EP4786625A1

EP4786625A1 - Grain-oriented electrical steel sheet and method for producing grain-oriented electrical steel sheet

Info

Publication number: EP4786625A1
Application number: EP24872571.5A
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: CN121941784A; WO2025070790A1; KR20260057198A; JPWO2025070790A1

Abstract

This grain-oriented electrical steel sheet is a grain-oriented electrical steel sheet including a plurality of magnetic domain control treatment lines on a surface thereof, in which in a case where a rectangular evaluation region in which a length of a side parallel to a rolling direction of the grain-oriented electrical steel sheet is 50 mm and a length of a side parallel to a transverse direction of the grain-oriented electrical steel sheet is 100 mm is set in the grain-oriented electrical steel sheet, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set inside the evaluation region at intervals of 5 mm in a direction parallel to the rolling direction, in at least one of the imaginary lines, the standard deviation of an interval between magnetic domain control points that are intersection points of the imaginary line and the magnetic domain control treatment line is 1.25 mm or more, and an average value |β_L| of absolute values of β angles measured between two magnetic domain control points at which the interval becomes an absolute 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.
The present application claims priority based on Japanese Patent Application No. 2023-166141 filed in Japan on September 27, 2023 , the contents of which are incorporated herein by reference.

BACKGROUND ART

The grain-oriented electrical steel sheet is a steel sheet containing Si in an amount of 7 mass% or less and having a secondary recrystallization texture in which { 110}<001> oriented grains (Goss oriented grains) as secondary recrystallized grains having an easy axis of magnetization <001> oriented in the rolling direction are integrated. Grain-oriented electrical steel sheets are mainly used as iron cores of power transformers. The 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. 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 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.).
In addition, in Patent Document 4, even in a case where local strain is applied for magnetic domain refinement, there are problems such as a decrease in magnetic permeability due to this strain, an increase in magnetic strain and an increase in noise, therefore a low-iron-loss grain-oriented electrical steel sheet in which problems such as a decrease in permeability and an increase in magnetostriction caused by linear grooves and local strain for magnetic domain refinement are reduced, and an advantageous method for manufacturing the same are proposed.

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
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. H11-293340

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.
Further, in Patent Document 4, although noise is mentioned, both noise reduction and iron loss reduction cannot be sufficiently achieved. Patent Document 4 discloses that the β angle in the vicinity of the center in the rolling direction of the grain is 0° on average, and it is possible to achieve both noise reduction and iron loss reduction by applying the magnetic domain control treatment only to the region where the iron loss reduction effect by the magnetic domain control is large. However, since the β angle near the center in the rolling direction of the grain is not necessarily 0°, both noise reduction and iron loss reduction cannot be sufficiently achieved even if the magnetic domain control treatment is performed by the method disclosed in Patent Document 4.
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 method for manufacturing the same.

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 is a grain-oriented electrical steel sheet including a plurality of magnetic domain control treatment lines on a surface thereof, wherein in a case where a rectangular evaluation region in which a length of a side parallel to a rolling direction of the grain-oriented electrical steel sheet is 50 mm and a length of a side parallel to a transverse direction of the grain-oriented electrical steel sheet is 100 mm is set in the grain-oriented electrical steel sheet, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set inside the evaluation region at intervals of 5 mm in a direction parallel to the rolling direction, in at least one of the imaginary lines, the standard deviation of an interval between magnetic domain control points that are intersection points of the imaginary line and the magnetic domain control treatment line is 1.25 mm or more, and an average value |β_L| of absolute values of β angles measured between two magnetic domain control points at which the interval becomes an absolute maximum value D_L, is 1.5° or more.
(2) Preferably, in the grain-oriented electrical steel sheet according to (1), in each of the two or more imaginary lines, a standard deviation of the interval between the magnetic domain control points is 1.25 mm or more, and an average value |β_L| of the absolute values of the β angles measured between the two magnetic domain control points at which the interval becomes the absolute maximum value D_L, is 1.5° or more.
(3) Preferably, in the grain-oriented electrical steel sheet according to (1) or (2), a ratio D_L/D_S between the absolute maximum value D_L of the interval of the magnetic domain control points and an absolute minimum value D_S of the interval of the magnetic domain control points is 2 or more.
(4) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (3), the D_L/D_S is 4 or more.
(5) Preferably, in the grain-oriented electrical steel sheet according to (3) or (4), the |β_L| and an average value |β_S| of absolute values of β angles measured between the two magnetic domain control points where the interval is the absolute minimum value D_S, satisfy the following formula. $0.5 ° \leq |β_{L}| - |β_{S}|$
(6) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (5), the magnetic domain control treatment line is a thermal strain.
(7) Preferably, in the grain-oriented electrical steel sheet according to (6), the absolute maximum value of the tensile stress introduced into the thermal strain in the magnetic domain control treatment line is non-uniform at each measurement point of the tensile stress.
(8) Preferably, in the grain-oriented electrical steel sheet according to (7), in a case where a rectangular evaluation region in which a length of a side parallel to the rolling direction is 50 mm and a length of a side parallel to the transverse direction of the grain-oriented electrical steel sheet is 100 mm is set on the surface, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set at intervals of 5 mm in a direction parallel to the rolling direction inside the evaluation region, when each of a plurality of intersection points of the imaginary lines and the plurality of magnetic domain control treatment lines is defined as a magnetic domain control point, and the absolute maximum value of the tensile stress in MPa measured at each of the magnetic domain control points is defined as TS_m, and a variance of the TS_m is defined as σ(TS_m)², $σ {({TS}_{m})}^{2} > 5.0$ is satisfied.
(9) Preferably, in the grain-oriented electrical steel sheet according to (8), when TS_{m(β < 2)} is an arithmetical mean value of absolute maximum values of the tensile stress in MPa introduced into the thermal strain, measured at each of the magnetic domain control points having a β angle of less than 2° among the magnetic domain control points, and TS_{m(β ≥ 2)} is an arithmetical mean value of absolute maximum values of the tensile stress in MPa introduced into the thermal strain, measured at each of the magnetic domain control points having a β angle of 2° or more among the magnetic domain control points, TS_{m(β < 2)} > TS_{m(β ≥ 2)} is satisfied.
(10) Preferably, in the grain-oriented electrical steel sheet according to any one of (1) to (5), the magnetic domain control treatment line is a groove.
(11) Preferably, in the grain-oriented electrical steel sheet according to (10), the absolute maximum value of the depth of the groove in the magnetic domain control treatment line is non-uniform at each measurement point of the depth of the groove.
(12) Preferably, in the grain-oriented electrical steel sheet according to (10), in a case where a rectangular evaluation region in which a length of a side parallel to the rolling direction is 50 mm and a length of a side parallel to the transverse direction of the grain-oriented electrical steel sheet is 100 mm is set on the surface, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set at intervals of 5 mm in a direction parallel to the rolling direction inside the evaluation region,
when each of a plurality of intersection points of the imaginary lines and the plurality of magnetic domain control treatment lines is defined as a magnetic domain control point, the absolute maximum value of the depth of the groove in µm measured at each of the magnetic domain control points is defined as D_m, and a variance of the D_m is defined as σ(D_m)², σ(D_m)² > 3.0 is satisfied.
(13) Preferably, in the grain-oriented electrical steel sheet according to (10) or (11), when D_{m(β < 2)} is an arithmetical mean value of absolute maximum values of depths of the grooves in µm, the absolute maximum values being measured at each of the magnetic domain control points having a β angle of less than 2° among the magnetic domain control points, and D_{m(β ≥ 2)} is an arithmetical mean value of absolute maximum values of depths of the grooves in µm, the absolute maximum values being measured at each of the magnetic domain control points having a β angle of 2° or more among the magnetic domain control points, D_{m(β < 2)} > D_{m(β ≥ 2)} is satisfied.
(14) 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 a 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 a spacing of magnetic domain walls, and in a case where a rectangular evaluation region in which a length of a side parallel to a rolling direction of the grain-oriented electrical steel sheet is 50 mm and a length of a side parallel to a transverse direction of the grain-oriented electrical steel sheet is 100 mm is set in the grain-oriented electrical steel sheet, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set inside the evaluation region at intervals of 5 mm in a direction parallel to the rolling direction, in at least one of the imaginary lines, a standard deviation of an interval along the imaginary line at an intersection point of the imaginary line and a magnetic domain control treatment line formed by the magnetic domain control treatment is 1.25 mm or more.
(15) Preferably, in the method for manufacturing a grain-oriented electrical steel sheet according to (14), in the step of determining the magnetic domain control treatment region, a region in which the spacing of magnetic domain walls is a predetermined value or more is set as the magnetic domain control treatment region.
(16) Preferably, in the method for manufacturing a grain-oriented electrical steel sheet according to (14) or (15), in the step of acquiring the magnetic domain image, a distribution of the spacings of magnetic domain walls is derived from the magnetic domain image using two-dimensional Fourier transform.
(17) Preferably, in the method for manufacturing a grain-oriented electrical steel sheet according to any one of (14) to (16), in the step of applying the magnetic domain control treatment, the magnetic domain control treatment is applied by laser or electron beam irradiation.

Advantageous Effects of Invention

According to the above aspect 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. 1A] A plan view of a grain-oriented electrical steel sheet according to an embodiment of the present disclosure.
[FIG. 1B] 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 diagram illustrating an example of distribution of a spacing of magnetic domain walls of a grain-oriented electrical steel sheet before a magnetic domain refinement treatment.
[FIG. 4B] A diagram illustrating an example of distribution of a spacing of magnetic domain walls of a grain-oriented electrical steel sheet after a magnetic domain refinement treatment.
[FIG. 4C] A graph illustrating a difference between FIGS. 4A and 4B.
[FIG. 5] A diagram 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.
[FIG. 13] A graph schematically showing a relationship between the size of spacing of magnetic domain walls and the magnetic domain control saturation strength.
[FIG. 14] A graph schematically showing a relationship between the magnitude of β angle and the magnetic domain control saturation strength.
[FIG. 15] A schematic cross-sectional view of a grain-oriented electrical steel sheet in which a magnetic domain control treatment line is a thermal strain.
[FIG. 16] A schematic cross-sectional view of a grain-oriented electrical steel sheet in which magnetic domain control treatment lines are grooves.
[FIG. 17] A schematic plan view showing a method of measuring a magnetic domain control strength at an intersection point of a magnetic domain control treatment line and an imaginary line in a case where the magnetic domain control treatment line is a thermal strain.
[FIG. 18] A schematic plan view showing a method of measuring the magnetic domain control strength at an intersection point of a magnetic domain control treatment line and an imaginary line in a case where the magnetic domain control treatment line is a groove.

DESCRIPTION OF EMBODIMENTS

(1. Grain-oriented electrical steel sheet 1)

As illustrated in FIG. 1, the grain-oriented electrical steel sheet 1 according to the present embodiment includes a plurality of magnetic domain control treatment lines 11 on the surface. Further, in the grain-oriented electrical steel sheet 1 according to the present embodiment, in a case where a rectangular evaluation region in which the length of the side parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is 50 mm and the length of the side parallel to the transverse direction TD of the grain-oriented electrical steel sheet 1 is 100 mm is set, and further, imaginary lines VL parallel to the transverse direction TD and having a length of 100 mm are set inside the evaluation region at intervals of 5 mm in the direction parallel to the rolling direction, in at least one imaginary line VL, the standard deviation of the interval between the magnetic domain control points VP which are the intersection points of the imaginary line VL and the magnetic domain control treatment line 11 is 1.25 mm or more, and |β_L| which is the average value of the absolute values of the β angles measured between the two magnetic domain control points at which the interval becomes the absolute 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 walls substantially parallel to the rolling direction RD. A distance (domain wall interval) between adjacent 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 a 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 due 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 provided as an exemplary example 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 provided as an exemplary example in FIG. 1A, 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. 1A, the magnetic domain control treatment line 11 is a straight line. On the other hand, as illustrated in FIG. 1B, 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. In a case where 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, in order to set an imaginary line VL to be described later, a rectangular evaluation region in which the length of the side parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is 50 mm and the length of the side parallel to the transverse direction TD of the grain-oriented electrical steel sheet 1 is 100 mm is set.

(Imaginary line VL parallel to transverse direction TD and having length of 100 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 the density of the magnetic domain control treatment lines 11. The imaginary lines VL are set inside the evaluation region at intervals of 5 mm in a direction parallel to the rolling direction. FIG. 1A 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. 1A. The length of the imaginary line VL is 100 mm. The imaginary line VL extends parallel to the transverse direction TD. 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 interval between the magnetic domain control points VP is an index of the density of the magnetic domain control treatment line 11.

(Standard deviation of interval between magnetic domain control points VP)

In the grain-oriented electrical steel sheet 1 according to the present embodiment, the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more in at least one imaginary line VL. The interval d between the magnetic domain control points VP is a distance between two magnetic domain control points VP adjacent to each other along the imaginary line VL. For example, the imaginary line VL of the grain-oriented electrical steel sheet 1 illustrated in FIG. 1A has five magnetic domain control points VP. In a case where the standard deviation of the intervals d1 to d4 of the magnetic domain control points VP is 1.25 mm or more, the grain-oriented electrical steel sheet 1 in FIG. 1A satisfies the requirement of the present disclosure regarding the interval of the magnetic domain control points VP.
As illustrated inFIG. 1A, the grain-oriented electrical steel sheet 1 in which one or more imaginary lines VL are arranged such that the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more includes a region X where the magnetic domain control treatment line 11 is not intentionally provided by interrupting the magnetic domain control treatment line.
The standard deviation of the interval between 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 standard deviation of the interval between the magnetic domain control points VP is less than 1.25 mm. However, it is considered that the grain-oriented electrical steel sheet 1 in which one or more imaginary lines VL in which the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more can be arranged at any place satisfies the requirement of the present disclosure regarding the interval between the magnetic domain control points VP. Therefore, the grain-oriented electrical steel sheet 1 ofFIG. 1A satisfies the requirement of the present disclosure regarding the interval 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 the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more 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 interval between the magnetic domain control points VP.

(β angle)

In the grain-oriented electrical steel sheet 1 according to the present embodiment, the β angle measured on the magnetic domain control treatment line 11 is within 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 rolling 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.
In the grain-oriented electrical steel sheet 1 (original sheet 2 to be described later) before the magnetic domain control treatment shown in FIG. 12, 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 spacings 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.

(|β_L|)

In the grain-oriented electrical steel sheet 1 according to the present embodiment, in the imaginary line VL where the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more, the β angle measured between the two magnetic domain control points VP having the longest interval is specified. Specifically, 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 interval becomes the above-described absolute 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 standard deviation of the interval between the magnetic domain control points VP is 1.25 mm 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 it is possible to achieve both a reduction in iron loss and a reduction in noise according to the grain-oriented electrical steel sheet 1 in which the imaginary line VL in which the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more can be set, and |β_L| measured in the imaginary line VL is 1.5° or more. 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 spacings 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 spacings 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 performing continuous wave laser irradiation along a direction inclined by 2° with respect to the rolling direction RD. The distribution of the spacings 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. In FIGS. 4A to 4C, the unit of the numerical value is µm.
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 original spacing of magnetic domain walls is about 500 µm or more. On the other hand, in the bright color portion 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. It can be seen that 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 having a narrow spacing of magnetic domain walls causes deterioration of noise characteristics due to the flux closure domain.
According to the above findings, it is considered that in the conventional magnetic domain control treatment of the grain-oriented electrical steel sheet 1, the magnetic domain control is also performed to a portion where the magnetic domain control is unnecessary, and this contributes to an increase in noise. In addition, it has been 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 having a small β angle) 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 the 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 in the region X, the standard deviation of the interval between the magnetic domain control points VP along the imaginary line VL is 1.25 mm or more. 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. In the grain-oriented electrical steel sheet 1 according to the present embodiment, the iron loss is not impaired 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.

(The number of imaginary lines VL in which the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more)

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 transverse direction TD and having a length of 100 mm is set at intervals of 5 mm inside the evaluation region, in each of the two or more imaginary lines VL, the standard deviation of the interval between the magnetic domain control points VP is preferably 1.25 mm or more, and the average value |β_L| of the absolute values of the β angles measured between the two magnetic domain control points at which the interval becomes the absolute maximum value D_L, is preferably 1.5° or more. That is, the grain-oriented electrical steel sheet 1 preferably includes the region X where the magnetic domain control treatment line 11 is not provided to such an extent that two or more imaginary lines VL can be set such that the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more and |β_L| is 1.5° or more. The number of the imaginary lines VL in which the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more and |β_L| is 1.5° or more is still more preferably 3 or more, 4 or more, 5 or more, or 10 or more. $(D_{I} / D_{S})$
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 between the absolute maximum value D_L and the absolute minimum value D_S particularly changes among the features described above because the steel sheet has a coarse grain size.
Specifically, in the grain-oriented electrical steel sheet 1 according to the present embodiment, the ratio D_L/D_S of the absolute maximum value D_L of the interval between the magnetic domain control points to the absolute minimum value D_S of the interval between the magnetic domain control points is preferably 2 or more. This further improves both the iron loss characteristics and the noise characteristics. More preferably, D_L/D_S is 4 or more. The upper limit of D_L/D_S is not limited. The upper limit of the D_L/D_S may be 24 as necessary.

(Relationship between |β_L| and |β_S|)

In the imaginary line VL where the standard deviation of the interval between the magnetic domain control points VP is 1.25 mm or more, it is more preferable that |β_L| and the average value |β_S| of the absolute values of the β angles measured between the two magnetic domain control points VP at which the interval becomes the absolute minimum value D_S, satisfy the following formula. $0.5 ° \leq |β_{L}| - |β_{S}|$
In a case where |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. The upper limit of |β_L|-|β_S| is not limited.

(Aspect of magnetic domain control treatment line 11)

The type of the magnetic domain control treatment line 11 is not particularly limited, but preferred examples thereof are a thermal strain and/or a 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 equivalent thereto. Therefore, in a case where 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, in a case where 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.
In the grain-oriented electrical steel sheet according to the present disclosure, the absolute maximum value of the depth of the groove or the tensile stress introduced into the thermal strain, which is an index of the strength of the magnetic domain control, in the magnetic domain control treatment line is preferably non-uniform for each depth of the groove or each measurement point of the tensile stress.
The higher the strength of magnetic domain control is, the higher the effect of magnetic domain refinement is, on the other hand, the higher the strength of the magnetic domain control is, the more easily the hysteresis loss is increased and the noise characteristics are deteriorated. According to the new findings of the present inventors, a grain-oriented electrical steel sheet has a non-uniform magnetic domain control saturation strength. Therefore, it is preferable to make the magnetic domain control strength non-uniform according to the magnetic domain control saturation strength.
The magnetic domain control saturation strength means a magnetic domain control strength at which the effect of magnetic domain refinement treatment is substantially saturated. In a case where the magnetic domain control strength is equal to or lower than the magnetic domain control saturation strength, a higher magnetic domain control strength leads to reduced iron loss. However, in a case where the magnetic domain control strength is more than the magnetic domain control saturation strength, the iron loss reduction effect is hardly enhanced even if the magnetic domain control strength is increased. On the other hand, even in a case where the magnetic domain control strength is more than the magnetic domain control saturation strength, a higher magnetic domain control strength leads to increased hysteresis loss and worsened noise characteristics. Therefore, it is extremely preferable that the magnetic domain control strength is within the range not exceeding the magnetic domain control saturation strength.
When the magnetic domain control treatment line is a thermal strain, it is more preferable that σ(TS_m)² > 5.0 is satisfied, where each of a plurality of intersection points between the imaginary line and the plurality of magnetic domain control treatment lines is a magnetic domain control point, the absolute maximum value of the tensile stress in MPa introduced into the thermal strain measured at each of the magnetic domain control points is TS_m, and the variance of TS_m is σ(TS_m)².
The "absolute maximum value of the tensile stress introduced into the thermal strain" is an absolute maximum value of the tensile stress measured in one arbitrary cross section for measurement. The tensile stress varies in one measurement cross section, and thus one "absolute maximum value of the tensile stress introduced into the thermal strain" is specified for one measurement cross section. As schematically illustrated in FIG. 15, the thermal strain 541 has a certain degree of spread in the cross section. The tensile stress is the highest at a site directly irradiated with the laser beam, and the tensile stress is low at a site away from the site. That is, the measured value of the tensile stress differs for each measurement site in the cross section. According to the method for measuring tensile stress as described later, the distribution and the absolute maximum value of tensile stress in the cross section can be derived.
In a case where the magnetic domain control strength is uniform, the absolute maximum value of the tensile stress introduced into the thermal strain 541 is a constant value over the entire magnetic domain control treatment line 11. On the other hand, in a case where the magnetic domain control strength is non-uniform, the absolute maximum value of the tensile stress introduced into the thermal strain in the magnetic domain control treatment line is non-uniform at each measurement point of the tensile stress. Hereinafter, the absolute maximum value of tensile stress introduced into a thermal strain may be simply referred to as "tensile stress".
In addition, the present inventors have found that the magnetic domain control saturation strength has a strong relationship with the β angle. The β angle is a deviation angle of grains from the Goss orientation around the axis of the transverse direction (TD). In a point where the β angle is small, the magnetic domain control saturation strength is high. In the grain-oriented electrical steel sheet before the magnetic domain control treatment, there is a relationship also between the β angle and the spacing of magnetic domain walls. In the grain-oriented electrical steel sheet before the magnetic domain control treatment, the larger the β angle, the smaller the spacing of magnetic domain walls. However, in the grain-oriented electrical steel sheet after the magnetic domain control treatment, the relationship between the spacing of magnetic domain walls and the β angle becomes small. This is because the magnetic domain control treatment changes the spacing of magnetic domain walls, but does not change the β angle.
Therefore, it is preferable to select the optimum magnetic domain control strength according to the size of the spacing of magnetic domain walls or the β angle. For example, it is preferable that the magnetic domain refinement treatment is performed with a large magnetic domain control strength at a portion where the spacing of magnetic domain walls is large and the β angle is small; and the magnetic domain refinement treatment is performed with a small magnetic domain control strength at a portion where the spacing of magnetic domain walls is small and the β angle is large. As described above, the magnetic domain refinement treatment is not performed on a region where the original spacing of magnetic domain walls is narrow.
Specifically, it is preferable that when TS_{m(β < 2)} is an arithmetical mean value of absolute maximum values of the tensile stress in MPa introduced into the thermal strain, measured at each of the magnetic domain control points having a β angle of less than 2° among the magnetic domain control points, and TS_{m(β ≥ 2)} is an arithmetical mean value of absolute maximum values of the tensile stress in MPa introduced into the thermal strain, measured at each of the magnetic domain control points having a β angle of 2° or more among the magnetic domain control points, TS_{m(β < 2)} > TS_{m(β ≥ 2)} is satisfied.
In this case, the iron loss of the grain-oriented electrical steel sheet after magnetic domain control is further reduced. On the other hand, in the grain-oriented electrical steel sheet after magnetic domain control, an increase in hysteresis loss and deterioration in noise characteristics are further suppressed.
An example of a method of measuring TS_m and σ(TS_m)² will be described with reference to FIG. 17. A broken line in FIG. 17 is a plurality of imaginary lines VL set at intervals of 5 mm in parallel along the transverse direction TD of the grain-oriented electrical steel sheet. An X mark and an O mark in FIG. 17 are intersection points of the imaginary line VL and the thermal strain 541 which is a magnetic domain control treatment line. The β angle is 2° or more at the point marked with the X mark, and the β angle is less than 2° at the point marked with the O mark. However, there is no need to consider the β angle at the intersection point for calculating σ(TS_m)².
First, the transverse direction TD of the grain-oriented electrical steel sheet is specified. The transverse direction TD can be specified by a method described later. Next, imaginary lines VL are set at intervals of 5 mm in parallel along the transverse direction TD of the grain-oriented electrical steel sheets. Then, an intersection point of the imaginary line VL and the thermal strain 541 which is the magnetic domain control treatment line is specified. In a case where the thermal strain 541 cannot be visually recognized with the naked eye, the thermal strain 541 is specified based on a magnetic domain image. The shape of the measurement region is preferably a rectangle whose size along the rolling direction RD is 50 mm or more and whose size along the transverse direction TD is 100 mm or more. One side of the rectangle is preferably parallel to the rolling direction RD.
Then, in a case where a rectangular evaluation region in which a length of a side parallel to the rolling direction is 50 mm and a length of a side parallel to the transverse direction is 100 mm is set on the surface, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set inside the evaluation region at intervals of 5 mm in a direction parallel to the rolling direction, TS_m at intersection points of all the imaginary lines in the set region and the magnetic domain control treatment line is measured, and a variance σ(TS_m)² of TS_m is calculated. The tensile stress TS_m introduced in the thermal strain is measured by an EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage.
When the magnitude of tensile stress introduced into the thermal strain is measured by the EBSD Wilkinson method and Cross Court manufactured by BLG Vantage, first, the thermal strain 541 as the magnetic domain control treatment line is specified by the above-described procedure. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control treatment line and perpendicularly to the magnetic domain control treatment line. This cut cross section is used as a measurement surface. The cross section of the magnetic domain control treatment line 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 tensile stress components in the rolling surface normal direction, in the direction parallel to the magnetic domain control treatment line, and in the direction perpendicular to the rolling surface normal direction and the magnetic domain control treatment line.
The variance σ(TS_M)² of the absolute maximum values TS_M of tensile stress specified at each of a plurality of the measurement points is derived in accordance with the method for deriving a population variance described in the paragraph 2.36 of JIS Z 8101-1:2015 "Statistics-Vocabulary and symbols-Part 1: General statistical terms and terms used in probability".
TS_{m(β < 2)} and TS_{m(β ≥ 2)} are measured by the following method.
First, the β angle is measured at each intersection point to specify the intersection points where the β angle is 2° or more and the intersection points where the β angle is less than 2°. The β angle in the grain-oriented electrical steel sheet 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.
Next, the absolute maximum value TS_m of tensile stress is specified for each of all the intersection points where the β angle is 2° or more, and the arithmetical mean value of these values is calculated. The value is regarded as TS_m(β≥2).
Furthermore, the absolute maximum value TS_m of the tensile stress is specified at each of all intersection points where the β angle is less than 2°, and the arithmetical mean value of these values is calculated. The value is regarded as TS_{m(β < 2)}. The method for measuring the absolute maximum value TS_m of the tensile stress introduced into the thermal strain 541 at the intersection point is as described above.
When the magnetic domain control treatment line is a groove, in a case where a rectangular evaluation region in which a length of a side parallel to the rolling direction is 50 mm and a length of a side parallel to the transverse direction is 100 mm is set on the surface, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set at intervals of 5 mm in a direction parallel to the rolling direction inside the evaluation region, when each of a plurality of intersection points of the imaginary lines and the plurality of magnetic domain control treatment lines is defined as a magnetic domain control point, the absolute maximum value of the depth of the groove in µm measured at each of the magnetic domain control points is defined as D_m, and a variance of the D_m is defined as σ(D_m)², it is more preferable to satisfy σ(D_m)² > 3.0.
In this case, the magnetic domain control strength is changed based on the size of the spacing of magnetic domain walls or the magnitude of the β angle, and in the grain-oriented electrical steel sheet after magnetic domain control, an increase in hysteresis loss and deterioration in noise characteristics are further suppressed.
Further, when D_{m(β < 2)} is an arithmetical mean value of absolute maximum values of depths of the grooves in µm, the absolute maximum values being measured at each of the magnetic domain control points having a β angle of less than 2° among the magnetic domain control points, and D_{m(β ≥ 2)} is an arithmetical mean value of absolute maximum values of depths of the grooves in µm, the absolute maximum values being measured at each of the magnetic domain control points having a β angle of 2° or more among the magnetic domain control points, it is more preferable that D_{m(β < 2)} > D_{m(β ≥ 2)} is satisfied.
In this case, in the magnetic domain control treatment line, the magnetic domain control strength is high at a place where the β angle is small, and the magnetic domain control strength is low at a place where the β angle is large. Therefore, the iron loss of the grain-oriented electrical steel sheet after magnetic domain control is further reduced. On the other hand, in the grain-oriented electrical steel sheet after magnetic domain control, an increase in hysteresis loss and deterioration in noise characteristics are further suppressed.
An example of a method of measuring D_m and σ(D_m)² is illustrated in FIG. 18. A broken line in FIG. 18 is a plurality of imaginary lines VL set at intervals of 5 mm in parallel along the transverse direction TD of the grain-oriented electrical steel sheet. An X mark and an O mark in FIG. 18 are intersection points of the imaginary line VL and the groove 542 which is a magnetic domain control treatment line. The β angle at the point marked with the X mark is 2° or more, and the β angle at the point marked with O is less than 2°. However, there is no need to consider the β angle at the intersection point for calculating σ(D_m)².
First, the rolling direction of the grain-oriented electrical steel sheet is specified. Next, imaginary lines VL are set at intervals of 5 mm in parallel along the transverse direction TD of the grain-oriented electrical steel sheets. Then, an intersection point of the imaginary line VL and the magnetic domain control treatment line is specified. In a case where the magnetic domain control treatment line is the groove 542 as shown in FIG. 16, it is easy to visually recognize the magnetic domain control treatment line with naked eyes. The shape of the measurement region is preferably a rectangle whose size along the rolling direction RD is 50 mm or more and whose size along the transverse direction TD is 100 mm or more. One side of the rectangle is preferably parallel to the rolling direction RD.
Then, in a case where a rectangular evaluation region in which the length of the side parallel to the rolling direction is 50 mm and the length of the side parallel to the transverse direction is 100 mm is set, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set inside the evaluation region at intervals of 5 mm in the direction parallel to the rolling direction, the absolute maximum value D_m of the depth of the groove at the intersection point of all the imaginary lines in the set region and the magnetic domain control treatment line is measured, and the variance σ(D_m)² of the absolute maximum value D_m of the depth of the groove is calculated. The method for measuring the absolute maximum value D_m of the depth of the groove is as follows.
Measurement is performed using a white interference microscope Contour GT-I manufactured by Bruker. As the lenses to be used, an objective lens of 5 times (numerical aperture: 0.12, optical resolution: 2.2 µm) and an inner lens of 1 time are used, and a white LED is used as the light source and a monochrome CCD (1200 × 1000 pixels) is used as the camera. The pixel size was 1.37 µm, inclination correction was performed by fitting to the least-square plane using analysis software Vision64 Map Premium9.2, and then undulation of long wavelength was removed using a Gaussian filter with a cutoff value of 2.5 mm for analysis. Resampling may be performed so that the pixel size is 10 µm as necessary at the time of analysis. In addition, a portion that is obviously determined to be an abnormal point may be excluded from the analysis, and the type of the lens, the value of the filter, and the correction method may be changed depending on the properties of the sample. In a case where a groove is formed in the grain-oriented electrical steel sheet, but the unevenness cannot be measured from the surface due to an insulating coating or the like, the measurement is performed after the insulating coating or the like is removed using a known method.
First, the β angle is measured at each intersection point to specify the intersection points where the β angle is 2° or more and the intersection points where the β angle is less than 2°. Next, an arithmetical mean value of D_m for all the intersection points where the β angle is 2° or more is calculated, which is regarded as D_m(β≥2). In addition, an arithmetical mean value of D_m for all the intersection points where the β angle is less than 2° is calculated, which is regarded as D_{m(β < 2)}. The method for measuring the absolute maximum value D_m of the depth of the groove at the intersection point is as described above.

(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 an exemplary example. 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.
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 condenser 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 Sign 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. In a case where 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 method for manufacturing 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 shown in FIG. 12 based on distribution of the spacings 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 spacings of magnetic domain walls. Further, in the method for manufacturing a grain-oriented electrical steel sheet 1 according to the present embodiment, in a case where a rectangular evaluation region in which the length of a side parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is 50 mm and the length of a side parallel to the transverse direction TD of the grain-oriented electrical steel sheet 1 is 100 mm is set in the grain-oriented electrical steel sheet 1, and an imaginary line VL parallel to the transverse direction TD and having a length of 100 mm is set at intervals of 5 mm inside the evaluation region, the standard deviation of an interval between the imaginary line VL and the magnetic domain control points VP, which are intersection points of the imaginary line VL and the magnetic domain control treatment lines 11, is 1.25 mm or more in at least one imaginary line VL.
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 spacings of magnetic domain walls of the 180° magnetic domain is derived from the magnetic domain image. The distribution of the spacings 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, or more than 500 µm) 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, and the spacing of magnetic domain walls of the non-magnetic domain control treatment region 22 is less than a predetermined value.
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.
Preferably, magnetic domain control strength is determined depending on the spacing of magnetic domain walls of the grain-oriented electrical steel sheet before the magnetic domain refinement treatment. The magnetic domain control strength means the amount of the thermal strain in a case where the magnetic domain control means is a thermal strain, and means the depth of the groove in a case where the magnetic domain control means is a groove. In this case, the absolute maximum value of the tensile strength introduced into the thermal strain or the depth of the groove in the magnetic domain control treatment line becomes non-uniform at each measurement point of the tensile strength or the depth of the groove.
The higher the strength of magnetic domain control is, the higher the effect of magnetic domain refinement is. On the other hand, the higher the strength of magnetic domain control is, the more easily the hysteresis loss is increased and the noise characteristics are deteriorated. According to the new findings of the present inventors, a grain-oriented electrical steel sheet has a non-uniform magnetic domain control saturation strength.
The magnetic domain control saturation strength means a magnetic domain control strength at which the effect of magnetic domain refinement treatment is saturated. In a case where the magnetic domain control strength is equal to or lower than the magnetic domain control saturation strength, a higher magnetic domain control strength leads to reduced iron loss. However, in a case where the magnetic domain control strength exceeds the magnetic domain control saturation strength, the iron loss reduction effect cannot be enhanced even if the magnetic domain control strength is increased. However, even in a case where the magnetic domain control strength is more than the magnetic domain control saturation strength, the higher the magnetic domain control strength is, the more hysteresis loss increases and noise characteristics deteriorate. Therefore, it is extremely preferable that the magnetic domain control strength is within the range not exceeding the magnetic domain control saturation strength.
Specifically, it is preferable that the magnetic domain refinement treatment is performed with a large magnetic domain control strength at a portion where the spacing of magnetic domain walls is large and the β angle is small; and the magnetic domain refinement treatment is performed with a small magnetic domain control strength at a portion where the spacing of magnetic domain walls is small and the β angle is large. In the region where the β angle is large, the magnetic domain control effect cannot be obtained, and thus the magnetic domain control saturation strength is 0. In the region where the β angle is smaller than a predetermined value, the magnetic domain control effect is obtained. For example, it is estimated that the magnetic domain control effect can be obtained in a case where the β angle is 2° or less. In the region where the β angle is smaller than a predetermined value, as the β angle increases, the magnetic domain control saturation strength also increases. In the region where the β angle is still smaller, the magnetic domain control saturation strength is substantially constant.
FIG. 18 is a graph schematically illustrating a method for determining the magnetic domain control strength based on the spacing of magnetic domain walls. In FIG. 18, the vertical axis represents the magnetic domain control strength, and the horizontal axis represents the size of the spacing of magnetic domain walls. A solid line graph in FIG. 18 indicates the magnetic domain control saturation strength. In the region where the spacing of magnetic domain walls is small, the effect of magnetic domain control cannot be obtained, and thus the magnetic domain control saturation strength is 0. In the region where the spacing of magnetic domain walls is more than 500 µm, the effect of magnetic domain control is obtained. In the region where the spacing of magnetic domain walls exceeds 500 µm, as the spacing of magnetic domain walls increases, the magnetic domain control saturation strength also increases. In the region where the spacing of magnetic domain walls is more than about 1200 µm, the magnetic domain control saturation strength is substantially constant.
FIG. 14 shows a graph schematically illustrating a method for determining the magnetic domain control strength based on the β angle. In FIG. 14, the vertical axis represents the magnetic domain control strength, and the horizontal axis represents the magnitude of the β angle. A solid line graph in FIG. 14 indicates the magnetic domain control saturation strength. In the region where the β angle is large, the magnetic domain control effect cannot be obtained, and thus the magnetic domain control saturation strength is 0. In the region where the β angle is smaller than a predetermined value, the magnetic domain control effect is obtained. For example, it is estimated that the magnetic domain control effect can be obtained in a case where the β angle is 2° or less. In the region where the β angle is smaller than a predetermined value, as the β angle increases, the magnetic domain control saturation strength also increases. In the region where the β angle is still smaller, the magnetic domain control saturation strength is substantially constant.
It is most preferable that the relationship between the spacing of magnetic domain walls of the portion where the magnetic domain control is performed and the magnetic domain control strength is on the solid line graph in FIG. 14. Alternatively, it is most preferable that the relationship between the β angle of the portion where the magnetic domain control is performed and the magnetic domain control strength is on the solid line graph in FIG. 14. The magnetic domain control saturation strength can be used as a target value of the magnetic domain control strength.
Furthermore, there is a magnetic domain control minimum strength, which is the minimum strength at which the magnetic domain control effect is exhibited. In a case where the magnetic domain control is performed, the magnetic domain control strength is more preferably equal to or more than the magnetic domain control minimum strength.
However, the magnetic domain control strength may slightly vary with respect to the magnetic domain control saturation strength as a target value. In FIGS. 13 and 14, the region equal to or higher than the magnetic domain control minimum strength and within a certain range from the graph of the magnetic domain control saturation strength is referred to as a target range of the magnetic domain control strength. The magnetic domain control strength and the spacing of magnetic domain walls of the part to be subjected to the magnetic domain control are preferably within the shaded region surrounded by broken lines in FIGS.13 and 14. In a case where the absolute maximum value of the tensile stress introduced into the thermal strain in the magnetic domain control treatment line is made non-uniform at each measurement point of the tensile stress, it is preferable to change the magnetic domain control strength. In this case, it is preferable to change inside the shaded region surrounded by the broken line.
In a case where the magnetic domain control treatment line is a thermal strain, the magnetic domain control strength can be changed by irradiation conditions of a laser or an electron beam. Specifically, the power, irradiation time, irradiation interval, and the like of the laser or electron beam may be changed to change the average irradiation energy density Ua (mJ/mm²) per unit area. In a case where the magnetic domain control treatment line is a groove, the depth of the groove formed in the grain-oriented electrical steel sheet may be changed by adjusting the time, strength, shape, and the like in a method of irradiation with a laser or an electron beam, a method by mechanical processing such as a gear, a method by chemical processing such as etching, and the like.
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. In a case where 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. In a case where 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 spacings of magnetic domain walls of original sheet 2 by using, for example, the two-dimensional 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, or more than 500 µm) as a portion to which the magnetic domain control treatment is preferentially applied.
The two-dimensional Fourier transform is particularly effective as a procedure 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 spacings 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, 1) 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 with two types of colors or an image expressed in three or more gradations (multiple gradations) such as gray scale.
In order to derive the distribution of the spacings of magnetic domain walls of the original sheet 2, the calculation unit 41 executes the following processes (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 spacings 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, 1) of a rectangular window in which a range in the k direction set to 0 ≤ k ≤ N_k-1 and a range in the l 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, 1) in the k direction and the 1 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, l-mS_l) of a partial region obtained by cutting out a range of nS_k ≤ k ≤ nS_k + N_k-1 and mS_l ≤ 1 ≤ mS_l + 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_l that define the range of the window function Wa (k, 1) 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_l 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] $\{\begin{matrix} Δ f_{k} = \frac{2}{N_{k} Δ k} \\ Δ f_{l} = \frac{2}{N_{l} Δ l} \end{matrix}$
Ak 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 spacings 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 region not surrounded by a broken line illustrated in FIG. 12. At this time, in a case where a rectangular evaluation region in which the length of a side parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is 50 mm and the length of the side parallel to the transverse direction TD of the grain-oriented electrical steel sheet 1 is 100 mm is set in the grain-oriented electrical steel sheet 1, and further, an imaginary line VL parallel to the transverse direction TD and having a length of 100 mm is set inside the evaluation region at intervals of 5 mm in the direction parallel to the rolling direction, the standard deviation of the interval along the imaginary line VL at the intersection point of the imaginary line VL and the magnetic domain control treatment line 11 in at least one imaginary line VL is 1.25 mm or more. As a result, the grain-oriented electrical steel sheet 1 of FIG. 1 in which |β_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 are 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, in a case where 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.

(Coating)

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, in a case where 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 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. In a case where 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.
On the other hand, as illustrated in FIG. 1A, the angle formed by the magnetic domain control treatment line 11 and the transverse direction TD needs to 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 2° 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. 1A, 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 2° 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.

(Interval P of Magnetic domain control treatment)

For example, the interval P of the magnetic domain control treatment determined by the irradiation pitch P of the laser beam LB illustrated in FIG. 8 is not particularly limited. As the interval P of the magnetic domain control treatment is smaller, the effect of reducing the iron loss is enhanced. On the other hand, the larger the interval P of the magnetic domain control treatment is, the more noise characteristics are improved. The interval can be appropriately selected according to the characteristics required for the grain-oriented electrical steel sheet 1.
The interval P at which the magnetic domain control treatment is performed corresponds to an interval between the magnetic domain control treatment lines 11 and imaginary lines along them in the grain-oriented electrical steel sheet 1 according to the present embodiment. An imaginary line along the magnetic domain control treatment line 11 provided in the grain-oriented electrical steel sheet 1 is set over the entire width of the grain-oriented electrical steel sheet 1, and an interval P of the magnetic domain control treatment is specified by measuring these intervals.
For example, the interval P of the magnetic domain control treatment may be 1.0 mm or more, 2.0 mm or more, 3.0 mm or more, or 5.0 mm or more. The interval P of the magnetic domain control treatment may be 10.0 mm or less, 9.0 mm or less, 8.0 mm or less, or 7.0 mm or less. The interval P of the magnetic domain control treatment is a value measured along the rolling direction RD. In FIG. 8, the magnetic domain control treatment line 11 is drawn substantially parallel to the transverse direction for simplification of illustration, but is actually inclined at a predetermined angle with respect to the transverse direction TD as described above.
In the grain-oriented electrical steel sheet 1 illustrated inFIG. 1A, the interval P of the magnetic domain control treatment is constant. On the other hand, the interval P of the magnetic domain control treatment may vary. For example, the average value of the intervals P of the magnetic domain control treatment may be 1.0 mm or more, 2.0 mm or more, 3.0 mm or more, or 5.0 mm or more. The average value of the intervals P of the magnetic domain control treatment may be 10.0 mm or less, 9.0 mm or less, 8.0 mm or less, or 7.0 mm or less.

(Magnitude of tensile stress introduced in thermal strain)

The magnetic domain control treatment line 11 may be a thermal strain. In the thermal strain, tensile stress is introduced. As the tensile stress is higher, the effect of reducing the iron loss is enhanced. On the other hand, the lower the tensile stress is, the more 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. In a case where 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 reducing 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 that variation is present, 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. 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. In a case where the grain-oriented electrical steel sheet 1 is a coil, a sample may be collected from an arbitrary position of the coil. In a case where 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. In a case where the size of the component is small, if the length of one side of the sample along the transverse direction TD is 100 mm or more, the length of one side of the sample along the rolling direction RD may be 50 mm or more and less than 100 mm. 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)

In a case where the magnetic domain control treatment line 11 is a groove, the magnetic domain control treatment line 11 can be visually identified. In a case where 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.
In a case where 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 provided as an exemplary example in FIG. 5. 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) In a case where 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) In a case where 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) In a case where 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.

(Standard deviation of interval between magnetic domain control points VP)

The standard deviation of the interval between the magnetic domain control points is calculated according to the following procedure. First, a rectangular evaluation region in which a length of a side parallel to the rolling direction RD of the grain-oriented electrical steel sheet 1 is 50 mm and a length of a side parallel to the transverse direction TD of the grain-oriented electrical steel sheet 1 is 100 mm is set in the grain-oriented electrical steel sheet 1. Then, an imaginary line VL parallel to the transverse direction TD and having a length of 100 mm is set on the surface of the grain-oriented electrical steel sheet 1 at intervals of 5 mm inside the evaluation region. 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 transverse direction TD and the magnetic domain control treatment line 11 is performed according to the above-described procedure. Then, an interval between adjacent magnetic domain control points VP is measured, and the standard deviation of these measurement values is calculated.
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 standard deviation of the interval between the magnetic domain control points VP falls 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 standard deviation of the interval between the magnetic domain control points VP falls within the range of the present disclosure cannot be found, it is estimated that the requirements of the present disclosure are not satisfied.

(Absolute minimum value D_S and absolute maximum value D_L of interval between magnetic domain control points VP)

The absolute minimum value D_S and the absolute maximum value D_L of the interval between the magnetic domain control treatment points are calculated according to the following procedure. First, the imaginary line VL described above is set 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 interval between the adjacent magnetic domain control points VP is measured, and the absolute minimum value and the absolute maximum value of these measurement values are obtained.

(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 interval becomes the absolute 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 interval 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 interval becomes the absolute 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 P_βL of the magnetic domain control points VP, and the average value of the absolute values of the β angles may be regarded as |β_L| on the 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 interval becomes the absolute 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 at intervals of 1 mm from the midpoint P_βS of the magnetic domain control points VP by the above-described procedure. Note that two or more portions at which the interval becomes D_s may be accidentally formed on one imaginary line VL. In this case, there are two or more sets of adjacent magnetic domain control points VP2 at which the interval becomes the absolute minimum value D_s. In this case, the β angle between the adjacent magnetic domain control points VP is measured at intervals of 1 mm from the midpoint P_βS of the magnetic domain control points VP, and the average value of the absolute values of the β angles may be regarded as |β_S| on the imaginary line VL.
In each of the plurality of imaginary lines VL, |β_L| is obtained. In one or more imaginary lines VL, in a case where the standard deviation of the interval between the magnetic domain control points is 1.25 mm or more and |β_L| is 1.5° or more, it 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 components 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 component 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 collecting 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 amounts of C and S, which are difficult to measure by ICP-AES, may be measured using a combustion-infrared light absorption method. The amount of N may be measured using an inert gas fusion-thermal conductivity method.
In a case where 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 components 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 of measuring interval P of magnetic domain control treatment)

The interval P of the magnetic domain control treatment is obtained by first specifying the magnetic domain control treatment line 11 and the rolling direction RD by the above-described procedure, then setting an imaginary line along the magnetic domain control treatment line 11, and measuring the interval of the imaginary lines using a known length measuring 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. In a case where the tensile stress in an arbitrary direction is 40 MPa or more (that is, in a case where the tensile stress in at least one direction is 40 MPa or more) in at least one portion of the grain-oriented electrical steel sheet 1, the absolute 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. Therefore, for the purpose of determining whether the absolute maximum value of the tensile stress is 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. However, in a case where σ(TS_m)², TS_{m(β < 2)}, or TS_{m(β ≥2)} to be described later is obtained, the measurement is not stopped, and the tensile stress at each measurement point is obtained.

(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. In a case where 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 of the same lot having a sheet thickness of 0.20 mm was used as the original sheet. The original sheet was subjected to a magnetic domain control treatment under various conditions shown in Table 1.
For the steel sheets of No. 1 to 13 obtained by each treatment, the number of VL (imaginary lines) having the standard deviation of 1.25 mm or more is shown in column A of Table 1, and further, the number of VL satisfying the relationship of |β_L| ≥ 1.5° in VL shown in column A is shown in column B of Table 1. In the column C of Table 1, further, the number of VLs satisfying the relationship of 2 ≤ D_L/D_S in the VL shown in the column B is shown, and in the column D of Table 1, further, the number of VLs satisfying the relationship of 0.5° <|β_L|-|β_S| in the VL shown in the column C is shown. The measurement of the standard deviation and |β_L| and |β_S| was performed according to the above-described procedure. 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 described later, and subjected to measurement. In this rectangular sample, a rectangular evaluation region in which the length of the side parallel to the rolling direction RD was 50 mm and the length of the side parallel to the transverse direction TD was 100 mm was set, and an imaginary lines VL parallel to the transverse direction TD and having a length of 100 mm were set at intervals of 5 mm inside the evaluation region. The number of the imaginary lines VL was nine.
The samples No. 1 to 10 shown in Table 1 are a sample in which a linear magnetic domain control treatment line is formed in a region having a wide spacing of magnetic domain walls. The sample No. 11 is a sample in which a linear magnetic domain control treatment line over the entire width is formed. The sample No. 12 is a sample in which a regular broken-linear magnetic domain control treatment line is formed. The sample No. 13 is a sample in which random broken-linear magnetic domain control treatment lines are formed. No. 14 is a sample in which a linear magnetic domain control treatment line including a curve is formed in a wide spacing of magnetic domain walls region. No. 15 is a sample in which a magnetic domain control treatment line is formed at intervals of 4 mm only in a region within ±4 mm in the rolling direction RD from the center in the rolling direction of each grain. The radius of curvature of the steel sheet at the position where the grains were present during the finish-annealing was 250 mm.
The sample described as the thermal strain in Table 1 is irradiated with a laser beam having an average irradiation energy density of 1.5 mJ/mm² at intervals of 4 mm, and subjected to magnetic domain control treatment.
In the sample described as a groove shown in Table 1, a groove (depth: 15 µm, width: 20 µm) is formed to perform magnetic domain control.
The mixture shown in Table 1 means a magnetic domain control treatment condition in which the above-described thermal strain and the above-described grooves are subjected to magnetic domain control such that the total length is 1 : 1.
Next, the noise and iron loss of the grain-oriented electrical steel sheets subjected to the magnetic domain control treatment were measured, and the measurement results are described in Table 2.
The method of measuring noise and iron loss was 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 50 Hz and an excitation magnetic flux density of 1.8 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 3 as the noise evaluation results (unit: dBA) of the grain-oriented electrical steel sheets. An example in which the evaluation result of noise was 43.50 dBA or less was determined to be an example in which noise reduction was achieved. In Table 2, 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 50 Hz and an excitation magnetic flux density of 1.8 T as described above. The obtained iron loss is described in Table 3 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 1.270 W/kg or less was determined to be an example in which iron loss reduction was achieved.

[Table 1]

Sample No.	A	B	C	D	E
Sample No.	Number of VL with standard deviation of 1.25 mm or more	Number of VL satisfying \|β_L\| ≥ 1.5° in VL of column A	Number of VL further satisfying 2 ≤ D_L/D_S in VL of column B	Number of VL further satisfying 0.5° ≤ \|β_L\|-\|β_S\| in VL of column C	Type of magnetic domain control treatment line
1	1	1	0	0	Thermal strain
2	1	1	0	0	Mixed
3	1	1	0	0	Groove
4	2	2	0	0	Thermal strain
5	5	4	0	0	Thermal strain
6	1	1	1	0	Thermal strain
7	2	2	2	0	Thermal strain
8	1	1	0	1	Thermal strain
9	1	1	1	1	Thermal strain
10	5	4	2	2	Thermal strain
11	0	0	0	0	Thermal strain
12	0	0	0	0	Thermal strain
13	1	0	0	0	Thermal strain
14	5	5	3	3	Thermal strain
15	5	0	0	0	Thermal strain

[Table 2]

Sample No.	Iron loss (W/Kg)	Noise characteristics (dBA)
1	1.222	43.31
2	1.245	42.57
3	1.266	41.88
4	1.218	42.89
5	1.162	41.42
6	1.227	42.85
7	1.154	40.48
8	1.189	42.64
9	1.189	41.41
10	1.185	40.27
11	1.175	44.99
12	1.284	43.84
13	1.332	43.22
14	1.150	39.84
15	1.324	42.12

The underlines indicate preferable values outside the range.
The samples of No. 1 to 3 and 14 shown in Table 2 were samples in which the standard deviation of the interval between the magnetic domain control points, which are the intersection points of the imaginary lines and the magnetic domain control treatment lines, was 1.25 mm or more, and the average value |β_L| of the absolute values of the β angles was 1.5° or more.
On the other hand, since the sample No. 11 is subjected to the magnetic domain control treatment over the entire width, the iron loss is good, but the noise characteristics are deteriorated. The sample No. 12 was subjected to magnetic domain control treatment in a broken line shape, and thus the noise was improved as compared with the sample No. 11, but both the iron loss characteristics and the noise characteristics were unacceptable. The sample No. 13 was subjected to random magnetic domain control treatment in a broken line shape, and thus the noise was further improved as compared with the sample No. 12, but the iron loss characteristics were unacceptable.
For No. 15, since the magnetic domain control treatment was performed only in the central region in the rolling direction of each grain, the noise was in a preferable range, but the iron loss characteristics were unacceptable.
The samples No. 4 and 5 are samples satisfying the condition satisfied by the samples No. 1 to 3 described above, in which the standard deviation of the interval between the magnetic domain control points is 1.25 mm or more, and the average value |β_L| of the absolute values of the β angles is 1.5° or more in each of two or more imaginary lines among a plurality of imaginary lines having intervals of 5 mm. The iron losses of the samples No. 4 and 5 were superior to the iron losses of the samples No. 1 and 2, and excellent noise characteristics equivalent to those of the samples No. 1 and 2 could be obtained.
The sample No. 6 is a sample satisfying the conditions satisfied by the samples No. 1 to 3 described above and having a D_L/D_S of 2 or more. The iron loss of the sample No. 6 corresponds to excellent characteristics among the iron losses of the samples No. 1 to 3, and the noise of the sample No. 6 corresponds to excellent characteristics among the noise of the samples No. 1 to 3. The sample No. 6 can be evaluated as having more excellent characteristics in both iron loss and noise.
The sample No. 7 is a sample that satisfies the conditions satisfied by No. 4 and 5 and has a D_L/D_S of 2 or more. The iron loss and noise of the sample No. 7 exhibited further excellent characteristics as compared with the iron loss and noise of the samples No. 1 to 3.
The sample No. 8 is a sample that satisfies the conditions satisfied by No. 1 to 3 and satisfies the relationship of 0.5° ≤ |β_L|-|β_S|. The iron loss and noise of the sample No. 8 exhibited further excellent characteristics as compared with the iron loss and noise of the samples No. 1 to 3.
The sample No. 9 is a sample satisfying both conditions satisfied by the samples No. 6 and No. 8.
The iron loss and noise of the sample No. 9 exhibited further excellent characteristics as compared with the iron loss and noise of the samples No. 1 to 3.
The sample No. 10 is a sample satisfying all the conditions satisfied by the samples No. 7 and No. 8. The iron loss and noise of the sample No. 10 exhibited further excellent characteristics as compared with the iron loss and noise of the samples No. 7 to 9.

(Example 2)

A grain-oriented electrical steel sheet of the same lot having a sheet thickness of 0.20 mm was used as the original sheet. The original sheet was subjected to a magnetic domain control treatment under various conditions shown in Table 3.
For the steel sheets of No. 16 to 23 obtained by each treatment, the number of VL (imaginary lines) having the standard deviation of 1.25 mm or more is shown in column A of Table 1, and further, the number of VL satisfying the relationship of |β_L| ≥ 1.5° in VL shown in column A is shown in column B of Table 1. In the column C of Table 1, further, the number of VLs satisfying the relationship of 4 ≤ D_L/D_S in the VL shown in the column B is shown, and in the column D of Table 1, further, the number of VLs satisfying the relationship of 0.5° <|β_L|-|β_S| in the VL shown in the column C is shown. The measurement of the standard deviation and |β_L| and |β_S| was performed according to the above-described procedure. 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 described later, and subjected to measurement. In this rectangular sample, a rectangular evaluation region in which the length of the side parallel to the rolling direction RD was 50 mm and the length of the side parallel to the transverse direction TD was 100 mm was set, and an imaginary lines VL parallel to the transverse direction TD and having a length of 100 mm were set at intervals of 5 mm inside the evaluation region. The number of the imaginary lines VL was nine.
The samples No. 16 to 22 shown in Table 3 are a sample in which a straight linear magnetic domain control treatment line is formed in a region having a wide spacing of magnetic domain walls. The sample No. 23 is a sample in which a linear magnetic domain control treatment line including a curve is formed in a wide spacing of magnetic domain walls region.
The sample described as the thermal strain in Table 3 is irradiated with a laser beam having an average irradiation energy density of 1.5 mJ/mm² at intervals of 4 mm, and subjected to magnetic domain control treatment.
In the sample described as a groove shown in Table 3, a groove (depth: 15 µm, width: 20 µm) is formed to perform magnetic domain control.
The mixture shown in Table 3 means a magnetic domain control treatment condition in which the above-described thermal strain and the above-described grooves are subjected to magnetic domain control such that the total length is 1 : 1.

The noise and iron loss of the grain-oriented electrical steel sheets subjected to the magnetic domain control treatment were measured in the same manner as in Example 1, and the measurement results are described in Table 4.

[Table 3]

Sample No.	A	B	C	D	E
Sample No.	Number of VL with standard deviation of 1.25 mm or more	Number of VL satisfying \|β_L\| ≥ 1.5° in VL of column A	Number of VL further satisfying 4 ≤ D_L/D_S in VL of column B	Number of VL further satisfying 0.5° ≤ \|β_L\|-\|β_S\| in VL of column C	Type of magnetic domain control treatment line
16	1	1	1	0	Thermal strain
17	1	1	1	0	Mixed
18	1	1	1	0	Groove
19	1	1	1	1	Thermal strain
20	2	2	2	0	Thermal strain
21	3	3	3	1	Thermal strain
22	3	3	3	2	Thermal strain
23	3	3	3	2	Thermal strain

[Table 4]

Sample No.	Iron loss (W/Kg)	Noise characteristics (dBA)
16	1.123	39.51
17	1.128	39.44
18	1.130	39.22
19	1.122	39.13
20	1.121	38.86
21	1.120	38.74
22	1.120	38.55
23	1.114	38.37

As can be seen from Tables 3 and 4, in these examples in which the D_L/D_S was 4 or more in at least one of the imaginary lines, more excellent characteristics were obtained in iron loss and noise as compared with the example of Example 1.

(Example 3)

A grain-oriented electrical steel sheet of the same lot having a sheet thickness of 0.20 mm was used as the original sheet. The original sheet was subjected to a magnetic domain control treatment under various conditions shown in Table 5.
For the steel sheets of No. 24 to 61 obtained by each treatment, the number of VL (imaginary lines) having a standard deviation of 1.25 mm or more is shown in column A of Table 1, and further, the number of VL satisfying the relationship of |β_L| ≥ 1.5° in VL shown in column A is shown in column B of Table 1. In the column C of Table 1, further, the number of VL satisfying the relationship of 2 ≤ D_L/D_S in the VL shown in the column B is shown, and in the column D of Table 1, further, the number of VL satisfying 4 ≤ D_L/D_S in the VL shown in the column B is shown, and in the column E, further, the number of VL satisfying the relationship of 0.5° < |β_L|-|β_S| in the VL shown in the column C is shown, and in the column F, further, the number of VL satisfying the relationship of 0.5° < |β_L|-|β_S| in the VL shown in the column D is shown. The measurement of the standard deviation and |β_L| and |β_S| was performed according to the above-described procedure. 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 described later, and subjected to measurement. In this rectangular sample, a rectangular evaluation region in which the length of the side parallel to the rolling direction RD was 50 mm and the length of the side parallel to the transverse direction TD was 100 mm was set, and an imaginary lines VL parallel to the transverse direction TD and having a length of 100 mm were set at intervals of 5 mm inside the evaluation region. The number of the imaginary lines VL was nine.
The samples No. 24 to 61 shown in Table 5 are a sample in which a straight linear magnetic domain control treatment line is formed in a region having a wide spacing of magnetic domain walls.
The sample described as the thermal strain in Table 5 is irradiated linearly with a laser beam having an average irradiation energy density of 0.5 mJ/mm² to 4.0 mJ/mm² at intervals of 4 mm, and subjected to magnetic domain control treatment.
In the sample described as a groove shown in Table 5, a groove (depth: 15 µm to 41 µm, width: 20 µm) is formed to perform magnetic domain control.

The noise and iron loss of the grain-oriented electrical steel sheets subjected to the magnetic domain control treatment were measured in the same manner as in Example 1, and the measurement results are described in Table 6.

[Table 5]

Sample No.	A	B	C	D	E	F	G
Sample No.	Number of VL with standard deviation of 1.25 mm or more	Number of VL satisfying \|β_L\| ≥ 1.5° in VL of column A	Number of VL further satisfying 2 ≤ D_L/D_S in VL of column B	Number of VL further satisfying 4 ≤ D_L/D_S in VL of column B	Number of VL further satisfying 0.5° ≤ \|β_L\|-\|β_S\| in VL of column C	Number of VL further satisfying 0.5° ≤ \|β_L\|-\|β_S\| in VL of column D	Type of magnetic domain control treatment line
24	2	2	0	0	0	0	Thermal strain
25	3	3	1	0	0	0	Thermal strain
26	3	3	1	0	0	0	Thermal strain
27	4	3	1	1	0	0	Thermal strain
28	4	3	1	1	1	1	Thermal strain
29	3	2	2	2	0	0	Thermal strain
30	3	3	3	3	2	1	Thermal strain
31	2	2	1	0	0	0	Thermal strain
32	2	2	2	0	1	0	Thermal strain
33	5	4	4	2	0	0	Thermal strain
34	4	4	4	2	2	2	Thermal strain
35	3	2	2	2	0	0	Thermal strain
36	3	3	3	2	2	1	Thermal strain
37	5	3	2	1	0	0	Thermal strain
38	4	3	1	1	1	1	Thermal strain
39	5	5	4	3	0	0	Thermal strain
40	4	2	2	1	1	1	Thermal strain
41	6	4	3	3	0	0	Thermal strain
42	6	4	3	3	2	2	Thermal strain
43	2	2	0	0	0	0	Groove
44	3	2	2	0	0	0	Groove
45	3	3	2	0	1	0	Groove
46	4	2	1	1	0	0	Groove
47	5	3	2	1	1	1	Groove
48	3	3	2	2	1	1	Groove
49	4	3	3	2	2	2	Groove
50	2	2	1	0	0	0	Groove
51	2	2	2	0	1	0	Groove
52	3	2	2	2	0	0	Groove
53	4	3	3	3	2	2	Groove
54	3	3	2	2	0	0	Groove
55	2	2	2	2	2	1	Groove
56	4	3	2	1	0	0	Groove
57	3	3	2	1	1	1	Groove
58	5	4	4	3	0	0	Groove
59	4	3	2	1	1	1	Groove
60	5	3	3	3	0	0	Groove
61	5	4	3	3	2	2	Groove

[Table 6]

Sample No.	Whether magnetic domain control strength is uniform	σ(TS_m)²	TS_{m(β < 2)}	TS_{m(β ≥ 2)}	σ(D_m)²	D_{m(β < 2)}	D_{m(β ≥ 2)}	Iron loss (W/Kg)	Noise characteristics (dBA)
24	Non-uniform	4.1	175	182	-	-	-	1.153	38.02
25	Non-uniform	4.4	168	183	-	-	-	1.152	37.54
26	Non-uniform	4.2	204	194	-	-	-	1.152	36.83
27	Non-uniform	4.3	174	193	-	-	-	1.131	36.36
28	Non-uniform	4.6	162	190	-	-	-	1.129	36.22
29	Non-uniform	4.5	165	197	-	-	-	1.127	36.02
30	Non-uniform	5.0	162	190	-	-	-	1.125	35.83
31	Non-uniform	5.2	161	192	-	-	-	1.142	37.82
32	Non-uniform	5.2	165	198	-	-	-	1.141	37.12
33	Non-uniform	5.4	160	193	-	-	-	1.117	36.40
34	Non-uniform	5.5	158	196	-	-	-	1.115	36.12
35	Non-uniform	5.4	195	162	-	-	-	1.114	35.46
36	Non-uniform	5.3	212	181	-	-	-	1.110	35.12
37	Non-uniform	5.5	226	187	-	-	-	1.118	35.46
38	Non-uniform	5.9	238	192	-	-	-	1.116	35.32
39	Non-uniform	4.2	213	196	-	-	-	1.132	35.52
40	Non-uniform	4.3	207	189	-	-	-	1.128	35.12
41	Non-uniform	4.7	201	178	-	-	-	1.126	35.42
42	Non-uniform	4.7	225	191	-	-	-	1.123	35.00
43	Non-uniform	-	-	-	0.9	25	26	1.156	37.86
44	Non-uniform	-	-	-	1.5	27	29	1.154	37.34
45	Non-uniform	-	-	-	1.5	25	23	1.154	36.62
46	Non-uniform	-	-	-	1.8	35	38	1.134	36.18
47	Non-uniform	-	-	-	1.6	34	36	1.130	36.02
48	Non-uniform	-	-	-	1.8	32	35	1.129	35.84
49	Non-uniform	-	-	-	1.7	35	38	1.128	35.65
50	Non-uniform	-	-	-	3.2	27	31	1.145	37.61
51	Non-uniform	-	-	-	3.5	28	32	1.144	36.92
52	Non-uniform	-	-	-	3.8	35	39	1.118	36.18
53	Non-uniform	-	-	-	4.0	35	40	1.117	35.95
54	Non-uniform	-	-	-	3.5	31	29	1.116	35.26
55	Non-uniform	-	-	-	3.8	29	27	1.113	34.93
56	Non-uniform	-	-	-	4.0	38	34	1.120	35.27
57	Non-uniform	-	-	-	3.1	37	36	1.118	35.12
58	Non-uniform	-	-	-	2.8	30	25	1.134	35.34
59	Non-uniform	-	-	-	2.7	31	25	1.130	34.95
60	Non-uniform	-	-	-	2.8	38	32	1.128	35.24
61	Non-uniform	-	-	-	2.9	41	35	1.125	34.80

As can be seen from Tables 5 and 6, in these examples satisfying σ(TS_m)² > 5.0, TS_{m(β < 2)} > TS_{m(β ≥ 2)}, σ(D_m)² > 3.0, and/or D_{m(β < 2)} > D_{m(β ≥ 2)}, more excellent characteristics were obtained in iron loss and noise as compared with the example of Example 1.

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. Therefore, the industrial applicability is high.

REFERENCE SIGNS LIST

RD Rolling direction
TD Transverse direction
ND Rolling surface normal direction
VL Imaginary line
VP Magnetic domain control point
D_L Absolute maximum value of interval between magnetic domain control points
D_S Absolute minimum value of interval between magnetic domain control points
P_βL Midpoint between two magnetic domain control points where interval is absolute maximum value
P_βS Midpoint between two magnetic domain control points where interval is absolute minimum value
X Region where magnetic domain control treatment line is not provided
1 Grain-oriented electrical steel sheet
2 Original sheet
11 Magnetic domain control treatment line
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 Condenser lens
509 Motor
511 Sensor
513 Control unit
515 Sheet passing device

Claims

A grain-oriented electrical steel sheet comprising a plurality of magnetic domain control treatment lines on a surface thereof, wherein
in a case where a rectangular evaluation region in which a length of a side parallel to a rolling direction of the grain-oriented electrical steel sheet is 50 mm and a length of a side parallel to a transverse direction of the grain-oriented electrical steel sheet is 100 mm is set in the grain-oriented electrical steel sheet, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set inside the evaluation region at intervals of 5 mm in a direction parallel to the rolling direction,

in at least one of the imaginary lines, a standard deviation of an interval between magnetic domain control points that are intersection points of the imaginary line and the magnetic domain control treatment line is 1.25 mm or more, and an average value |β_L| of absolute values of β angles measured between two magnetic domain control points at which the interval becomes an absolute maximum value D_L, is 1.5° or more.
The grain-oriented electrical steel sheet according to claim 1, wherein
in each of the two or more imaginary lines, a standard deviation of the interval between the magnetic domain control points is 1.25 mm or more, and an average value |β_L| of the absolute values of the β angles measured between the two magnetic domain control points at which the interval becomes the absolute maximum value D_L, is 1.5° or more.
The grain-oriented electrical steel sheet according to claim 1 or 2, wherein
a ratio D_L/D_S between the absolute maximum value D_L of the interval of the magnetic domain control points and an absolute minimum value D_S of the interval of the magnetic domain control points is 2 or more.
The grain-oriented electrical steel sheet according to claim 3, wherein
the D_L/D_S is 4 or more.
The grain-oriented electrical steel sheet according to claim 3 or 4, wherein
the |β_L| and an average value |β_S| of absolute values of β angles measured between the two magnetic domain control points where the interval is the absolute minimum value D_S, satisfy the following formula: $0.5 ° \leq |β_{L}| - |β_{S}| .$
The grain-oriented electrical steel sheet according to any one of claims 1 to 5, wherein
the magnetic domain control treatment line is a thermal strain.
The grain-oriented electrical steel sheet according to claim 6, wherein
the absolute maximum value of the tensile stress introduced into the thermal strain in the magnetic domain control treatment line is non-uniform at each measurement point of the tensile stress.
The grain-oriented electrical steel sheet according to claim 7, wherein
in a case where a rectangular evaluation region in which a length of a side parallel to the rolling direction is 50 mm and a length of a side parallel to the transverse direction of the grain-oriented electrical steel sheet is 100 mm is set on the surface, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set at intervals of 5 mm in a direction parallel to the rolling direction inside the evaluation region,

when each of a plurality of intersection points of the imaginary lines and the plurality of magnetic domain control treatment lines is defined as a magnetic domain control point, and the absolute maximum value of the tensile stress in MPa measured at each of the magnetic domain control points is defined as TS_m, and a variance of the TS_m is defined as σ(TS_m)², $σ {({TS}_{m})}^{2} > 5.0$ is satisfied.
The grain-oriented electrical steel sheet according to claim 7 or 8, wherein
when TS_{m(β < 2)} is an arithmetical mean value of absolute maximum values of the tensile stress in MPa introduced into the thermal strain, measured at each of the magnetic domain control points having a β angle of less than 2° among the magnetic domain control points, and TS_{m(β ≥ 2)} is an arithmetical mean value of absolute maximum values of the tensile stress in MPa introduced into the thermal strain, measured at each of the magnetic domain control points having a β angle of 2° or more among the magnetic domain control points, ${TS}_{m (β < 2)} > {TS}_{m (β \geq 2)}$ is satisfied.
The grain-oriented electrical steel sheet according to any one of claims 1 to 5, wherein
the magnetic domain control treatment line is a groove.
The grain-oriented electrical steel sheet according to claim 10, wherein
an absolute maximum value of a depth of the groove in the magnetic domain control treatment line is non-uniform at each measurement point of the depth of the groove.
The grain-oriented electrical steel sheet according to claim 11, wherein
in a case where a rectangular evaluation region in which a length of a side parallel to the rolling direction is 50 mm and a length of a side parallel to the transverse direction of the grain-oriented electrical steel sheet is 100 mm is set on the surface, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set at intervals of 5 mm in a direction parallel to the rolling direction inside the evaluation region,

when each of a plurality of intersection points of the imaginary lines and the plurality of magnetic domain control treatment lines is defined as a magnetic domain control point, the absolute maximum value of the depth of the groove in µm measured at each of the magnetic domain control points is defined as D_m, and a variance of the D_m is defined as σ(D_m)², $σ {(D_{m})}^{2} > 3.0$ is satisfied.
The grain-oriented electrical steel sheet according to claim 11 or 12, wherein
when D_{m(β < 2)} is an arithmetical mean value of absolute maximum values of depths of the grooves in µm,the absolute maximum values being measured at each of the magnetic domain control points having a β angle of less than 2° among the magnetic domain control points, and D_{m(β ≥2)} is an arithmetical mean value of absolute maximum values of depths of the grooves in µm, the absolute maximum values being measured at each of the magnetic domain control points having a β angle of 2° or more among the magnetic domain control points, $D_{m (β < 2)} > D_{m (β \geq 2)}$ is satisfied.
A method for manufacturing a grain-oriented electrical steel sheet, the method 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 a 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 a spacing of magnetic domain walls;

wherein

in a case where a rectangular evaluation region in which a length of a side parallel to a rolling direction of the grain-oriented electrical steel sheet is 50 mm and a length of a side parallel to a transverse direction of the grain-oriented electrical steel sheet is 100 mm is set in the grain-oriented electrical steel sheet, and further, imaginary lines parallel to the transverse direction and having a length of 100 mm are set inside the evaluation region at intervals of 5 mm in a direction parallel to the rolling direction,

in at least one of the imaginary lines, a standard deviation of an interval along the imaginary line at an intersection point of the imaginary line and a magnetic domain control treatment line formed by the magnetic domain control treatment is 1.25 mm or more.
The method for manufacturing a grain-oriented electrical steel sheet according to claim 14, wherein
in the step of determining the magnetic domain control treatment region, a region in which 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 14 or 15, wherein
in the step of acquiring the magnetic domain image, a distribution of the spacings of magnetic domain walls is derived from the magnetic domain image using two-dimensional Fourier transform.
The method for manufacturing a grain-oriented electrical steel sheet according to any one of claims 14 to 16, wherein
in the step of applying the magnetic domain control treatment, the magnetic domain control treatment is applied by laser or electron beam irradiation.