Grain-oriented electrical steel sheet

Abstract

This grain-oriented electrical steel sheet has magnetic domain refinement treatment lines on the surface thereof. If the relationship between the sheet thickness t (mm) and an iron loss W17 / 50 (W / kg) satisfies W17 / 50<1.350t+0.450, the peak-peak value of the magnetostriction at a magnetic flux density of 1.7 T is denoted as λ1 pp, and the peak-peak value of the magnetostriction at a magnetic flux density of 1.9 T is denoted as λ2 pp, λ2 pp / λ1 pp<2.2 is satisfied. Preferably, the magnetic domain refinement treatment lines represent the thermal strain or grooves.

Description

grain-oriented electrical steel sheet

[0001] This application claims priority to Japanese Patent Application No. 2023-165201, filed on September 27, 2023, the contents of which are incorporated herein by reference.

[0002] Grain-oriented electrical steel sheets are steel sheets containing 7 mass% or less of Si and having a secondary recrystallization texture in which secondary recrystallized grains are concentrated in the {110}<001> orientation (Goss orientation). Grain-oriented electrical steel sheets are mainly used as iron cores for power transformers, and there is a growing need for reduced noise as well as reduced energy loss (iron loss).

[0003] To reduce iron loss, a magnetic domain refining technique has long been known in which the surface of a grain-oriented electrical steel sheet is irradiated with a laser or electron beam in a direction intersecting the rolling direction to narrow the magnetic domain width. In recent years, various improved techniques for magnetic domain refining have been proposed in order to provide grain-oriented electrical steel sheets with good iron loss characteristics (see, for example, Patent Documents 1 and 2).

[0004] JP 2012-57219 A JP 2012-12664 A

[0005] However, when grain-oriented electrical steel sheets are subjected to magnetic domain refinement, the formation of closure domains is unavoidable. Therefore, in ordinary grain-oriented electrical steel sheets with magnetic domain refinement, the magnetostriction waveform in high magnetic fields (near 1.9 T) becomes significantly large due to the closure domains. Magnetostriction in high magnetic fields occurs in areas where magnetic flux is concentrated, such as the corners of transformers, and the transformer noise generated from these areas is very loud. As such, there is a trade-off between reducing iron loss and reducing noise in grain-oriented electrical steel sheets, and an optimal magnetic domain refinement technology that can achieve both is needed.

[0006] The present disclosure has been made in view of the above-mentioned problems, and has an object to provide a grain-oriented electrical steel sheet that can achieve both low iron loss and low noise.

[0007] (1) A grain-oriented electrical steel sheet according to one aspect of the present disclosure has magnetic domain refinement treatment lines on its surface, in which the relationship between the sheet thickness t (mm) and the iron loss W17 / 50 (W / kg) satisfies W17 / 50<1.350t+0.450, and where the peak-to-peak value of magnetostriction at a magnetic flux density of 1.7 T is denoted as λ1pp and the peak-to-peak value of magnetostriction at a magnetic flux density of 1.9 T is denoted as λ2pp, the relationship λ2pp / λ1pp<2.2 is satisfied. (2) Preferably, in the grain-oriented electrical steel sheet described in (1) above, the magnetic domain refinement treatment lines represent thermal strain. (3) Preferably, in the grain-oriented electrical steel sheet described in (1) above, the magnetic domain refinement treatment lines represent grooves. (4) Preferably, in the grain-oriented electrical steel sheet described in (2) above, the maximum value of tensile strength introduced by the thermal strain in the magnetic domain refinement treatment lines is non-uniform at each measurement point of the tensile strength. (5) Preferably, in the grain-oriented electrical steel sheet described in (4) above, σ ２ (TS ｍ ) > 5.0, and TS ｍ is the maximum value of the tensile strength in unit MPa introduced into the thermal strain, measured at each of a plurality of magnetic domain refinement points, which are intersections of a plurality of imaginary lines set in parallel along the rolling direction of the grain-oriented electrical steel sheet at intervals of 5 mm and the magnetic domain refinement treatment lines, and σ ２ (TS ｍ ) is T.S. ｍ (6) Preferably, in the grain-oriented electrical steel sheet according to (4) or (5) above, TS ｍ（β＜２） >TS ｍ（β≧２） Satisfying TS ｍ（β＜２） is the arithmetic mean value of the maximum values ​​of the tensile strength in unit MPa introduced into the thermal strain, measured at each of a plurality of magnetic domain refinement points, which are intersections of a plurality of imaginary lines set at 5 mm intervals in parallel along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment lines, and which have a β angle of less than 2°; and TS ｍ（β≧２）is the arithmetic mean value of the maximum values ​​of the tensile strength in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or more. (7) Preferably, in the grain-oriented electrical steel sheet described in (3) above, the maximum value of the groove depth in the magnetic domain refinement treatment line is non-uniform for each measurement point of the groove. (8) Preferably, in the grain-oriented electrical steel sheet described in (7) above, σ ２ (D ｍ ) > 3.0, and D ｍ is the maximum value of the depth of the groove in μm at the magnetic domain refinement points, which are the intersections of the magnetic domain refinement treatment lines and a plurality of imaginary lines set in parallel along the rolling direction of the grain-oriented electrical steel sheet at intervals of 5 mm, and σ ２ (D ｍ ) is D ｍ (9) Preferably, in the grain-oriented electrical steel sheet according to (7) or (8), D ｍ（β＜２） >D ｍ（β≧２） and D ｍ（β＜２） is the arithmetic mean value of the maximum groove depth in μm measured at each of a plurality of magnetic domain refinement points, which are intersections of a plurality of imaginary lines set in parallel along the rolling direction of the grain-oriented electrical steel sheet at intervals of 5 mm with the magnetic domain refinement treatment lines, and which have a β angle of less than 2°; and D ｍ（β≧２） is the arithmetic mean value of the maximum depth of the groove in μm measured at each of the magnetic domain refinement points where the β angle is 2° or more.

[0008] According to the present disclosure, by providing a grain-oriented electrical steel sheet having magnetic domain refinement treatment lines on the surface and in which the relationship between sheet thickness and iron loss and the peak-to-peak ratio of magnetostriction satisfy predetermined formulas, it is possible to achieve both low iron loss and low noise.

[0009] 1B 。 FIG. 1C is a graph showing an example of the spatial distribution of the magnetic domain width of a grain-oriented electrical steel sheet before magnetic domain refinement treatment. FIG. 1D is a graph showing an example of the spatial distribution of the magnetic domain width of a grain-oriented electrical steel sheet after magnetic domain refinement treatment. FIG. 1E is a graph showing regions where the magnetic domain width has been refined by 50 μm or more before and after the magnetic domain refinement treatment shown in FIGS. 1A and 1B. FIG. 1F is a graph showing the relationship between the magnetic domain width before laser irradiation and the magnetic domain width after laser irradiation. FIG. 1F is a block diagram showing the hardware configuration of an image acquisition device according to the present embodiment. FIG. 1G is a block diagram showing the hardware configuration of an analysis device according to the present embodiment. FIG. 1H is a schematic diagram showing the configuration of a laser irradiation device according to the present embodiment. 1 is a graph showing magnetostriction waveforms when a grain-oriented electrical steel sheet that has been selectively irradiated with a laser and a grain-oriented electrical steel sheet that has been uniformly irradiated with a laser over its entire surface are subjected to AC excitation up to ±1.9 T. FIG. 2 is a graph showing data on the ratio (λ2pp / λ1pp) of the peak-to-peak value λ2pp of magnetostriction at a magnetic flux density of 1.9 T to the peak-to-peak value λ1pp of magnetostriction at a magnetic flux density of 1.7 T, for a plurality of grain-oriented electrical steel sheets that have been selectively irradiated with a laser and a plurality of grain-oriented electrical steel sheets that have been uniformly irradiated with a laser over their entire surface. FIG. 3 is a graph showing a relationship between the magnetic domain width and the magnetic domain control saturation strength. FIG. 4 is a graph showing a relationship between the β angle and the magnetic domain control saturation strength. FIG. 5 is a cross-sectional schematic diagram of a grain-oriented electrical steel sheet in which the magnetic domain refinement treatment lines are thermally strained. FIG. 6 is a cross-sectional schematic diagram of a grain-oriented electrical steel sheet in which the magnetic domain refinement treatment lines are grooves. FIG. 7 is a plan view schematic diagram illustrating a method for measuring the magnetic domain control strength at the intersection of the magnetic domain refinement treatment lines and the virtual line when the magnetic domain refinement treatment lines are thermally strained. FIG. 10 is a schematic plan view illustrating a method for measuring the magnetic domain control strength at the intersection of a magnetic domain refining treatment line and a virtual line when the magnetic domain refining treatment line is a groove.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] First, we compare the magnetic domain structures of grain-oriented electrical steel sheets before and after magnetic domain refinement treatment. Fig. 1A shows the spatial distribution of the width of the 180° magnetic domains (hereinafter simply referred to as "magnetic domain width") of a grain-oriented electrical steel sheet before magnetic domain refinement treatment. Fig. 1B shows the spatial distribution of the magnetic domain width after magnetic domain refinement treatment was performed on the surface of the grain-oriented electrical steel sheet of Fig. 1A. The magnetic domain refinement treatment here was performed by irradiating a continuous wave laser along a magnetic domain control treatment line that was approximately perpendicular to the rolling direction (RD).

[0012] Here, the term "180° magnetic domain" refers to a magnetic domain whose magnetization direction is the <100> orientation of the crystal and is sandwiched between two 180° magnetic domain walls that are substantially parallel to the rolling direction. The "width" of a 180° magnetic domain refers to the distance between adjacent magnetic domain walls (magnetic domain wall spacing).

[0013] The spatial distribution of the magnetic domain width shown in FIGS. 1A and 1B was derived from a magnetic domain image of a grain-oriented electromagnetic steel sheet using a two-dimensional Fourier transform (see JP 2021-169655 A and JP 2021-169979 A).

[0014] FIG. 1C shows regions in which the magnetic domain width has been refined by 50 μm or more before and after the magnetic domain refinement process shown in FIGS. 1A and 1B, and visualizes the values ​​of the original magnetic domain width at which refinement occurred.

[0015] 1C shows that the areas where the effect of magnetic domain refining was 50 μm or more were areas where the original magnetic domain width was wide, and that the effect of magnetic domain refining was particularly pronounced in areas where the original magnetic domain width was 500 μm or more. In other words, the effect of magnetic domain refining differs depending on the original magnetic domain width.

[0016] 2 shows the relationship between the magnetic domain width before and after laser irradiation at the same position. Here, the irradiation conditions are an average irradiation energy density Ua (mJ / mm ２ ), and irradiation pitch PL (mm), respectively, Ua = 1.5 mJ / mm ２ , PL=4 mm.

[0017] It can be seen from FIG. 2 that even if a region having a magnetic domain width of approximately 500 μm or less is irradiated with a laser, the effect of refining the magnetic domain is small.

[0018] From the above, it is thought that the iron loss reduction effect can be obtained by subdividing regions with originally wide magnetic domain widths, and that even if magnetic domain subdivision is performed on regions with originally narrow magnetic domain widths, the iron loss reduction effect is small and results in increased hysteresis loss and deterioration of noise characteristics.

[0019] Therefore, in this embodiment, magnetic domain control is performed so that magnetic domain refinement is performed only in areas of the grain-oriented electrical steel sheet where the original magnetic domain width is relatively wide (for example, areas of 500 μm or more).

[0020] In this embodiment, the magnetic domain control strength is preferably determined according to the magnetic domain width of the grain-oriented electrical steel sheet before the magnetic domain refinement treatment, which is the amount of thermal distortion when the magnetic domain control method is thermal distortion, or the groove depth when the magnetic domain control method is grooves.

[0021] The stronger the magnetic domain control strength, the greater the effect of magnetic domain refinement. On the other hand, the stronger the magnetic domain control strength, the more likely it is to lead to increased hysteresis loss and deterioration of noise characteristics. Furthermore, according to new findings by the inventors, the magnetic domain control saturation strength is not uniform in grain-oriented electrical steel sheets.

[0022] The magnetic domain control saturation strength is the magnetic domain control strength at which the effect of the magnetic domain refinement process is substantially saturated. When the magnetic domain control strength is equal to or less than the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the reduction in iron loss. However, when the magnetic domain control strength exceeds the magnetic domain control saturation strength, increasing the magnetic domain control strength hardly improves the iron loss reduction effect. On the other hand, even when the magnetic domain control strength exceeds the magnetic domain control saturation strength, the greater the magnetic domain control strength, the greater the hysteresis loss and the worse the noise characteristics. Therefore, it is extremely preferable to set the magnetic domain control strength within a range that does not exceed the magnetic domain control saturation strength.

[0023] The inventors also found that the magnetic domain control saturation strength has a strong correlation with the β angle. The β angle is the angle of deviation from the Goss orientation of the crystal grains around the axis transverse to the rolling direction (TD). The magnetic domain control saturation strength is high where the β angle is small. Furthermore, in grain-oriented electrical steel sheets before magnetic domain control treatment, there is a correlation between the β angle and the magnetic domain width. In grain-oriented electrical steel sheets before magnetic domain control treatment, the larger the β angle, the smaller the magnetic domain width. However, in grain-oriented electrical steel sheets after magnetic domain control treatment, the correlation between the magnetic domain width and the β angle becomes weaker. This is because the magnetic domain control treatment changes the magnetic domain width but does not change the β angle.

[0024] Therefore, it is preferable to select an optimal magnetic domain control strength depending on the magnetic domain width or β angle. Specifically, it is preferable to perform a magnetic domain refining process with a high magnetic domain control strength in areas where the magnetic domain width is large and the β angle is small, and to perform a magnetic domain refining process with a low magnetic domain control strength in areas where the magnetic domain width is small and the β angle is large. Furthermore, as mentioned above, the magnetic domain refining process is not performed in areas where the original magnetic domain width is smaller than a predetermined value.

[0025] FIG. 11 shows a graph that schematically illustrates a method for determining the magnetic domain control strength based on the magnetic domain width. The vertical axis of FIG. 11 represents the magnetic domain control strength, and the horizontal axis represents the magnetic domain width. The solid line in FIG. 11 represents the magnetic domain control saturation strength. In regions where the magnetic domain width is small, the magnetic domain control effect is not obtained, so the magnetic domain control saturation strength is 0. In regions where the magnetic domain width exceeds 500 μm, the magnetic domain control effect is obtained. Furthermore, in regions where the magnetic domain width exceeds 500 μm, the magnetic domain control saturation strength increases as the magnetic domain width increases. Furthermore, in regions where the magnetic domain width exceeds approximately 1200 μm, the magnetic domain control saturation strength is approximately constant.

[0026] FIG. 12 shows a graph that schematically illustrates a method for determining the magnetic domain control strength based on the β angle. The vertical axis of FIG. 12 represents the magnetic domain control strength, and the horizontal axis represents the magnitude of the β angle. The solid line in FIG. 12 represents the magnetic domain control saturation strength. In regions where the β angle is large, the magnetic domain control effect is not obtained, so the magnetic domain control saturation strength is 0. In regions where the β angle is below a predetermined value, the magnetic domain control effect is obtained. For example, when the β angle is 2.0° or less, it is estimated that the magnetic domain control effect is obtained. In regions where the β angle is below a predetermined value, the larger the β angle, the greater the magnetic domain control saturation strength. In regions where the β angle is even smaller, the magnetic domain control saturation strength is approximately constant.

[0027] It is most preferable that the relationship between the magnetic domain width at the location where magnetic domain control is performed and the magnetic domain control strength is on the solid line graph in Figure 11. Alternatively, it is most preferable that the relationship between the β angle at the location where magnetic domain control is performed and the magnetic domain control strength is on the solid line graph in Figure 12. The magnetic domain control saturation strength can be used as a target value for the magnetic domain control strength.

[0028] Furthermore, there is a minimum magnetic domain control strength, which is the minimum strength at which the magnetic domain control effect is exhibited. When magnetic domain control is performed, it is more preferable that the magnetic domain control strength is equal to or greater than the minimum magnetic domain control strength.

[0029] However, the magnetic domain control strength may vary slightly from the target value of the magnetic domain control saturation strength. In Figures 11 and 12, the region that is equal to or greater than the minimum magnetic domain control strength and that is within a certain range of the graph of the magnetic domain control saturation strength is referred to as the target range of the magnetic domain control strength. It is preferable that the magnetic domain control strength and the magnetic domain width of the magnetic domain control target portion are within the shaded region surrounded by dashed lines in Figures 11 and 12.

[0030] This results in a grain-oriented electrical steel sheet with non-uniform magnetic domain control strength. In such grain-oriented electrical steel sheets, the magnetic domain control strength varies depending on the β angle. In such grain-oriented electrical steel sheets, the iron loss of the grain-oriented electrical steel sheet after magnetic domain control is further reduced. Meanwhile, the increase in hysteresis loss and the deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0031] The β angle of grain-oriented electrical steel sheets is measured by the side reflection Laue method, which is widely known as a method for measuring crystal orientation.

[0032] Next, the configuration of a device that realizes magnetic domain control of the grain-oriented electrical steel sheet according to this embodiment will be described with reference to FIGS.

[0033] 3 shows the hardware configuration of an image acquisition device 30 that acquires magnetic domain images of grain-oriented electrical steel sheets. 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.

[0034] The light source unit 31 has a light source made up of a light emitting diode (LED), and irradiates the MO sensor 33 with light having a uniform polarization plane.

[0035] The MO sensor 33 is a device for measuring the magnetic domain structure of a magnetic material, and has an observation surface on which a magnetic sample to be measured is placed. Light emitted from the light source unit 31 passes through the interior of the MO sensor 33 and is reflected by a reflective layer. The reflected light passes through the interior of the MO sensor 33 again and is output to the outside of the MO sensor 33. When a grain-oriented electromagnetic steel sheet is placed on the observation surface of the MO sensor 33 as a magnetic sample, a leakage magnetic field corresponding to the direction of spontaneous magnetization of the grain-oriented electromagnetic steel sheet is generated inside the MO sensor 33, and this leakage magnetic field rotates the plane of polarization of the reflected light.

[0036] The image sensor 35 is a complementary metal-oxide-semiconductor (CMOS) image sensor that forms an image of the reflected light from the MO sensor 33 on its light-receiving surface, photoelectrically converts the image, and outputs the photoelectrically converted analog signal to the signal processing unit 37. By detecting the reflected light with its polarization plane rotated by the image sensor 35, the spatial distribution of the leakage magnetic field can be obtained, and the magnetic domain structure of the grain-oriented electrical steel sheet can be clarified.

[0037] The signal processing unit 37 includes an amplifier, an AD converter, a digital signal processor (DSP), etc. The analog signal output from the image sensor 35 is amplified by the amplifier and converted into a digital signal by the AD converter. This digital signal is subjected to predetermined digital processing by the DSP to generate an image signal. The image signal generated by the signal processing unit 37 is output to an analysis device 40 (see FIG. 4 ) via a cable or wireless communication.

[0038] 4 shows the hardware configuration of an analysis device 40 that analyzes the magnetic domain structure of a 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.

[0039] The calculation unit 41 has a central processing unit (CPU) and analyzes the magnetic domain structure from the magnetic domain image of the grain-oriented electrical steel sheet in accordance with a program stored in the memory 43, and determines the locations to which the magnetic domain refinement process should be applied (see FIG. 6 described later).

[0040] 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 programs and data stored in the ROM are loaded into the RAM and executed.

[0041] 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 and data may be stored in a computer-readable recording medium that is 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.

[0042] The display unit 45 has a display such as a liquid crystal display (LCD), a plasma display, or an organic electroluminescence (EL) display, and displays an image based on the image signal output from the image acquisition device 30, and also displays the analysis results of the magnetic domain structure by the calculation unit 41.

[0043] The input unit 47 has input devices such as a mouse, a keyboard, etc. The communication I / F 49 is an interface for transmitting and receiving data to and from external devices via a network such as a local area network (LAN), a wide area network (WAN), or the Internet.

[0044] In addition, instead of general-purpose hardware such as a CPU, the calculation unit 41 may be dedicated hardware such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA) specialized for analyzing magnetic domain structures.

[0045] Although FIGS. 3 and 4 show the case where the image acquisition device 30 and the analysis device 40 are separate devices, a system in which the image acquisition device 30 and the analysis device 40 are integrated may also be employed.

[0046] As a means for performing the magnetic domain refinement treatment on the surface of the grain-oriented electrical steel sheet, known means such as laser irradiation, electron beam irradiation, etc. The configuration of a laser irradiation device that performs the magnetic domain refinement treatment by laser irradiation will be described below.

[0047] 5 shows the configuration 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 condenser lens 507, a motor 509, a sensor 511, a control unit 513, and a strip threading device 515.

[0048] The sheet threading device 515 threads the grain-oriented electrical steel sheet 50 in the rolling direction (RD).

[0049] The polygon mirror 501 has, for example, a regular polygonal prism shape, and a plurality of plane mirrors are provided on each of the side surfaces of the regular polygonal prism. A laser beam LB is emitted from a light source device 503 via a collimator 505 and is incident on the plane mirror of the polygon mirror 501 in one direction (horizontal direction) and is reflected by the plane mirror.

[0050] The polygon mirror 501 is rotatable around a rotation axis O1 by being driven by a motor 509. The angle of incidence of the laser beam LB with respect to the plane mirror changes sequentially in accordance with the rotation angle of the polygon mirror 501, thereby sequentially changing the reflection direction of the laser beam LB, and enabling scanning along the magnetic domain control processing lines 52 of the grain-oriented electrical steel sheet 50. Here, the magnetic domain control processing lines 52 are multiple parallel straight or curved lines that form an angle of 0° to 45° with respect to the transverse direction (TD) of rolling on the surface of the grain-oriented electrical steel sheet 50 and are arranged at equal intervals in the rolling direction (RD). The interval P between adjacent magnetic domain control processing lines 52 represents the irradiation pitch.

[0051] The light source device 503 outputs a laser beam LB in a predetermined irradiation method (for example, a continuous irradiation method or a pulse irradiation method) under the control of the control unit 513 .

[0052] The condenser lens 507 is provided in the optical path of the laser beam LB reflected from the polygon mirror 501, and constitutes a condensing optical system with a predetermined focal length. The laser beam LB reflected from the polygon mirror 501 is condensed onto the surface of the grain-oriented electromagnetic steel sheet 50 via the condenser lens 507, thereby forming grooves or introducing thermal strain along the magnetic domain control treatment lines 52 on the surface of the grain-oriented electromagnetic steel sheet 50.

[0053] The motor 509 is connected to the polygon mirror 501 and drives the polygon mirror 501 to rotate under the control of the control unit 513 .

[0054] 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 the rotation angle signal) to the control unit 513.

[0055] The control unit 513 is made up of a processor and is connected to the light source device 503, the motor 509, the sensor 511, and the strip threading device 515. The control unit 513 receives a speed signal from the strip threading device 515 and outputs a signal to the motor 509 to instruct the motor 509 to rotate the polygon mirror 501.

[0056] Furthermore, the control unit 513 controls the on / off of the power of the laser beam LB output by the light source device 503 based on a magnetic domain refining signal that indicates the location of the magnetic domain control processing line 52 where the magnetic domain refining processing is to be applied, and on the 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 refining signal is input from the analysis device 40 to the laser irradiation device 500. Note that the magnetic domain refining signal may also be input to the laser irradiation device 500 by an operator.

[0057] Next, a method for manufacturing the grain-oriented electrical steel sheet 50 according to this embodiment will be described with reference to FIG.

[0058] First, the image acquisition device 30 acquires a magnetic domain image of the grain-oriented electromagnetic steel sheet 50 (step S62). Next, the calculation unit 41 of the analysis device 40 derives the spatial distribution of the 180° magnetic domain width (magnetic domain width) from the magnetic domain image using line segmentation or two-dimensional Fourier transform. Methods for deriving the spatial distribution of magnetic domain width using two-dimensional Fourier transform are disclosed in Japanese Patent Application Laid-Open Nos. 2021-169655 and 2021-169979. Then, the calculation unit 41 determines, among the magnetic domain control processing lines 52 of the grain-oriented electromagnetic steel sheet 50, locations where the magnetic domain width is equal to or greater than a predetermined value (for example, 500 μm or greater) as locations to which the magnetic domain refinement process is to be applied (step S64).

[0059] In step S64, the operator may visually observe the magnetic domain image displayed on the display unit 45 of the analysis device 40 to determine the location to which the magnetic domain refinement process is to be applied, and a magnetic domain refinement signal representing the determined location may be input to the laser irradiation device 500.

[0060] Next, magnetic domain refinement is performed on the portions of the magnetic domain control treatment line 52 of the grain-oriented electrical steel sheet 50 determined in step S64 (step S66). The control unit 513 of the laser irradiation device 500 controls the laser beam LB so that it is turned on for the portions of the magnetic domain control treatment line 52 to be subjected to the magnetic domain refinement treatment, and is turned off for the other portions. As a result, thermal distortion or grooves are formed in the portions to which the magnetic domain refinement treatment has been performed.

[0061] The magnetic domain refining process of step S66 may be performed by irradiating the laser beam LB using the laser irradiation device 500 as described above, or other means such as irradiating an electron beam may be employed. In Fig. 7, the portion of the magnetic domain control process line 52 (dashed line) to which the magnetic domain refining process has been selectively (partially) applied is shown as a magnetic domain refining process line 54 (thick solid line).

[0062] Next, the relationship between the sheet thickness and iron loss of the grain-oriented electrical steel sheet 50 will be described. FIG. 8 shows the results of measuring the iron loss W17 / 50 (W / kg) for grain-oriented electrical steel sheets 50 having various sheet thicknesses t (mm) that have been selectively subjected to magnetic domain refinement treatment. The iron loss is a value measured using a 100 mm wide single sheet testing machine specified in JIS C 2556:2015. It can be seen that, assuming the sheet thickness is x and the iron loss is y, the measured value of the iron loss W17 / 50 (W / kg) is smaller than the approximate expression given by y = 1.350x + 0.450. That is, in this embodiment, the grain-oriented electrical steel sheet 50 having magnetic domain refinement treatment lines 54 on its surface satisfies W17 / 50 < 1.350t + 0.450.

[0063] Next, the magnetostriction of the grain-oriented electrical steel sheet 50 will be described. FIG. 9A shows the results of measuring the magnetostriction λ versus magnetic flux density B when an AC excitation of ±1.7 T is performed on a grain-oriented electrical steel sheet selectively irradiated with a laser (hereinafter referred to as grain-oriented electrical steel sheet 50a) and a grain-oriented electrical steel sheet uniformly irradiated with a laser over the entire surface (hereinafter referred to as grain-oriented electrical steel sheet 50b). FIG. 9B shows the results of measuring the magnetostriction λ versus magnetic flux density B when an AC excitation of ±1.9 T is performed on the grain-oriented electrical steel sheet 50a and the grain-oriented electrical steel sheet 50b. The magnetostriction is a value measured using the method specified in IEC 60404-17:2021. Here, "uniformly irradiated with a laser over the entire surface" means that the laser is uniformly irradiated over the entire magnetic domain control processing line 52.

[0064] 9A shows that the grain-oriented electrical steel sheet 50a selectively irradiated with a laser has a larger amplitude of magnetostriction λ but smaller waveform distortion than the grain-oriented electrical steel sheet 50b fully irradiated with a laser. Furthermore, as shown in FIG. 9B , when subjected to AC excitation up to a high magnetic field (±1.9 T), the grain-oriented electrical steel sheets 50a and 50b contract (the magnetostriction λ takes a negative value) and then rapidly elongate (the magnetostriction λ changes to a positive value) near ±1.9 T, but the amount of elongation is smaller for the grain-oriented electrical steel sheet 50a than for the grain-oriented electrical steel sheet 50b. This is because the grain-oriented electrical steel sheet 50a is selectively irradiated with a laser and therefore has fewer closure domains than the grain-oriented electrical steel sheet 50b fully irradiated with a laser. Therefore, the amount of closure domains that disappear when the sample is excited by applying a high magnetic field is similarly small.

[0065] Hereinafter, the peak-to-peak value of magnetostriction when AC excited up to ±1.7 T as shown in FIG. 9A will be denoted as λ1pp, and the peak-to-peak value of magnetostriction when AC excited up to ±1.9 T as shown in FIG. 9B will be denoted as λ2pp.

[0066] Fig. 10 shows the results of calculating the ratio of λ2pp to λ1pp (λ2pp / λ1pp) for 40 samples of grain-oriented electrical steel sheets 50a that were selectively irradiated with a laser and 40 samples of grain-oriented electrical steel sheets 50b that were entirely irradiated with a laser. The horizontal axis of Fig. 10 shows the sample number, with sample numbers 1 to 40 corresponding to the grain-oriented electrical steel sheets 50a and sample numbers 41 to 80 corresponding to the grain-oriented electrical steel sheets 50b.

[0067] 10 , the grain-oriented electrical steel sheet 50a has a significantly smaller λ2pp / λ1pp value than the grain-oriented electrical steel sheet 50b, and a reduction in the peak-to-peak value of magnetostriction at 1.9 T can be confirmed. Specifically, λ2pp / λ1pp for the grain-oriented electrical steel sheet 50a is less than 2.2, while λ2pp / λ1pp for the grain-oriented electrical steel sheet 50b is 2.2 or greater. That is, in this embodiment, the grain-oriented electrical steel sheet that has been selectively subjected to magnetic domain refinement treatment satisfies λ2pp / λ1pp<2.2.

[0068] As described above, according to this embodiment, in a grain-oriented electrical steel sheet that has been selectively subjected to magnetic domain refinement, the relationship between the sheet thickness t (mm) and the iron loss W17 / 50 (W / kg) satisfies W17 / 50 < 1.350t + 0.450, and the peak-to-peak ratio of magnetostriction satisfies λ2pp / λ1pp < 2.2. By providing such a grain-oriented electrical steel sheet, it is possible to minimize adverse effects such as increased hysteresis loss and deterioration of noise characteristics, and to maximize the effects of magnetic domain refinement. This makes it possible to achieve both low iron loss and low noise.

[0069] Preferably, in the grain-oriented electrical steel sheet according to this embodiment, the magnetic domain control strength is made non-uniform in the magnetic domain refinement treatment lines 54. The magnetic domain control strength is the maximum value of the tensile strength introduced by the thermal strain 541 when the magnetic domain control means is thermal strain 541, and is the maximum value of the depth of the grooves 542 when the magnetic domain control means is grooves 542.

[0070] The "maximum value of tensile strength introduced into thermal strain 541" refers to the maximum value of tensile strength measured at a single arbitrary measurement cross-section. It should be noted here that the magnitude and direction of tensile strength vary within a single measurement cross-section, and therefore, a single "maximum value of tensile strength introduced into thermal strain 541" is identified for a single measurement cross-section. As shown schematically in FIG. 13 , thermal strain 541 has a certain degree of spread across the cross-section. The tensile strength is greatest at the location directly irradiated with the laser, and is smaller at locations distant from that location. In other words, the measured tensile strength value differs for each measurement location and measurement direction on the cross-section. Using the tensile strength measurement method described below, the distribution and maximum value of tensile strength across the cross-section can be derived.

[0071] When the magnetic domain control strength is uniform, the maximum value of the tensile strength introduced into the thermal strain 541 is constant throughout the entire magnetic domain refinement treatment line 54. On the other hand, when the magnetic domain control strength is non-uniform, the maximum value of the tensile strength introduced into the thermal strain on the magnetic domain refinement treatment line is non-uniform for each tensile strength measurement point. Hereinafter, the maximum value of the tensile strength introduced into the thermal strain may be simply referred to as "tensile strength."

[0072] The "maximum depth of the groove 542" is the maximum depth of the groove 542 at one arbitrary measurement point, measured by the method described below. As shown schematically in FIG. 14, the depth of the groove 542 is also not 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 depth of the groove 542" is identified for one measurement cross section.

[0073] When the magnetic domain control strength is uniform, the maximum depth of the grooves 542 is constant across the entire magnetic domain refining process line 54. On the other hand, when the magnetic domain control strength is non-uniform, the maximum depth of the grooves 542 on the magnetic domain refining process line is non-uniform for each measurement point of the groove depth. Hereinafter, the maximum depth of the grooves 542 may be simply referred to as the "groove depth."

[0074] As described above, the magnetic domain control saturation strength is high in areas with small β angles. It is preferable to perform a magnetic domain refinement process with high magnetic domain control strength in areas with small β angles, and to perform a magnetic domain refinement process with low magnetic domain control strength in areas with large β angles. In this way, in grain-oriented electrical steel sheets that have undergone a magnetic domain refinement process that selects the optimal magnetic domain control strength depending on the size of the β angle, the magnetic domain control strength in the magnetic domain refinement processed wire 54 becomes non-uniform. In magnetic domain refinement processed wires provided in areas with large β angles, the grooves are shallow or the tensile strength induced by thermal strain is low. In magnetic domain refinement processed wires provided in areas with small β angles, the grooves are deep or the tensile strength induced by thermal strain is high. In such grain-oriented electrical steel sheets, the iron loss of the grain-oriented electrical steel sheet after magnetic domain control is further reduced. Meanwhile, the increase in hysteresis loss and the deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0075] When the magnetic domain refinement treatment line is thermally strained, the grain-oriented electrical steel sheet is σ ２ (TS ｍ ) > 5.0. ｍ is the maximum value of the tensile strength in units of MPa introduced by thermal strain, measured at each of a plurality of magnetic domain refinement points, which are the intersections of a plurality of imaginary lines set at 5 mm intervals in parallel along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment lines. ２ (TS ｍ ) is T.S. ｍ is the variance of

[0076] σ ２ (TS ｍ ) > 5.0, the magnetic domain control strength is changed based on the size of the magnetic domain width or the size of the β angle, and the increase in hysteresis loss and the deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0077] TS ｍ and σ ２ (TS ｍAn example of a method for measuring β angle σ is shown in Figure 15. The dashed lines in Figure 15 are multiple imaginary lines VL set at 5 mm intervals in parallel along the rolling direction RD of the grain-oriented electrical steel sheet. The X and O marks in Figure 15 are intersections of the imaginary lines VL and the thermal strain 541, which is the magnetic domain refinement treatment line. The β angle at the location marked with an X is 2° or more, and the β angle at the location marked with an O is less than 2°. However, σ ２ (TS ｍ ) the β angle at the intersection point does not need to be taken into account.

[0078] First, the rolling direction RD of the grain-oriented electrical steel sheet is identified. The rolling direction RD can be easily identified based on roll scratches on the surface of the grain-oriented electrical steel sheet, the extension direction of crystal grains, the extension direction of magnetic domains in a magnetic domain image, and the like. Next, imaginary lines VL are set parallel to the rolling direction RD of the grain-oriented electrical steel sheet at 5 mm intervals. Then, the intersections of the imaginary lines VL and the thermal strain 541, which is the magnetic domain refinement treatment line, are identified. If the thermal strain 541 is not visible to the naked eye, the thermal strain 541 is identified based on the magnetic domain image. Note that the shape of the measurement region is preferably a rectangle whose size along the rolling direction RD is 100 mm or more and whose size along the rolling perpendicular direction TD is 100 mm or more. One side of the rectangle is preferably parallel to the rolling direction RD.

[0079] Then, TS at all intersections of the measurement area ｍ Measure TS ｍ Variance σ ２ (TS ｍ ) is calculated. ｍ is measured using the EBSD Wilkinson method and a Cross Court manufactured by BLG Vantage. The EBSD Wilkinson method is described in detail in A. J. Wilkinson, et al., "High-resolution elastic strain measurement from electron backscatter diffraction patterns: New levels of sensitivity," Ultramicroscopy, Vol. 106, No. 4-5, March 2006, pp. 307-313.

[0080] When measuring the magnitude of the tensile strength introduced by thermal strain using the EBSD Wilkinson method and BLG Vantage's Cross Court, first, the thermal strain 541, which is the magnetic domain control treatment line, is identified using the procedure described above. Next, the grain-oriented electrical steel sheet 1 is cut through the magnetic domain control treatment line and perpendicular to the magnetic domain control treatment line. This cut surface is used as the measurement surface. The cross section of the magnetic domain control treatment line included in the measurement surface is analyzed using the EBSD Wilkinson method and BLG Vantage's Cross Court to extract tensile strength components in any direction and measure their magnitude. For example, tensile strength components can be extracted in the direction normal to the rolling surface, the direction parallel to the magnetic domain control treatment line, and the direction perpendicular to the rolling surface normal and the magnetic domain control treatment line. The maximum tensile strength value TS identified at each of the multiple measurement points Ｍ Variance σ ２ (TS Ｍ ) is derived in accordance with the method for deriving population variance described in paragraph 2.36 of JIS Z 8101-1:2015 "Statistics - Terms and symbols - Part 1: General statistical terms and terms used in probability."

[0081] Or, if the magnetic domain refinement treatment line is thermally strained, the grain-oriented electrical steel sheet is TS ｍ（β＜２） >TS ｍ（β≧２） It is preferable to satisfy the following. ｍ（β＜２） is the arithmetic mean value of the maximum tensile strength in unit MPa introduced by thermal strain, measured at each of a plurality of magnetic domain refinement points, which are the intersections of a plurality of imaginary lines set at 5 mm intervals in parallel along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment lines, and which have a β angle of less than 2°. ｍ（β≧２） is the arithmetic mean value of the maximum thermally strained tensile strength in MPa measured at each magnetic domain refinement point with a β angle of 2° or more.

[0082] TS ｍ（β＜２） >TS ｍ（β≧２）When the above condition is satisfied, the magnetic domain control strength is high where the β angle is small, and low 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, the increase in hysteresis loss and the deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0083] TS ｍ（β＜２） and T.S. ｍ（β≧２） An example of a method for measuring this is shown in Fig. 15. As described above, the X and O marks in Fig. 15 are the intersections of the virtual line VL and the thermal distortion 541, which is the magnetic domain refining treatment line. The β angle at the location marked with an X is 2° or more, and the β angle at the location marked with an O is less than 2°.

[0084] First, the β angles at the intersections are measured to identify intersections with β angles of 2° or more and intersections with β angles of less than 2°. Next, the maximum tensile strength TS is calculated for each of the intersections with β angles of 2° or more. ｍ The arithmetic mean value of these values ​​is calculated. This value is called TS ｍ（β≧２） Furthermore, at each of the intersections where the β angle is less than 2°, the maximum tensile strength TS ｍ The arithmetic mean value of these values ​​is calculated. This value is called TS ｍ（β＜２） The maximum value TS of the tensile strength introduced into the thermal strain 541 at the intersection ｍ The measurement method is as described above.

[0085] On the other hand, when the magnetic domain refinement treatment lines are grooves 542, it is preferable that the grain-oriented electrical steel sheet has a σ ２ (D ｍ ) > 3.0. ｍ is the depth of the groove 542 in μm at the magnetic domain refinement points, which are the intersections of multiple imaginary lines set in parallel at 5 mm intervals along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment lines. ２ (D ｍ ) is D ｍ is the variance of

[0086] σ ２ (D ｍ) > 3.0, the magnetic domain control strength is changed based on the size of the magnetic domain width or the size of the β angle, and the increase in hysteresis loss and the deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0087] D ｍ and σ ２ (D ｍ An example of a method for measuring the β angle is shown in Figure 16. The dashed lines in Figure 16 are multiple imaginary lines VL set at 5 mm intervals in parallel along the rolling direction RD of the grain-oriented electrical steel sheet. The X and O marks in Figure 16 are intersections of the imaginary lines VL and the grooves 542, which are magnetic domain refinement treatment lines. The β angle at the locations marked with an X is 2° or more, and the β angle at the locations marked with an O is less than 2°. However, σ ２ (D ｍ ) the β angle at the intersection point does not need to be taken into account.

[0088] First, the rolling direction of the grain-oriented electrical steel sheet is identified. Next, imaginary lines VL are set parallel to the rolling direction RD of the grain-oriented electrical steel sheet at 5 mm intervals. Then, the intersections of the imaginary lines VL and the magnetic domain refinement treatment lines are identified. When the magnetic domain refinement treatment lines are grooves 542, the magnetic domain refinement treatment lines are easily visible with the naked eye. The shape of the measurement region is preferably a rectangle whose size along the rolling direction RD is 100 mm or more and whose size along the rolling perpendicular direction TD is 100 mm or more. One side of the rectangle is preferably parallel to the rolling direction RD.

[0089] The maximum value D of the groove depth at all intersections in the measurement area ｍ The maximum groove depth D ｍ Variance σ ２ (D ｍ ) is calculated. ｍThe measurement method is as follows. Measurements are performed using a Bruker Control GT-I white light interference microscope. The lens used is a 5x objective (numerical aperture 0.12, optical resolution 2.2 μm) with an internal 1x magnification. The light source is a white LED, and the camera is a monochrome CCD (1200 x 1000 pixels). The pixel size is 1.37 μm, and after performing tilt correction by fitting to a least-squares plane using the analysis software Vision64 Map Premium 9.2, long-wavelength undulations are removed using a Gaussian filter with a cutoff value of 2.5 mm. Note that the pixel size may be resampled to 10 μm if necessary during analysis. Additionally, areas that are clearly deemed to be abnormal may be excluded from the analysis. The lens type, filter value, and correction method may be changed depending on the properties of the sample. In addition, if grooves are 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 insulating coating or the like is removed using a known method and the above measurement is carried out.

[0090] Alternatively, when the magnetic domain refinement processing lines are grooves 542, the grain-oriented electrical steel sheet is D ｍ（β＜２） >D ｍ（β≧２） It is preferable to satisfy the following. ｍ（β＜２） is the arithmetic mean value of the maximum groove depth in μm measured at each of a plurality of magnetic domain refinement points, which are the intersections of a plurality of imaginary lines VL set at 5 mm intervals in parallel along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment lines, and which have a β angle of less than 2°. ｍ（β≧２） is the arithmetic mean value of the maximum groove depth in μm measured at each magnetic domain refinement point where the β angle is 2° or more.

[0091] In a magnetic domain refinement processed wire that satisfies this formula, the magnetic domain control strength is high where the β angle is small and low where the β angle is large. Therefore, the iron loss of the grain-oriented electrical steel sheet after magnetic domain control is further reduced. At the same time, the increase in hysteresis loss and the deterioration of noise characteristics of the grain-oriented electrical steel sheet after magnetic domain control are further suppressed.

[0092] TS ｍ（β＜２） and T.S. ｍ（β≧２）An example of a method for measuring this is shown in Fig. 16. As described above, the X and O marks in Fig. 16 are the intersections of the imaginary line VL and the grooves 542, which are magnetic domain refining processing lines. The β angle at the locations marked with an X is 2° or more, and the β angle at the locations marked with an O is less than 2°.

[0093] First, by measuring the β angles at the intersections, intersections with β angles of 2° or more and intersections with β angles of less than 2° are identified. Next, D at all intersections with β angles of 2° or more is determined. ｍ The arithmetic mean value of ｍ（β≧２） Furthermore, the β angle is less than 2° at all intersection points. ｍ The arithmetic mean value of ｍ（β≧２） The maximum depth of the groove at the intersection D ｍ The measurement method is as described above.

[0094] The effects of one embodiment of the present disclosure will be explained in more detail using examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present disclosure. The present disclosure is not limited to this example of conditions. Various conditions may be adopted in the present disclosure as long as they do not deviate from the gist of the disclosure and achieve the purpose.

[0095] (1. Effect of Non-Uniformity in Magnetic Domain Control Strength) In order to evaluate the properties of grain-oriented electrical steel sheets with non-uniformity in magnetic domain control strength, the following experiments were carried out.

[0096] Grain-oriented electrical steel sheets from the same lot, classified as 23P085 in Table 2 of JIS C 2553:2019 "Grain-oriented electrical steel strip," with a thickness of 0.23 mm were used as the base sheets. Magnetic domain refinement treatment lines were formed on these sheets according to the method shown in the flowchart in Figure 6. First, magnetic domain images of the grain-oriented electrical steel sheets were acquired using an image acquisition device. Next, the spatial distribution of the 180° magnetic domain width (magnetic domain width) was derived from the magnetic domain image using the line segment method or two-dimensional Fourier transform using the calculation unit of the analysis device. Then, locations with a magnetic domain width of 500 μm or more were determined as locations to which magnetic domain refinement treatment should be applied. Furthermore, the magnetic domain control intensity was set under various conditions shown in Tables 1 and 2.

[0097] The SST iron loss W17 / 50 and λ2pp / λ1pp of the various grain-oriented electrical steel sheets Nos. A1 to A5 and B1 to B5 obtained in this manner were measured. As described above, the SST iron loss W17 / 50 is a value measured using a 100 mm wide single sheet testing machine 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 magnetostriction λ versus magnetic flux density B when the grain-oriented electrical steel sheet is excited by AC up to ±1.7 T. λ2pp is a value measured using a similar method, and as described above, is the peak-to-peak value of magnetostriction in the measurement results of magnetostriction λ versus magnetic flux density B when the grain-oriented electrical steel sheet is excited by AC up to ±1.9 T.

[0098] As a result, in all the examples disclosed in Tables 1 and 2, the conditions W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2 were satisfied.

[0099] Furthermore, the noise and transformer iron loss W16 / 50 of Nos. A1 to A5 and Nos. B1 to B5 were also evaluated. The evaluation method for noise and transformer iron loss W16 / 50 was as follows. First, a three-phase transformer core was fabricated by laminating 180 grain-oriented electrical steel sheets with a thickness of 0.23 mm. The widths of the legs and yoke of the three-phase transformer core were both 150 mm. The height and width of the external dimensions of the three-phase transformer core were both 750 mm. The noise and iron loss of these three-phase transformer cores were measured. The measurement conditions were a frequency of 50 Hz and an excitation magnetic flux density of 1.6 T.

[0100] To measure the noise, microphones were placed at equal intervals around eight locations around the transformer in which the three-phase transformer core was installed. The distance between the transformer and the microphones was 30 cm. The noise measurement results from these microphones were A-weighted corrected and averaged to obtain values, which are listed in Table 2 as the noise evaluation results (unit: dBA) of the grain-oriented electrical steel sheets. Examples with a noise evaluation result of 25.5 dBA or less were determined to be examples in which low noise was achieved.

[0101] The iron loss of the three-phase transformer was determined by measuring the voltage and current on the primary and secondary sides with a power analyzer when excitation was performed at a frequency of 50 Hz and an excitation magnetic flux density of 1.6 T, as described above. The determined iron loss is shown in Table 2 as the iron loss evaluation results (unit: W / kg) of the three-phase transformer. Examples in which the evaluation result of the transformer iron loss W16 / 50 was 0.770 W / kg or less were determined to be examples in which low iron loss was achieved.

[0102]

[0103] No. A1 satisfied the conditions W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and therefore showed better iron loss evaluation results and noise evaluation results than conventional grain-oriented electrical steel sheets.

[0104] On the other hand, No. A2 not only satisfied the conditions W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, but also the maximum tensile strength value introduced by thermal strain in the magnetic domain refinement treated wire was non-uniform at each tensile strength measurement point. The evaluation results of iron loss and noise of No. A2 were even better than those of No. A1.

[0105] No. A3 satisfies the conditions W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and also satisfies the conditions σ ２ (TS ｍ ) > 5.0. The evaluation results of iron loss and noise of No. A3 were even better than those of No. A1 and No. A2.

[0106] No. A4 satisfies W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and also satisfies TS ｍ（β＜２） >TS ｍ（β≧２） The evaluation results of iron loss and noise of No. A4 were even better than those of No. A1 and No. A2.

[0107] No. A5 satisfies the conditions W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and also satisfies the conditions σ ２ (TS ｍ ) > 5.0 and TS ｍ（β＜２） >TS ｍ（β≧２）The evaluation results for iron loss and noise of No. A5 were the best among Nos. A1 to A5.

[0108]

[0109] No. B1 satisfied the conditions W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and therefore showed better iron loss evaluation results and noise evaluation results than the conventional grain-oriented electrical steel sheets.

[0110] On the other hand, No. B2 satisfied the conditions W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and in addition, the maximum groove depth was not uniform at each measurement point of the groove. The evaluation results of iron loss and noise of No. B2 were even better than those of No. B1.

[0111] No. B3 satisfies the conditions W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and also satisfies the conditions σ ２ (D ｍ ) > 3.0. The evaluation results of iron loss and noise of No. B3 were even better than those of No. B1 and No. B2.

[0112] No. B4 satisfies W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and also satisfies D ｍ（β＜２） >D ｍ（β≧２） The evaluation results of iron loss and noise of No. B4 were even better than those of No. B1 and No. B2.

[0113] No. B5 satisfies the requirements of W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2, and also satisfies the requirements of σ ２ (D ｍ ) > 3.0 and D ｍ（β＜２） >D ｍ（β≧２） The evaluation results for iron loss and noise of No. B5 were the best among Nos. B1 to B5.

[0114] (2. Effect of magnetic domain control treatment based on magnetic domain width distribution) A manufacturing method in which the placement of magnetic domain control treatment lines is determined based on the shape of crystal grains was compared with a manufacturing method in which the placement of magnetic domain control treatment lines is determined based on the distribution of magnetic domain width.

[0115] Nos. C1 to C8 in Table 3 were manufactured using the following procedure. First, the distribution of secondary recrystallized grains was determined in grain-oriented electrical steel sheets in which secondary recrystallized grains had been formed before magnetic domain control treatment. The distribution of secondary recrystallized grains was determined by photographing the above-mentioned magnetic domain images while the steel sheet was magnetized in the rolling direction and observing the images. Then, in Examples Nos. C1 to C4, magnetic domain refinement treatment lines were formed by laser irradiation or groove formation only in regions within ±6 mm from the center of the secondary recrystallized grains in the rolling direction RD. In Examples Nos. C5 to C8, magnetic domain refinement treatment lines were formed by laser irradiation or groove formation only in regions within ±10 mm from the center of the secondary recrystallized grains in the rolling direction RD. The radius of curvature of the steel sheet at the position where the crystal grains were present during final annealing was R = 300 mm.

[0116] In Nos. C1 to C8 in Table 3, the magnetic domain refining treatment lines 54 were provided along the magnetic domain control treatment lines 52, as shown in FIG. 7. The magnetic domain control treatment lines 52 extended in a direction substantially perpendicular to the rolling direction RD. A plurality of magnetic domain control treatment lines 52 were provided repeatedly in the rolling direction. The spacing between the magnetic domain control treatment lines 52 along the rolling direction was 4 mm. In Nos. C1 to C4, the number of magnetic domain control treatment lines 52 was four. In Nos. C5 to C8, the number of magnetic domain control treatment lines 52 was six.

[0117] The SST iron loss W17 / 50 and λ2pp / λ1pp of Nos. C1 to C8 obtained by the above procedure were measured. The measurement procedure was as described above. SST iron loss W17 / 50 that did not satisfy W17 / 50<1.350t+0.450 and λ2pp / λ1pp that did not satisfy λ2pp / λ1pp<2.2 are underlined.

[0118] Furthermore, the iron loss W16 / 50 and noise of transformers No. C1 to C8 were also measured using the above-mentioned procedures. Examples with noise evaluation results of 25.5 dBA or less were judged to be examples in which low noise was achieved. Also, examples with transformer iron loss W16 / 50 evaluation results of 0.770 W / kg or less were judged to be examples in which low iron loss was achieved. The noise evaluation results and iron loss evaluation results that were judged to be unacceptable are underlined.

[0119]

[0120] As described above, for Nos. A1 to A5 and B1 to B5, in which the placement of magnetic domain refining lines was determined based on the magnetic domain width, both W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2 were satisfied. The transformer iron loss W16 / 50 and noise for Nos. A1 to A5 and B1 to B5 were judged to be acceptable.

[0121] On the other hand, in C1 to C8, in which the arrangement of the magnetic domain refining treatment lines was determined based on the shape of the crystal grains, at least one of W17 / 50<1.350t+0.450 and λ2pp / λ1pp<2.2 was not satisfied.

[0122] In Nos. C1 to C4, the number of magnetic domain control processing lines was small, so there was no significant expansion of the magnetostriction waveform. However, in Nos. C1 to C4, the iron loss could not be sufficiently suppressed, and W17 / 50 < 1.350t + 0.450 was not satisfied. The iron loss W16 / 50 of the transformers Nos. C1 to C4 was judged to be unacceptable.

[0123] Nos. C5 to C8 had a larger number of magnetic domain control processed wires, which allowed for reduced iron loss compared to Nos. C1 to C4. However, the transformer iron loss W16 / 50 of Nos. C5 to C8 was judged to be unacceptable. Furthermore, in Nos. C5 to C8, the magnetostriction waveform in high magnetic fields (near 1.9 T) due to closure domains became significantly larger, and λ2pp / λ1pp<2.2 was not met. The noise of Nos. C5 to C8 was also judged to be unacceptable.

[0124] 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 processing line 54 Magnetic domain refinement processing line 500 Laser irradiation device

Claims

1. A grain-oriented electrical steel sheet having magnetic domain refinement lines on its surface, in which the relationship between sheet thickness t (mm) and iron loss W17 / 50 (W / kg) satisfies W17 / 50 < 1.350t + 0.450, and in which, when the peak-to-peak value of magnetostriction at a magnetic flux density of 1.7 T is expressed as λ1pp, and the peak-to-peak value of magnetostriction at a magnetic flux density of 1.9 T is expressed as λ2pp, the grain-oriented electrical steel sheet satisfies λ2pp / λ1pp < 2.

2.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain refinement lines represent thermal distortion.

3. The grain-oriented electrical steel sheet according to claim 1, wherein the magnetic domain refinement lines represent grooves.

4. The grain-oriented electrical steel sheet according to claim 2, characterized in that the maximum value of the tensile strength introduced by the thermal strain in the magnetic domain refinement treatment wire is non-uniform for each measurement point of the tensile strength.

5. σ ２ (TS ｍ )>5.0, TS ｍ is the maximum value of the tensile strength in unit MPa introduced into the thermal strain, measured at each of a plurality of magnetic domain refinement points, which are the intersections of a plurality of imaginary lines set in parallel at intervals of 5 mm along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment lines, and σ ２ (TS ｍ ) is T.S. ｍ The grain-oriented electrical steel sheet according to claim 4, characterized in that the dispersion is 6. T.S. ｍ（β＜２） >T.S. ｍ（β≧２） Fulfilling the requirements, TS ｍ（β＜２） is the arithmetic average value of the maximum values ​​of the tensile strength in unit MPa introduced into the thermal strain, which are measured at each of a plurality of magnetic domain refinement points, which are intersections of a plurality of imaginary lines set at 5 mm intervals in parallel along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment line, and which have a β angle of less than 2°; and TS ｍ（β≧２） is the arithmetic mean value of the maximum values ​​of the tensile strength in unit MPa introduced into the thermal strain, measured at each of the magnetic domain refinement points where the β angle is 2° or more.

7. The grain-oriented electrical steel sheet according to claim 3, characterized in that the maximum value of the depth of the groove in the magnetic domain refinement treatment line is non-uniform for each measurement point of the groove.

8. σ ２ (D ｍ ) > 3.0, D ｍ is the maximum value of the depth of the groove in units of μm at the magnetic domain refinement points, which are the intersections of a plurality of imaginary lines set in parallel at intervals of 5 mm along the rolling direction of the grain-oriented electrical steel sheet and the magnetic domain refinement treatment lines, and σ ２ (D ｍ ) is D ｍ The grain-oriented electrical steel sheet according to claim 7, characterized in that the dispersion is 9. D ｍ（β＜２） >D ｍ（β≧２） Satisfying D ｍ（β＜２） is the arithmetic average value of the maximum groove depth in the unit of μm measured at each of a plurality of magnetic domain refinement points, which are intersections of a plurality of imaginary lines set in parallel along the rolling direction of the grain-oriented electrical steel sheet at intervals of 5 mm with the magnetic domain refinement treatment line, and which have a β angle of less than 2°; D ｍ（β≧２） is an arithmetic mean value of the maximum groove depths in unit μm measured at each of the magnetic domain subdivision points where the β angle is 2° or more.

Images