EP4786623A1

EP4786623A1 - Grain-oriented electrical steel sheet

Info

Publication number: EP4786623A1
Application number: EP24872566.5A
Authority: EP
Inventors: Yusuke Kawamura
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: WO2025070785A1; CN121511319A; JPWO2025070785A1; KR20260013989A

Abstract

The grain-oriented electrical steel sheet includes a magnetic domain refinement treatment line on a surface, wherein a sheet thickness t (mm) and an iron loss W17/50 (W/kg) satisfy a relationship of W17/50 < 1.350t + 0.450; and when a peak-to-peak value of a magnetostriction under a magnetic flux density of 1.7 T is expressed as λ1pp, and a peak-to-peak value of a magnetostriction under a magnetic flux density of 1.9 T is expressed as λ2pp, λ2pp/λ1pp < 2.2 is satisfied. Preferably, the magnetic domain refinement treatment line is a thermal strain or a groove.

Description

TECHNICAL FIELD

The present disclosure relates to a grain-oriented electrical steel sheet.
The present application claims priority based on Japanese Patent Application No. 2023-165201 filed in Japan on September 27, 2023 , the contents of which are incorporated herein by reference.

BACKGROUND ART

A grain-oriented electrical steel sheet is a steel sheet containing 7% by mass or less of Si and having a secondary recrystallization texture in which secondary recrystallized grains are accumulated in the {110}<001> orientation (Goss orientation). The grain-oriented electrical steel sheet is mainly used as a core of an electric power transformer, and there is an increasing need for reduction of noise in addition to reduction of energy loss (iron loss).
For reduction in iron loss, there has been known a magnetic domain refinement technique for reducing a magnetic domain width by irradiating a surface of a grain-oriented electrical steel sheet with a laser or an electron beam in a direction intersecting a rolling direction. 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 and 2.).

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

SUMMARY OF INVENTION

Technical Problem

However, when the grain-oriented electrical steel sheet is subjected to the magnetic domain refinement treatment, a flux closure domain is inevitably generated. Therefore, the grain-oriented electrical steel sheet subjected to magnetic domain refinement usually has a remarkably large magnetostriction waveform under a high magnetic field (around 1.9 T) due to the flux closure domain. The magnetostriction under a high magnetic field is generated at a location where magnetic flux concentrates, such as a corner portion of a transformer, and the noise from the transformer generated at the portion is very large. As described above, since there is a trade-off relationship between the reduction in iron loss and the reduction in noise of the grain-oriented electrical steel sheet, there is a demand for an optimal magnetic domain refinement technique that can achieve both of them.
In view of the above-described problems, 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.

Solution to Problem

(1) The grain-oriented electrical steel sheet according to one embodiment of the present disclosure includes a magnetic domain refinement treatment line on a surface, wherein a sheet thickness t (mm) and an iron loss W17/50 (W/kg) satisfy a relationship of W17/50 < 1.350t + 0.450, a peak-to-peak value of a magnetostriction under a magnetic flux density of 1.7 T is expressed as λ1pp, and a peak-to-peak value of a magnetostriction under a magnetic flux density of 1.9 T is expressed as λ2pp, and λ2pp/λ1pp < 2.2 is satisfied.
(2) Preferably, in the grain-oriented electrical steel sheet according to (1), the magnetic domain refinement treatment line is a thermal strain.
(3) Preferably, in the grain-oriented electrical steel sheet according to (1), the magnetic domain refinement treatment line is a groove.
(4) Preferably, in the grain-oriented electrical steel sheet according to (2), in the magnetic domain refinement treatment line, maximum values of tensile strength introduced into the thermal strain are non-uniform at each measurement point of the tensile strength.
(5) Preferably, the grain-oriented electrical steel sheet according to (4) satisfies σ²(TS_m) > 5.0, wherein TS_m are maximum values of the tensile strength in a unit of MPa introduced into the thermal strain, the maximum values being measured at each of a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line; and σ²(TS_m) is a variance of TS_m.
(6) Preferably, the grain-oriented electrical steel sheet according to (4) or (5) satisfies TS_m(β<2) > TS_m(β≥2), wherein TS_m(β<2) is an arithmetical mean value of maximum values of the tensile strength in a unit of MPa introduced into the thermal strain, the maximum values being measured at each of magnetic domain refinement points having a β angle of less than 2° among a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line; and TS_m(β≥2) is an arithmetical mean value of the maximum values of the tensile strength in a unit of MPa introduced into the thermal strain, the maximum values being measured at each of the magnetic domain refinement points having the β angle of 2° or more.
(7) Preferably, in the grain-oriented electrical steel sheet according to (3), in the magnetic domain refinement treatment line, maximum values of a depth of the groove are non-uniform at each measurement point of the groove.
(8) Preferably, the grain-oriented electrical steel sheet according to (7) satisfies σ²(D_m) > 3.0, wherein D_m are maximum values of a depth of the groove in a unit of µm at each of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line; and σ²(D_m) is a variance of D_m.
(9) Preferably, the grain-oriented electrical steel sheet according to (7) or (8) satisfies D_m(β<2) > D_m(β≥2), wherein D_m(β<2) is an arithmetical mean value of maximum values of a depth of the groove in a unit of µm, the maximum values being measured at each of magnetic domain refinement points having a β angle of less than 2° among a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line; and D_m(β≥2) is an arithmetical mean value of maximum values of a depth of the groove in a unit of µm, the maximum values being measured at each of the magnetic domain refinement points having the β angle of 2° or more.

Advantageous Effects of Invention

According to the present disclosure, it is possible to achieve both iron loss reduction and noise reduction by providing a grain-oriented electrical steel sheet having a magnetic domain refinement treatment line on the surface thereof and satisfying a predetermined formula in the relationship between sheet thickness and iron loss and the ratio of peak-to-peak value of magnetostriction.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1A] A graph showing an example of a spatial distribution of a spacing of magnetic domain walls of a grain-oriented electrical steel sheet before a magnetic domain refinement treatment.
[FIG. 1B] A graph showing an example of a spatial distribution of a spacing of magnetic domain walls of a grain-oriented electrical steel sheet after a magnetic domain refinement treatment.
[FIG. 1C] A graph showing regions where the spacing of magnetic domain walls is refined by 50 µm or more before and after the magnetic domain refinement shown in FIGS. 1A and 1B.
[FIG. 2] A graph showing a relationship between the spacing of magnetic domain walls before laser irradiation and the spacing of magnetic domain walls after laser irradiation.
[FIG. 3] A block diagram illustrating the hardware constitution of an image acquisition device according to the present embodiment.
[FIG. 4] A block diagram illustrating the hardware constitution of an analysis device according to the present embodiment.
[FIG. 5] A schematic view illustrating the constitution of a laser irradiation device according to the present embodiment.
[FIG. 6] A flowchart illustrating a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment.
[FIG. 7] A schematic view illustrating a magnetic domain refinement treatment line that represents a portion where magnetic domain refinement treatment is selectively performed on a grain-oriented electrical steel sheet.
[FIG. 8] A graph showing a relationship between sheet thickness and iron loss in a grain-oriented electrical steel sheet that has been selectively subjected to magnetic domain refinement treatment.
[FIG. 9A] A graph showing magnetostriction waveforms obtained when a grain-oriented electrical steel sheet selectively subjected to laser irradiation and a grain-oriented electrical steel sheet uniformly subjected to laser irradiation on the entire surface thereof are excited with alternating-current up to ±1.7 T.
[FIG. 9B] A graph showing magnetostriction waveforms obtained when a grain-oriented electrical steel sheet selectively subjected to laser irradiation and a grain-oriented electrical steel sheet uniformly subjected to laser irradiation on the entire surface thereof are excited with alternating-current up to ±1.9 T.
[FIG. 10] A graph showing data of the ratio of the peak-to-peak value λ2pp of magnetostriction under a magnetic flux density of 1.9 T with respect to the peak-to-peak value λ1pp of magnetostriction under a magnetic flux density of 1.7 T (λ2pp/λ1pp) for a plurality of grain-oriented electrical steel sheets selectively subjected to laser irradiation and a plurality of grain-oriented electrical steel sheets uniformly subjected to laser irradiation on the entire surface thereof.
[FIG. 11] A graph schematically showing a relationship between the size of spacing of magnetic domain walls and the magnetic domain control saturation strength.
[FIG. 12] A graph schematically showing a relationship between the magnitude of β angle and the magnetic domain control saturation strength.
[FIG. 13] A schematic cross-sectional view of a grain-oriented electrical steel sheet in which the magnetic domain refinement treatment line is a thermal strain.
[FIG. 14] A schematic cross-sectional view of a grain-oriented electrical steel sheet in which the magnetic domain refinement treatment line is a groove.
[FIG. 15] A schematic plan view for explaining a method for measuring magnetic domain control strength at intersections between magnetic domain refinement treatment lines and imaginary lines when the magnetic domain refinement treatment line is a thermal strain.
[FIG. 16] A schematic plan view for explaining a method for measuring magnetic domain control strength at intersections between magnetic domain refinement treatment lines and imaginary lines when the magnetic domain refinement treatment line is a groove.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure are described with reference to the drawings.
First, the magnetic domain structures of the grain-oriented electrical steel sheets before and after the magnetic domain refinement treatment are compared. FIG. 1A illustrates the spatial distribution of spacing of the 180° magnetic domain walls of a grain-oriented electrical steel sheet (Hereinafter, it is simply referred to as a "spacing of magnetic domain walls".) before a magnetic domain refinement treatment. FIG. 1B illustrates the spatial distribution of the spacing of magnetic domain walls after the magnetic domain refinement treatment is performed on the surface of the grain-oriented electrical steel sheet in FIG. 1A. The magnetic domain refinement treatment here is performed by performing continuous wave laser irradiation along a magnetic domain control treatment line substantially perpendicular to the rolling direction (RD).
The "180° magnetic domain" refers to 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. The "spacing" of the 180° magnetic domain walls refers to a distance between adjacent magnetic walls (magnetic wall interval).
The spatial distribution of the spacing of magnetic domain walls shown in FIGS. 1A and 1B is derived from the magnetic domain image of the grain-oriented electrical steel sheet using a two-dimensional Fourier transform (see, Japanese Unexamined Patent Application, First Publication No. 2021-169655 and No. 2021-169979 ).
FIG. 1C illustrates regions where the spacing of magnetic domain walls is refined by 50 µm or more before and after the magnetic domain refinement treatment shown in FIGS. 1A and 1B, and visualizes the value of an original spacing of magnetic domain walls at which refinement occurs.
From FIG. 1C, it can be seen that the region where the effect of the magnetic domain refinement was 50 µm or more is a region where the original spacing of magnetic domain walls is wide, and in particular, the effect of the magnetic domain refinement remarkably appears in a region where the original spacing of magnetic domain walls is 500 µm or more. That is, the effect of magnetic domain refinement varies depending on the original spacing of magnetic domain walls.
FIG. 2 shows a relationship between the spacing of magnetic domain walls before laser irradiation and the spacing of magnetic domain walls after laser irradiation at the same position. As the irradiation conditions, the average irradiation energy density Ua (mJ/mm²) and the irradiation pitch PL (mm) were set to Ua = 1.5 mJ/mm² and PL = 4 mm, respectively.
As can be seen from FIG. 2, even if laser irradiation is applied to a region having a spacing of magnetic domain walls of about 500 µm or less, the effect of magnetic domain refinement is small.
From the above, it is considered that the effect of reducing the iron loss is obtained by magnetic domain refinement of a region having a large original spacing of magnetic domain walls, and even if the magnetic domain refinement treatment is performed on a region having a small original spacing of magnetic domain walls, the effect of reducing the iron loss is small, leading to an increase in hysteresis loss and deterioration of noise characteristics.
Therefore, in the present embodiment, magnetic domain control is performed so as to perform the magnetic domain refinement treatment only on the region having a relatively large original spacing of magnetic domain walls (for example, a region having an original spacing of magnetic domain walls of 500 µm or more) of the grain-oriented electrical steel sheet.
Preferably, in the present embodiment, 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 a thermal strain when the magnetic domain control means is a thermal strain, and means the depth of a groove when the magnetic domain control means is a groove.
The higher the strength of magnetic domain control, the higher the effect of magnetic domain refinement. On the other hand, the higher the strength of magnetic domain control, 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 substantially saturated. When 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, when the magnetic domain control strength is more than the magnetic domain control saturation strength, the effect of iron loss reduction is hardly enhanced even if the magnetic domain control strength is increased. On the other hand, even when 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 a range not exceeding the magnetic domain control saturation strength.
In addition, the present inventors have found that the magnetic domain control saturation strength strongly correlates 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 large. In the grain-oriented electrical steel sheet before the magnetic domain control treatment, there is a correlation 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 correlation 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. Specifically, it is preferable that the magnetic domain refinement treatment is performed with a large magnetic domain control strength at a point 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 point 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 smaller than a predetermined value.
FIG. 11 is a graph schematically showing a method for determining the magnetic domain control strength based on the spacing of magnetic domain walls. In FIG. 11, the vertical axis represents the magnetic domain control strength, and the horizontal axis represents the size of the spacing of magnetic domain walls. In FIG. 11, the solid line graph 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 exceeds 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 exceeds about 1200 µm, the magnetic domain control saturation strength is substantially constant.
FIG. 12 is a graph schematically showing a method for determining the magnetic domain control strength based on the β angle. In FIG. 12, the vertical axis represents the magnetic domain control strength, and the horizontal axis represents the magnitude of the β angle. In FIG. 12, the solid line graph indicates the magnetic domain control saturation strength. In the region where the β angle is large, the effect of magnetic domain control 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 effect of magnetic domain control is obtained. For example, it is estimated that the effect of magnetic domain control can be obtained when the β angle is 2.0° 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 point where the magnetic domain control is performed and the magnetic domain control strength is on the solid line graph in FIG. 11. Alternatively, it is most preferable that the relationship between the β angle of the point where the magnetic domain control is performed and the magnetic domain control strength is on the solid line graph in FIG. 12. 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 effect of magnetic domain control is exhibited. When 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. 11 and 12, 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. 11 and 12.
As a result, a grain-oriented electrical steel sheet having non-uniform magnetic domain control strength is obtained. In such a grain-oriented electrical steel sheet, the magnetic domain control strength varies depending on the β angle. In such a grain-oriented electrical steel sheet, 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.
The β angle in the grain-oriented electrical steel sheet is measured by the side reflection Laue method. The side reflection Laue method is widely known as a method for measuring a crystal orientation.
Next, the constitution of a device that realizes magnetic domain control of the grain-oriented electrical steel sheet according to the present embodiment is described with reference to FIGS. 3 to 5.
FIG. 3 illustrates the hardware constitution of an image acquisition device 30 that acquires a magnetic domain image of a grain-oriented electrical steel sheet. The image acquisition device 30 includes a light source unit 31, a magneto-optical (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 the magnetic structure of a magnetic body, and has an observed section on which a magnetic body sample to be measured is placed. The light emitted from the light source unit 31 passes through the inside of the MO sensor 33 and is reflected by a reflection layer, and 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 grain-oriented electrical steel sheet is placed as the magnetic body sample on the observed section of the MO sensor 33, a leakage magnetic field corresponding to the direction of spontaneous magnetization of the grain-oriented electrical steel sheet is generated inside the MO sensor 33, and the polarization plane of the reflected light is rotated by the leakage magnetic field.
The image sensor 35 is a Complementary Metal-Oxide-Semiconductor (CMOS) image sensor, forms an image of reflected light from the MO sensor 33 on a light receiving surface, performs photoelectric conversion, and an analog signal after photoelectric conversion is output to the signal processing unit 37. The spatial 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 grain-oriented electrical steel sheet 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 the amplifier and converted into a digital signal by the AD converter. The DSP performs predetermined digital processing on the digital signal to generate an image signal. The image signal generated by the signal processing unit 37 is output to an analysis device 40 (see FIG. 4) via a cable or by wireless communication.
FIG. 4 illustrates the hardware constitution of the analysis device 40 that analyzes the magnetic domain structure of the grain-oriented electrical steel sheet. The analysis device 40 is a computer device such as a personal computer (PC), and includes a calculation unit 41, a memory 43, a display unit 45, an input unit 47, and a communication I/F 49.
The calculation unit 41 includes a Central Processing Unit (CPU), analyzes a magnetic domain structure from a magnetic domain image of the grain-oriented electrical steel sheet according to a program stored in the memory 43, and determines a point to which the magnetic domain refinement treatment is applied (see FIG. 6 described 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 at the time of executing these programs. The program and data stored in the ROM are loaded into the RAM and executed.
Note that 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 program or data may be stored in a computer-readable recording medium detachable from the analysis device 40. Alternatively, the program executed by the calculation unit 41 may be received from an external device 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, displays an image on the basis of an image signal output from the image acquisition device 30, and displays an analysis result of the magnetic domain structure by the calculation unit 41.
The input unit 47 includes an input device such as a mouse or a keyboard. The communication I/F 49 is an interface for transmitting and receiving data to and from an external device via a network such as a Local Area Network (LAN), a Wide Area Network (WAN), or the Internet.
Instead of general-purpose hardware such as a CPU, dedicated hardware specialized for analyzing a magnetic domain structure, such as an application specific integrated circuit (ASIC) or a Field Programmable Gate Array (FPGA), may be adopted as the calculation unit 41.
Note that FIGS. 3 and 4 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.
Known means such as laser irradiation and electron beam irradiation can be adopted as means for performing the magnetic domain refinement treatment on the surface of the grain-oriented electrical steel sheet. Hereinafter, the constitution of a laser irradiation device that performs the magnetic domain refinement treatment by laser irradiation is described.
FIG. 5 illustrates the constitution of a laser irradiation device 500. The laser irradiation device 500 includes a polygon mirror 501, a light source device 503, a collimator 505, a condensing lens 507, a motor 509, a sensor 511, a control unit 513, and a sheet passing device 515.
The sheet passing device 515 passes the grain-oriented electrical steel sheet 50 in the rolling direction (RD).
The polygon mirror 501 has, for example, a regular polygonal prism shape, and a plurality of plane mirrors is provided on a plurality of side surfaces constituting the regular polygonal prism. A laser beam LB enters the plane mirror of the polygon mirror 501 from the light source device 503 via the collimator 505 in one direction (horizontal direction) and is reflected by the plane mirror.
The polygon mirror 501 is rotatable about the rotation axis O1 by driving from the motor 509. By sequentially changing the incident angle of the laser beam LB with respect to the plane mirror according to the rotation angle of the polygon mirror 501, the reflection direction of the laser beam LB is sequentially changed, and scanning can be performed along the magnetic domain control treatment line 52 of the grain-oriented electrical steel sheet 50. The magnetic domain control treatment line 52 forms an angle of 0° to 45° with respect to the transverse direction (TD) on the surface of the grain-oriented electrical steel sheet 50, and is a plurality of parallel straight lines or curve lines arranged at equal intervals in the rolling direction (RD). The interval P between the adjacent magnetic domain control treatment lines 52 represents an irradiation pitch.
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 condensing lens 507 is provided on the optical path of the laser beam LB reflected from the polygon mirror 501, and constitutes a condensing optical system having a predetermined focal length. When the laser beam LB reflected from the polygon mirror 501 is condensed on the surface of the grain-oriented electrical steel sheet 50 via the condensing lens 507, a groove is formed or a thermal strain is introduced along the magnetic domain control treatment line 52 on the surface of the grain-oriented electrical steel sheet 50.
The motor 509 is coupled to the polygon mirror 501, and rotationally drives the polygon mirror 501 under the control of the control unit 513.
The sensor 511 is connected to the drive shaft of the motor 509, detects the rotation angle of the polygon mirror 501 rotated by the motor 509, and outputs a signal indicating the detected rotation angle (hereinafter, referred to as a rotation angle signal) to the control unit 513.
The control unit 513 includes a processor and 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, and 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 on the basis of a magnetic domain refinement signal indicating a point to which magnetic domain refinement treatment is applied in the magnetic domain control treatment line 52 and a rotation angle signal output from the sensor 511. When the laser irradiation device 500 is electrically connected to the analysis device 40, the magnetic domain refinement signal is input from the analysis device 40 to the laser irradiation device 500. The magnetic domain refinement signal may be input to the laser irradiation device 500 by an operator.
Next, a method for manufacturing the grain-oriented electrical steel sheet 50 according to the present embodiment is described with reference to FIG. 6.
First, the image acquisition device 30 is used to acquire a magnetic domain image of the grain-oriented electrical steel sheet 50 (step S62). Next, the calculation unit 41 of the analysis device 40 derives the spatial distribution of the spacing of the 180° magnetic domain walls (spacing of magnetic domain walls) from the magnetic domain image by using the line segment method or two-dimensional Fourier transform. The method for deriving the spatial distribution of the spacing of magnetic domain walls using two-dimensional Fourier transform is disclosed in Japanese Unexamined Patent Application, First Publication No. 2021-169655 and No. 2021-169979 . Thus, the calculation unit 41 determines the point where the spacing of magnetic domain walls is greater than or equal to a predetermined value (for example, 500 µm or more) in the magnetic domain control treatment line 52 of the grain-oriented electrical steel sheet 50, as the point to which the magnetic domain refinement treatment is applied (step S64).
In the step S64, the point to which the magnetic domain refinement treatment is applied may be determined by the operator visually observing the magnetic domain image displayed on the display unit 45 of the analysis device 40, so that a magnetic domain refinement signal indicating the determined point is input to the laser irradiation device 500.
Next, the magnetic domain refinement treatment is applied to the point determined in the step S64 in the magnetic domain control treatment line 52 of the grain-oriented electrical steel sheet 50 (step S66). 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 point to which the magnetic domain refinement treatment is applied in the magnetic domain control treatment line 52, and to turn off the power of the laser beam LB with respect to other points. As a result, a thermal strain or a groove is formed at the point to which the magnetic domain refinement treatment is applied.
The magnetic domain refinement treatment of the step S66 may be performed by irradiation with the laser beam LB from the laser irradiation device 500 as described above, or other means such as electron beam irradiation may be adopted. In FIG. 7, the point to which the magnetic domain refinement treatment is selectively (partially) applied in the magnetic domain control treatment line 52 (broken line) is represented as the magnetic domain refinement treatment line 54 (thick solid line).
Next, the relationship between the sheet thickness and the iron loss of the grain-oriented electrical steel sheet 50 will be described. FIG. 8 shows the results of measurement of iron loss W17/50 (W/kg) for the grain-oriented electrical steel sheets 50 having various sheet thicknesses t (mm) and selectively subjected to the magnetic domain refinement treatment. The iron loss is a value measured using a single sheet tester with a width of 100 mm, which is specified in JIS C 2556:2015. When the sheet thickness is x and the iron loss is y, it can be found that the measured value of the iron loss W17/50 (W/kg) is a value smaller than the approximation expression given by y = 1.350x + 0.450. That is, in the present embodiment, the grain-oriented electrical steel sheet 50 having a magnetic domain refinement treatment line 54 on the surface thereof satisfies W17/50 < 1.350t + 0.450.
Next, the magnetostriction of the grain-oriented electrical steel sheet 50 will be described. FIG. 9A shows the measurement results of the magnetostriction λ with respect to the magnetic flux density B obtained when a grain-oriented electrical steel sheet selectively subjected to laser irradiation (hereinafter, referred to as grain-oriented electrical steel sheet 50a) and a grain-oriented electrical steel sheet uniformly subjected to laser irradiation on the entire surface thereof (hereinafter, referred to as grain-oriented electrical steel sheet 50b) are excited with alternating-current up to ±1.7 T. FIG. 9B shows the measurement results of the magnetostriction λ with respect to the magnetic flux density B obtained when the grain-oriented electrical steel sheet 50a and the grain-oriented electrical steel sheet 50b are excited with alternating-current up to ±1.9 T. The magnetostriction is a value measured using the method specified in IEC 60404-17:2021. Here, "uniformly subjected to laser irradiation on the entire surface thereof" means that the entire magnetic domain control treatment line 52 is uniformly irradiated with a laser beam.
As can be seen from FIG. 9A, the grain-oriented electrical steel sheet 50a, selectively subjected to laser irradiation, has a larger amplitude of the magnetostriction λ and a smaller waveform distortion than the grain-oriented electrical steel sheet 50b, subjected to laser irradiation on the entire surface thereof. As shown in FIG. 9B, when excited with alternating-current up to a high magnetic field (±1.9 T), the grain-oriented electrical steel sheets 50a and 50b shrink once (the magnetostriction λ becomes a negative value) and then rapidly stretch near ±1.9 T (the magnetostriction λ changes to a positive value), but the grain-oriented electrical steel sheet 50a has a smaller elongation amount than the grain-oriented electrical steel sheet 50b. This is because the grain-oriented electrical steel sheet 50a, selectively subjected to laser irradiation, has fewer flux closure domains than the grain-oriented electrical steel sheet 50b, subjected to laser irradiation on the entire surface thereof, and similarly, fewer flux closure domains disappear when the sample is excited by applying a high magnetic field.
Hereinafter, as shown in FIG. 9A, the peak-to-peak value of magnetostriction under alternating-current excitation up to ±1.7 T is expressed as λ1pp, and as shown in FIG. 9B, the peak-to-peak value of magnetostriction under alternating-current excitation up to ±1.9 T is expressed as λ2pp.
FIG. 10 shows the calculation results of the ratio of λ2pp to λ1pp (λ2pp/λ1pp) for 40 samples of the grain-oriented electrical steel sheet 50a, which is selectively subjected to laser irradiation, and 40 samples of the grain-oriented electrical steel sheet 50b, which is subjected to laser irradiation on the entire surface thereof. In FIG. 10, the horizontal axis represents the sample numbers. The sample numbers 1 to 40 correspond to the grain-oriented electrical steel sheet 50a, and the sample numbers 41 to 80 correspond to the grain-oriented electrical steel sheet 50b.
As shown in FIG. 10, the grain-oriented electrical steel sheet 50a has a significantly smaller value of λ2pp/λ1pp than the grain-oriented electrical steel sheet 50b, and it can be confirmed that the peak-to-peak value of magnetostriction is reduced under 1.9 T. Specifically, λ2pp/λ1pp for the grain-oriented electrical steel sheet 50a is less than 2.2, and λ2pp/λ1pp for the grain-oriented electrical steel sheet 50b is 2.2 or more. That is, in the present embodiment, the grain-oriented electrical steel sheet selectively subjected to the magnetic domain refinement treatment satisfies λ2pp/λ1pp < 2.2.
As described above, according to the present embodiment, the grain-oriented electrical steel sheet selectively subjected to the magnetic domain refinement treatment satisfies W17/50 < 1.350t + 0.450 in the relationship between the sheet thickness t (mm) and the iron loss W17/50 (W/kg), and satisfies λpp/λ1pp < 2.2 in the ratio of the peak-to-peak value of magnetostriction. When the grain-oriented electrical steel sheet is provided as described above, adverse effects such as an increase in hysteresis loss and deterioration of noise characteristics can be minimized, and the effect of magnetic domain refinement can be maximized. This makes it possible to achieve both iron loss reduction and noise reduction.
Preferably, the grain-oriented electrical steel sheet according to the present embodiment has non-uniform magnetic domain control strength in the magnetic domain refinement treatment line 54. The magnetic domain control strength means the maximum value of tensile strength introduced into a thermal strain 541 when the magnetic domain control means is a thermal strain 541, and means the maximum value of the depth of a groove 542 when the magnetic domain control means is a groove 542.
The "maximum value of tensile strength introduced into a thermal strain 541" is the maximum value of tensile strength measured in one arbitrary measurement cross section. It should be noted here that the magnitude and direction of tensile strength vary in one measurement cross section, and therefore one "maximum value of tensile strength introduced into a thermal strain 541" is specified for one measurement cross section. As schematically illustrated in FIG. 13, the thermal strain 541 has a certain extent in the cross section. The tensile strength is largest at the point to which laser is directly irradiated, and the tensile strength is small at the points away from the point. That is, the measured value of tensile strength differs for each measurement portion and measurement direction in the cross section. According to the method for measuring tensile strength as described later, the distribution and the maximum value of tensile strength in the cross section can be derived.
When the magnetic domain control strength is uniform, the maximum value of tensile strength introduced into the thermal strain 541 is constant over the entire magnetic domain refinement treatment line 54. On the other hand, when the magnetic domain control strength is non-uniform, in the magnetic domain refinement treatment line, maximum values of tensile strength introduced into the thermal strain are non-uniform at each measurement point of tensile strength. Hereinafter, the maximum value of tensile strength introduced into a thermal strain may be simply referred to as "tensile strength".
The "maximum value of the depth of a groove 542" is the maximum value of the depth of a groove 542 at one arbitrary measurement point measured by a method described later. As schematically illustrated in FIG. 14, the depth of the groove 542 is also non-uniform at one measurement point. In general, the closer to the edge of the groove, the smaller the depth of the groove. Therefore, one "maximum value of the depth of a groove 542" is specified for one measurement cross section.
When the magnetic domain control strength is uniform, the maximum value of the depth of the groove 542 is constant over the entire magnetic domain refinement treatment line 54. On the other hand, when the magnetic domain control strength is non-uniform, in the magnetic domain refinement treatment line, maximum values of the depth of the groove 542 are non-uniform at each measurement point of the depth of the groove. Hereinafter, the maximum value of the depth of a groove 542 may be simply referred to as "the depth of a groove".
As described above, in a point where the β angle is small, the magnetic domain control saturation strength is large. It is preferable that the magnetic domain refinement treatment is performed with a large magnetic domain control strength at a point where the β angle is small; and the magnetic domain refinement treatment is performed with a small magnetic domain control strength at a point where the β angle is large. As described above, in the grain-oriented electrical steel sheet subjected to the magnetic domain refinement treatment in which the optimum magnetic domain control strength is selected according to the magnitude of β angle, the magnetic domain control strength is non-uniform in the magnetic domain refinement treatment line 54. In the magnetic domain refinement treatment line provided at a point with a large β angle, the groove is shallow, or the tensile strength introduced into the thermal strain is small. In the magnetic domain refinement treatment line provided at a point with a small β angle, the groove is deep, or the tensile strength introduced into the thermal strain is large. In such a grain-oriented electrical steel sheet, 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.
When the magnetic domain refinement treatment line is a thermal strain, the grain-oriented electrical steel sheet preferably satisfies σ²(TS_m) > 5.0. Here, TS_m is a maximum value of tensile strength in a unit of MPa introduced into a thermal strain, and measured at each of a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line. σ²(TS_m) is a variance of TS_m.
When σ²(TS_m) > 5.0 is satisfied, 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.
An example of a method for measuring TS_m and (σ²(TS_m) is illustrated in FIG. 15. In FIG. 15, the broken lines represent a plurality of imaginary lines VL set at intervals of 5 mm in parallel along the rolling direction RD of the grain-oriented electrical steel sheet. In FIG. 15, the X marks and the O marks are intersections between the imaginary lines VL and the thermal strains 541 as the magnetic domain refinement 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 for calculating σ²(TS_m).
First, the rolling direction RD of the grain-oriented electrical steel sheet is specified. The rolling direction RD can be easily specified based on a roll flaw on the surface, the stretching direction of grains, the extending direction of magnetic domains in a magnetic domain image, and the like of the grain-oriented electrical steel sheet. Next, imaginary lines VL are set at intervals of 5 mm in parallel along the rolling direction RD of the grain-oriented electrical steel sheet. Then intersections between the imaginary lines VL and the thermal strains 541 as the magnetic domain refinement treatment line are specified. When 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 having a size of 100 mm or more along the rolling direction RD and a size of 100 mm or more along the direction TD perpendicular to the rolling direction. One side of the rectangle is preferably parallel to the rolling direction RD.
Then, TS_m is measured at all the intersections in the measurement region, and the variance σ²(TS_m) of TS_m is calculated. The tensile strength TS_m introduced into 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 tensile strength 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 procedures. 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. The cut surface 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 strength component in an arbitrary direction is extracted and the magnitude thereof is measured. For example, it is possible to extract tensile strength components in the normal direction of the rolled surface, in the direction parallel to the magnetic domain control treatment line, and in the direction perpendicular to the normal direction of the rolled surface and the magnetic domain control treatment line.
The variance σ²(TS_M) of the maximum values TS_M of tensile strength specified at each of the plurality of 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".
Alternatively, when the magnetic domain refinement treatment line is a thermal strain, the grain-oriented electrical steel sheet preferably satisfies TS_m(β<2) > TS_m(β≥2). TS_m(β<2) is an arithmetical mean value of maximum values of tensile strength in a unit of MPa introduced into the thermal strain, the maximum values being measured at each of the magnetic domain refinement points having a β angle of less than 2° among a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line. TS_m(β≥2) is an arithmetical mean value of the maximum values of tensile strength in a unit of MPa introduced into the thermal strain, the maximum values being measured at each of the magnetic domain refinement points having the β angle of 2° or more.
When TS_m(β<2) > TS_m(β≥2) is satisfied, the magnetic domain control strength is large at the place where the β angle is small, and the magnetic domain control strength is small at the 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 for measuring TS_m(β<2) and TS_m(β≥2) is illustrated in FIG. 15. As described above, in FIG. 15, the X marks and the O marks are intersections between the imaginary lines VL and the thermal strains 541 as the magnetic domain refinement 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.
First, the β angle is measured at each intersection to specify the intersections where the β angle is 2° or more and the intersections where the β angle is less than 2°. Next, the maximum value TS_m of tensile strength is specified for each of all the intersections 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). In addition, the maximum value TS_m of tensile strength is specified for each of all the intersections 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 maximum value TS_m of tensile strength introduced into the thermal strain 541 at the intersection is as described above.
On the other hand, when the magnetic domain refinement treatment line is a groove 542, the grain-oriented electrical steel sheet preferably satisfies σ²(D_m) > 3.0. D_m is the depth of the groove 542 in a unit of µm at each of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line. σ²(D_m) is a variance of D_m.
When σ²(D_m) > 3.0 is satisfied, 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.
An example of a method for measuring D_m and σ²(D_m) is illustrated in FIG. 16. In FIG. 16, the broken lines represent a plurality of imaginary lines VL set at intervals of 5 mm in parallel along the rolling direction RD of the grain-oriented electrical steel sheet. In FIG. 16, the X marks and the O marks are intersections between the imaginary lines VL and the grooves 542 as the magnetic domain refinement 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 for calculating σ²(D_m).
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 rolling direction RD of the grain-oriented electrical steel sheet. Then intersections between the imaginary lines VL and the magnetic domain refinement treatment lines are specified. When the magnetic domain refinement treatment line is a groove 542, it is easy to visually recognize the magnetic domain refinement treatment line with the naked eye. The shape of the measurement region is preferably a rectangle having a size of 100 mm or more along the rolling direction RD and a size of 100 mm or more along the direction TD perpendicular to the rolling direction. One side of the rectangle is preferably parallel to the rolling direction RD.
Then, the maximum value D_m of the depth of the groove is measured for all the intersections in the measurement region, and the variance σ²(D_m) of the maximum value D_m of the depth of the groove is calculated. The method for measuring the maximum value D_m of the depth of the groove is as follows. Measurement is performed using a white interference microscope Controur GT-1 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. Note that 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. When a groove is formed in the grain-oriented electrical steel sheet but the unevenness cannot be measured from the surface due to an insulating film or the like, the measurement is performed after the insulating film or the like is removed using a known method.
Alternatively, when the magnetic domain refinement treatment line is a groove 542, the grain-oriented electrical steel sheet preferably satisfies D_m(β<2) > D_m(β≥2). D_m(β<2) is an arithmetical mean value of maximum values of the depth of the groove in a unit of µm, the maximum values being measured at each of the magnetic domain refinement points having a β angle of less than 2° among a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines VL set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line. D_m(β≥2) is an arithmetical mean value of the maximum values of the depth of the groove in a unit of µm, the maximum values being measured at each of the magnetic domain refinement points having the β angle of 2° or more.
In the magnetic domain refinement treatment line satisfying the formula, the magnetic domain control strength is large at the place where the β angle is small, and the magnetic domain control strength is small at the 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 for measuring TS_m(β<2) and TS_m(β≥2) is illustrated in FIG. 16. As described above, in FIG. 16, the X marks and the O marks are intersections between the imaginary lines VL and the grooves 542 as the magnetic domain refinement 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.
First, the β angle is measured at each intersection to specify the intersections where the β angle is 2° or more and the intersections where the β angle is less than 2°. Next, an arithmetical mean value of D_m for all the intersections 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 intersections where the β angle is less than 2° is calculated, which is regarded as D_m(β≥2). The method for measuring the maximum value D_m of the depth of the groove at the intersection is as described above.

Examples

The effect of an embodiment 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 thereof is achieved without departing from the gist thereof.

(1. Effect of non-uniform magnetic domain control strength)

In order to evaluate the characteristics of the grain-oriented electrical steel sheet having a non-uniform magnetic domain control strength, experiments described below were conducted.
Grain-oriented electrical steel sheets in the same lot having a sheet thickness of 0.23 mm and classified into 23P085 in the table 2 of JIS C 2553:2019 "Cold-rolled grain-oriented electrical steel strip and sheet delivered in the fully-processed state" were used as original sheets. These were provided with magnetic domain refinement treatment lines in accordance with a method in line with the flowchart shown in FIG. 6. First, an image acquisition device was used to acquire a magnetic domain image of the grain-oriented electrical steel sheet. Next, the calculation unit of an analysis device derived the spatial distribution of the spacing of the 180° magnetic domain walls (spacing of magnetic domain walls) from the magnetic domain image by using the line segment method or two-dimensional Fourier transform. Then, the point where the spacing of magnetic domain walls was 500 µm or more was determined as the point to which the magnetic domain refinement treatment was applied. Furthermore, the magnetic domain control strength was set under various conditions shown in Tables 1 and 2.
For the various grain-oriented electrical steel sheets Nos. A1 to A5 and Nos. B1 to B5 thus obtained, the SST iron loss W17/50 and λ2pp/λ1pp were measured. As described above, the SST iron loss W17/50 is a value measured using a single sheet tester with a width of 100 mm, which is specified in JIS C 2556:2015. λ1pp is a value measured using the method specified in IEC 60404-17:2021, and as described above, is the peak-to-peak value of magnetostriction in the measurement results of the magnetostriction λ with respect to the magnetic flux density B obtained when a grain-oriented electrical steel sheet is excited with alternating-current up to ±1.7 T. λ2pp is a value measured using the same method, and as described above, is the peak-to-peak value of magnetostriction in the measurement results of the magnetostriction λ with respect to the magnetic flux density B obtained when a grain-oriented electrical steel sheet is excited with alternating-current up to ±1.9 T.
As a result, in all the examples disclosed in Tables 1 and 2, W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2 were satisfied.
Furthermore, the noise and the transformer iron loss W16/50 of Nos. A1 to A5 and Nos. B1 to B5 were also evaluated. The evaluation methods for the noise and the transformer iron loss W16/50 were as follows. First, 180 grain-oriented electrical steel sheets having a sheet thickness of 0.23 mm were laminated to form a three-phase transformer core. The widths of the foot 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 1.6 T.
In measuring the noise, microphones were arranged at equal intervals at eight points around the transformer in which the three-phase transformer core was incorporated. The distance between the transformer and the microphone was 30 cm. The values obtained by correcting the A characteristics to the noise measurement results by the microphones and averaging the results are described in Table 2 as the noise evaluation results (unit: dBA) of the grain-oriented electrical steel sheets. An example in which the evaluation result of noise was 25.5 dBA or less was determined to be an example in which noise reduction was achieved.

The iron loss of the three-phase transformer was determined 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 1.6 T as described above. The determined iron loss is described in Table 2 as an iron loss evaluation result (unit: W/kg) of the three-phase transformer. An example in which the evaluation result of the transformer iron loss W16/50 was 0.770 W/kg or less was determined to be an example in which iron loss reduction was achieved.

[Table 1]

Evaluation result of example in which magnetic domain refinement treatment line is thermal strain
No.	σ²(TS_m)	TS_m(β<2)	TS_m(β≥2)	Transformer iron loss W16/50	Noise evaluation result	SST iron loss W17/50	λ2pp/ λ1pp
A1	1.3	150	153	0.743	25.2	0.754	2.1
A2	4.8	158	181	0.736	24.6	0.751	2.0
A3	5.1	143	170	0.712	23.8	0.744	2.1
A4	4.9	167	125	0.726	23.3	0.757	2.1
A5	5.5	204	110	0.704	22.8	0.762	2.0

No. A1 satisfied W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2, and thus showed an iron loss evaluation result and a noise evaluation result better than those of the conventional grain-oriented electrical steel sheet.
On the other hand, in No. A2, not only W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2 were satisfied, but also, in the magnetic domain refinement treatment line, maximum values of tensile strength introduced into the thermal strain were non-uniform at each measurement point of tensile strength. The evaluation results of iron loss and noise of No. A2 were more excellent than those of No. A1.
No. A3 satisfied not only W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2, but also satisfied σ²(TS_m) > 5.0. The evaluation results of iron loss and noise of No. A3 were more excellent than those of Nos. A1 and A2.
No. A4 satisfied not only W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2, but also satisfied TS_m(β<2) > TS_m(β≥2). The evaluation results of iron loss and noise of No. A4 were more excellent than those of Nos. A1 and A2.

No. A5 satisfied not only W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2, but also satisfied σ²(TS_m) > 5.0 and TS_m(β<2) > TS_m(β≥2). The evaluation results of iron loss and noise of No. A5 were the most excellent of Nos. A1 to A5.

[Table 2]

Evaluation result of example in which magnetic domain refinement treatment line is groove
No.	σ²(D_m)	D_m(β<2)	D_m(β≥2)	Transformer iron loss W16/50	Noise evaluation result	SST iron loss W17/50	λ2pp/ λ1pp
B1	0.9	36	38	0.764	23.2	0.763	2.0
B2	2.5	24	41	0.757	22.4	0.754	2.0
B3	3.1	21	38	0.733	21.7	0.751	2.1
B4	2.8	27	15	0.745	21.3	0.753	2.1
B5	3.6	32	10	0.723	20.4	0.754	2.0

No. B1 satisfied W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2, and thus showed an iron loss evaluation result and a noise evaluation result better than those of the conventional grain-oriented electrical steel sheet.
On the other hand, in No. B2, not only W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2 were satisfied, but also maximum values of the depth of the groove were non-uniform at each measurement point of the groove. The evaluation results of iron loss and noise of No. B2 were more excellent than those of No. B1.
No. B3 satisfied not only W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2, but also satisfied σ²(D_m) > 3.0. The evaluation results of iron loss and noise of No. B3 were more excellent than those of Nos. B1 and B2.
No. B4 satisfied not only W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2, but also satisfied D_m(β<2) > D_m(β≥2). The evaluation results of iron loss and noise of No. B4 were more excellent than those of Nos. B1 and B2.
No. B5 satisfied not only W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2, but also satisfied σ²(D_m) > 3.0 and D_m(β<2) > D_m(β≥2). The evaluation results of iron loss and noise of No. B5 were the most excellent of Nos. B1 to B5.

(2. Effect of magnetic domain control treatment based on distribution of spacing of magnetic domain walls)

The manufacturing method in which the arrangement of magnetic domain control treatment lines is determined based on the shape of grains and the manufacturing method in which the arrangement of magnetic domain control treatment lines is determined based on the distribution of spacing of magnetic domain walls are compared.
Nos. C1 to C8 in Table 3 were produced by the following procedure. First, the distribution of secondary recrystallized grains was specified in a grain-oriented electrical steel sheet in which secondary recrystallized grains were formed before magnetic domain control treatment. The distribution of secondary recrystallized grains was specified by photographing the magnetic domain image in a state where the steel sheet was magnetized in the rolling direction and observing the same. For the examples Nos. C1 to C4, a laser was irradiated or a groove was formed to form magnetic domain refinement treatment lines only in the region of within ± 6 mm from the center of the rolling direction of secondary recrystallized grains in the rolling direction RD. For the examples Nos. C5 to C8, a laser was irradiated or a groove was formed to form magnetic domain refinement treatment lines only in the region of within ± 10 mm from the center of the rolling direction of secondary recrystallized grains in the rolling direction RD. The radius of curvature of the steel sheet at the position where the grains were present during the finish annealing was R = 300 mm.
In Nos. C1 to C8 in Table 3, the magnetic domain refinement treatment lines 54 were provided along the magnetic domain control treatment lines 52 as illustrated in FIG. 7. The magnetic domain control treatment line 52 was extended in a direction substantially orthogonal to the rolling direction RD. In addition, a plurality of magnetic domain control treatment lines 52 was provided repeatedly in the rolling direction. The interval of the magnetic domain control treatment lines 52 along the rolling direction was 4 mm. In Nos. C1 to C4, the number of the magnetic domain control treatment lines 52 was four. In Nos. C5 to C8, the number of the magnetic domain control treatment lines 52 was six.
For Nos. C1 to C8 obtained by the above-described procedure, SST iron loss W17/50 and λ2pp/λ1pp were measured. The measurement procedure was as described above. The SST iron loss W17/50 not satisfying W17/50 < 1.350t + 0.450 and the λ2pp/λ1pp not satisfying λpp/λ1pp < 2.2 are underlined.

Further, for Nos. C1 to C8, transformer iron loss W16/50 and noise were also measured by the above-described procedure. An example in which the evaluation result of noise was 25.5 dBA or less was determined to be an example in which noise reduction was achieved. An example in which the evaluation result of the transformer iron loss W16/50 was 0.770 W/kg or less was determined to be an example in which iron loss reduction was achieved. The noise evaluation result and iron loss evaluation result determined to be unacceptable were underlined.

[Table 3]

No.	Sheet thickness	Type	SST iron loss W17/50	λ2pp/ λ1pp	Transformer iron loss W16/50	Noise evaluation result
C1	0.20	Laser	0.755	2.0	0.792	23.8
C2	0.27	Laser	0.854	2.1	0.894	24.2
C3	0.20	Groove	0.766	1.9	0.801	23.6
C4	0.27	Groove	0.864	2.0	0.893	24.2
C5	0.20	Laser	0.704	2.9	0.771	25.6
C6	0.27	Laser	0.798	3.1	0.854	25.6
C7	0.20	Groove	0.718	3.2	0.776	25.7
C8	0.27	Groove	0.810	3.0	0.871	25.8

As described above, in Nos. A1 to A5 and Nos. B1 to B5, in which the arrangement of the magnetic domain refinement treatment lines was determined based on spacing of magnetic domain walls, both W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2 were satisfied. For Nos. A1 to A5 and Nos. B1 to B5, transformer iron loss W16/50 and noise were determined to be acceptable.
On the other hand, in C1 to C8, in which the arrangement of the magnetic domain refinement treatment lines was determined based on the shape of grains, at least one of W17/50 < 1.350t + 0.450 and λ2pp/λ1pp < 2.2 was not satisfied.
In Nos. C1 to C4, the number of magnetic domain control treatment lines was small, and therefore the magnetostriction waveform was not remarkably expanded. However, in Nos. C1 to C4, the iron loss could not be sufficiently suppressed, and W17/50 < 1.350t + 0.450 was not satisfied. For Nos. C1 to C4, transformer iron loss W16/50 was determined to be unacceptable.
In Nos. C5 to C8, the number of magnetic domain control treatment lines was large, and therefore iron loss was suppressed as compared with Nos. C1 to C4. However, for Nos. C5 to C8, transformer iron loss W16/50 was determined to be unacceptable. Further, in Nos. C5 to C8, the magnetostriction waveform became remarkably large under a high magnetic field (around 1.9 T) due to the flux closure domain, and λ2pp/λ1pp < 2.2 was not satisfied. For Nos. C5 to C8, noise was determined to be unacceptable.

REFERENCE SIGNS LIST

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
50 Grain-oriented electrical steel sheet
52 Magnetic domain control treatment line
54 Magnetic domain refinement treatment line
500 Laser irradiation device

Claims

A grain-oriented electrical steel sheet comprising a magnetic domain refinement treatment line on a surface, wherein
a sheet thickness t (mm) and an iron loss W17/50 (W/kg) satisfy a relationship of W17/50 < 1.350t + 0.450,

a peak-to-peak value of a magnetostriction under a magnetic flux density of 1.7 T is expressed as λ1pp, and a peak-to-peak value of a magnetostriction under a magnetic flux density of 1.9 T is expressed as λ2pp, and

λpp/λ1pp < 2.2 is satisfied.
The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain refinement treatment line is a thermal strain.
The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain refinement treatment line is a groove.
The grain-oriented electrical steel sheet according to claim 2, wherein, in the magnetic domain refinement treatment line, maximum values of tensile strength introduced into the thermal strain are non-uniform at each measurement point of the tensile strength.
The grain-oriented electrical steel sheet according to claim 4, satisfying σ²(TS_m) > 5.0, wherein
TS_m are maximum values of the tensile strength in a unit of MPa introduced into the thermal strain, the maximum values being measured at each of a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line; and

σ²(TS_m) is a variance of TS_m.
The grain-oriented electrical steel sheet according to claim 4 or 5, satisfying TS_m(β<2) > TS_m(β≥2), wherein
TS_m(β<2) is an arithmetical mean value of maximum values of the tensile strength in a unit of MPa introduced into the thermal strain, the maximum values being measured at each of magnetic domain refinement points having a β angle of less than 2° among a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line; and

TS_m(β≥2) is an arithmetical mean value of the maximum values of the tensile strength in a unit of MPa introduced into the thermal strain, the maximum values being measured at each of the magnetic domain refinement points having the β angle of 2° or more.
The grain-oriented electrical steel sheet according to claim 3, wherein, in the magnetic domain refinement treatment line, maximum values of a depth of the groove are non-uniform at each measurement point of the groove.
The grain-oriented electrical steel sheet according to claim 7, satisfying σ²(D_m) > 3.0, wherein
D_m are maximum values of a depth of the groove in a unit of µm at each of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line; and

σ²(D_m) is a variance of D_m.
The grain-oriented electrical steel sheet according to claim 7 or 8, satisfying D_m(β<2) > D_m(β≥2), wherein
D_m(β<2) is an arithmetical mean value of maximum values of a depth of the groove in a unit of µm, the maximum values being measured at each of magnetic domain refinement points having a β angle of less than 2° among a plurality of magnetic domain refinement points, which are intersections between a plurality of imaginary lines set at intervals of 5 mm in parallel along a rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line; and

D_m(β≥2) is an arithmetical mean value of maximum values of a depth of the groove in a unit of µm, the maximum values being measured at each of the magnetic domain refinement points having the β angle of 2° or more.