Grain-oriented electromagnetic steel sheet, method for manufacturing grain-oriented electromagnetic steel sheet, wound core, and laminated core

Abstract

Provided are: a grain-oriented electromagnetic steel sheet capable of preferably controlling the flow of magnetic flux between adjacent steel sheets when laminated; a method for manufacturing the grain-oriented electromagnetic steel sheet; and a wound core.　This grain-oriented electromagnetic steel sheet has, within a 200 μm wide region in a specific direction parallel to the surface of the steel sheet in a cross-section orthogonal to the surface of the steel sheet, a first tensile strain region and a second tensile strain region, which are two tensile strain regions into which tensile strain in the specific direction has been introduced, and a compressive strain region 12 into which compressive strain in the specific direction has been introduced. The first tensile strain region 14A and the second tensile strain region 14B are disposed with the compressive strain region 12 interposed therebetween in the specific direction, are defined by points at which the amount of compressive strain in the compressive strain region 12 is maximum, and are in a state in which the shapes of the first tensile strain region 14A and the second tensile strain region 14B and / or the distribution of the magnitudes of the amounts of tensile strain are different from each other with respect to a symmetry axis A0 extending in a direction perpendicular to the surface of the steel sheet.

Description

Directional electromagnetic steel sheet, method for manufacturing the same, wound core, and stacked core

[0001] The present invention relates to a directional electromagnetic steel sheet, a method for manufacturing the same, and a wound core.

[0002] It is known to perform magnetic domain control for introducing residual stress by scanning a laser beam linearly in a direction substantially perpendicular to the rolling direction on the surface of a grain-oriented electromagnetic steel sheet, and to control the compressive stress value and the strain interval. Thus, a technique has been known that enables the realization of a grain-oriented electromagnetic steel sheet having excellent iron loss characteristics (Patent Document 1).

[0003] Also, a directional electromagnetic steel sheet having a reflux magnetic domain in a thermal strain region extending in a direction crossing the rolling direction is known. A directional electromagnetic steel sheet is known in which the thermal strain region has maximum points of tensile strain on both outer sides in the rolling direction of the reflux magnetic domain, and the strain on both outer sides of the reflux magnetic domain is tensile strain larger than the strain at the center between the maximum points (Patent Document 2).

[0004] Japanese Patent No. 5613972 International Publication No. 2022 / 255014

[0005] However, in the technique described in Patent Document 1, in the two-dimensional distribution of residual stress in a cross section perpendicular to the sheet width direction, the residual stress is symmetrically distributed with respect to the laser irradiation position. Also in Patent Document 2, in the rolling direction, the strain is symmetrically distributed with respect to the center between the maximum points of tensile strain. In such a configuration, when grain-oriented electromagnetic steel sheets are laminated, the magnetic resistance of adjacent grain-oriented electromagnetic steel sheets is made uniform, and the flow of magnetic flux in the sheet thickness direction between adjacent grain-oriented electromagnetic steel sheets changes, resulting in a problem of increased noise.

[0006] In view of the above problems, an object of the present disclosure is to provide a directional electromagnetic steel sheet, a method for manufacturing the same, and a low-noise core that can preferably control the flow of magnetic flux in the sheet thickness direction between adjacent steel sheets when laminated.

[0007] The gist of the present disclosure is as follows.

[0008] (1) A grain-oriented electrical steel sheet having, in a cross section perpendicular to the surface of the steel sheet, a first tensile strain region and a second tensile strain region, which are two tensile strain regions in which tensile strain in the specific direction is introduced, and a compressive strain region in which compressive strain in the specific direction is introduced, wherein the first tensile strain region and the second tensile strain region are arranged with the compressive strain region in between in the specific direction, and are defined by the point where the amount of compressive strain in the compressive strain region is maximum, and at least one of the shapes of the first tensile strain region and the second tensile strain region or the distribution of the magnitude of the tensile strain is different with respect to the axis of symmetry extending perpendicular to the surface of the steel sheet.

[0009] (2) The grain-oriented electrical steel sheet described in (1) above, wherein the distance between the first perpendicular line extending perpendicularly to the surface of the steel sheet and defined by the point where the tensile strain in the first tensile strain region is maximum, and the axis of symmetry is L1 [μm], and the distance between the second perpendicular line extending perpendicularly to the surface of the steel sheet and the axis of symmetry is L2 [μm], and the larger of L1 and L2 is denoted as LL and the smaller of L2 as LS, such that the following equation (1) holds: 1.00 < LL / LS ≤ 8.00 ... (1)

[0010] (3) The grain-oriented electrical steel sheet described in (1) or (2) above, wherein the distribution width in the specific direction of the first tensile strain region is W1 [μm], and the distribution width in the specific direction of the second tensile strain region is W2 [μm], and the larger of W1 and W2 is denoted as WL and the smaller as WS, such that the following relationship (2) holds: 1.00 < WL / WS < 5.00 ... (2)

[0011] (4) The grain-oriented electrical steel sheet described in (1) to (3) above, wherein the distribution width perpendicular to the surface of the steel sheet in the first tensile strain region is T1 [μm], and the distribution width perpendicular to the surface of the steel sheet in the second tensile strain region is T2 [μm], and the larger of T1 and T2 is denoted as TL and the smaller as TS, such that the following relationship (3) holds: 1.00 < TL / TS ≤ 5.82 ... (3)

[0012] (5) The grain-oriented electrical steel sheet according to any one of (1) to (4) above, wherein the specific direction is parallel to the surface of the steel sheet and parallel to the boundary between adjacent 180° magnetic domains of the grain-oriented electrical steel sheet.

[0013] (6) The grain-oriented electrical steel sheet according to any one of (1) to (5) above, wherein the distribution width T1 [μm] perpendicular to the surface of the steel sheet in the first tensile strain region and the distribution width T2 [μm] perpendicular to the surface of the steel sheet in the second tensile strain region are 1 / 4 or less of the thickness of the steel sheet.

[0014] (7) A method for manufacturing a grain-oriented electrical steel sheet according to any one of (1) to (6) above, wherein a laser or electron beam is irradiated onto the surface of the grain-oriented electrical steel sheet in a direction intersecting the specific direction to form the first tensile strain region, the second tensile strain region and the compressive strain region.

[0015] (8) A wound core in which a grain-oriented electrical steel sheet described in any of (1) to (6) above is wound, wherein the specified direction is the winding direction.

[0016] (9) A laminated core comprising grain-oriented electrical steel sheets as described in any of (1) to (6) above, wherein the specific direction is the excitation direction.

[0017] This disclosure provides grain-oriented electrical steel sheets, a method for manufacturing grain-oriented electrical steel sheets, and a wound core, which are capable of favorably controlling the flow of magnetic flux between adjacent steel sheets when they are laminated.

[0018] This diagram schematically shows the arrangement of strain regions in a cross-section perpendicular to the surface of a grain-oriented electrical steel sheet according to this embodiment. This is a schematic diagram showing the observation method. This is a schematic diagram for explaining a specific direction of the grain-oriented electrical steel sheet. This is a perspective view of a steel sheet, schematically showing how the tensile strain region and the compressive strain region are arranged to extend in a direction intersecting a specific direction. This diagram shows how a laser is irradiated onto the outer surface (convex surface) of a steel sheet bent with a specific curvature along a specific direction. This diagram shows a wound core and its dimensions. This diagram shows a stacked core and its dimensions.

[0019] Several embodiments of the present invention will be described below with reference to the drawings. However, these descriptions are intended to be merely illustrative of preferred embodiments of the present invention and are not intended to limit the present invention to such specific embodiments. In the following description, similar components will be given the same reference numerals.

[0020] The following describes in detail a grain-oriented electrical steel sheet according to one embodiment of the present invention. The grain-oriented electrical steel sheet according to one embodiment of the present invention can be applied to various forms such as wound cores and stacked cores. When applied to these cores, the excitation direction of the core may be the rolling direction of the steel sheet. The excitation direction of the core may also be the {110}<001> direction of the steel sheet. The rolling direction of the steel sheet may also be the {110}<001> direction of the steel sheet.

[0021] The present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible without departing from the spirit of the invention. The numerical limits described below include both lower and upper limits. Values ​​indicated as "greater than" or "less than" are not included in the numerical range. Furthermore, "%" in relation to chemical composition means "mass percent" unless otherwise specified.

[0022] Furthermore, terms such as "parallel," "perpendicular," "identical," and "right-angled," as well as values ​​for length and angle, used in this specification to specify shapes, geometric conditions, and their degrees, shall not be strictly interpreted, but shall be interpreted to include a range that can be expected to perform similar functions.

[0023] Furthermore, in this specification, "grain-oriented electrical steel sheet" may also be referred to simply as "steel sheet" or "electrical steel sheet."

[0024] A grain-oriented electrical steel sheet 1 according to one embodiment of the present invention will now be described. The thickness of the grain-oriented electrical steel sheet 1 used in this embodiment is not particularly limited and can be appropriately selected according to the application, etc., but is usually in the range of 0.15 mm to 0.35 mm, and preferably in the range of 0.18 mm to 0.27 mm.

[0025] Figure 1 is a schematic diagram showing the arrangement of strain regions in a cross-section perpendicular to the surface of a grain-oriented electrical steel sheet 1 according to this embodiment. As shown in Figure 1, the steel sheet is provided with a compressive strain region 12 in which compressive strain is introduced in a specific direction parallel to the surface of the steel sheet, and tensile strain regions 14A and 14B in which tensile strain is introduced in a specific direction. Hereafter, when describing the state of strain in the field of view of Figure 1, the direction parallel to the surface of the steel sheet will be described as the "specific direction". The distribution width of the tensile strain regions 14A and 14B in the thickness direction of the steel sheet is 1 / 4 or less of the thickness of the steel sheet. The method of introducing tensile strain and compressive strain unique to this embodiment into the steel sheet will be described in detail later.

[0026] The amount of strain in the compressive strain region 12 and the tensile strain regions 14A and 14B of the steel sheet 1 is determined as follows: A strain-free cross-section is prepared by ion milling, in which an argon ion beam is irradiated onto the cross section of the grain-oriented electrical steel sheet in a specific direction at an irradiation angle ranging from 0° to 90°, and an observation sample is obtained. Observation is performed on this cross section. The observation is performed by EBSD (Electron Back Scattered Diffraction) using a FE-SEM (Field Emission Scanning Electron Microscope).

[0027] Observation can be performed by using a rectangular pixel as shown in Figure 2 and measuring the relevant area. The probe diameter will be set to 10 nm and measurements will be taken in 1 μm steps. The dashed lines shown in Figure 2 pass through the center of each pixel. Since each pixel is 1 μm × 1 μm in size, measurements will be taken in 1 μm steps. This measurement will yield a Kikuchi pattern for each measurement point in 1 μm steps. The measurement will be taken over a 200 μm area in a specific direction, and the entire thickness of the plate will be observed in the plate thickness direction. In other words, the observation area is a 200 μm wide area in a specific direction parallel to the surface of the steel plate 1, in a cross section perpendicular to the surface of the steel plate 1.

[0028] Next, the amount of strain is determined from the Kikuchi pattern data obtained above using the EBSD-Wilkinson method. For this EBSD-Wilkinson method, we use analysis software called "CrossCourt" manufactured by TSL Solutions Co., Ltd. The software is used to set the analysis conditions. First, BCC iron is specified as the material to determine the Young's modulus. The software is also set to single crystal. To calculate the strain tensor, the measured shift value is set to 20. Finally, the amount of strain is calculated from the deformation amount of the Kikuchi pattern at each point, but it is necessary to correct the amount of strain at each point by defining a reference point (temporary reference point) where no deformation has occurred using the following procedure.

[0029] First, an arbitrary point in the center of the observation area in the thickness direction is designated as a provisional reference point, excluding grain boundaries where the orientation difference between adjacent pixels is 5° or more. Next, the distribution of strain magnitude is profiled along a straight line drawn from that point in the thickness direction. Finally, the amount of strain at the aforementioned provisional reference point is evaluated from the obtained strain distribution, and the strain amounts at each point are corrected so that the strain at this point becomes zero. The present invention is defined by the strain amounts at each point obtained in this way. Preferably, a provisional reference point with a strain amount close to zero is found, and then the strain amounts at each point are corrected so that the strain at this point becomes zero.

[0030] Furthermore, by following the procedure below, a total of three regions are identified: one compressive strain region 12 along a specific direction (X direction) as shown in Figure 1, and one tensile strain region 14A and 14B on both sides of the compressive strain region 12 in that specific direction (on both sides of the symmetry axis A0, which will be described later).

[0031] First, within the observation area, the compressive strain region 12 and the tensile strain regions 14A and 14B are identified. The compressive strain region is an area where measurement points with a compressive strain of 0.0004 or more in a specific direction are consecutive. Similarly, the tensile strain region is an area where measurement points with a tensile strain of 0.0004 or more in a specific direction are consecutive. It should be noted here that "consecutive" refers to a situation where two measurement points with a strain of 0.0004 or more are adjacent in the plate thickness direction or a specific direction. In other words, in an oblique direction (±45° from the plate thickness direction), even if two measurement points with a strain of 0.0004 or more are adjacent, they are not considered consecutive.

[0032] If multiple compressive strain regions exist within the observation area, the region with the largest area among the compressive strain regions shall be defined as the compressive strain region 12 in this disclosure. If there are multiple compressive strain regions with the largest area and the same area, the compressive strain region with the largest maximum width in a specific direction among the multiple compressive strain regions shall be defined as the compressive strain amount region 12 in this disclosure. If there are multiple compressive strain regions with the largest area and the same area, and there are multiple compressive strain regions with the same maximum width in a specific direction among the multiple compressive strain regions, the compressive strain region with the largest maximum width in the plate thickness direction among them shall be defined as the compressive strain amount region 12 in this disclosure. Furthermore, if multiple tensile strain regions exist within the observation area, the two tensile strain regions with the largest areas shall be selected in order and defined as the tensile strain regions 14A and 14B in this disclosure. If there are multiple tensile strain regions with the same area, the tensile strain region with the largest maximum width in a specific direction among the multiple tensile strain regions shall be selected and defined as the tensile strain regions 14A and 14B in this disclosure. In that case, if there are multiple tensile strain regions with the same maximum width in a particular direction, the tensile strain region with the largest maximum width in the plate thickness direction is given priority, and two tensile strain regions are selected, which are defined as tensile strain regions 14A and 14B in this disclosure. Such regions are easily observed, for example, directly beneath a magnetic domain control unit such as a laser irradiation or electron beam. Below, the arrangement and morphological features of the compression strain region 12 and tensile strain regions 14A and 14B, which are the greatest features of the present invention, will be described.

[0033] As shown in Figure 1, let O be the point in the compressive strain region 12 where the amount of compressive strain is maximum. Draw a straight line in the thickness direction passing through point O and define it as the axis of symmetry A0. If there are multiple points where the amount of compressive strain is maximum, define the position of the leftmost point in a particular direction within the compressive strain region 12 as the origin of that direction, and calculate the distance from the origin to each point where the amount of compressive strain is maximum along that direction. Then, set the axis of symmetry A0 at a position that is the average distance from the origin to each point along that direction. Tensile strain regions 14A and 14B exist on both sides of the axis of symmetry A0 in the particular direction, and the strain distribution in each tensile strain region 14A and 14B is asymmetrical with respect to the axis of symmetry A0.

[0034] In Figure 1, of the left and right tensile strain regions 14A and 14B, the left tensile strain region 14A is designated as the first tensile strain region, and the right tensile strain region 14B is designated as the second tensile strain region. Here, asymmetry means that in a specific direction, with respect to the axis of symmetry A0 as the central axis, at least one of the shapes or distributions of the magnitude of the tensile strain between the first tensile strain region and the second tensile strain region is different.

[0035] More specifically, let O1 and O2 be the points where the tensile strain is maximum in the two tensile strain regions 14A and 14B, i.e., the first tensile strain region and the second tensile strain region, respectively. Draw lines A1 and A2 in the thickness direction passing through points O1 and O2. If we let LL be the larger of the distances L1 and L2 from the axis of symmetry A0 to lines A1 and A2, and LS be the smaller of the two distances, then the following relationship (1) holds. If there are multiple points in each region where the tensile strain is maximum, define the position of the leftmost point in a particular direction in the tensile strain regions 14A and 14B as the origin in that direction, and find the distance from the origin to each point where the tensile strain is maximum along that direction. Then, set lines A1 and A2 at a position that is the average distance from the origin to each point along that direction. The upper limit of equation (1) is preferably 4.0, more preferably 3.5. The lower limit of equation (1) is preferably 1.3, more preferably 2.0. 1.00 < LL / LS ≤ 8.00 ... (1) The strain distribution in the tensile strain regions 14A and 14B is asymmetrical with respect to the axis of symmetry A0, specifically satisfying equation (1), which makes it possible to favorably control the flow of magnetic flux between adjacent steel plates when they are stacked, and improve the flow of magnetic flux between the steel plates.

[0036] Furthermore, for the two tensile strain regions 14A and 14B, if we denote the larger of the distribution widths W1 and W2 in a specific direction shown in Figure 1 as WL and the smaller as WS, the following relationship (2) holds. The upper limit of equation (2) is preferably 3.8, and more preferably 3.3. The lower limit of equation (2) is preferably 1.2, and more preferably 1.8. 1.00 < WL / WS ≤ 5.00 ... (2) By satisfying equation (2) in the strain distribution of the tensile strain regions 14A and 14B, it becomes more difficult for magnetic flux to pass from the surface of the steel plate to adjacent steel plates when they are laminated, thereby improving the flow of magnetic flux between the steel plates.

[0037] Furthermore, for the two tensile strain regions 14A and 14B, if we denote the larger of the distribution widths T1 and T2 in the thickness direction shown in Figure 1 as TL and the smaller as TS, the following relationship (3) holds. The upper limit of equation (3) is preferably 3.8, and more preferably 3.3. The lower limit of equation (3) is preferably 1.3, and more preferably 1.5. 1.00 < TL / TS ≤ 5.82 ... (3) By satisfying equation (3) in the strain distribution of the tensile strain regions 14A and 14B, magnetic flux can be less likely to leak to the surface of the steel plates when they are laminated, and magnetic flux can be less likely to transfer to adjacent steel plates, thereby improving the flow of magnetic flux between steel plates.

[0038] As described above, in this embodiment, the distribution of strain in the tensile strain regions 14A and 14B is asymmetrical with respect to the axis of symmetry A0. This configuration suppresses noise generation when the steel plates 1 are magnetized in a stacked state. The reason for this is not clear, but the noise of the iron core is partly caused by vibrations of the steel plates in the thickness direction due to the flow of magnetic flux in the thickness direction within the steel plates. It is thought that the asymmetrical tensile strain region suppresses the thickness-direction component of the magnetic flux within the steel plates, which in turn suppresses vibrations of the steel plates in the thickness direction. It should be noted that this is merely a hypothesis at present to theoretically support an empirical rule discovered by the inventors through diligent research. We hope that the academically correct mechanism will be elucidated in the future. Although the relationship between the strain region and the maximum strain amount is not described in detail in this invention, it can be said that as the strain region expands, the absolute amount of strain at the point of maximum strain within it generally tends to increase.

[0039] Figure 3 is a schematic diagram illustrating an example of a characteristic specific direction of grain-oriented electrical steel sheet 1. Figure 3 shows a rectangular steel sheet 1 as viewed from the surface (a plan view of the steel sheet). The specific direction, which will be explained in detail later, is a direction determined based on, for example, the boundary 20 of adjacent magnetic domains of the steel sheet. For example, in the case of a typical grain-oriented electrical steel sheet, the specific direction may be the rolling direction of the steel sheet or the {110}<001> direction. As mentioned above, the use of grain-oriented electrical steel sheet 1 is not limited to constructing wound cores, but when constructing a wound core using grain-oriented electrical steel sheet 1, the wound core may be constructed such that the specific direction is the winding direction of the wound core. Also, when constructing a stacked core using grain-oriented electrical steel sheet 1, the specific direction generally coincides with the longitudinal direction of the grain-oriented electrical steel sheet 1 (the excitation direction of the stacked core).

[0040] The magnetic domains of the grain-oriented electrical steel sheet in this embodiment generally consist mainly of 180° magnetic domains arranged in parallel. In this case, an example of a specific direction in the present invention can also be identified in such a region where 180° magnetic domains are arranged in parallel. In Figure 3, the specific direction is the direction parallel to the boundary 20 of the 180° magnetic domains.

[0041] For the determination of the above characteristic specific direction, for example, the magnetic domains of a steel plate are observed from the steel plate surface using CMOS-MAGVIEW, TYPE XL, sensor type: TYPE A, measurement area 58.5MM X43.5MM, 10MPX resolution 30μm, manufactured by MATESY GMB. And as shown in FIG. 3, the boundary 20 of the 180° magnetic domains existing in the steel plate can be observed. For a general directionality electromagnetic steel plate, if an area of about 10 mm square is observed, it is divided into several parts by 180° magnetic domains, and the linear and parallel magnetic domain boundaries 20 can be observed.

[0042] Next, an example of the distribution situation in the direction perpendicular to the specific direction within the plate surface of the two types of strain regions in the present embodiment will be described. FIG. 4 is a perspective view of a steel plate, schematically showing a state in which the compressive strain region 12 and the tensile strain regions 14A and 14B are provided so as to extend in a direction intersecting the specific direction. Alternatively, the compressive strain region 12 and the tensile strain regions 14A and 14B may be provided intermittently without extending in the direction intersecting the specific direction. The compressive strain region 12 and the tensile strain regions 14A and 14B preferably extend in a direction forming an angle of 60 to 120° with respect to the specific direction in the field of view in the direction perpendicular to the surface of the steel plate. More preferably, they are extended in a direction forming an angle of 80 to 110°.

[0043] Further, the combination of the compressive strain region 12 and the two tensile strain regions 14A and 14B is periodically provided at a pitch of several millimeters, for example, a pitch of about 3 mm to 8 mm, in the specific direction. FIG. 4 shows an example in which the combination of the compressive strain region 12 and the two tensile strain regions 14A and 14B is provided at a pitch of 5 mm in the specific direction.

[0044] In the method for manufacturing the directionality electromagnetic steel plate 1 according to the present embodiment, it is characterized in that the steel plate surface is irradiated with high-energy rays twice during the manufacturing process of the steel plate. In the first irradiation, the above-mentioned distances L1 and L2 are controlled by the beam diameter and the radius of curvature, and in the second irradiation, the distribution widths W1 and W2 of the above-mentioned specific direction are controlled by the beam diameter and the radius of curvature, and in the second irradiation, the distribution widths T1 and T2 in the plate thickness direction are controlled by the energy density Ua, the line speed, and the temperature.

[0045] Other conditions are not particularly limited, and a conventionally well-known method for manufacturing a grain-oriented electrical steel sheet can be appropriately selected. Preferred specific examples of the manufacturing method include, for example, setting C to 0.040 to 0.100% by mass, heating a slab having the chemical composition of the above grain-oriented electrical steel sheet to 1000°C or higher and performing hot rolling, then performing hot-rolled sheet annealing as necessary, and then making it into a cold-rolled steel sheet by cold rolling one or two or more times with an intermediate annealing interposed therebetween. The cold-rolled steel sheet is heated to 700 to 900°C in a wet hydrogen-inert gas atmosphere for decarburization annealing, and if necessary, further nitriding annealing is performed. After applying an annealing separating agent, finish annealing is performed at about 1100°C, an insulating film is formed at about 900°C, and then, if necessary, a tension film is formed.

[0046] In the present embodiment, irradiation with high-energy rays for controlling the amount of strain of the grain-oriented electrical steel sheet may be performed on the steel sheet on which the insulating film has been formed in the above-described conventionally well-known process. The insulating film may include either or both of a tension film and an oxide film. Examples of the high-energy rays include a laser and an electron beam. Hereinafter, the high-energy rays will be described as a laser, but the same control is possible even with high-energy rays different from a laser such as an electron beam. Although the control range may be somewhat different, it is not difficult for those skilled in the art who routinely use these high-energy rays as means for magnetic domain control to appropriately adjust them.

[0047] First, in the first irradiation, the laser is irradiated not onto a flat surface, but onto the outer surface (convex surface) of a steel plate bent with a specific curvature along a specific direction. For example, as shown in Figure 5, the steel plate is transported by winding it from the original coil 24 to the winding coil 26, and a convex surface with a larger radius of curvature than that of the coiled state is formed between the two coils, and the laser is irradiated. At this time, the beam diameter is preferably 60 μm to 380 μm, and the radius of curvature of the steel plate irradiation surface is preferably 251 mm to 30,000 mm. This makes it possible to control the distances L1 and L2 from the axis of symmetry A0 to the perpendiculars A1 and A2, respectively. If the beam diameter is less than 60 μm, the energy is too concentrated, and the adverse effects of thermal strain itself become stronger along with the manifestation of the magnetic domain control effect. Also, if the beam diameter exceeds 380 μm, the energy is too dispersed, and the magnetic domain control effect does not manifest. If the radius of curvature of the irradiated surface is 250 mm or less, the inclination of the steel plate surface in the specific direction to which the beam is irradiated is too large, resulting in excessively uneven (asymmetrical) formation of the heat-affected zone in that specific direction, and consequently, the difference between distances L1 and L2 becomes too large. If the radius of curvature of the irradiated surface is 30,000 mm or more, conversely, the inclination of the steel plate surface in that specific direction is too small, resulting in the same effect as irradiating a flat surface. When a laser is irradiated onto a convex surface, the formation of the heat-affected zone can be asymmetrical in a specific direction, causing the distances L1 and L2 to the tensile strain regions 14A and 14B to change asymmetrically.

[0048] Next, a second laser irradiation is performed. For the second irradiation, the laser is again directed not to a flat surface, but to the outer surface (convex) of a steel plate bent with a specific curvature. At this time, the beam diameter is set to 300 μm to 450 μm, and the radius of curvature of the irradiation surface is set to 150 mm to 600 mm. This makes it possible to control the distribution widths W1 and W2 in specific directions. If the beam diameter is less than 300 μm, the energy is too concentrated, causing a significant change in the already introduced strain distribution, as well as increasing the number of areas negatively affected by the strain. If the beam diameter exceeds 450 μm, the energy is too dispersed, so it does not significantly affect the already introduced strain distribution. If the radius of curvature of the irradiation surface is less than 150 mm, either W1 or W2 becomes excessively long, falling outside the optimal range. If the radius of curvature of the irradiation surface exceeds 600 mm, W1 and W2 become equal due to the inclination and the thermal effects of the beam. As mentioned above, irradiating a convex surface allows for the formation of a heat-affected zone asymmetrically in a specific direction, resulting in an asymmetrical change in the distribution width of the tensile strain region in that specific direction. Irradiating the same region twice allows for optimal control of the shape of the already formed heat-affected zone and thus control of the strain distribution, resulting in an asymmetrical change in the distribution width of the tensile strain region in that specific direction.

[0049] Furthermore, with the second irradiation, the energy density Ua was increased to 0.5 mJ / mm². ２ ~2.2 mJ / mm ２ The line speed is set to 50 m / min to 200 m / min, and the temperature of the steel plate when irradiated is set to -20°C to 20°C. This makes it possible to control T1 and T2. The energy density Ua is 0.5 mJ / mm². ２ Below this value, the energy introduced in the thickness direction of the plate is weak, making it impossible to set the distribution widths T1 and T2 to the optimal depth. Energy density Ua is 2.2 mJ / mm². ２If the line speed exceeds a certain value, the energy introduced in the thickness direction of the plate becomes too strong, making it impossible to set the distribution widths T1 and T2 to the optimal depth. If the line speed is less than 50 m / min, the heat introduction due to irradiation becomes too large, so plastic deformation due to thermal strain becomes significant, and noise tends to worsen. If the line speed exceeds 200 m / min, the heat introduction due to irradiation becomes too small, making it impossible to set the distribution widths T1 and T2 to the optimal depth. If the steel plate temperature is below -20°C, the range of rapid cooling after heat introduction due to irradiation becomes wide, and a lot of strain that negatively affects noise is introduced. If the steel plate temperature exceeds 20°C, the range of rapid cooling after heat introduction due to irradiation becomes too narrow, so it no longer affects the strain distribution. When irradiating a convex surface, as mentioned above, the formation of the heat-affected zone can be asymmetrical in a specific direction, so the distances L1 and L2 to the tensile strain regions 14A and 14B change asymmetrically. By irradiating the same region twice, it becomes possible to control the width and depth of the tensile strain, resulting in an asymmetrical change in the distances L1 and L2 to the tensile strain regions 14A and 14B.

[0050] Here, the irradiation position for the first and second irradiations must be the same. This is because irradiating the same location twice under the above conditions changes the characteristic shape of the strained region in this embodiment. Between the first and second irradiations, necessary steps may be taken as long as the temperature of the steel plate is 500°C or less. For example, a tension film may be formed after the first irradiation, and then the second irradiation may be performed.

[0051] The grain-oriented electrical steel sheets according to this embodiment can be applied to wound cores and stacked cores, but here we will describe an example of application to a wound core. In this embodiment, a wound core composed of grain-oriented electrical steel sheets 1 having the above configuration is formed by stacking individually bent grain-oriented electrical steel sheets 1 in layers and assembling them into a wound shape, with multiple grain-oriented electrical steel sheets 1 connected to each other via at least one joint in each winding.

[0052] Before cutting the grain-oriented electrical steel sheet 1, or during the bending process after cutting the grain-oriented electrical steel sheet 1, high-energy ray irradiation may be performed on the grain-oriented electrical steel sheet 1 to control the tensile strain regions 14A, 14B and the compressive strain region 12.

[0053] In the resulting wound core, the radius of curvature on the inside of the bend in the bent section, where the bending process creates a bend perpendicular to the winding direction, becomes extremely small, resulting in a significant noise reduction effect when applying the grain-oriented electrical steel sheet of this embodiment. The effect is particularly pronounced when the radius of curvature of the bent section is 5 mm or less. This is thought to be because the area where the strain introduced into the steel sheet by beam irradiation and the plastically deformed area of ​​the bent section overlap becomes smaller. The structure of the wound core in which the effect is pronounced can be any, for example, that conforms to the description in Japanese Patent Application No. 2020-178904.

[0054] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure.

[0055] The present disclosure will be specifically explained below with reference to examples of embodiments. The conditions in the embodiments are merely examples adopted to confirm the feasibility and effectiveness of the present disclosure, and the present disclosure is not limited to the conditions in the embodiments. The present disclosure may adopt various conditions as long as they do not depart from its essence and achieve its objectives.

[0056] Table 1 shows the chemical composition in mass percent of the slab used to manufacture grain-oriented electrical steel sheet 1. In this example, two types of steel, steel grade A and steel grade B, as shown in Table 1, were used.

[0057]

[0058] Table 2 also shows the chemical composition of grain-oriented electrical steel sheet 1 in its final product state, expressed in mass percent.

[0059]

[0060] Table 3 shows the manufacturing process conditions for the manufactured steel plates No. A and No. B.

[0061]

[0062] Then, wound cores and stacked cores were manufactured from the steel plates shown in Table 3. Detailed dimensions of the wound cores and stacked cores are shown in Figures 6 and 7 and Table 4. Figure 6 shows the wound core 10 and its dimensions. Figure 7 shows the stacked core 30 and its dimensions. In Table 4, core No. a is a wound core and core No. b is a stacked core. Note that Figures 6 and 7 schematically show the shapes of the wound core 10 and stacked core 30, and their shapes do not strictly match the dimensions listed in Table 4. The dimensions of the wound core 10 and stacked core 30 are specified by the values ​​listed in Table 4.

[0063]

[0064] Then, the fabricated wound iron core was evaluated. The results are shown in Tables 5 and 6 below.

[0065]

[0066]

[0067] Note that LL / LS, WL / WS, and TL / TS in Table 6 correspond to LL / LS in equation (1), WL / WS in equation (2), and TL / TS in equation (3), respectively. In the evaluation in Table 6, the invention is defined as having a noise level of less than 55 dBA, and the comparative example is defined as having a noise level of 55 dBA or higher. In the noise evaluation, the noise of the core was measured in an anechoic chamber with an ambient noise level of 16 dBA, with a sound level meter placed 0.3 m away from the surface of the core, and A-weighting was used as the auditory correction. At that time, the core was excited with an excitation frequency of 50 Hz so that the magnetic flux density inside the core was 1.7 T.

[0068] 1. Grain-oriented electrical steel sheet 12. Compression strain region 14A, 14B 20. Tensile strain region 20. Boundary

Claims

1. A grain-oriented electrical steel sheet comprising, in a cross section perpendicular to the surface of the steel sheet, a first tensile strain region and a second tensile strain region, which are two tensile strain regions in which tensile strain in the specific direction is introduced, and a compressive strain region in which compressive strain in the specific direction is introduced, wherein the first tensile strain region and the second tensile strain region are arranged with the compressive strain region in between in the specific direction, and are defined by the point where the amount of compressive strain in the compressive strain region is maximum, and at least one of the shapes or the distribution of the magnitude of tensile strain of the first tensile strain region and the second tensile strain region is different with respect to the axis of symmetry extending perpendicular to the surface of the steel sheet.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the distance between the first perpendicular line extending perpendicularly to the surface of the steel sheet and the axis of symmetry is defined by the point where the tensile strain in the first tensile strain region is maximum, and L1 [μm], and the distance between the second perpendicular line extending perpendicularly to the surface of the steel sheet and the axis of symmetry is defined by the point where the tensile strain in the second tensile strain region is maximum, and L2 [μm], and the larger of L1 and L2 is denoted as LL and the smaller as LS, such that the following equation (1) holds: 1.00 < LL / LS ≤ 8.00 ... (1) 3. The grain-oriented electrical steel sheet according to claim 1, wherein the distribution width in the specific direction of the first tensile strain region is W1 [μm], and the distribution width in the specific direction of the second tensile strain region is W2 [μm], and the larger of W1 and W2 is denoted as WL and the smaller as WS, such that the following relationship (2) holds: 1.00 < WL / WS ≤ 5.00 ... (2) 4. The grain-oriented electrical steel sheet according to claim 1, wherein the distribution width perpendicular to the surface of the steel sheet in the first tensile strain region is T1 [μm], and the distribution width perpendicular to the surface of the steel sheet in the second tensile strain region is T2 [μm], and the larger of T1 and T2 is denoted as TL and the smaller as TS, such that the following relationship (3) holds: 1.00 < TL / TS ≤ 5.82 ... (3) 5. The grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the specific direction is parallel to the surface of the steel sheet and parallel to the boundary between adjacent 180° magnetic domains of the grain-oriented electrical steel sheet.

6. The grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the distribution width T1 [μm] perpendicular to the surface of the steel sheet in the first tensile strain region and the distribution width T2 [μm] perpendicular to the surface of the steel sheet in the second tensile strain region are 1 / 4 or less of the thickness of the steel sheet.

7. A method for manufacturing a grain-oriented electrical steel sheet according to any one of claims 1 to 4, comprising irradiating the surface of the grain-oriented electrical steel sheet with a laser or electron beam along a direction intersecting the specific direction to form the first tensile strain region, the second tensile strain region and the compressive strain region.

8. A wound core comprising a grain-oriented electrical steel sheet as described in any one of claims 1 to 4, wherein the specific direction is the winding direction.

9. A laminated core comprising grain-oriented electrical steel sheets according to any one of claims 1 to 4, wherein the specific direction is the excitation direction.

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