Groove processing method for grain-oriented electromagnetic steel sheet, groove processing device for grain-oriented electromagnetic steel sheet, grain-oriented electromagnetic steel sheet, wound iron core, and method for manufacturing wound iron core

Abstract

This groove processing method for a grain-oriented electromagnetic steel sheet is to be used for performing groove processing on the surface of a grain-oriented electromagnetic steel sheet, wherein: the groove processing method comprises a first irradiation step for irradiating the surface of the grain-oriented electromagnetic steel sheet with a first beam under a first irradiation condition with which it is possible to form a linear groove extending in a direction corresponding to the plate width direction of the grain-oriented electromagnetic steel sheet, and a second irradiation step for irradiating the surface of the grain-oriented electromagnetic steel sheet with a second beam along the groove and under a second irradiation condition different from the first irradiation condition; the grain-oriented electromagnetic steel sheet is subjected to final finish annealing; and the second irradiation condition corresponds to a heat treatment condition with which it is possible to apply a predefined heat treatment to a steel sheet portion of the grain-oriented electromagnetic steel sheet, the steel sheet portion being within a prescribed range from the surface of the groove.

Description

Groove processing method for grain-oriented electromagnetic steel sheet, groove processing device for grain-oriented electromagnetic steel sheet, grain-oriented electromagnetic steel sheet, wound iron core, and method for manufacturing wound iron core

[0001] The present disclosure relates to a groove processing method for grain-oriented electromagnetic steel sheets, a groove processing device for grain-oriented electromagnetic steel sheets, grain-oriented electromagnetic steel sheets, wound iron cores, and methods for manufacturing wound iron cores.

[0002] One example of a method for manufacturing grain-oriented electrical steel sheet includes a casting process, a hot rolling process, an annealing process, a cold rolling process, a decarburization annealing process, an annealing and separating coating process, a final annealing process, an insulating coating forming process, a groove forming process, and an insulating coating re-forming process. In the groove forming process, periodic grooves are formed in the grain-oriented electrical steel sheet using a laser beam, and in the insulating coating re-forming process, a tension-applying coating is formed, thereby subdividing the magnetic domains of the grain-oriented electrical steel sheet.

[0003] Although the above manufacturing method requires two steps of forming an insulating coating, namely, an insulating coating forming step and a re-insulating coating forming step, it is excellent in terms of the stability of iron loss improvement and prevention of adhesion of melted and removed materials. However, when a wound core of a transformer is manufactured from grain-oriented electrical steel sheet manufactured by the above manufacturing method, there is a problem that iron loss deteriorates in the stress relief annealing step performed after the winding of the grain-oriented electrical steel sheet. This problem is thought to occur because subgrain boundaries are generated around the grooves during the stress relief annealing step due to distortions generated around the grooves when the grooves are formed by a laser beam.

[0004] Therefore, the following techniques have been proposed as measures to suppress the deterioration of iron loss in the stress relief annealing process. For example, Japanese Patent No. 7031364 (Patent Document 1) describes a method of suppressing the occurrence of subgrain boundaries by performing heat treatment in which the steel sheet is heated to 1000°C or higher and 1100°C or lower after the groove formation process. Furthermore, Japanese Patent No. 6614398 (Patent Document 2) describes a method of suppressing the occurrence of subgrain boundaries by adjusting the cooling rate in the insulating coating re-formation process to set the KAM (Kernel Average Misorientation) value around the groove to 0.1 or higher and 3.0 or lower. Furthermore, International Publication No. 2022 / 045264 (Patent Document 3) describes a method of suppressing the deterioration of iron loss in the groove formation process by linearly irradiating the surface of the steel sheet with a laser beam that has a ring-shaped intensity distribution that is lower at the periphery than at the center in a direction intersecting with the rolling direction.

[0005] Japanese Patent Laid-Open Publication No. 2012-126995 (Patent Document 4) discloses a method for introducing thermal strain by irradiating the surface of a grain-oriented electrical steel sheet that has been final-annealed with an electron beam in multiple rounds to perform magnetic domain refinement treatment. International Publication No. 2024 / 111642 (Patent Document 5) also discloses a groove formation process between a cold rolling process and a final annealing process, which includes a first stage in which a laser beam is irradiated onto the surface of the steel sheet to form grooves on the surface of the steel sheet and protrusions are formed on the side or bottom of the grooves, and a method in which a laser beam is irradiated onto the same locations as those irradiated with the laser beam in the first stage subsequent to the first stage, thereby setting the misorientation between the average crystal orientation of the protrusions and the Goss orientation to 10 degrees or more.

[0006] The method described in Patent Document 1 requires additional heat treatment of the entire steel sheet after the groove formation process to suppress the generation of subgrain boundaries, resulting in reduced production efficiency. The method described in Patent Document 2 requires adjusting the cooling rate to adjust the KAM value around the grooves, resulting in reduced production efficiency. The method described in Patent Document 3 makes it difficult to control the irradiation of the steel sheet surface with a laser beam that produces a ring-shaped intensity distribution, resulting in reduced production stability. The methods described in Patent Documents 4 and 5 do not take any measures to prevent the generation of subgrain boundaries around the grooves during the stress relief annealing process due to strain generated around the grooves when the grooves are formed by the laser beam.

[0007] The present disclosure provides a groove processing method for grain-oriented electromagnetic steel sheets, a groove processing device for grain-oriented electromagnetic steel sheets, grain-oriented electromagnetic steel sheets, wound iron cores, and methods for manufacturing wound iron cores, which do not deteriorate iron loss when manufacturing wound iron cores and can improve production efficiency and production stability.

[0008] A first aspect of the present disclosure is a groove processing method for processing a grain-oriented electromagnetic steel sheet by processing grooves on a surface of the grain-oriented electromagnetic steel sheet, the method comprising: a first irradiation step of irradiating the surface of the grain-oriented electromagnetic steel sheet with a first beam under first irradiation conditions that can form linear grooves on the surface of the grain-oriented electromagnetic steel sheet, the linear grooves extending in a direction corresponding to the sheet width direction of the grain-oriented electromagnetic steel sheet; and a second irradiation step of irradiating the surface of the grain-oriented electromagnetic steel sheet with a second beam along the grooves under second irradiation conditions that are different from the first irradiation conditions, wherein the grain-oriented electromagnetic steel sheet has undergone final annealing, and the second irradiation conditions are irradiation conditions that correspond to heat treatment conditions that can apply a predetermined heat treatment to a steel sheet portion in a predetermined range from the surface of the groove in the grain-oriented electromagnetic steel sheet.

[0009] A second aspect of the present disclosure is a groove processing method for grain-oriented electrical steel sheet according to the first aspect, wherein the heat treatment conditions are heat treatment conditions that eliminate distortion within the steel sheet portion.

[0010] A third aspect of the present disclosure is a groove processing method for grain-oriented electromagnetic steel sheet according to the first or second aspect, wherein the second beam has a lower power density than the first beam.

[0011] A fourth aspect of the present disclosure is a groove processing method for grain-oriented electromagnetic steel sheet according to any one of the first to third aspects, wherein the center of the second beam corresponds to the center of the first beam.

[0012] A fifth aspect of the present disclosure is a groove processing method for grain-oriented electromagnetic steel sheet according to any one of the first to fourth aspects, wherein the first irradiation step uses a fiber laser device, and the second irradiation step uses a semiconductor laser device that outputs a laser beam that has a higher absorption rate in the steel sheet and a shorter wavelength than the fiber laser device.

[0013] A sixth aspect of the present disclosure is a groove processing method for grain-oriented electrical steel sheet according to any one of the first to fifth aspects, wherein the heat treatment conditions are such that the temperature at the opening edge of the groove, the side surface of the groove, and within a range of 10 μm from the bottom of the groove is 1000°C or higher for 0.1 msec or more, and the temperature in the range is maintained at 1600°C or lower.

[0014] A seventh aspect of the present disclosure is a groove processing method for grain-oriented electromagnetic steel sheet according to any one of the first to sixth aspects, wherein the first irradiation process and the second irradiation process are performed while the grain-oriented electromagnetic steel sheet is being transported.

[0015] An eighth aspect of the present disclosure is a groove processing device for grain-oriented electromagnetic steel sheets that processes grooves on the surface of grain-oriented electromagnetic steel sheets, the groove processing device comprising: a first irradiation unit that irradiates a first beam under first irradiation conditions that can form linear grooves on the surface of the grain-oriented electromagnetic steel sheet, the grooves extending in a direction that corresponds to the sheet width direction of the grain-oriented electromagnetic steel sheet; and a second irradiation unit that irradiates the surface of the grain-oriented electromagnetic steel sheet with a second beam along the grooves under second irradiation conditions that are different from the first irradiation conditions, wherein the grain-oriented electromagnetic steel sheet has undergone final annealing, and the second irradiation conditions are irradiation conditions that correspond to heat treatment conditions that can apply a predetermined heat treatment to a steel sheet portion in a predetermined range from the surface of the groove in the grain-oriented electromagnetic steel sheet.

[0016] A ninth aspect of the present disclosure is the groove processing device for grain-oriented electromagnetic steel sheet according to the eighth aspect, wherein the heat treatment conditions are heat treatment conditions that eliminate distortion within the steel sheet portion.

[0017] A tenth aspect of the present disclosure is a groove processing device for grain-oriented electromagnetic steel sheets according to the eighth or ninth aspect, wherein the first irradiation unit and the second irradiation unit operate when transporting the grain-oriented electromagnetic steel sheet.

[0018] An eleventh aspect of the present disclosure is a groove processing device for grain-oriented electromagnetic steel sheets according to any one of the eighth to tenth aspects, wherein the distance between the first irradiation unit and the second irradiation unit is set to a length that is a natural number multiple of the pitch of the grooves.

[0019] A twelfth aspect of the present disclosure is a grain-oriented electrical steel sheet having linear grooves, and a coating covering a portion of the steel sheet within a predetermined range from the grooves, the coating having an affected portion.

[0020] A thirteenth aspect of the present disclosure is the grain-oriented electrical steel sheet according to the twelfth aspect, wherein the KAM value of a steel sheet portion within a predetermined range from the surface of the groove is 0.1 or more and 3.0 or less.

[0021] A fourteenth aspect of the present disclosure is a wound core formed from a grain-oriented electromagnetic steel sheet, the grain-oriented electromagnetic steel sheet having linear grooves, and a coating covering a portion of the steel sheet within a predetermined range from the groove having an affected portion.

[0022] A fifteenth aspect of the present disclosure is a method for manufacturing a wound core, comprising: a grain-oriented electromagnetic steel sheet manufacturing process for manufacturing a grain-oriented electromagnetic steel sheet; a wound core forming process for forming a wound core from the grain-oriented electromagnetic steel sheet; and a stress relief annealing process for performing stress relief annealing on the wound core, wherein the grain-oriented electromagnetic steel sheet manufacturing process comprises a groove processing process for processing grooves on a surface of the grain-oriented electromagnetic steel sheet, and the groove processing process comprises: a first irradiation process for irradiating the surface of the grain-oriented electromagnetic steel sheet with a first beam under first irradiation conditions that form linear grooves on the surface of the grain-oriented electromagnetic steel sheet in a direction that corresponds to the sheet width direction of the grain-oriented electromagnetic steel sheet; and a second irradiation process for irradiating the surface of the grain-oriented electromagnetic steel sheet with a second beam along the grooves under second irradiation conditions that are different from the first irradiation conditions, wherein the grain-oriented electromagnetic steel sheet has undergone final annealing, and the second irradiation conditions are irradiation conditions that correspond to heat treatment conditions that can apply a predetermined heat treatment to a steel sheet portion in a predetermined range from the surface of the groove in the grain-oriented electromagnetic steel sheet.

[0023] According to the present disclosure, there are provided a groove processing method for grain-oriented electromagnetic steel sheets, a groove processing device for grain-oriented electromagnetic steel sheets, grain-oriented electromagnetic steel sheets, wound iron cores, and methods for manufacturing wound iron cores, which do not deteriorate iron loss when manufacturing wound iron cores and can improve production efficiency and production stability.

[0024] FIG. 1 is a two-sided view showing an example of a groove processing device according to an embodiment of the present disclosure and a steel sheet to be processed. FIG. 2 is a cross-sectional view showing an example of a region on the surface of the steel sheet to which a second laser beam is irradiated. FIG. 3 is a view showing a first example of a method for manufacturing a grain-oriented electrical steel sheet. FIG. 4 is a view showing a second example of a method for manufacturing a grain-oriented electrical steel sheet. FIG. 5 is a view showing an example of the results of comparing iron loss improvement rates between an embodiment of the present disclosure and a comparative example. FIG. 6 is a schematic view comparing cross sections around grooves in wound cores after a stress relief annealing process according to an embodiment of the present disclosure and a comparative example. FIG. 7 is a view showing an example of a method for manufacturing a wound core according to an embodiment of the present disclosure. FIG. 8 is a view showing an example of the results of a temperature distribution in the sheet width direction on the surface of a steel sheet obtained by heat transfer calculation. FIG. 9 is a view showing an example of a temperature distribution in the sheet thickness direction of a steel sheet obtained by heat transfer calculation. FIG. 10 is a view showing an example of irradiation conditions for a second laser beam that satisfy the heat treatment conditions obtained from the heat transfer calculation. FIG. 11 is a cross-sectional view showing a first example of the cross-sectional structure of a grain-oriented electrical steel sheet according to an embodiment of the present disclosure. FIG. 12 is a cross-sectional view showing an example of the cross-sectional structure of a grain-oriented electrical steel sheet according to a comparative example.

[0025] Hereinafter, one embodiment of the present disclosure will be described.

[0026] 1 shows an example of a groove processing device 10 and a steel sheet 30 to be processed according to an embodiment of the present disclosure. The groove processing device 10 is an apparatus that forms a plurality of grooves 32 extending in a direction intersecting the conveyance direction at predetermined intervals in the conveyance direction on the surface of a steel sheet 30 that is conveyed in the conveyance direction indicated by arrow X for the purpose of magnetic domain control (i.e., magnetic domain refinement) in a groove forming step in a manufacturing method of grain-oriented electrical steel sheet. The conveyance direction is substantially parallel to the longitudinal direction (i.e., the rolling direction) of the steel sheet 30. The groove processing device 10 includes a first laser beam irradiation unit 12, a second laser beam irradiation unit 14, and a control unit 16.

[0027] The first laser beam irradiating unit 12 and the second laser beam irradiating unit 14 output laser beams under the control of the control unit 16. Specifically, the first laser beam irradiating unit 12 outputs a first laser beam L1, and the second laser beam irradiating unit 14 outputs a second laser beam L2. The first laser beam irradiating unit 12 is an example of a "first irradiating unit" in the present disclosure, and the second laser beam irradiating unit 14 is an example of a "second irradiating unit" in the present disclosure. Furthermore, the first laser beam L1 is an example of a "first beam" in the present disclosure, and the second laser beam L2 is an example of a "second beam" in the present disclosure.

[0028] The first laser beam irradiation unit 12 irradiates the surface of the steel sheet 30 with the first laser beam L1 under first irradiation conditions capable of forming linear grooves 32 extending in a direction corresponding to the sheet width direction of the steel sheet 30 (a predetermined first direction). Here, the steel sheet 30 is a grain-oriented electrical steel sheet after final finish annealing, e.g., a grain-oriented electrical steel sheet after the insulating coating formation process (see FIG. 3 ) or a grain-oriented electrical steel sheet after the final finish annealing process (see FIG. 4 ). The direction corresponding to the sheet width direction of the steel sheet 30 refers to a direction substantially parallel to the sheet width direction. The direction substantially parallel to the sheet width direction refers to a direction intersecting the conveyance direction and intersecting the sheet width direction of the steel sheet 30 at a predetermined angle. For example, the predetermined angle refers to an angle within a range of ±30 degrees with respect to the sheet width direction (i.e., −30°≦predetermined angle≦+30°). The depth of the grooves 32 is, for example, 10 μm to 30 μm. Here, the depth of the groove 32 refers to the depth including the coating if the steel plate 30 has a coating (e.g., a glass coating or an insulating coating). Furthermore, the steel plate 30 referred to in this specification refers to only the steel plate portion 30A (see FIG. 2 ) if there is no coating such as a glass coating or an insulating coating, and includes the steel plate portion 30A and the coating if there is a coating. The steel plate portion 30A has a predetermined thickness, and the coating is provided on at least one surface of the steel plate portion 30A (at least one of both surfaces in the thickness direction). For simplicity, FIG. 2 shows the steel plate 30 without a coating.

[0029] The second laser beam irradiation unit 14 irradiates the surface of the steel sheet 30 along the groove 32 with the second laser beam L2 under second irradiation conditions different from the first irradiation conditions. The second laser beam irradiation unit 14 irradiates the second laser beam L2 so that the irradiation area irradiated with the second laser beam L2 overlaps at least a portion of the surface of the groove 32. The second laser beam irradiation unit 14 irradiates the surface of the steel sheet 30 with the second laser beam L2 along the scanning path on the steel sheet 30 by the first laser beam irradiation unit 12. Here, the second irradiation conditions correspond to heat treatment conditions that can apply a predetermined heat treatment to the steel sheet portion 30A within a predetermined range from the surface of the groove 32. The heat treatment conditions are heat treatment conditions that eliminate distortion in the steel sheet portion 30A around the groove 32 that occurs when the groove 32 is formed. The heat treatment conditions are conditions under which the steel sheet 30 is heated to a temperature equal to or higher than the temperature required for heat treatment without melting the steel sheet 30. Eliminating strain includes not only completely eliminating strain, but also suppressing strain to an extent that sub-grain boundaries generated in the stress relief annealing process do not become a problem.

[0030] Although described in detail below, the heat treatment conditions are, for example, conditions under which the temperature at the opening edge of the groove 32, the side surface of the groove 32, and the range up to 10 μm from the bottom of the groove 32 remains at 1000°C or higher for 0.1 msec or more, and the temperature in the above range is maintained at 1600°C or lower. The opening edge of the groove 32, the side surface of the groove 32, and the region up to 10 μm from the bottom of the groove 32 are an example of a predetermined range to which the above-mentioned heat treatment is to be applied. The range up to 10 μm from the opening edge of the groove 32 refers to the range on one side of the groove 32 in the width direction. The second irradiation conditions do not need to be equal to the heat treatment conditions and may be set based on the heat treatment conditions. Furthermore, the second irradiation conditions may be set based on heat transfer calculations, experiments, etc.

[0031] The scanning paths of the first laser beam irradiating unit 12 and the second laser beam irradiating unit 14 will now be described with reference to FIG. 1 . The first laser beam irradiating unit 12 irradiates the surface of the steel sheet 30 with the first laser beam L1 while moving the first laser beam L1 in the movement direction indicated by arrow Y1. The second laser beam irradiating unit 14 irradiates the surface of the steel sheet 30 with the second laser beam L2 while moving the second laser beam L2 in the movement direction indicated by arrow Y2. That is, the second laser beam irradiating unit 14 irradiates the surface of the steel sheet 30 with the second laser beam L2 along the path (arrow Y1) along which the first laser beam L1 is irradiated from the first laser beam irradiating unit 12 to the surface of the steel sheet 30. The movement directions of the first laser beam L1 and the second laser beam L2 are the same, and are substantially parallel to the sheet width direction of the steel sheet 30.

[0032] The first laser beam irradiator 12 includes a first laser light source that outputs the first laser beam L1 and a first movement mechanism that moves the first laser beam L1. The first movement mechanism includes, for example, a polygon mirror and a motor that rotates the polygon mirror. Similarly, the second laser beam irradiator 14 includes a second laser light source that outputs the second laser beam L2 and a second movement mechanism that moves the second laser beam L2. The second movement mechanism includes, for example, a polygon mirror and a motor that rotates the polygon mirror. Note that the groove machining device 10 may include a common polygon mirror and motor for the first laser beam irradiator 12 and the second laser beam irradiator 14 as the movement mechanisms that move the first laser beam L1 and the second laser beam L2, or may include separate polygon mirrors and motors. Furthermore, when the first laser beam irradiating unit 12 and the second laser beam irradiating unit 14 are equipped with separate polygon mirrors and motors, the moving speeds of the first laser beam L1 and the second laser beam L2 may be the same or different. Furthermore, at least one of the first laser beam irradiating unit 12 and the second laser beam irradiating unit 14 may be equipped with a configuration other than a polygon mirror (for example, a galvanometer mirror, etc.).

[0033] Furthermore, the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 preferably irradiate the first laser beam L1 and the second laser beam L2 while the steel sheet 30 is being transported, but may also irradiate the first laser beam L1 and the second laser beam L2 while the steel sheet 30 is stopped. Furthermore, the first laser beam irradiation unit 12 and the second laser beam irradiating unit 14 may irradiate the first laser beam L1 and the second laser beam L2 so that they move in the same direction, or may irradiate the first laser beam L1 and the second laser beam L2 so that they move in different directions. Furthermore, the second laser beam irradiating unit 14 preferably irradiates the second laser beam L2 continuously along the scanning path on the steel sheet 30 by the first laser beam irradiating unit 12, but may also irradiate one groove 32 with the second laser beam L2 intermittently in the length direction of the groove 32, or may irradiate multiple grooves 32 selectively (e.g., every other groove 32) with the second laser beam L2.

[0034] The first laser beam irradiating unit 12 is disposed upstream in the conveying direction of the second laser beam irradiating unit 14. The groove processing device 10 forms a linear groove 32 extending in a direction substantially parallel to the sheet width direction by irradiating the surface of the steel sheet 30 with a first laser beam L1 from the first laser beam irradiating unit 12, and heat-treats a steel sheet portion 30A around the groove 32 by irradiating the surface of the steel sheet 30 with a second laser beam L2 from the second laser beam irradiating unit 14 so as to trace the groove 32. Hereinafter, the irradiation area of ​​the first laser beam L1 focused on the surface of the steel sheet 30 will be referred to as a "first focused spot S1," and the irradiation area of ​​the second laser beam L2 focused on the surface of the steel sheet 30 will be referred to as a "second focused spot S2." In addition, the area irradiated with the second laser beam L2 is referred to as the "second laser beam irradiation area 34," and the area heat-treated by irradiating the second laser beam L2 from the second laser beam irradiation unit 14 under second irradiation conditions corresponding to the above-mentioned heat treatment conditions is referred to as the "heat-treated area 36."

[0035] In order to overlap the irradiation areas of the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14, the distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 is preferably set to a natural number multiple of the pitch of the grooves 32. The distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 is determined by the distance between the centers of the first laser beam L1 and the second laser beam L2. When the distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 is set to a natural number multiple of the pitch of the grooves 32, the configuration of the groove machining device 10 can be simplified compared to when the distance is set to a length other than a natural number multiple of the pitch of the grooves 32. When a single polygon mirror is commonly used for both the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14, the distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 is set to a natural number multiple of the pitch of the grooves 32 with respect to the width in the conveyance direction of the polygon mirror having a rotation axis substantially parallel to the conveyance direction.

[0036] For example, a fiber laser device with high light-gathering characteristics may be used as the first laser light source serving as the laser light source of the first laser beam irradiating unit 12, as a laser beam irradiating device suitable for forming the grooves 32. Furthermore, a semiconductor laser device or the like that has a higher absorption rate in the steel sheet than a fiber laser device and is capable of outputting a laser with a shorter wavelength may be used as the second laser light source serving as the laser light source of the second laser beam irradiating unit 14, as a laser beam irradiating device suitable for heat treatment of the periphery of the grooves 32.

[0037] 2 shows an example of a second laser beam irradiation region 34 on the surface of the steel sheet 30, where the second laser beam L2 is irradiated. The groove 32 has a side surface 32B connected to an opening edge 32A, which is the boundary between the surface of the steel sheet 30 and the groove 32 (depression), and a bottom surface 32C continuous with the side surface 32B. The side surface 32B is connected to the surface (region 32A1) of the steel sheet 30 via the opening edge 32A. In other words, the surface of the groove 32 includes the side surface 32B and the bottom surface 32C. More specifically, the second laser beam irradiation region 34 is a region that includes the region 32A1 adjacent to the opening edge 32A, the side surface 32B of the groove 32, and the bottom surface 32C of the groove 32. In other words, the second laser beam irradiation region 34 overlaps with the groove 32 and has a width greater than that of the groove 32 on both sides in the conveyance direction.

[0038] Generally, when a groove 32 is formed by irradiating the surface of a steel sheet 30 with a laser beam, distortion occurs around the groove 32. Figure 2 shows an example of a region around the groove 32 where distortion occurs (hereinafter referred to as a "distortion generation region 38"). When a wound core of a transformer is manufactured from a grain-oriented electrical steel sheet, there is a problem that iron loss deteriorates in the stress relief annealing process performed after the grain-oriented electrical steel sheet is wound. The cause of this problem is thought to be that subgrain boundaries are generated around the groove 32 during the stress relief annealing process due to distortion generated in the strain generation region 38 when the groove 32 is formed with a laser beam.

[0039] Therefore, the groove processing device 10 includes a first laser beam irradiating unit 12 that irradiates a first laser beam L1 to form the grooves 32, and a second laser beam irradiating unit 14 that irradiates a second laser beam L2 to perform heat treatment (i.e., high-temperature strain relief annealing heat treatment) on the strain generated region 38 to eliminate the distortion. In other words, the groove processing device 10 is configured to irradiate the surface of the steel plate 30 with the first laser beam L1, which is the main beam for forming the grooves 32, and the second laser beam L2, which is the sub-beam for performing heat treatment on the strain generated region 38.

[0040] By irradiating the second laser beam L2 and performing heat treatment on the strain generation region 38 under predetermined conditions, the strain generated in the strain generation region 38 can be eliminated, and by eliminating the strain generated in the strain generation region 38, it is possible to suppress the generation of subgrain boundaries around the grooves 32 in the stress relief annealing process after the grain-oriented electrical steel sheet is rolled. It is preferable that the heat treatment region 36 that is heat-treated by irradiating the second laser beam L2 includes the strain generation region 38 so that the strain generated around the grooves 32 can be eliminated.

[0041] The heat treatment conditions for the strain-generated region 38 can be set by adjusting the power density and energy density of the second laser beam L2. Here, the power density is the power input from the second laser beam irradiating unit 14 to a unit area on the surface of the steel sheet 30, and is calculated by dividing the output of the second laser beam L2 by the area of ​​the second focused spot S2, and is expressed in W / mm2. The energy density is the amount of heat input per unit time, and is calculated by multiplying the power density by the irradiation time, and is expressed in J / mm2. The irradiation time is calculated by dividing the beam diameter in the sheet width direction by the movement speed. That is, the second irradiation conditions by the second laser beam irradiating unit 14 can be set by adjusting the output and irradiation time of the second laser beam L2, and the area of ​​the second focused spot S2.

[0042] The second laser beam irradiating unit 14 irradiates the strain-generated region 38 around the groove 32 to perform heat treatment. On the other hand, the first laser beam irradiating unit 12 irradiates the strain-generated region 38 to form the groove 32. Therefore, the second laser beam irradiating unit 14 irradiates the strain-generated region 38 at a power density lower than the power density required for the first laser beam irradiating unit 12 to form the groove. In other words, the second laser beam L2 has a lower power density than the first laser beam L1.

[0043] For example, even if the output of the first laser beam L1 and the output of the second laser beam L2 are the same, the second laser beam irradiator 14 can adjust the area of ​​the second focused spot S2 to be larger than that of the first focused spot S1 in order to irradiate at a lower power density than the first laser beam irradiator 12. Furthermore, as described above, since the energy density is calculated by multiplying the power density by the irradiation time, the power density can be reduced by extending the irradiation time to obtain a target energy density. Therefore, the second laser beam irradiator 14 may set the shape of the second focused spot S2 to have a major axis so that the scanning direction of the second laser beam L2 and the major axis direction of the second focused spot S2 are the same as each other, thereby lengthening the irradiation time. That is, the length of the second focused spot S2 in the sheet width direction of the steel sheet 30 may be set longer than that of the first focused spot S1.

[0044] Furthermore, the heat treatment region 36 that is heat treated by irradiating the second laser beam L2 preferably has a length in the conveyance direction of the steel sheet 30 (direction perpendicular to the sheet width direction) that is the same as or longer than the region (distortion generation region 38) that contains distortion that occurs when forming the grooves 32. Therefore, the length of the second focused spot S2 in the conveyance direction of the steel sheet 30 is preferably set to be longer than the first focused spot S1.

[0045] Furthermore, in order to eliminate distortion occurring around the groove 32, it is preferable to make the beam diameter of the second laser beam L2 irradiated around the groove 32 larger than that of the first laser beam L1 that forms the groove 32. For this reason, the second laser beam irradiating unit 14 irradiates the second laser beam L2 having a larger beam diameter than the first laser beam L1 irradiated by the first laser beam irradiating unit 12. For example, the beam diameter of the first laser beam L1 is determined by the length of the first focused spot S1 in the sheet width direction of the steel sheet 30, and the beam diameter of the second laser beam L2 is determined by the length of the second focused spot S2 in the sheet width direction of the steel sheet 30.

[0046] When the groove 32 is formed, distortion occurs around the center of the first laser beam L1. Therefore, the center of the second laser beam L2 used to eliminate the distortion preferably corresponds to the center of the first laser beam L1. That is, the second laser beam irradiating unit 14 preferably irradiates the second laser beam L2 so that the center of the second laser beam L2 approximately coincides with the center of the first laser beam L1. This allows the second laser beam L2 to be irradiated symmetrically in the width direction with respect to the center of the groove 32, making it easier for the irradiation area 34 of the second laser beam L2 to cover the entire distortion-occurring area 38. However, as long as distortion occurring around the groove 32 can be eliminated, the center of the second laser beam L2 may be offset from the center of the first laser beam L1. For example, the center of the second laser beam L2 may be offset from the center of the first laser beam L1 within the width of the groove 32.

[0047] Furthermore, in the groove forming process, as long as the distortion occurring around the groove 32 can be eliminated, the distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 (i.e., the length that is a natural number multiple of the pitch of the groove 32) may be set to any length.

[0048] So far, the irradiation conditions of the second laser beam irradiation portion 14 have been described in comparison with the irradiation conditions of the first laser beam portion 12, but detailed heat treatment conditions will be explained together with heat transfer calculations to be described later.

[0049] 1 , the control unit 16 is a device that controls the first laser beam irradiating unit 12 and the second laser beam irradiating unit 14. The control unit 16 is configured by a computer that includes, for example, a processor such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and storage.

[0050] The control unit 16 has, as its functional configuration, a first control unit 18 and a second control unit 20. The first control unit 18 and the second control unit 20 are realized, for example, by a processor executing a program stored in a ROM or storage. Note that the control unit 16 may include an electronic circuit such as a programmable logic device (PLD) or an application specific integrated circuit (ASIC) instead of or in addition to the processor. Furthermore, part or all of the first control unit 18 and the second control unit 20 may be realized by an electronic circuit such as a PLD or an ASIC.

[0051] The first control unit 18 controls the first laser beam irradiating unit 12 to irradiate the surface of the steel sheet 30 with the first laser beam L1 so as to form grooves 32 on the surface of the steel sheet 30. The first control unit 18 calculates the movement speed of the first laser beam L1 corresponding to the conveyance speed of the steel sheet 30, for example, based on a signal from a speed sensor that detects the conveyance speed of the steel sheet 30, and controls the first laser beam irradiating unit 12 (for example, a motor that rotates a polygon mirror) so that the first laser beam L1 moves at the calculated movement speed. The movement speed of the first laser beam L1 refers to, for example, the movement speed in the direction of arrow Y1 in FIG. 1 . The second control unit 20 controls the second laser beam irradiating unit 14 to irradiate the second laser beam L2 along the scanning path of the first laser beam irradiating unit 12 that formed the grooves 32, under irradiation conditions corresponding to heat treatment conditions that eliminate distortions that occur in the distortion-generated regions 38 when the grooves 32 are formed. The second control unit 20 calculates the moving speed of the second laser beam L2 corresponding to the conveying speed of the steel sheet 30, for example, based on a signal from a speed sensor that detects the conveying speed of the steel sheet 30, and controls the second laser beam irradiating unit 14 (for example, a motor that rotates the polygon mirror) so that the second laser beam L2 moves at the calculated moving speed. The moving speed of the second laser beam L2 refers to, for example, the moving speed in the direction of arrow Y2 in Figure 1.

[0052] A first example of a method for manufacturing a grain-oriented electrical steel sheet is shown in Fig. 3. The manufacturing method shown in Fig. 3 includes a casting process, a hot rolling process, an annealing process, a cold rolling process, a decarburization annealing process, an annealing separator coating process, a final annealing process, an insulating coating forming process, a groove forming process, and an insulating coating re-forming process.

[0053] The casting process is a process of producing a slab by a continuous casting method. The hot rolling process is a process of hot rolling a slab heated to a predetermined heating temperature (e.g., 1100°C to 1400°C) to obtain a hot-rolled steel sheet. The annealing process is a process of annealing the hot-rolled steel sheet immediately or within a short period of time to obtain an annealed steel sheet. The cold rolling process is a process of cold-rolling the annealed steel sheet once, or cold-rolling it multiple times (e.g., two or more times) via intermediate annealing to obtain a cold-rolled steel sheet. The decarburization annealing process is a process of decarburization annealing the cold-rolled steel sheet to obtain a decarburization-annealed steel sheet in which primary recrystallization has occurred.

[0054] The annealing separator application process is a process of applying an annealing separator to a decarburized annealed steel sheet. The final annealing process is a process of subjecting the decarburized annealed steel sheet coated with the annealing separator to finish annealing to cause secondary recrystallization and obtain a finish annealed steel sheet. Here, the finish annealed steel sheet refers to a steel sheet in which secondary recrystallization occurs when a decarburized annealed steel sheet coated with an annealing separator is finish annealed. The insulating coating formation process is a process of applying a coating solution to the surface of the finish annealed steel sheet and baking it to form an insulating coating on the surface of the finish annealed steel sheet. Steel sheet 30 shown in FIG. 1 corresponds to the finish annealed steel sheet.

[0055] The groove forming process is a process for forming a plurality of grooves 32 extending in a direction intersecting the conveyance direction at predetermined intervals in the surface of a finish-annealed steel sheet conveyed in the conveyance direction indicated by arrow X (see FIG. 1 ) for the purpose of magnetic domain control. The groove forming process includes a first laser beam irradiation process and a second laser beam irradiation process. The first laser beam irradiation process is a process for irradiating the surface of the finish-annealed steel sheet with a first laser beam L1 from a first laser beam irradiation unit 12 to form the grooves 32 in the surface of the finish-annealed steel sheet. The second laser beam irradiation process is a process for irradiating the surface of the finish-annealed steel sheet with a second laser beam L2 from a second laser beam irradiation unit 14 after the first laser beam irradiation process, along the grooves 32 in the surface of the finish-annealed steel sheet under second irradiation conditions corresponding to heat treatment conditions for eliminating strain generated in a strain generation region 38 when the grooves 32 were formed.

[0056] The first laser beam irradiation step and the second laser beam irradiation step are both performed when the steel plate 30 is being transported. That is, the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 both operate when the steel plate 30 is being transported, and irradiate the first laser beam L1 and the second laser beam L2, respectively, onto the surface of the steel plate 30. The first laser beam irradiation step is an example of a "first irradiation step" in the present disclosure, and the second laser beam irradiation step is an example of a "second irradiation step" in the present disclosure.

[0057] The insulating coating re-forming step is a step of applying a coating solution to the surface of the finish-annealed steel sheet in which the grooves 32 have been formed, and baking the solution to form an insulating coating again on the surface of the finish-annealed steel sheet.

[0058] Figure 4 shows a second example of a method for manufacturing a grain-oriented electrical steel sheet. In the manufacturing method shown in Figure 4, the insulating coating formation step before the groove formation step is omitted compared to the manufacturing method shown in Figure 3, and the insulating coating formation step is performed after the groove formation step. In other words, in the manufacturing method shown in Figure 4, the groove formation step is performed on a finish-annealed steel sheet before an insulating coating is formed on the surface. The steel sheet 30 shown in Figure 1 corresponds to a finish-annealed steel sheet.

[0059] In this way, the groove processing method using the groove processing device 10 according to this embodiment may be applied to either of the groove forming steps in the method for manufacturing grain-oriented electrical steel sheets shown in FIGS. 3 and 4 .

[0060] FIG. 7 shows an example of a method for manufacturing a wound core according to an embodiment of the present disclosure. The method for manufacturing a wound core includes a grain-oriented electrical steel sheet manufacturing process, a wound core forming process, and a stress relief annealing process. The grain-oriented electrical steel sheet manufacturing process is a process for manufacturing the above-described steel sheet 30, and includes a groove processing process for processing grooves in the surface of the steel sheet 30 that has been subjected to final annealing. As described above, the groove processing process includes a first laser beam irradiation process and a second laser beam irradiation process. As described above, the steel sheet 30 includes linear grooves 32 extending in a direction corresponding to the sheet width direction and heat treatment regions 36 formed along the grooves 32. The wound core forming process is a process for forming a wound core 50 from the steel sheet 30. Specifically, the steel sheet 30 is wound into a roll and then cut into pieces when wound to a desired size, thereby forming the wound core 50. The stress relief annealing process is a process for performing stress relief annealing on the wound core 50 to remove distortion that occurs in the wound core 50 during its formation. The stress relief annealing is a process of heat treating the wound core 50 under temperature conditions that can remove the strain that occurred in the wound core 50 when the wound core 50 was formed.

[0061] Next, an experimental example will be described. In this experimental example, a steel sheet according to the present disclosure and a steel sheet according to a comparative example were prepared. Specifically, as the steel sheet according to the present disclosure, a steel sheet was prepared in which, in the groove forming step, a groove 32 was formed on the surface of the steel sheet by irradiating the first laser beam L1 from the first laser beam irradiating unit 12, and a second laser beam L2 was irradiated from the second laser beam irradiating unit 14 along the groove 32 so as to trace the groove 32, thereby performing heat treatment on the periphery of the groove 32 (i.e., the strain generation region 38). Furthermore, as the steel sheet according to the comparative example, a steel sheet was prepared in which, in the groove forming step, a groove 32 was formed on the surface of the steel sheet by irradiating the first laser beam L1 from the first laser beam irradiating unit 12, and irradiation with the second laser beam L2 from the second laser beam irradiating unit 14 was omitted.

[0062] The test samples used in the present disclosure and comparative examples were common to both the present disclosure and comparative examples, and were manufactured using the method for manufacturing grain-oriented electrical steel sheets of the first example shown in FIG. 3. Details are shown below. Test sample: Steel sheet after the insulating coating formation process, magnetic flux density B ８ = 1.91T, iron loss W17 / 50 = 0.9W / kg

[0063] The irradiation conditions of the first laser beam L1 were common to the disclosed example and the comparative example, and were as follows: output: 1000 W, moving speed in the sheet width direction: 30 m / s, irradiation pitch in the conveying direction: 3 mm, beam diameter: 0.05 mm (conveying direction) × 0.1 mm (sheet width direction), groove depth: 20 μm, groove width: 50 μm.

[0064] The irradiation conditions of the second laser beam L2 (only in the present disclosure example) were as follows: output: 2000 W, moving speed in the sheet width direction: 30 m / s, irradiation pitch in the conveying direction: 3 mm, beam diameter: 0.15 mm (conveying direction) × 15 mm (sheet width direction).

[0065] In this experimental example, a steel sheet before the groove forming process (i.e., a finish-annealed steel sheet without grooves) was prepared as a steel sheet according to a reference example. The above-mentioned test sample was used as the steel sheet according to the reference example. Then, the iron loss improvement rates of the steel sheets according to the present disclosure and the steel sheets according to the comparative examples were compared with those of the reference example after the re-insulation coating process.

[0066] In this experimental example, a wound core according to the present disclosure and a wound core according to the comparative example were prepared as wound cores of transformers manufactured from steel sheets after the groove forming process. A wound core according to the reference example was prepared as wound cores of transformers manufactured from steel sheets before the groove forming process. The iron loss improvement rates after the stress relief annealing process for the wound core according to the present disclosure and the wound core according to the comparative example were compared relative to the wound core according to the reference example.

[0067] In this experimental example, each wound core was a 20 kVA single-phase wound core. The stress relief annealing process was performed at 800°C for 3 hours in a 100% nitrogen atmosphere. A primary winding (excitation winding) and a secondary winding (search coil) were then wound around each wound core, and the iron loss of each wound core was measured with a wattmeter.

[0068] 5 shows an example of the results of comparing the iron loss improvement rate [%] between the disclosed example and the comparative example. Bar graph G1 shows the iron loss improvement rate for the steel sheet according to the disclosed example relative to the steel sheet according to the reference example. Bar graph G2 shows the iron loss improvement rate for the wound core according to the disclosed example after the stress relief annealing process relative to the wound core according to the reference example. Bar graph G3 shows the iron loss improvement rate for the steel sheet according to the comparative example relative to the steel sheet according to the reference example. Bar graph G4 shows the iron loss improvement rate for the wound core according to the comparative example after the stress relief annealing process relative to the wound core according to the reference example.

[0069] In this experimental example, when comparing the steel plate according to the present disclosure with the steel plate according to the comparative example, there was no difference in the iron loss improvement rate after the groove forming process. However, when comparing the wound core according to the present disclosure with the wound core according to the comparative example, the wound core according to the present disclosure had a better iron loss improvement rate after the stress relief annealing process by 3% or more than the wound core according to the comparative example.

[0070] 6A and 6B are schematic diagrams comparing the cross sections of the periphery of the grooves 32 of the wound cores according to the present disclosure and the comparative example after the stress relief annealing process. Fig. 6A shows the comparative example, and Fig. 6B shows the present disclosure. As shown in Fig. 6A, subgrain boundaries were generated around the grooves 32 in the wound core according to the comparative example, while as shown in Fig. 6B, no subgrain boundaries were generated around the grooves 32 in the wound core according to the present disclosure.

[0071] In this way, this experimental example confirmed that if heat treatment is not performed on the strain generation region 38, subgrain boundaries will occur around the grooves 32 during the strain relief annealing process, and that if subgrain boundaries occur around the grooves 32, iron loss will deteriorate during the strain relief annealing process.

[0072] Furthermore, this experimental example revealed that the region where subgrain boundaries occur is within a range of 5 to 10 μm from the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the bottom surface 32C of the groove 32. It is believed that the region where subgrain boundaries occur substantially coincides with the strain generation region 38 described above. Therefore, in order to prevent subgrain boundaries from occurring around the groove 32, it is considered necessary to perform a heat treatment (i.e., a high-temperature strain relief annealing heat treatment) using the second laser beam L2 in a range of at least 10 μm from the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the bottom surface 32C of the groove 32, as an example of a predetermined range from the surface of the groove 32, to eliminate the strain present in this range. In other words, it was found that the heat treatment region 36 should be within a range of at least 10 μm from the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the bottom surface 32C of the groove 32.

[0073] The above-described irradiation conditions for the second laser beam L2 in this experimental example are merely examples, and other irradiation conditions may be used as long as they satisfy the irradiation conditions corresponding to the heat treatment conditions for eliminating distortion. Here, while it is desirable to define the predetermined conditions for performing heat treatment on the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the area up to 10 μm from the bottom surface 32C of the groove 32 using heating temperature, in this experimental example, it is difficult to directly measure the temperatures in the area up to 10 μm from the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the bottom surface 32C of the groove 32. Therefore, the predetermined conditions for performing heat treatment on the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the area up to 10 μm from the bottom surface 32C of the groove 32 are defined using heat transfer calculations.

[0074] In the heat transfer calculation, the irradiation conditions of the second laser beam L2 were set to the same conditions as those in the present disclosure, which are capable of suppressing deterioration of iron loss. Specifically, the irradiation conditions of the second laser beam L2 were set to the following conditions: output: 2000 W, moving speed in the sheet width direction: 30 m / s, irradiation pitch in the conveying direction: 3 mm, beam diameter: 0.15 mm (conveying direction) × 15 mm (sheet width direction). In the heat transfer calculation, the laser beam absorptance of the steel sheet 30 was set to 60%.

[0075] FIG. 8 shows an example of the results of heat transfer calculations of the temperature distribution in the sheet width direction when an arbitrary point on the surface of the steel sheet 30 is used as a reference. In FIG. 8 , the horizontal axis represents time [msec] based on the moment when the second laser beam L2 passes the arbitrary point. Specifically, it represents the elapsed time when the time when the center of the second focused spot S2 in the conveying direction overlaps the arbitrary point is set to 0.00 seconds. The vertical axis represents the position [mm] in the sheet width direction of the steel sheet 30 when the position on the optical axis of the second laser beam L2 is set to 0 mm. As shown in FIG. 8 , under the above-described irradiation conditions of the second laser beam L2 (i.e., irradiation conditions that can suppress deterioration of iron loss), calculations were performed to show that the surface temperature of the steel sheet 30 on the optical axis of the second laser beam L2 is below 1600°C, which is the melting temperature of the steel sheet 30. If the surface temperature of the steel sheet 30 exceeds 1600°C, the surface of the steel sheet 30 will melt. Therefore, it is considered that the surface temperature of the steel sheet 30 needs to be below 1600°C.

[0076] Furthermore, the calculation results showed that the range in the conveying direction where the surface temperature of the steel sheet 30 becomes 1000°C or higher is within a range of ±40 μm (80 μm in total) from the position on the optical axis of the second laser beam L2, which is wider than the groove width of 50 μm plus 10 μm on each side of the groove 32, totaling 70 μm (corresponding to the length of the strain generation region 38 in the conveying direction). In other words, the calculation results showed that the range in the conveying direction where the surface temperature of the steel sheet 30 becomes 1000°C or higher includes a range of 10 μm from the opening edge 32A of the groove 32.

[0077] FIG. 9 shows an example of the temperature distribution in the thickness direction of the steel sheet 30 obtained by heat transfer calculation. In FIG. 9 , the horizontal axis represents time [msec] relative to the moment when the second laser beam L2 passes through an arbitrary point, and the vertical axis represents the position [μm] in the thickness direction of the steel sheet 30 when the surface of the steel sheet 30 is set to 0 μm. As shown in FIG. 9 , under the above irradiation conditions of the second laser beam L2 (i.e., irradiation conditions capable of suppressing deterioration in iron loss), a calculation result was obtained in which, for example, the temperature in the thickness direction range from the surface of the steel sheet 30 to 10 μm remains at least 1000°C for 0.1 msec. Therefore, in order to suppress deterioration in iron loss, it is considered sufficient that the temperature in the range from the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the bottom surface 32C of the groove 32 to 10 μm remains at 1000°C or higher for 0.1 msec or more.

[0078] From the above heat transfer calculations, it was found that in the second laser beam irradiation process in which the second laser beam L2 is irradiated, the second laser beam L2 should be irradiated along the groove 32 under the conditions that the temperature of the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the range up to 10 μm from the bottom surface 32C of the groove 32 (heat treatment region 36) remains at 1000°C or higher for 0.1 msec or more, and the temperature of region 34 is maintained at 1600°C or lower.

[0079] 10 shows an example of the irradiation conditions of the second laser beam L2 that satisfy the heat treatment conditions obtained from the heat transfer calculation (i.e., the conditions that can suppress the deterioration of iron loss). The example shown in FIG. 10 is an example of the irradiation conditions of the second laser beam L2 when the heat transfer calculation is performed under the following irradiation conditions of the second laser beam L2: beam diameter in the conveying direction of the second laser beam L2: 0.15 mm, moving speed of the second laser beam L2 in the sheet width direction: 30 m / s, laser beam absorptance of the steel sheet 30: 60%

[0080] 10, the horizontal axis represents the output power [W] of the second laser beam L2, and the vertical axis represents the beam diameter [mm] of the second laser beam L2 in the sheet width direction. In Fig. 10, the "range satisfying the heat treatment conditions" represents the irradiation conditions of the second laser beam L2 when the heat treatment conditions are satisfied, that is, the temperature of the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the range up to 10 µm from the bottom surface 32C of the groove 32 remains at 1000°C or higher for 0.1 msec or more, and the temperature of the region 34 is maintained at 1600°C or lower.

[0081] 10, the "range not satisfying the first heat treatment condition" indicates the irradiation condition of the second laser beam L2 when the first heat treatment condition, that is, the temperature of the opening edge 32A of the groove 32, the side surface 32B of the groove 32, and the range up to 10 μm from the bottom 32C of the groove 32 remains at 1000° C. or higher for 0.1 msec or more, is not satisfied. Also, in FIG. 10, the "range not satisfying the second heat treatment condition" indicates the irradiation condition of the second laser beam L2 when the second heat treatment condition, that is, the temperature of the region 34 is maintained at 1600° C. or lower, is not satisfied.

[0082] The "range satisfying the heat treatment conditions" shown in Figure 10 can be expressed by the following formula: 0.0105 x P - 6.5 ≤ dc ≤ 0.0155 x P - 12.0, where P is the output [W] of the second laser beam L2, and dc is the beam diameter [mm] in the plate width direction.

[0083] For example, by setting the irradiation conditions of the second laser beam L2 within the "range satisfying the heat treatment conditions" shown in Figure 10 and irradiating the second laser beam L2, the KAM value around the groove 32 can be set to 0.1 or more and 3.0 or less. This makes it possible to suppress the occurrence of subgrain boundaries, thereby suppressing deterioration of iron loss. Note that while etching can reduce the KAM value to 0, laser beam irradiation, in principle, cannot reduce the KAM value to 0.1 or less.

[0084] FIG. 11 shows a first example of the cross-sectional structure of a grain-oriented electrical steel sheet according to an embodiment of the present disclosure. The steel sheet 30 shown in FIG. 11 is manufactured by the first example of the manufacturing method for grain-oriented electrical steel sheet shown in FIG. 3. The steel sheet 30 includes a glass coating 40, an insulating coating 42 formed by an insulating coating forming process, and a re-insulating coating 44 formed by a re-insulating coating forming process. In the example shown in FIG. 11(A), an altered portion 42A is formed in a portion of the insulating coating 42 (i.e., the portion irradiated with the second laser beam L2). In the example shown in FIG. 11(B), the altered portion 42B is a region where a portion of the insulating coating 42 (i.e., the portion irradiated with the second laser beam L2) is thinned or missing. Note that, in the example shown in FIG. 11(A), the altered portion 42A remains in the insulating coating 42, but the altered portion 42A may be formed in both the insulating coating 42 and the glass coating 40. That is, although the altered portion 42A occurs only in the insulating coating 42, the altered portion 42A may also exist in the insulating coating 42 and the insulating coating 40 in at least a portion of the region where the altered portion 42A occurs. The same applies to the altered portion 42B shown in FIG. 11(B).

[0085] FIG. 12 shows a second example of the cross-sectional structure of a grain-oriented electrical steel sheet according to an embodiment of the present disclosure. The steel sheet 30 shown in FIG. 12 is manufactured by the second example of the method for manufacturing a grain-oriented electrical steel sheet shown in FIG. 4. The steel sheet 30 includes a glass coating 40 and an insulating coating 46 formed by an insulating coating formation process performed after the groove formation process. In the example shown in FIG. 12(A), an altered portion 40A is formed in a portion of the glass coating 40 (i.e., the portion irradiated with the second laser beam L2). In the example shown in FIG. 12(B), the altered portion 40B is a region where a portion of the glass coating 40 (i.e., the portion irradiated with the second laser beam L2) is thinned or missing.

[0086] FIG. 13 shows an example of the cross-sectional structure of a grain-oriented electrical steel sheet according to a comparative example. The steel sheet 130 shown in FIG. 13(A) was manufactured by a manufacturing method that omits the second laser beam irradiation step from the first example of the manufacturing method for grain-oriented electrical steel sheet shown in FIG. 3 . The steel sheet 130 shown in FIG. 13(A) is similar to the steel sheet 30 shown in FIG. 11 in that it includes a glass coating 40, an insulating coating 42 formed by an insulating coating forming step, and a second insulating coating 44 formed by a second insulating coating forming step. However, it differs from the steel sheet 30 shown in FIG. 11 in that it does not include the affected portion 42A or 42B in part of the insulating coating 42. In other words, the steel sheet 130 according to the comparative example shown in FIG. 13(A) does not include the affected portion 42A or 42B, whereas the example shown in FIG. 11 includes the affected portion 42A or 42B in the coating covering the surface of the steel sheet portion 30A within a predetermined range from the groove 32 (more specifically, the opening edge 32A of the groove 32).

[0087] The steel sheet 130 shown in Fig. 13(B) was manufactured by a manufacturing method that omits the second laser beam irradiation step from the second example of the manufacturing method of the grain-oriented electrical steel sheet shown in Fig. 4. The steel sheet 130 shown in Fig. 13(B) is similar to the steel sheet 30 shown in Fig. 12 in that it includes a glass coating 40 and an insulating coating 46 formed by an insulating coating formation step performed after the groove formation step. However, it differs from the steel sheet 30 shown in Fig. 12 in that it does not include the affected portion 40A or 40B in part of the glass coating 40. In other words, the steel sheet 130 according to the comparative example shown in Fig. 13(B) does not include the affected portion 40A or 40B, whereas the example shown in Fig. 12 includes the affected portion 40A or 40B in the coating covering the surface of the steel sheet portion 30A within a predetermined range from the groove 32 (more specifically, the opening edge 32A of the groove 32).

[0088] In this way, the steel sheet 30 manufactured by the first example of the manufacturing method for grain-oriented electrical steel sheet shown in Figure 3 or the second example of the manufacturing method for grain-oriented electrical steel sheet shown in Figure 4 has a cross-sectional structure different from that of the steel sheet 130 according to the comparative example, which was manufactured by a manufacturing method that omits the second laser beam irradiation process.

[0089] As described above in detail, in this embodiment, in the groove forming step, the second laser beam L2 is irradiated from the second laser beam irradiation unit 14 along the grooves 32 under irradiation conditions corresponding to the heat treatment conditions for eliminating the distortion that occurs when the grooves 32 are formed, thereby making it possible to eliminate the distortion that occurs around the grooves 32 when the grooves 32 are formed. Therefore, even when a wound core of a transformer is manufactured from a grain-oriented electromagnetic steel sheet, it is possible to suppress the occurrence of subgrain boundaries around the grooves 32 in the stress relief annealing step that is performed after the grain-oriented electromagnetic steel sheet is wound, and therefore it is possible to suppress deterioration of iron loss.

[0090] Furthermore, production efficiency can be improved because there is no need to perform additional heat treatment on the entire steel sheet 30 after the groove forming process, and there is no need to adjust the cooling rate to adjust the KAM value around the grooves 32. Furthermore, there is no need for advanced control, such as irradiating the surface of the steel sheet 30 with a laser beam that has a ring-shaped intensity distribution, so production stability can be improved.

[0091] In the above embodiment, the first laser beam L1 and the second laser beam L2 are used in the groove formation process. However, an electron beam may be used instead of at least one of the first laser beam L1 and the second laser beam L2. When a first electron beam irradiation unit that irradiates an electron beam is used instead of the first laser beam irradiation unit 12 that irradiates the first laser beam L1, the first electron beam irradiation unit is an example of a "first irradiation unit" in the present disclosure. Furthermore, when a second electron beam irradiation unit that irradiates an electron beam is used instead of the second laser beam irradiation unit 14 that irradiates the second laser beam L2, the second electron beam irradiation unit is an example of a "second irradiation unit" in the present disclosure. The electron beam irradiation unit may be any type of irradiation device capable of irradiating an electron beam, such as a thermionic emission type, a field emission type, or a Schottky type.

[0092] The above describes one embodiment of the present disclosure, but the present disclosure is not limited to the above, and it goes without saying that various modifications can be made to the present disclosure without departing from the spirit of the present disclosure.

[0093] All documents, patent applications, and technical standards described herein are incorporated by reference herein to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference. In addition, the disclosure of Japanese Patent Application No. 2024-031639, filed March 1, 2024, is incorporated by reference in its entirety herein.

[0094] REFERENCE SIGNS LIST 10 Groove machining device 12 First laser beam irradiation unit 14 Second laser beam irradiation unit 16 Control unit 18 First control unit 20 Second control unit 30 Steel plate 30A Steel plate portion 32 Groove 34 Second laser beam irradiation area 36 Heat treatment area 38 Distortion occurring area L1 First laser beam L2 Second laser beam

Claims

1. A groove processing method for grain-oriented electromagnetic steel sheet, which processes grooves on the surface of grain-oriented electromagnetic steel sheet, comprising: a first irradiation step of irradiating the surface of the grain-oriented electromagnetic steel sheet with a first beam under first irradiation conditions that can form linear grooves on the surface of the grain-oriented electromagnetic steel sheet, the grooves extending in a direction corresponding to the sheet width direction of the grain-oriented electromagnetic steel sheet; and a second irradiation step of irradiating the surface of the grain-oriented electromagnetic steel sheet with a second beam along the grooves under second irradiation conditions that are different from the first irradiation conditions, wherein the grain-oriented electromagnetic steel sheet has undergone final annealing, and the second irradiation conditions are irradiation conditions that correspond to heat treatment conditions that can apply a predetermined heat treatment to a steel sheet portion in a predetermined range from the surface of the groove in the grain-oriented electromagnetic steel sheet.

2. The groove processing method for grain-oriented electrical steel sheet according to claim 1, wherein the heat treatment conditions are heat treatment conditions that eliminate distortion within the steel sheet portion.

3. A method for processing grooves in grain-oriented electrical steel sheets according to claim 1 or claim 2, wherein the second beam has a lower power density than the first beam.

4. A groove processing method for grain-oriented electrical steel sheets according to any one of claims 1 to 3, wherein the center of the second beam corresponds to the center of the first beam.

5. A groove processing method for grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the first irradiation step uses a fiber laser device, and the second irradiation step uses a semiconductor laser device that outputs a laser beam with a higher absorption rate in the steel sheet and a shorter wavelength than the fiber laser device.

6. A groove processing method for grain-oriented electrical steel sheet according to any one of claims 1 to 5, wherein the heat treatment conditions are such that the temperature at the opening edge of the groove, the side surface of the groove, and within 10 μm from the bottom of the groove remains at 1000°C or higher for 0.1 msec or more, and the temperature in the range is maintained at 1600°C or lower.

7. A groove processing method for grain-oriented electrical steel sheets according to any one of claims 1 to 6, wherein the first irradiation step and the second irradiation step are performed while the grain-oriented electrical steel sheets are being transported.

8. A groove processing device for grain-oriented electromagnetic steel sheets that processes grooves on the surface of grain-oriented electromagnetic steel sheets, comprising: a first irradiation unit that irradiates a first beam under first irradiation conditions that can form linear grooves on the surface of the grain-oriented electromagnetic steel sheet, the grooves extending in a direction corresponding to the sheet width direction of the grain-oriented electromagnetic steel sheet; and a second irradiation unit that irradiates the surface of the grain-oriented electromagnetic steel sheet with a second beam under second irradiation conditions that are different from the first irradiation conditions, along the grooves, wherein the grain-oriented electromagnetic steel sheet has undergone final annealing, and the second irradiation conditions are irradiation conditions that correspond to heat treatment conditions that can apply a predetermined heat treatment to a steel sheet portion in a predetermined range from the surface of the groove in the grain-oriented electromagnetic steel sheet.

9. The groove processing device for grain-oriented electrical steel sheets according to claim 8, wherein the heat treatment conditions are heat treatment conditions that eliminate distortion within the steel sheet portion.

10. A groove processing device for grain-oriented electromagnetic steel sheets according to claim 8 or claim 9, wherein the first irradiation unit and the second irradiation unit operate when the grain-oriented electromagnetic steel sheets are transported.

11. A groove processing device for grain-oriented electromagnetic steel sheets as described in any one of claims 8 to 10, wherein the distance between the first irradiation unit and the second irradiation unit is set to a length that is a natural number multiple of the pitch of the grooves.

12. A grain-oriented electrical steel sheet having linear grooves, and a coating covering a portion of the steel sheet within a predetermined range from the grooves, which coating has an altered portion.

13. The grain-oriented electrical steel sheet according to claim 12, wherein the KAM value of the steel sheet portion within a predetermined range from the surface of the groove is 0.1 or more and 3.0 or less.

14. A wound core formed from grain-oriented electromagnetic steel sheets, wherein the grain-oriented electromagnetic steel sheets have linear grooves, and a coating covering a portion of the steel sheet within a predetermined range from the grooves has an altered portion.

15. A method for manufacturing a wound core, comprising: a grain-oriented electromagnetic steel sheet manufacturing process for manufacturing grain-oriented electromagnetic steel sheets; a wound core forming process for forming a wound core from the grain-oriented electromagnetic steel sheets; and a stress relief annealing process for performing stress relief annealing on the wound core, wherein the grain-oriented electromagnetic steel sheet manufacturing process comprises a groove processing process for processing grooves on the surface of the grain-oriented electromagnetic steel sheet, wherein the groove processing process comprises: a first irradiation process for irradiating the surface of the grain-oriented electromagnetic steel sheet with a first beam under first irradiation conditions that form linear grooves on the surface of the grain-oriented electromagnetic steel sheet, the linear grooves extending in a direction corresponding to the sheet width direction of the grain-oriented electromagnetic steel sheet; and a second irradiation process for irradiating the surface of the grain-oriented electromagnetic steel sheet with a second beam along the grooves under second irradiation conditions that are different from the first irradiation conditions, wherein the grain-oriented electromagnetic steel sheet has undergone final annealing, and the second irradiation conditions are irradiation conditions that correspond to heat treatment conditions that can apply a predetermined heat treatment to a steel sheet portion in a predetermined range from the surface of the groove in the grain-oriented electromagnetic steel sheet.

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