Grain-oriented electrical steel sheet and method for manufacturing grain-oriented electrical steel sheet

Abstract

This grain-oriented electrical steel sheet has a plurality of magnetic domain control processing lines on the surface thereof. When a virtual line is set at a spacing of 5 mm inside an evaluation region, the minimum value DS of the spacing between magnetic domain control points, which are points of intersection between the virtual line and the magnetic domain control processing lines, is at least 2 mm but less than 20 mm for at least one such virtual line. The ratio DL / DS between the maximum value DL and the minimum value DS of the spacing between the magnetic domain control points is 3 or more, and the average value |βL| of the absolute value of the β angle, as measured between the two magnetic domain control points for which the spacing is the maximum value DL, is 1.5° or more.

Description

Grain-oriented electrical steel sheet and method for manufacturing grain-oriented electrical steel sheet

[0001] This disclosure relates to a grain-oriented electrical steel sheet and a method for manufacturing the grain-oriented electrical steel sheet. This application claims priority to Japanese Patent Application No. 2023-166102, 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 technology using 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. In other words, 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.

[0007] In recent years, there has been a growing 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.

[0008] An object of the present disclosure is to provide a grain-oriented electrical steel sheet that can achieve both low iron loss and low noise, and a method for manufacturing the same.

[0009] The gist of the present disclosure is as follows.

[0010] (1) A grain-oriented electrical steel sheet according to one aspect of the present disclosure includes a plurality of magnetic domain control treatment lines on a surface thereof, and the grain-oriented electrical steel sheet has a square evaluation area with one side 50 mm long and parallel to the rolling direction of the grain-oriented electrical steel sheet. Furthermore, within the evaluation area, imaginary lines 50 mm long and parallel to the rolling direction are set at 5 mm intervals. In this case, for at least one of the imaginary lines, the minimum value D of the interval between magnetic domain control points, which are intersections of the imaginary line and the magnetic domain control treatment line, is Ｓ is 2 mm or more and less than 20 mm, and the maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ is 3 or more, and the interval is the maximum value DＬ The average value of the absolute value of the β angle |β measured between the two magnetic domain control points Ｌ (2) In the grain-oriented electrical steel sheet according to (1) above, preferably, the minimum value D | of the distance between the magnetic domain control points is 1.5° or more on each of the two or more imaginary lines. Ｓ is 2 mm or more and less than 20 mm, and the maximum value D Ｌ and the minimum value D Ｓ The ratio D Ｌ / D Ｓ is 3 or more, and the interval is the maximum value D Ｌ the average value |β of the absolute values ​​of the β angles measured between the two magnetic domain control points Ｌ (3) In the grain-oriented electrical steel sheet according to (1) or (2), the D Ｓ is 2 mm or more and less than 20 mm, and Ｌ / D Ｓ is 3 or more, and the |β Ｌ In the virtual line where | is 1.5° or more, Ｌ | and the interval between the magnetic domain control points is the minimum value D Ｓ The average value of the absolute value of the β angle measured between the two magnetic domain control points |β Ｓ | and satisfy the following formula: 0.5°≦|β Ｌ |-|β Ｓ | (4) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (3) above, in at least one of the imaginary lines, the minimum value D of the interval between the magnetic domain control points, which are intersections of the imaginary line and the magnetic domain control processing line, Ｓ is 2 mm or more and less than 20 mm, and the maximum value D Ｌ and the minimum value D Ｓ The ratio D Ｌ / D Ｓ is 5 or more, and the interval is the maximum value D Ｌ the average value |β of the absolute values ​​of the β angles measured between the two magnetic domain control points Ｌ(5) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (4) above, the minimum value D | of the interval between the magnetic domain control points is 1.5° or more in each of the two or more imaginary lines. Ｓ is 2 mm or more and less than 20 mm, and the maximum value D Ｌ and the minimum value D Ｓ The ratio D Ｌ / D Ｓ is 5 or more, and the interval is the maximum value D Ｌ the average value |β of the absolute values ​​of the β angles measured between the two magnetic domain control points Ｌ (6) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (5) above, the D Ｓ is 2 mm or more and less than 20 mm, and Ｌ / D Ｓ is 5 or more, and the |β Ｌ In the virtual line where | is 1.5° or more, Ｌ | and the interval between the magnetic domain control points is the minimum value D Ｓ The average value of the absolute value of the β angle measured between the two magnetic domain control points |β Ｓ | and satisfy the following formula: 0.5°≦|β Ｌ |-|β Ｓ | (7) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (6) above, the maximum value D of the spacing between the magnetic domain control points Ｌ and the minimum value D Ｓ The ratio D Ｌ / D Ｓ(8) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (7) above, the number of grain boundary points, which are intersections between the virtual line and a grain boundary, is 2 or less in at least one of the virtual lines where the ratio D is 3 or more. (9) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (8) above, the number of grain boundary points is 2 or less in each of two or more of the virtual lines. (10) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (9) above, the magnetic domain control treatment lines are thermal strains. (11) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (10) above, the magnetic domain control treatment lines are grooves. (12) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (10) above, the ratio D is 2 or less in at least one of the virtual lines. Ｌ / D Ｓ is less than 3.

[0011] (12) A method for manufacturing a grain-oriented electrical steel sheet according to another aspect of the present disclosure includes the steps of: acquiring a magnetic domain image of an original sheet of the grain-oriented electrical steel sheet; determining a magnetic domain control treatment area based on the distribution of magnetic domain widths in the magnetic domain image; and applying a magnetic domain control treatment to the magnetic domain control treatment area determined based on the distribution of magnetic domain widths; wherein a square evaluation area is set in the grain-oriented electrical steel sheet, with one side 50 mm long and parallel to the rolling direction of the grain-oriented electrical steel sheet; and further, when virtual lines 50 mm long and parallel to the rolling direction are set within the evaluation area at 5 mm intervals, the minimum value of the interval between magnetic domain control points, which are intersections of the virtual line and the magnetic domain control treatment line formed by the magnetic domain control treatment, on at least one of the virtual lines is 2 mm or more and less than 20 mm, and the ratio of the maximum value of the interval between the magnetic domain control points to the minimum value is 3 or more. (13) Preferably, in the method for producing a grain-oriented electrical steel sheet according to (12) above, a region where the magnetic domain width is equal to or greater than a predetermined value is defined as the magnetic domain control treatment region. (14) Preferably, in the method for producing a grain-oriented electrical steel sheet according to (12) or (13) above, the distribution of the magnetic domain width is derived from the magnetic domain image using a two-dimensional Fourier transform. (15) Preferably, in the method for producing a grain-oriented electrical steel sheet according to any one of (12) to (14) above, the magnetic domain control treatment is applied by irradiation with a laser or an electron beam.

[0012] According to the above-described aspects of the present disclosure, it is possible to provide a grain-oriented electrical steel sheet that can achieve both low iron loss and low noise, and a method for manufacturing the same.

[0013] FIG. 4B is a plan view of a grain-oriented electrical steel sheet according to an embodiment of the present disclosure. FIG. 4C is a plan view of a normal grain-oriented electrical steel sheet. FIG. 4D is a graph showing the relationship between β angle and magnetic domain width. FIG. 4E is a diagram showing an example of the distribution of magnetic domain width in a grain-oriented electrical steel sheet before magnetic domain refinement treatment. FIG. 4F is a diagram showing an example of the distribution of magnetic domain width in a grain-oriented electrical steel sheet after magnetic domain refinement treatment. FIG. 4G is a diagram showing the difference between FIG. 4A and FIG. 4B. FIG. 4C is a graph showing the relationship between the magnetic domain width before and after magnetic domain control treatment. FIG. 4D is a block diagram showing an example of the hardware configuration of an image acquisition device. FIG. 4E is a block diagram showing an example of the hardware configuration of an analysis device. FIG. 4F is a schematic diagram showing an example of the configuration of a laser irradiation device. FIG. 4G is a flowchart showing a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present disclosure. FIG. 4C is a schematic diagram explaining a method for cutting out multiple partial regions from a magnetic domain image of a grain-oriented electrical steel sheet. FIG. 4D is an example of multiple partial Fourier images obtained by applying a two-dimensional Fourier transform to each of multiple partial regions cut out from the magnetic domain image of the grain-oriented electrical steel sheet. FIG. 4F is a plan view of an original sheet of a grain-oriented electrical steel sheet.

[0014] (1. Grain-oriented electrical steel sheet 1) The grain-oriented electrical steel sheet 1 according to this embodiment has a plurality of magnetic domain control treatment lines 11 on its surface, and a square evaluation area is set in the grain-oriented electrical steel sheet 1, with each side being 50 mm long and parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1, and virtual lines VL, each 50 mm long and parallel to the rolling direction RD, are set at 5 mm intervals within the evaluation area. In this case, the minimum value D of the distance between the magnetic domain control points VP, which are the intersections of the virtual line VL and the magnetic domain control treatment lines 11, is Ｓ is 2 mm or more and less than 20 mm, and the maximum distance D between the magnetic domain control points VP Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ is 3 or more, and the interval is the maximum value D Ｌ The average value of the absolute value of the β angle |β measured between two magnetic domain control points VP Ｌ | is 1.5° or more.

[0015] (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."

[0016] Suitable examples of the magnetic domain control processed wire 11 are thermal distortion and grooves. By subdividing the magnetic domains, it is possible to suppress the iron loss of the grain-oriented electrical steel sheet 1. However, the magnetic domain control processed wire 11 changes the magnetostriction characteristics of the grain-oriented electrical steel sheet 1 due to closure domains. This deteriorates the noise characteristics of the grain-oriented electrical steel sheet 1.

[0017] The magnetic domain control treatment lines 11 are formed in a direction intersecting the rolling direction RD of the grain-oriented electrical steel sheet 1. In a typical grain-oriented electrical steel sheet 1 such as the one illustrated in Fig. 2, the magnetic domain control treatment lines 11 are formed across the entire width of the grain-oriented electrical steel sheet 1. However, in the grain-oriented electrical steel sheet 1 according to this embodiment such as the one illustrated in Fig. 1, it is not essential to provide the magnetic domain control treatment lines 11 across the entire width of the grain-oriented electrical steel sheet 1.

[0018] In the grain-oriented electrical steel sheet 1 exemplified in FIG. 1 , the magnetic domain control treatment lines 11 are straight. However, the magnetic domain control treatment lines 11 may also be curved. The magnetic domain control treatment lines 11 may have a shape including straight portions and bent portions. Furthermore, the magnetic domain control treatment lines 11 may be on one or both sides of the grain-oriented electrical steel sheet 1. When the magnetic domain control treatment lines 11 are on both sides of the grain-oriented electrical steel sheet 1, it is sufficient that the various aspects of the grain-oriented electrical steel sheet 1 according to this embodiment are applied to at least one side of the grain-oriented electrical steel sheet 1.

[0019] (Evaluation area) In the grain-oriented electrical steel sheet 1 according to this embodiment, in order to set the virtual line VL described later, a square evaluation area is set, with one side having a length of 50 mm and one side parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1.

[0020] (Imaginary line VL parallel to the rolling direction RD and 50 mm long) In the grain-oriented electrical steel sheet 1 according to this embodiment, imaginary lines VL are used for convenience to define the spacing between the magnetic domain control treatment lines 11. The imaginary lines VL are set at 5 mm intervals within the evaluation area. FIG. 1 shows, as an example, a state in which only one imaginary line VL is drawn. When multiple imaginary lines VL are set, a required number of other imaginary lines can be set parallel to the imaginary line VL in FIG. 1. The length of the imaginary line VL is 50 mm. The imaginary line VL extends parallel to the rolling direction RD. The intersections of the imaginary line VL and the magnetic domain control treatment lines 11 are defined as magnetic domain control points VP. The spacing between the magnetic domain control points VP is an index of the density of the magnetic domain control treatment lines 11. The spacing between the magnetic domain control points VP is the distance between two adjacent magnetic domain control points VP along the virtual line VL.

[0021] (Minimum distance between magnetic domain control points VP D Ｓ In the grain-oriented electrical steel sheet 1 according to this embodiment, the minimum value D of the interval between the magnetic domain control points VP on at least one virtual line VL is Ｓ The minimum distance D between the magnetic domain control points VP is 2 mm or more and less than 20 mm. Ｓ If the distance D between the magnetic domain control points VP is less than 2 mm, the density of the magnetic domain control processing lines 11 becomes too high, making it difficult to improve noise characteristics. Ｓ If the distance D exceeds 20 mm, the density of the magnetic domain control processing lines 11 becomes too low, making it difficult to improve the iron loss characteristics. Ｓ is preferably 3 mm or more, 4 mm or more, or 5 mm or more. Ｓ is preferably 18 mm or less, 15 mm or less, or 10 mm or less.

[0022] (Minimum distance between magnetic domain control points VP D Ｓ and maximum value D Ｌ Ratio D Ｌ / D ＳIn addition, in the grain-oriented electrical steel sheet 1 according to this embodiment, at least one imaginary line VL has a D Ｓ is 2 mm or more and less than 20 mm, and the maximum value D of the interval between the magnetic domain control points VP Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ is 3 or more. Ｓ is 2 mm or more and less than 20 mm and D Ｌ / D Ｓ The grain-oriented electrical steel sheet 1 capable of arranging one or more imaginary lines VL such that the number of magnetic domains is 3 or more includes an area X where no magnetic domain control processing line 11 is provided, as illustrated in FIG. 1 .

[0023] The maximum distance D between the magnetic domain control points VP is set according to the position where the evaluation area and the virtual line VL are arranged. Ｌ and minimum value D Ｓ In the grain-oriented electrical steel sheet 1 shown in FIG. Ｌ / D Ｓ It is also possible to position the evaluation area and the virtual line VL so that 2 mm≦D Ｓ <20mm and 3≦D Ｌ / D Ｓ The grain-oriented electrical steel sheet 1 in which one or more virtual lines VL can be arranged at any location is considered to satisfy the requirements of the present disclosure regarding the spacing between magnetic domain control points VP. Therefore, the grain-oriented electrical steel sheet 1 in FIG. 1 satisfies the requirements of the present disclosure regarding the spacing between magnetic domain control points VP.

[0024] On the other hand, the grain-oriented electrical steel sheet 1 shown in Fig. 2 in which a plurality of magnetic domain control treatment lines 11 extending across the entire width of the grain-oriented electrical steel sheet 1 are arranged at equal intervals does not include an area X where no magnetic domain control treatment lines 11 are provided. Ｌ / D Ｓ Therefore, the grain-oriented electrical steel sheet 1 in Fig. 2 does not satisfy the requirement of the present disclosure regarding the spacing between the magnetic domain control points VP.

[0025] Maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D ＳThe upper limit is not particularly limited as long as the maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ The upper limit may be set to 24.

[0026] (β angle) In the grain-oriented electrical steel sheet 1 according to this embodiment, the β angle measured at the magnetic domain control treatment line 11 is set to be within a predetermined range. The β angle is the angle of deviation of crystal grains from the Goss orientation around the axis of the direction transverse to the rolling direction TD. It is known that controlling the β angle is effective in controlling the magnetic properties of the grain-oriented electrical steel sheet 1. The angle of deviation of crystal grains from the Goss orientation around the axis of the normal direction ND of the rolling surface is called the α angle, and the angle of deviation of crystal grains from the Goss orientation around the axis of the rolling direction RD is called the γ angle.

[0027] As shown in Figure 3, in grain-oriented electrical steel sheet 1 (original sheet 2 described later) before magnetic domain control treatment, there is a close relationship between the β angle and the magnetic domain width. Figure 3 is a graph showing an example of the relationship between the β angle and the average value of the magnetic domain width in grain-oriented electrical steel sheet 1 before magnetic domain control treatment. In grain-oriented electrical steel sheet 1 before magnetic domain control treatment, the smaller the β angle, the larger the magnetic domain width. However, the relationship shown in Figure 3 does not hold for grain-oriented electrical steel sheet 1 after magnetic domain control treatment. This is because the magnetic domain control treatment reduces the magnetic domain width in areas where the magnetic domain width was wide before magnetic domain control, but does not change the orientation of the crystal grains (α angle, β angle, γ angle).

[0028] (|β Ｌ In the grain-oriented electrical steel sheet 1 according to this embodiment, the β angle measured between the two magnetic domain control points VP having the longest distance is defined. Specifically, at least one D Ｓ is 2 mm or more and less than 20 mm and D Ｌ / D Ｓ In the virtual line VL where the number of the lines is 3 or more, the distance is the maximum value D Ｌ The average value of the absolute value of the β angle |β measured between two magnetic domain control points VP Ｌ As shown in FIG. 1, the grain-oriented electrical steel sheet 1 according to this embodiment has a D Ｓ is 2 mm or more and less than 20 mm and D Ｌ / DＳ On the virtual line VL where the value of the domain control treatment is 3 or more, there are regions X where the magnetic domain control treatment has not been performed, and there are locations where adjacent magnetic domain control points VP are widely separated. On the other hand, in a grain-oriented electrical steel sheet 1 after a normal magnetic domain control treatment, in which multiple magnetic domain control treatment lines 11 extending across the entire width are arranged at equal intervals, there are no regions X where the magnetic domain control treatment has not been performed. Furthermore, even if a grain-oriented electrical steel sheet 1 after a normal magnetic domain control treatment has regions X where the magnetic domain control treatment has not been performed, that is, even if the grain-oriented electrical steel sheet 1 has multiple magnetic domain control treatment lines 11 arranged randomly and unevenly, the magnetic domain width in the region X is wide and the β angle is small. Therefore, if a normal grain-oriented electrical steel sheet 1 has regions X where the magnetic domain control treatment has not been performed, the average absolute value of the β angle on the virtual line VL passing through the region will be small, and the magnetic domain width will be large. A person skilled in the art would try to make the regions X where the magnetic domain control treatment has not been performed as small as possible. However, in the grain-oriented electrical steel sheet 1 according to this embodiment, the magnetic domain width in the region X where the magnetic domain control treatment has not been performed is narrow, and the |β measured in the region X Ｌ | is considered to be a large value.

[0029] |β Ｌ More preferably, |β is 1.5° or more, 2.0° or more, or 2.5° or more. Ｌ The upper limit of | is not particularly limited, but is more preferably 10.0° or less, 7.0° or less, or 5.0° or less, for example.

[0030] (Basic Principle and Effects) The present inventors have found that 2 mm≦D Ｓ <20 mm, 3≦D Ｌ / D Ｓ , and 1.5°≦|β ＬIt has been discovered that both low iron loss and low noise can be achieved in a grain-oriented electrical steel sheet in which one or more virtual lines VL where | are settable. This is because, in such grain-oriented electrical steel sheet 1, magnetic domain control treatment is applied only to portions that contribute to reducing iron loss, and magnetic domain control treatment lines 11 are not provided in portions where magnetic domain control treatment is not required. The basic principles and effects of the present disclosure will be described below with reference to Figures 4A to 4C, etc.

[0031] First, the inventors compared the magnetic domain structure of the grain-oriented electrical steel sheet 1 before and after magnetic domain control treatment. Fig. 4A shows an example of the magnetic domain width distribution of the grain-oriented electrical steel sheet 1 before magnetic domain control treatment. Fig. 4B shows the magnetic domain width distribution after magnetic domain control treatment was performed on the surface of the grain-oriented electrical steel sheet 1 of Fig. 4A. The magnetic domain control treatment here was performed by irradiating the surface with a continuous wave laser in a direction approximately perpendicular to the rolling direction RD. The magnetic domain width distributions shown in Figs. 4A and 4B were derived from magnetic domain images of the grain-oriented electrical steel sheet 1 using a two-dimensional Fourier transform, which will be described later.

[0032] Furthermore, Fig. 4C shows the difference between Fig. 4A and Fig. 4B. Fig. 4C shows the regions where the magnetic domain width has been subdivided by 50 μm or more before and after the magnetic domain control process shown in Fig. 4A and Fig. 4B. Fig. 4C visualizes the regions where the magnetic domain width has been subdivided by the magnetic domain control process.

[0033] 4C shows that the regions where magnetic domain refining of 50 μm or more has occurred as a result of the magnetic domain control treatment are the dark areas in FIG. 4A, i.e., regions where the magnetic domain width was wide before the magnetic domain control treatment. It can be seen that the magnetic domain refining effect is particularly pronounced in regions where the original magnetic domain width was approximately 500 μm or more. On the other hand, the effect of the magnetic domain control treatment is hardly apparent in the light areas in FIG. 4A, i.e., regions where the magnetic domain width was narrow before the magnetic domain control treatment. The effect of the magnetic domain control treatment differs depending on the magnetic domain width before the magnetic domain control treatment.

[0034] The present inventors further investigated in detail the relationship between the amount of reduction in magnetic domain width caused by the magnetic domain control treatment and the magnetic domain width before the magnetic domain control treatment. Figure 5 shows the relationship between the magnetic domain width before the magnetic domain control treatment and the magnetic domain width before the magnetic domain control treatment at the same position. The magnetic domain control treatment was performed by laser irradiation. During the laser irradiation, the average irradiation energy density Ua (mJ / mm ２ ), and irradiation pitch PL (mm), respectively, Ua = 1.5 mJ / mm ２ , PL=4 mm.

[0035] 5, it can be seen that the magnetic domain refinement effect of the magnetic domain control treatment is difficult to achieve in regions with narrow magnetic domain widths. In particular, in regions with magnetic domain widths of approximately 500 μm or less, the magnetic domain widths were substantially the same before and after the magnetic domain control treatment. Therefore, it is believed that the iron loss reduction effect of the magnetic domain control treatment is large in regions where the magnetic domain width before the magnetic domain control treatment was wide, but is insufficient in regions where the magnetic domain width before the magnetic domain control treatment was sufficiently narrow. It is believed that the magnetic domain control treatment line 11 formed in regions with narrow magnetic domain widths leads to deterioration of noise characteristics due to closure domains.

[0036] Based on the above findings, it has become clear that in the magnetic domain control treatment of conventional grain-oriented electrical steel sheets 1, magnetic domain control is performed even in areas where magnetic domain control is not required, which contributes to increased noise. It has also been found that performing magnetic domain control treatment preferentially in areas with wide magnetic domain widths (i.e., areas with small β angles) is extremely effective in achieving both low iron loss and low noise. Magnetic domain control treatment in areas with wide magnetic domain widths can reduce iron loss. Furthermore, minimizing magnetic domain control treatment in areas with narrow magnetic domain widths (i.e., areas with large β angles) can prevent deterioration of noise characteristics.

[0037] In the grain-oriented electrical steel sheet 1 according to this embodiment, the magnetic domain control treatment lines 11 are not provided in the regions where the magnetic domain width was narrow before the magnetic domain control treatment. Therefore, the grain-oriented electrical steel sheet 1 according to this embodiment includes a region X where the magnetic domain control treatment lines 11 are not provided. When the evaluation region and the virtual line VL are set to cross this region X, 2 mm≦D Ｓ <20 mm and 3≦D Ｌ / D ＳBy not providing the magnetic domain control treatment lines 11, the noise characteristics of the grain-oriented electrical steel sheet 1 according to this embodiment are improved.

[0038] Furthermore, the region X where the magnetic domain control treatment lines 11 are not provided is a region where the magnetic domain width was narrow and the β angle was large before the magnetic domain control treatment. Therefore, in the grain-oriented electrical steel sheet 1 according to this embodiment, the β angle is also large in the region X where the magnetic domain control treatment lines 11 are not provided. Therefore, when the evaluation region and the virtual line VL are set to cross this region X, 1.5°≦|β Ｌ In the grain-oriented electrical steel sheet 1 according to this embodiment, the regions X where the magnetic domain control treatment lines 11 are not provided do not deteriorate the iron loss characteristics.

[0039] Additionally, in the grain-oriented electrical steel sheet 1 according to this embodiment, the magnetic domain control treatment is performed in the regions with wide magnetic domain widths before the magnetic domain control treatment is performed, and therefore the iron loss of the grain-oriented electrical steel sheet 1 according to this embodiment is improved by the magnetic domain control treatment.

[0040] The above has described the most basic aspect of the grain-oriented electrical steel sheet 1 according to this embodiment. A more preferred aspect will now be described.

[0041] (2 mm ≦ D Ｓ <20 mm, 3≦D Ｌ / D Ｓ , and 1.5°≦|β Ｌ |) According to the results of investigations by the present inventors, in the original sheet 2 before the magnetic domain control treatment, regions with narrow magnetic domain widths (regions that do not require magnetic domain control treatment) were scattered across the entire surface of the original sheet 2. It is preferable to avoid all of the regions with narrow magnetic domain widths scattered across the entire surface of the original sheet 2 and perform appropriate magnetic domain control. As a result, it is desirable that in the grain-oriented electrical steel sheet 1 after the magnetic domain control treatment, regions X where no magnetic domain control treatment lines 11 are provided are scattered across the entire surface.

[0042] Therefore, in the grain-oriented electrical steel sheet 1 according to this embodiment, when imaginary lines VL parallel to the rolling direction RD and 50 mm long are set at 5 mm intervals within the evaluation region, the minimum value D of the interval between the magnetic domain control points VP on each of the two or more imaginary lines is Ｓ is 2 mm or more and less than 20 mm, and the maximum distance D between the magnetic domain control points VPＬ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ is 3 or more, and the interval is the maximum value D Ｌ The absolute value of the β angle |β measured between two magnetic domain control points VP Ｌ It is preferable that | is 1.5° or more. Ｓ <20 mm, 3≦D Ｌ / D Ｓ , and 1.5°≦|β Ｌ It is more preferable that the number of virtual lines VL is 3 or more, 4 or more, 5 or more, or 10 or more.

[0043] (|β Ｌ | and | β Ｓ Relationship with | 2 mm ≦ D Ｓ <20 mm, 3≦D Ｌ / D Ｓ , and 1.5°≦|β Ｌ On the virtual line VL where | Ｌ | and the interval is the minimum value D Ｓ The average value of the absolute value of the β angle measured between two magnetic domain control points VP is |β Ｓ It is more preferable that | and | satisfy the following formula: 0.5°≦|β Ｌ |-|β Ｓ | |β Ｌ |-|β Ｓ When | is 0.5° or more, it indicates that the region to which the magnetic domain control treatment is applied is selectively determined by the β angle. Since the magnetic domain control treatment is applied intensively to the region where the magnetic domain width before the magnetic domain control is wide and where the iron loss reduction effect is large, further improvement in noise characteristics is achieved.

[0044] (Mode of magnetic domain control processing line 11) The type of magnetic domain control processing line 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, etc.

[0045] 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.

[0046] (Maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ The grain-oriented electrical steel sheet 1 according to this embodiment is characterized in that the magnetic domain control treatment is selectively performed on regions with a wide magnetic domain width before magnetic domain control. In this case, more significant effects can be obtained by performing the above treatment on a steel sheet with a coarse crystal grain size than on a steel sheet with a typical crystal grain size.

[0047] For example, generally, when an attempt is made to increase the degree of orientation concentration in the Goss orientation in order to increase magnetic flux density, the grain size tends to become larger due to the manufacturing method. Steel sheets with such coarse grain sizes have excellent magnetic flux density, but because the grains are too large, they tend to have high iron loss unless magnetic domain control treatment is performed. Therefore, magnetic domain control is essentially required. However, as mentioned above, while conventional magnetic domain control treatments are effective in reducing the iron loss of grain-oriented electrical steel sheets, they tend to deteriorate the noise characteristics of the grain-oriented electrical steel sheets.

[0048] On the other hand, if a steel sheet having a coarse crystal grain size is subjected to a magnetic domain control treatment selectively in the region where the magnetic domain width is wide before magnetic domain control, as in the present embodiment, a grain-oriented electrical steel sheet can be obtained that not only has excellent magnetic flux density but also can achieve both low iron loss and low noise.

[0049] If the magnetic domain control treatment specific to the present embodiment is performed on a steel sheet having a coarse crystal grain size, the steel sheet has the coarse crystal grain size, and among the above-mentioned characteristics, in particular, the maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ The value of changes.

[0050] Specifically, the grain-oriented electrical steel sheet 1 according to this embodiment preferably satisfies the following characteristics: In at least one imaginary line VL, the minimum value D of the distance between the imaginary line VL and the magnetic domain control points VP, which are the intersections of the imaginary line VL and the magnetic domain control processing line 11, is Ｓ is 2 mm or more and less than 20 mm, and the maximum distance D between the magnetic domain control points VP Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ is 5 or more, and the interval is the maximum value D Ｌ The average value of the absolute value of the β angle |β measured between two magnetic domain control points VP Ｌ is preferably 1.5° or more.

[0051] In addition to the above, it is preferable that the grain-oriented electrical steel sheet 1 according to this embodiment further satisfies the following characteristics: Ｓ is 2 mm or more and less than 20 mm, and the maximum distance D between the magnetic domain control points VP Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ is 5 or more, and the interval is the maximum value D Ｌ The average value of the absolute value of the β angle |β measured between two magnetic domain control points VP Ｌ is preferably 1.5° or more.

[0052] In addition to the above, it is preferable that the grain-oriented electrical steel sheet 1 according to this embodiment further satisfies the following characteristics: Ｓ is 2 mm or more and less than 20 mm, and D Ｌ / D Ｓ is 5 or more, and |β Ｌ On the virtual line VL where | is 1.5° or more, |β Ｌ | and the interval between the magnetic domain control points VP is the minimum value D Ｓ The average value of the absolute value of the β angle measured between two magnetic domain control points VP is |β Ｓ It is preferable that | and | satisfy the following formula: 0.5°≦|β Ｌ |-|β Ｓ |

[0053] By performing the magnetic domain control process specific to this embodiment on a steel sheet having a coarse crystal grain size, the maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ Since the value of is the characteristic value described above, in this embodiment, it is not necessary to specify the grain size of the grain-oriented electrical steel sheet 1. Ｌ / D Ｓ Assuming that the value of is 3 or more, then the ratio D Ｌ / D Ｓ When the value of is 5 or more, the grain size of the grain-oriented electrical steel sheet 1 can be considered to be coarse compared to conventional grains.

[0054] In addition, in the case of grain-oriented electrical steel sheets having a general crystal grain size, the maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ The value is often less than 5.

[0055] However, a method for determining whether a steel sheet has a coarse grain size may be to use the number of intersections between the imaginary lines and the grain boundaries as an index. For example, in the grain-oriented electrical steel sheet 1 according to this embodiment, the maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ It is sufficient that the number of grain boundary points, which are intersections between the virtual line VL and the crystal grain boundary, is two or less in at least one of the virtual lines VL having three or more virtual lines VL.

[0056] In addition to the above, in the grain-oriented electrical steel sheet 1 according to this embodiment, the number of grain boundary points may be two or less on each of two or more imaginary lines VL.

[0057] In addition, in a grain-oriented electrical steel sheet having a general crystal grain size, the number of grain boundary points is about 3 to 10.

[0058] (Maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D ＳThe number of imaginary lines VL where D is less than 3) In addition, the grain-oriented electrical steel sheet 1 according to this embodiment is characterized in that the magnetic domain control treatment is selectively performed on the region where the magnetic domain width is wide before the magnetic domain control. In this case, in at least one imaginary line VL, Ｓ is 2 mm or more and less than 20 mm, and the ratio D Ｌ / D Ｓ is 3 or more, and |β Ｌ | is 1.5° or more, while the maximum value D Ｌ and the minimum value D Ｓ Relative to D Ｌ / D Ｓ may be less than 3.

[0059] Therefore, in the grain-oriented electrical steel sheet 1 according to this embodiment, the above ratio D Ｌ / D Ｓ may be less than 3.

[0060] In the grain-oriented electrical steel sheet 1 according to this embodiment, the ratio D Ｌ / D Ｓ The imaginary line VL where the value of the square is less than 3 is not necessarily included in the square evaluation area where one side is 50 mm long and one side is parallel to the rolling direction of the grain-oriented electrical steel sheet. For example, when 20 evaluation areas are set as described above, at least one evaluation area has a value of D Ｓ is 2 mm or more and less than 20 mm, and the ratio D Ｌ / D Ｓ is 3 or more, and |β Ｌ | is 1.5° or more, and the virtual line VL, the ratio D Ｌ / D Ｓ If both the imaginary line VL and the imaginary line VL where V is less than 3 are included, it can be considered that the magnetic domain control process is selectively performed on the region where the magnetic domain width is wide before the magnetic domain control.

[0061] (2. Manufacturing Apparatus for Manufacturing Grain-Oriented Electrical Steel Sheet 1) Next, an example of a manufacturing apparatus for the grain-oriented electrical steel sheet 1 according to this embodiment will be described. However, the manufacturing apparatus described below is merely illustrative. The grain-oriented electrical steel sheet 1 according to this embodiment can be manufactured using any apparatus.

[0062] 6 shows an example of the hardware configuration of an image acquisition device 30 that acquires magnetic domain images of the original sheet 2, i.e., the grain-oriented electrical steel sheet 1 before the magnetic domain control process. 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.

[0063] 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.

[0064] 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 a 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 the original plate 2, 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 2 is generated inside the MO sensor 33. This leakage magnetic field rotates the polarization plane of the reflected light.

[0065] 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 a 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 plate 2 can be clarified.

[0066] 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. 7 ) via a cable or wireless communication.

[0067] 7 shows the hardware configuration of an analysis device 40 that analyzes the magnetic domain structure of the original sheet 2. The analysis device 40 is a computer device such as a personal computer (PC), and includes a calculation unit 41, a memory 43, a display unit 45, an input unit 47, and a communication I / F 49.

[0068] 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 2 in accordance with a program stored in the memory 43. The calculation unit 41 then determines the magnetic domain control processing region 21, which is the location where the magnetic domain control processing is to be applied. The processing executed by the calculation unit 41 will be described in detail later.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Although FIGS. 6 and 7 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.

[0075] Known means such as laser irradiation, electron beam irradiation, ion implantation, etc. can be used as a means for introducing thermal strain into the surface of the original plate 2. Known means such as laser irradiation, electron beam irradiation, mechanical processing, etc. can be used as a means for forming grooves in the surface of the original plate 2. The configuration of a laser irradiation device 500 that introduces thermal strain by laser irradiation will be described below.

[0076] 8 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.

[0077] The strip threading device 515 threads the original strip 2 in the rolling direction RD.

[0078] 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.

[0079] 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 plate 2. The symbol P in Figure 8 represents the interval between adjacent magnetic domain control processing lines 11, i.e., the irradiation pitch of the laser beam LB.

[0080] 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 .

[0081] 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 plate 2 via the condenser lens 507, thereby introducing thermal strain into the surface of the original plate 2.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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 introduction signal representing the magnetic domain control processing region 21 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 introduction signal is input from the analysis device 40 to the laser irradiation device 500. Note that the stress introduction signal may also be input to the laser irradiation device 500 by an operator.

[0086] (3. Manufacturing Method of Grain-Oriented Electrical Steel Sheet 1) Next, a manufacturing method of the grain-oriented electrical steel sheet 1 according to this embodiment will be described. According to the manufacturing method of the grain-oriented electrical steel sheet 1 according to this embodiment, the grain-oriented electrical steel sheet 1 according to this embodiment can be suitably manufactured. However, the manufacturing method described below is merely one example of a suitable manufacturing method of the grain-oriented electrical steel sheet 1, and does not limit the grain-oriented electrical steel sheet 1. For ease of explanation, manufacturing equipment will be referred to as appropriate in the description of the manufacturing method. However, the manufacturing equipment referred to below is merely a suitable example for carrying out the manufacturing method of the grain-oriented electrical steel sheet 1 according to this embodiment.

[0087] As shown in the flowchart of FIG. 9 , the method for manufacturing the grain-oriented electrical steel sheet 1 according to this embodiment includes step S62 of acquiring a magnetic domain image of the original sheet 2 of the grain-oriented electrical steel sheet 1, step S64 of determining a magnetic domain control treatment area 21 based on the distribution of magnetic domain widths in the magnetic domain image, and step S66 of applying magnetic domain control treatment to the magnetic domain control treatment area 21 determined based on the distribution of magnetic domain widths. In this method, when a square evaluation area with a side length of 50 mm and parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is set in the grain-oriented electrical steel sheet 1, and when virtual lines VL with a length of 50 mm are set inside the evaluation area at intervals of 5 mm, the minimum value D of the interval between magnetic domain control points VP, which are intersections of the virtual line VL and the magnetic domain control treatment line 11, is set within at least one virtual line VL. Ｓ is set to 2 mm or more and less than 20 mm, and the maximum distance D between the magnetic domain control points VP Ｌ The ratio of the maximum value to the minimum value is 3 or more.

[0088] First, a magnetic domain image of the original sheet 2 is acquired (see S62 in FIG. 9 ). The original sheet 2 refers to the grain-oriented electrical steel sheet 1 before the magnetic domain control process is applied. The magnetic domain image can be acquired, for example, by the image acquisition device 30. 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 2 can be derived, for example, by using the calculation unit 41 of the analysis device 40.

[0089] Then, regions where the magnetic domain width is equal to or greater than a predetermined value (for example, equal to or greater than approximately 500 μm) are determined to be magnetic domain control processing regions 21 (see S64 in FIG. 9). FIG. 12 shows the original sheet 2 of the grain-oriented electrical steel sheet 1 in FIG. 1. The shaded regions in FIG. 12 are magnetic domain control processing regions 21. The white regions in FIG. 12 are non-magnetic domain control processing regions 22. The magnetic domain width of the magnetic domain control processing regions 21 is equal to or greater than a predetermined value. The magnetic domain width of the non-magnetic domain control processing regions 22 is less than the predetermined value. The absolute value of the β angle in the magnetic domain control processing regions 21 tends to be smaller than that of the non-magnetic domain control processing regions 22.

[0090] The magnetic domain control processing region 21 may be determined by the operator visually observing the magnetic domain image displayed on the display unit 45, and a stress introduction signal representing the magnetic domain control processing region 21 may be input to the laser irradiation device 500.

[0091] Next, the magnetic domain control treatment is preferentially performed on the magnetic domain control treatment region 21 (see S66 in FIG. 9). Preferably, the magnetic domain control treatment is performed only on the magnetic domain control treatment region 21. If the magnetic domain control treatment line 11 is a thermal distortion, the magnetic domain control treatment may be performed by irradiation with a laser beam LB by a laser irradiation device 500, or other means such as ion implantation or electron beam irradiation may be employed. If the magnetic domain control treatment line 11 is a groove, the magnetic domain control treatment may be performed using a machining tool.

[0092] A detailed description will be given of an example of a method for determining the magnetic domain control processing area 21. The processing for identifying the magnetic domain control processing area 21 is executed by the calculation unit 41 of the analysis device 40, for example.

[0093] The calculation unit 41 uses, for example, a line segment method or a Fourier transform to derive the distribution of the magnetic domain width of the original sheet 2. Then, the calculation unit 41 determines regions where the magnetic domain width is equal to or greater than a predetermined value (for example, equal to or greater than approximately 500 μm) as locations where the magnetic domain control process should be applied preferentially.

[0094] 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.

[0095] The Fourier transform is particularly effective as a means for analyzing the magnetic domain structure of a magnetic material having a periodic magnetic domain structure, such as the grain-oriented electrical steel sheet 1 and the original sheet 2. Below, we will explain a method for deriving the distribution of the magnetic domain width of the original sheet 2 using the short-term two-dimensional Fourier transform (hereinafter referred to as "ST2DFT"), which is an extension of the short-term Fourier transform, a signal processing method that has long been used in the time-frequency analysis of audio signals, to a two-dimensional region.

[0096] 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, such as grayscale, or an image expressed in three or more gradations (multi-gradation).

[0097] 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.

[0098] (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 Nｌ (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.

[0099] 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.

[0100] Figure 10 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.

[0101] 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.

[0102] (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. where f ｋ and f ｌis the spatial frequency.

[0103] 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). Here, Δk and Δl are the spatial resolutions in the k and l directions, respectively, of the magnetic domain image.

[0104] 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.

[0105] (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 (n, m)) can be obtained. Note that, 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.

[0106] 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).

[0107] In this way, by using ST2DFT, it is possible to quantitatively derive the magnetic domain width distribution L(n, m) while preserving the position information of the magnetic domain image. Figures 4A to 4C above show the analysis results of the magnetic domain width derived by ST2DFT.

[0108] FIG. 12 shows a plan view of an example of a master sheet 2. The master sheet 2 in FIG. 12 is the material of the grain-oriented electrical steel sheet 1 in FIG. 1. FIG. 12 shows a magnetic domain control treatment region 21 and a non-magnetic domain control treatment region 22 of the master sheet 2 identified based on a magnetic domain image. The magnetic domain control treatment region 21 is a region where the magnetic domain width is equal to or greater than a predetermined value. The magnetic domain control treatment region 21 of the master sheet 2 roughly corresponds to a region in the grain-oriented electrical steel sheet 1 where the β angle is small. Furthermore, the non-magnetic domain control treatment region 22 of the master sheet 2 roughly corresponds to a region in the grain-oriented electrical steel sheet 1 where the β angle is large. The non-magnetic domain control treatment region 22 is a region where the magnetic domain width is less than a predetermined value and where the β angle is large. Magnetic domain control treatment is applied to the dashed lines provided inside the magnetic domain control treatment region 21 shown in FIG. 12. In this case, a square evaluation area with a side length of 50 mm and parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is set on the grain-oriented electrical steel sheet 1, and virtual lines VL with a length of 50 mm and parallel to the rolling direction RD are set inside the evaluation area at intervals of 5 mm, and in at least one virtual line VL, the minimum value of the interval between magnetic domain control points, which are the intersections of the virtual line and the magnetic domain control processing line, is set to be 2 mm or more and less than 20 mm, and the ratio of the maximum value to the minimum value of the interval between the magnetic domain control points is set to be 3 or more. Ｌ The average value of the absolute value of the β angle between two magnetic domain control points |β Ｌ Therefore, the grain-oriented electrical steel sheet 1 shown in FIG. 1 is obtained, in which | is 1.5° or more.

[0109] When the calculation unit 41 derives the magnetic domain width distribution L(n, m), the calculation unit 41 determines regions where the magnetic domain width is equal to or greater than a predetermined value as magnetic domain control processing regions 21 (i.e., regions to which magnetic domain control processing is applied). The control unit 513 of the laser irradiation device 500 controls the power of the laser beam LB to be on for the magnetic domain control processing regions 21, and preferably to be off for the non-magnetic domain control processing regions 22 (i.e., regions other than the magnetic domain control processing regions 21). This introduces magnetic domain control processing lines 11 into the magnetic domain control processing regions 21 of the original sheet 2. Furthermore, the introduction of magnetic domain control processing lines 11 is minimized in the non-magnetic domain control processing regions 22 of the original sheet 2.

[0110] 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 the magnetic domain image of the grain-oriented electrical steel sheet 1, the magnetic domain control treatment lines 11 may be unclear. 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.

[0111] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. A more preferred example of the grain-oriented electrical steel sheet 1 according to the present embodiment and the manufacturing method thereof will be described below. Unless otherwise specified, the preferred aspects described below are applicable to both the grain-oriented electrical steel sheet 1 and the manufacturing method thereof. The grain-oriented electrical steel sheet according to the present embodiment may have a forsterite coating and / or an insulating coating on the surface of the base steel sheet, as described below.

[0112] Each of these will be explained below. However, when a 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 processed line, magnetic domain control region, and non-magnetic domain control processed line 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.

[0113] (Chemical Composition and Sheet Thickness) The chemical composition of the grain-oriented electrical steel sheet 1 and the base sheet 2 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 and the base sheet 2 may have the following chemical composition, in mass %, Si: 2.500 to 7.000%, Mn: 0.00 to 1.000%, 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%, and the like. : 0-0.300%, 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%, Ti: 0-0.015%. The balance of the chemical composition includes Fe and impurities.

[0114] The thickness of the grain-oriented electrical steel sheet 1 and the base sheet 2 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.

[0115] (Surface Treatment) The grain-oriented electrical steel sheet 1 and the base sheet 2 may have a forsterite coating. The grain-oriented electrical steel sheet 1 and the base sheet 2 may also have an insulating coating. The forsterite coating and the insulating coating may be formed on one side or both sides of the grain-oriented electrical steel sheet 1.

[0116] 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 ３When an annealing separator containing mainly SiO 2 is used, the forsterite film may not be formed.

[0117] 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.

[0118] The insulating coating is preferably formed after the final annealing and the magnetic domain control treatment. Alternatively, the insulating coating may be formed after the final annealing step and before the magnetic domain control treatment. If the insulating coating is formed before the magnetic domain control treatment, the insulating coating may peel off from the magnetic domain control treatment wire 11. Therefore, it is preferable to form an insulating coating again on the magnetic domain control treatment wire 11 after the magnetic domain control treatment.

[0119] (Angle Between Magnetic Domain Control Processing Line 11 and the Direction Orthogonal to Rolling TD) The angle between the magnetic domain control processing line 11 and the direction orthogonal to rolling TD is not particularly limited. The magnetic domain control processing line 11 and the direction orthogonal to rolling TD may be approximately parallel. That is, the angle between the magnetic domain control processing line 11 and the direction orthogonal to rolling TD may be substantially 0°. On the other hand, as exemplified in FIG. 1 , the angle between the magnetic domain control processing line 11 and the direction orthogonal to rolling TD may be greater than 0°. For example, the angle between the magnetic domain control processing line 11 and the direction orthogonal to rolling TD may be any value within the range of 0° to 45°. The angle between the magnetic domain control processing line 11 and the direction orthogonal to rolling 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.

[0120] As exemplified in Fig. 1 , the angles formed by all the magnetic domain control processing lines 11 and the direction transverse to rolling TD may be the same. That is, all the magnetic domain control processing lines 11 may extend parallel to one another. On the other hand, the angles formed by the magnetic domain control processing lines 11 and the direction transverse to rolling TD may vary. That is, some or all of the multiple magnetic domain control processing lines 11 may extend non-parallel to one another. The average value of the angles formed by the magnetic domain control processing 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 processing 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 processing line and the direction perpendicular to the rolling direction TD at multiple positions, or by measuring the angles between multiple magnetic domain control processing lines and the direction perpendicular to the rolling direction TD at one point or multiple positions and then calculating the average value.

[0121] (Magnitude of tensile stress introduced by thermal strain) The magnetic domain control treatment wire 11 may be thermally strained. In the thermal strain, tensile stress is introduced. The larger 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.

[0122] The magnitude of the tensile stress is not particularly limited, but for example, in at least a portion of the magnetic domain control processing line 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, the requirement of "tensile stress in any direction is 40 MPa or more" is considered to be met. Furthermore, for example, in at least a portion of the magnetic domain control processing line 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 processing line 11 may be uniform or may vary.

[0123] (Groove Depth and Width) The magnetic domain control treatment line 11 may be a groove. The greater the groove depth and width, the greater the effect of improving iron loss. On the other hand, the smaller the groove depth and width, the more the noise characteristics are improved. The shape of the groove can be selected appropriately depending on the characteristics required of the grain-oriented electrical steel sheet 1.

[0124] The depth of the groove is not particularly limited, but is preferably 5 μm to 50 μm, for example. The depth of the groove may be 6 μm or more, 7 μm or more, or 10 μm or more. The depth of the groove may be 48 μm or less, 45 μm or less, or 40 μm or less.

[0125] The width of the groove (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 depth and width of the groove may be uniform or may vary. If there is variation, it is preferable that the average depth and width of multiple grooves be within the above range.

[0126] (Measurement Method) The following describes a method for measuring various parameters of the grain-oriented electrical steel sheet 1 according to this embodiment. All parameters are measured using a sample taken from the grain-oriented electrical steel sheet 1. 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. Furthermore, when the grain-oriented electrical steel sheet 1 is a component incorporated into an electrical product such as a transformer or a 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 using a method such as wire cutting to minimize the influence of mechanical distortion on the sample.

[0127] (Method for Identifying Magnetic Domain Control Treatment Lines 11) 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 insulating coating can be removed using a known stripping agent, thereby making the magnetic domain control treatment lines 11 visible.

[0128] If the magnetic domain control treatment lines 11 are thermally strained, they may not be identifiable by visual inspection. In this case, a magnetic domain image is taken using, for example, an image acquisition device 30 as shown in FIG. 6 . If necessary, the magnetic domain image is taken while applying a DC magnetic field along the normal direction ND of the rolled surface of the grain-oriented electrical steel sheet 1. By observing the magnetic domain image, the location of the thermal strain can be identified.

[0129] (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 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 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 rolling direction TD.

[0130] (Minimum distance between magnetic domain control points VP D Ｓ and maximum value D Ｌ ) Minimum distance D between magnetic domain control processing points Ｓand maximum value D Ｌ is calculated according to the following procedure. First, a square evaluation area with one side 50 mm long and parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is set on the grain-oriented electrical steel sheet 1. Then, within the evaluation area, imaginary lines VL parallel to the rolling direction RD and 50 mm long are set on the surface of the grain-oriented electrical steel sheet 1 at 5 mm intervals. Next, magnetic domain control points VP are identified, which are the intersections of the imaginary lines VL and the magnetic domain control processing lines 11. The rolling direction RD and the magnetic domain control processing lines 11 are identified according to the procedure described above. Then, the distance between adjacent magnetic domain control points VP is measured, and the minimum and maximum values ​​of these measurements are obtained.

[0131] There are no limitations on the location where the evaluation area and the virtual line VL are set. Ｓ and D Ｌ / D Ｓ The imaginary line VL may be set at any location where the imaginary line VL can be set within the scope of the present disclosure. For example, the imaginary line VL may be set so as to pass through the area X where the magnetic domain control processing line 11 is not provided. Ｓ and D Ｌ / D Ｓ If no location can be found where a virtual line VL can be set that falls within the scope of the present disclosure, it is presumed that the requirements of the present disclosure are not met.

[0132] (Method for measuring β angles) β angles are measured using the side reflection Laue method. The side reflection Laue method is widely known as a method for measuring crystal orientation. However, the β angle is a value obtained by rounding off the measured value to one decimal place. In other words, the significant figures for the β angle are rounded to one decimal place.

[0133] (|β Ｌ | and |β Ｓ |) |β Ｌ | is measured by the following procedure. First, the distance is measured by the above-mentioned means to find the maximum value D Ｌ Two adjacent magnetic domain control points VP are identified such that the angle β between these magnetic domain control points VP is measured at intervals of 1 mm from the midpoint of the magnetic domain control points VP by the above-mentioned means. ＬIn this case, two or more points where the distance is equal to the maximum value D Ｌ In this case, the β angle between each of the adjacent magnetic domain control points VP is measured at intervals of 1 mm from the midpoint of the magnetic domain control point VP, and the average value of the absolute values ​​of the β angles is calculated as |β Ｌ |β Ｓ The procedure for measuring | is |β Ｌ First, by the above-mentioned means, the distance is determined to be the minimum value D Ｓ Two adjacent magnetic domain control points VP are identified such that the angle β between these magnetic domain control points VP is measured by the above-mentioned means. Ｓ In this case, two or more points where the distance is the minimum value D Ｓ In this case, the β angle between each of the adjacent magnetic domain control points VP is measured at intervals of 1 mm, and the average value of the absolute values ​​of the β angles is calculated as |β Ｓ |You can just consider it that way.

[0134] In each of the plurality of virtual lines VL, D Ｓ , D Ｌ , |β Ｌ | and |β Ｓ In one or more imaginary lines VL, 2 mm≦D Ｓ ≦20 mm, 3≦D Ｌ / D Ｓ , and 1.5°≦|β Ｌ If |, the sample is considered to be a grain-oriented electrical steel sheet according to the present disclosure. The more the number of virtual lines VL that satisfy the requirements of the present disclosure, the more preferable it is.

[0135] (Method for measuring the chemical composition of the master sheet 2 and the grain-oriented electrical steel sheet 1) The chemical compositions of the grain-oriented electrical steel sheet 1 and the master sheet 2 may be measured by a general steel analysis method. For example, the chemical composition 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 and the master sheet 2 can be measured by measuring the test piece 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 content of N may be measured using an inert gas fusion-thermal conductivity method.

[0136] If a forsterite coating and / or an insulating coating is formed on the grain-oriented electrical steel sheet 1 and the base sheet 2, the forsterite coating and / or the insulating coating can be removed from the grain-oriented electrical steel sheet 1 and the base sheet 2 before analyzing the chemical composition of the grain-oriented electrical steel sheet 1 and the base sheet 2. The forsterite coating 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 coating 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. Then, the sample is dried. Next, the sample is immersed in 10% nitric acid at room temperature for approximately 5 seconds while stirring. The insulating coating can be removed, for example, by immersing the sample in a sodium hydroxide solution, followed by immersion in dilute sulfuric acid and nitric acid. The temperature and concentration of the sodium hydroxide, dilute sulfuric acid, and nitric acid solutions, as well as the immersion time, are adjusted appropriately to prevent excessive dissolution of 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. Next, the sample is immersed in a 10% dilute sulfuric acid solution at 80°C for 4 minutes. After that, any sludge adhering to the sample surface is removed using a rag or similar. Next, the sample is immersed in a 10% nitric acid solution at room temperature for approximately 10 seconds while stirring.

[0137] (Method for measuring the angle between the magnetic domain control processing line 11 and the direction transverse to rolling TD) The angle between the magnetic domain control processing line 11 and the direction transverse to rolling TD can be measured using a known angle measuring means after the magnetic domain control processing line 11 and the direction transverse to rolling TD have been identified using the procedure described above.

[0138] (Method for measuring the magnitude of tensile stress induced by thermal strain) The magnitude of tensile stress induced by thermal strain is measured by the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage. The EBSD Wilkinson method is described 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. 111-115, 2006. 307-313.

[0139] 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 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 can be extracted.

[0140] 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 line of the grain-oriented electrical steel sheet 1 is determined to be 40 MPa or more. 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.

[0141] (Method for Measuring Groove Depth and Width) 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.

[0142] The effects of one embodiment of the present disclosure will be explained in more detail using examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this example of conditions. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the present disclosure and the object of the present disclosure is achieved.

[0143] Example 1 Grain-oriented electrical steel sheets (grain-oriented electrical steel sheets with a typical crystal grain size) from the same lot with a sheet thickness of 0.20 mm were used as base sheets. For example, in the temperature-raising process of the final annealing, the average temperature rise rate from 1000°C to 1200°C was set to 15°C / hour. This base sheet was subjected to magnetic domain control treatment under various conditions shown in Table 1. The noise and iron loss of the grain-oriented electrical steel sheets obtained after the magnetic domain control treatment were evaluated and are shown in Table 2. In Table 2, values ​​that were determined to be unacceptable are underlined.

[0144] The magnetic domain control treatment lines were formed in one of the following shapes. The shapes applied to the samples are listed in the "Remarks" column of Table 1. A: As described above, magnetic domain control treatment lines were formed in the region with a small β angle. B: Magnetic domain control treatment lines were formed in a straight line across the entire width of the original sheet. C: Random dashed magnetic domain control treatment lines were formed. D: 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 the rolling direction of each crystal grain. The radius of curvature of the steel sheet at the position where the crystal grain was located during final annealing was 250 mm.

[0145] The noise and iron loss were evaluated as follows. First, a three-phase transformer core was created 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 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 1.5 T.

[0146] 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 30.25 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.

[0147] 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 1.5 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 0.756 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.

[0148] Furthermore, the minimum value D of the interval between magnetic domain control points in the magnetic domain control processed grain-oriented electrical steel sheet Ｓ is 2 mm or more and less than 20 mm, and D Ｌ / D Ｓ The number of virtual lines with a value of 3 or more was measured and listed in Table 1. The measurement method essentially followed the procedure described above. A rectangular sample with both sides 100 mm long was cut out from a three-phase transformer core for measuring noise and iron loss, and used for measurement. A square evaluation area with one side 50 mm long and parallel to the rolling direction of the grain-oriented electrical steel sheet was set in this rectangular sample, and virtual lines VL with a length of 50 mm and parallel to the rolling direction were set at 5 mm intervals inside the evaluation area. The number of virtual lines was 9. These nine virtual lines V Ｌ The standard deviation of the interval between the magnetic domain control points was measured for each. Ｓ is 2 mm or more and less than 20 mm, and D Ｌ / D Ｓ The virtual line V where Ｌ The number of the magnetic domain control points is set to the "minimum value D Ｓ is 2 mm or more and less than 20 mm and DＬ / D Ｓ V is 3 or more Ｌ The number is listed in the "Number of items" column.

[0149] Also, D identified by the above procedure Ｓ is 2 mm or more and less than 20 mm and D Ｌ / D Ｓ The β angle was measured along each imaginary line VL where the value of D was 3 or more. Ｓ is 2 mm or more and less than 20 mm and D Ｌ / D Ｓ Among the virtual lines VL where the distance between the magnetic domain control points is 3 or more, the maximum value D Ｌ The average value of the absolute value of the β angle measured between two magnetic domain control points, Ｌ The number of VLs for which | is 1.5° or more is shown in Table 1 as "|β Ｌ The number of VL lines of 1.5° or more is listed in the "Number of VL lines of 1.5° or more" column. The sample with the number of 1 in this column has the minimum value D Ｓ is 2 mm or more and less than 20 mm, and D Ｌ / D Ｓ is 3 or more, and |β Ｌ The sample having two or more virtual lines corresponds to a grain-oriented electrical steel sheet having a | of 1.5° or more. Ｓ is 2 mm or more and less than 20 mm, D Ｌ / D Ｓ is 3 or more, and |β Ｌ This corresponds to a grain-oriented electrical steel sheet in which | is 1.5° or more.

[0150] Furthermore, D Ｓ is 2 mm or more and less than 20 mm, D Ｌ / D Ｓ is 3 or more, and |β Ｌ Among the virtual lines VL where | is 1.5° or more, |β Ｌ | and the average value of the absolute value of the β angle measured between two magnetic domain control points where the spacing between the magnetic domain control points is the smallest |β Ｓ |Toga 0.5°≦|β Ｌ |-|β Ｓ The number of VLs that satisfy |β Ｌ |-|β Ｓ | Number of VLs that satisfy ≧ 0.5°” column.

[0151] Although not shown in the table, D Ｓ is 2 mm or more and less than 20 mm and D Ｌ / D Ｓ In any of the imaginary lines VL where the number of intersecting points between the imaginary line VL and the grain boundary is 3 or more, the number of intersecting points between the imaginary line VL and the grain boundary is 3 or more. Ｓ is 2 mm or more and less than 20 mm and D Ｌ / D Ｓ In any of the virtual lines VL where D is 3 or more, Ｌ / D Ｓ The value of was less than 5.

[0152]

[0153]

[0154] In Example 9, the magnetic domain control processing lines were formed linearly across the entire width of the master sheet. Ｌ / D Ｓ It was not possible to set the virtual line VL such that the value of VL was 3 or more. In Example 9, the iron loss evaluation result was good, but the noise evaluation result was poor. This is presumably because the magnetic domain control processing line was formed in places where magnetic domain control was not required.

[0155] In Example 10, dashed magnetic domain control processing lines were formed. The interval between the magnetic domain control processing lines in one dashed line was set to a random value. Ｌ / D Ｓ However, in all of these virtual lines, the average value of the absolute value of the β angle |β Ｌ was less than 1.5°. In Example 10, the noise evaluation result was good, but the iron loss evaluation result was poor. This is presumably because the magnetic domain control processing lines were not formed in the locations where magnetic domain control was required.

[0156] In Example 11, magnetic domain control treatment lines were formed at intervals of 4 mm only in the region within ±4 mm from the center of each crystal grain in the rolling direction RD. The radius of curvature of the steel sheet at the position where the crystal grain was located during the final annealing was 250 mm. The results of Example 11 were similar to those of Example 10. That is, in Example 11, DＬ / D Ｓ However, in all of these virtual lines, the average value of the absolute value of the β angle |β Ｌ was less than 1.5°. In Example 11, the noise evaluation result was good, but the iron loss evaluation result was poor. This is presumably because the magnetic domain control processing lines were not formed in the locations where magnetic domain control was required.

[0157] On the other hand, D Ｓ is 2 mm or more and less than 20 mm, D Ｌ / D Ｓ is 3 or more, and |β Ｌ In the example where it was possible to set one or more virtual lines VL where | was 1.5° or more, both the iron loss evaluation results and the noise evaluation results were good.

[0158] Example 2: A magnetic domain control treatment was performed on a grain-oriented electrical steel sheet under the same conditions as in Example 1, except for the type of grain-oriented electrical steel sheet used as the base sheet. Specifically, grain-oriented electrical steel sheets (grain-oriented electrical steel sheets with coarse crystal grain sizes) from the same lot with a sheet thickness of 0.20 mm were used as the base sheet. For example, the average heating rate of this electrical steel sheet from 1000°C to 1200°C during the temperature rise process of final annealing was set to less than 5°C / hour. This base sheet was subjected to a magnetic domain control treatment under various conditions shown in Table 3. The magnetic flux density, noise, and iron loss of the grain-oriented electrical steel sheets obtained after the magnetic domain control treatment were evaluated and the results are shown in Table 4. In Table 4, values ​​determined to be unacceptable are underlined.

[0159] The shape of the magnetic domain control processing line is the same as that of Example 1 described above, the method of evaluating noise and iron loss is the same as that of Example 1 described above, and the method of notating the manufacturing results and evaluation results in the tables is also the same as that of Example 1 described above.

[0160] The magnetic flux density was evaluated as follows. The magnetic flux density was measured by the Epstein method specified in JIS C 2550-1:2011. The magnetic flux density B in the rolling direction of the steel sheet when excited at 800 A / m was ８The magnetic flux density (T) was measured. The measured magnetic flux densities are shown in Table 4 as the magnetic flux density evaluation results (unit: T) of the grain-oriented electrical steel sheets. Examples with a magnetic flux density evaluation result of 1.935 T or more were determined to be examples with magnetic flux density preferably superior to that of grain-oriented electrical steel sheets having a general crystal grain size.

[0161] Although not shown in the table, D Ｓ is 2 mm or more and less than 20 mm and D Ｌ / D Ｓ In any of the imaginary lines VL having a number of 3 or more, the number of grain boundary points, which are intersections between the imaginary line VL and the grain boundary, was 2 or less.

[0162]

[0163]

[0164] D Ｓ is 2 mm or more and less than 20 mm, D Ｌ / D Ｓ is 5 or more, and |β Ｌ In the examples where one or more virtual lines VL with | of 1.5° or more could be set, the magnetic flux density results, iron loss evaluation results, and noise evaluation results were all good. Generally, steel sheets with coarse crystal grain sizes have excellent magnetic flux density, but noise characteristics tend to deteriorate when subjected to conventional magnetic domain control treatment. On the other hand, in Examples 12 to 19 shown in Tables 3 and 4, magnetic domain control treatment lines were selectively formed in areas with small β angles, and as described above, the magnetic flux density results, iron loss evaluation results, and noise evaluation results were all good.

[0165] Similarly, D Ｓ is 2 mm or more and less than 20 mm and D Ｌ / D Ｓ In Examples 12 to 19, in which the number of grain boundary points, which are intersections with the grain boundaries, of the virtual line VL where VL is 3 or more is 2 or less, the magnetic flux density results, iron loss evaluation results, and noise evaluation results were all good.

[0166] According to the present disclosure, it is possible to provide a grain-oriented electrical steel sheet that can achieve both low iron loss and low noise, and a method for manufacturing the same, which is therefore highly industrially applicable.

[0167] 1 Grain-oriented electrical steel sheet 11 Magnetic domain control processing line RD Rolling direction TD Direction perpendicular to rolling ND Direction normal to rolling surface VL Virtual line VP Magnetic domain control point D Ｌ Maximum spacing between magnetic domain control points D Ｓ Minimum value X of the interval between magnetic domain control points Area where magnetic domain control processing lines are not provided 2 Original sheet 21 Magnetic domain control processing area 22 Non-magnetic domain control processing area 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 500 Laser irradiation device 501 Polygon mirror 503 Light source device 505 Collimator 507 Condenser lens 509 Motor 511 Sensor 513 Control unit 515 Strip threading device

Claims

1. A grain-oriented electrical steel sheet having a plurality of magnetic domain control processing lines on its surface, wherein a square evaluation area is set in the grain-oriented electrical steel sheet, one side of which is 50 mm long and parallel to the rolling direction of the grain-oriented electrical steel sheet, and virtual lines, each 50 mm long and parallel to the rolling direction, are set inside the evaluation area at intervals of 5 mm. In this case, the minimum value D of the distance between magnetic domain control points, which are the intersections of the virtual line and the magnetic domain control processing lines, is 1. Ｓ is 2 mm or more and less than 20 mm, and the maximum distance D between the magnetic domain control points is Ｌ and the minimum value D Ｓ Compared to D Ｌ / D Ｓ is 3 or more, and the interval is the maximum value D Ｌ The average value of the absolute value of the β angle |β measured between the two magnetic domain control points Ｌ | is 1.5° or more.

2. The minimum value D of the distance between the magnetic domain control points on each of the two or more virtual lines. Ｓ is 2 mm or more and less than 20 mm, and the maximum value D Ｌ and the minimum value D Ｓ The ratio D Ｌ / D Ｓ is 3 or more, and the interval is the maximum value D Ｌ The average value |β of the absolute value of the β angle measured between two of the magnetic domain control points Ｌ The grain-oriented electrical steel sheet according to claim 1 , wherein | is 1.5° or more.

3. The above D Ｓ is 2 mm or more and less than 20 mm, Ｌ / D Ｓ is 3 or more, and the |β Ｌ In the virtual line where |β is 1.5° or more, Ｌ | and the interval between the magnetic domain control points is the minimum value D Ｓ The average value of the absolute value of the β angle measured between the two magnetic domain control points |β Ｓ The grain-oriented electrical steel sheet according to claim 1 or 2, wherein | and | satisfy the following formula: 0.5°≦|β Ｌ |-|β Ｓ | 4. In at least one of the imaginary lines, the minimum value D of the interval between the magnetic domain control points which are intersections of the imaginary line and the magnetic domain control processing line Ｓ is 2 mm or more and less than 20 mm, and the maximum value D Ｌ and the minimum value D Ｓ The ratio D Ｌ / D Ｓ is 5 or more, and the interval is the maximum value D Ｌ The average value |β of the absolute value of the β angle measured between two of the magnetic domain control points Ｌ The grain-oriented electrical steel sheet according to claim 1 , wherein | is 1.5° or more.

5. The minimum value D of the distance between the magnetic domain control points on each of the two or more virtual lines. Ｓ is 2 mm or more and less than 20 mm, and the maximum value D Ｌ and the minimum value D Ｓ The ratio D Ｌ / D Ｓ is 5 or more, and the interval is the maximum value D Ｌ The average value |β of the absolute value of the β angle measured between two of the magnetic domain control points Ｌ The grain-oriented electrical steel sheet according to claim 4, wherein | is 1.5° or more.

6. D above Ｓ is 2 mm or more and less than 20 mm, Ｌ / D Ｓ is 5 or more, and the |β Ｌ In the virtual line where |β is 1.5° or more, Ｌ | and the interval between the magnetic domain control points is the minimum value D Ｓ The average value of the absolute value of the β angle measured between the two magnetic domain control points |β Ｓ The grain-oriented electrical steel sheet according to claim 4 or 5, wherein | and satisfies the following formula: 0.5°≦|β Ｌ |-|β Ｓ | 7. The maximum distance D between the magnetic domain control points Ｌ and the minimum value D Ｓ The ratio D Ｌ / D Ｓ The grain-oriented electrical steel sheet according to claim 1 , wherein the number of grain boundary points, which are intersections between the imaginary line and a crystal grain boundary, is two or less in at least one of the imaginary lines, which has a number of three or more.

8. The grain-oriented electrical steel sheet according to claim 7, wherein the number of grain boundary points is two or less on each of the two or more imaginary lines.

9. The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain control treatment line is a thermal strain.

10. The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain control treatment lines are grooves.

11. In at least one of the virtual lines, the ratio D Ｌ / D Ｓ The grain-oriented electrical steel sheet according to claim 1 , wherein 12. A method for manufacturing grain-oriented electromagnetic steel sheet, comprising the steps of: acquiring a magnetic domain image of an original sheet of grain-oriented electromagnetic steel sheet; determining a magnetic domain control treatment area based on the distribution of magnetic domain widths in the magnetic domain image; and applying magnetic domain control treatment to the magnetic domain control treatment area determined based on the distribution of magnetic domain widths, wherein a square evaluation area with one side 50 mm long and parallel to the rolling direction of the grain-oriented electromagnetic steel sheet is set in the grain-oriented electromagnetic steel sheet, and virtual lines 50 mm long and parallel to the rolling direction are set at 5 mm intervals inside the evaluation area, wherein: in at least one of the virtual lines, the minimum value of the interval between magnetic domain control points, which are the intersections of the virtual line and the magnetic domain control treatment line formed by the magnetic domain control treatment, is 2 mm or more and less than 20 mm, and the ratio of the maximum value of the interval between the magnetic domain control points and the minimum value is 3 or more.

13. The method for producing grain-oriented electrical steel sheet according to claim 12, wherein the magnetic domain control treatment area is an area in which the magnetic domain width is equal to or greater than a predetermined value.

14. A method for producing a grain-oriented electrical steel sheet according to claim 12 or 13, wherein the distribution of the magnetic domain widths is derived from the magnetic domain image using a two-dimensional Fourier transform.

15. The method for producing grain-oriented electrical steel sheet according to claim 12 or 13, wherein the magnetic domain control treatment is applied by irradiation with a laser or an electron beam.

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