WO2025070776A1 - Grain-oriented electrical steel sheet and method for manufacturing grain-oriented electrical steel sheet - Google Patents

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 D_S 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 D_L/D_S between the maximum value D_L and the minimum value D_S of the spacing between the magnetic domain control points is 3 or more, and the average value |β_L| 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 D_L, is 1.5° or more.

Description

Grain-oriented electrical steel sheet and manufacturing method thereof

The present disclosure relates to a grain-oriented electrical steel sheet and a method for manufacturing a grain-oriented electrical steel sheet.
This application claims priority based on Japanese Patent Application No. 2023-166102, filed on September 27, 2023, the contents of which are incorporated herein by reference.

Grain-oriented electrical steel sheet is a steel sheet that contains 7 mass% or less of Si and has a secondary recrystallized texture in which secondary recrystallized grains are concentrated in the {110}<001> orientation (Goss orientation) with the magnetization easy axis <001> oriented in the rolling direction. Grain-oriented electrical steel sheet is mainly used as the iron core of power transformers. Reduction of energy loss (iron loss) is required for grain-oriented electrical steel sheet.

　Technology for narrowing the magnetic domain width of grain-oriented electromagnetic steel sheets to reduce iron loss (magnetic domain refinement technology using magnetic domain control processing) has long been known. The magnetic domain width can be narrowed by irradiating the surface of the grain-oriented electromagnetic steel sheet with a laser or electron beam in a direction intersecting the rolling direction to introduce thermal distortion. The magnetic domain width can also be narrowed by forming grooves on the surface of the grain-oriented electromagnetic steel sheet in a direction intersecting the rolling direction. Methods for forming grooves include a method using a laser or electron beam, a method using mechanical processing such as gears, and a method using chemical processing such as etching.

In recent years, various improved techniques for magnetic domain refinement have been proposed to provide grain-oriented electrical steel sheets with good iron loss characteristics (see, for example, Patent Documents 1 to 3).

Japanese Patent Application Publication No. 2012-57219 Japanese Patent Application Publication No. 2012-12664 Japanese Patent Application Publication No. 2012-57218

When the magnetic domain control treatment is applied to the grain-oriented electromagnetic steel sheet, the magnetostriction characteristics of the grain-oriented electromagnetic steel sheet change due to the return magnetic domain. This deteriorates the noise characteristics of the grain-oriented electromagnetic steel sheet. The noise characteristics refer to the level of noise generated by an electrical product (e.g., a transformer, a motor, etc.) manufactured using the grain-oriented electromagnetic steel sheet as a material. Magnetostriction is a phenomenon in which the outer shape of a ferromagnetic material is slightly deformed when it is magnetized. When the grain-oriented electromagnetic steel sheet is excited with an alternating current, the magnitude of the magnetostriction changes with the change in the strength of the magnetization, causing vibration. The magnitude of this magnetostriction is very small, on the order of 10 ⁻⁶ , but the magnetostriction generates vibration in the iron core, which propagates to external structures such as the tank of a transformer and becomes noise. That is, while the magnetic domain control treatment is effective for reducing the iron loss of the grain-oriented electromagnetic steel sheet, it deteriorates the noise characteristics of the grain-oriented electromagnetic steel sheet.

In recent years, there has been an increasing demand for grain-oriented electrical steel sheets to not only reduce iron loss, but also reduce noise. However, no magnetic domain refining technology has been proposed to adequately achieve both low noise and low iron loss.

The purpose of this disclosure is to provide a grain-oriented electrical steel sheet that can achieve both low iron loss and low noise, and a manufacturing method thereof.

The gist of this disclosure is as follows:

(1) A grain-oriented electrical steel sheet according to one aspect of the present disclosure includes a plurality of magnetic domain control processing lines on a surface thereof, the grain-oriented electrical steel sheet is provided with a square evaluation area with one side having a length of 50 mm and parallel to a rolling direction of the grain-oriented electrical steel sheet, and virtual lines parallel to the rolling direction and having a length of 50 mm are further provided inside the evaluation area at intervals of 5 mm, the minimum value D _S of the spacing between magnetic domain control points which are intersections of the virtual line and the magnetic domain control processing line in at least one of the virtual lines is 2 mm or more and less than 20 mm, the ratio D _L /D _{S of the maximum value D L of} the spacing between the magnetic domain control points to the minimum value D _S is 3 or more, and the average value |β _L | of the absolute values of the β angles measured between two of the magnetic domain control points where the spacing is the maximum value D _L is 1.5° or more.
(2) Preferably, in the grain-oriented electrical steel sheet according to (1) above, in each of two or more of the virtual lines, the minimum value D _S of the spacing between the magnetic domain control points is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points to the minimum value D _S is 3 or more, and the average value |β _L | of the absolute values of the β angles measured between the two magnetic domain control points where the spacing is the maximum value _{D L} is 1.5° or more.
(3) Preferably, in the grain-oriented electrical steel sheet according to the above (1) or (2), in the imaginary line where the D _S is 2 mm or more and less than 20 mm, the D _L /D _S is 3 or more, and the |β _L | is 1.5° or more, the |β _L | and an average value |β _S | of absolute values of β angles measured between two magnetic domain control points where the distance between the magnetic domain control points is the minimum value D _S 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 virtual lines, the minimum value D _S of the spacing between the magnetic domain control points, which are intersections between the virtual line and the magnetic domain control processing line, is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points to the minimum value D _S is 5 or more, and the average value |β _L | of the absolute values of the β angles measured between two of the magnetic domain control points at which the spacing is the maximum value D _L is 1.5° or more.
(5) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (4) above, in each of two or more of the imaginary lines, the minimum value D _S of the spacing between the magnetic domain control points is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points to the minimum value D _S is 5 or more, and the average value |β _L | of the absolute values of the β angles measured between two of the magnetic domain control points where the spacing is the maximum value D _L is 1.5° or more.
(6) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (5) above, on the imaginary line where the D _S is 2 mm or more and less than 20 mm, the D _L /D _S is 5 or more, and the |β _L | is 1.5° or more, the |β _L | and an average value |β _S | of absolute values of β angles measured between two magnetic domain control points where the distance between the magnetic domain control points is the minimum value D _S satisfy the following formula:
0.5°≦｜β _L ｜-｜β _S ｜
(7) Preferably, in the grain-oriented electrical steel sheet according to any one of the above (1) to (6), among the imaginary lines in which the ratio D _L /D _S of the maximum value D _L to the minimum value D _S of the spacing between the magnetic domain control points is 3 or more, at least one of the imaginary lines has a number of grain boundary points, which are intersections between the imaginary line and a crystal boundary, of 2 or less.
(8) In the grain-oriented electrical steel sheet according to any one of (1) to (7) above, preferably, the number of the grain boundary points is two or less on each of the two or more imaginary lines.
(9) In the grain-oriented electrical steel sheet according to any one of (1) to (8) above, the magnetic domain control treatment lines are preferably thermally strained.
(10) In the grain-oriented electrical steel sheet according to any one of (1) to (9) above, the magnetic domain control treatment lines are preferably grooves.
(11) In the grain-oriented electrical steel sheet according to any one of (1) to (10) above, the ratio D _L /D _S is preferably less than 3 in at least one of the imaginary lines.

(12) A manufacturing method of 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 a 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 having a side length of 50 mm and parallel to a rolling direction of the grain-oriented electrical steel sheet is set in the grain-oriented electrical steel sheet, and virtual lines having a length of 50 mm and parallel to the rolling direction are set inside the evaluation area at intervals of 5 mm, wherein, in at least one of the virtual lines, a minimum value of a distance 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, is 2 mm or more and less than 20 mm, and a ratio of a maximum value of the distance between the magnetic domain control points and the minimum value is 3 or more.
(13) In the method for producing a grain-oriented electrical steel sheet according to (12) above, preferably, a region in which 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.

The above aspects of the present disclosure provide a grain-oriented electrical steel sheet that can achieve both low iron loss and low noise, and a method for manufacturing the same.

FIG. 1 is a plan view of a grain-oriented electrical steel sheet according to an embodiment of the present disclosure. FIG. 1 is a plan view of a typical grain-oriented electrical steel sheet. 1 is a graph showing the relationship between the β angle and the magnetic domain width. FIG. 2 is a diagram showing an example of the distribution of magnetic domain widths in a grain-oriented electrical steel sheet before magnetic domain refinement treatment. FIG. 2 is a diagram showing an example of the distribution of magnetic domain widths of a grain-oriented electrical steel sheet after magnetic domain refinement treatment. FIG. 4C is a diagram showing the difference between FIG. 4A and FIG. 4B. 1 is a graph showing the relationship between the magnetic domain width before and after a magnetic domain control process. FIG. 2 is a block diagram showing an example of a hardware configuration of the image acquisition device. FIG. 2 is a block diagram showing an example of a hardware configuration of an analysis device. FIG. 2 is a schematic diagram showing an example of the configuration of a laser irradiation device. 1 is a flowchart showing a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present disclosure. FIG. 13 is a schematic diagram illustrating a method for extracting a plurality of partial regions from a magnetic domain image of a grain-oriented electrical steel sheet. 13 is an example of a plurality of partial Fourier images obtained by performing a two-dimensional Fourier transform on each of a plurality of partial regions cut out from a magnetic domain image of a grain-oriented electrical steel sheet. FIG. 2 is a plan view of an original sheet of a grain-oriented electrical steel sheet.

(1. Grain-oriented electrical steel sheet 1)
The grain-oriented electrical steel sheet 1 according to this embodiment has a surface including a plurality of magnetic domain control processing lines 11, and a square evaluation area is set in the grain-oriented electrical steel sheet 1, one side of which is 50 mm long and parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1. Furthermore, when virtual lines VL of 50 mm long and parallel to the rolling direction RD are set inside the evaluation area at intervals of 5 mm, in at least one virtual line VL, the minimum value D _S of the spacing between magnetic domain control points VP which are intersections of the virtual line VL and the magnetic domain control processing lines 11 is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points VP to the minimum value D _S is 3 or more, and the average value |β _L | of the absolute values of the β angles measured between two magnetic domain control points VP having the maximum spacing D _L is 1.5° or more.

(Magnetic domain control processing line 11)
The multiple magnetic domain control processing lines 11 provided on the surface of the grain-oriented electromagnetic steel sheet 1 have the function of subdividing the 180° magnetic domains. Subdividing the magnetic domains can reduce the iron loss of the grain-oriented electromagnetic 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 moment is 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 magnetic domain walls of the 180° magnetic domain (magnetic domain wall spacing) is referred to as the width of the 180° magnetic domain. Hereinafter, unless otherwise specified, the width of the 180° magnetic domain will be simply referred to as the "magnetic domain width".

Suitable examples of the magnetic domain control processing line 11 are thermal distortion and grooves. By subdividing the magnetic domains, it is possible to suppress the iron loss of the directional electromagnetic steel sheet 1. However, the magnetic domain control processing line 11 changes the magnetostrictive characteristics of the directional electromagnetic steel sheet 1 due to the return magnetic domains. This deteriorates the noise characteristics of the directional electromagnetic steel sheet 1.

The magnetic domain control processing lines 11 are formed in a direction intersecting the rolling direction RD of the grain-oriented electromagnetic steel sheet 1. In a typical grain-oriented electromagnetic steel sheet 1 as illustrated in FIG. 2, the magnetic domain control processing lines 11 are formed across the entire width of the grain-oriented electromagnetic steel sheet 1. However, in the grain-oriented electromagnetic steel sheet 1 according to this embodiment as illustrated in FIG. 1, it is not essential to provide the magnetic domain control processing lines 11 across the entire width of the grain-oriented electromagnetic steel sheet 1.

In the grain-oriented electromagnetic steel sheet 1 illustrated in FIG. 1, the magnetic domain control processing line 11 is straight. On the other hand, the magnetic domain control processing line 11 may be curved. The magnetic domain control processing line 11 may have a shape having straight portions and curved portions. Furthermore, the magnetic domain control processing line 11 may be on one or both sides of the grain-oriented electromagnetic steel sheet 1. When the magnetic domain control processing line 11 is on both sides of the grain-oriented electromagnetic steel sheet 1, it is sufficient that the various aspects of the grain-oriented electromagnetic steel sheet 1 according to this embodiment are applied to at least one side of the grain-oriented electromagnetic steel sheet 1.

(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.

(Virtual line VL parallel to the rolling direction RD and 50 mm long)
In the grain-oriented electrical steel sheet 1 according to the present embodiment, a virtual line VL is used for convenience in order to define the interval between the magnetic domain control processing lines 11. The virtual lines VL are set at intervals of 5 mm inside the evaluation region. FIG. 1 shows a state in which only one virtual line VL is drawn as an example. When multiple virtual lines VL are set, a required number of other virtual lines can be set parallel to the virtual line VL in FIG. 1. The length of the virtual line VL is 50 mm. The virtual line VL extends parallel to the rolling direction RD. The intersection of the virtual line VL and the magnetic domain control processing line 11 is defined as a magnetic domain control point VP. The interval between the magnetic domain control points VP is an index of the density of the magnetic domain control processing line 11. The interval between the magnetic domain control points VP is the distance between two adjacent magnetic domain control points VP along the virtual line VL.

(Minimum distance D _S between magnetic domain control points VP)
In the grain-oriented electrical steel sheet 1 according to this embodiment, the minimum value D _S of the interval between the magnetic domain control points VP is 2 mm or more and less than 20 mm in at least one virtual line VL. If the minimum value D _S of the interval 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 the noise characteristics. If the minimum value D _S of the interval between the magnetic domain control points VP 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. D _S is preferably 3 mm or more, 4 mm or more, or 5 mm or more. _{D S} is preferably 18 mm or less, 15 mm or less, or 10 mm or less.

(Ratio D _L /D _S of minimum value D _S to maximum value D _L of spacing between magnetic domain control points VP)
Furthermore, in the grain-oriented electrical steel sheet 1 according to this embodiment, in at least one virtual line VL, D _S is 2 mm or more and less than 20 mm, and the ratio D _L / _{D S} of the maximum value D _L of the spacing between the magnetic domain control points VP to the minimum value D _S is 3 or more. A grain-oriented electrical steel sheet 1 capable of arranging one or more virtual lines VL such that D S is 2 mm or more and less than 20 mm and D _L /D _S is 3 or more includes an area X where no magnetic domain control processing lines 11 are provided, as exemplified in FIG.

The maximum value D _L and the minimum value D _S of the spacing between the magnetic domain control points VP can change depending on the positions at which the evaluation area and the virtual line VL are arranged. In the grain-oriented electrical steel sheet 1 illustrated in Fig. 1, it is also possible to position the evaluation area and the virtual line VL so that D _L /D _S is less than 3. However, a grain-oriented electrical steel sheet 1 in which one or more virtual lines VL satisfying 2 mm ≦ D _S < 20 mm and 3 ≦ D _L /D _S can be arranged at any position is considered to satisfy the requirements of the present disclosure regarding the spacing between the 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 the magnetic domain control points VP.

On the other hand, the grain-oriented electrical steel sheet 1 illustrated in Fig. 2 in which a plurality of magnetic domain control processing 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 processing lines 11 are provided. The grain-oriented electrical steel sheet 1 in Fig. 2 cannot have a virtual line VL with 3≦D _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 interval between magnetic domain control points VP.

There is no particular upper limit to the ratio D _L /D _S between the maximum value D _L and the minimum value D _S , as long as the ratio D _{L /D S is equal to or greater than 3. However, the upper limit of the ratio D L} /D _S between the maximum value D _L and the minimum value D _S may be set to 24, if necessary.

(β angle)
In the grain-oriented electrical steel sheet 1 according to this embodiment, the β angle measured in the magnetic domain control processing line 11 is set within a predetermined range. The β angle is the deviation angle of the crystal grains from the Goss orientation around the axis of the direction perpendicular 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 deviation angle of the 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 deviation angle of the crystal grains from the Goss orientation around the axis of the rolling direction RD is called the γ angle.

As shown in Figure 3, in grain-oriented electromagnetic steel sheet 1 (original sheet 2 described later) before magnetic domain control processing, 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 magnetic domain width of grain-oriented electromagnetic steel sheet 1 before magnetic domain control processing. In grain-oriented electromagnetic steel sheet 1 before magnetic domain control processing, the smaller the β angle, the larger the magnetic domain width. However, the relationship shown in Figure 3 does not hold for grain-oriented electromagnetic steel sheet 1 after magnetic domain control processing. This is because the magnetic domain control processing 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).

(|β _L |)
In the grain-oriented electrical steel sheet 1 according to the present embodiment, the β angle measured between two magnetic domain control points VP having the longest distance is specified. Specifically, in at least one virtual line VL where D _S is 2 mm or more and less than 20 mm and D _L /D _S is 3 or more, the average value |β L | of the absolute value of the β angle measured between two magnetic domain control points VP having the above-mentioned maximum distance D _L is 1.5° or _more . As shown in FIG. 1, in the grain-oriented electrical steel sheet 1 according to the present embodiment, in the virtual line VL where D _S is 2 mm or more and less than 20 mm and D _L /D _S is 3 or more, there is an area X where the magnetic domain control process has not been performed, and there is a location where the adjacent magnetic domain control points VP are widely separated. On the other hand, in the grain-oriented electrical steel sheet 1 after the normal magnetic domain control process, in which a plurality of magnetic domain control process lines 11 extending over the entire width are arranged at equal intervals, there is no area X where the magnetic domain control process has not been performed. Furthermore, even if there is a region X in which the magnetic domain control process has not been performed in the grain-oriented electrical steel sheet 1 after the normal magnetic domain control process, that is, even if the grain-oriented electrical steel sheet 1 is a grain-oriented electrical steel sheet 1 in which a plurality of magnetic domain control process lines 11 are randomly and unequally spaced, 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 a region X in which the magnetic domain control process has not been performed, the average value of the absolute value of the β angle on the virtual line VL passing through the region is small, and the magnetic domain width is large. A person skilled in the art would try to make the region X in which the magnetic domain control process 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 in which the magnetic domain control process has not been performed is narrow, and the |β _L | measured in the region X is set to a large value.

is more preferably 1.5° or more, 2.0° or more, or 2.5° or more. The upper limit _{of |β L |} is not particularly limited, but is more preferably, for example, 10.0° or less, 7.0° or less, or 5.0° or less.

(Basic principles and effects)
The present inventors have found that it is possible to achieve both low iron loss and low noise in a grain-oriented electrical steel sheet in which one or more virtual lines VL can be set such that 2 mm≦D _S <20 _mm , ₃ ≦D L /D S , and 1.5°≦|β _L |. This is because, in such a grain-oriented electrical steel sheet 1, the magnetic domain control treatment is applied only to portions that contribute to reducing iron loss, and the magnetic domain control treatment line 11 is not provided in portions where the magnetic domain control treatment is not required. Hereinafter, the basic principle and effects of the present disclosure will be described with reference to Figures 4A to 4C, etc.

First, the inventors compared the magnetic domain structure of the grain-oriented electromagnetic steel sheet 1 before and after the magnetic domain control treatment. Figure 4A shows an example of the distribution of magnetic domain widths of the grain-oriented electromagnetic steel sheet 1 before the magnetic domain control treatment. Figure 4B shows the distribution of magnetic domain widths after the magnetic domain control treatment was applied to the surface of the grain-oriented electromagnetic steel sheet 1 in Figure 4A. The magnetic domain control treatment here was performed by irradiating a continuous wave laser along a direction approximately perpendicular to the rolling direction RD. The distribution of magnetic domain widths shown in Figures 4A and 4B was derived from the magnetic domain image of the grain-oriented electromagnetic steel sheet 1 using the two-dimensional Fourier transform described below.

Furthermore, Fig. 4C shows the difference between Fig. 4A and Fig. 4B. Fig. 4C shows the area 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 makes visible the area where the magnetic domain width has been subdivided by the magnetic domain control process.

According to Figure 4C, the areas where domain refinement of 50 μm or more has occurred as a result of the domain control process are the dark areas in Figure 4A, i.e., areas where the domain width was wide prior to the domain control process. In particular, the effect of domain refinement is evident in areas where the original domain width was approximately 500 μm or more. On the other hand, in the light areas in Figure 4A, i.e., areas where the domain width was narrow prior to the domain control process, the effect of the domain control process is barely noticeable. The effect of the domain control process differs depending on the domain width prior to the domain control process.

The present inventors further investigated the relationship between the amount of reduction in the magnetic domain width caused by the magnetic domain control process and the magnetic domain width before the magnetic domain control process. Fig. 5 shows the relationship between the magnetic domain width before the magnetic domain control process and the magnetic domain width before the magnetic domain control process at the same position. The magnetic domain control process was performed by laser irradiation. During the laser irradiation, the average irradiation energy density Ua (mJ/ ^mm2 ) and the irradiation pitch PL (mm) were set to Ua = 1.5 mJ/ ^mm2 and PL = 4 mm, respectively.

As can be seen from Figure 5, in areas with narrow domain widths, the magnetic domain refinement effect of magnetic domain control processing is less likely to be observed. In particular, in areas with a magnetic domain width of approximately 500 μm or less, the magnetic domain width was approximately the same before and after magnetic domain control processing. Therefore, it is believed that the iron loss reduction effect of magnetic domain control processing is large in areas where the magnetic domain width before magnetic domain control is wide, but is not sufficient in areas where the magnetic domain width before magnetic domain control is sufficiently narrow. It is believed that magnetic domain control processing lines 11 formed in areas with narrow magnetic domain widths cause deterioration of noise characteristics due to return domains.

The above findings reveal that in the conventional magnetic domain control process for grain-oriented electrical steel sheet 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 process preferentially in areas with a wide magnetic domain width (i.e. areas with a small β angle) is extremely effective in achieving both low iron loss and low noise. Magnetic domain control process in areas with a wide magnetic domain width can reduce iron loss. Furthermore, by minimizing magnetic domain control process in areas with a narrow magnetic domain width (i.e. areas with a large β angle), it is possible to prevent a deterioration in noise characteristics.

In the grain-oriented electrical steel sheet 1 according to this embodiment, the magnetic domain control processing lines 11 are not provided in the regions where the magnetic domain width was narrow before the magnetic domain control processing. Therefore, the grain-oriented electrical steel sheet 1 according to this embodiment includes a region X where the magnetic domain control processing 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 _S are satisfied. By not providing the magnetic domain control processing lines 11, the noise characteristics of the grain-oriented electrical steel sheet 1 according to this embodiment are improved.

Moreover, the region X where the magnetic domain control processing 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 processing. 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 processing 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 | is satisfied. In the grain-oriented electrical steel sheet 1 according to this embodiment, the region X where the magnetic domain control processing lines 11 are not provided does not deteriorate the iron loss characteristics.

In addition, in the grain-oriented electromagnetic steel sheet 1 according to this embodiment, a magnetic domain control process is performed in areas with a wide magnetic domain width before the magnetic domain control process. Therefore, the iron loss of the grain-oriented electromagnetic steel sheet 1 according to this embodiment is improved by the magnetic domain control process.

The above describes the most basic aspect of the grain-oriented electrical steel sheet 1 according to this embodiment. Below, we will explain a more preferred aspect.

(The number of virtual lines VL satisfying 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 not requiring magnetic domain control treatment) were scattered across the entire surface of the original sheet 2. It is preferable to perform appropriate magnetic domain control by avoiding all of the regions with narrow magnetic domain widths scattered across the entire surface of the original sheet 2. Thus, it is preferable that in the grain-oriented electrical steel sheet 1 after the magnetic domain control treatment, the regions X where the magnetic domain control treatment lines 11 are not provided are scattered across the entire surface.

Therefore, in the grain-oriented electrical steel sheet 1 according to this embodiment, when virtual lines VL parallel to the rolling direction RD and having a length of 50 mm are set at intervals of 5 mm inside the evaluation region, it is preferable that in each of two or more virtual lines, the minimum value D _S of the spacing between the magnetic domain control points VP is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points VP to the minimum value D _S is 3 or more, and the absolute value |β _L | of the β angle measured between the two magnetic domain control points VP with the maximum spacing D _L is 1.5° or more. It is even more preferable that the number of virtual lines VL satisfying 1 mm≦D _S < 20 mm, 3≦D _L /D _S and 1.5°≦|β _L | is 3 or more, 4 or more, 5 or more, or 10 or more.

(Relationship between |β _L | and |β _S |)
For the imaginary line VL where 2 mm≦D _S <20 mm, 3≦D _L /D _S , and 1.5°≦|β _L |, it is more preferable that |β _L | and the average value |β _S | of the absolute values of the β angles measured between two magnetic domain control points VP whose distance is the above-mentioned minimum value D _S satisfy the following formula:
0.5°≦｜β _L ｜-｜β _S ｜
When |β _L |-|β _S | is 0.5° or more, this 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 concentrated on the region with a wide magnetic domain width before the magnetic domain control and with a large iron loss reduction effect, further improvement in noise characteristics is achieved.

(Aspects of the magnetic domain control processing line 11)
The type of the magnetic domain control processing line 11 is not particularly limited, but a suitable example is a thermal distortion and/or a groove. The thermal distortion can be formed by means of, for example, laser irradiation, electron beam irradiation, ion implantation, etc. The groove can be formed by means of, for example, laser irradiation, electron beam irradiation, machining, etc.

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

(The ratio D _L /D _S of the maximum value D _L to the minimum value D _S is 5 or more.)
The grain-oriented electrical steel sheet 1 according to this embodiment is characterized in that a magnetic domain control process is selectively applied to areas with a wide magnetic domain width before magnetic domain control. In this case, more significant effects can be obtained by applying the above process to a steel sheet having a coarse crystal grain size rather than to a steel sheet having a typical crystal grain size.

For example, generally, when trying to increase the degree of orientation concentration in the Goss orientation in order to increase the magnetic flux density, the crystal grain size tends to become larger due to the manufacturing method. Steel sheets with such coarse crystal grain sizes have excellent magnetic flux density, but because the crystal grains are too large, they tend to have high iron loss if magnetic domain control processing is not performed, making it practically necessary to perform magnetic domain control. However, as mentioned above, while conventional magnetic domain control processing is effective in reducing the iron loss of directional electrical steel sheets, it is likely to deteriorate the noise characteristics of the directional electrical steel sheets.

On the other hand, if a steel sheet with a coarse crystal grain size is subjected to a magnetic domain control process selectively in the areas with a wide magnetic domain width before magnetic domain control, as in this embodiment, a grain-oriented electrical steel sheet can be obtained that has excellent magnetic flux density as well as low iron loss and low noise.

When the magnetic domain control treatment specific to the present embodiment described above is applied to a steel sheet having a coarse crystal grain size, the steel sheet has a coarse crystal grain size, and as a result, among the above-mentioned characteristics, in particular, the value of the ratio D _L /D _S of the maximum value D _L to the minimum value D _S changes.

Specifically, the grain-oriented electrical steel sheet 1 according to this embodiment preferably satisfies the following characteristics: In at least one virtual line VL, the minimum value D _S of the spacing between magnetic domain control points VP, which are intersections between the virtual line VL and the magnetic domain control processing line 11, is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points VP to the minimum value D _S is 5 or more, and _the average value |β _L | of the absolute value of the β angle measured between two magnetic domain control points VP having the maximum spacing D L is 1.5° or more.

In addition to the above, the grain-oriented electrical steel sheet 1 according to this embodiment preferably further satisfies the following characteristics: In each of two or more virtual lines VL, the minimum value D _S of the spacing between the magnetic domain control points VP is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points VP to the minimum value D _S is 5 or more, and the average value |β _L | of the absolute value of the β angle measured between the two magnetic domain control points VP having the maximum spacing _D L is 1.5° or more.

In addition to the above, the grain-oriented electrical steel sheet 1 according to this embodiment preferably further satisfies the following characteristic: On a virtual line VL where D _S is 2 mm or more and less than 20 mm, D _L /D _S is 5 or more, and |β _L | is 1.5° or more, |β _L | and the average value |β _S | of the absolute values of the β angles measured between two magnetic domain control points VP at which the distance between the magnetic domain control points VP is the minimum value D _S preferably satisfy the following formula:
0.5°≦｜β _L ｜-｜β _S ｜

By subjecting a steel sheet having a coarse crystal grain size to the magnetic domain control treatment specific to this embodiment described above, the ratio D _L /D _S of the maximum value D _L to the minimum value D _S becomes the characteristic value described above, so in this embodiment, there is no need to specify the crystal grain size of the grain-oriented electrical steel sheet 1. On the premise that the ratio D _L /D _S is 3 or more after the magnetic domain control treatment specific to this embodiment is applied, when the ratio D _L /D _S 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.

In addition, in grain-oriented electrical steel sheets having a typical crystal grain size, the ratio D _L /D _S of the maximum value D _L to the minimum value D _S is often less than 5.

However, the number of intersections between virtual lines and grain boundaries may be used as an index to determine whether a steel sheet has a coarse crystal grain size. For example, in the grain-oriented electrical steel sheet 1 according to this embodiment, among the virtual lines VL having a ratio D _L /D _S of the maximum value D _L to the minimum value D _S of the spacing between the magnetic domain control points VP of 3 or more, the number of grain boundary points, which are the intersections between the virtual line VL and the grain boundaries, may be 2 or less.

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 virtual lines VL.

In addition, in grain-oriented electrical steel sheets with typical crystal grain sizes, the number of grain boundary points is approximately 3 to 10.

(The number of virtual lines VL having a ratio D _L /D _S of the maximum value D _L to the minimum value D _S of less than 3)
Furthermore, the grain-oriented electrical steel sheet 1 according to this embodiment is characterized in that a magnetic domain control process is selectively applied to regions with a wide magnetic domain width before magnetic domain control. In this case, in at least one virtual line VL, D _S is 2 mm or more and less than 20 mm, the ratio D _L /D _S is 3 or more, and |β _L | is 1.5° or more, while in at least one virtual line VL, the ratio D _L /D _S of the maximum value D _L to the minimum value D _S may be less than 3.

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 in at least one imaginary line VL.

In the grain-oriented electrical steel sheet 1 according to this embodiment, the virtual line VL in which the ratio D _L /D _S is less than 3 is not necessarily included in a square evaluation area with one side having a length of 50 mm and parallel to the rolling direction of the grain-oriented electrical steel sheet. For example, when 20 evaluation areas are set as described above, if at least one evaluation area includes both a virtual line VL in which D _S is 2 mm or more and less than 20 mm, a ratio D _L /D _S is 3 or more, and |β _L | is 1.5° or more, and a virtual line VL in which the ratio D _L /D _S is less than 3, it can be regarded that the magnetic domain control treatment has been selectively performed on the area with a wide magnetic domain width before magnetic domain control.

(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 the present embodiment will be described. However, the manufacturing apparatus described below is merely illustrative. The grain-oriented electrical steel sheet 1 according to the present embodiment can be manufactured using any apparatus.

FIG. 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 electromagnetic 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.

The light source unit 31 has a light source consisting of a light emitting diode (LED) and irradiates the MO sensor 33 with light with a uniform polarization plane.

The MO sensor 33 is a device that measures the magnetic domain structure of a magnetic material. The MO sensor 33 has an observation surface on which the magnetic material sample to be measured is placed. Light irradiated from the light source unit 31 passes through the inside of the MO sensor 33 and is reflected by the reflective layer. The reflected light passes through the inside of the MO sensor 33 again and is output to the outside of the MO sensor 33. When the original plate 2, which is the magnetic material 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.

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, photoelectrically converts it, and outputs the analog signal after photoelectric conversion to the signal processing unit 37. By detecting the reflected light with a rotated polarization plane using the image sensor 35, the distribution of the leakage magnetic field can be obtained, and the magnetic domain structure of the original plate 2 becomes clear.

The signal processing unit 37 has 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. An image signal is generated by performing a predetermined digital processing on this digital signal using the DSP. The image signal generated by the signal processing unit 37 is output to the analysis device 40 (see Figure 7) via a cable or wireless communication.

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

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 plate 2 according to a program stored in the memory 43. The calculation unit 41 then determines the magnetic domain control processing area 21, which is the location where the magnetic domain control processing is applied. The processing executed by the calculation unit 41 will be described in detail later.

Memory 43 has 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 required for the execution of these programs. The programs and data stored in the ROM are loaded into the RAM and executed.

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

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.

The input unit 47 has input devices such as a mouse and a keyboard. 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.

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

Note that although Figures 6 and 7 show a 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 adopted.

As a means for introducing thermal strain into the surface of the original plate 2, known means such as laser irradiation, electron beam irradiation, ion injection, etc. can be used. As a means for forming grooves in the surface of the original plate 2, known means such as laser irradiation, electron beam irradiation, mechanical processing, etc. can be used. Below, the configuration of the laser irradiation device 500 that introduces thermal strain by laser irradiation is described.

FIG. 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 plate threading device 515.

The plate threading device 515 threads the original plate 2 in the rolling direction RD.

Polygon mirror 501 is, for example, in the shape of a regular polygonal prism. A number of plane mirrors are provided on each of the multiple side surfaces that make up polygon mirror 501 in the shape of a regular polygonal prism. A laser beam LB is incident on the plane mirror of polygon mirror 501 in one direction (horizontal direction) from light source device 503 via collimator 505 and is reflected by the plane mirror.

The polygon mirror 501 can be rotated around the 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, making it possible to scan the surface of the original plate 2. The symbol P in FIG. 8 represents the distance between adjacent magnetic domain control processing lines 11, i.e., the irradiation pitch of the laser beam LB.

The light source device 503 outputs a laser beam LB in a predetermined irradiation method (e.g., continuous irradiation method or pulse irradiation method) under the control of the control unit 513.

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 focusing optical system with a predetermined focal length. The laser beam LB reflected from the polygon mirror 501 is focused on the surface of the original plate 2 via the condenser lens 507, thereby introducing thermal distortion into the surface of the original plate 2.

The motor 509 is connected to the polygon mirror 501. The motor 509 drives and rotates the polygon mirror 501 under the control of the control unit 513.

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 the rotation angle signal) to the control unit 513.

The control unit 513 is composed of a processor. The control unit 513 is connected to the light source device 503, the motor 509, the sensor 511, and the plate threading device 515. The control unit 513 receives a speed signal from the plate threading device 515. Furthermore, the control unit 513 outputs a signal to the motor 509 to instruct the motor 509 to rotate the polygon mirror 501.

The control unit 513 also controls the power of the laser beam LB output by the light source device 503 to be turned on and off based on the stress introduction signal representing the magnetic domain control processing region 21 and the 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. The stress introduction signal may also be input to the laser irradiation device 500 by an operator.

(3. Manufacturing method of grain-oriented electrical steel sheet 1)
Next, a method for manufacturing the grain-oriented electromagnetic steel sheet 1 according to the present embodiment will be described. According to the method for manufacturing the grain-oriented electromagnetic steel sheet 1 according to the present embodiment, the grain-oriented electromagnetic steel sheet 1 according to the present embodiment can be suitably manufactured. However, the manufacturing method described below is merely one example of a suitable method for manufacturing the grain-oriented electromagnetic steel sheet 1, and does not limit the grain-oriented electromagnetic steel sheet 1. For ease of explanation, a manufacturing apparatus will be referred to as appropriate in the explanation of the manufacturing method. However, the manufacturing apparatus referred to below is merely a suitable example for carrying out the method for manufacturing the grain-oriented electromagnetic steel sheet 1 according to the present embodiment.

9 , the manufacturing method of the grain-oriented electrical steel sheet 1 according to this embodiment includes a step S62 of acquiring a magnetic domain image of an original sheet 2 of the grain-oriented electrical steel sheet 1, a step S64 of determining a magnetic domain control treatment region 21 based on the distribution of magnetic domain widths in the magnetic domain image, and a step S66 of applying a magnetic domain control treatment to the magnetic domain control treatment region 21 determined based on the distribution of magnetic domain widths. In the grain-oriented electrical steel sheet 1, a square evaluation region with one side having a length of 50 mm and parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is set, and virtual lines VL with a length of 50 mm are set inside the evaluation region at intervals of 5 mm. In this case, in at least one virtual line VL, the minimum value D _S of the spacing between magnetic domain control points VP, which are intersections of the virtual line VL and the magnetic domain control treatment line 11, is set to 2 mm or more and less than 20 mm, and the ratio of the maximum value D _L of the spacing between the magnetic domain control points VP to the minimum value is set to 3 or more.

First, a magnetic domain image of the original sheet 2 is obtained (see S62 in FIG. 9). The original sheet 2 refers to the directional electromagnetic steel sheet 1 before the application of the magnetic domain control process. The magnetic domain image can be obtained, 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.

Then, the regions where the magnetic domain width is equal to or greater than a predetermined value (e.g., equal to or greater than about 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 electromagnetic 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 in the non-magnetic domain control processing regions 22.

The magnetic domain control processing area 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 area 21 may be input to the laser irradiation device 500.

Then, the magnetic domain control processing is preferentially performed on the magnetic domain control processing area 21 (see S66 in FIG. 9). Preferably, the magnetic domain control processing is performed only on the magnetic domain control processing area 21. If the magnetic domain control processing line 11 is a thermal distortion, the magnetic domain control processing may be performed by irradiation with a laser beam LB by a laser irradiation device 500, or other means such as ion injection or irradiation with an electron beam may be used. If the magnetic domain control processing line 11 is a groove, the magnetic domain control processing may be performed using a tool for machining.

An example of a method for determining the magnetic domain control processing area 21 will be described in detail. The process for identifying the magnetic domain control processing area 21 is executed by, for example, the calculation unit 41 of the analysis device 40.

The calculation unit 41 derives the distribution of the magnetic domain width of the original plate 2, for example, using a line segment method or a Fourier transform. The calculation unit 41 then determines the areas where the magnetic domain width is equal to or greater than a predetermined value (for example, equal to or greater than about 500 μm) as the areas where the magnetic domain control process should be applied preferentially.

In the line segment method, evaluation is performed by drawing lines perpendicular to the magnetic domains. The lines are spaced so that there are three lines per cm in the direction parallel to the magnetic domains. The magnetic domain width is calculated based on the distance between the intersections of the 180° domain walls and the lines.

The Fourier transform is particularly effective as a means of analyzing the magnetic domain structure of magnetic materials with periodic magnetic domain structures, such as the grain-oriented electromagnetic steel sheet 1 and the original sheet 2. Below, we will explain a method of 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 the two-dimensional domain.

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 with two types of colors, such as grayscale, or an image expressed in three or more gradations (multiple gradations).

In order to derive the distribution of the magnetic domain width of the original sheet 2, the calculation unit 41 executes the following processes (A-1), (A-2) and (A-3).
(A-1) A process of extracting a plurality of partial regions from a magnetic domain image;
(A-2) Processing for performing ST2DFT;
(A-3) Processing for deriving distribution of magnetic domain width.
The processes A-1 to A-3 will be described in detail below.

(A-1) Processing for Cutting out Multiple Partial Regions from a Magnetic Domain Image In order to cut out multiple partial regions from a magnetic domain image and analyze the frequency structure of each partial region, a rectangular window function Wa(k,l) is used in which the range in the k direction is 0≦k≦N _k -1 and the range in the _l direction is 0≦l≦N l-1 (N _k and N _l are natural numbers). As the window function Wa(k,l), a Hamming window, a Hanning window, a Blackman window, etc. can be used.

If the observation position in the data sequence x(k,l) of the magnetic domain image is expressed as an index (n,m) and the shift amounts of the window function Wa(k,l) in the k and l directions are expressed as S _k and S _l , respectively (n, m, S _k , and S _l are integers), then a data sequence x nm ( _k -nS _k , _l -mS l ) of a partial region cut out from the magnetic domain image in the range nS _k ≦k≦nS _k +N _k -1, _{mS l} ≦l≦mS _l +N l-1 can be obtained as shown in _equation (1).

Figure 10 shows an example of partial regions cut out from the magnetic domain image G, each corresponding to the observation positions (n, m) = (1, 1), (2, 2), (3, 3), ..., (P, Q) (P and Q are natural numbers).

In this embodiment, N _k and N _l that define the range of the window function Wa(k, l) are parameters that correspond to the number of pixels in the k direction and the number of pixels in the l direction, respectively, in the partial region.

　ここで、ｆ_ｋ及びｆ_ｌは空間周波数である。 (A-2) Processing to perform ST2DFT By defining the data sequence of a partial region as x _nm (n', m') = x _nm (k-nS _k , l-mS _l ) and performing a two-dimensional Fourier transform on x _nm (n', m'), a partial Fourier image X(f _k , f _l , n, m) corresponding to the partial region at the observation position (n, m) is obtained as shown in equation (2).

where f _k and f _l are spatial frequencies.

　
　ここで、Δｋ及びΔｌは、それぞれ、磁区画像におけるｋ方向の空間分解能及びｌ方向における空間分解能である。 When the resolution of spatial frequency f _k is denoted as Δf _k and the resolution of spatial frequency f ₁ is denoted as Δf ₁ , Δf _k and Δf ₁ are defined as shown in Equation (3).

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

For example, when a two-dimensional Fourier transform is applied to the data sequence x _nm (k-nS _k , lmS _l ) of each partial region shown in FIG. 10, a partial Fourier image X(f _k , f _l , n, m) is obtained for each observation position (n, m), as shown in FIG. 11.

(A-3) Process for deriving distribution of magnetic domain width Once the partial Fourier image X( _fk , _fl , n, m) is obtained, the coordinates (k component _fkmax (n, m) and l component _flmax (n, m)) of the peak position of the spot in the partial Fourier image ^X ( _fk , _fl , n, m) are obtained. Note that in deriving the peak position, the area near k=0, l=0 ^is excluded because this area is highly dependent on the image contrast.

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

In this way, by using ST2DFT, it is possible to quantitatively derive the distribution of magnetic domain width 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.

FIG. 12 shows a plan view of an example of the original sheet 2. The original sheet 2 in FIG. 12 is the material of the grain-oriented electromagnetic steel sheet 1 in FIG. 1. FIG. 12 shows a magnetic domain control processing region 21 and a non-magnetic domain control processing region 22 of the original sheet 2 identified based on the magnetic domain image. The magnetic domain control processing region 21 is a region where the magnetic domain width is equal to or greater than a predetermined value. The magnetic domain control processing region 21 of the original sheet 2 roughly corresponds to a region in the grain-oriented electromagnetic steel sheet 1 where the β angle is small. Moreover, the non-magnetic domain control processing region 22 of the original sheet 2 roughly corresponds to a region in the grain-oriented electromagnetic steel sheet 1 where the β angle is large. The non-magnetic domain control processing 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 processing is applied to the dashed lines provided inside the magnetic domain control processing region 21 shown in FIG. 12. In this case, 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 in 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 of the virtual lines VL, the minimum value of the interval between magnetic domain control points which are 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. This provides the grain-oriented electrical steel sheet 1 of FIG. 1 in which the average value |β _L | of the absolute values of the β angles of two magnetic domain control points having a maximum interval D _L is 1.5° or more.

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

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

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

Each of these is 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 regulations regarding the chemical composition, magnetic domain control processing line, magnetic domain control area, and non-magnetic domain control processing line apply to the base steel sheet. However, the regulations regarding sheet thickness apply to the entire grain-oriented electrical steel sheet, including the base steel sheet and the forsterite coating and/or insulating coating.

(Chemical composition and thickness)
The chemical composition of the grain-oriented electrical steel sheet 1 and the original sheet 2 is not limited, and may be the same as that of the known grain-oriented electrical steel sheet 1. For example, the grain-oriented electrical steel sheet 1 and the original sheet 2 have a chemical composition, in mass %, of 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 0.500%, and Mn: 0 to 0.500%. : 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.

The thickness of the grain-oriented electrical steel sheet 1 and the original sheet 2 is not limited, but is preferably, for example, 0.15 mm to 0.30 mm. By making the thickness 0.30 mm or less, classical eddy current loss can be suppressed and iron loss can be further improved. On the other hand, by making the thickness 0.15 mm or more, rolling efficiency can be improved, and productivity can be improved.

(Surface Treatment)
The grain-oriented electrical steel sheet 1 and the original sheet 2 may have a forsterite coating. Furthermore, the grain-oriented electrical steel sheet 1 and the original sheet 2 may 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.

The forsterite coating is, for example, an inorganic coating mainly composed of magnesium silicate. The forsterite coating is formed, for example, in the final 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, for example, a composition derived from the components of the annealing separator and the base steel sheet (more specifically, a composition mainly composed of Mg ₂ SiO ₄ ). On the other hand, when an annealing separator mainly composed of Al ₂ O ₃ is used in the final annealing, the forsterite coating may not be formed.

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

The insulating coating is preferably formed after the final annealing and after 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 the insulating coating again on the magnetic domain control treatment wire 11 after the magnetic domain control treatment.

(Angle between magnetic domain control processing line 11 and rolling direction TD)
The angle between the magnetic domain control processing line 11 and the rolling-perpendicular direction TD is not particularly limited. The magnetic domain control processing line 11 and the rolling-perpendicular direction TD may be substantially parallel. That is, the angle between the magnetic domain control processing line 11 and the rolling-perpendicular direction TD may be substantially 0°. On the other hand, as illustrated in FIG. 1, the angle between the magnetic domain control processing line 11 and the rolling-perpendicular direction TD may be more than 0°. For example, the angle between the magnetic domain control processing line 11 and the rolling-perpendicular direction TD may be any value within the range of 0° to 45°. The angle between the magnetic domain control processing line 11 and the rolling-perpendicular direction TD may be 1° or more, 3° or more, or 5° or more. The angle between the magnetic domain control processing line 11 and the rolling-perpendicular direction TD may be 40° or less, 35° or less, or 30° or less.

As illustrated in FIG. 1, the angles formed by all the magnetic domain control processing lines 11 and the direction perpendicular to the 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 perpendicular to the 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 perpendicular to the 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 perpendicular to the rolling TD may be 40° or less, 35° or less, or 30° or less. The average angle can be calculated by measuring the angle that one magnetic domain control processing line makes with the direction perpendicular to the rolling direction TD at multiple positions, or by measuring the angles that multiple magnetic domain control processing lines make with the direction perpendicular to the rolling direction TD at one point or multiple positions, and then calculating the average value.

(The magnitude of tensile stress introduced in thermal strain)
The magnetic domain control processing line 11 may be thermally strained. In the thermal strain, a 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 the noise characteristics are improved. The tensile stress can be appropriately selected according to the characteristics required for the grain-oriented electrical steel sheet 1.

The magnitude of the tensile stress is not particularly limited, but 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. When the tensile stress in at least one direction is 40 MPa or more, the requirement that "tensile stress in any direction is 40 MPa or more" is deemed to be satisfied. Also, 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.

(Groove depth and width)
The magnetic domain control processing line 11 may be a groove. The greater the depth and width of the groove, the greater the effect of improving iron loss. On the other hand, the smaller the depth and width of the groove, the greater the improvement in noise characteristics. The shape of the groove can be appropriately selected according to the characteristics required for the grain-oriented electrical steel sheet 1.

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.

The width of the groove (width at the opening) is not particularly limited, but is preferably, for example, 10 μm to 300 μm. The width of the groove may be specified as 20 μm or more, 30 μm or more, or 50 μm or more. The width of the groove 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 they vary, it is preferable that the average depth and width of multiple grooves is within the above range.

(Measurement method)
A method for measuring various parameters of the grain-oriented electrical steel sheet 1 according to this embodiment will be described below. Note that all of the parameters are measured on a sample taken from the grain-oriented electrical steel sheet 1. For example, a rectangular sample with both sides of 100 mm (or 100 mm or more) can be cut out from the grain-oriented electrical steel sheet 1 and used for measurement. When the grain-oriented electrical steel sheet 1 is a coil, the sample may be taken from any location of the coil. Also, when the grain-oriented electrical steel sheet 1 is a component incorporated in an electrical product such as a transformer or a motor, the sample may be taken from any location of the component. When the size of the component is small, the length of one side of the sample may be less than 100 mm as long as the length of one side is 50 mm or more. In this case, it is desirable to take the sample by a method such as wire cutting in order to minimize the influence of mechanical distortion on the sample.

(Method of Identifying Magnetic Domain Control Processing Line 11)
When the magnetic domain control processing lines 11 are grooves, the magnetic domain control processing lines 11 can be identified visually. When the grain-oriented electrical steel sheet 1 has an insulating coating, the magnetic domain control processing lines 11 can be visually observed by removing the insulating coating using a known stripping agent.

If the magnetic domain control processing line 11 is thermally distorted, it may not be possible to visually identify the magnetic domain control processing line 11. In this case, a magnetic domain image is taken using an image acquisition device 30 as illustrated in FIG. 6, for example. 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 position of the thermal distortion can be identified.

(Method of determining rolling direction RD and rolling transverse direction TD)
The rolling direction RD and the direction perpendicular to the rolling direction TD of the grain-oriented electrical steel sheet 1 are specified by the following means.
(1) In the case where the sample is cut out from a coil-shaped grain-oriented electrical steel sheet 1, the width direction of the coil is regarded as the direction transverse to rolling TD. In addition, the direction perpendicular to the direction transverse to rolling TD and the normal direction ND of the rolling surface is regarded as the rolling direction RD.
(2) When the sample is cut out from a part of an electrical product, the rolling direction RD and the direction perpendicular to the rolling direction TD are identified from the rolling scratches on the surface of the grain-oriented electrical steel sheet 1. The direction in which the rolling scratches extend is regarded as the rolling direction RD. The direction perpendicular to the rolling direction RD and the normal direction ND to the rolling surface is regarded as the direction perpendicular to the rolling direction RD and the normal direction ND to the rolling surface is regarded as the direction perpendicular to the rolling direction TD.
(3) When it is difficult to identify the rolling direction RD and the direction perpendicular to the rolling direction TD from the rolling scratches on the surface of the grain-oriented electrical steel sheet 1, the rolling direction RD and the direction perpendicular to the rolling direction TD are identified from the crystal orientation of the grain-oriented electrical steel sheet 1. Specifically, the crystal orientation of the grain-oriented electrical steel sheet 1 to be evaluated is measured at multiple points. Then, the direction in which the angle between the crystal orientation at the measurement point and the rolling surface normal direction ND (sheet thickness direction) is closest to a right angle and the deviation angle from the easy axis of magnetization <001> is the smallest is regarded as the rolling direction RD, and the direction perpendicular to the rolling direction RD and the rolling surface normal direction ND is regarded as the rolling direction perpendicular to the rolling direction RD.

(Minimum value D _S and maximum value D _L of the spacing between magnetic domain control points VP)
The minimum value D _S and maximum value D _L of the distance between the magnetic domain control processing points are calculated according to the following procedure. First, a square evaluation area with one side having a length of 50 mm and parallel to the rolling direction RD of the magnetic domain control processing sheet 1 is set on the grain-oriented magnetic steel sheet 1. Then, inside the evaluation area, imaginary lines VL parallel to the rolling direction RD and having a length of 50 mm are set on the surface of the grain-oriented magnetic steel sheet 1 at intervals of 5 mm. Next, magnetic domain control points VP, which are intersections of the imaginary lines VL and the magnetic domain control processing lines 11, are identified. 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 measured values are obtained.

The location where the evaluation area and the virtual line VL are set is not limited. The virtual line VL may be set at any location where the virtual line VL can be set so that D _S and D _L /D _S are within the range of the present disclosure. For example, the virtual line VL may be set so as to pass through the area X where the magnetic domain control processing line 11 is not provided. On the other hand, if a location where the virtual line VL can be set so that D _S and D _L /D _S are within the range of the present disclosure cannot be found, it is presumed that the requirements of the present disclosure are not met.

(Method of measuring β angle)
The β angle is measured by 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 the value obtained by rounding off the measured value to one decimal place. In other words, the significant figures of the β angle are rounded to one decimal place.

(|β _L | and |β _S |)
|β _L | is measured by the following procedure. First, two adjacent magnetic domain control points VP whose interval is the maximum value D _L on the virtual line VL are identified by the above-mentioned means. The β angle between these magnetic domain control points VP is measured by the above-mentioned means at 1 mm intervals from the midpoints of the magnetic domain control points VP. Incidentally, two or more locations whose interval is D _L may be formed on one virtual line VL by chance. In this case, there are two or more sets of two adjacent magnetic domain control points VP whose interval is the maximum value D _L. In this case, the β angle between each adjacent magnetic domain control point VP is measured at 1 mm intervals from the midpoints of the magnetic domain control points VP, and the average value of the absolute values of the β angles may be regarded as |β _L | on the virtual line VL.
The measurement procedure for |β _S | is the same as that for |β _L |. First, two adjacent magnetic domain control points VP whose interval is the minimum value D _S on the virtual line VL are identified by the above-mentioned means. The β angle between these magnetic domain control points VP is measured by the above-mentioned means. Incidentally, two or more locations whose interval is D _S may be formed on one virtual line VL by chance. In this case, there are two or more sets of two adjacent magnetic domain control points VP whose interval is the minimum value D _S. In this case, the β angle between each adjacent magnetic domain control point VP is measured at intervals of 1 mm, and the average value of the absolute values of the β angles may be regarded as |β _S | on the virtual line VL.

For each of the multiple virtual lines VL, D _S , D _L , |β _L | and |β _S | are determined according to the above-mentioned procedure. If 2 mm≦D _S ≦20 mm, 3≦D _L /D _S , and 1.5°≦|β _L | are satisfied for one or more virtual lines VL, the sample is deemed to be a grain-oriented electrical steel sheet according to the present disclosure. The more virtual lines VL that satisfy the requirements of the present disclosure, the more preferable it is.

(Method of measuring chemical composition of original sheet 2 and grain-oriented electrical steel sheet 1)
The chemical compositions of the grain-oriented electrical steel sheet 1 and the original sheet 2 may be measured by a general analysis method for steel. 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 thickness direction of the sample, and the chemical composition of the grain-oriented electrical steel sheet 1 and the original sheet 2 can be measured by measuring under conditions based on a calibration curve created in advance using a measuring device such as ICPS-8100 manufactured by Shimadzu Corporation. 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.

If a forsterite coating and/or insulating coating is formed on the grain-oriented electrical steel sheet 1 and the original sheet 2, the forsterite coating and/or insulating coating may be removed from the grain-oriented electrical steel sheet 1 and the original sheet 2 before analyzing the chemical composition of the grain-oriented electrical steel sheet 1 and the original sheet 2. The forsterite coating can be removed, for example, by immersing the sample in sulfuric acid and then immersing it in nitric acid. The conditions such as the temperature and concentration of the sulfuric acid and nitric acid and the immersion time are appropriately adjusted so that the base iron of the sample is not excessively dissolved. 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 sludge adhering to the surface. Then, the sample is dried. Furthermore, the sample is immersed in 10% nitric acid at room temperature for about 5 seconds while stirring. The insulating coating can be removed, for example, by immersing the sample in a sodium hydroxide solution and then immersing it in dilute sulfuric acid and nitric acid. The conditions such as the temperature and concentration of the sodium hydroxide, dilute sulfuric acid, and nitric acid solutions, and the immersion time are adjusted appropriately so that the base steel of the sample does not dissolve excessively. An example of the conditions for removing the insulating coating is as follows. First, the sample is immersed in a 20% sodium hydroxide solution at 80°C for 15 minutes. The sample is then dried. The sample is then immersed in a 10% dilute sulfuric acid solution at 80°C for 4 minutes. The sludge adhering to the surface of the sample is then removed with a rag or similar. The sample is then immersed in a 10% nitric acid solution at room temperature for about 10 seconds while stirring.

(Method of measuring the angle between the magnetic domain control processing line 11 and the direction perpendicular to the rolling direction TD)
The angle between the magnetic domain control process line 11 and the direction perpendicular to the rolling direction TD can be measured using a known angle measuring means after the magnetic domain control process line 11 and the direction perpendicular to the rolling direction TD are specified by the above-mentioned procedure.

(Method of measuring the magnitude of tensile stress induced by thermal strain)
The magnitude of the tensile stress introduced 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 detail in A. J. Wilkinson, et al. "High-resolution elastic strain measurement from electron backscatter diffraction patterns: New levels of sensitivity", Ultramicroscopy Vol. 106, No. 4-5, March 2006, pp. 307-313.

When measuring the magnitude of the tensile stress induced by thermal distortion using the EBSD Wilkinson method and BLG Vantage's Cross Court, first, the magnetic domain control processing line 11 is identified using the procedure described above. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control processing line 11 and perpendicular to the magnetic domain control processing line 11. This cut surface is used as the measurement surface. The cross section of the magnetic domain control processing line 11 included in the measurement surface is analyzed using the EBSD Wilkinson method and BLG Vantage's Cross Court to extract the tensile stress components in any direction and measure their magnitude. For example, the tensile stress components can be extracted in the normal direction ND of the rolling surface, in a direction parallel to the magnetic domain control processing line 11, and in a direction perpendicular to the normal direction ND of the rolling surface and the magnetic domain control processing line 11.

The number of measurement points is, for example, 10. If the tensile stress in any direction is 40 MPa or more at at least one point of 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 processing 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.

(Method of 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 above-mentioned procedure before three-dimensional measurement of the sample surface is performed.

The effect of one aspect of the present disclosure will be explained in more detail using an example. However, the conditions in the example are merely one example of conditions adopted to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this one 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 purpose of the present disclosure is achieved.

Example 1
Grain-oriented electrical steel sheets (grain-oriented electrical steel sheets having a general crystal grain size) from the same lot with a sheet thickness of 0.20 mm were used as the original sheets. For example, the average heating rate of this electrical steel sheet from 1000°C to 1200°C during the temperature rise process of the finish annealing was set to 15°C/hour. This original 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 by 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.

The shapes of the magnetic domain control processing lines were any of the following: The shapes applied to the samples are listed in the “Remarks” column of Table 1.
A: As described above, the magnetic domain control processing line was formed in the area with a small β angle.
B: A linear magnetic domain control processing line was formed across the entire width of the original sheet.
C: Randomly dotted magnetic domain control processing 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 each crystal grain in the rolling direction. The radius of curvature of the steel sheet at the position where the crystal grain was located during the final annealing was 250 mm.

The noise and iron loss were evaluated as follows. First, a three-phase transformer core was created by stacking 205 grain-oriented electromagnetic 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 external height and width of the three-phase transformer core were both 750 mm. The noise and iron loss of these three-phase transformer cores were measured. The measurement conditions were a frequency of 60 Hz and an excitation magnetic flux density of 1.5 T.

To measure the noise, microphones were placed at equal intervals around eight points around the transformer in which the three-phase transformer core was installed. 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 shown in Table 2 as the noise evaluation results (unit: dBA) for 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 had been achieved. Noise evaluation results that were determined to be unsatisfactory are underlined.

As mentioned above, the iron loss was determined by using a power analyzer to measure the voltage and current on the primary and secondary sides when excitation was performed at a frequency of 60 Hz and an excitation magnetic flux density of 1.5 T. The determined iron loss is shown in Table 2 as the iron loss evaluation results (units: 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 had been achieved. Noise evaluation results that were determined to be unsatisfactory are underlined.

Furthermore, the number of virtual lines in which the minimum value D _S of the interval between the magnetic domain control points in the grain-oriented electrical steel sheet that had been subjected to the magnetic domain control treatment was 2 mm or more and less than 20 mm, and D _L /D _S was 3 or more, was measured and listed in Table 1. The measurement method basically followed the above-mentioned procedure. A rectangular sample with both sides of 100 mm was cut out from a three-phase transformer core for measuring noise and iron loss, and was used for measurement. A square evaluation area with one side of 50 mm and one side 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. The standard deviation of the interval between the magnetic domain control points in each of the nine virtual lines V _L was measured. The number of virtual lines _VL for which the minimum value D _S of the spacing between the magnetic domain control points was 2 mm or more and less than 20 mm and D _L /D _S was 3 or more is listed in the column of Table 1 entitled "Number of _VLs for which the minimum value D _S of the spacing between the magnetic domain control points was 2 mm or more and less than 20 mm and D _L /D _S was 3 or more."

The β angle was measured along each of the virtual lines VL where D _S was 2 mm or more and less than 20 mm and D _L /D _S was 3 or more, as specified by the above procedure. Then, among the virtual lines VL where D _S was 2 mm or more and less than 20 mm and D _L /D _S was 3 or more, the number of VLs where the average value of the absolute value of the β angle |β _L | was 1.5° or more, measured between two magnetic domain control points where the magnetic domain control point interval is the maximum value D _L , was recorded in the "Number of VLs with |β _L | 1.5° or more" column in Table 1. The sample with the number recorded in this column being 1 corresponds to a grain-oriented electrical steel sheet where the minimum value D _S is 2 mm or more and less than 20 mm, D _L /D _S is 3 or more, and |β _L | is 1.5° or more in one virtual line. The samples with two or more numbers written in the column correspond to grain-oriented electrical steel sheets in which D _S is 2 mm or more and less than 20 mm, D _L /D _S is 3 or more, and |β _L | is 1.5° or more, in each of two or more imaginary lines.

Furthermore, among the virtual lines VL where D _S is 2 mm or more and less than 20 mm, D _L /D _S is 3 or more, and |β _L | is 1.5° or more, the number of VLs where |β _L | and the average value |β _S | of the absolute value of the β angle measured between two magnetic domain control points having the smallest distance between the magnetic domain control points satisfy 0.5°≦|β _L |-|β _S | is listed in the column of Table 1 "Number of VLs that satisfy |β _L |-|β _S |≧0.5°".

Although not shown in the table, the number of grain boundary points, which are intersections between the virtual line VL and the grain boundaries, was 3 or more for all of the virtual lines VL where D _S was 2 mm _or more and less than ₂₀ mm and D L /D _S was 3 or more. Also, although not shown in the table, the value of D _L /D _S was less than 5 for all of the virtual lines VL where D S was 2 mm or more and less than 20 mm and D _L /D _S was 3 or more.

In Example 9, the magnetic domain control processing lines were formed linearly across the entire width of the original sheet. Therefore, in Example 9, it was not possible to set the virtual line VL such that D _L /D _S was 3 or more. In Example 9, the iron loss evaluation results were good, but the noise evaluation results were poor. This is presumably because the magnetic domain control processing lines were formed in places where magnetic domain control was not required.

In Example 10, dashed magnetic domain control processing lines were formed. The spacing between the magnetic domain control processing lines in one dashed line was set to a random value. In Example 10, it was possible to set a virtual line VL such that D _L /D _S was 3 or more. However, in all of these virtual lines, the average value |β _L | of the absolute value of the β angle was less than 1.5°. In Example 10, the noise evaluation result was good, but the iron loss evaluation result was poor. It is presumed that this is because the magnetic domain control processing lines were not formed in the places where magnetic domain control was required.

In Example 11, magnetic domain control processing lines were formed at intervals of 4 mm only in the region within ±4 mm from the center of the rolling direction 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 present during the final annealing was 250 mm. The results of Example 11 were similar to those of Example 10. That is, in Example 11, it was possible to set a virtual line VL such that D _L /D _S was 3 or more. However, in all of these virtual lines, the average value |β _L | of the absolute value of the β angle was less than 1.5°. In Example 11, the noise evaluation result was good, but the iron loss evaluation result was poor. It is presumed that this is because magnetic domain control processing lines were not formed in the places where magnetic domain control was required.

On the other hand, in the case where it was possible to set one or more virtual lines VL in which D _S was 2 mm or more and less than 20 mm, D _L /D _S was 3 or more, and |β _L | was 1.5° or more, both the iron loss evaluation results and the noise evaluation results were good.

Example 2
A magnetic domain control treatment was carried out on the 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 original sheet. Specifically, grain-oriented electrical steel sheets (grain-oriented electrical steel sheets having coarse crystal grain sizes) of the same lot with a sheet thickness of 0.20 mm were used as the original sheet. For example, the average heating rate of this electrical steel sheet from 1000°C to 1200°C during the temperature rise process of the finish annealing was set to less than 5°C/hour. The magnetic domain control treatment was carried out on this original sheet under various conditions shown in Table 3. The magnetic flux density, noise, and iron loss of the grain-oriented electrical steel sheets obtained by this magnetic domain control treatment were evaluated and listed in Table 4. In Table 4, values that were determined to be unacceptable are underlined.

The shape of the magnetic domain control processing line is the same as in Example 1 described above, the method of evaluating noise and iron loss is the same as in Example 1 described above, and the method of presenting the manufacturing results and evaluation results in the table is also the same as in Example 1 described above.

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

Although not shown in the table, for any imaginary line VL where D _S was 2 mm or more and less than 20 mm and D _L /D _S was 3 or more, the number of grain boundary points, which are the intersections between the imaginary line VL and the crystal grain boundaries, was 2 or less.

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

Similarly, for the imaginary line VL where _D is 2 mm or more and less than 20 mm and _D / _D is 3 or more, in Examples 12 to 19 where the number of grain boundary points that are intersections with the crystal grain boundaries is 2 or less, the magnetic flux density results, the iron loss evaluation results, and the noise evaluation results were all good.

The present disclosure provides a grain-oriented electrical steel sheet that can achieve both low iron loss and low noise, and a manufacturing method thereof. Therefore, it has high industrial applicability.

1 Grain-oriented electrical steel sheet 11 Magnetic domain control processing line RD Rolling direction TD Direction perpendicular to rolling ND Rolling surface normal direction VL Virtual line VP Magnetic domain control point D Maximum distance D between _L magnetic domain control points Minimum distance X between _S magnetic domain control points Region where no magnetic domain control processing line is provided 2 Original sheet 21 Magnetic domain control processing region 22 Non-magnetic domain control processing region 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 (15)

A grain-oriented electrical steel sheet having a plurality of magnetic domain control processing lines on a surface thereof,
In the grain-oriented electrical steel sheet, a square evaluation area with one side having a length of 50 mm and parallel to the rolling direction of the grain-oriented electrical steel sheet is set, and further, virtual lines having a length of 50 mm and parallel to the rolling direction are set at 5 mm intervals inside the evaluation area.
a grain-oriented electrical steel sheet in which, for at least one of the virtual lines, a minimum value D _S of the spacing between magnetic domain control points which are intersections between the virtual line and the magnetic domain control processing line is 2 mm or more and less than 20 mm, a ratio D _L /D _S of a maximum value _{D L} of the spacing between the magnetic domain control points to the minimum value D S is 3 or more, and an average value |β _L | of the absolute value of the β angle measured between two of the magnetic domain control points where the spacing is the maximum value D _L is 1.5° or more. 2. The grain-oriented electrical _steel sheet according to claim 1, wherein, in each of two or more of the virtual lines, the minimum value D _S of the spacing between the magnetic domain control points is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points to the minimum value D _S is 3 or more, and the average value |β _L | of the absolute values of the β angles measured between the two magnetic domain control points where the spacing is the maximum value D L is 1.5° or more. 3. The grain-oriented electrical steel sheet according to claim 1 , wherein, on the imaginary line where D _S is 2 mm or more and less than 20 mm, D _L /D _S is 3 or more, and |β _L | is 1.5° or more, |β _L | and an average value |β _S | of absolute values of β angles measured between two magnetic domain control points where the distance between the magnetic domain control points is the minimum value D _S satisfy the following formula:
0.5°≦｜β _L ｜-｜β _S ｜ 2. The grain-oriented electrical steel sheet according to claim 1, wherein, for at least one of the virtual lines, the minimum value D _S of the spacing between the magnetic domain control points, which are intersections between the virtual line and the magnetic domain control processing line _{, is 2 mm or more and less than 20 mm, the ratio D L /} D _S of the maximum value D _L of the spacing between the magnetic domain control points to the minimum value D _S is 5 or more, and the average value |β _L | of the absolute values of the β angles measured between two of the magnetic domain control points where the spacing is the maximum value D L is 1.5° or more. _5. The grain-oriented electrical steel sheet according to claim 4, wherein, in each of two or more of the virtual lines, the minimum value D _S of the spacing between the magnetic domain control points is 2 mm or more and less than 20 mm, the ratio D _L /D _S of the maximum value D _L of the spacing between the magnetic domain control points to the minimum value D _S is 5 or more, and the average value |β _L | of the absolute values of the β angles measured between the two magnetic domain control points where the spacing is the maximum value D L is 1.5° or more. 6. The grain-oriented electrical steel sheet according to claim 4, wherein, in the imaginary line where D _S is 2 mm or more and less than 20 mm, D _L /D _S is 5 or more, and |β _L | is 1.5° or more, |β _L | and an average value |β _S | of absolute values of β angles measured between two magnetic domain control points where the distance between the magnetic domain control points is the minimum value D _S satisfy the following formula:
0.5°≦｜β _L ｜-｜β _S ｜ 2. The grain-oriented electrical steel sheet according to claim 1, wherein the ratio D _L /D S of the maximum value _{D L} of the spacing between the magnetic domain control points to the minimum value D _S is 3 or more, and in at least one of the virtual lines, the number of grain boundary points that are intersections between the virtual line and a crystal boundary is 2 or less. The grain-oriented electrical steel sheet according to claim 7 , wherein the number of the grain boundary points is two or less on each of the two or more imaginary lines. The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain control processing line is thermal distortion. The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain control processing lines are grooves. The grain-oriented electrical steel sheet according to claim 1 , wherein the ratio D _L /D _S is less than 3 in at least one of the imaginary lines. Obtaining a magnetic domain image of an original sheet of grain-oriented electrical steel sheet;
determining a magnetic domain control processing area based on a distribution of magnetic domain widths in the magnetic domain image;
applying a magnetic domain control treatment to the magnetic domain control treatment area determined based on a distribution of magnetic domain widths;
Equipped with
In the grain-oriented electrical steel sheet, a square evaluation area with one side having a length of 50 mm and parallel to the rolling direction of the grain-oriented electrical steel sheet is set, and further, virtual lines having a length of 50 mm and parallel to the rolling direction are set at 5 mm intervals inside the evaluation area.
A method for manufacturing a grain-oriented electrical steel sheet, wherein, for at least one of the virtual lines, the minimum value of the spacing between magnetic domain control points, which are the intersections of the virtual line and a magnetic domain control processing line formed by the magnetic domain control processing, is 2 mm or more and less than 20 mm, and the ratio of the maximum value of the spacing between the magnetic domain control points to the minimum value is 3 or more. The method for manufacturing grain-oriented electrical steel sheet according to claim 12, wherein the magnetic domain control treatment area is an area where the magnetic domain width is equal to or greater than a predetermined value. The method for manufacturing grain-oriented electrical steel sheet according to claim 12 or 13, in which the distribution of the magnetic domain width is derived from the magnetic domain image using a two-dimensional Fourier transform. The method for manufacturing grain-oriented electrical steel sheet according to claim 12 or 13, in which the magnetic domain control treatment is applied by irradiation with a laser or an electron beam.

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