Grain-oriented electrical steel sheet and manufacturing method therefor

Abstract

This grain-oriented electrical steel sheet has a plurality of magnetic domain control processing lines formed on a surface thereof, said magnetic domain control processing lines extending in a direction that intersects the rolling direction, wherein when a first magnetic domain image is a magnetic domain image of the surface, a second magnetic domain image is a magnetic domain image of the same location as the first magnetic domain image after the grain-oriented electrical steel sheet has been subjected to annealing in which the same is held at 800°C for 240 minutes or longer and cooled to 50°C or below at an average cooling speed of 25°C / h or less to 200°C and then 100°C / h or less thereafter, magnetized to a magnetic density of 1.9 T or greater by applying an AC magnetic field, and demagnetized by attenuating the AC magnetic field, a first region is a region in which the magnetic domain width derived from the second magnetic domain image is greater than the magnetic domain width derived from the first magnetic domain image by 100 μm or more, and a second region is a region other than the first region, the line density of the magnetic domain control processing lines in the second region in units of mm / mm2 is smaller than the line density of the magnetic domain control processing lines in the first region in units of mm / mm2.

Description

Grain-oriented electrical steel sheet and its manufacturing method

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof. This application claims priority to Japanese Patent Application No. 2023-166134, filed on September 27, 2023, the contents of which are incorporated herein by reference.

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

[0003] A technique for narrowing the magnetic domain width of grain-oriented electrical steel sheets (magnetic domain refinement technique by magnetic domain control treatment) has long been known to reduce iron loss. The magnetic domain width can be narrowed by irradiating the surface of the grain-oriented electrical steel sheet with a laser or electron beam in a direction intersecting the rolling direction to introduce thermal strain. The magnetic domain width can also be narrowed by forming grooves in the surface of the grain-oriented electrical steel sheet in a direction intersecting the rolling direction. Groove formation methods include laser or electron beam irradiation, mechanical processing such as gear machining, and chemical processing such as etching.

[0004] In recent years, various improved techniques for magnetic domain refining have been proposed in order to provide grain-oriented electrical steel sheets with good iron loss characteristics (see, for example, Patent Documents 1 to 3). Furthermore, Patent Document 4 proposes a low-iron-loss grain-oriented electrical steel sheet and an advantageous manufacturing method thereof that alleviates the problems of reduced magnetic permeability and increased magnetostriction caused by linear grooves and local strain for magnetic domain refining, since even when local strain is applied for magnetic domain refining, this strain can cause problems such as increased noise due to the reduced magnetic permeability and increased magnetostriction.

[0005] Japanese Patent Publication No. 2012-57219 Japanese Patent Publication No. 2012-12664 Japanese Patent Publication No. 2012-57218 Japanese Patent Publication No. H11-293340

[0006] When magnetic domain control treatment is applied to grain-oriented electrical steel sheet, the magnetostriction characteristics of the grain-oriented electrical steel sheet change due to the closure magnetic domains. This causes the noise characteristics of the grain-oriented electrical steel sheet to deteriorate. The noise characteristics refer to the level of noise generated by electrical products (e.g., transformers, motors, etc.) manufactured using grain-oriented electrical steel sheet as a material. Magnetostriction is a phenomenon in which the external shape of a ferromagnetic material is slightly deformed when it is magnetized. When grain-oriented electrical steel sheet is excited with an alternating current, the magnitude of magnetostriction changes with the change in the strength of the magnetization, causing vibration. The magnitude of this magnetostriction is 10 －６ Although the magnitude of the magnetostriction is very small, it generates vibrations in the iron core, which then propagate to external structures such as transformer tanks, resulting in noise. While magnetic domain control treatment is effective in reducing the iron loss of grain-oriented electrical steel sheets, it also worsens the noise characteristics of grain-oriented electrical steel sheets. In recent years, there has been an increasing demand for grain-oriented electrical steel sheets to reduce not only iron loss but also noise. However, no magnetic domain refining technology capable of sufficiently achieving both low noise and low iron loss has been proposed to date. Furthermore, Patent Document 4 mentions noise, but is unable to sufficiently achieve both low noise and low iron loss. Patent Document 4 discloses that the β angle near the center of the crystal grains in the rolling direction is on average 0°, and that by applying magnetic domain control treatment only to this region where magnetic domain control has a significant effect on iron loss reduction, both low noise and low iron loss can be achieved. However, there are also results showing that the magnetic domain width in each crystal grain is approximately the same within the grain, and the β angle near the center of the crystal grain in the rolling direction is not necessarily 0°. Therefore, even if magnetic domain control treatment is performed using the method disclosed in Patent Document 4, it is not possible to sufficiently achieve both low noise and low iron loss.

[0007] The present disclosure aims to provide a grain-oriented electrical steel sheet that has low iron loss (low iron loss) and produces little noise when used in electrical products (excellent noise characteristics), and a method for manufacturing the same.

[0008] The present inventors have conducted research into grain-oriented electrical steel sheets with low iron loss and excellent noise characteristics. As a result, they have found that while magnetic domain control treatment is effective in reducing the iron loss of grain-oriented electrical steel sheets, it also deteriorates the noise characteristics of the grain-oriented electrical steel sheets, and that providing non-magnetic domain control regions can suppress the deterioration of noise characteristics. The present invention was made in light of the above findings. [1] A grain-oriented electrical steel sheet according to one aspect of the present disclosure is a grain-oriented electrical steel sheet having a surface on which a plurality of magnetic domain control treatment lines extending in a direction intersecting the rolling direction are formed, wherein a magnetic domain image of the surface is a first magnetic domain image, and the sheet is annealed by holding the sheet at 800°C for 240 minutes or more, cooling to 200°C at an average cooling rate of 25°C / h or less down to 200°C and then at an average cooling rate of 100°C / h or less down to 50°C or less, applying an AC magnetic field to magnetize the sheet to a magnetic flux density of 1.9 T or more, and attenuating the AC magnetic field to demagnetize the sheet, and the magnetic domain image at the same position as the first magnetic domain image is a second magnetic domain image, and a region where the magnetic domain width derived from the second magnetic domain image is 100 μm or more larger than the magnetic domain width derived from the first magnetic domain image is defined as a first region, and the remaining region is defined as a second region. The units of the magnetic domain control treatment lines in the second region are mm / mm. ２ The linear density of the magnetic domain control processing line in the first region is expressed in mm / mm ２ [2] In the grain-oriented electrical steel sheet according to [1], the difference between the linear density of the magnetic domain control treated wires in the second region and the linear density of the magnetic domain control treated wires in the first region is 0.20 mm / mm ２or more. [3] In the grain-oriented electrical steel sheet according to [1] or [2], the plurality of magnetic domain control treatment lines may be thermally strained, or may have grooves and thermal strain. [4] In the grain-oriented electrical steel sheet according to any of [1] to [3], the plurality of magnetic domain control treatment lines may be thermally strained with a tensile stress of 40 MPa or more introduced. [5] A method for producing a grain-oriented electrical steel sheet according to another aspect of the present disclosure includes a first magnetic domain image acquisition step of acquiring a magnetic domain image of the surface of the grain-oriented electrical steel sheet before magnetic domain control treatment, a magnetic domain width distribution acquisition step of acquiring a distribution of magnetic domain widths in the grain-oriented electrical steel sheet based on the magnetic domain image before magnetic domain control treatment acquired in the first magnetic domain image acquisition step, a magnetic domain control treatment line formation step of forming magnetic domain control treatment lines on the surface of the grain-oriented electrical steel sheet, a second magnetic domain image acquisition step of acquiring a magnetic domain image of the surface of the grain-oriented electrical steel sheet on which the magnetic domain control treatment lines have been formed after magnetic domain control treatment, and a magnetic domain image acquisition step of comparing the magnetic domain image before magnetic domain control treatment and the magnetic domain image after magnetic domain control treatment. and, if necessary, an additional magnetic domain control treatment line forming step of forming a magnetic domain control treatment line on the surface of the grain-oriented electrical steel sheet after the magnetic domain image comparing step, wherein in the magnetic domain control treatment line forming step, the magnetic domain control treatment line is formed in a region where the magnetic domain width exceeds 500 μm based on the distribution of the magnetic domain width obtained in the magnetic domain width distribution acquiring step, and in the magnetic domain image comparing step, when a region where the magnetic domain width derived from the magnetic domain image before the magnetic domain control treatment is 100 μm or more larger than the magnetic domain width derived from the magnetic domain image after the magnetic domain control treatment is defined as a first region, and the other region is defined as a second region, the magnetic domain control treatment line in the second region is measured in mm / mm. ２ and the linear density in mm / mm of the magnetic domain control processing line in the first region. ２and in the additional magnetic domain control treatment line forming step, if the linear density of the second region is the same as or greater than the linear density of the first region, the magnetic domain control treatment line is formed in the first region, and the second magnetic domain image acquiring step, the magnetic domain image comparing step, and the additional magnetic domain control treatment line forming step are repeated until the linear density of the magnetic domain control treatment line in the second region becomes smaller than the linear density of the magnetic domain control treatment line in the first region.

[0009] According to the above aspects of the present disclosure, it is possible to provide a grain-oriented electrical steel sheet that has low iron loss (low iron loss) and produces little noise when made into an electrical product (excellent noise characteristics), and a method for manufacturing the same.

[0010] 3C is a schematic diagram showing an example of a grain-oriented electrical steel sheet according to the present embodiment; FIG. 3D is a schematic diagram showing an example of a grain-oriented electrical steel sheet according to the present embodiment; FIG. 3E is a graph showing the relationship between the magnetic domain width before laser irradiation and the magnetic domain width after laser irradiation; FIG. 3F is a diagram showing an example of the distribution of the magnetic domain width of a grain-oriented electrical steel sheet before magnetic domain refinement treatment; FIG. 3G is a diagram showing an example of the distribution of the magnetic domain width of a grain-oriented electrical steel sheet after magnetic domain refinement treatment; FIG. 3H is a diagram showing an example of a magnetic domain image acquired by an image acquisition device; FIG. 3I is a schematic diagram showing FIG. 3C;

[0011] A grain-oriented electrical steel sheet according to an embodiment of the present disclosure (grain-oriented electrical steel sheet according to the present embodiment) and a method for manufacturing the same will be described. As shown in FIG. 1A , the grain-oriented electrical steel sheet 1 according to the present embodiment is a grain-oriented electrical steel sheet having a plurality of magnetic domain control treatment lines 11 formed on its surface, the magnetic domain lines extending in a direction intersecting the rolling direction RD. Furthermore, in the grain-oriented electrical steel sheet 1 according to the present embodiment, a magnetic domain image of the surface is defined as a first magnetic domain image, and a magnetic domain image at the same position as the first magnetic domain image after annealing, magnetization, and demagnetization under predetermined conditions is defined as a second magnetic domain image. A region where the magnetic domain width derived from the second magnetic domain image is 100 μm or more larger than the magnetic domain width derived from the first magnetic domain image is defined as a first region 21, and the remaining region is defined as a second region 22. The units of the magnetic domain control treatment lines in the second region 22 are mm / mm. ２ The linear density of the magnetic domain control processing line in the first region 21 is expressed in mm / mm ２ The linear density is smaller than that at the temperature of 1000°C. As will be described later, the grain-oriented electrical steel sheet 1 according to this embodiment may have a forsterite coating and / or an insulating coating on the surface of the steel sheet that serves as the base steel sheet. Each of these will be explained below. However, when the grain-oriented electrical steel sheet has a base steel sheet and a forsterite coating and / or an insulating coating, the following specifications regarding the chemical composition, magnetic domain control treatment line, and magnetic domain width apply to the base steel sheet. However, the specifications regarding the sheet thickness apply to the entire grain-oriented electrical steel sheet, including the base steel sheet and the forsterite coating and / or the insulating coating.

[0012] [Grain-oriented electrical steel sheet] (Chemical composition) The chemical composition of the grain-oriented electrical steel sheet 1 is not limited, and may be the same as that of a known grain-oriented electrical steel sheet 1. For example, the grain-oriented electrical steel sheet 1 has the following chemical composition, in mass %, Si: 2.50 to 7.00%, Mn: 0 to 1.00%, C: 0 to 0.085%, acid-soluble Al: 0 to 0.065%, N: 0 to 0.012%, Cr: 0 to 0.300%, Cu: 0 to 0.400%, P: 0 to 0.500%, Sn: 0 to 0.300%, and Sb: 0 to 0.012%. 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 balance of the chemical composition includes Fe and impurities.

[0013] The chemical composition of the grain-oriented electrical steel sheet 1 may be measured by a general steel analysis method. For example, the chemical components may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, a test piece is obtained from the center of the sample in the thickness direction, and the chemical composition of the grain-oriented electrical steel sheet 1 is measured using a measuring device such as an ICPS-8100 manufactured by Shimadzu Corporation under conditions based on a pre-created calibration curve. The contents of C and S, which are difficult to measure using ICP-AES, may be measured using a combustion-infrared absorption method. The N content may be measured using an inert gas fusion-thermal conductivity method.

[0014] If a forsterite coating and / or an insulating coating is formed on the grain-oriented electrical steel sheet 1, the forsterite coating and / or the insulating coating can 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 dilute sulfuric acid and nitric acid. The temperature and concentration of the sodium hydroxide, dilute sulfuric acid, and nitric acid solutions, as well as the immersion time, are appropriately adjusted so as not to excessively dissolve the steel substrate of the sample. An example of the conditions for removing the insulating coating is as follows: First, the sample is immersed in a 20% sodium hydroxide solution at 80°C for 15 minutes. The sample is then dried. The sample is then immersed in a 10% dilute sulfuric acid solution at 80°C for 4 minutes. Sludge adhering to the surface of the sample is then removed with a rag or the like. The sample is then immersed in a 10% nitric acid solution at room temperature for approximately 10 seconds while being stirred. The forsterite film can be removed, for example, by immersing the sample in sulfuric acid and then in nitric acid. The conditions, such as the temperature and concentration of the sulfuric acid and nitric acid, and the immersion time, are adjusted appropriately so as not to excessively dissolve the base steel of the sample. An example of the conditions for removing the forsterite film is as follows: First, the sample is immersed in 10% sulfuric acid at 80°C for 3 minutes. Then, the surface of the sample is washed with water using a rag or the like to remove any sludge adhering to the surface. The sample is then dried. Next, the sample is immersed in 10% nitric acid at room temperature for approximately 5 seconds while stirring.

[0015] The thickness of the grain-oriented electrical steel sheet 1 is not limited, but is preferably 0.15 mm to 0.30 mm, for example. By setting the thickness to 0.30 mm or less, classical eddy current loss can be suppressed and iron loss can be further improved. On the other hand, by setting the thickness to 0.15 mm or more, rolling efficiency can be improved, thereby improving productivity.

[0016] (Magnetic Domain Control Treatment Lines 11) In the grain-oriented electrical steel sheet 1 according to this embodiment, multiple magnetic domain control treatment lines 11 extending in a direction intersecting the rolling direction are formed on the surface. The magnetic domain control treatment lines 11 provided on the surface of the grain-oriented electrical steel sheet 1 function to subdivide the 180° magnetic domains. Subdividing the magnetic domains can reduce the iron loss of the grain-oriented electrical steel sheet 1. A magnetic domain is a collection of magnetic dipoles present inside a ferromagnetic material, and is a small region in which the magnetic moments are aligned in one direction. A 180° magnetic domain is a magnetic domain whose magnetization direction is the <100> orientation of the crystal and is sandwiched between two 180° magnetic domain walls that are approximately parallel to the rolling direction RD. The distance between adjacent domain walls of a 180° magnetic domain (domain wall spacing) is referred to as the width of the 180° magnetic domain. Hereinafter, unless otherwise specified, the width of a 180° magnetic domain will be simply referred to as the "magnetic domain width."

[0017] The extension direction of the magnetic domain control process line 11 is not particularly limited as long as it intersects with the rolling direction (as long as it is not parallel to the rolling direction). The magnetic domain control process line 11 may be substantially perpendicular to the rolling direction RD (substantially parallel to the rolling-orthogonal direction TD). That is, the angle formed by the magnetic domain control process line 11 and the rolling-orthogonal direction TD may be substantially 0°. On the other hand, as exemplified in FIG. 1A , the angle formed by the magnetic domain control process line 11 and the rolling-orthogonal direction TD may be greater than 0°. For example, the angle formed by the magnetic domain control process line 11 and the rolling-orthogonal direction TD may be any value within the range of 0° to 45°. The angle formed by the magnetic domain control process line 11 and the rolling-orthogonal direction TD may be 1° or more, 3° or more, or 5° or more. The angle formed by the magnetic domain control processing line 11 and the direction perpendicular to the rolling direction TD may be 40° or less, 35° or less, or 30° or less.

[0018] 1A , the angles formed by all the magnetic domain control process lines 11 and the direction transverse to rolling TD may be the same. That is, all the magnetic domain control process lines 11 may extend parallel to one another. On the other hand, the angles formed by the magnetic domain control process lines 11 and the direction transverse to rolling TD may vary. That is, some or all of the multiple magnetic domain control process lines 11 may extend non-parallel to one another. The average value of the angles formed by the magnetic domain control process lines 11 and the direction transverse to rolling TD may be 1° or more, 3° or more, or 5° or more. The average value of the angles formed by the magnetic domain control process lines 11 and the direction transverse to rolling TD may be 40° or less, 35° or less, or 30° or less. The average value of the angle can be calculated by measuring the angle formed by one magnetic domain control treatment line with the transverse direction TD at multiple positions, or by measuring the angles formed by multiple magnetic domain control treatment lines with the transverse direction TD at one point or multiple positions and calculating the average value. Furthermore, as shown in Figure 1B, the magnetic domain control treatment line 11 may include a curved portion (i.e., may be composed of only straight lines), or may be interrupted halfway (i.e., may be formed across the entire width of the steel sheet).

[0019] At least a portion of the magnetic domain control treatment line 11 is thermally strained. Thermal strain disappears by stress relief annealing or a heat treatment equivalent thereto, and therefore the magnetic domain width changes before and after heat treatment under specified conditions. On the other hand, thermal strain may be used in combination with grooves or other magnetic domain control treatment lines. When the magnetic domain control treatment line 11 is a groove, the magnetic domain control treatment line 11 can be identified visually. When the grain-oriented electrical steel sheet 1 has an insulating coating, the insulating coating can be removed using a known stripping agent, thereby making the magnetic domain control treatment line 11 visible.

[0020] If the magnetic domain control treatment lines 11 are thermally strained, the magnetic domain control treatment lines 11 may not be identifiable visually. In this case, the location of the thermal strain can be identified by photographing a magnetic domain image using an image acquisition device 30 configured as shown in Fig. 4, for example, and observing the photographed magnetic domain image. When photographing, the magnetic domain image is photographed while applying a DC magnetic field along the normal direction ND of the rolled surface of the grain-oriented electrical steel sheet 1, as necessary.

[0021] (Spacing of magnetic domain control treatment lines 11 along the rolling direction RD) Among multiple magnetic domain control treatment lines 11, the spacing along the rolling direction RD between adjacent magnetic domain control treatment lines 11 is not particularly limited. The smaller the spacing, the greater the effect of improving (reducing) iron loss. On the other hand, the larger the spacing, the more improved the noise characteristics. The spacing can be appropriately selected depending on the characteristics required of the grain-oriented electrical steel sheet 1. For example, the spacing along the rolling direction RD between adjacent magnetic domain control treatment 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 spacing along the rolling direction RD between adjacent magnetic domain control treatment 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 between adjacent magnetic domain control processing lines 11 along the rolling direction RD may be constant or 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 intersections LP of the straight lines L and the magnetic domain control processing lines. To calculate the average spacing, multiple measurements of the distance between two adjacent points LP can be taken and the average of the measurements can be calculated.

[0022] The angle between the magnetic domain control processing line 11 and the direction transverse to the rolling direction TD can be measured using a known angle measuring means after the magnetic domain control processing line 11 and the direction transverse to the rolling direction TD are identified using the procedures described above and below.

[0023] The spacing of the magnetic domain control treatment lines 11 along the rolling direction RD can be measured using a known length measuring means after the magnetic domain control treatment lines 11 and the rolling direction RD have been identified by the procedures described above and below. Here, the spacing of the magnetic domain control treatment lines 11 along the rolling direction RD is the distance from the center of the width of one magnetic domain control treatment line in the rolling direction RD to the center of the width of an adjacent magnetic domain control treatment line in the rolling direction RD.

[0024] As described above, at least a portion of the magnetic domain control processing lines 11 is thermally strained. That is, the magnetic domain control processing lines 11 are thermally strained or other magnetic domain control processing lines such as thermally strained and grooves. The thermal strain can be formed by means of, for example, laser irradiation, electron beam irradiation, ion implantation, etc. The grooves can be formed by means of, for example, laser irradiation, electron beam irradiation, machining, etching, etc.

[0025] Furthermore, when the magnetic domain control treatment wire is thermally strained, it is preferable that tensile stress is introduced during 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 more improved the noise characteristics. The tensile stress can be appropriately selected according to the characteristics required of the grain-oriented electrical steel sheet 1. The magnitude of the tensile stress is not particularly limited, but for example, in at least a portion of the magnetic domain control treatment wire 11, the tensile stress in any direction is preferably 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, it is considered that the requirement of "tensile stress in any direction of 40 MPa or more" is satisfied. Furthermore, for example, in at least a portion of the magnetic domain control treatment wire 11, the tensile stress in any direction is preferably 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 treatment wire 11 may be uniform or may vary.

[0026] The magnitude of the tensile stress introduced by thermal strain is measured using the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage Corp. The EBSD Wilkinson method is described in detail in A. J. 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 the tensile stress induced by thermal strain using the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage, first, the magnetic domain control treatment line 11 is identified using the procedure described above. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control treatment line 11 and perpendicular to the magnetic domain control treatment line 11. This cut surface is used as the measurement surface. The cross section of the magnetic domain control treatment line 11 included in the measurement surface is analyzed using the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage, and tensile stress components in any direction are extracted and their magnitudes are measured. For example, tensile stress components can be extracted in the normal direction ND of the rolling surface, the direction parallel to the magnetic domain control treatment line 11, and the direction perpendicular to the normal direction ND of the rolling surface and the magnetic domain control treatment line 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 point in the grain-oriented electrical steel sheet 1 (i.e., if the tensile stress in at least one direction is 40 MPa or more), the maximum value of the tensile stress in any direction in the magnetic domain control treatment lines of the grain-oriented electrical steel sheet 1 is determined to be 40 MPa or more (multiple magnetic domain control treatment lines are thermal distortions into which a tensile stress of 40 MPa or more has been introduced). When a measurement point where the tensile stress in any direction is 40 MPa or more is found, the measurement of the tensile stress may be stopped.

[0027] The greater the groove depth and width of the magnetic domain control processing lines, the greater the effect of improving iron loss. On the other hand, the smaller the groove depth and width, the more improved the noise characteristics. The groove shape can be appropriately selected according to the characteristics required of the grain-oriented electrical steel sheet 1. The groove depth is not particularly limited, but is preferably 5 μm to 50 μm, for example. 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 10 μm to 300 μm, for example. The groove width may be specified as 20 μm or more, 30 μm or more, or 50 μm or more. The groove width may 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 may vary. When the depth and width vary, it is preferable that the average of the depth and width of the plurality of grooves is within the above range.

[0028] The depth and width of the groove can be measured by identifying 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 three-dimensional measurement of the sample surface is performed.

[0029] (Method for determining the rolling direction RD and the transverse direction TD) The rolling direction RD and the transverse direction TD of the grain-oriented electrical steel sheet 1 are determined by the following means. (1) When the sample is cut out from a coil-shaped grain-oriented electrical steel sheet 1, the width direction of the coil is considered to be the transverse direction TD. Also, the direction perpendicular to the transverse direction TD and the normal direction ND to the rolling surface is considered to be the rolling direction RD. (2) When the sample is cut out from a part of an electrical product, etc., the rolling direction RD and the transverse direction TD are determined from rolling defects on the surface of the grain-oriented electrical steel sheet 1. The extension direction of the rolling defects is considered to be the rolling direction RD. The direction perpendicular to the rolling direction RD and the normal direction ND to the rolling surface is considered to be the transverse direction TD. (3) When it is difficult to identify the rolling direction RD and the direction transverse to the rolling direction TD from the rolling defects on the surface of the grain-oriented electrical steel sheet 1, the rolling direction RD and the direction transverse to the rolling direction TD are identified 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 is measured at multiple points. Then, the direction in which the angle between the crystal orientation at the measurement point and the direction normal to the rolling surface ND (sheet thickness direction) is closest to a right angle and which has the smallest deviation angle from the axis of easy magnetization <001> is regarded as the rolling direction RD, and the direction perpendicular to the rolling direction RD and the direction normal to the rolling surface ND is regarded as the direction transverse to the rolling direction TD.

[0030] (Magnetic Domain Width) In the grain-oriented electrical steel sheet according to this embodiment, a magnetic domain image acquired from the surface is defined as a first magnetic domain image, and the grain-oriented electrical steel sheet is annealed by holding the temperature of 800°C for 240 minutes or more, cooling down to 200°C at an average cooling rate of 25°C / h or less and then cooling down to 50°C or less at an average cooling rate of 100°C / h or less, applying an AC magnetic field to the grain-oriented electrical steel sheet to magnetize it to a magnetic flux density of 1.9 T or more (magnetize it so that the magnetic flux density becomes 1.9 T), and then attenuating the AC magnetic field to demagnetize it. The magnetic domain image taken at the same position as the position where the first magnetic domain image was acquired is defined as a second magnetic domain image, and a region where the magnetic domain width derived from the second magnetic domain image is 100 μm or more larger than the magnetic domain width derived from the first magnetic domain image is defined as a first region, and the other region is defined as a second region. ２ ) is the linear density (mm / mm) of the magnetic domain control processing lines in the first region ２ ) is smaller than

[0031] As described above, the magnetic domain control treatment lines 11 provided on the surface of the grain-oriented electrical steel sheet 1 have the function of subdividing the 180° magnetic domains. Therefore, they are effective in reducing the iron loss of the grain-oriented electrical steel sheet. On the other hand, while magnetic domain control treatment is effective in reducing the iron loss of the grain-oriented electrical steel sheet, it also deteriorates the noise characteristics of the grain-oriented electrical steel sheet. Therefore, by providing non-magnetic domain control regions, the deterioration of noise characteristics can be suppressed. In other words, a good balance can be achieved between low noise and low iron loss.

[0032] Further investigations by the inventors revealed that, after analyzing the changes in magnetic domains in grain-oriented electrical steel sheets before and after magnetic domain control, there are regions where the magnetic domain width is narrowed by magnetic domain control and regions where it is barely narrowed. In other words, the inventors found that the magnetic domain refinement effect of magnetic domain control treatment varies depending on the magnetic domain width before magnetic domain control. More specifically, it was found that the magnetic domain refinement effect of magnetic domain control treatment is less apparent in regions with narrow magnetic domain widths. For example, as shown in Figure 2, in regions where the magnetic domain width before magnetic domain control is approximately 500 μm or less, the magnetic domain width is approximately the same before and after magnetic domain control treatment. In some cases, the magnetic domain refinement effect of magnetic domain control is considered to be almost nonexistent in regions where the magnetic domain width before magnetic domain control is approximately 500 μm or less. Based on these findings, it can be seen that preferentially performing magnetic domain control treatment on regions with wide magnetic domain widths is extremely effective in achieving both low iron loss and low noise. Magnetic domain control treatment in regions with wide magnetic domain widths can reduce iron loss. Since magnetic domain control treatment wires formed in narrow magnetic domain width regions are thought to cause deterioration of noise characteristics due to closure domains, minimizing magnetic domain control treatment in narrow magnetic domain width regions can prevent deterioration of noise characteristics. The grain-oriented electrical steel sheet according to this embodiment is a grain-oriented electrical steel sheet in which magnetic domain control treatment is selectively performed in wide magnetic domain width regions, which have a significant magnetic domain refinement effect, in order to minimize deterioration of noise characteristics while achieving iron loss reduction. While it is preferable to perform magnetic domain control treatment only in wide magnetic domain width regions, performing magnetic domain control treatment in narrow magnetic domain width regions is acceptable because the deterioration of noise characteristics is small if the proportion is small. Furthermore, while it is preferable to perform magnetic domain control treatment in all wide magnetic domain width regions, some regions may not be subjected to magnetic domain control treatment as long as the relationship between the line density of the magnetic domain control treatment wire after annealing under the above-mentioned specified conditions is satisfied.

[0033] However, in grain-oriented electrical steel sheets after magnetic domain control treatment, the magnetic domain width has narrowed even in areas where it was previously wide. This makes it difficult to directly determine whether magnetic domain control treatment has been performed only in areas where the magnetic domain refinement effect is significant (although this can be determined indirectly from noise characteristics and magnetic characteristics). On the other hand, in areas where the magnetic domain width was wide but narrowed by the formation of magnetic domain control treatment lines (by magnetic domain control), the effect of magnetic domain control disappears when heat treatment such as stress relief annealing is performed, and the magnetic domain width widens (returns to its original state). In contrast, in areas where the magnetic domain width was relatively narrow before the formation of magnetic domain control treatment lines, the magnetic domain width hardly widens even after heat treatment such as stress relief annealing. In other words, in grain-oriented electrical steel sheets that have not been subjected to stress relief annealing after the formation of magnetic domain control treatment lines, there is no difference in the magnetic domain width (it is narrower overall), so it is impossible to determine the magnetic domain width before the formation of magnetic domain control treatment lines. However, by subjecting this grain-oriented electrical steel sheet to stress relief annealing (or equivalent annealing), it is possible to determine whether the region had a wide magnetic domain width (a region where the magnetic domain refinement effect is large) or a narrow magnetic domain width (a region where the magnetic domain refinement effect by magnetic domain control is small) before the formation of the magnetic domain control treatment line.

[0034] Furthermore, by observing the change in magnetic domain width before and after stress relief annealing and the position where the magnetic domain control treatment lines were formed, it is possible to determine whether the magnetic domain control treatment lines were formed in a region where the magnetic domain refinement effect is large or in a region where the effect of magnetic domain refinement by magnetic domain control is small. In other words, it is possible to determine whether the grain-oriented electrical steel sheet has been subjected to magnetic domain control treatment to obtain the effect of reducing iron loss while minimizing the deterioration of noise characteristics.

[0035] The grain-oriented electrical steel sheet according to this embodiment is a grain-oriented electrical steel sheet that has been subjected to magnetic domain control treatment to obtain the effect of reducing iron loss while minimizing the deterioration of noise characteristics. Specifically, as described above, a magnetic domain image of the surface is taken as the first magnetic domain image, and annealing equivalent to stress relief annealing is performed in which the grain-oriented electrical steel sheet is held at 800°C for 240 minutes or more, and then cooled at an average cooling rate of 25°C / h or less to 200°C and then 100°C / h or less to 50°C or less, an AC magnetic field is applied to magnetize the steel sheet to a magnetic flux density of 1.9 T or more, and the AC magnetic field is attenuated to demagnetize the steel sheet, and the magnetic domain image at the same position as the first magnetic domain image is taken as the second magnetic domain image, and the region where the magnetic domain width derived from the second magnetic domain image is 100 μm or more larger than the magnetic domain width derived from the first magnetic domain image is taken as the first region, and the remaining region is taken as the second region. The unit of the magnetic domain control treatment line in the second region is mm / mm ２ The linear density of the magnetic domain control processing line in the first region is mm / mm ２ The fact that the linear density of the magnetic domain control processed lines in the second region is smaller than the linear density of the magnetic domain control processed lines in the first region means that the magnetic domain control processed lines are formed mainly in regions where the magnetic domain width is wide (regions where the magnetic domain refinement effect is large). Preferably, the difference between the linear density of the magnetic domain control processed lines in the second region and the linear density of the magnetic domain control processed lines in the first region is 0.20 mm / mm ２ or more (i.e., the linear density of the magnetic domain control processing lines in the second region - the linear density of the magnetic domain control processing lines in the first region ≦-0.20 mm / mm ２ In this case, the magnetic domain control processing lines are formed in areas with wider magnetic domain widths (areas with a greater magnetic domain refinement effect), which makes it possible to minimize the deterioration of noise characteristics while achieving a reduced iron loss effect.

[0036] The line density of the magnetic domain control processing lines in the first region is 0.05 mm / mm ２ It is preferable that the thickness is 0.10 mm / mm or more. ２ The line density of the magnetic domain control processing lines in the second region is more preferably 0.40 mm / mm ２ Preferably, it is 0.20 mm / mm or less. ２The line density of the magnetic domain control processing lines in the second region is more preferably 0.00 mm / mm or less. ２ That's fine too.

[0037] In regions where the magnetic domain width has expanded by 100 μm or more due to stress relief annealing, the magnetic domain control process has a certain degree of iron loss reduction effect.In addition, it is considered that the magnetic domain control process has little effect on reducing iron loss in regions where the magnetic domain width has expanded by less than 100 μm due to stress relief annealing and may worsen noise characteristics.Therefore, the region in which the magnetic domain width derived from the second magnetic domain image is 100 μm or more larger than the magnetic domain width derived from the first magnetic domain image is defined as the first region.

[0038] The magnetic domain width can be determined by the following method. For example, a sample with a side length of 100 mm (or 100 mm or more) can be cut out from the grain-oriented electrical steel sheet 1 and used for measurement. When the grain-oriented electrical steel sheet 1 is a coil, the sample can be taken from any location on the coil. Also, when the grain-oriented electrical steel sheet 1 is a component incorporated into an electrical product such as a transformer or motor, the sample can be taken from any location on the component. When the component is small, the length of one side of the sample can be less than 100 mm. In this case, the total sample area is 10,000 mm. ２The above is ensured. At this time, it is desirable to collect the sample by a method such as wire cutting to minimize the influence of mechanical strain on the sample. A magnetic domain image (first magnetic domain image) is acquired from this sample using an image acquisition device equipped with a light source, a magneto-optical sensor (MO sensor), an image sensor, and a signal processing unit. This magnetic domain image is output via a 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, a display unit, an input unit, and a communication I / F. The calculation unit analyzes the magnetic domain structure from the magnetic domain image using a line segment method. An example of measurement using the line segment method will be described. FIG. 3C is a magnetic domain image acquired using a CMOS-MagView manufactured by Matesy GmbH. FIG. 3D is a schematic diagram of FIG. 3C for explaining the measurement. In the line segment method, evaluation is performed by drawing a line segment Ls perpendicular to the magnetic domain. The line segments are drawn so that there are three lines per 1 cm in the rolling direction RD. The magnetic domain width is derived based on the distance w between the intersections Ip of the 180° domain wall and the line segment Ls. However, if there are closure domains 301 or noise 302, these are not counted as domain walls. To calculate the average magnetic domain width, the average distance is calculated from the length of each line segment Ls and the number of intersections Ip. The magnetic domain width of the second magnetic domain image of grain-oriented electrical steel sheet is measured by annealing the sample from which the first magnetic domain image was obtained by holding it at 800°C for 240 minutes or more, cooling it to 200°C at an average cooling rate of 25°C / h or less and then cooling it to 50°C or less at an average cooling rate of 100°C / h or less, applying an AC magnetic field to magnetize it to a magnetic flux density of 1.9 T or more, and then demagnetizing the sample by attenuating the AC magnetic field. A magnetic domain image (second magnetic domain image) is then acquired using an image acquisition device equipped with a light source, a magneto-optical sensor (MO sensor), an image sensor, and a signal processing unit. The magnetic domain width of this magnetic domain image can be measured in the same manner as described above.

[0039] By comparing the magnetic domain width derived from the obtained first magnetic domain image with the magnetic domain width derived from the second magnetic domain image, the first region and the second region can be defined.

[0040] The linear density of the first and second regions is determined by the following method: In the sample in which the magnetic domain width has been measured, the total length (mm) of the magnetic domain control processing lines included in the first and second regions is measured, and this is then converted into the area (mm) of each region. ２ It can be calculated by dividing by

[0041] Measurement of all of the above-mentioned parameters is performed 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 may be taken from any location on the coil. Also, if the grain-oriented electrical steel sheet 1 is a component incorporated into an electrical product such as a transformer or a motor, the sample may be taken from any location on the component. If the component is small, the length of one side of the sample may be reduced, provided that the total sample area remains the same. When taking the sample, it is desirable to take the sample by a method such as wire cutting in order to minimize the effects of mechanical distortion on the sample.

[0042] (Coating) The grain-oriented electrical steel sheet 1 may have a forsterite coating on its surface (i.e., the grain-oriented electrical steel sheet may be made 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 be made 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 may be made 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 or both sides of the grain-oriented electrical steel sheet 1.

[0043] The forsterite coating is an inorganic coating containing, for example, magnesium silicate as a main component. The forsterite coating is formed, for example, during finish annealing, by a reaction between an annealing separator containing magnesia (MgO) applied to the surface of the base steel sheet and the components of the surface of the base steel sheet. The forsterite coating has a composition derived from the components of the annealing separator and the base steel sheet (more specifically, Mg ２ SiO ４On the other hand, in the final annealing, ２ O ３ When an annealing separator containing mainly SiO 2 is used, the forsterite film may not be formed.

[0044] The insulating coating has the function of imparting electrical insulation and tension to the grain-oriented electrical steel sheet 1. By applying tension to the grain-oriented electrical steel sheet 1 and facilitating domain wall movement in the grain-oriented electrical steel sheet 1, it is possible to reduce iron loss in the grain-oriented electrical steel sheet 1. The insulating coating also provides the grain-oriented electrical steel sheet 1 with various properties such as corrosion resistance, heat resistance, and slip resistance. The insulating coating may be a known coating formed, for example, by applying a coating solution containing phosphate and colloidal silica as main components to the surface of a forsterite coating and baking it.

[0045] [Manufacturing Method] The grain-oriented electrical steel sheet according to this embodiment can achieve the effects described above, regardless of the manufacturing method. However, the following method is preferred because it allows stable manufacturing. That is, the grain-oriented electrical steel sheet according to this embodiment can be manufactured by a manufacturing method including the following steps (I) to (VI). (I) a first magnetic domain image acquisition step of acquiring a magnetic domain image of the surface of the grain-oriented electromagnetic steel sheet before magnetic domain control treatment, (II) a magnetic domain width distribution acquisition step of acquiring a distribution of magnetic domain widths in the grain-oriented electromagnetic steel sheet based on the magnetic domain image of before magnetic domain control treatment acquired in the first magnetic domain image acquisition step, (III) a magnetic domain control treatment line forming step of forming magnetic domain control treatment lines on the surface of the grain-oriented electromagnetic steel sheet, (IV) a second magnetic domain image acquisition step of acquiring a magnetic domain image of after magnetic domain control treatment on the surface of the grain-oriented electromagnetic steel sheet on which the magnetic domain control treatment lines have been formed, (V) a magnetic domain image comparison step of comparing the magnetic domain image of before magnetic domain control treatment with the magnetic domain image of after magnetic domain control treatment, and (VI) an additional magnetic domain control treatment line forming step of forming magnetic domain control treatment lines on the surface of the grain-oriented electromagnetic steel sheet after the magnetic domain image comparison step, as necessary. Each step will be described below.

[0046] First, the grain-oriented electrical steel sheet (original sheet) used in the first magnetic domain image acquisition step may be a known grain-oriented electrical steel sheet. For example, the original sheet may have the following chemical composition, in mass %, Si: 2.50 to 7.00%, Mn: 0 to 1.00%, C: 0 to 0.085%, acid-soluble Al: 0 to 0.065%, N: 0 to 0.012%, Cr: 0 to 0.300%, Cu: 0 to 0.400%, P: 0 to 0.500%, Sn: 0 to 0.300%, Sb: 0 to 0.300. %, Ni: 0 to 1.000%, S: 0 to 0.015%, Se: 0 to 0.015%, Bi: 0 to 0.020%, Nb: 0 to 0.030%, V: 0 to 0.030%, Mo: 0 to 0.030%, Ta: 0 to 0.030%, W: 0 to 0.030%, B: 0 to 0.080%, and Ti: 0 to 0.015%. The balance of the chemical composition includes Fe and impurities. The grain-oriented electrical steel sheet used as the base sheet may have a forsterite coating formed on the surface.

[0047] (First magnetic domain image acquisition process) In the first magnetic domain image acquisition process, a magnetic domain image of the surface of the grain-oriented electrical steel sheet before the magnetic domain control process is acquired. As will be described later, in the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment, the magnetic domain control process lines are formed so that the line density of the magnetic domain control process lines in the second region is smaller than the line density of the magnetic domain control process lines in the first region. At this time, it is necessary to determine the first region and the second region. Therefore, in the first magnetic domain image acquisition process, a magnetic domain image before the magnetic domain control process is acquired from the magnetic domain images used when determining the first region and the second region. The magnetic domain image can be acquired as described later.

[0048] (Magnetic domain width distribution acquisition process) In the magnetic domain width distribution acquisition process, the magnetic domain width distribution in the grain-oriented electrical steel sheet (the distribution of magnetic domain widths before forming the magnetic domain control treatment lines) is acquired based on the pre-magnetic domain image obtained in the first magnetic domain image acquisition process. Based on this distribution, the positions at which to form the magnetic domain control treatment lines can be determined in the magnetic domain control treatment line process, and when determining the first and second regions in the magnetic domain image comparison process described below, the magnetic domain width distribution derived from the reference pre-magnetic domain image can be obtained.

[0049] (Magnetic Domain Control Treatment Line Forming Process) In the magnetic domain control treatment line forming process, the magnetic domain control treatment lines are formed primarily in the regions identified in the region identification process where the magnetic domain width exceeds 500 μm, thereby forming multiple magnetic domain control treatment lines extending in a direction intersecting the rolling direction on the surface of the grain-oriented electrical steel sheet. As described above, the magnetic domain refinement effect is small in regions with narrow magnetic domain widths, and it is believed that the magnetic domain refinement effect due to magnetic domain control is hardly obtained in regions with magnetic domain widths of approximately 500 μm or less. Therefore, it is preferable not to perform magnetic domain control in these regions. It is preferable not to form magnetic domain control treatment lines in regions with magnetic domain widths of 500 μm or less, but this is acceptable as long as the proportion is small. Forming these magnetic domain control treatment lines can narrow the magnetic domain width in the vicinity thereof. However, this effect disappears when stress relief annealing is performed, so in regions where magnetic domain control treatment lines are formed due to thermal distortion, stress relief annealing widens the magnetic domain width.

[0050] At least a portion of the magnetic domain control treatment line is thermally strained. Thermal strain and other magnetic domain control treatments such as grooves may be used in combination. When thermal strain is used, the magnetic domain control treatment line is formed by irradiation with a laser or electron beam. The irradiation conditions may be within known ranges. When grooves are used, methods such as irradiation with a laser or electron beam, mechanical processing such as gears, and chemical processing such as etching may be used.

[0051] The direction in which the magnetic domain control treatment lines are formed (the scanning direction in the case of a laser, etc.), the spacing of the magnetic domain control treatment lines in the rolling direction RD, the width of the magnetic domain control treatment lines, and the depth of the grooves, if any, may be controlled by a known method so as to fall within the range of the grain-oriented electrical steel sheet according to this embodiment described above.

[0052] (Second magnetic domain image acquisition process) In the second magnetic domain image acquisition process, a post-magnetic domain control treatment magnetic domain image of the surface of the grain-oriented electrical steel sheet on which the magnetic domain control treatment lines have been formed is acquired. That is, of the magnetic domain images used when determining the first region and the second region, a post-magnetic domain control treatment magnetic domain image is acquired. The magnetic domain image can be acquired as described below. Furthermore, at this stage, the distribution of magnetic domain widths in the grain-oriented electrical steel sheet (the distribution of magnetic domain widths after the formation of the magnetic domain control treatment lines) may be acquired based on the acquired post-magnetic domain control treatment magnetic domain image.

[0053] (Magnetic domain image comparison step) In the magnetic domain image comparison step, when a region where the magnetic domain width derived from the magnetic domain image before the magnetic domain control processing is 100 μm or more larger than the magnetic domain width derived from the magnetic domain image after the magnetic domain control processing is defined as a first region, and the other region is defined as a second region, the magnetic domain control processing line in the second region is expressed in mm / mm. ２ and the unit of the magnetic domain control processing line in the first region is mm / mm ２ The linear density is calculated by measuring the total length (mm) of the magnetic domain control processing lines included in the first and second regions, and multiplying this by the area (mm) of each region. ２ The linear density is calculated by dividing by . If the linear density comparison shows that the linear density of the magnetic domain control processing lines in the second region is smaller than the linear density of the magnetic domain control processing lines in the first region, the next step, the additional magnetic domain control processing line forming step, does not need to be performed. On the other hand, if the linear density comparison shows that the linear density of the magnetic domain control processing lines in the second region is the same as or larger than the linear density of the magnetic domain control processing lines in the first region, the next step, the additional magnetic domain control processing line forming step, is performed.

[0054] (Additional magnetic domain control processing line forming process) In the additional magnetic domain control processing line forming process, if it is determined in the magnetic domain image comparison process that the line density of the magnetic domain control processing line in the second region is the same as or greater than the line density of the magnetic domain control processing line in the first region, further magnetic domain control processing lines are formed in the first region to increase the line density in the first region.

[0055] In the manufacturing method of the grain-oriented electrical steel sheet according to this embodiment, the line density of the magnetic domain control treatment lines in the second region is set to be smaller than the line density of the magnetic domain control treatment lines in the first region. However, at the stage of forming the magnetic domain control treatment lines, the distribution of the magnetic domain widths in the first and second regions after the magnetic domain control treatment lines are formed is unknown. Therefore, after forming the magnetic domain control treatment lines, magnetic domain images before and after the formation of the magnetic domain control treatment lines are compared to compare the line densities of the magnetic domain control treatment lines in the first and second regions. If the result shows that the line density of the magnetic domain control treatment lines in the second region is smaller than the line density of the magnetic domain control treatment lines in the first region, the process ends there. On the other hand, if the line density is not smaller than the line density of the magnetic domain control treatment lines in the first region, an additional magnetic domain control treatment line forming step is performed. Furthermore, after the additional magnetic domain control treatment line forming step, a magnetic domain image after the magnetic domain control treatment is acquired again on the surface of the grain-oriented electrical steel sheet on which the magnetic domain control treatment lines have been formed (submitted to the second magnetic domain image acquisition step). Then, the magnetic domain images before the formation of the magnetic domain control processing lines and after the additional magnetic domain control processing line forming step are compared, and the line densities of the magnetic domain control processing lines in the first and second regions are compared. If the result shows that the line density of the magnetic domain control processing lines in the second region is smaller than the line density of the magnetic domain control processing lines in the first region, the process ends there. On the other hand, if the line density of the magnetic domain control processing lines is not yet smaller than the line density of the magnetic domain control processing lines in the first region, the additional magnetic domain control processing line forming step is carried out again. That is, the second magnetic domain image acquisition step, the magnetic domain image comparison step, and the additional magnetic domain control processing line forming step are repeated until the line density of the magnetic domain control processing lines in the second region becomes smaller than the line density of the magnetic domain control processing lines in the first region. That is, as shown in Fig. 7, a predetermined grain-oriented electrical steel sheet may be obtained by S1 → S2 → S3 → S4 → S5, or by S1 → S2 → S3 → S4 → S5 → S6 → S4 → S5, or by S1 → S2 → S3 → S4 → S5 → S6 → S4 → S5 → S6 → S4 → S5. Furthermore, S4 → S5 → S6 may be repeated.

[0056] (Specific methods for acquiring magnetic domain images, acquiring magnetic domain width distributions, and forming magnetic domain control treatment lines) Acquiring magnetic domain images and acquiring magnetic domain width distributions can be performed using the following methods. A magnetic domain image of the surface can be acquired, for example, using an image acquisition device. Next, the distribution of 180° magnetic domain widths (magnetic domain widths) is derived from the magnetic domain image. The distribution of magnetic domain widths in the original sheet can be derived, for example, using an analysis device. From this magnetic domain width distribution, regions where the magnetic domain width is equal to or greater than a predetermined value (for example, if magnetic domain control treatment lines are to be formed in regions where the magnetic domain width exceeds 500 μm in a subsequent process, then greater than approximately 500 μm) can be determined as regions where magnetic domain control treatment should be performed (hereinafter sometimes simply referred to as treatment regions).

[0057] The processing region may be determined by the operator visually observing the magnetic domain image displayed on the display unit of the analysis device.

[0058] 4 shows an example of the hardware configuration of an image acquisition device 30 that acquires magnetic domain images of the original sheet (grain-oriented electrical steel sheet 1 before magnetic domain control processing). The image acquisition device 30 includes a light source unit 31, a magneto-optical sensor (MO sensor 33), an image sensor 35, and a signal processing unit 37.

[0059] The light source unit 31 has a light source made up of a light emitting diode (LED), and irradiates the MO sensor 33 with light having a uniform polarization plane.

[0060] 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 sample to be measured is placed. Light emitted from the light source unit 31 passes through the interior of the MO sensor 33 and is reflected by the reflective layer. The reflected light passes through the interior of the MO sensor 33 again and is output to the outside of the MO sensor 33. When an original plate, which is a magnetic sample, is placed on the observation surface of the MO sensor 33, a leakage magnetic field corresponding to the direction of spontaneous magnetization of the original plate is generated inside the MO sensor 33. This leakage magnetic field rotates the polarization plane of the reflected light.

[0061] 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 photoelectrically converted analog signal to the signal processing unit 37. By detecting the reflected light with a rotated polarization plane using the image sensor 35, the distribution of the leakage magnetic field can be obtained, and the magnetic domain structure of the original sheet can be clarified.

[0062] 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. This digital signal is subjected to predetermined digital processing using the DSP to generate an image signal. The image signal generated by the signal processing unit 37 is output to an analysis device 40 (see FIG. 5 ) via a cable or wireless communication.

[0063] 5 shows the hardware configuration of an analysis device 40 that analyzes the magnetic domain structure of a master sheet. The analysis device 40 is a computer device such as a personal computer (PC). The analysis device 40 includes a calculation unit 41, a memory 43, a display unit 45, an input unit 47, and a communication I / F 49.

[0064] The calculation unit 41 has a central processing unit (CPU). The calculation unit 41 analyzes the magnetic domain structure from the magnetic domain image of the original sheet in accordance with a program stored in the memory 43. The calculation unit 41 then determines a processing region where magnetic domain control processing is to be applied. The processing executed by the calculation unit 41 will be described in detail later.

[0065] The memory 43 includes a read-only memory (ROM) and a random access memory (RAM). The ROM stores programs executed by the CPU of the calculation unit 41 and data necessary for executing these programs. The programs and data stored in the ROM are loaded into the RAM and executed.

[0066] The memory 43 may include a magnetic memory such as a hard disk drive (HDD) or an optical memory such as an optical disk. Alternatively, the memory 43 may store programs and data in a computer-readable recording medium that is detachable from the analysis device 40. Alternatively, the memory 43 may receive the programs executed by the calculation unit 41 from a network via the communication I / F 49.

[0067] The display unit 45 has a display such as a liquid crystal display (LCD), a plasma display, or an organic electroluminescence (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 analysis results of the magnetic domain structure by the calculation unit 41.

[0068] The input unit 47 has input devices such as a mouse, a keyboard, etc. The communication I / F 49 is an interface for transmitting and receiving data to and from external devices via a network such as a local area network (LAN), a wide area network (WAN), or the Internet.

[0069] As the calculation unit 41, instead of general-purpose hardware such as a CPU, dedicated hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA) specialized for analyzing magnetic domain structures may be adopted.

[0070] 4 and 5 show the case where the image acquisition device 30 and the analysis device 40 are separate devices, a system in which the image acquisition device 30 and the analysis device 40 are integrated may also be employed.

[0071] As a means for introducing thermal strain into the surface of the original sheet, known means such as laser irradiation, electron beam irradiation, ion implantation, etc. As a means for forming grooves in the surface of the original sheet, known means such as laser irradiation, electron beam irradiation, mechanical processing, etc. The configuration of a laser irradiation device 500 that introduces thermal strain by laser irradiation will be described below.

[0072] 6 shows the configuration of the laser irradiation device 500. The laser irradiation device 500 includes a polygon mirror 501, a light source device 503, a collimator 505, a condenser lens 507, a motor 509, a sensor 511, a control unit 513, and a strip threading device 515.

[0073] The strip threading device 515 threads the original strip in the rolling direction RD.

[0074] The polygon mirror 501 has, for example, a regular polygonal prism shape. A plurality of plane mirrors are provided on each of the plurality of side surfaces constituting the regular polygonal prism-shaped polygon mirror 501. A laser beam LB is emitted from a light source device 503, passes through a collimator 505, and is incident on the plane mirror of the polygon mirror 501 in one direction (horizontal direction) and is reflected by the plane mirror.

[0075] The polygon mirror 501 can be rotated around a rotation axis O1 by being driven by a motor 509. The angle of incidence of the laser beam LB with respect to 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, enabling scanning of the surface of the original sheet. The symbol P in Figure 6 represents the interval between adjacent magnetic domain control processing lines 11, i.e., the irradiation pitch of the laser beam LB.

[0076] The light source device 503 outputs a laser beam LB in a predetermined irradiation method (for example, a continuous irradiation method or a pulse irradiation method) under the control of the control unit 513 .

[0077] The condenser lens 507 is provided in the optical path of the laser beam LB reflected from the polygon mirror 501. The condenser lens 507 constitutes a condensing optical system with a predetermined focal length. The laser beam LB reflected from the polygon mirror 501 is condensed onto the surface of the original sheet via the condenser lens 507, thereby introducing thermal distortion into the surface of the original sheet.

[0078] The motor 509 is connected to the polygon mirror 501. The motor 509 drives the polygon mirror 501 to rotate under the control of the control unit 513.

[0079] The sensor 511 is connected to the drive shaft of the motor 509. The sensor 511 detects the rotation angle of the polygon mirror 501 rotated by the motor 509. Furthermore, the sensor 511 outputs a signal indicating the detected rotation angle (hereinafter referred to as a rotation angle signal) to the control unit 513.

[0080] The control unit 513 is made up of a processor. The control unit 513 is connected to the light source device 503, the motor 509, the sensor 511, and the strip threading device 515. The control unit 513 receives a speed signal from the strip threading device 515. The control unit 513 also outputs a signal to the motor 509 to instruct the motor 509 to rotate the polygon mirror 501.

[0081] Furthermore, the control unit 513 controls the power of the laser beam LB output by the light source device 503 to be turned on and off based on a stress application signal representing the processing region and a rotation angle signal output from the sensor 511. When the laser irradiation device 500 is electrically connected to the analysis device 40, the stress application signal is input from the analysis device 40 to the laser irradiation device 500. The stress application signal may be input to the laser irradiation device 500 by an operator.

[0082] Next, an example of a method for determining the processing region will be described in detail. The process for specifying the processing region is executed by the calculation unit 41 of the analysis device 40, for example.

[0083] The calculation unit 41 derives the distribution of the magnetic domain width of the original sheet using, for example, a line segment method, and then determines regions where the magnetic domain width is equal to or greater than a predetermined value (for example, greater than approximately 500 μm) as locations where the magnetic domain control process should be applied preferentially.

[0084] In the line segment method, evaluation is performed by drawing line segments perpendicular to the magnetic domains. The line segments are drawn at intervals of three per centimeter in the direction parallel to the magnetic domains. The magnetic domain width is calculated based on the intervals between the intersections of the 180° domain walls and the line segments.

[0085] FIG. 3A shows an example of the distribution of magnetic domain widths of a grain-oriented electrical steel sheet 1 before magnetic domain control treatment, obtained by further analyzing a magnetic domain image acquired using a CMOS-MagView manufactured by Matesy GmbH using a two-dimensional Fourier transform. FIG. 3B shows the distribution of magnetic domain widths after magnetic domain control treatment was performed on the surface of the grain-oriented electrical steel sheet 1 of FIG. 3A , obtained in a manner similar to that of FIG. 3A . The magnetic domain control treatment here was performed by irradiating the surface with a continuous wave laser in a direction substantially perpendicular to the rolling direction RD. In FIGS. 3A and 3B , the units of values ​​are μm. As an example of analysis using two-dimensional Fourier transform, a method of deriving the distribution of magnetic domain widths using short-term two-dimensional Fourier transform (hereinafter referred to as "ST2DFT"), which is a signal processing method long used in the time-frequency analysis of audio signals, extended to a two-dimensional region, will be described.

[0086] The image (magnetic domain image) represented by the image signal acquired by the image acquisition device 30 is expressed as a data string of two-dimensional coordinates (k-l coordinates) as x(k, l). The magnetic domain image to be analyzed in this embodiment is an image binarized using two types of colors, or an image expressed in three or more gradations (multi-gradation), such as grayscale.

[0087] In order to derive the distribution of magnetic domain widths of the original sheet 2, the calculation unit 41 executes the following processes (A-1), (A-2), and (A-3): (A-1) Process of extracting multiple partial regions from the magnetic domain image; (A-2) Process of performing ST2DFT; (A-3) Process of deriving the distribution of magnetic domain widths. Processes A-1 to A-3 will be explained in detail below.

[0088] (A-1) Processing for extracting multiple partial regions from a magnetic domain image In order to extract multiple partial regions from a magnetic domain image and analyze the frequency structure of each partial region, the range in the k direction is set to 0≦k≦N. ｋ -1, and the range in the l direction is 0≦l≦N ｌ -1 is used as the rectangular window function Wa(k, l) (N ｋ and N ｌis a natural number). As the window function Wa(k, l), a Hamming window, a Hanning window, a Blackman window, or the like can be applied.

[0089] The observation position in the data sequence x(k, l) of the magnetic domain image is expressed by an index (n, m), and the shift amounts of the window function Wa(k, l) in the k direction and the l direction are respectively expressed as S ｋ and S ｌ When written as (n, m, S ｋ , S ｌ is an integer), and nS is calculated from the magnetic domain image as in equation (1). ｋ ≦k≦nS ｋ +N ｋ -1, mS ｌ ≦l≦mS ｌ +N ｌ Data string x of the partial region cut out from the range of -1 ｎｍ (k-nS ｋ , l-mS ｌ ) is obtained.

[0090]

[0091] Figure 8 shows an example in which partial regions corresponding to the 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.

[0092] In this embodiment, N which determines the range of the window function Wa(k, l) ｋ and N 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.

[0093] (A-2) Processing to perform ST2DFT The data sequence of the partial region is x ｎｍ (n', m') = x ｎｍ (k-nS ｋ , l-mS ｌ ) and x ｎｍ When a two-dimensional Fourier transform is performed on (n', m'), a partial Fourier image X(f ｋ , f ｌ , n, m) are obtained.

[0094] where f ｋ and f ｌ is the spatial frequency.

[0095] 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 is defined as in equation (3).

[0096] Here, Δk and Δl are the spatial resolutions in the k and l directions, respectively, of the magnetic domain image.

[0097] For example, the data string x of each partial region shown in FIG. ｎｍ (k-nS ｋ , l-mS ｌ ) is subjected to a two-dimensional Fourier transform, a partial Fourier image X(f ｋ , f ｌ , n, m) are obtained.

[0098] (A-3) Processing to derive the distribution of magnetic domain widths Partial Fourier image X(f ｋ , f ｌ , n, m) is obtained, the partial Fourier image X(f ｋ , f ｌ , n, m) ｋ ｍａｘ (n, m) and l component f ｌ ｍａｘ In deriving the peak position, the region near k=0, l=0 is excluded because it is a portion that is highly dependent on the contrast of the image.

[0099] Then, from the spatial frequency resolution defined by equation (3) and the peak positions of the spots in the partial Fourier image, the distribution L(n, m) of the magnetic domain width is derived as shown in equation (4).

[0100]

[0101] In this way, by using ST2DFT, it is possible to quantitatively derive the distribution L(n, m) of magnetic domain widths while maintaining the position information of the magnetic domain image.

[0102] When the calculation unit 41 derives the magnetic domain width distribution, the calculation unit 41 determines the region where the magnetic domain width is equal to or greater than a predetermined value as the processing region (i.e., the region to which the 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 on for the processing region, and preferably to be off for regions other than the processing region. This introduces the magnetic domain control processing lines 11 into the processing region of the original sheet. Furthermore, the introduction of the magnetic domain control processing lines 11 is suppressed in other regions.

[0103] The above-described procedure can also be used to obtain a magnetic domain image of the grain-oriented electrical steel sheet 1 after the magnetic domain control treatment. In some cases, the magnetic domain control treatment lines 11 are unclear in the magnetic domain image of the grain-oriented electrical steel sheet 1. In this case, the observation conditions may be adjusted so that the magnetic domain control treatment lines 11 can be clearly seen. For example, the magnetic domain control treatment lines 11 can be made clear by applying a DC magnetic field in the direction perpendicular to the sheet surface (thickness direction) of the grain-oriented electrical steel sheet 1.

[0104] (Insulating Coating Forming Step) When forming an insulating coating on the surface of the grain-oriented electrical steel sheet, an insulating coating forming step may be performed after the finish annealing by forming the insulating coating by a known method. The insulating coating forming step may be performed before or after the magnetic domain control treatment line forming step, as long as it is performed after the finish annealing. However, if the insulating coating is formed before the magnetic domain control treatment line forming step, the insulating coating may peel off from the magnetic domain control treatment line 11, so it is preferable to perform it after the magnetic domain control treatment line forming step. When the insulating coating forming step is performed before the magnetic domain control treatment line forming step, it is preferable to form an insulating coating again on the magnetic domain control treatment line 11 after the magnetic domain control treatment line forming step.

[0105] The effects of the embodiments of the present invention will be explained more specifically using examples. However, the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to these examples. Various conditions may be adopted as long as they do not deviate from the gist of the present invention and achieve the object of the present invention. Grain-oriented electrical steel sheets from the same lot, each with a thickness of 0.20 mm, were used as base sheets. These grain-oriented electrical steel sheets had a base steel sheet containing 3.40% Si, a forsterite coating, and an insulating coating. Grain-oriented electrical steel sheets No. 1 to No. 35 were cut from these grain-oriented electrical steel sheets, and magnetic domain images (magnetic domain images before magnetic domain control treatment) of the surface of each grain-oriented electrical steel sheet were obtained. Furthermore, based on the obtained magnetic domain images, the distribution of magnetic domain widths in the grain-oriented electrical steel sheets was obtained, and regions with magnetic domain widths exceeding 500 μm were identified. Subsequently, magnetic domain control treatment was performed on each grain-oriented electrical steel sheet (base sheet) under various conditions. The procedure for forming the magnetic domain control treatment lines is shown in Table 1. The direction, spacing and type of the magnetic domain control processing lines formed were as shown in Table 2. When thermal distortion and grooves were formed, the ratio was approximately 1:1 in total length.

[0106] Thereafter, a magnetic domain image (a magnetic domain image after magnetic domain control treatment) of the surface of the grain-oriented electrical steel sheet after the formation of the magnetic domain control treatment lines was obtained, and the distribution of the magnetic domain width was obtained from this magnetic domain image. Using the magnetic domain image before magnetic domain control treatment and the magnetic domain image after magnetic domain control treatment, a region that is 100 μm or more larger than the magnetic domain width derived from the magnetic domain image after magnetic domain control treatment was defined as a first region, and the other region was defined as a second region. The unit of the magnetic domain control treatment lines in the second region was mm / mm. ２ and the linear density in mm / mm of the magnetic domain control processing line in the first region. ２ The linear density in the second region was compared with that in the first region. As a result of the comparison, the relationship between the linear density in the second region and the linear density in the first region is shown in Table 1. In the table, OK indicates that the linear density in the second region is smaller than that in the first region, and NG indicates that the linear density in the second region is larger than that in the first region or is the same as that in the first region.

[0107] Next, in some examples, further magnetic domain control processing lines were formed (formation of additional magnetic domain control processing lines). In this case, magnetic domain control processing lines were formed in the first region. Furthermore, for the examples in which these additional magnetic domain control processing lines were formed, the linear densities of the first and second regions were compared. As a result of the comparison, the relationship between the linear density of the second region and the linear density of the first region is shown in Table 1. In the table, OK indicates that the linear density of the second region is smaller than the linear density of the first region, and NG indicates that the linear density of the second region is greater than the linear density of the first region or that the linear density of the second region is the same as the linear density of the first region.

[0108] In this way, grain-oriented electrical steel sheets were produced.

[0109] For the obtained grain-oriented electrical steel sheet, when the magnetic domain control treatment line was thermally strained, the maximum value of tensile stress in any direction in the magnetic domain control treatment line was measured. The results are shown in Table 2. Furthermore, a 100 mm x 100 mm sample was taken from the obtained grain-oriented electrical steel sheet, and a first magnetic domain image of the surface of this sample was obtained using an image acquisition device equipped with a light source, a magneto-optical sensor (MO sensor), an image sensor, and a signal processing unit, and the magnetic domain width and linear density of the magnetic domain control treatment line were measured. Furthermore, this sample was annealed by holding it at 800°C for 240 minutes, cooling it to 200°C at an average cooling rate of 25°C / h and then 100°C / h to 50°C, applying an AC magnetic field to magnetize it to a magnetic flux density of 1.9 T (so that the magnetic flux density was 1.9 T), and then demagnetizing it by attenuating the AC magnetic field. Thereafter, a second magnetic domain image was obtained for this sample in the same manner as for the first magnetic domain image, and the magnetic domain width and linear density of the magnetic domain control treatment line were measured. The results are shown in Table 3.

[0110] The noise characteristics and iron loss of the obtained grain-oriented electrical steel sheets were evaluated as follows. The results are shown in Table 3.

[0111] [Noise characteristics] The noise characteristics and iron loss were evaluated as follows. 205 of the obtained grain-oriented electrical steel sheets, each with a thickness of 0.20 mm, were stacked to produce a three-phase transformer core. During production, the widths of the legs and yoke of the three-phase transformer core were both 150 mm. The height and width of the three-phase transformer core's outer shape were both 750 mm. The noise and iron loss of these three-phase transformer cores were measured. The measurement conditions were a frequency of 60 Hz and an excitation magnetic flux density of 1.7 T.

[0112] To measure the noise, microphones were placed at equal intervals around eight locations around the transformer incorporating 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 corrected and averaged to obtain a value that was used as the noise evaluation result (unit: dBA) for the grain-oriented electrical steel sheet. Examples with a noise evaluation result of 37.00 dBA or less were determined to be examples in which low noise was achieved.

[0113] [Iron Loss] The iron loss was determined by measuring the voltage and current on the primary and secondary sides with a power analyzer when excitation was performed at a frequency of 60 Hz and an excitation magnetic flux density of 1.7 T, as described above. The determined iron loss is shown in Table 3 as the iron loss evaluation results (unit: W / kg) of the grain-oriented electrical steel sheet. Examples with an iron loss evaluation result of 1.03 W / kg or less were determined to be examples in which low iron loss was achieved.

[0114] As shown in Tables 1 to 3, in the inventive examples, the linear density of the second region was smaller than that of the first region, and both iron loss and noise were kept low. Iron loss was lower especially when the difference between the linear density of the second region and that of the first region was large. Furthermore, noise was lower when the magnetic domain control processing lines were grooves and thermal distortion. On the other hand, in the comparative examples, the linear density of the second region was not smaller than that of the first region, and one or both of iron loss and noise were higher.

[0115]

[0116]

[0117]

[0118] According to the present disclosure, it is possible to provide a grain-oriented electrical steel sheet that has low iron loss (low iron loss) and produces low noise when used in electrical products (excellent noise characteristics), and a method for manufacturing the same, which is therefore highly industrially applicable.

[0119] REFERENCE SIGNS LIST 1 Grain-oriented electrical steel sheet 11 Magnetic domain control treatment line 21 First region 22 Second region RD Rolling direction TD Direction perpendicular to rolling (sheet width direction) ND Normal direction to rolling surface 30 Image acquisition device 31 Light source unit 33 MO sensor 35 Image sensor 37 Signal processing unit 40 Analysis device 41 Calculation unit 43 Memory 45 Display unit 47 Input unit 49 Communication I / F 301 Closure domain 302 Noise Ls Line segment Ip Intersection 500 Laser irradiation device 501 Polygon mirror 503 Light source device 505 Collimator 507 Condenser lens 509 Motor 511 Sensor 513 Control unit 515 Sheet threading device

Claims

1. A grain-oriented electrical steel sheet having a surface on which a plurality of magnetic domain control processing lines extending in a direction intersecting the rolling direction are formed, wherein a magnetic domain image of the surface is a first magnetic domain image, and a magnetic domain image at the same position as the first magnetic domain image after annealing at 800°C for 240 minutes or more, followed by cooling to 50°C or less at an average cooling rate of 25°C / h or less until 200°C and then 100°C / h or less, magnetizing to a magnetic flux density of 1.9 T or more by applying an AC magnetic field, and demagnetizing by attenuating the AC magnetic field is a second magnetic domain image, and a region where the magnetic domain width derived from the second magnetic domain image is 100 μm or more larger than the magnetic domain width derived from the first magnetic domain image is a first region, and the remaining region is a second region, the unit of the magnetic domain control processing lines in the second region is mm / mm ２ The linear density of the magnetic domain control processing line in the first region is expressed in mm / mm ２ It has a linear density smaller than that of grain-oriented electrical steel.

2. The difference between the line density of the magnetic domain control processing line in the second region and the line density of the magnetic domain control processing line in the first region is 0.20 mm / mm ２ The grain-oriented electrical steel sheet according to claim 1 .

3. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the plurality of magnetic domain control treatment lines are thermal distortion, or grooves and thermal distortion.

4. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the plurality of magnetic domain control treatment lines are thermally strained to which a tensile stress of 40 MPa or more has been introduced.

5. A method for manufacturing a grain-oriented electromagnetic steel sheet comprising: a first magnetic domain image acquisition step of acquiring a magnetic domain image of the surface of the grain-oriented electromagnetic steel sheet before magnetic domain control treatment; a magnetic domain width distribution acquisition step of acquiring a distribution of magnetic domain widths in the grain-oriented electromagnetic steel sheet based on the magnetic domain image of the surface of the grain-oriented electromagnetic steel sheet before magnetic domain control treatment acquired in the first magnetic domain image acquisition step; a magnetic domain control treatment line forming step of forming a magnetic domain control treatment line on the surface of the grain-oriented electromagnetic steel sheet; a second magnetic domain image acquisition step of acquiring a magnetic domain image of the surface of the grain-oriented electromagnetic steel sheet after the magnetic domain control treatment line has been formed; a magnetic domain image comparison step of comparing the magnetic domain image before magnetic domain control treatment with the magnetic domain image after magnetic domain control treatment; and, as necessary, an additional magnetic domain control treatment line forming step of further forming a magnetic domain control treatment line on the surface of the grain-oriented electromagnetic steel sheet after the magnetic domain image comparison step, wherein in the magnetic domain control treatment line forming step, the magnetic domain control treatment line is formed in an area where the magnetic domain width exceeds 500 μm based on the distribution of the magnetic domain width acquired in the magnetic domain width distribution acquisition step, In the magnetic domain image comparison step, a region in which the magnetic domain width derived from the magnetic domain image before the magnetic domain control processing is 100 μm or more larger than the magnetic domain width derived from the magnetic domain image after the magnetic domain control processing is defined as a first region, and the other region is defined as a second region, and the unit of the magnetic domain control processing line in the second region is mm / mm ２ and the unit of the magnetic domain control processing line in the first region is mm / mm ２ and in the additional magnetic domain control processing line forming step, if the line density of the second region is the same as or greater than the line density of the first region, forming the magnetic domain control processing line in the first region, and repeating the second magnetic domain image acquiring step, the magnetic domain image comparing step, and the additional magnetic domain control processing line forming step until the line density of the magnetic domain control processing line in the second region becomes smaller than the line density of the magnetic domain control processing line in the first region.

6. The method for producing grain-oriented electrical steel sheet according to claim 5, wherein in the magnetic domain control treatment line forming step, the magnetic domain control treatment line is formed by irradiating with a laser or an electron beam.

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