Grain-oriented electrical steel sheet and method for manufacturing same

Abstract

This grain-oriented electrical steel sheet is provided with, on the surface thereof, a plurality of magnetic domain control processing lines that extend in a direction intersecting the rolling direction. When a square evaluation region in which the length of one side is 50 mm and one side is parallel to the rolling direction is set on the surface, and imaginary lines that are parallel to the rolling direction and that have a length of 50 mm are set inside the evaluation region at 5 mm intervals in a direction perpendicular to the rolling direction, in at least one of the imaginary lines, the maximum value of the spacing, in the rolling direction, between adjacent intersections from among the plurality of intersections between the imaginary line and the plurality of magnetic domain control processing lines is over 20 mm, and the average value of the magnetic domain width measured along the imaginary line is 600 μm or below.

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 based on Japanese Patent Application No. 2023-166097, 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 relating to magnetic domain refinement 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).

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

[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 it is only on the order of magnitude, this magnetostriction generates vibrations in the iron core, which then propagate to external structures such as transformer tanks and cause noise. While magnetic domain control treatment is effective in reducing the iron loss of grain-oriented electrical steel sheets, it also worsens their noise characteristics. In recent years, there has been an increasing demand for grain-oriented electrical steel sheets to not only reduce iron loss, but also reduce noise. However, no magnetic domain refining technology has been proposed to date that can adequately 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 investigated methods for reducing iron loss while suppressing deterioration of noise characteristics, and have found that by widening the intervals between magnetic domain control treatments in at least some specific regions, it is possible to obtain a grain-oriented electrical steel sheet with low iron loss and excellent noise characteristics.

[0009] The present disclosure has been made in light of the above findings. The gist of the present disclosure is as follows. [1] A grain-oriented electrical steel sheet according to one aspect of the present disclosure includes, on a surface thereof, a plurality of magnetic domain control treatment lines extending in a direction intersecting the rolling direction, and a square evaluation area is defined on the surface, with one side 50 mm long and one side parallel to the rolling direction. Furthermore, within the evaluation area, imaginary lines parallel to the rolling direction and 50 mm long are defined at 5 mm intervals in a direction perpendicular to the rolling direction. In this case, for at least one of the imaginary lines, among a plurality of intersections between the imaginary line and the plurality of magnetic domain control treatment lines, the maximum distance in the rolling direction between adjacent intersections exceeds 20 mm, and the average magnetic domain width measured along the imaginary line is 600 μm or less. [2] In the grain-oriented electrical steel sheet according to [1], the average magnetic domain width measured along the imaginary lines may be 500 μm or less. [3] In the grain-oriented electrical steel sheet according to [1], for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm, the average value of the magnetic domain width measured along the imaginary line may be 600 μm or less. [4] In the grain-oriented electrical steel sheet according to any of [1] to [3], for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm, the average value of the magnetic domain width measured along the imaginary line may be 500 μm or less. [5] In the grain-oriented electrical steel sheet according to any of [1] to [4], the maximum value of the spacing in the rolling direction may be more than 30 mm. [6] A grain-oriented electrical steel sheet according to another aspect of the present disclosure includes, on a surface thereof, a plurality of magnetic domain control treatment lines extending in a direction intersecting the rolling direction, and a square evaluation area is set on the surface, with one side 50 mm long and one side parallel to the rolling direction, and further, within the evaluation area, imaginary lines parallel to the rolling direction and 50 mm long are set at 5 mm intervals in a direction perpendicular to the rolling direction, wherein, for at least one of the imaginary lines, among a plurality of intersections between the imaginary line and the plurality of magnetic domain control treatment lines, the maximum value of the distance in the rolling direction between adjacent intersections exceeds 20 mm, and the maximum value of the magnetic domain width measured along the imaginary line is 1200 μm or less.[7] In the grain-oriented electrical steel sheet according to [6], the maximum value of the magnetic domain width measured along the imaginary line may be 800 μm or less. [8] In the grain-oriented electrical steel sheet according to [6], the maximum value of the magnetic domain width measured along the imaginary line may be 1200 μm or less for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm. [9] In the grain-oriented electrical steel sheet according to any of [6] to [8], the maximum value of the magnetic domain width measured along the imaginary line may be 800 μm or less for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm.

[10] In the grain-oriented electrical steel sheet according to any of [6] to [9], the maximum value of the spacing in the rolling direction may exceed 30 mm.

[11] In the grain-oriented electrical steel sheet according to any of [1] to

[10] , the multiple magnetic domain control treatment lines may be grooves.

[12] In the grain-oriented electrical steel sheet according to any one of [1] to

[10] , the plurality of magnetic domain control treatment lines may be thermally strained.

[13] A method for producing a grain-oriented electrical steel sheet according to another aspect of the present disclosure is the method for producing a grain-oriented electrical steel sheet according to any one of [1] to [9], comprising: a magnetic domain image acquisition step of acquiring a magnetic domain image of the surface of the grain-oriented electrical steel sheet; a region identification step of identifying regions in the grain-oriented electrical steel sheet where a magnetic domain width exceeds 500 μm based on the magnetic domain image acquired in the magnetic domain image acquisition step; and a magnetic domain control treatment line forming step of forming magnetic domain control treatment lines on the surface of the grain-oriented electrical steel sheet after the region identification step, wherein in the magnetic domain control treatment line forming step, the magnetic domain control treatment lines are formed in the regions where the magnetic domain width exceeds 500 μm.

[14] In the method for producing a grain-oriented electrical steel sheet according to

[13] , the magnetic domain control treatment line forming step may form the magnetic domain control treatment lines by irradiation with a laser or an electron beam.

[0010] 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.

[0011] 3C is a schematic diagram illustrating an example of a grain-oriented electrical steel sheet according to the present embodiment. FIG. 3D is a schematic diagram illustrating an example of a grain-oriented electrical steel sheet according to the present embodiment. FIG. 3E is a schematic diagram illustrating an example of a grain-oriented electrical steel sheet according to the present embodiment. FIG. 3F is a graph illustrating the relationship between the magnetic domain width before laser irradiation and the magnetic domain width after laser irradiation. FIG. 3G is a diagram illustrating an example of the distribution of the magnetic domain width of a grain-oriented electrical steel sheet before magnetic domain refinement treatment. FIG. 3H is a diagram illustrating an example of the distribution of the magnetic domain width of a grain-oriented electrical steel sheet after magnetic domain refinement treatment. FIG. 3I is a diagram illustrating an example of a magnetic domain image acquired by an image acquisition device. FIG. 3I is a schematic diagram illustrating FIG. 3C. FIG. 3H is a block diagram illustrating an example of the hardware configuration of an image acquisition device. FIG. 3I is a block diagram illustrating an example of the hardware configuration of an analysis device. FIG. 3I is a schematic diagram illustrating an example of the configuration of a laser irradiation device. FIG. 3I is a schematic diagram illustrating a method of extracting multiple partial regions from a magnetic domain image of a grain-oriented electrical steel sheet. FIG. 3I is an example of multiple partial Fourier images obtained by applying a two-dimensional Fourier transform to each of multiple partial regions extracted from the magnetic domain image of the grain-oriented electrical steel sheet.

[0012] 1A , a grain-oriented electrical steel sheet 1 according to the present embodiment includes, on its surface, a plurality of magnetic domain control treatment lines 11 extending in a direction intersecting the rolling direction RD, and a square evaluation area is set on the surface, with one side 50 mm long and one side parallel to the rolling direction RD. Furthermore, within the evaluation area, virtual lines VL, each 50 mm long and parallel to the rolling direction RD, are set at 5 mm intervals in a direction perpendicular to the rolling direction RD. In at least one (preferably two or more) virtual line VL, among a plurality of intersections VP between the virtual line VL and the plurality of magnetic domain control treatment lines 11, the maximum distance (dmax) between adjacent intersections in the rolling direction RD (d1 to d7) exceeds 20 mm (preferably exceeds 30 mm). Furthermore, the average magnetic domain width measured along the virtual line VL is 600 μm or less, or the maximum magnetic domain width is 1200 μm or less. As will be described later, the grain-oriented electrical steel sheet according to this embodiment may have a forsterite coating and / or an insulating coating on the surface of the steel sheet that serves as the base steel sheet. Each of these will be described 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, intersection spacing, 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.

[0013] [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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] (Magnetic Domain Control Processing Lines 11) The multiple magnetic domain control processing 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."

[0018] 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-perpendicular direction TD). That is, the angle formed by the magnetic domain control process line 11 and the rolling-perpendicular 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-perpendicular direction TD may be greater than 0°. For example, the angle formed by the magnetic domain control process line 11 and the rolling-perpendicular 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-perpendicular 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.

[0019] 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 angle can be calculated by measuring the angle between one magnetic domain control treatment line and the transverse direction TD at multiple positions, or by measuring the angles between multiple magnetic domain control treatment lines and the transverse direction TD at one point or multiple positions and calculating the average value. Furthermore, if dmax (the maximum distance in the rolling direction between adjacent intersections of a virtual line and the multiple magnetic domain control treatment lines) is greater than 20 mm, the magnetic domain control treatment lines 11 do not have to be interrupted halfway as shown in Figure 1B (i.e., all of the magnetic domain control treatment lines may be formed across the entire width direction of the steel sheet), and the magnetic domain control treatment lines 11 may include curved portions as shown in Figure 1C (i.e., they do not have to be composed of only straight lines).

[0020] The type of the magnetic domain control processing lines 11 is not particularly limited, but suitable examples are thermal distortion and / or grooves. Thermal distortion can be formed by means of, for example, laser irradiation, electron beam irradiation, ion implantation, etc. Grooves can be formed by means of, for example, laser irradiation, electron beam irradiation, machining, etching, etc.

[0021] Thermal distortion disappears by stress relief annealing or a heat treatment equivalent thereto. Therefore, when the grain-oriented electrical steel sheet 1 is heat treated, it is preferable to form the magnetic domain control treatment lines 11 as grooves. On the other hand, since thermal distortion can be easily formed, when simplification of the manufacturing process is required, it is preferable to form the magnetic domain control treatment lines 11 as thermal distortion. The grain-oriented electrical steel sheet 1 may have both thermal distortion and grooves.

[0022] When the magnetic domain control treatment lines 11 are grooves, the magnetic domain control treatment lines 11 can be identified visually. When the grain-oriented electrical steel sheet 1 has an insulating coating, the magnetic domain control treatment lines 11 can be made visible by removing the insulating coating using a known stripping agent.

[0023] 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.

[0024] (Spacing Between Intersections of Imaginary Lines Parallel to the Rolling Direction and Magnetic Domain Control Treatment Lines) (Magnetic Domain Width) As described above, the magnetic domain control treatment lines 11 provided on the surface of the grain-oriented electrical steel sheet 1 function to subdivide 180° magnetic domains. Furthermore, the smaller the spacing between the magnetic domain control treatment lines, the greater the effect of improving iron loss. Therefore, in a typical magnetic domain control treatment, the magnetic domain control treatment lines are formed so that the spacing between them does not exceed 20 mm. In contrast, in the grain-oriented electrical steel sheet according to this embodiment, when a square evaluation area with one side 50 mm long and one side parallel to the rolling direction RD is set on the surface, and when virtual lines VL with a length of 50 mm and parallel to the rolling direction RD are further set within the evaluation area at 5 mm intervals in a direction perpendicular to the rolling direction, in at least one virtual line VL, among multiple intersections VP between the virtual line VL and multiple magnetic domain control treatment lines 11, the maximum spacing in the rolling direction RD between adjacent intersections exceeds 20 mm. That is, in at least some parts, the spacing between the magnetic domain control treatment lines in the rolling direction exceeds 20 mm. FIG. 1A shows, as an example, a state in which only one virtual line VL is drawn. When multiple virtual lines VL are set, a necessary number of other virtual lines can be set parallel to the virtual line VL in FIG. 1A. Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, the virtual lines VL whose maximum spacing in the rolling direction RD exceeds 20 mm satisfy at least one of the following requirements: (1) The average value of the magnetic domain width measured along the virtual line VL is 600 μm or less. (2) The maximum value of the magnetic domain width measured along the virtual line VL is 1200 μm or less. Both the above-mentioned requirements (1) and (2) may be satisfied. That is, the average value of the magnetic domain width measured along the virtual line VL may be 600 μm or less and the maximum value may be 1200 μm or less.

[0025] As described above, while magnetic domain control treatment is effective in reducing iron loss in grain-oriented electrical steel sheets, it also deteriorates the noise characteristics of the grain-oriented electrical steel sheets. Therefore, reducing the density of magnetic domain control treatment lines can suppress the deterioration of noise characteristics. In other words, both noise reduction and iron loss reduction can be achieved in a balanced manner. A maximum spacing between intersections exceeding 20 mm means that there are regions in the steel sheet where the spacing between magnetic domain control treatment lines in the rolling direction exceeds 20 mm, which is more preferable from the perspective of low noise. From the perspective of low noise, preferably, of the multiple intersections VP between the virtual line VL and the multiple magnetic domain control treatment lines 11, the maximum spacing in the rolling direction RD between adjacent intersections exceeds 30 mm. If the magnetic domain control treatment specific to this embodiment is performed on a steel sheet having coarse crystal grains, the maximum spacing in the rolling direction RD is likely to be large due to the steel sheet having coarse crystal grains. In the grain-oriented electrical steel sheet according to this embodiment, it is more preferable that the imaginary line VL, whose maximum spacing in the rolling direction RD exceeds 30 mm, satisfies at least one of the following requirements: (1) The average magnetic domain width measured along the imaginary line VL is 600 μm or less. (2) The maximum magnetic domain width measured along the imaginary line VL is 1200 μm or less.

[0026] The inventors further investigated and analyzed the changes in magnetic domains before and after magnetic domain control in grain-oriented electrical steel sheets. They found that there are areas where the magnetic domain width is narrowed by magnetic domain control and areas where it is barely narrowed. In other words, they 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, they found that the magnetic domain refinement effect of magnetic domain control treatment is less likely to be seen in areas where the magnetic domain width is narrow.

[0027] Generally, when attempting to increase the degree of orientation concentration in the Goss orientation to increase magnetic flux density, the crystal grain size tends to become larger due to the manufacturing method. Steel sheets with such coarse crystal grain sizes have excellent magnetic flux density, but because the crystal grains are too large, they tend to have high iron loss unless magnetic domain control treatment is performed, making magnetic domain control essentially necessary. However, while conventional magnetic domain control treatments are effective in reducing iron loss in grain-oriented electrical steel sheets, they tend to deteriorate the noise characteristics of the grain-oriented electrical steel sheets. In contrast, the above findings show 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 lines formed in regions with narrow magnetic domain widths are thought to cause deterioration of noise characteristics due to closure domains, minimizing magnetic domain control treatment in regions with narrow magnetic domain widths can prevent deterioration of noise characteristics. Therefore, to minimize the deterioration of noise characteristics while achieving the iron loss reduction effect, magnetic domain control treatment is mainly performed on wide magnetic domain regions where the magnetic domain refinement effect is large. While it is preferable to perform magnetic domain control treatment only on wide magnetic domain regions, performing magnetic domain control treatment on narrow magnetic domain regions is acceptable because the deterioration of noise characteristics is small if the proportion is small. Furthermore, it is preferable to perform magnetic domain control treatment on all wide magnetic domain regions, but it is also possible to include regions where magnetic domain control treatment is not performed as long as the iron loss reduction effect is sufficient.

[0028] As a result of further investigations into the magnetic domain refinement effect by the present inventors, as shown in FIG. 2 , in regions where the magnetic domain width is approximately 500 μm or less, the magnetic domain width is approximately the same before and after the magnetic domain control treatment. In other words, it is believed that the magnetic domain refinement effect due to the magnetic domain control treatment is hardly obtained in regions where the magnetic domain width is approximately 500 μm or less. Therefore, in the grain-oriented electrical steel sheet according to this embodiment, to obtain a sufficient iron loss reduction effect while reducing the density of the magnetic domain control treatment lines, magnetic domain control is not intentionally performed in such regions where the magnetic domain width is 500 μm or less, and the magnetic domain control treatment lines are formed mainly in regions where the magnetic domain width is greater than 500 μm. As a result, in the grain-oriented electrical steel sheet according to this embodiment, at the imaginary line VL where the maximum spacing in the rolling direction RD exceeds 20 mm, the magnetic domain width measured along the imaginary line has an average value of 600 μm or less, or a maximum value of 1200 μm or less. That is, in the grain-oriented electrical steel sheet 1 that satisfies at least one of the requirements (1) and (2), the magnetic domain width is small across the entire imaginary line VL, thereby achieving a good balance between low noise and low iron loss.

[0029] In the grain-oriented electrical steel sheet according to this embodiment, it is preferable that, in two or more virtual lines VL, the maximum distance in the rolling direction between adjacent intersections VP among the multiple intersections VP exceeds 20 mm (more preferably exceeds 30 mm), and that at least one of the following requirements is satisfied: (1) The average value of the magnetic domain width measured along each virtual line VL is 600 μm or less; (2) The maximum value of the magnetic domain width measured along each virtual line VL is 1200 μm or less. Both of the above requirements (1) and (2) may be satisfied. That is, the average value of the magnetic domain width measured along the virtual line VL may be 600 μm or less, and the maximum value may be 1200 μm or less. The presence of regions in which the maximum distance between intersections exceeds 20 mm in multiple virtual lines means that there are regions in multiple positions in the steel sheet in which the distance between magnetic domain control treatment lines in the rolling direction exceeds 20 mm, which is more preferable from the viewpoint of low noise.

[0030] More preferably, the average value of the magnetic domain width is 500 μm or less, 450 μm or less, 400 μm or less, 380 μm or less, 350 μm or less, or 300 μm or less, and more preferably, the maximum value of the magnetic domain width is 1000 μm or less, 800 μm or less, 600 μm or less, 500 μm or less, 450 μm or less, or 400 μm or less.

[0031] The rolling direction spacing between the intersections of the virtual line and the multiple magnetic domain control processing lines, and the average and maximum magnetic domain widths measured along the virtual line are determined by the following method. For example, a rectangular sample with both sides measuring 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 used as 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 may be less than 100 mm as long as the length of one side is 50 mm or more. In this case, it is desirable to take the sample by a method such as wire cutting to minimize the influence of mechanical distortion on the sample. A 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. In this magnetic domain image, a square evaluation area is set, one side of which is 50 mm long and parallel to the rolling direction. Furthermore, within the evaluation area, virtual lines VL, each 50 mm long and parallel to the rolling direction, are set at 5 mm intervals in a direction perpendicular to the rolling direction. The distances between the intersections of the virtual lines VL and multiple magnetic domain control processing lines 11 are measured, and the maximum value is taken as the maximum distance in the rolling direction between adjacent intersections. The average and maximum magnetic domain widths measured along the virtual lines VL are set using multiple sub-virtual lines that are perpendicular to the sheet surface normal (thickness direction) and perpendicular to the virtual lines VL. The sub-virtual lines are 5 mm long and set at 2 mm intervals in the rolling direction. The sub-virtual lines are set so as to intersect with the virtual line VL at their centers. The number of magnetic domains contained in each sub-virtual line is measured, and the value obtained by dividing the length of the sub-virtual line by the number of magnetic domains contained in the sub-virtual line is regarded as the magnetic domain width on the sub-virtual line. The average magnetic domain width on the sub-imaginary line is the average magnetic domain width measured along the imaginary line, and the maximum magnetic domain width on the sub-imaginary line is the maximum magnetic domain width measured along the imaginary line. That is, in this embodiment, "along the imaginary line VL" means that the centers of the sub-imaginary lines are located at equal intervals on the imaginary line. The locations where the evaluation region and imaginary line VL are set are not limited.The evaluation area and virtual line VL may be set at any location where a virtual line VL can be set so that the maximum distance between adjacent intersections VP in the rolling direction falls within the range of the present disclosure. For example, the virtual line VL may be set so that it passes through an area where no magnetic domain control processing line 11 is provided. On the other hand, if a location where a virtual line VL can be set so that the maximum distance between adjacent intersections falls within the range of the present disclosure cannot be found, it is presumed that the requirements of the present disclosure are not met. Furthermore, this magnetic domain image is output via a cable or wirelessly to an analysis device, which is a computing device such as a personal computer (PC) equipped with a calculation unit, memory, display unit, input unit, and 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 to explain the measurement. In the line segment method, evaluation is performed by drawing line segments Ls perpendicular to the magnetic domains. The line segments are drawn at intervals of three per 1 cm in the rolling direction RD. The magnetic domain width is calculated based on the interval w between the intersections Ip of the 180° domain wall and the line segments Ls. However, if there are closure domains 301 or noise 302, these are not counted as domain walls. Furthermore, when calculating the average magnetic domain width, the average interval is calculated from the length of each line segment Ls and the number of intersections Ip.

[0032] Among the 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 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 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 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 along the rolling direction RD between adjacent magnetic domain control treatment lines 11 may be constant or may vary (fluctuate). If there is variation, for example, the average value of 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 average value of 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 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 treatment 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. In the grain-oriented electrical steel sheet 1 according to this embodiment, the spacing VP varies along the virtual line VL, which is the measurement position for the magnetic domain width. In other words, even if the average spacing of the magnetic domain control processing lines 11 is within the above range, the virtual line VL, which is the measurement position of the magnetic domain width, passes through an area where the magnetic domain control processing lines 11 are not provided, and therefore the maximum spacing in the rolling direction at the intersection of the virtual line VL and the magnetic domain control processing lines 11 exceeds 20 mm.

[0033] 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.

[0034] 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.

[0035] Furthermore, when the magnetic domain control treatment line 11 is thermally strained, it is preferable that tensile stress is introduced in the thermal strain. The greater the tensile stress, the greater the effect of improving iron loss. On the other hand, the smaller the tensile stress, the 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.

[0036] When the magnetic domain control processing lines 11 are grooves, the greater the groove depth and width, the greater the effect of improving iron loss. On the other hand, the smaller the groove depth and width, the greater the improvement in 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.

[0037] 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.

[0038] (Method for determining the rolling direction RD and the transverse direction TD) The rolling direction RD and the transverse direction (sheet width 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 the 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 (sheet width direction) TD.

[0039] (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.

[0040] 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 ４ On 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.

[0041] 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.

[0042] [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 preferable 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 (III). When the magnetic domain width distribution is clear, such as when the magnetic domain width distribution is estimated by a method other than image acquisition, steps (I) and (II) may be omitted. (I) A magnetic domain image acquisition step of acquiring a magnetic domain image of the grain-oriented electrical steel sheet. (II) A region identification step of identifying regions in the grain-oriented electrical steel sheet where the magnetic domain width exceeds 500 μm based on the magnetic domain image obtained in the magnetic domain image acquisition step. (III) A magnetic domain control treatment line formation step of forming magnetic domain control treatment lines on the surface of the grain-oriented electrical steel sheet after the region identification step. Each step will be described below.

[0043] First, the grain-oriented electrical steel sheet (base sheet) to be subjected to the magnetic domain image acquisition step, or to the magnetic domain control treatment line forming step if the magnetic domain image acquisition step or the magnetic domain image acquisition step and the region identification step are not performed, may be a known grain-oriented electrical steel sheet. For example, the base sheet may have, in mass %, a chemical composition of 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.

[0044] (Magnetic Domain Image Acquisition Process) (Region Identification Process) In the magnetic domain image acquisition process, a magnetic domain image of the surface of the grain-oriented electrical steel sheet is acquired before the magnetic domain control treatment line formation process. In the region identification process, regions in the grain-oriented electrical steel sheet where the magnetic domain width exceeds 500 μm are identified based on the magnetic domain image acquired in the magnetic domain image acquisition process. As described above, the magnetic domain refinement effect is small in regions with small magnetic domain widths, and it is thought that the magnetic domain refinement effect of magnetic domain control is hardly obtained in regions where the magnetic domain width is approximately 500 μm or less. Therefore, it is preferable not to perform magnetic domain control in these regions. In the subsequent magnetic domain treatment line formation process, magnetic domain control treatment is mainly performed in regions where the magnetic domain width exceeds 500 μm, thereby reducing the magnetic domain control treatment lines and reducing iron loss while suppressing deterioration of noise characteristics.

[0045] (Magnetic Domain Control Treatment Line Forming Step) In the magnetic domain control treatment line forming step, magnetic domain control treatment lines are formed mainly in the regions identified in the region identifying step 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. In this case, the magnetic domain control treatment lines are formed so that there are regions where the spacing in the rolling direction exceeds 20 mm. Examples of methods for this include forming magnetic domain control treatment lines in a direction intersecting the rolling direction at positions more than 20 mm in the rolling direction from adjacent magnetic domain control treatment lines based on the magnetic domain width distribution obtained in the region identifying step, or, as shown in FIG. 1A , forming magnetic domain control treatment lines in a direction intersecting the rolling direction such that, even if the starting point is within 20 mm in the rolling direction from an adjacent magnetic domain control treatment line, no magnetic domain control treatment lines are formed in a partial range, thereby forming magnetic domain control treatment lines so that, at some positions, the spacing between adjacent intersections exceeds 20 mm in the rolling direction.

[0046] The magnetic domain control processing lines may be thermal distortions or grooves. In the case of thermal distortions, the magnetic domain control processing lines are formed by irradiating with a laser or electron beam. The irradiation conditions may be within known ranges. In the case of grooves, methods include irradiating with a laser or electron beam, mechanical processing such as gears, and chemical processing such as etching.

[0047] 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.

[0048] (Specific methods in the magnetic domain image acquisition process to the magnetic domain control treatment line formation process) Acquiring a magnetic domain image and identifying areas where the magnetic domain width exceeds 500 μm can be performed by the following method. The magnetic domain image can be acquired, for example, by an image acquisition device. Next, the distribution of the widths of the 180° magnetic domains (magnetic domain widths) is derived from the magnetic domain image. The distribution of the magnetic domain widths in the original sheet can be derived, for example, by using an analysis device. Areas where the magnetic domain width is equal to or greater than a predetermined value (for example, greater than approximately 500 μm) are determined to be areas where magnetic domain control treatment should be performed (hereinafter sometimes simply referred to as treatment areas).

[0049] The processing region may be determined by the operator visually observing the magnetic domain image displayed on the display unit of the analysis device.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] The strip threading device 515 threads the original strip in the rolling direction RD.

[0066] 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.

[0067] 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.

[0068] 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 .

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] In order to derive the distribution of magnetic domain widths of the original plate 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 The processes A-1 to A-3 will be explained in detail below.

[0080] (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 ｌ(k, l is a natural number). As the window function Wa(k, l), a Hamming window, a Hanning window, a Blackman window, etc. can be applied.

[0081] 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.

[0082]

[0083] Figure 7 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.

[0084] 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.

[0085] (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.

[0086] where f ｋ and f ｌ is the spatial frequency.

[0087] 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).

[0088] Here, Δk and Δl are the spatial resolutions in the k and l directions, respectively, of the magnetic domain image.

[0089] 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.

[0090] (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.

[0091] 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).

[0092]

[0093] 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.

[0094] 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.

[0095] 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.

[0096] (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.

[0097] 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 in the present invention as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

[0098] Example 1 Grain-oriented electrical steel sheets from the same lot with a sheet thickness of 0.20 mm were used as the base sheet. Magnetic domain control treatment was performed on the base sheet to obtain the types and shapes of magnetic domain control treatment lines shown in Table 1. The magnetic domain control treatment line shapes A to E and A-2 in the table indicate the following: A: Linear magnetic domain control treatment lines were formed in areas where the magnetic domain width exceeded a predetermined value (500 μm). B: Linear magnetic domain control treatment lines were formed across the entire width of the base sheet. C: Regular dashed magnetic domain control treatment lines were formed. D: Random dashed magnetic domain control treatment lines were formed. E: Magnetic domain control treatment lines were formed at 4 mm intervals only in areas within ±4 mm in the rolling direction RD from the center of each crystal grain in the rolling direction. The radius of curvature of the steel sheet at the position where the crystal grain was located during final annealing was 250 mm. A-2: A linear magnetic domain control treatment line including a curve was formed in the region where the magnetic domain width exceeded a predetermined value (500 μm). The region where the magnetic domain width exceeded 500 μm was identified by the method described above.

[0099] The noise and iron loss of the resulting grain-oriented electrical steel sheets that had been subjected to the magnetic domain control treatment were evaluated and the results are shown in Table 2.

[0100] The noise and iron loss were evaluated as follows. First, a three-phase transformer core was fabricated by stacking 205 grain-oriented electrical steel sheets with a thickness of 0.20 mm. The widths of the legs and yoke of the three-phase transformer core were both 150 mm. The height and width of the outer shape of the three-phase transformer core were both 750 mm. The noise and iron loss of these three-phase transformer cores were measured. The measurement conditions were a frequency of 50 Hz and an excitation magnetic flux density of 1.5 T.

[0101] 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 values, which are listed in Table 2 as the noise evaluation results (unit: dBA) of the grain-oriented electrical steel sheet. Examples with a noise evaluation result of 25.1 dBA or less were determined to be examples in which low noise was achieved. Noise evaluation results that were determined to be unacceptable are underlined.

[0102] 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 50 Hz and an excitation magnetic flux density of 1.5 T, as described above. The determined iron loss is shown in Table 2 as the iron loss evaluation results (unit: W / kg) of the grain-oriented electrical steel sheet. Examples with an iron loss evaluation result of 0.580 W / kg or less were determined to be examples in which low iron loss was achieved. Noise evaluation results that were determined to be unacceptable are underlined.

[0103] Furthermore, a rectangular sample with both sides measuring 100 mm was cut from a three-phase transformer core for measuring noise and iron loss. A square evaluation area with one side 50 mm long and one side parallel to the rolling direction was set in this rectangular sample. Within the evaluation area, virtual lines VL, each 50 mm long and parallel to the rolling direction, were set at 5 mm intervals in a direction perpendicular to the rolling direction. There were nine virtual lines. For each of the nine virtual lines VL, the maximum distance between adjacent intersections in the rolling direction (intersection distance), the average magnetic domain width measured along the virtual line, and the maximum magnetic domain width measured along the virtual line were measured as described above. Table 1 shows the number of virtual lines with a maximum intersection distance exceeding 20 mm, and the number of virtual lines with a maximum intersection distance exceeding 20 mm for which the average and maximum magnetic domain widths were equal to or less than a predetermined value.

[0104]

[0105]

[0106] As can be seen from Tables 1 and 2, when magnetic domain control treatment lines were formed in regions where the magnetic domain width exceeded a predetermined value (500 μm) (Samples Nos. 1 to 15, 20, and 21), the maximum distance in the rolling direction between adjacent intersections of the virtual line and the magnetic domain control treatment line in at least one virtual line exceeded 20 mm, and the average magnetic domain width measured along the virtual line was 600 μm or less, or the maximum magnetic domain width measured along the virtual line was 1200 μm or less. As a result, iron loss was low and noise was also low. In contrast, when the magnetic domain control treatment lines were regularly or randomly dotted, or when the magnetic domain control treatment lines were formed only in a central region of each crystal grain in the rolling direction, the maximum distance in the rolling direction between adjacent intersections of the virtual line and the magnetic domain control treatment line, or the average and maximum magnetic domain widths measured along the virtual line, were outside the range of the present invention. As a result, either or both of the iron loss characteristics and noise characteristics are poor.

[0107] Example 2 A grain-oriented electrical steel sheet (grain-oriented electrical steel sheet having a coarse crystal grain size) from the same lot with a sheet thickness of 0.20 mm was used as the base sheet. This electrical steel sheet was subjected to a final annealing temperature increase process from 1000°C to 1200°C at an average heating rate of less than 5°C / hour, resulting in an average grain boundary spacing in the rolling direction RD of 31 mm to 40 mm. The base sheet was subjected to magnetic domain control treatment so as to obtain the types and shapes of magnetic domain control treatment lines shown in Table 3. The magnetic domain control treatment line shapes A to E and A-2 in the table indicate the following: A: Linear magnetic domain control treatment lines were formed in areas where the magnetic domain width exceeded a predetermined value (500 μm). B: Linear magnetic domain control treatment lines were formed across the entire width of the base sheet. C: Regular dashed magnetic domain control treatment lines were formed. D: Random dashed magnetic domain control treatment lines were formed. E: Magnetic domain control treatment lines were formed at intervals of 4 mm only in the region within ±4 mm in the rolling direction RD from the center of each crystal grain in the rolling direction. The radius of curvature of the steel sheet at the position where the crystal grain was located during finish annealing was 250 mm. A-2: Linear magnetic domain control treatment lines including curves were formed in the region where the magnetic domain width exceeded a predetermined value (500 μm). The region where the magnetic domain width exceeded 500 μm was identified in the same manner as in Example 1.

[0108] The noise and iron loss were evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0109]

[0110]

[0111] As can be seen from Tables 3 and 4, when magnetic domain control treatment lines were formed in regions where the magnetic domain width exceeded a predetermined value (500 μm) (Samples Nos. 31 to 45, 50, and 51), the maximum distance in the rolling direction between adjacent intersections of the virtual line and the magnetic domain control treatment line in at least one virtual line exceeded 30 mm, and the average magnetic domain width measured along the virtual line was 600 μm or less, or the maximum magnetic domain width measured along the virtual line was 1200 μm or less. As a result, iron loss was low and noise was also low. In contrast, when the magnetic domain control treatment lines were regularly or randomly dotted, or when the magnetic domain control treatment lines were formed only in a central region of each crystal grain in the rolling direction, the maximum distance in the rolling direction between adjacent intersections of the virtual line and the magnetic domain control treatment line, or the average and maximum magnetic domain widths measured along the virtual line, were outside the range of the present invention. As a result, either or both of the iron loss characteristics and noise characteristics are poor.

[0112] 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.

[0113] REFERENCE SIGNS LIST 1 Grain-oriented electrical steel sheet 11 Magnetic domain control treatment line RD Rolling direction TD Direction perpendicular to rolling (sheet width direction) ND Rolling surface normal direction VL Virtual line VP Intersection 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 comprising: a surface having a plurality of magnetic domain control processing lines extending in a direction intersecting the rolling direction; a square evaluation area having one side 50 mm long and parallel to the rolling direction set on the surface; and imaginary lines 50 mm long and parallel to the rolling direction set within the evaluation area at intervals of 5 mm in a direction perpendicular to the rolling direction; wherein, for at least one of the imaginary lines, the maximum distance in the rolling direction between adjacent intersections of the imaginary line and the plurality of magnetic domain control processing lines exceeds 20 mm, and the average magnetic domain width measured along the imaginary lines is 600 μm or less.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the average value of the magnetic domain width measured along the imaginary line is 500 μm or less.

3. The grain-oriented electrical steel sheet according to claim 1, characterized in that, for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm, the average value of the magnetic domain width measured along the imaginary line is 600 μm or less.

4. The grain-oriented electrical steel sheet according to claim 3, wherein, for each of two or more imaginary lines where the maximum value of the spacing in the rolling direction exceeds 20 mm, the average value of the magnetic domain width measured along the imaginary line is 500 μm or less.

5. The grain-oriented electrical steel sheet according to claim 1, characterized in that the maximum value of the gap in the rolling direction exceeds 30 mm.

6. A grain-oriented electrical steel sheet comprising: a surface having a plurality of magnetic domain control processing lines extending in a direction intersecting the rolling direction; a square evaluation area having one side 50 mm long and parallel to the rolling direction set on the surface; and imaginary lines 50 mm long and parallel to the rolling direction set within the evaluation area at intervals of 5 mm in a direction perpendicular to the rolling direction; wherein, in at least one of the imaginary lines, the maximum distance in the rolling direction between adjacent intersections of the imaginary line and the plurality of magnetic domain control processing lines exceeds 20 mm, and the maximum magnetic domain width measured along the imaginary line is 1200 μm or less.

7. The grain-oriented electrical steel sheet according to claim 6, wherein the maximum value of the magnetic domain width measured along the imaginary line is 800 μm or less.

8. The grain-oriented electrical steel sheet according to claim 6, wherein, for each of two or more imaginary lines in which the maximum value of the interval in the rolling direction exceeds 20 mm, the maximum value of the magnetic domain width measured along the imaginary line is 1,200 μm or less.

9. The grain-oriented electrical steel sheet according to claim 6, wherein, for each of two or more imaginary lines in which the maximum value of the spacing in the rolling direction exceeds 20 mm, the maximum value of the magnetic domain width measured along the imaginary line is 800 μm or less.

10. The grain-oriented electrical steel sheet according to claim 6, characterized in that the maximum value of the spacing in the rolling direction exceeds 30 mm.

11. The grain-oriented electrical steel sheet according to any one of claims 1 to 10, wherein the plurality of magnetic domain control treatment lines are grooves.

12. The grain-oriented electrical steel sheet according to any one of claims 1 to 10, wherein the plurality of magnetic domain control treatment lines are thermally strained.

13. A method for manufacturing grain-oriented electromagnetic steel sheet according to any one of claims 1 to 10, comprising: a magnetic domain image acquisition step of acquiring a magnetic domain image of a surface of the grain-oriented electromagnetic steel sheet; a region identification step of identifying a region in the grain-oriented electromagnetic steel sheet where the magnetic domain width exceeds 500 μm based on the magnetic domain image acquired in the magnetic domain image acquisition step; and 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 after the region identification step, wherein in the magnetic domain control treatment line forming step, the magnetic domain control treatment line is formed in the region where the magnetic domain width exceeds 500 μm.

14. A method for producing grain-oriented electrical steel sheet as set forth in claim 13, characterized in that 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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