EP4786619A1

EP4786619A1 - Grain-oriented electrical steel sheet and method for manufacturing grain-oriented electrical steel sheet

Info

Publication number: EP4786619A1
Application number: EP24872557.4A
Authority: EP
Inventors: Ryo Matsubara; Yusuke Kawamura; Rei Honma; Toshiyuki Suzuma
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2023-09-27
Filing date: 2024-09-27
Publication date: 2026-08-05
Also published as: JPWO2025070776A1; CN121909297A; WO2025070776A1; KR20260057208A

Abstract

A grain-oriented electrical steel sheet has plural magnetic domain control treatment lines on a surface thereof, when imaginary lines are set with a spacing of 5 mm in an evaluation region, in at least one of the imaginary lines, a minimum value D_S of distances of magnetic domain control points which are intersection points between the imaginary lines and the magnetic domain control treatment lines is 2 mm or more and less than 20 mm, a ratio D_L/D_S of a maximum value D_L of the distances of the magnetic domain control points to the minimum value D_S is 3 or more, and an average value |β_L| of absolute values of β angles which are measured between two of the magnetic domain control points whose distance is the maximum value D_L is 1.5° or more.

Description

TECHNICAL FIELD

The present disclosure relates to a grain-oriented electrical steel sheet and a method for manufacturing a grain-oriented electrical steel sheet.
Priority is claimed on Japanese Patent Application No. 2023-166102, filed September 27, 2023 , the content of which is incorporated herein by reference.

BACKGROUND ART

The grain-oriented electrical steel sheet is a steel sheet containing 7 mass% or less of Si and having a secondary recrystallization structure in which secondary recrystallized grains are accumulated in a { 110}<001> orientation (Goss orientation) in which an easy axis of magnetization <001> is oriented in a rolling direction. Grain-oriented electrical steel sheets are mainly used as iron cores of power transformers. Grain-oriented electrical steel sheets are required to reduce energy loss (iron loss).
A technique of narrowing a spacing of magnetic domain walls of a grain-oriented electrical steel sheet (magnetic domain refinement technique by magnetic domain control treatment) for reducing iron loss has been known for a long time. The spacing of magnetic domain walls can be narrowed by irradiating the surface of the grain-oriented electrical steel sheet with a laser or an electron beam in a direction intersecting the rolling direction to introduce a thermal strain. The spacing of magnetic domain walls can also be narrowed by forming a groove in the direction intersecting the rolling direction on the surface of the grain-oriented electrical steel sheet. Examples of a method of forming the groove include a method of irradiating with a laser or an electron beam, a method by mechanical processing such as gear, and a method by chemical processing such as etching.
In recent years, in order to provide a grain-oriented electrical steel sheet having good iron loss characteristics, various improved techniques related to magnetic domain refinement have been proposed (see, for example, Patent Documents 1 to 3.).

Citation List

Patent Documents

Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2012-57219
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2012-12664
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2012-57218

SUMMARY OF INVENTION

Technical Problem

When the magnetic domain control treatment is applied to the grain-oriented electrical steel sheet, the magnetostrictive characteristic of the grain-oriented electrical steel sheet changes depending on the flux closure domain. As a result, noise characteristics of the grain-oriented electrical steel sheet deteriorate. The noise characteristic is a degree of noise generated by an electrical product (for example, a transformer, a motor, and the like) manufactured using a grain-oriented electrical steel sheet as a material. Magnetostriction is a phenomenon in which an outer shape is slightly deformed when a ferromagnetic material is magnetized. When the grain-oriented electrical steel sheet is excited by alternating current, the magnitude of the magnetostriction changes with a change in the strength of magnetization, and thus vibration occurs. The magnitude of the magnetostriction is very small on the order of 10^-6, but the magnetostriction generates vibration in the iron core, and the vibration propagates to an external structure such as a tank of a transformer to become noise. That is, the magnetic domain control treatment is effective for reducing iron loss of the grain-oriented electrical steel sheet, but deteriorates noise characteristics of the grain-oriented electrical steel sheet.
In recent years, there is an increasing demand for not only a reduction in iron loss but also a reduction in noise for grain-oriented electrical steel sheets. However, no magnetic domain refinement technique capable of sufficiently achieving both noise reduction and iron loss reduction has been proposed so far.
An object of the present disclosure is to provide a grain-oriented electrical steel sheet capable of achieving both iron loss reduction and noise reduction, and a manufacturing method therefore.

Solution to Problem

The gist of the present disclosure is as follows.

(1) A grain-oriented electrical steel sheet according to an aspect of the present disclosure has plural magnetic domain control treatment lines on a surface thereof, wherein,
- when an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to a rolling direction of the grain-oriented electrical steel sheet is determined in the grain-oriented electrical steel sheet and when imaginary lines parallel to the rolling direction with a length of 50 mm are set with a spacing of 5 mm in the evaluation region,
- in at least one of the imaginary lines, a minimum value D_S of distances of magnetic domain control points which are intersection points between the imaginary lines and the magnetic domain control treatment lines is 2 mm or more and less than 20 mm, a ratio D_L/D_S of a maximum value D_L of the distances of the magnetic domain control points to the minimum value D_S is 3 or more, and an average value |β_L| of absolute values of β angles which are measured between two of the magnetic domain control points whose distance is the maximum value D_L is 1.5° or more.
(2) Preferably, in the grain-oriented electrical steel sheet according to (1),
in each of two or more of the imaginary lines, the minimum value D_S of the distances of 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 distances of 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 which are measured between two of the magnetic domain control points whose distance is the maximum value D_L is 1.5° or more.
(3) Preferably, in the grain-oriented electrical steel sheet according to (1) or (2),
in the imaginary lines 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 which are measured between two of the magnetic domain control points whose distance of the magnetic domain control points is the minimum value D_S satisfy a following expression, 0.5° ≤ |β_L| - |β_S|.
(4) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (3),
in at least one of the imaginary lines, the minimum value D_S of the distances of the magnetic domain control points which are intersection points between the imaginary lines and the magnetic domain control treatment lines is 2 mm or more and less than 20 mm, the ratio D₁/Ds of the maximum value D_L of the distances of 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 which are measured between two of the magnetic domain control points whose distance 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),
in each of two or more of the imaginary lines, the minimum value D_S of the distances of 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 distances of 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 which are measured between two of the magnetic domain control points whose distance 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),
in the imaginary lines 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 which are measured between two of the magnetic domain control points whose distance of the magnetic domain control points is the minimum value D_S satisfy a following expression, 0.5° ≤ |β_L| - |β_S|.
(7) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (6),
in at least one of the imaginary lines in the imaginary lines where the ratio D_L/D_S of the maximum value D_L of the distances of the magnetic domain control points to the minimum value D_S is 3 or more, a number of grain boundary points which are intersection points between the imaginary lines and grain boundaries is 2 points or less.
(8) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (7), in each of two or more of the imaginary lines, the number of grain boundary points is 2 points or less.
(9) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (8), the magnetic domain control treatment lines are thermal strain.
(10) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (9), the magnetic domain control treatment lines are grooves.
(11) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (10), in at least one of the imaginary lines, the ratio D_L/D_S is less than 3.
(12) A method for manufacturing a grain-oriented electrical steel sheet according to another aspect of the present disclosure includes:
- a step of acquiring a magnetic domain image of an original sheet of a grain-oriented electrical steel sheet;
- a step of determining a magnetic domain control treatment region based on a distribution of spacing of magnetic domain walls in the magnetic domain image; and
- a step of applying a magnetic domain control treatment to the magnetic domain control treatment region determined based on the distribution of the spacing of magnetic domain walls; wherein,
- when an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to a rolling direction of the grain-oriented electrical steel sheet is determined in the grain-oriented electrical steel sheet and when imaginary lines parallel to the rolling direction with a length of 50 mm are set with a spacing of 5 mm in the evaluation region,
- in at least one of the imaginary lines, a minimum value of distances of magnetic domain control points which are intersection points between the imaginary lines and the magnetic domain control treatment lines formed by the magnetic domain control treatment is controlled to 2 mm or more and less than 20 mm, and a ratio of a maximum value of the distances of the magnetic domain control points to the minimum value is controlled to 3 or more.
(13) Preferably, in the method for manufacturing the grain-oriented electrical steel sheet according to (12), a region where the spacing of magnetic domain walls is a predetermined value or more is set as the magnetic domain control treatment region.
(14) Preferably, in the method for manufacturing a grain-oriented electrical steel sheet according to (12) or (13), a distribution of the spacing of magnetic domain walls is derived from the magnetic domain image using a two-dimensional Fourier transform.
(15) Preferably, in the method for manufacturing a grain-oriented electrical steel sheet according to any one of (12) to (14), the magnetic domain control treatment is applied by irradiation with a laser or an electron beam.

Advantageous Effects of Invention

According to the above aspects of the present disclosure, it is possible to provide a grain-oriented electrical steel sheet capable of achieving both iron loss reduction and noise reduction, and a method for manufacturing the same.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A plan view of a grain-oriented electrical steel sheet according to an embodiment of the present disclosure.
[FIG. 2] A plan view of a normal grain-oriented electrical steel sheet.
[FIG. 3] A graph illustrating a relationship between a β angle and a spacing of magnetic domain walls.
[FIG. 4A] A schema illustrating an example of distribution of the spacing of magnetic domain walls of a grain-oriented electrical steel sheet before a magnetic domain control treatment.
[FIG. 4B] A schema illustrating an example of distribution of the spacing of magnetic domain walls of a grain-oriented electrical steel sheet after a magnetic domain control treatment.
[FIG. 4C] A schema illustrating a difference between FIGS. 4A and 4B.
[FIG. 5] A graph illustrating a relationship between a spacing of magnetic domain walls before a magnetic domain control treatment and a spacing of magnetic domain walls after the magnetic domain control treatment.
[FIG. 6] A block diagram illustrating an example of a hardware constitution of the image acquisition device.
[FIG. 7] A block diagram illustrating an example of a hardware constitution of an analysis device.
[FIG. 8] A schematic diagram illustrating an example of a constitution of a laser irradiation device.
[FIG. 9] A flowchart illustrating a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present disclosure.
[FIG. 10] A schematic view showing a method of cutting out a plurality of partial regions from a magnetic domain image of a grain-oriented electrical steel sheet.
[FIG. 11] An example of a plurality of partial Fourier images obtained by applying two-dimensional Fourier transform to each of a plurality of partial regions cut out from a magnetic domain image of a grain-oriented electrical steel sheet.
[FIG. 12] A plan view of an original sheet of a grain-oriented electrical steel sheet.

DESCRIPTION OF EMBODIMENTS

(1. Grain-oriented electrical steel sheet 1)

The grain-oriented electrical steel sheet 1 according to the present embodiment has plural magnetic domain control treatment lines 11 on a surface thereof, wherein,

when an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to a rolling direction RD of the grain-oriented electrical steel sheet 1 is determined in the grain-oriented electrical steel sheet 1 and when imaginary lines VL parallel to the rolling direction RD with a length of 50 mm are set with a spacing of 5 mm in the evaluation region,
in at least one of the imaginary lines VL, a minimum value D_S of distances of magnetic domain control points VP which are intersection points between the imaginary lines VL and the magnetic domain control treatment lines 11 is 2 mm or more and less than 20 mm, a ratio D_L/D_S of a maximum value D_L of the distances of the magnetic domain control points VP to the minimum value D_S is 3 or more, and an average value |β_L| of absolute values of β angles which are measured between two of the magnetic domain control points VP whose distance is the maximum value D_L is 1.5° or more.

(Magnetic domain control treatment line 11)

A plurality of the magnetic domain control treatment lines 11 provided on the surface of the grain-oriented electrical steel sheet 1 have a function of refining a 180° magnetic domain. By refining the magnetic domain, the iron loss of the grain-oriented electrical steel sheet 1 can be reduced. The magnetic domain is a collection of magnetic dipoles existing inside a ferromagnetic material, and is a small region where magnetic moments are aligned in one direction. The 180° magnetic domain is a magnetic domain in which the magnetization direction is the <100> orientation of the crystal and which is sandwiched between two 180° magnetic domain walls substantially parallel to the rolling direction RD. A distance (magnetic domain wall interval) between adjacent magnetic domain walls of the 180° magnetic domain is referred to as a spacing of the 180° magnetic domain walls. Hereinafter, unless otherwise specified, the spacing of the 180° magnetic domain walls is simply referred to as "spacing of magnetic domain walls".
Suitable examples of the magnetic domain control treatment line 11 are the thermal strain and the groove. By refining the magnetic domain, the iron loss of the grain-oriented electrical steel sheet 1 can be suppressed. However, the magnetic domain control treatment line 11 changes the magnetostrictive characteristic of the grain-oriented electrical steel sheet 1 according to the flux closure domain. As a result, noise characteristics of the grain-oriented electrical steel sheet 1 deteriorate.
The magnetic domain control treatment line 11 is formed in a direction intersecting the rolling direction RD of the grain-oriented electrical steel sheet 1. In the general grain-oriented electrical steel sheet 1 as exemplified in FIG. 2, the magnetic domain control treatment line 11 is formed over the entire width of the grain-oriented electrical steel sheet 1. However, in the grain-oriented electrical steel sheet 1 according to the present embodiment as exemplified in FIG. 1, it is not essential to provide the magnetic domain control treatment line 11 over the entire width of the grain-oriented electrical steel sheet 1.
In the grain-oriented electrical steel sheet 1 illustrated in FIG. 1, the magnetic domain control treatment line 11 is a straight line. On the other hand, the magnetic domain control treatment line 11 may be a curve. The magnetic domain control treatment line 11 may have a shape having a straight line portion and a bent portion. The magnetic domain control treatment line 11 may be provided on one surface or both surfaces of the grain-oriented electrical steel sheet 1. When the magnetic domain control treatment line 11 is provided on both surfaces of the grain-oriented electrical steel sheet 1, various aspects of the grain-oriented electrical steel sheet 1 according to the present embodiment may be applied to at least one surface of the grain-oriented electrical steel sheet 1.

(Evaluation region)

In the grain-oriented electrical steel sheet 1 according to the present embodiment, an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to a rolling direction RD of the grain-oriented electrical steel sheet 1 is determined in order to set imaginary lines VL explained below.

(Imaginary lines VL parallel to the rolling direction RD with a length of 50 mm)

In the grain-oriented electrical steel sheet 1 according to the present embodiment, the imaginary line VL is used for convenience in order to define a spacing of the magnetic domain control treatment lines 11. The imaginary lines VL are set inside the evaluation region with a spacing of 5 mm. FIG. 1 illustrates a state in which only one imaginary line VL is drawn as an example. In a case where a plurality of imaginary lines VL is set, the required number of other imaginary lines can be set in parallel to the imaginary line VL of FIG. 1. The length of the imaginary line VL is 50 mm. The imaginary line VL extends parallel to the rolling direction RD. An intersection point of the imaginary line VL and the magnetic domain control treatment line 11 is defined as a magnetic domain control point VP. The distance of the magnetic domain control points VP is an index of the density of the magnetic domain control treatment lines 11. The distance of the magnetic domain control points VP is a spacing of two magnetic domain control points VP which are adjacent in the imaginary line VL.

(Minimum value D_S of distances of magnetic domain control points VP)

In the grain-oriented electrical steel sheet 1 according to the present embodiment, in at least one of the imaginary lines VL, the minimum value D_S of distances of magnetic domain control points VP is 2 mm or more and less than 20 mm. When the minimum value D_S of distances of magnetic domain control points VP is less than 2 mm, the density of the magnetic domain control treatment lines 11 is excessively high, and it is difficult to improve the noise characteristics. When the minimum value D_S of distances of magnetic domain control points VP is more than 20 mm, the density of the magnetic domain control treatment lines 11 is excessively low, and it is difficult to improve the iron loss characteristics. The D_S is preferably 3 mm or more, 4 mm or more, or 5 mm or more. The D_S is preferably 18 mm or less, 15 mm or less, or 10 mm or less.

(Ratio D_L/D_S of maximum value D_L and minimum value D_S of the distances of the magnetic domain control points VP)

Moreover, in the grain-oriented electrical steel sheet 1 according to the present embodiment, in at least one of the imaginary lines VL, in addition that the D_S is 2 mm or more and less than 20 mm, the ratio D_L/D_S of the maximum value D_L to the minimum value D_S of the distances of the magnetic domain control points VP is 3 or more. As illustrated in FIG. 1, the grain-oriented electrical steel sheet 1 in which one or more imaginary lines VL are arranged such that the D_S is 2 mm or more and less than 20 mm and the D_L/D_S is 3 or more includes a region X where the magnetic domain control treatment line 11 is not provided.
Herein, the maximum value D_L and the minimum value D_S of the distances of the magnetic domain control points VP may change according to the position where the evaluation region and the imaginary line VL are arranged. In the grain-oriented electrical steel sheet 1 provided as an exemplary example in FIG. 1A, it is also possible to position the evaluation region and the imaginary line VL such that the D_L/D_S is less than 3. However, it is considered that the grain-oriented electrical steel sheet 1 in which one or more imaginary lines VL in which 2 mm ≤ D_S < 20 mm and 3 ≤ D_L/D_S can be arranged at any place satisfies the requirement of the present disclosure regarding the distance between the magnetic domain control points VP. Therefore, the grain-oriented electrical steel sheet 1 of FIG. 1 satisfies the requirement of the present disclosure regarding the distance between the magnetic domain control points VP.
On the other hand, the grain-oriented electrical steel sheet 1 illustrated in FIG. 2 in which the plurality of magnetic domain control treatment lines 11 extending over the entire width of the grain-oriented electrical steel sheet 1 are arranged at equal intervals does not include the region X where the magnetic domain control treatment lines 11 are not provided. In the grain-oriented electrical steel sheet 1 of FIG. 2, an imaginary line VL in which 3 ≤ D_L/D_S cannot be arranged. Therefore, the grain-oriented electrical steel sheet 1 of FIG. 2 does not satisfy the requirement of the present disclosure regarding the distance between the magnetic domain control points VP.
The ratio D_L/D_S of the maximum value D_L to the minimum value D_S is 3 or more, and an upper limit is not particularly limited. However, as necessary, the upper limit of the ratio D_L/D_S of the maximum value D_L to the minimum value D_S may be 24.

(β angle)

In the grain-oriented electrical steel sheet 1 according to the present embodiment, the β angles measured in the magnetic domain control treatment line 11 satisfy a predetermined range. The β angle is a deviation angle of crystal grains from the Goss orientation about the axis in the transverse direction TD. It is known that controlling the β angle is effective for controlling the magnetic characteristics of the grain-oriented electrical steel sheet 1. The deviation angle of the crystal grains from the Goss orientation about the axis in the rolled surface normal direction ND is referred to as an α angle, and the deviation angle of the crystal grains from the Goss orientation about the axis in the rolling direction RD is referred to as a γ angle.
As shown in FIG. 3, in the grain-oriented electrical steel sheet 1 (original sheet 2 described later) before the magnetic domain control treatment, there is a close relationship between the β angle and the spacing of magnetic domain walls. FIG. 3 is a graph illustrating an example of the relationship between the β angle of the grain-oriented electrical steel sheet 1 before the magnetic domain control treatment and the average value of the spacing of magnetic domain walls. In the grain-oriented electrical steel sheet 1 before the magnetic domain control treatment, the smaller the β angle, the larger the spacing of magnetic domain walls. However, in the grain-oriented electrical steel sheet 1 after the magnetic domain control treatment, the relationship illustrated in FIG. 3 is not established. This is because the magnetic domain control treatment decreases the spacing of magnetic domain walls in the region where the spacing of magnetic domain walls is wide before the magnetic domain control, but does not change the orientation (α angle, β angle, γ angle) of the crystal grains.

(|βL|)

In the grain-oriented electrical steel sheet 1 according to the present embodiment, the β angle measured between the two magnetic domain control points VP having the longest distance is specified. Specifically, in at least one of the imaginary lines VL where the D_S is 2 mm or more and less than 20 mm and the D_L/D_S is 3 or more, the average value |β_L| of the absolute values of the β angles measured between the two magnetic domain control points VP at which the distance becomes the above-described maximum value D_L is 1.5° or more.
As shown in FIG. 1A, in the grain-oriented electrical steel sheet 1 according to the present embodiment, in the imaginary line VL where the D_S is 2 mm or more and less than 20 mm and the D_L/D_S is 3 or more, there is a region X where the magnetic domain control treatment has not been performed, and there are portions 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 treatment in which the plurality of magnetic domain control treatment lines 11 extending over the entire width are arranged at equal intervals, there is no region X where the magnetic domain control treatment is not performed. Even if there is a region X in which the magnetic domain control treatment is not performed in the grain-oriented electrical steel sheet 1 after the normal magnetic domain control treatment, that is, even if the grain-oriented electrical steel sheet 1 is the grain-oriented electrical steel sheet 1 in which the plurality of magnetic domain control treatment lines 11 are randomly arranged at uneven intervals, the spacing of magnetic domain walls in the region X is wide and the β angle is small.
Therefore, if the region X where the magnetic domain control treatment is not performed is provided in the normal grain-oriented electrical steel sheet 1, the average value of the absolute values of the β angles on the imaginary line VL passing through the region is a small value, and the spacing of magnetic domain walls is a large value. A person skilled in the art would try to reduce the region X where the magnetic domain control treatment is not performed as much as possible. However, in the grain-oriented electrical steel sheet 1 according to the present embodiment, the spacing of magnetic domain walls in the region X where the magnetic domain control treatment is not performed is narrow, and |β_L| measured in the region X is a large value.
|β_L| is still more preferably 1.5° or more, 2.0° or more, or 2.5° or more. The upper limit value 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 principle and effects)

The present inventors have found that, according to the grain-oriented electrical steel sheet in which one or more imaginary lines VL in which 2 mm ≤ D_S < 20 mm, 3 ≤ D_L/D_S, and 1.5° ≤ |β_L| can be arranged, both iron loss and noise can be reduced. This is because, in such a grain-oriented electrical steel sheet 1, the magnetic domain control treatment is applied only to a portion contributing to reduction of iron loss, and the magnetic domain control treatment line 11 is not provided in a portion where the magnetic domain control treatment is unnecessary. Hereinafter, the basic principle and effects of the present disclosure will be described with reference to FIGS. 4A to 4C and the like.
First, the present inventors compared the magnetic domain structure of the grain-oriented electrical steel sheet 1 before and after the magnetic domain control treatment. FIG. 4A shows an example of distribution of the spacing of magnetic domain walls of the grain-oriented electrical steel sheet 1 before the magnetic domain control treatment. FIG. 4B illustrates the distribution of the spacing of magnetic domain walls after the magnetic domain control treatment is performed on the surface of the grain-oriented electrical steel sheet 1 of FIG. 4A. The magnetic domain control treatment here is performed by applying continuous wave laser irradiation along a direction substantially perpendicular to the rolling direction RD. The distribution of the spacing of magnetic domain walls shown in FIGS. 4A and 4B is derived from the magnetic domain image of the grain-oriented electrical steel sheet 1 using two-dimensional Fourier transform described later.
FIG. 4C illustrates a difference between FIGS. 4A and 4B. FIG. 4C illustrates a region refined to a spacing of magnetic domain walls of 50 µm or more before and after the magnetic domain control treatment illustrated in FIGS. 4A and 4B. According to FIG. 4C, the region in which the spacing of magnetic domain walls is refined by the magnetic domain control treatment is visualized.
According to FIG. 4C, it can be seen that the region where the magnetic domain refinement of 50 µm or more has occurred by the magnetic domain control treatment is the dark color part of FIG. 4A, that is, the region where the spacing of magnetic domain walls is wide before the magnetic domain control treatment. In particular, it can be seen that the magnetic domain refinement effect remarkably appears in a region where the spacing of magnetic domain walls is originally about 500 µm or more. On the other hand, in the bright color part of FIG. 4A, that is, in the region where the spacing of magnetic domain walls is narrow before the magnetic domain control treatment, the effect of the magnetic domain control treatment hardly appears. The effect of the magnetic domain control treatment varies depending on the spacing of magnetic domain walls before the magnetic domain control treatment.
The present inventors investigated in more detail the relationship between the reduction amount of the spacing of magnetic domain walls caused by the magnetic domain control treatment and the spacing of magnetic domain walls before the magnetic domain control treatment. FIG. 5 shows the relationship between the spacing of magnetic domain walls before the magnetic domain control treatment and the spacing of magnetic domain walls before the magnetic domain control treatment at the same position. The magnetic domain control treatment was performed by laser irradiation. At the time of 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.
According to FIG. 5, it can be seen that the magnetic domain refinement effect by the magnetic domain control treatment is less likely to appear in the region where the spacing of magnetic domain walls is narrow. In particular, in the region where the spacing of magnetic domain walls was about 500 µm or less, the spacing of magnetic domain walls were substantially the same before and after the magnetic domain control treatment. Therefore, it is considered that the effect of reducing the iron loss by the magnetic domain control treatment is large in a region where the spacing of magnetic domain walls before magnetic domain control is wide, but is not sufficiently obtained in a region where the spacing of magnetic domain walls before magnetic domain control is sufficiently narrow. It is considered that the magnetic domain control treatment line 11 formed in a region where the spacing of magnetic domain walls is narrow causes deterioration of noise characteristics due to the flux closure domain.
According to the above findings, in the conventional magnetic domain control treatment of the grain-oriented electrical steel sheet 1, the magnetic domain control is performed to a portion where the magnetic domain control is unnecessary, and this contributes to an increase in noise. In addition, it is found that it is extremely effective to preferentially perform the magnetic domain control treatment in a region having a wide spacing of magnetic domain walls (that is, a region where β angle is small) in order to achieve both iron loss reduction and noise reduction. Magnetic domain control treatment in a region having a wide spacing of magnetic domain walls can reduce iron loss. In addition, by minimizing the magnetic domain control treatment in a region where the spacing of magnetic domain walls is narrow (that is, a region where β angle is large), deterioration of noise characteristics can be prevented.
In the grain-oriented electrical steel sheet 1 according to the present embodiment, the magnetic domain control treatment line 11 is not provided in a region where the spacing of magnetic domain walls was narrow before the magnetic domain control treatment. Therefore, the grain-oriented electrical steel sheet 1 according to the present embodiment includes the region X where the magnetic domain control treatment line 11 is not provided. In a case where the evaluation region and the imaginary line VL are set to cross the region X, 2 mm ≤ D_S < 20 mm and 3 ≤ D_L/D_S are satisfied. By not providing the magnetic domain control treatment line 11, noise characteristics of the grain-oriented electrical steel sheet 1 according to the present embodiment are improved.
The region X where the magnetic domain control treatment line 11 is not provided is a region where the spacing of magnetic domain walls is narrow and the β angle is large before the magnetic domain control treatment. Therefore, in the grain-oriented electrical steel sheet 1 according to the present embodiment, the β angle is large even in the region X where the magnetic domain control treatment line 11 is not provided. Thus, in a case where the evaluation region and the imaginary line VL are set to cross the region X, 1.5° ≤ |β_L| is satisfied. In the grain-oriented electrical steel sheet 1 according to the present embodiment, the iron loss is not deteriorated in the region X where the magnetic domain control treatment line 11 is not provided.
In addition, in the grain-oriented electrical steel sheet 1 according to the present embodiment, the magnetic domain control treatment is performed on a region having a wide spacing of magnetic domain walls before the magnetic domain control treatment. Therefore, the iron loss of the grain-oriented electrical steel sheet 1 according to the present embodiment is reduced by the magnetic domain control treatment.
The most basic aspect of the grain-oriented electrical steel sheet 1 according to the present embodiment has been described above. Hereinafter, a more preferred aspect will be described.
(Number of imaginary lines VL where 2 mm ≤ D_S < 20 mm, 3 ≤ D_L/D_S, and 1.5° ≤|β_L|)
According to the examination results of the present inventors, in the original sheet 2 before the magnetic domain control treatment, regions having a narrow spacing of magnetic domain walls (regions not requiring the magnetic domain control treatment) were scattered on the entire surface of the original sheet 2. It is preferable to appropriately perform the magnetic domain control by avoiding all the regions with narrow spacing of magnetic domain walls scattered on the entire surface of the original sheet 2. Accordingly, also in the grain-oriented electrical steel sheet 1 after the magnetic domain control treatment, it is desirable that the regions X where the magnetic domain control treatment lines 11 are not provided are scattered on the entire surface.
Therefore, in the grain-oriented electrical steel sheet 1 according to the present embodiment, in a case where the imaginary line VL parallel to the rolling direction RD with a length of 50 mm is set at intervals of 5 mm inside the evaluation region, in each of two or more imaginary lines VL, it is preferable that the minimum value D_S of the distances of 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 distances of 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 which are measured between two of the magnetic domain control points VP whose distance is the maximum value D_L is 1.5° or more. The number of the imaginary lines VL where 2 mm ≤ D_S < 20 mm, 3 ≤ D_L/D_S, and 1.5° ≤ |β_L| is more preferably 3 or more, 4 or more, 5 or more, or 10 or more.

(Relation between |B_L| and |B_S|)

In the imaginary lines VL where 2 mm ≤ D_S < 20 mm, 3 ≤ D_L/D_S, and 1.5° ≤ |β_L|, the |B_L| and an average value |β_S| of absolute values of β angles which are measured between two of the magnetic domain control points VP whose distance is the minimum value D_S satisfy a following expression. $0.5 ° \leq |β_{L}| - |β_{S}|$
When |β_L| - |β_S| is 0.5° or more, it indicates that the region to be subjected to the magnetic domain control treatment is selectively determined by the β angle. Since the magnetic domain control treatment is performed in a concentrated manner in a region where the spacing of magnetic domain walls before the magnetic domain control is large and the iron loss reduction effect is large, the noise characteristics are further improved.

(Aspect of magnetic domain control treatment line 11)

The type of the magnetic domain control treatment line 11 is not particularly limited, but suitable examples thereof are the thermal strain and/or the groove. The thermal strain can be formed using means such as laser irradiation, electron beam irradiation, and ion implantation. The groove can be formed using means such as laser irradiation, electron beam irradiation, and machining.
The thermal strain disappears by the stress relief annealing or the heat treatment according thereto. Therefore, when the grain-oriented electrical steel sheet 1 is subjected to a heat treatment, the magnetic domain control treatment line 11 is preferably a groove. On the other hand, since the thermal strain can be easily formed, when simplification of a manufacturing step is required, it is preferable to set the magnetic domain control treatment line 11 to the thermal strain. The grain-oriented electrical steel sheet 1 may include both the thermal strain and groove.

(Ratio D_L/D_S of maximum value D_L and minimum value D_S is 5 or more)

The grain-oriented electrical steel sheet 1 according to the present embodiment is characterized by selectively applying a magnetic domain control treatment to a region having a wide spacing of magnetic domain walls before magnetic domain control. In this case, a more remarkable effect can be obtained by applying the above treatment to a steel sheet having a coarse grain size than a steel sheet having a general grain size.
For example, in general, when the orientation development degree in the Goss orientation is to be increased in order to increase the magnetic flux density, the grain size tends to increase due to the manufacturing method. A steel sheet having such a coarse grain size has excellent magnetic flux density, but the iron loss tends to be high in a case where the magnetic domain control treatment is not performed because the grains are too large, and thus it is substantially necessary to perform the magnetic domain control. However, as described above, the conventional magnetic domain control treatment is effective in reducing the iron loss of the grain-oriented electrical steel sheet, but tends to deteriorate the noise characteristics of the grain-oriented electrical steel sheet.
On the other hand, when a magnetic domain control treatment is selectively performed on a steel sheet having a coarse grain size in a region having a wide spacing of magnetic domain walls before magnetic domain control as in the present embodiment, it is possible to obtain a grain-oriented electrical steel sheet capable of achieving both iron loss reduction and noise reduction in addition to excellent magnetic flux density.
When the magnetic domain control treatment unique to the present embodiment is performed on a steel sheet having a coarse grain size, the value of the ratio D_L/D_S of the maximum value D_L to the minimum value D_S particularly changes among the features described above because the steel sheet has a coarse grain size.
Specifically, it is preferable that the grain-oriented electrical steel sheet 1 according to the present embodiment satisfies the following feature. It is preferable that, in at least one of the imaginary lines VL, the minimum value D_S of the distances of the magnetic domain control points VP which are intersection points between the imaginary lines VL and the magnetic domain control treatment 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 distances of 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 values of the β angles which are measured between two of the magnetic domain control points VP whose distance is the maximum value D_L is 1.5° or more.
In addition, it is more preferable that the grain-oriented electrical steel sheet 1 according to the present embodiment satisfies the following feature. It is preferable that, in each of two or more of the imaginary lines VL, the minimum value D_S of the distances of 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 distances of 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 values of the β angles which are measured between two of the magnetic domain control points VP whose distance is the maximum value D_L is 1.5° or more.
In addition, it is more preferable that the grain-oriented electrical steel sheet 1 according to the present embodiment satisfies the following feature. It is preferable that, in the imaginary lines VL 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 |B_L| and an average value |β_S| of absolute values of β angles which are measured between two of the magnetic domain control points VP whose distance of the magnetic domain control points VP is the minimum value D_S satisfy a following expression. $0.5 ° \leq |β_{L}| - |β_{S}|$
In a case where the magnetic domain control treatment unique to the present embodiment is performed on a steel sheet having a coarse grain size, the value of the ratio D_L/D_S of the maximum value D_L to the minimum value D_S becomes the above specific value, and thus, it is unnecessary to specify the grain size of the grain-oriented electrical steel sheet 1 in the present embodiment. When the value of the ratio D_L/D_S is 5 or more on the premise of satisfying that the value of the ratio D_L/D_S is 3 or more by performing the magnetic domain control treatment unique to the present embodiment, it is possible to consider that the grain size of the grain-oriented electrical steel sheet 1 is coarse as compared to conventional steel sheet.
Herein, in the grain-oriented electrical steel sheet having a general grain size, the value of the ratio D_L/D_S of the maximum value D_L to the minimum value D_S is usually less than 5.
However, a method for judging whether a steel sheet has a coarse grain size may be to use the number of intersection points between imaginary lines and grain boundaries as an index. For instance, in the grain-oriented electrical steel sheet 1 according to the present embodiment, in at least one of the imaginary lines VL in the imaginary lines VL where the ratio D_L/D_S of the maximum value D_L of the distances of the magnetic domain control points VP to the minimum value D_S is 3 or more, a number of grain boundary points which are intersection points between the imaginary lines VL and grain boundaries may be 2 points or less.
In addition, in the grain-oriented electrical steel sheet 1 according to the present embodiment, in each of two or more of the imaginary lines VL, the number of grain boundary points may be 2 points or less.
Herein, in the grain-oriented electrical steel sheet having a general grain size, the number of grain boundary points is approximately 3 to 10.

(Number of imaginary lines VL where ratio D_L/D_S of maximum value D_L to minimum value D_S is less than 3)

Moreover, the grain-oriented electrical steel sheet 1 according to the present embodiment is characterized by selectively applying a magnetic domain control treatment to a region having a wide spacing of magnetic domain walls before magnetic domain control. In this case, in at least one of the imaginary lines VL, the D_S is 2 mm or more and less than 20 mm, the D_L/D_S is 3 or more, and the |B_L| is 1.5° or more. On the other hand, in at least one of the imaginary lines VL, the ratio D_L/D_S of the maximum value D_L to the minimum value D_S may be less than 3.
Thus, in the grain-oriented electrical steel sheet 1 according to the present embodiment, in at least one of the imaginary lines VL, the ratio D_L/D_S may be less than 3.
Herein, in the grain-oriented electrical steel sheet 1 according to the present embodiment, the imaginary line VL where the ratio D_L/D_S is less than 3 is not necessarily included in the evaluation region with the square shape where a length of each side is 50 mm and a side is parallel to the rolling direction of the grain-oriented electrical steel sheet. For instance, when the evaluation region is set to 20 areas, and when both of the imaginary line VL 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 and the imaginary line VL where the ratio D_L/D_S may be less than 3 are included in at least one of the evaluation regions, it can be considered that the magnetic domain control treatment is selectively applied to a region having a wide spacing of magnetic domain walls before magnetic domain control.

(2. Manufacturing apparatus of grain-oriented electrical steel sheet 1)

Next, an example of a manufacturing apparatus of the grain-oriented electrical steel sheet 1 according to the present embodiment will be described. However, the manufacturing apparatus described below is merely exemplary. The grain-oriented electrical steel sheet 1 according to the present embodiment can be manufactured using an arbitrary device.
FIG. 6 illustrates an example of a hardware constitution of the image acquisition device 30 that acquires a magnetic domain image of the original sheet 2, that is, the grain-oriented electrical steel sheet 1 before the magnetic domain control treatment. 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 includes a light source including a light emitting diode (LED), and irradiates the MO sensor 33 with light having a uniform polarization plane.
The MO sensor 33 is a device that measures a magnetic domain structure of a magnetic material. The MO sensor 33 has an observed section on which a magnetic sample to be measured is placed. The light irradiated from the light source unit 31 passes through the inside of the MO sensor 33 and is reflected by the reflection 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 sheet 2 as a magnetic sample is placed on the observed section of the MO sensor 33, a leakage magnetic field corresponding to the direction of spontaneous magnetization of the original sheet 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 the light receiving surface to perform photoelectric conversion, and outputs an analog signal after the photoelectric conversion to the signal processing unit 37. The distribution of the leakage magnetic field can be obtained by detecting the reflected light in which the polarization plane is rotated by the image sensor 35, and the magnetic domain structure of the original sheet 2 becomes clear.
The signal processing unit 37 includes an amplifier, an AD converter, a Digital Signal Processor (DSP), and the like. The analog signal output from the image sensor 35 is amplified by an amplifier. Then, the analog signal is converted into a digital signal by an AD converter. The digital signal is subjected to predetermined digital processing using a DSP to generate an image signal. The image signal generated by the signal processing unit 37 is output to the analysis device 40 (see FIG. 7) via a cable or by wireless communication.
FIG. 7 illustrates a hardware constitution of an analysis device 40 that analyzes the magnetic domain structure of the original sheet 2. The analysis device 40 is a computer device such as a personal computer (PC). 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 includes a Central Processing Unit (CPU). The calculation unit 41 analyzes the magnetic domain structure from the magnetic domain image of the original sheet 2 according to the program stored in the memory 43. Then, the calculation unit 41 determines a magnetic domain control treatment region 21 to which the magnetic domain control treatment is applied. The processing executed by the calculation unit 41 is described in detail later.
The memory 43 includes a Read Only Memory (ROM) and a Random Access Memory (RAM). The ROM stores programs executed by the CPU of the calculation unit 41 and data required for executing these programs. The program and data stored in the ROM are loaded into the RAM and executed.
The memory 43 may include a magnetic memory such as a hard disk drive (HDD) or an optical memory such as an optical disk. Alternatively, the memory 43 may be detachable from the analysis device 40 and store programs and data in a computer-readable recording medium. Alternatively, the memory 43 may receive the program executed by the calculation unit 41 from the network via the communication I/F 49.
The display unit 45 includes 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 on the basis of the image signal output from the image acquisition device 30. In addition, the display unit 45 displays the analysis result of the magnetic domain structure by the calculation unit 41.
The input unit 47 includes an input device such as a mouse or a keyboard. The communication I/F 49 is an interface for transmitting and receiving data to and from an external device 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, dedicated hardware specialized for analyzing a magnetic domain structure, such as an application specific integrated circuit (ASIC) or a Field Programmable Gate Array (FPGA), may be adopted as the calculation unit 41.
Note that FIGS. 6 and 7 illustrate a case where the image acquisition device 30 and the analysis device 40 are separate devices, but a system in which the image acquisition device 30 and the analysis device 40 are integrated may be adopted.
As means for introducing the thermal strain into the surface of the original sheet 2, known means such as laser irradiation, electron beam irradiation, and ion implantation can be adopted. As means for forming a groove on the surface of the original sheet 2, known means such as laser irradiation, electron beam irradiation, and machining can be adopted. Hereinafter, a constitution of the laser irradiation device 500 that introduces the thermal strain by laser irradiation will be described.
FIG. 8 illustrates a constitution 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 condensing lens 507, a motor 509, a sensor 511, a control unit 513, and a sheet passing device 515.
The sheet passing device 515 passes the original sheet 2 in the rolling direction RD.
The polygon mirror 501 has, for example, a regular polygonal prism shape. A plurality of the plane mirrors is provided on each of a plurality of side surfaces constituting the polygon mirror 501 having a regular polygonal prism shape. The laser beam LB enters the plane mirror of the polygon mirror 501 in one direction (horizontal direction) from the light source device 503 via the collimator 505 and is reflected by the plane mirror.
The polygon mirror 501 is rotatable about the rotary shaft O1 by driving from the motor 509. The incident angle of the laser beam LB with respect to the plane mirror sequentially changes according to the rotation angle of the polygon mirror 501. As a result, the reflection direction of the laser beam LB is sequentially changed, and the surface of the original sheet 2 can be scanned. A Reference Number P in FIG. 8 represents an interval between the adjacent magnetic domain control treatment lines 11, that is, an irradiation pitch of the laser beam LB.
The light source device 503 outputs the laser beam LB by a predetermined irradiation system (for example, a continuous irradiation system or a pulse irradiation system) under the control of the control unit 513.
The condenser lens 507 is provided on the optical path of the laser beam LB reflected from the polygon mirror 501. The condenser lens 507 constitutes a condenser optical system having a predetermined focal distance. The laser beam LB reflected from the polygon mirror 501 is condensed on the surface of the original sheet 2 via the condenser lens 507, whereby the thermal strain is introduced into the surface of the original sheet 2.
The motor 509 is coupled to the polygon mirror 501. The motor 509 rotationally drives the polygon mirror 501 under the control of the control unit 513.
The sensor 511 is connected to a drive shaft of the motor 509. The sensor 511 detects a rotation angle of the polygon mirror 501 rotated by the motor 509. Furthermore, the sensor 511 outputs a signal (Hereinafter, the rotation angle signal is referred to as a rotation angle signal.) indicating the detected rotation angle to the control unit 513.
The control unit 513 includes a processor. The control unit 513 is connected to the light source device 503, the motor 509, the sensor 511, and the sheet passing device 515. The control unit 513 receives an input of a speed signal from the sheet passing device 515. Further, the control unit 513 outputs a signal instructing the motor 509 to rotationally drive the polygon mirror 501.
In addition, the control unit 513 controls on and off of the power of the laser beam LB output from the light source device 503 based on the stress introduction signal representing the magnetic domain control treatment 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 be input to the laser irradiation device 500 by an operator.

(3. Method for manufacturing grain-oriented electrical steel sheet 1)

Next, a method for manufacturing the grain-oriented electrical steel sheet 1 according to the present embodiment will be described. According to the method for manufacturing a grain-oriented electrical steel sheet 1 according to the present embodiment, the grain-oriented electrical steel sheet 1 according to the present embodiment can be suitably manufactured. However, the manufacturing method described below is merely an example of a suitable manufacturing method of the grain-oriented electrical steel sheet 1, and does not limit the grain-oriented electrical steel sheet 1. For convenience of description, the manufacturing apparatus will be appropriately referred to in the description of the manufacturing method. However, the manufacturing apparatus mentioned below is merely a preferred example for carrying out the method for manufacturing the grain-oriented electrical steel sheet 1 according to the present embodiment.
As shown in the flowchart of FIG. 9, the method for manufacturing a grain-oriented electrical steel sheet 1 according to the present embodiment includes a step S62 of acquiring a magnetic domain image of an original sheet 2 of a grain-oriented electrical steel sheet 1, a step S64 of determining a magnetic domain control treatment region 21 based on distribution of the spacing of magnetic domain walls in the magnetic domain image, and a step S66 of applying the magnetic domain control treatment to the magnetic domain control treatment region 21 determined based on the distribution of the spacing of magnetic domain walls; wherein,

when an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to a rolling direction RD of the grain-oriented electrical steel sheet 1 is determined in the grain-oriented electrical steel sheet 1 and when imaginary lines VL parallel to the rolling direction RD with a length of 50 mm are set with a spacing of 5 mm in the evaluation region,
in at least one of the imaginary lines VL, a minimum value D_S of distances of magnetic domain control points VP which are intersection points between the imaginary lines VL and the magnetic domain control treatment lines 11 formed by the magnetic domain control treatment is controlled to 2 mm or more and less than 20 mm, and a ratio of a maximum value D_L of the distances of the magnetic domain control points VP to the minimum value is controlled to 3 or more.

First, a magnetic domain image of the original sheet 2 is acquired (see S62 in FIG. 9). The original sheet 2 is the grain-oriented electrical steel sheet 1 before the magnetic domain control treatment is applied. The magnetic domain image can be acquired by, for example, the image acquisition device 30. Next, the distribution of the spacing of the 180° magnetic domain walls (spacing of magnetic domain walls) is derived from the magnetic domain image. The distribution of the spacing of magnetic domain walls in the original sheet 2 can be derived by using, for example, the calculation unit 41 of the analysis device 40.
Then, a region having a spacing of magnetic domain walls of a predetermined value or more (For example, about 500 µm or more) is determined as the magnetic domain control treatment region 21 (see S64 in FIG. 9). FIG. 12 shows an original sheet 2 of the grain-oriented electrical steel sheet 1 of FIG. 1. The shaded region in FIG. 12 is the magnetic domain control treatment region 21. The white region in FIG. 12 is the non-magnetic domain control treatment region 22. The spacing of magnetic domain walls of the magnetic domain control treatment region 21 is a predetermined value or more. The spacing of magnetic domain walls of the non-magnetic domain control treatment region 22 is less than a predetermined value. The absolute value of β angle in the magnetic domain control treatment region 21 tends to be smaller than that in the non-magnetic domain control treatment region 22.
The magnetic domain control treatment region 21 may be determined by visually observing the magnetic domain image displayed on the display unit 45 by the operator, and a stress introduction signal representing the magnetic domain control treatment region 21 may be input to the laser irradiation device 500.
Next, the magnetic domain control treatment is preferentially performed on the magnetic domain control treatment region 21 (see S66 in FIG. 9). Preferably, the magnetic domain control treatment is performed only on the magnetic domain control treatment region 21. When the magnetic domain control treatment line 11 is a thermal strain, the magnetic domain control treatment may be executed by irradiation of the laser beam LB by the laser irradiation device 500, or other means such as ion implantation or electron beam irradiation may be adopted. When the magnetic domain control treatment line 11 is a groove, the magnetic domain control treatment may be executed using a tool for machining.
An example of a method for determining the magnetic domain control treatment region 21 will be described in detail. The processing for specifying the magnetic domain control treatment region 21 is executed by, for example, the calculation unit 41 of the analysis device 40.
The calculation unit 41 derives the distribution of the spacing of magnetic domain walls of the original sheet 2 using, for example, a line segment method or Fourier transform. Then, the calculation unit 41 determines a region where the spacing of magnetic domain walls is a predetermined value or more (For example, about 500 µm or more) as a portion to which the magnetic domain control treatment is preferentially applied.
In the line segment method, evaluation is performed by drawing a line segment perpendicular to the magnetic domain. The line segments are drawn at intervals of three lines per 1 cm in a direction parallel to the magnetic domain. A spacing of magnetic domain walls is derived based on a distance between the intersection points of 180° magnetic domain walls and line segments.
The Fourier transform is particularly effective as a means for analyzing a magnetic domain structure of a magnetic material having a periodic magnetic domain structure such as the grain-oriented electrical steel sheet 1 and the original sheet 2. Hereinafter, a method for deriving a distribution of a spacing of magnetic domain walls of the original sheet 2 is described using a short-term two-dimensional Fourier transform (Hereinafter, it is referred to as "ST2DFT".) obtained by expanding a short-term Fourier transform, which is one of signal processing methods that have been used for time-frequency analysis of audio signals for a long time, to a two-dimensional region.
An image (magnetic domain image) represented by an image signal acquired by the image acquisition device 30 is expressed as x (k, l) as a data column of two-dimensional coordinates (k-l coordinates). In the present embodiment, the magnetic domain image to be analyzed is an image binarized by two types of colors such as gray scale, or an image expressed by three or more gradations (multiple gradations).
In order to derive the distribution of the spacing of magnetic domain walls of the original sheet 2, the calculation unit 41 executes the following treatments of (A-1), (A-2), and (A-3).

(A-1) Treatment of cutting out a plurality of partial regions from magnetic domain image;
(A-2) Treatment of performing ST2DFT;
(A-3) Treatment of deriving distribution of spacing of magnetic domain walls. Hereinafter, the treatment of A-1 to A-3 will be described in detail.

(A-1) Treatment of cutting out a plurality of partial regions from magnetic domain image

In order to cut out a plurality of partial regions from a magnetic domain image and analyze each frequency structure, a window function Wa (k, l) of a rectangular window in which a range in the k direction set to 0 ≤ k ≤ N_k-1 and a range in the 1 direction set to 0 ≤ 1 ≤ N_l-1 is used (N_k and N_l are natural numbers). As the window function Wa (k, 1), a Hamming window, a Hanning window, a Blackman window, or the like can be applied.
When the observation position in the data column x (k, 1) of the magnetic domain image is expressed by an index (n, m), and the shift amounts of the window function Wa (k, l) in the k direction and the l direction are expressed as S_k and S_l, respectively (n, m, S_k, and S_l are integers.), a data column x_nm (k-nS_k, 1-mS_l) of a partial region obtained by cutting out a range of nS_k ≤ k ≤ nS_k + N_k-1 and mS₁ ≤ 1 ≤ mS₁ + N_l-1 from the magnetic domain image is obtained as in Expression (1).
[Mathematical Formula 1] $x_{nm} (k - {nS}_{k}, l - {mS}_{l}) = W_{a} (k - {nS}_{k}, l - {mS}_{l}) x (k, l)$
FIG. 10 illustrates an example in which partial regions respectively corresponding to the observation positions (n, m) = (1, 1), (2, 2), (3, 3),..., and (P, Q) (P and Q are natural numbers) are cut out from the magnetic domain image G.
In the present embodiment, N_k and N_j that define the range of the window function Wa (k, l) are parameters corresponding to the number of pixels in the k direction and the number of pixels in the l direction in the partial region, respectively.

(A-2) Treatment of performing ST2DFT

When the data column of the partial region is defined as x_nm (n', m') = x_nm (k-nS_k, l-mS_l), and the two-dimensional Fourier transform is performed on x_nm (n', m'), a partial Fourier image X (f_k, f_l, n, m) corresponding to the partial region of the observation position (n, m) is obtained as in Expression (2).
[Mathematical Formula 2] $X (f_{k}, f_{l}, n, m) = \sum_{n' = 0}^{N_{k} - 1} \sum_{m' = 0}^{N_{l} - 1} x_{nm} (n', m') \exp \{- 2 πj (\frac{f_{k} n'}{N_{k}} + \frac{f_{l} m'}{N_{l}})\}$
Here, f_k and f_j are space frequencies.
When the resolution of the space frequency f_k is denoted by Δf_k and the resolution of the space frequency f_l is denoted by Δf_l, Δf_k and Δf_l are defined as in Expression (3).
[Mathematical Formula 3] $\{\begin{matrix} Δ f_{k} = \frac{2}{N_{k} Δ k} \\ Δ f_{l} = \frac{2}{N_{l} Δ l} \end{matrix}$
Δk and Δl are the space resolution in the k direction and the space resolution in the l direction in the magnetic domain image, respectively.
For example, when the two-dimensional Fourier transform is performed on the data column x_nm (k-nS_k, l-mS_l) of each partial region illustrated in FIG. 10, a partial Fourier image X (f_k, f_l, n, m) is obtained for each observation position (n, m) as illustrated in FIG. 11.

(A-3) Treatment of deriving distribution of spacing of magnetic domain walls

When the partial Fourier image X (f_k, f_l, n, m) is obtained, the coordinates (k component f_k ^max (n, m) and l component f_l ^max (n, m)) of the peak position of the spot of the partial Fourier image X (f_k, f_l, n, m) are obtained. Note that, regarding the derivation of the peak position, a region in the vicinity of k = 0 and l = 0 is a part that greatly depends on the contrast of the image, and thus is excluded.
Then, the distribution L (n, m) of the spacing of magnetic domain walls is derived as in Expression (4) from the resolution of the space frequency defined by Expression (3) and the peak position of the spot of the partial Fourier image.
[Mathematical Formula 4] $L (n, m) = \frac{1}{\sqrt{{(Δ f_{k} f_{k}^{\max} (n, m))}^{2} + {(Δ f_{l} f_{l}^{\max} (n, m))}^{2}}}$
As described above, by using ST2DFT, it is possible to quantitatively derive the distribution L (n, m) of the spacing of magnetic domain walls while maintaining the position information of the magnetic domain image. FIGS. 4A to 4C described above illustrate the analysis result of the spacing of magnetic domain walls derived by ST2DFT.
FIG. 12 is a plan view of an example of the original sheet 2. The original sheet 2 of FIG. 12 is a material of the grain-oriented electrical steel sheet 1 of FIG. 1. FIG. 12 illustrates a magnetic domain control treatment region 21 and a non-magnetic domain control treatment region 22 of the original sheet 2 which are specified based on the magnetic domain image. The magnetic domain control treatment region 21 is a region where the spacing of magnetic domain walls is a predetermined value or more. The magnetic domain control treatment region 21 of the original sheet 2 substantially corresponds to a region where the β angle is small in the grain-oriented electrical steel sheet 1. The non-magnetic domain control treatment region 22 of the original sheet 2 substantially corresponds to the region where the β angle is large in the grain-oriented electrical steel sheet 1. The non-magnetic domain control treatment region 22 is a region where the spacing of magnetic domain walls is less than a predetermined value, and is a region where the β angle is large. The magnetic domain control treatment is applied to a broken line provided inside the magnetic domain control treatment region 21 illustrated in FIG. 12. At this time, when an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to a rolling direction RD of the grain-oriented electrical steel sheet 1 is determined in the grain-oriented electrical steel sheet 1 and when imaginary lines VL parallel to the rolling direction RD with a length of 50 mm are set with a spacing of 5 mm in the evaluation region, in at least one of the imaginary lines VL, a minimum value of distances of magnetic domain control points which are intersection points between the imaginary lines and the magnetic domain control treatment lines is controlled to 2 mm or more and less than 20 mm, and a ratio of a maximum value of the distances of the magnetic domain control points to the minimum value is controlled to 3 or more. As a result, 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 whose distance is the maximum value D_L is 1.5° or more is obtained.
When the calculation unit 41 derives the distribution L(n, m) of the spacing of magnetic domain walls, the calculation unit 41 determines the region where the spacing of magnetic domain walls is the predetermined value or more as the magnetic domain control treatment region 21 (that is, a region to which the magnetic domain control treatment is applied). The control unit 513 of the laser irradiation device 500 performs control to turn on the power of the laser beam LB with respect to the magnetic domain control treatment region 21, and preferably, to turn off the power of the laser beam LB with respect to the non-magnetic domain control treatment region 22 (that is, a region other than the magnetic domain control treatment region 21). As a result, the magnetic domain control treatment line 11 is introduced into the magnetic domain control treatment region 21 of the original sheet 2. Further, in the non-magnetic domain control treatment region 22 of the original sheet 2, introduction of the magnetic domain control treatment line 11 is suppressed to a minimum.
The magnetic domain image of the grain-oriented electrical steel sheet 1 after the magnetic domain control treatment can also be obtained by the above-described procedure. In the magnetic domain image of the grain-oriented electrical steel sheet 1, the magnetic domain control treatment line 11 may be unclear. In this case, the observation conditions may be adjusted so that the magnetic domain control treatment line 11 can be clearly confirmed. For example, the magnetic domain control treatment line 11 can be clarified by applying a DC magnetic field along the sheet surface perpendicular direction (thickness direction) of the grain-oriented electrical steel sheet 1.
Although embodiments of the present disclosure have been described above, the present disclosure is not limited thereto, and can be appropriately modified without departing from the technical idea of the invention. Hereinafter, a more preferable example of the grain-oriented electrical steel sheet 1 according to the present embodiment and the method for manufacturing the same will be described. Unless otherwise specified, the preferred aspect described below is applicable to both the grain-oriented electrical steel sheet 1 and the method for manufacturing the same. As described later, the grain-oriented electrical steel sheet according to the present embodiment may have a forsterite film and/or an insulating coating on the surface of the base steel sheet.
Each will be described below. However, when the grain-oriented electrical steel sheet includes a base steel sheet and a forsterite film and/or an insulating coating, the following regulations regarding the chemical composition, the magnetic domain control treatment line, the magnetic domain control region, and the non-magnetic domain control treatment line are regulations regarding the base steel sheet. However, the provision regarding the sheet thickness is a provision regarding the entire grain-oriented electrical steel sheet including the base steel sheet, and the forsterite film and/or the insulating coating.

(Chemical composition and sheet thickness)

The chemical compositions of the grain-oriented electrical steel sheet 1 and the original sheet 2 are not limited as long as they are equivalent to those of the known grain-oriented electrical steel sheet 1. For example, the grain-oriented electrical steel sheet 1 and the original sheet 2 can contain, as a chemical composition, Si: 2.500 to 7.000%, Mn: 0.00 to 1.000%, C: 0 to 0.085%, acid-soluble Al: 0 to 0.065%, N: 0 to 0.012%, Cr: 0 to 0.300%, Cu: 0 to 0.400%, P: 0 to 0.500%, Sn: 0 to 0.300%, Sb: 0 to 0.300%, Ni: 0 to 1.000%, S: 0 to 0.015%, Se: 0 to 0.015%, Bi: 0 to 0.020%, Nb: 0 to 0.030%, V: 0 to 0.030%, Mo: 0 to 0.030%, Ta: 0 to 0.030%, W: 0 to 0.030%, B: 0 to 0.080%, and Ti: 0 to 0.015% in mass%. The balance of the chemical composition includes Fe and impurities.
The sheet thicknesses of the grain-oriented electrical steel sheet 1 and the original sheet 2 are not limited, but are preferably 0.15 mm to 0.30 mm, for example. When the thickness is 0.30 mm or less, classical eddy-current loss can be suppressed, and iron loss can be further improved. On the other hand, when the sheet thickness is 0.15 mm or more, rolling efficiency can be improved to improve productivity.

(Surface treatment)

The grain-oriented electrical steel sheet 1 and the original sheet 2 may have a forsterite film. The grain-oriented electrical steel sheet 1 and the original sheet 2 may have an insulating coating. The forsterite film and the insulating coating may be formed on one surface or both surfaces of the grain-oriented electrical steel sheet 1.
The forsterite film is, for example, an inorganic coating film containing magnesium silicate as a main component. The forsterite film is formed, for example, by a reaction between an annealing separator containing magnesia (MgO) applied to the surface of the base steel sheet and a component of the surface of the base steel sheet in final annealing. The forsterite film has, for example, a composition (more specifically, a composition containing Mg₂SiO₄ as a main component) derived from the components of the annealing separator and the base steel sheet. On the other hand, when an annealing separator mainly containing Al₂O₃ is used in final annealing, a forsterite film may not be formed.
The insulating coating has a function of applying electrical insulation properties and tension to the grain-oriented electrical steel sheet 1. The tension is applied to the grain-oriented electrical steel sheet 1 to facilitate magnetic domain wall movement in the grain-oriented electrical steel sheet 1, and thus, the iron loss of the grain-oriented electrical steel sheet 1 can be reduced. In addition, according to the insulating coating, various characteristics such as corrosion resistance, heat resistance, and slippage can be provided to the grain-oriented electrical steel sheet 1. The insulating coating may be, for example, a known coating formed by applying a coating solution containing phosphate and colloidal silica as main components to the surface of the forsterite film and baking the coating solution.
The insulating coating is preferably formed after the final annealing and after the magnetic domain control treatment. On the other hand, the insulating coating may be formed after the final annealing step and before the magnetic domain control treatment. When the insulating coating is formed before the magnetic domain control treatment, the insulating coating may be peeled off in the magnetic domain control treatment line 11. Therefore, it is preferable to form the insulating coating again on the magnetic domain control treatment line 11 after the magnetic domain control treatment.

(Angle formed by magnetic domain control treatment line 11 and transverse direction TD)

The angle formed by the magnetic domain control treatment line 11 and the transverse direction TD is not particularly limited. The magnetic domain control treatment line 11 and the transverse direction TD may be substantially parallel. That is, the angle formed by the magnetic domain control treatment line 11 and the transverse direction TD may be substantially 0°. On the other hand, as illustrated in FIG. 1, the angle formed by the magnetic domain control treatment line 11 and the transverse direction TD may be more than 0°. For example, the angle formed by the magnetic domain control treatment line 11 and the transverse direction TD may be an arbitrary value within the range of 0° to 45°. The angle formed by the magnetic domain control treatment line 11 and the transverse direction TD may be 1° or more, 3° or more, or 5° or more. The angle formed by the magnetic domain control treatment line 11 and the transverse 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 treatment lines 11 and the transverse direction TD may be the same. That is, all the magnetic domain control treatment lines 11 may extend in parallel to each other. On the other hand, the angle formed by the magnetic domain control treatment line 11 and the transverse direction TD may vary. That is, some or all of a plurality of the magnetic domain control treatment lines 11 may extend non-parallel to each other. The average value of the angles formed by the magnetic domain control treatment line 11 and the transverse direction 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 treatment line 11 and the transverse direction TD may be 40° or less, 35° or less, or 30° or less. The average value of the angles may be calculated by measuring an angle formed with the transverse direction TD at a plurality of positions with respect to one magnetic domain control treatment line, or by measuring an angle formed with the transverse direction TD by a plurality of magnetic domain control treatment lines at one point or a plurality of positions.

(Magnitude of tensile stress introduced in thermal strain)

The magnetic domain control treatment line 11 may be due to a thermal strain. In the thermal strain, tensile stress is introduced. As the tensile stress is larger, the effect of improving the iron loss is enhanced. On the other hand, as the tensile stress is smaller, the noise characteristics are improved. Tensile stress according to characteristics required for the grain-oriented electrical steel sheet 1 can be appropriately selected.
The magnitude of the tensile stress is not particularly limited, but for example, in at least a part of the magnetic domain control treatment line 11, the tensile stress in an arbitrary 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, it is considered that the requirement that "the tensile stress in an arbitrary direction is 40 MPa or more" is satisfied. For example, in at least a part of the magnetic domain control treatment line 11, the tensile stress in an arbitrary direction is preferably 300 MPa or less, 200 MPa or less, 180 MPa or less, or 150 MPa or less. The tensile stress in an arbitrary direction in the magnetic domain control treatment line 11 may be uniform or may vary.

(Depth and width of groove)

The magnetic domain control treatment line 11 may be a groove. As the depth and width of the groove are larger, the effect of improving the iron loss is enhanced. On the other hand, the noise characteristics are improved as the depth and width of the groove are smaller. 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, for example, 5 µm to 50 µm. 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 part) is not particularly limited, but is preferably, for example, 10 µm to 300 µm. The width of the groove may be defined as 20 µm or more, 30 µm or more, or 50 µm or more. The width of the groove may be defined 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. In the case of variation, the average of the depths and widths of a plurality of the grooves is preferably in the above range.

(Measurement method)

Hereinafter, a method for measuring various parameters of the grain-oriented electrical steel sheet 1 according to the present embodiment will be described. Note that measurement of any parameter is performed on a sample collected from the grain-oriented electrical steel sheet 1. For example, a rectangular sample having both sides of 100 mm (or 100 mm or more) in length can be cut out from the grain-oriented electrical steel sheet 1 and subjected to measurement. When the grain-oriented electrical steel sheet 1 is a coil, a sample may be collected from an arbitrary position of the coil. When the grain-oriented electrical steel sheet 1 is a component incorporated in an electrical product such as a transformer or a motor, a sample may be collected from any place 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 in so far as the length of one side of the sample is 50 mm or more. At that time, it is desirable to collect a sample by a method such as wire cutting in order to minimize the influence of mechanical strain or the like on the sample.

(Method of identifying magnetic domain control treatment line 11)

When the magnetic domain control treatment line 11 is a groove, the magnetic domain control treatment line 11 can be visually identified. When the grain-oriented electrical steel sheet 1 has an insulating coating, the magnetic domain control treatment line 11 becomes visible by removing the insulating coating using a known peeling agent.
When the magnetic domain control treatment line 11 is a thermal strain, the magnetic domain control treatment line 11 may not be visually identified. In this case, for example, the magnetic domain image is photographed using the image acquisition device 30 as exemplified in FIG. 6. If necessary, a magnetic domain image is photographed while a DC magnetic field is applied along the rolling surface normal direction ND of the grain-oriented electrical steel sheet 1. The position of the thermal strain can be identified by observing the magnetic domain image.

(Method for specifying rolling direction RD and transverse direction TD)

The rolling direction RD and the transverse direction TD of the grain-oriented electrical steel sheet 1 are specified by the following means.

(1) When the sample is cut out from the coil-shaped grain-oriented electrical steel sheet 1, the width direction of the coil is regarded as the transverse direction TD. A direction perpendicular to the transverse direction TD and the rolling surface normal direction ND is regarded as the rolling direction RD.
(2) When the sample is cut out from a part or the like of an electrical product, the rolling direction RD and the transverse direction TD are specified from rolling defects on the surface of the grain-oriented electrical steel sheet 1. The extending direction of the rolling defect is regarded as a rolling direction RD. A direction perpendicular to the rolling direction RD and the rolling surface normal direction ND is regarded as a transverse direction TD.
(3) When it is difficult to specify the rolling direction RD and the transverse direction TD from a rolling defect on the surface of the grain-oriented electrical steel sheet 1, the rolling direction RD and the transverse direction TD are specified 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 a plurality of points. Then, the direction in which the deviation angle from the easy axis of magnetization <001> at which the angle formed by the crystal orientation at the measurement point with the rolling surface normal direction ND (sheet thickness direction) is the closest to the right angle is minimized 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 transverse direction TD.

(Minimum value D_S and maximum value D_L of distances between magnetic domain control points VP)

The minimum value D_S and the maximum value D_L of the distances between the magnetic domain control treatment points are calculated according to the following procedure. First, an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is determined in the grain-oriented electrical steel sheet 1. Then, imaginary lines VL parallel to the rolling direction RD with a length of 50 mm are set with a spacing of 5 mm in the evaluation region on the surface of the grain-oriented electrical steel sheet 1. Next, a magnetic domain control point VP which is an intersection point of the imaginary line VL and the magnetic domain control treatment line 11 is specified. The specification of the rolling direction RD and the magnetic domain control treatment line 11 is performed according to the above-described procedure. Then, the distances between the adjacent magnetic domain control points VP are measured, and the minimum value and the maximum value of these measurement values are obtained.
The place where the evaluation region and the imaginary line VL are set is not limited. The imaginary line VL may be set at any place where the imaginary line VL in which the D_S and the D_L/D_S fall within the range of the present disclosure can be set. For example, the imaginary line VL may be set so as to pass through the region X where the magnetic domain control treatment line 11 is not provided. On the other hand, in a case where a place where the imaginary line VL can be set such that the D_S and the D_L/D_S fall within the range of the present disclosure cannot be found, it is estimated that the requirements of the present disclosure are not satisfied.

(Method for measuring β angle)

The β angle is measured by the side surface reflection Laue method. The side surface reflection Laue method is widely known as a method for measuring a crystal orientation. However, the β angle is a value obtained by rounding off the measured numerical value to the second decimal place. That is, the significant digits of the β angle are up to the first decimal place.

(|β_L| and |β_S|)

|β_L| is measured by the following procedure. First, two adjacent magnetic domain control points VP whose distance becomes the maximum value D_L in the imaginary line VL are specified by the above-described procedure. The β angle between these magnetic domain control points VP is measured at intervals of 1 mm from the midpoint P_βL of the magnetic domain control points VP by the above-described procedure. Two or more portions where the distance becomes D_L may be accidentally formed on one imaginary line VL. In this case, there are two or more sets of two adjacent magnetic domain control points VP at which the distance becomes the maximum value D_L. In this case, the β angle between the adjacent magnetic domain control points VP is measured at intervals of 1 mm from the midpoint of the magnetic domain control points VP, and the average value of the absolute value of the β angle may be regarded as |β_L| on the imaginary line VL.
The measurement procedure of |β_S| is similar to that of |β_L|. First, two adjacent magnetic domain control points VP whose distance becomes the minimum value D_S in the imaginary line VL are specified by the above-described procedure. The β angle between these magnetic domain control points VP is measured by the above-described procedure. Note that two or more portions at which the distance becomes D_S may be accidentally formed on one imaginary line VL. In this case, there are two or more sets of two adjacent magnetic domain control points VP at which the distance becomes the maximum value D_L. In this case, the β angle between the adjacent magnetic domain control points VP is measured at intervals of 1 mm, and the average value of the absolute value of the β angle may be regarded as |β_L| on the imaginary line VL.
In each of plural imaginary lines VL, the D_S, the D_L, and the |β_L| are obtained by the above-described procedure. In one or more imaginary lines VL, in a case where 2 mm ≤ D_S < 20 mm, 3 ≤ D_L/D_S, and 1.5° ≤ |β_L|, the sample is regarded as the grain-oriented electrical steel sheet according to the present disclosure. The number of the imaginary lines VL satisfying the requirements of the present disclosure is preferably as large as possible.

(Method for 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 of steel. For example, the chemical composition may be measured using inductively coupled plasma-atomic emission spectrometry (ICP-AES). Specifically, the chemical composition of the grain-oriented electrical steel sheet 1 and the original sheet 2 can be measured by acquiring a test piece from the center portion in the thickness direction of the sample, and measuring the test piece under a condition based on a calibration curve prepared in advance using ICPS-8100 manufactured by Shimadzu Corporation or the like (measuring device). The contents of C and S, which are difficult to measure by ICP-AES, may be measured using a combustion-infrared light absorption method. The content of N may be measured using an inert gas fusion-thermal conductivity method.
When a forsterite film and/or an insulating coating are/is formed on the grain-oriented electrical steel sheet 1 and the original sheet 2, chemical compositions of the grain-oriented electrical steel sheet 1 and the original sheet 2 may be analyzed after removing the forsterite film and/or the insulating coating from the grain-oriented electrical steel sheet 1 and the original sheet 2.
The forsterite film can be removed, for example, by immersing the sample in sulfuric acid followed by immersion in nitric acid. Conditions such as the temperature and concentration of sulfuric acid and nitric acid and the time for immersion are appropriately adjusted so that the base metal of the sample is not excessively dissolved. An example of conditions of the removal operation of the forsterite film is as follows. First, the sample is immersed in sulfuric acid having a concentration of 10% at 80°C for 3 minutes. Thereafter, the surface of the sample is washed with water using a waste cloth or the like to remove the sludge adhering to the surface. Thereafter, the sample is dried. Further, the sample is immersed in nitric acid having a concentration of 10% at room temperature while being stirred for about 5 seconds.
The insulating coating can be removed, for example, by immersing the sample in a sodium hydroxide solution and then immersing the sample in dilute sulfuric acid and nitric acid. Conditions such as the temperature and concentration of sodium hydroxide, dilute sulfuric acid, and nitric acid solution, and the time for immersion are appropriately adjusted so that the base metal of the sample is not excessively dissolved. An example of the conditions of the removal operation of the insulating coating is as follows. First, the sample is immersed in a sodium hydroxide solution having a concentration of 20% at 80°C for 15 minutes. Thereafter, the sample is dried. Then, the sample is immersed in diluted sulfuric acid having a concentration of 10% at 80°C for 4 minutes. Thereafter, the sludge adhering to the surface of the sample is removed with a waste cloth or the like. Further, the sample is immersed in nitric acid having a concentration of 10% at room temperature while being stirred for about 10 seconds.

(Method of measuring angle formed by magnetic domain control treatment line 11 and transverse direction TD)

The angle formed by the magnetic domain control treatment line 11 and the transverse direction TD can be measured using a known angle measuring means after the magnetic domain control treatment line 11 and the transverse direction TD are specified by the above-described procedure.

(Method for measuring magnitude of tensile stress introduced in thermal strain)

The magnitude of the tensile stress introduced in the thermal strain is measured by the EBSD Wilkinson method and 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, P. 307-313.
When the magnitude of the tensile stress introduced in the thermal strain is measured by the EBSD Wilkinson method and the Cross Court manufactured by BLG Vantage, first, the magnetic domain control treatment line 11 is specified by the above-described procedure. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control treatment line 11 and perpendicularly to the magnetic domain control treatment line 11. This cut cross section is used as a measurement surface. The cross section of the magnetic domain control treatment line 11 included in the measurement surface is analyzed by the EBSD Wilkinson method and Cross Court manufactured by BLG Vantage, and a tensile stress component in an arbitrary direction is extracted and the magnitude thereof is measured. For example, it is possible to extract a tensile stress component in a rolling surface normal direction ND, a direction parallel to the magnetic domain control treatment line 11, and a direction perpendicular to the rolling surface normal direction ND and the magnetic domain control treatment line 11.
The number of measurement points is, for example, 10. When the tensile stress in an arbitrary direction is 40 MPa or more (that is, when the tensile stress in at least one direction is 40 MPa or more,) in at least one location of the grain-oriented electrical steel sheet 1, the maximum value of the tensile stress in an arbitrary direction in the magnetic domain control treatment line of the grain-oriented electrical steel sheet 1 is determined to be 40 MPa or more. The measurement of the tensile stress may be stopped when a measurement point at which the tensile stress in an arbitrary direction is 40 MPa or more is found.

(Method of measuring depth and width of groove)

The depth and width of the groove can be measured by specifying the surface shape of the sample using a known three-dimensional measuring machine. When the grain-oriented electrical steel sheet 1 has an insulation coating, the insulating coating is removed by the above-described procedure, and then the three-dimensional measurement of the sample surface is performed.

Examples

The effect of an aspect of the present disclosure will be described more specifically with reference to Examples. However, the conditions in Examples are merely one condition example adopted to confirm the enablement and effects of the present disclosure. The present disclosure is not limited to this one condition example. The present disclosure can adopt various conditions as long as the object of the present disclosure is achieved without departing from the gist of the present disclosure.

(Example 1)

A grain-oriented electrical steel sheet (grain-oriented electrical steel sheet having general grain size) of the same lot having a sheet thickness of 0.20 mm was used as the original sheet. In these grain-oriented electrical steel sheets, for instance, the average temperature rising rate in a range from 1000 to 1200°C was 15°C/h during temperature rising process of final annealing. The original sheet was subjected to a magnetic domain control treatment under various conditions shown in Table 1. The noise and iron loss of the grain-oriented electrical steel sheets subjected to the magnetic domain control treatment obtained as a result were evaluated and are described in Table 2. In Table 2, values determined to be unacceptable are underlined.
Herein, the shapes of the magnetic domain control treatment lines were as follows. The shape applied to the sample is noted in the column "Remarks" of Table 1.

A: A magnetic domain control treatment line was formed in a region where the β angle was small as explained above.
B: A magnetic domain control treatment line was straight linearly formed over the entire width of the original sheet.
C: A magnetic domain control treatment line with a random broken linear shape was formed.
D: A magnetic domain control treatment line having an interval of 4 mm was formed only in a region within ±4 mm from the center of each crystal grain in the rolling direction RD. The radius of curvature of the steel sheet at the position where the grains were present during the final annealing was 250 mm.

The methods for evaluating the noise and iron loss were as follows. First, 205 grain-oriented electrical steel sheets having a sheet thickness of 0.20 mm were laminated to form a three-phase transformer core. The widths of the leg and the yoke of the three-phase transformer core were both 150 mm. The height and width of the outer shape of the three-phase transformer core were both 750 mm. 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.
In measuring the noise, microphones were arranged at equal intervals at eight points around the transformer in which the three-phase transformer core was incorporated. The distance between the transformer and the microphone was 30 cm. The values obtained by correcting the A characteristics to the noise measurement results by the microphones and averaging the results are described in Table 2 as the noise evaluation results (unit: dBA) of the grain-oriented electrical steel sheets. An example in which the evaluation result of noise was 30.25 dBA or less was determined to be an example in which noise reduction was achieved. The noise evaluation result determined to be unacceptable was underlined.
The iron loss was obtained by measuring voltages and currents on the primary side and the secondary side with a power analyzer when excitation was performed at a frequency of 60 Hz and an excitation magnetic flux density of 1.5 T as described above. The obtained iron loss is described in Table 2 as an iron loss evaluation result (unit: W/kg) of the grain-oriented electrical steel sheet. An example in which the evaluation result of the iron loss was 0.756 W/kg or less was determined to be an example in which iron loss reduction was achieved. The noise evaluation result determined to be unacceptable was underlined.
Further, a number of imaginary lines where a minimum value D_S of distances of magnetic domain control points was 2 mm or more and less than 20 mm and D_L/D_S was 3 or more in the grain-oriented electrical steel sheets subjected to the magnetic domain control treatment were measured and described in Table 1. The measurement method was in principle according to the procedure described above. A rectangular sample having both sides of 100 mm in length was cut out from a three-phase transformer core for measuring noise and iron loss, and subjected to measurement.
In this rectangular sample, a square evaluation region having a side length of 50 mm and a side parallel to the rolling direction of the grain-oriented electrical steel sheet was set, and imaginary lines VL parallel to the rolling direction and having a length of 50 mm were set at intervals of 5 mm inside the evaluation region. The number of imaginary lines was nine.
In each of nine imaginary lines VL, standard deviation of distances of magnetic domain control points was measured. The number of imaginary lines VL where the minimum value D_S of distances of magnetic domain control points was 2 mm or more and less than 20 mm and the D_L/D_S was 3 or more is noted in the column "Number of imaginary lines VL where minimum value D_S of distances of magnetic domain control points is 2 mm or more and less than 20 mm and D_L/D_S is 3 or more" of Table 1.
Moreover, β angles in the respective imaginary lines VL where the minimum value D_S of distances of magnetic domain control points was 2 mm or more and less than 20 mm and the D_L/D_S was 3 or more measured by the above-described procedure. In the imaginary lines VL where the D_S was 2 mm or more and less than 20 mm and the D_L/D_S was 3 or more, the number of VL where an average value |β_L| of absolute values of the β angles which were measured between two of the magnetic domain control points whose distance was the maximum value D_L was 1.5° or more is noted in the column "Number of VL where |β_L| is 1.5° or more" of Table 1. The sample in which the number in the column is 1 is regarded as the grain-oriented electrical steel sheet where the minimum value 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 in one imaginary line. The sample in which the number in the column is 2 or more is regarded as the grain-oriented electrical steel sheet 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 in each of two or more imaginary lines.
Moreover, in the imaginary lines VL where the D_S was 2 mm or more and less than 20 mm, the D_L/D_S was 3 or more, the |β_L| was 1.5° or more, the number of VL where the |β_L| and an average value |β_S| of absolute values of β angles which were measured between two of the magnetic domain control points whose distance of the magnetic domain control points was the minimum value satisfied 0.5° ≤ |β_L| - |β_S| is noted in the column "Number of VL satisfying |β_L| - |β_S| ≥ 0.5°" of Table 1.

Although not shown in the tables, in any imaginary lines VL where the D_S was 2 mm or more and less than 20 mm and the D_L/D_S was 3 or more, a number of grain boundary points which were intersection points between the imaginary lines VL and grain boundaries was 3 or more. Moreover, although not shown in the tables, in any imaginary lines VL where the D_S was 2 mm or more and less than 20 mm and the D_L/D_S was 3 or more, the value of D_L/D_S was less than 5.

[Table 1]

	NUMBER OF VL WHERE D_S IS 2mm OR MORE AND LESS THAN 20mm AND D_L/D_S IS 3 OR MORE	NUMBER OF VL WHERE \|β _L\| IS 1.5° OR MORE	NUMBER OF VL SATISFYING \|β _L\| - \|β _S\| ≧ 0.5°	TYPE OF MAGNETIC DOMAIN CONTROL TREATMENT LINE	REMARKS
1	1	1	0	THERMAL STRAIN	A
2	1	1	0	MIXED	A
3	1	1	0	GROOVE	A
4	6	2	0	THERMAL STRAIN	A
5	7	4	0	THERMAL STRAIN	A
6	7	5	0	THERMAL STRAIN	A
7	1	1	1	THERMAL STRAIN	A
8	7	5	3	THERMAL STRAIN	A
9	0	0	0	THERMAL STRAIN	B
10	7	0	0	THERMAL STRAIN	C
11	9	0	0	THERMAL STRAIN	D

[Table 2]

	EVALUATION OF IRON LOSS W/kg	EVALUATION OF NOISE dBA
1	0.701	30.24	INVENTIVE EXAMPLE
2	0.722	29.84	INVENTIVE EXAMPLE
3	0.741	28.85	INVENTIVE EXAMPLE
4	0.715	27.99	INVENTIVE EXAMPLE
5	0.712	27.52	INVENTIVE EXAMPLE
6	0.714	27.25	INVENTIVE EXAMPLE
7	0.711	26.62	INVENTIVE EXAMPLE
8	0.715	26.31	INVENTIVE EXAMPLE
9	0.705	31.64	COMPARATIVE EXAMPLE
10	0.789	28.60	COMPARATIVE EXAMPLE
11	0.782	28.30	COMPARATIVE EXAMPLE

In Example No. 9, the magnetic domain control treatment line was straight linearly formed over the entire width of the original sheet. Thus, in Example No. 9, the imaginary line VL where the D_L/D_S was 3 or more could not be set. In Example No. 9, although the evaluation result of iron loss was sufficient, the evaluation result of noise was insufficient. This is presumably because the magnetic domain control treatment line was formed in areas where the magnetic domain control was not needed.
In Example No. 10, the magnetic domain control treatment line with the broken linear shape was formed. The interval between the magnetic domain control treatment lines in one broken line was a random value. In Example No. 10, the imaginary lines VL where the D_L/D_S was 3 or more could be set. However, in all of the imaginary lines, the average value |β_L| of the absolute values of the β angles was less than 1.5°. In Example No. 10, although the evaluation result of noise was sufficient, the evaluation result of iron loss was insufficient. This is presumably because the magnetic domain control treatment line was not formed in areas where the magnetic domain control was needed.
In Example No. 11, the magnetic domain control treatment line having an interval of 4 mm was formed only in a region within ±4 mm from the center of each crystal grain in the rolling direction RD. The radius of curvature of the steel sheet at the position where the grains were present during the final annealing was 250 mm. The results of Example No. 11 were similar to those of Example 10. Specifically, in Example No. 11, the imaginary lines VL where the D_L/D_S was 3 or more could be set. However, in all of the imaginary lines, the average value |β_L| of the absolute values of the β angles was less than 1.5°. In Example No. 11, although the evaluation result of noise was sufficient, the evaluation result of iron loss was insufficient. This is presumably because the magnetic domain control treatment line was not formed in areas where the magnetic domain control was needed.
On the other hand, in the examples in which at least one imaginary line VL where the D_S was 2 mm or more and less than 20 mm, the D_L/D_S was 3 or more, the |β_L| was 1.5° or more could be set, both the evaluation result of iron loss and the evaluation result of noise were sufficient.

(Example 2)

The magnetic domain control treatment was carried out on the grain-oriented electrical steel sheet under the same conditions as in the above Example 1, except for the type of grain-oriented electrical steel sheet used as the original sheet. Specifically, a grain-oriented electrical steel sheet (grain-oriented electrical steel sheet having coarse grain size) of the same lot having a sheet thickness of 0.20 mm was used as the original sheet. In these grain-oriented electrical steel sheets, for instance, the average temperature rising rate in a range from 1000 to 1200°C was less than 5°C/h during temperature rising process of final annealing. The original sheet was subjected to a magnetic domain control treatment under various conditions shown in Table 3. The magnetic flux density, noise, and iron loss of the grain-oriented electrical steel sheets subjected to the magnetic domain control treatment obtained as a result were evaluated and are described in Table 4. In Table 4, values determined to be unacceptable are underlined.
The shapes of the magnetic domain control treatment lines were the same as in the above Example 1. The methods for evaluating the noise and iron loss were also the same as in the above Example 1. Notating the manufacturing results and evaluation results in the tables was the same as in the above Example 1.
The method for evaluating the magnetic flux density was as follows. The magnetic flux density was obtained by measuring using the Epstein method specified in JIS C 2550-1:2011. The magnetic flux density B₈ (T) in the rolling direction of the steel sheet was measured under the condition such that the steel sheet was excited at 800 A/m. The measured magnetic flux density are described in Table 4 as the evaluation result of magnetic flux density (unit: T) of the grain-oriented electrical steel sheet. An example in which the evaluation result of magnetic flux density was 1.935 T or more was determined to be an example in which the magnetic flux density was more excellent than that of the grain-oriented electrical steel sheet having the general grain size.

Although not shown in the tables, in any imaginary lines VL where the D_S was 2 mm or more and less than 20 mm and the D_L/D_S was 3 or more, a number of grain boundary points which were intersection points between the imaginary lines VL and grain boundaries was 2 or less.

[Table 3]

	NUMBER OF VL WHERE D_S IS 2mm OR MORE AND LESS THAN 20mm AND D_L/D_S IS 5 OR MORE	NUMBER OF VL WHERE \|β _L\| IS 1.5° OR MORE	NUMBER OF VL SATISFYING \|β _L\| - \|β _S\| ≧ 0.5°	TYPE OF MAGNETIC DOMAIN CONTROL TREATMENT LINE	REMARKS
12	1	1	0	THERMAL STRAIN	A
13	1	1	0	MIXED	A
14	1	1	0	GROOVE	A
15	4	2	0	THERMAL STRAIN	A
16	6	4	0	THERMAL STRAIN	A
17	7	5	0	THERMAL STRAIN	A
18	1	1	1	THERMAL STRAIN	A
19	7	5	3	THERMAL STRAIN	A
20	0	0	0	THERMAL STRAIN	B
21	6	0	0	THERMAL STRAIN	C
22	9	0	0	THERMAL STRAIN	D

[Table 4]

	EVALUATION OF MAGNETIC FLUX DENSITY	EVALUATION OF IRON LOSS	EVALUATION OF NOISE
	T	W/kg	dBA
12	1.935	0.670	26.20	INVENTIVE EXAMPLE
13	1.941	0.691	26.12	INVENTIVE EXAMPLE
14	1.938	0.699	26.09	INVENTIVE EXAMPLE
15	1.936	0.688	25.71	INVENTIVE EXAMPLE
16	1.940	0.685	25.32	INVENTIVE EXAMPLE
17	1.936	0.687	24.98	INVENTIVE EXAMPLE
18	1.941	0.690	24.57	INVENTIVE EXAMPLE
19	1.935	0.670	24.03	INVENTIVE EXAMPLE
20	1.937	0.675	30.28	COMPARATIVE EXAMPLE
21	1.939	0.761	26.48	COMPARATIVE EXAMPLE
22	1.941	0.769	26.15	COMPARATIVE EXAMPLE

In the examples in which at least one imaginary line VL where the D_S was 2 mm or more and less than 20 mm, the D_L/D_S was 5 or more, the |β_L| was 1.5° or more could be set, all of the evaluation results of the magnetic flux density, the iron loss, and the noise were sufficient. In general, the steel sheet having a coarse grain size has excellent magnetic flux density, the noise characteristics tend to deteriorate when the conventional magnetic domain control treatment is performed. On the other hand, in the examples 12 to 19 shown in Table 3 and Table 4, the magnetic domain control treatment line was formed in the region where the β angle was small, and thus, all of the evaluation results of the magnetic flux density, the iron loss, and the noise were sufficient as explained above.
In the same way, in the examples 12 to 19 where the number of grain boundary points which were the intersection points of the grain boundaries in the imaginary lines VL where the D_S was 2 mm or more and less than 20 mm and the D_L/D_S was 3 or more was 2 or less, all of the evaluation results of the magnetic flux density, the iron loss, and the noise were sufficient as explained above.

INDUSTRIAL APPLICABILITY

According to the present disclosure, it is possible to provide a grain-oriented electrical steel sheet capable of achieving both iron loss reduction and noise reduction, and a method for manufacturing the same. Accordingly, the present invention has significant industrial applicability.

REFERENCE SIGNS LIST

1: Grain-oriented electrical steel sheet
11: Magnetic domain control treatment line
RD: Rolling direction
TD: Transverse direction
ND: Rolled surface normal direction
VL: Imaginary line
VP: Magnetic domain control point
DL: Maximum value of distances of magnetic domain control points
DS: Minimum value of distances of magnetic domain control points
X: Region where no magnetic domain control treatment line is formed
2: Original sheet
21: Magnetic domain control treatment region
22: Non-magnetic domain control treatment 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: Condensing lens
509: Motor
511: Sensor
513: Control unit
515: Sheet passing device

Claims

A grain-oriented electrical steel sheet having plural magnetic domain control treatment lines on a surface thereof, wherein,
when an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to a rolling direction of the grain-oriented electrical steel sheet is determined in the grain-oriented electrical steel sheet and when imaginary lines parallel to the rolling direction with a length of 50 mm are set with a spacing of 5 mm in the evaluation region,

in at least one of the imaginary lines, a minimum value D_S of distances of magnetic domain control points which are intersection points between the imaginary lines and the magnetic domain control treatment lines is 2 mm or more and less than 20 mm, a ratio D_L/D_S of a maximum value D_L of the distances of the magnetic domain control points to the minimum value D_S is 3 or more, and an average value |β_L| of absolute values of β angles which are measured between two of the magnetic domain control points whose distance is the maximum value D_L is 1.5° or more.
The grain-oriented electrical steel sheet according to claim 1, wherein,
in each of two or more of the imaginary lines, the minimum value D_S of the distances of 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 distances of 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 which are measured between two of the magnetic domain control points whose distance is the maximum value D_L is 1.5° or more.
The grain-oriented electrical steel sheet according to claim 1 or 2, wherein,
in the imaginary lines 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 which are measured between two of the magnetic domain control points whose distance of the magnetic domain control points is the minimum value D_S satisfy a following expression, 0.5° ≤ |β_L| - |β_S|.
The grain-oriented electrical steel sheet according to claim 1, wherein,
in at least one of the imaginary lines, the minimum value D_S of the distances of the magnetic domain control points which are intersection points between the imaginary lines and the magnetic domain control treatment 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 distances of 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 which are measured between two of the magnetic domain control points whose distance is the maximum value D_L is 1.5° or more.
The grain-oriented electrical steel sheet according to claim 4, wherein,
in each of two or more of the imaginary lines, the minimum value D_S of the distances of 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 distances of 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 which are measured between two of the magnetic domain control points whose distance is the maximum value D_L is 1.5° or more.
The grain-oriented electrical steel sheet according to claim 4 or 5, wherein,
in the imaginary lines 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 which are measured between two of the magnetic domain control points whose distance of the magnetic domain control points is the minimum value D_S satisfy a following expression, 0.5° ≤ |β_L| - |β_S|.
The grain-oriented electrical steel sheet according to claim 1, wherein,
in at least one of the imaginary lines in the imaginary lines where the ratio D_L/D_S of the maximum value D_L of the distances of the magnetic domain control points to the minimum value D_S is 3 or more, a number of grain boundary points which are intersection points between the imaginary lines and grain boundaries is 2 points or less.
The grain-oriented electrical steel sheet according to claim 7, wherein, in each of two or more of the imaginary lines, the number of grain boundary points is 2 points or less.
The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain control treatment lines are thermal strain.
The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain control treatment lines are grooves.
The grain-oriented electrical steel sheet according to claim 1, wherein, in at least one of the imaginary lines, the ratio D_L/D_S is less than 3.
A method for manufacturing a grain-oriented electrical steel sheet comprising:
a step of acquiring a magnetic domain image of an original sheet of a grain-oriented electrical steel sheet;

a step of determining a magnetic domain control treatment region based on a distribution of spacing of magnetic domain walls in the magnetic domain image; and

a step of applying a magnetic domain control treatment to the magnetic domain control treatment region determined based on the distribution of the spacing of magnetic domain walls; wherein,

when an evaluation region with a square shape where a length of each side is 50 mm and a side is parallel to a rolling direction of the grain-oriented electrical steel sheet is determined in the grain-oriented electrical steel sheet and when imaginary lines parallel to the rolling direction with a length of 50 mm are set with a spacing of 5 mm in the evaluation region,

in at least one of the imaginary lines, a minimum value of distances of magnetic domain control points which are intersection points between the imaginary lines and the magnetic domain control treatment lines formed by the magnetic domain control treatment is controlled to 2 mm or more and less than 20 mm, and a ratio of a maximum value of the distances of the magnetic domain control points to the minimum value is controlled to 3 or more.
The method for manufacturing the grain-oriented electrical steel sheet according to claim 12, wherein a region where the spacing of magnetic domain walls is a predetermined value or more is set as the magnetic domain control treatment region.
The method for manufacturing a grain-oriented electrical steel sheet according to claim 12 or 13, wherein a distribution of the spacing of magnetic domain walls is derived from the magnetic domain image using a two-dimensional Fourier transform.
The method for manufacturing a grain-oriented electrical steel sheet according to claim 12 or 13, wherein the magnetic domain control treatment is applied by irradiation with a laser or an electron beam.