region where the magnetic domain width is greater than or equal to a predetermined value as the processing region (i.e., the region to which magnetic domain control processing is applied). The control unit 513 of the laser irradiation device 500 controls the power of the laser beam LB to be turned on for the processing region, and preferably to be turned off for regions other than the processing region. As a result, magnetic domain control processing lines 11 are introduced into the processing region of the original plate. In other regions, the introduction of magnetic domain control processing lines 11 is suppressed.

[0122] The procedure described above can also be used to obtain a magnetic domain image of the grain-oriented electrical steel sheet 1 after magnetic domain control processing. In the magnetic domain image of the grain-oriented electrical steel sheet 1, the magnetic domain control processing lines 11 may be unclear. In this case, the observation conditions may be adjusted so that the magnetic domain control processing lines 11 can be clearly identified. For example, the magnetic domain control processing lines 11 can be made clearer by applying a DC magnetic field along the direction perpendicular to the surface of the grain-oriented electrical steel sheet 1 (thickness direction).

[0123] (Insulating film formation process) When forming an insulating film on the surface of a grain-oriented electrical steel sheet, the process may include an insulating film formation step in which the insulating film is formed by a known method after finish annealing. The insulating film formation step may be performed before the magnetic domain control processing line formation step or after the magnetic domain control processing line formation step, as long as it is performed after finish annealing. However, if the insulating film is formed before the magnetic domain control processing line formation step, the insulating film may peel off on the magnetic domain control processing line 11, so it is preferable to perform it after the magnetic domain control processing line formation step. If the insulating film formation step is performed before the magnetic domain control processing line formation step, it is preferable to re-form the insulating film on the magnetic domain control processing line 11 after the magnetic domain control processing line formation step. [Examples]

[0124] The effects of embodiments of the present invention will be further explained in detail by the examples. However, the conditions in the examples are merely one example of conditions adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to this one example of conditions. The present invention can adopt various conditions as long as it does not depart from the spirit of the invention and achieves the objectives of the present invention.

[0125] (Example 1) A grain-oriented electrical steel sheet with a thickness of 0.23 mm, classified as 23P085 in Table 2 of JIS C 2553:2019 "Grain-oriented electrical steel strips," was used as the base material. This grain-oriented electrical steel sheet consisted of a base steel sheet with a Si content of 3.40%, a forsterite coating, and an insulating coating. From this grain-oriented electrical steel sheet, grain-oriented electrical steel sheets No. 1 to No. 33 were cut out, and magnetic domain images were obtained from the surface of each grain-oriented electrical steel sheet. Based on the obtained magnetic domain images, regions in the grain-oriented electrical steel sheet with a magnetic domain width exceeding 500 μm were identified. Subsequently, magnetic domain control processing was performed on each grain-oriented electrical steel sheet (raw material) under various conditions. The procedure for forming the magnetic domain control lines is shown in Table 1. The direction, spacing, and type of the formed magnetic domain control lines are shown in Table 2. When the magnetic domain control lines consisted of grooves and thermal strains, their ratio was set to 1:1 in total length. For samples No. 31 and No. 32, as described above, regions with a magnetic domain width exceeding 500 μm were identified, and linear magnetic domain control lines including curves were formed. For sample No. 33, magnetic domain control lines were formed only in the region within ±4 mm of the center of each crystal grain in the rolling direction RD, with a spacing of 4 mm. The radius of curvature of the steel sheet at the location of the crystal grain during finish annealing was 250 mm.

[0126] When the magnetic domain control processing line was subjected to thermal strain, the maximum tensile stress in any direction along the magnetic domain control processing line was measured. The results are shown in Table 2. Furthermore, we determined whether non-magnetic domain control regions (regions more than 10 mm away from all magnetic domain control lines) existed in the grain-oriented electrical steel sheet after the formation of magnetic domain control lines. Furthermore, if a non-magnetic domain control region exists, |βDr|-|βNDr| was calculated. Furthermore, the average and maximum values ​​of the magnetic domain width in the magnetic domain control region were determined. The results are shown in Table 3.

[0127] Furthermore, the noise characteristics and iron loss of the magnetic domain-controlled grain-oriented electrical steel sheets were evaluated according to the following procedure. The results are shown in Table 3.

[0128] [Noise characteristics] A three-phase transformer core was fabricated by laminating 180 sheets of 0.23 mm thick grain-oriented electrical steel. The width of the legs and yoke of the three-phase transformer core was set to 150 mm. The height and width of the outer dimensions of the three-phase transformer core were both set to 750 mm. The noise and iron loss of these three-phase transformer cores were measured. The measurement conditions were a frequency of 50 Hz and an excitation magnetic flux density of 1.8 T.

[0129] For noise measurement, microphones were placed at equal intervals around the transformer containing the three-phase transformer core. The distance between the transformer and the microphones was 30 cm. The noise measurement results from these microphones were A-weighted and averaged to obtain the noise evaluation result (unit dBA) for the grain-oriented electrical steel sheet. Examples with a noise evaluation result of 43.50 dBA or less were judged to be examples where noise reduction was achieved.

[0130] [Iron loss] Iron loss was determined by measuring the primary and secondary voltages and currents with a power analyzer when excitation was performed at a frequency of 50 Hz and an excitation magnetic flux density of 1.8 T, as described above. Examples in which the iron loss evaluation result was 1.07 W / kg or less were judged to be examples in which low iron loss was achieved.

[0131] As shown in Tables 1 to 3, in the inventive example, a non-magnetic domain control region exists, and in the non-magnetic domain control region, |βDr|-|βNDr|≦-0.1° is satisfied, and both noise and iron loss are kept low. In particular, iron loss was lower when the domain width in the non-domain-controlled region was narrow. Also, noise was lower when the domain-controlled processing line was a groove. In contrast, in the comparative example, there was no non-magnetic domain control region, or if there was, the condition |βDr|-|βNDr|≦-0.1° was not satisfied in the non-magnetic domain control region. As a result, either or both of the noise and iron loss were high.

[0132] [Table 1]

[0133] [Table 2]

[0134] [Table 3]

[0135] (Example 2) A grain-oriented electrical steel sheet from the same lot with a thickness of 0.23 mm, classified as 23P085 in Table 2 of JIS C 2553:2019 "Grain-oriented electrical steel strip," was used as the base sheet. Magnetic domain control processing was performed on the base sheet while varying Ua, as shown in Table 4. The direction, spacing, and type of the formed magnetic domain control processing lines are shown in Table 5.

[0136] When the magnetic domain control processing line was subjected to thermal strain, the maximum tensile stress in any direction along the magnetic domain control processing line was measured. The results are shown in Table 5. Furthermore, we determined whether a non-domain-controlled region (a region more than 10 mm away from all of the domain-controlled lines) existed in the grain-oriented electrical steel sheet after the formation of the domain-controlled lines. If a non-domain-controlled region existed, we calculated |βDr|-|βNDr|. We also calculated the average and maximum domain widths of the domain-controlled region. Additionally, we calculated σ(D m ) 2 , D m(β<2) , D m(β≧2) , σ(TS m ) 2 , TS m(β<2) , TS m(β≧2) The result was calculated and is shown in Table 6.

[0137] Furthermore, the noise characteristics and iron loss of the magnetic domain-controlled grain-oriented electrical steel sheet were evaluated in the same manner as in Example 1. The results are shown in Table 6.

[0138] [Table 4]

[0139] [Table 5]

[0140] [Table 6]

[0141] As can be seen from Tables 4-6, in all examples, a non-magnetic domain control region exists, and in the non-magnetic domain control region, |βDr|-|βNDr|≦-0.1° is satisfied, and both noise and iron loss are kept low. Also, σ(D m ) 2 >3.0, D m(β<2) >D m(β≧2) , σ(TSm ) 2 >5.0, TS m(β<2) >TS m(β≧2) If one or more of the following conditions are met, iron loss and / or noise are further reduced. [Industrial applicability]

[0142] This disclosure provides grain-oriented electrical steel sheets that exhibit low iron loss and low noise levels when used in electrical products (excellent noise characteristics), as well as a method for manufacturing the same. Therefore, it has high potential for industrial application. [Explanation of Symbols]

[0143] 1 Grain-oriented electrical steel sheet 11 Magnetic Domain Control Processing Line 12 Magnetic domain control region 13 Non-magnetic domain control region RD (Rolling Direction) TD (Rolling direction perpendicular to the width of the sheet) ND (Direction normal to the rolling surface) 30 Image acquisition device 31 Light source section 33 MO Sensor 35 Image Sensors 37 Signal Processing Unit 40 Analyzer 41 Arithmetic section 43 memory 45 Display section 47 Input section 49 Communication I / F 301 Reflux Domain 302 Noise Ls line segment IP intersection 500 Laser Irradiation Devices 501 Polygon Mirror 503 Light source device 505 Collimator 507 Focusing lens 509 Motor 511 Sensor 513 Control Unit 515 Threading device

Claims

1. On the surface, Multiple magnetic domain control processing lines extending in directions intersecting the rolling direction, The magnetic domain control region is the area within 10 mm from the aforementioned magnetic domain control processing line, A non-magnetic domain control region is a region that is more than 10 mm away from all of the aforementioned magnetic domain control processing lines, Equipped with, The average value of the absolute values ​​of the β angles in the non-magnetic domain control region |βNDr| and the average value of the absolute values ​​of the β angles in the magnetic domain control region |βDr| satisfy the following equation (5): The aforementioned β angle is the angle of deviation of the crystal grain from the Goss orientation around the axis perpendicular to the rolling direction TD. Grain-oriented electrical steel sheet. |βDr|-|βNDr|≦-0.1° (5)

2. The average value of the magnetic domain width in the non-magnetic domain control region is 500 μm or less. The grain-oriented electrical steel sheet according to claim 1.

3. The maximum value of the magnetic domain width in the non-magnetic domain control region is 1000 μm or less. The grain-oriented electrical steel sheet according to claim 1.

4. The maximum value of the magnetic domain width in the non-magnetic domain control region is 1000 μm or less. The grain-oriented electrical steel sheet according to claim 2.

5. The plurality of magnetic domain control processing lines are grooves. A grain-oriented electrical steel sheet according to any one of claims 1 to 4.

6. The grain-oriented electrical steel sheet according to claim 5, characterized in that the maximum value of the groove depth in the magnetic domain control processing line is non-uniform at each measurement point of the groove depth.

7. When a square evaluation area is set on the surface, with one side having a length of 50 mm and one side parallel to the rolling direction, and further, virtual lines parallel to the rolling direction and with a length of 50 mm are set inside the evaluation area at 5 mm intervals perpendicular to the rolling direction, Each of the multiple intersections between the virtual line and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the maximum value of the depth of the groove in units of μm, measured at each of the magnetic domain subdivision points, is defined as D ｍ , the aforementioned D ｍ The variance of σ(D) ｍ ) ２ In that case, σ(D) ｍ ) ２ > Satisfying 3.0, The grain-oriented electrical steel sheet according to commodity 6.

8. When a square evaluation area with a side length of 50 mm and one side parallel to the rolling direction is set on the surface, and virtual lines parallel to the rolling direction and with a length of 50 mm are set within the evaluation area at 5 mm intervals perpendicular to the rolling direction, each of the multiple intersections between the virtual lines and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the arithmetic mean of the maximum value of the groove depth in units of μm measured at each of the magnetic domain subdivision points where the β angle is less than 2° is D ｍ（β＜２） D is the arithmetic mean of the maximum groove depth in units of μm, measured at each of the magnetic domain subdivision points where the β angle is 2° or more. ｍ（β≧２） In that case, D ｍ（β＜２） > D ｍ（β≧２） satisfying The grain-oriented electrical steel sheet according to commodity 6.

9. When a square evaluation area with a side length of 50 mm and one side parallel to the rolling direction is set on the surface, and virtual lines parallel to the rolling direction and with a length of 50 mm are set within the evaluation area at 5 mm intervals perpendicular to the rolling direction, each of the multiple intersections between the virtual lines and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the arithmetic mean of the maximum value of the groove depth in units of μm measured at each of the magnetic domain subdivision points where the β angle is less than 2° is D ｍ（β＜２） D is the arithmetic mean of the maximum groove depth in units of μm, measured at each of the magnetic domain subdivision points where the β angle is 2° or more. ｍ（β≧２） In that case, D ｍ（β＜２） >D ｍ（β≧２） Satisfying The grain-oriented electrical steel sheet according to feature 7.

10. The aforementioned multiple magnetic domain control processing lines are subjected to thermal strain in which a tensile stress of 40 MPa or more is introduced. A grain-oriented electrical steel sheet according to any one of claims 1 to 4.

11. In the magnetic domain control processing line, the maximum value of the tensile stress introduced into the thermal strain is non-uniform at each measurement point of the tensile stress. The grain-oriented electrical steel sheet according to feature 10.

12. When a square evaluation area is set on the surface, with one side having a length of 50 mm and one side parallel to the rolling direction, and further, virtual lines parallel to the rolling direction and with a length of 50 mm are set inside the evaluation area at 5 mm intervals perpendicular to the rolling direction, Each of the multiple intersections between the virtual line and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the maximum value of the tensile stress in units of MPa introduced into the thermal strain, measured at each of the magnetic domain subdivision points, is defined as TS ｍ , the TS ｍ The variance of σ(TS) ｍ ) ２ In that case, σ(TS) ｍ ) ２ > Satisfying 5.0, The grain-oriented electrical steel sheet according to feature 11.

13. When a square evaluation area with a side length of 50 mm and one side parallel to the rolling direction is set on the surface, and virtual lines parallel to the rolling direction and with a length of 50 mm are set within the evaluation area at 5 mm intervals perpendicular to the rolling direction, each of the multiple intersections between the virtual lines and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the arithmetic mean of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain subdivision points where the β angle is less than 2°, is defined as TS ｍ（β＜２） The arithmetic mean of the maximum tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or more, is TS ｍ（β≧２） In that case, TS ｍ（β＜２） >TS ｍ（β≧２） Satisfying The grain-oriented electrical steel sheet according to feature 11.

14. When a square evaluation area with a side length of 50 mm and one side parallel to the rolling direction is set on the surface, and virtual lines parallel to the rolling direction and with a length of 50 mm are set within the evaluation area at 5 mm intervals perpendicular to the rolling direction, each of the multiple intersections between the virtual lines and the multiple magnetic domain control processing lines is defined as a magnetic domain subdivision point, and the arithmetic mean of the maximum value of the tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain subdivision points where the β angle is less than 2°, is defined as TS ｍ（β＜２） The arithmetic mean of the maximum tensile stress in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or more, is TS ｍ（β≧２） In that case, TS ｍ（β＜２） >TS ｍ（β≧２） Satisfying The grain-oriented electrical steel sheet according to feature 12.

15. A magnetic domain image acquisition process for acquiring a magnetic domain image of the surface of a grain-oriented electrical steel sheet, A region identification step, based on the magnetic domain image obtained in the magnetic domain image acquisition step, identifies a region in the grain-oriented electrical steel sheet in which the magnetic domain width exceeds 500 μm. A magnetic domain control processing line formation process for forming magnetic domain control processing lines on the surface of a grain-oriented electrical steel sheet, Equipped with, The magnetic domain control processing line formation step comprises a magnetic domain control region which is within 10 mm of the magnetic domain control processing line, and a non-magnetic domain control region which is more than 10 mm away from all of the magnetic domain control processing lines, and the magnetic domain control processing line is formed in a region where the magnetic domain width is more than 500 μm such that the average value of the absolute values ​​of the β angles in the non-magnetic domain control region |βNDr| and the average value of the absolute values ​​of the β angles in the magnetic domain control region |βDr| are |βDr| - |βNDr| ≤ -0.1°, and the β angle is the deviation angle of the crystal grain from the Goss orientation around the axis perpendicular to the rolling direction TD. A method for manufacturing grain-oriented electrical steel sheets.

16. In the magnetic domain control processing line formation step, the magnetic domain control processing line is formed by irradiation with a laser or electron beam. A method for manufacturing grain-oriented electrical steel sheets according to claim 15.

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