Method for grooving grain-oriented electrical steel sheets, apparatus for grooving grain-oriented electrical steel sheets, and method for manufacturing wound iron cores.

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

Technical Field

[0001] The present disclosure relates to a method for grooving a grain-oriented electrical steel sheet, a grooving apparatus for a grain-oriented electrical steel sheet, , and and a method for manufacturing a wound core.

Background Art

[0002] As an example of a method for manufacturing a grain-oriented electrical steel sheet, there is a method including a casting process, a hot rolling process, an annealing process, a cold rolling process, a decarburization annealing process, an annealing separation coating process, a final finishing annealing process, an insulating film forming process, a groove forming process, and a re-insulating film forming process. In the groove forming process, periodic grooves are formed in the grain-oriented electrical steel sheet by a laser beam, and in the re-insulating film forming process, a tension-applying film is formed, whereby the magnetic domains of the grain-oriented electrical steel sheet are subdivided.

[0003] In the above manufacturing method, although two processes for forming an insulating film, such as an insulating film forming process and a re-insulating film forming process, are required, it is excellent in the stability of improving iron loss and the prevention of adhesion of molten removal products. However, when manufacturing a wound core of a transformer from the grain-oriented electrical steel sheet manufactured by the above manufacturing method, there is a problem that the iron loss deteriorates in the stress relief annealing process performed after the winding of the grain-oriented electrical steel sheet. It is considered that the cause of this problem is that sub-grain boundaries are generated around the grooves in the stress relief annealing process due to the distortion generated around the grooves when the grooves are formed by a laser beam.

[0004] Therefore, the following technologies have been proposed as countermeasures to suppress the deterioration of iron loss during the strain-relieving annealing process. For example, Japanese Patent Publication No. 7031364 (Patent Document 1) describes a method to suppress the generation of subgrain boundaries by performing a heat treatment to heat the steel plate to 1000°C or more and 1100°C or less after the groove formation process. Also, Japanese Patent Publication No. 6614398 (Patent Document 2) describes a method to suppress the generation of subgrain boundaries by adjusting the cooling rate in the re-insulating film formation process to make the KAM (Kernel Average Misorientation) value around the grooves between 0.1 and 3.0. Furthermore, International Publication No. 2022 / 045264 (Patent Document 3) describes a method to suppress the deterioration of iron loss during the groove formation process by linearly irradiating the surface of the steel plate with a laser beam that has a ring-shaped intensity distribution with lower intensity at the periphery compared to the center, in a direction intersecting the rolling direction.

[0005] Furthermore, Japanese Patent 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 undergone final finish annealing with an electron beam in multiple stages when performing magnetic domain subdivision processing. In addition, International Publication No. 2024 / 111642 (Patent Document 5) discloses a groove formation process between a cold rolling process and a finish annealing process, comprising a first step of forming grooves on the surface of a steel sheet by irradiating the surface of the steel sheet with a laser beam and forming protrusions on the side or bottom surface of the grooves, and a method of making the orientation difference between the average crystal orientation of the protrusions and the Goss orientation 10 degrees or more by irradiating the same location where the laser beam was irradiated in the first step following the first step. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In the method described in Patent Document 1, production efficiency is reduced because additional heat treatment is required on the entire steel sheet after the groove formation process to suppress the generation of subgrain boundaries. In the method described in Patent Document 2, production efficiency is reduced because the cooling rate needs to be adjusted to adjust the KAM value around the grooves. In the method described in Patent Document 3, production stability is reduced because it is difficult to control the irradiation of the laser beam, which creates a ring-shaped intensity distribution, onto the surface of the steel sheet. Furthermore, in the methods described in Patent Documents 4 and 5, no measures are taken to address the generation of subgrain boundaries around the grooves during the strain-relieving annealing process due to the strain generated around the grooves when the grooves are formed by the laser beam.

[0007] This disclosure relates to a groove processing method and apparatus for grain-oriented electrical steel sheets, which prevent deterioration of iron loss during the manufacture of wound cores and improve production efficiency and production stability. , and The present invention provides a method for manufacturing a wound iron core. [Means for solving the problem]

[0008] A first aspect of this disclosure is a method for grooving a grain-grain electrical steel sheet, comprising: a first irradiation step of irradiating the surface of the grain-grain electrical steel sheet with a first beam under first irradiation conditions that enable the formation of linear grooves extending in a direction corresponding to the width direction of the grain-grain electrical steel sheet; and a second irradiation step of irradiating the surface of the grain-grain electrical steel sheet along the grooves with a second beam under second irradiation conditions different from the first irradiation conditions, wherein the grain-grain electrical steel sheet has undergone final finish annealing, and the second irradiation conditions are applied to a predetermined range of the steel sheet portion from the surface of the grooves in the grain-grain electrical steel sheet. 、 predetermined To eliminate distortion within the aforementioned steel plate portion. Add heat treatment heat Irradiation conditions corresponding to processing conditions The second irradiation step involves irradiating the second beam such that the irradiation area to which the second beam is irradiated overlaps with at least a portion of the surface of the groove. This is a method for grooving grain-oriented electrical steel sheets.

[0010] History of this disclosure 2 The manner is, First aspectIn the groove processing method for grain-oriented electrical steel sheets relating to the above, the second beam has a lower power density than the first beam.

[0011] History of this disclosure 3 The embodiments are: 1st embodiment or second aspect In the groove processing method for grain-oriented electrical steel sheets relating to the above, the center of the second beam corresponds to the center of the first beam, and the groove processing method for grain-oriented electrical steel sheets relating to the above.

[0012] History of this disclosure 4 The embodiments are, from the first embodiment to the second embodiment. 3 A groove processing method for grain-oriented electrical steel sheets according to any one of the embodiments, 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 steel sheet absorption rate and shorter wavelength than the fiber laser device.

[0013] History of this disclosure 5 The embodiments are, from the first embodiment to the second embodiment. 4 A groove processing method for grain-oriented electrical steel sheets according to any one of the embodiments, wherein the heat treatment conditions are such that the temperature of the opening edge of the groove, the side surface of the groove, and the area up to 10 μm from the bottom surface of the groove is 1000°C or higher for 0.1 msec or longer, and the temperature in the area is maintained at 1600°C or lower.

[0014] History of this disclosure 6 The embodiments are, from the first embodiment to the second embodiment. 5 A groove processing method for grain-oriented electrical steel sheets according to any one of the embodiments, wherein the first irradiation step and the second irradiation step are performed when the grain-oriented electrical steel sheet is being transported.

[0015] History of this disclosure 7The embodiment is a grooving apparatus for grain-grained electrical steel sheets that performs groove processing on the surface of grain-grained electrical steel sheets, comprising: a first irradiation unit that irradiates the surface of the grain-grained electrical steel sheet with a first beam under first irradiation conditions that enable the formation of linear grooves extending in a direction corresponding to the width direction of the grain-grained electrical steel sheet; and a second irradiation unit that irradiates the surface of the grain-grained electrical steel sheet along the grooves with a second beam under second irradiation conditions different from the first irradiation conditions, wherein the grain-grained electrical steel sheet has undergone final finish annealing, and the second irradiation conditions are applied to a predetermined range of the steel sheet portion from the surface of the grooves in the grain-grained electrical steel sheet. 、 predetermined To eliminate distortion within the aforementioned steel plate portion. Add heat treatment heat These are irradiation conditions corresponding to the processing conditions. The second irradiation unit irradiates the second beam such that the irradiation area to which the second beam is irradiated overlaps with at least a portion of the surface of the groove. This is a grooving machine for grain-oriented electrical steel sheets.

[0017] History of this disclosure 8 The manner is, Seventh aspect In the groove processing device for grain-oriented electrical steel sheets relating to the above, the first irradiation unit and the second irradiation unit are groove processing devices for grain-oriented electrical steel sheets that operate when the grain-oriented electrical steel sheet is transported.

[0018] History of this disclosure 9 The aspect is, 7 manner Or the eighth aspect In a groove processing apparatus for grain-oriented electrical steel sheets relating to the above, the distance between the first irradiation section and the second irradiation section is set to a length that is a natural number multiple of the pitch of the groove.

[0022] History of this disclosure 10An aspect includes a process for manufacturing a grain-oriented electrical steel sheet, a process for forming a wound core from the grain-oriented electrical steel sheet, and a stress-relieving annealing process for performing stress-relieving annealing on the wound core. The process for manufacturing the grain-oriented electrical steel sheet includes a grooving process for grooving the surface of the grain-oriented electrical steel sheet. The grooving process includes a first irradiation step of irradiating a first beam under a first irradiation condition for forming linear grooves extending in a direction corresponding to the sheet width direction of the grain-oriented electrical steel sheet on the surface of the grain-oriented electrical steel sheet, and a second irradiation step of irradiating a second beam under a second irradiation condition different from the first irradiation condition along the grooves on the surface of the grain-oriented electrical steel sheet. The grain-oriented electrical steel sheet is finally finish-annealed, and the second irradiation condition is 、 predetermined To eliminate distortion within the aforementioned steel plate portion. heat treatment is applied heat and is an irradiation condition corresponding to the treatment conditions, The second irradiation unit irradiates the second beam such that the irradiation area to which the second beam is irradiated overlaps with at least a portion of the surface of the groove. and is a method for manufacturing a wound core.

Advantages of the Invention

[0023] According to the present disclosure, there are provided a grooving method for a grain-oriented electrical steel sheet, a grooving apparatus for a grain-oriented electrical steel sheet, , and and a method for manufacturing a wound core, in which iron loss does not deteriorate even when a wound core is manufactured, and production efficiency and production stability can be improved.

Brief Description of the Drawings

[0024] [Figure 1] It is a two-dimensional view showing an example of a grooving apparatus according to an embodiment of the present disclosure and a steel sheet as a processing target. [Figure 2] It is a cross-sectional view showing an example of a region on the surface of the steel sheet irradiated with a second laser beam. [Figure 3] It is a view showing a first example of a method for manufacturing a grain-oriented electrical steel sheet. [Figure 4] It is a view showing a second example of a method for manufacturing a grain-oriented electrical steel sheet. [Figure 5] It is a view showing an example of a result of comparing the iron loss improvement rate between the present disclosure example and a comparative example. [Figure 6] This is a schematic diagram comparing the cross-section around the groove of a wound iron core after the strain-relieving annealing process in the disclosed example and comparative example. [Figure 7] This figure shows an example of a method for manufacturing a wound iron core according to one embodiment of the present disclosure. [Figure 8] This figure shows an example of the results obtained by heat transfer calculations for the temperature distribution in the width direction on the surface of a steel plate. [Figure 9] This figure shows an example of the results obtained by heat transfer calculations for the temperature distribution in the thickness direction of a steel plate. [Figure 10] This figure shows an example of irradiation conditions for a second laser beam that satisfy the heat treatment conditions obtained from heat transfer calculations. [Figure 11] This is a cross-sectional view showing a first example of the cross-sectional structure of a grain-oriented electrical steel sheet according to one embodiment of the present disclosure. [Figure 12] This is a cross-sectional view showing a first example of the cross-sectional structure of a grain-oriented electrical steel sheet according to one embodiment of the present disclosure. [Figure 13] This is a cross-sectional view showing an example of the cross-sectional structure of a grain-oriented electrical steel sheet relating to a comparative example. [Modes for carrying out the invention]

[0025] An embodiment of this disclosure will be described below.

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

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

[0028] The first laser beam irradiation unit 12 irradiates the surface of the steel sheet 30 with a first laser beam L1 under first irradiation conditions that enable the formation of linear grooves 32 extending in a direction corresponding to the 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, and corresponds to, for example, a grain-oriented electrical steel sheet after the insulating film formation process (see Figure 3) or a grain-oriented electrical steel sheet after the final finish annealing process (see Figure 4). The direction corresponding to the width direction of the steel sheet 30 refers to a direction approximately parallel to the width direction. Furthermore, the direction approximately parallel to the width direction refers to a direction that intersects with respect to the transport direction, and refers to a direction that intersects with the width direction of the steel sheet 30 at a predetermined angle. For example, the predetermined angle refers to an angle within the range of ±30 degrees with respect to the 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 (for example, a glass coating or an insulating coating) if the steel plate 30 has a coating. Furthermore, the steel plate 30 as referred to herein is only the steel plate portion 30A (see Figure 2) if there is no coating such as a glass coating or an insulating coating, and if there is a coating, it includes the steel plate portion 30A and the coating. The steel plate portion 30A has a predetermined thickness, and the coating is provided on the surface of at least one side of the steel plate portion 30A (at least one side of both surfaces in the thickness direction). Note that Figure 2 shows a steel plate 30 without a coating for simplification.

[0029] The second laser beam irradiation unit 14 irradiates the surface of the steel plate 30 with a second laser beam L2 along the groove 32 under second irradiation conditions different from the first irradiation conditions. The second laser beam irradiation unit 14 irradiates the second laser beam L2 such that the irradiation area to which the second laser beam L2 is irradiated overlaps with at least a part of the surface of the groove 32. The second laser beam irradiation unit 14 irradiates the surface of the steel plate 30 with the second laser beam L2 along the scanning path on the steel plate 30 made by the first laser beam irradiation unit 12. Here, the second irradiation conditions are irradiation conditions corresponding to heat treatment conditions that allow a predetermined heat treatment to be applied to a predetermined range of the steel plate portion 30A from the surface of the groove 32. The heat treatment conditions are heat treatment conditions that eliminate the strain in the steel plate portion 30A around the groove 32 that occurred when the groove 32 was formed. The heat treatment conditions are conditions that heat the steel plate 30 to a temperature above the temperature required for heat treatment, within a range where the steel plate 30 does not melt. Relieving strain includes not only completely eliminating strain, but also suppressing strain to the extent that the subgrain boundaries generated during the strain-relieving annealing process do not pose a problem.

[0030] As will be explained in more detail later, the heat treatment conditions are, for example, that the temperature of the opening edge of the groove 32, the side surface of the groove 32, and the area up to 10 μm from the bottom surface of the groove 32 remains at 1000°C or higher for 0.1 msec or longer, and that the temperature in the above area is maintained at 1600°C or lower. The area from the opening edge of the groove 32, the side surface of the groove 32, and the area up to 10 μm from the bottom surface of the groove 32 is an example of a predetermined area to which the above heat treatment is to be applied. The area from the opening edge of the groove 32 up to 10 μm refers to the area on one side in the width direction of the groove 32. The second irradiation conditions do not have to be the same as the heat treatment conditions and may be set based on the heat treatment conditions. Also, the second irradiation conditions may be set based on heat transfer calculations or experiments, etc.

[0031] Here, the scanning paths of the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 will be explained using Figure 1. The first laser beam irradiation unit 12 irradiates the surface of the steel plate 30 with the first laser beam L1 while moving the first laser beam L1 in the direction of movement indicated by arrow Y1. The second laser beam irradiation unit 14 irradiates the surface of the steel plate 30 with the second laser beam L2 while moving the second laser beam L2 in the direction of movement indicated by arrow Y2. That is, the second laser beam irradiation unit 14 irradiates the surface of the steel plate 30 with the second laser beam L2 along the path (arrow Y1) from the first laser beam irradiation unit 12 to the surface of the steel plate 30. The direction of movement of the first laser beam L1 and the second laser beam L2 is the same direction and is approximately parallel to the width direction of the steel plate 30.

[0032] The first laser beam irradiation unit 12 comprises a first laser light source, which is a laser light source that outputs a first laser beam L1, and a first moving mechanism, which is a moving mechanism for moving the first laser beam L1. The first moving mechanism includes, for example, a polygon mirror and a motor for rotating the polygon mirror. Similarly, the second laser beam irradiation unit 14 comprises a second laser light source, which is a laser light source that outputs a second laser beam L2, and a second moving mechanism, which is a moving mechanism for moving the second laser beam L2. The second moving mechanism includes, for example, a polygon mirror and a motor for rotating the polygon mirror. The groove processing device 10 may have a polygon mirror and motor common to the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 as a moving mechanism for moving the first laser beam L1 and the second laser beam L2, or it may have separate polygon mirrors and motors. Furthermore, when the first laser beam irradiation unit 12 and the second laser beam irradiation 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. Also, at least one of the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 may be equipped with a configuration other than a polygon mirror (for example, a galvanometer mirror).

[0033] Furthermore, the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 preferably irradiate the steel plate 30 with the first laser beam L1 and the second laser beam L2 while the steel plate 30 is being transported, but they may also irradiate the steel plate 30 with the first laser beam L1 and the second laser beam L2 while the steel plate 30 is stopped. Also, the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 may irradiate the steel plate 30 so that the first laser beam L1 and the second laser beam L2 move in the same direction, or they may irradiate the steel plate 30 so that the first laser beam L1 and the second laser beam L2 move in different directions. Furthermore, the second laser beam irradiation unit 14 preferably irradiates the steel plate 30 with the second laser beam L2 continuously along the scanning path on the steel plate 30 by the first laser beam irradiation unit 12, but they may also irradiate a single groove 32 intermittently in the longitudinal direction of the groove 32, or they may selectively irradiate a plurality of grooves 32 (for example, every other groove) with the second laser beam L2.

[0034] The first laser beam irradiation unit 12 is positioned upstream of the second laser beam irradiation unit 14 in the transport direction. The grooving device 10 irradiates the surface of the steel plate 30 with a first laser beam L1 from the first laser beam irradiation unit 12 to form a linear groove 32 extending in a direction substantially parallel to the width direction of the plate, and then irradiates the steel plate portion 30A around the groove 32 with a second laser beam L2 from the second laser beam irradiation unit 14, tracing the groove 32, thereby applying heat treatment to the steel plate portion 30A around the groove 32. Hereinafter, the irradiation area of ​​the first laser beam L1 focused on the surface of the steel plate 30 will be referred to as the "first focused spot S1", and the irradiation area of ​​the second laser beam L2 focused on the surface of the steel plate 30 will be referred to as the "second focused spot S2". Furthermore, the region irradiated by the second laser beam L2 is referred to as the "second laser beam irradiation region 34," and the region 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 heat treatment conditions is referred to as the "heat treatment region 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, it is preferable that the distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 be set to a length that is a natural number multiple of the pitch of the groove 32. The distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 is defined 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 length that is a natural number multiple of the pitch of the groove 32, the configuration of the groove processing device 10 can be simplified compared to when it is set to a length other than a natural number multiple of the pitch of the groove 32. When both the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 use a single polygon mirror in common, the distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 is set to a length that is a natural number multiple of the pitch of the groove 32 with respect to the width in the transport direction of the polygon mirror having a rotation axis substantially parallel to the transport direction.

[0036] For example, the first laser light source of the first laser beam irradiation unit 12 may be a fiber laser device with high focusing characteristics, suitable for forming the grooves 32. Furthermore, the second laser light source of the second laser beam irradiation unit 14 may be a semiconductor laser device or the like, capable of outputting a laser with a higher steel plate absorption rate and shorter wavelength than a fiber laser device, suitable for heat treatment around the grooves 32.

[0037] Figure 2 shows an example of a second laser beam irradiation region 34 on the surface of the steel plate 30 to which the second laser beam L2 is irradiated. The groove 32 has a side surface 32B connected to the opening edge 32A, which is the boundary between the surface of the steel plate 30 and the groove 32 (recess), and a bottom surface 32C that is connected to the side surface 32B. The side surface 32B is connected to the surface of the steel plate 30 (region 32A1) 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 the 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. That is, the second laser beam irradiation region 34 overlaps with the groove 32 and has a width that is longer on both sides in the transport direction than the groove 32.

[0038] Incidentally, when a laser beam is irradiated onto the surface of a steel sheet 30 to form grooves 32, strain is generated around the grooves 32 when the grooves 32 are formed. Figure 2 shows an example of the strain-generating region around the grooves 32 (hereinafter referred to as the "strain generation region 38"). When manufacturing a winding core for a transformer from grain-oriented electrical steel sheets, there is a problem in that the iron loss deteriorates during the strain-relieving annealing process performed after winding the grain-oriented electrical steel sheets. It is believed that the cause of this problem is that the strain generated in the strain generation region 38 when the grooves 32 are formed by the laser beam causes subgrain boundaries to be generated around the grooves 32 during the strain-relieving annealing process.

[0039] Therefore, the grooving apparatus 10 includes a first laser beam irradiation unit 12 that irradiates a first laser beam L1 for forming grooves 32, as well as a second laser beam irradiation unit 14 that irradiates a second laser beam L2 for performing heat treatment (i.e., high-temperature strain-relieving annealing heat treatment) on the strain-generating region 38 to eliminate strain. In other words, the grooving apparatus 10 is configured to irradiate the surface of the steel plate 30 with a first laser beam L1, which is the main beam for forming grooves 32, and a second laser beam L2, which is the sub-beam for performing heat treatment on the strain-generating region 38.

[0040] By irradiating the strain generation region 38 with the second laser beam L2 and performing heat treatment under predetermined conditions, the strain generated in the strain generation region 38 can be eliminated. By eliminating the strain generated in the strain generation region 38, the generation of subgrain boundaries around the groove 32 during the strain-relieving annealing process after winding of the grain-oriented electrical steel sheet can be suppressed. To eliminate the strain generated around the groove 32, it is preferable that the heat treatment region 36, which is heat-treated by irradiation with the second laser beam L2, includes the strain generation region 38.

[0041] The heat treatment conditions applied to the strain generation region 38 can be set by adjusting the power density and energy density of the second laser beam L2. Here, power density is the power supplied from the second laser beam irradiation unit 14 to a unit area of ​​the surface of the steel plate 30, and is obtained by dividing the output of the second laser beam L2 by the area of ​​the second focused spot S2, with units of W / mm2. Energy density is the amount of heat supplied per unit time, and is obtained by multiplying the power density by the irradiation time, with units of J / mm2. Irradiation time is obtained by dividing the beam diameter in the plate width direction by the moving speed. In other words, the second irradiation conditions by the second laser beam irradiation unit 14 can be set by adjusting the output of the second laser beam L2, the irradiation time, and the area of ​​the second focused spot S2.

[0042] The second laser beam irradiation unit 14 irradiates the strain generation region 38 around the groove 32 in order to perform heat treatment. Meanwhile, the first laser beam irradiation unit 12 irradiates to form the groove 32. Therefore, the second laser beam irradiation unit 14 irradiates at a power density lower than that required by the first laser beam irradiation 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 irradiation unit 14 can be adjusted to irradiate at a lower power density than the first laser beam irradiation unit 12 by setting the area of ​​the second focusing spot S2 to be larger than that of the first focusing spot S1. Also, as described above, energy density is the power density multiplied by the irradiation time, so the power density can be lowered by increasing the irradiation time to obtain the target energy density. For this reason, the second laser beam irradiation unit 14 may set the shape of the second focusing spot S2 to have a long axis so that the irradiation time is longer, and the scanning direction of the second laser beam L2 and the long axis direction of the second focusing spot S2 are the same. That is, the length of the second focusing spot S2 in the width direction of the steel plate 30 may be set to be longer than that of the first focusing spot S1.

[0044] Furthermore, it is preferable that the heat treatment region 36, which is heat-treated by irradiation with the second laser beam L2, has a length in the transport direction of the steel plate 30 (direction perpendicular to the plate width direction) that is the same length as or longer than the region containing the strain generated when forming the groove 32 (strain generation region 38). Therefore, it is preferable that the length of the second focusing spot S2 in the transport direction of the steel plate 30 be set to be longer than that of the first focusing spot S1.

[0045] Furthermore, in order to eliminate the strain generated 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 irradiation unit 14 irradiates with a second laser beam L2 that has a larger beam diameter than the first laser beam L1 irradiated by the first laser beam irradiation unit 12. For example, the beam diameter of the first laser beam L1 is defined by the length of the first focusing spot S1 in the width direction of the steel plate 30, and the beam diameter of the second laser beam L2 is defined by the length of the second focusing spot S2 in the width direction of the steel plate 30.

[0046] Since distortion occurs around the groove 32 when the groove 32 is formed, with the center of the first laser beam L1 being approximately at its center, it is preferable that the center of the second laser beam L2, which is used to eliminate the distortion, corresponds to the center of the first laser beam L1. That is, it is preferable that the second laser beam irradiation unit 14 irradiates the second laser beam L2 such that the center of the second laser beam L2 approximately coincides with the center of the first laser beam L1. As a result, the second laser beam L2 is 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 generation area 38. However, as long as the distortion generated 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 a range that fits within the width of the groove 32.

[0047] Furthermore, if the strain generated around the groove 32 can be eliminated during the groove formation process, the distance between the first laser beam irradiation unit 12 and the second laser beam irradiation unit 14 (i.e., a length that is a natural number multiple of the pitch of the groove 32) can be set to any length.

[0048] Up to this point, we have described the irradiation conditions of the second laser beam irradiation unit 14 in comparison to the irradiation conditions of the first laser beam unit 12. Detailed heat treatment conditions will be explained in conjunction with the heat transfer calculations described later.

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

[0050] The control unit 16 comprises, functionally, a first control unit 18 and a second control unit 20. The first control unit 18 and the second control unit 20 are implemented, for example, by the processor executing a program stored in ROM or storage. The control unit 16 may also include electronic circuits such as a PLD (Programmable Logic Device) or ASIC (Application Specific Integrated Circuit) instead of, or in addition to, the processor. Furthermore, some or all of the first control unit 18 and the second control unit 20 may be implemented by electronic circuits such as a PLD or ASIC.

[0051] The first control unit 18 controls the first laser beam irradiation unit 12 to irradiate the surface of the steel plate 30 with a first laser beam L1 so that grooves 32 are formed on the surface of the steel plate 30. The first control unit 18 calculates the moving speed of the first laser beam L1 corresponding to the transport speed of the steel plate 30 based on a signal from a speed sensor that detects the transport speed of the steel plate 30, and controls the first laser beam irradiation unit 12 (for example, a motor that rotates a polygon mirror) so that the first laser beam L1 moves at the calculated moving speed. The moving speed of the first laser beam L1 refers to, for example, the moving speed in the direction of arrow Y1 in Figure 1. The second control unit 20 controls the second laser beam irradiation unit 14 to irradiate the second laser beam L2 along the scanning path of the first laser beam irradiation unit 12 that formed the grooves 32, using irradiation conditions corresponding to the heat treatment conditions that eliminate the strain generated in the strain generation region 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 transport speed of the steel plate 30 based on a signal from a speed sensor that detects the transport speed of the steel plate 30, and controls the second laser beam irradiation unit 14 (for example, a motor that rotates a 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] Figure 3 shows a first example of a method for manufacturing grain-oriented electrical steel sheets. The manufacturing method shown in Figure 3 comprises a casting process, a hot rolling process, an annealing process, a cold rolling process, a decarburization annealing process, an annealing separation and coating process, a final finish annealing process, an insulating film formation process, a groove formation process, and a re-insulating film formation process.

[0053] The casting process is the process of manufacturing slabs using a continuous casting method. The hot rolling process is the process of hot rolling a slab heated to a predetermined heating temperature (for example, 1100°C to 1400°C) to obtain a hot-rolled steel sheet. The annealing process is the process of annealing the hot-rolled steel sheet immediately or in a short time to obtain an annealed steel sheet. The cold rolling process is the process of obtaining a cold-rolled steel sheet by cold rolling the annealed steel sheet once, or by cold rolling multiple times (for example, two or more times) with intermediate annealing. The decarburization annealing process is the process of decarburizing the cold-rolled steel sheet to obtain a decarburized annealed steel sheet in which primary recrystallization has occurred.

[0054] The annealing separation coating process involves applying an annealing separation agent to the decarburized annealed steel sheet. The final finish annealing process involves performing finish annealing on the decarburized annealed steel sheet to which the annealing separation agent has been applied, thereby causing secondary recrystallization and obtaining a finish annealed steel sheet. Here, a finish annealed steel sheet refers to a steel sheet that has undergone finish annealing on a decarburized annealed steel sheet to which the annealing separation agent has been applied, resulting in secondary recrystallization. The insulating film formation process involves applying a coating solution to the surface of the finish annealed steel sheet and baking it to form an insulating film on the surface of the finish annealed steel sheet. The steel sheet 30 shown in Figure 1 corresponds to a finish annealed steel sheet.

[0055] The groove formation process is a process in which, for the purpose of magnetic domain control, a plurality of grooves 32 extending in a direction intersecting the conveying direction are formed at predetermined intervals in the conveying direction on the surface of a finish annealed steel sheet that is conveyed in the conveying direction indicated by arrow X (see Figure 1). The groove formation process comprises a first laser beam irradiation process and a second laser beam irradiation process. The first laser beam irradiation process is a process in which a first laser beam L1 is irradiated onto the surface of the finish annealed steel sheet from a first laser beam irradiation unit 12 to form grooves 32 on the surface of the finish annealed steel sheet. The second laser beam irradiation process is a process in which, after the first laser beam irradiation process, a second laser beam L2 is irradiated from a second laser beam irradiation unit 14 along the grooves 32 on the surface of the finish annealed steel sheet under second irradiation conditions corresponding to heat treatment conditions that eliminate the strain generated in the strain generation region 38 when the grooves 32 were formed.

[0056] The first laser beam irradiation process and the second laser beam irradiation process 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 surface of the steel plate 30 with the first laser beam L1 and the second laser beam L2, respectively. The first laser beam irradiation process is an example of the "first irradiation process" in this disclosure, and the second laser beam irradiation process is an example of the "second irradiation process" in this disclosure.

[0057] The re-insulating coating formation process involves applying a coating solution to the surface of the finished annealed steel sheet on which the grooves 32 have been formed, and baking it to re-form an insulating coating on the surface of the finished annealed steel sheet.

[0058] Figure 4 shows a second example of a manufacturing method for grain-oriented electrical steel sheets. 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 the finish-annealed steel sheet before the insulating coating is formed on the surface. The steel sheet 30 shown in Figure 1 corresponds to the finish-annealed steel sheet.

[0059] Thus, the groove processing method using the groove processing apparatus 10 according to this embodiment may be applied to either the groove formation step in the manufacturing method of grain-oriented electrical steel sheet shown in Figures 3 and 4.

[0060] Figure 7 shows an example of a method for manufacturing a wound core according to one embodiment of the present disclosure. The method for manufacturing a wound core comprises a grain-oriented electrical steel sheet manufacturing step, a wound core formation step, and a strain-relieving annealing step. The grain-oriented electrical steel sheet manufacturing step is a step for manufacturing the steel sheet 30 described above, and includes a grooving step for grooving the surface of the steel sheet 30 that has undergone final finish annealing. As described above, the grooving step includes a first laser beam irradiation step and a second laser beam irradiation step. As described above, the steel sheet 30 includes linear grooves 32 extending in a direction corresponding to the sheet width direction and heat-treated regions 36 formed along the grooves 32. The wound core formation step is a step for forming a wound core 50 from the steel sheet 30. Specifically, the steel sheet 30 is wound into a roll shape, and the wound core 50 is formed by cutting it when it has been wound to a desired size. The strain-relieving annealing step is a step in which strain-relieving annealing treatment is performed on the wound core 50 to remove the strain that occurred in the wound core 50 when it was formed. The strain-relieving annealing process is a step in which the wound core 50 is heated under temperature conditions that can remove the strain that occurred in the wound core 50 when it was formed.

[0061] Next, we will describe the experimental examples. In these experimental examples, we prepared a steel sheet according to the present disclosure and a steel sheet according to the comparative example. Specifically, as the steel sheet according to the present disclosure, we prepared a steel sheet in which grooves 32 were formed on the surface of the steel sheet by irradiating it with a first laser beam L1 from a first laser beam irradiation unit 12 during the groove formation process, and the area around the grooves 32 (i.e., the strain generation region 38) was heat-treated by irradiating it with a second laser beam L2 from a second laser beam irradiation unit 14 in a manner that traces along the grooves 32. As the steel sheet according to the comparative example, we prepared a steel sheet in which grooves 32 were formed on the surface of the steel sheet by irradiating it with a first laser beam L1 from a first laser beam irradiation unit 12 during the groove formation process, but the irradiation of the second laser beam L2 from the second laser beam irradiation unit 14 was omitted.

[0062] The test samples used in this disclosure and comparative example were common to both and were manufactured using the manufacturing method for grain-oriented electrical steel sheet of the first example shown in Figure 3. Details are provided below. Test sample: Steel sheet after insulating coating process, magnetic flux density B8 = 1.91T, iron loss W17 / 50 = 0.9W / kg

[0063] The irradiation conditions for the first laser beam L1 were the same for both the disclosed example and the comparative example, and were as follows: Output: 1000W, Moving speed in the plate width direction: 30m / s, Irradiation pitch in the transport direction: 3mm, Beam diameter: 0.05mm (transport direction) × 0.1mm (plate width direction), Groove depth: 20μm, Groove width: 50μm

[0064] The irradiation conditions for the second laser beam L2 (in this disclosure only) were as follows: Output: 2000W, Movement speed in the plate width direction: 30m / s, Irradiation pitch in the transport direction: 3mm, Beam diameter: 0.15mm (transport direction) x 15mm (plate width direction)

[0065] Furthermore, in this experimental example, a steel sheet before the groove formation process (i.e., a finish annealed steel sheet without grooves) was prepared as the steel sheet for the reference example. The above test sample was used for the steel sheet for the reference example. The rate of iron loss improvement for the steel sheet for the disclosed example and the steel sheet for the comparative example was compared with that of the steel sheet for the reference example after the re-insulating coating process.

[0066] Furthermore, in this experimental example, a transformer winding core manufactured from a steel sheet after the groove formation process was prepared as the winding core according to the disclosed example and the winding core according to the comparative example. In addition, a transformer winding core manufactured from a steel sheet before the groove formation process was prepared as the winding core according to the standard example. The iron loss improvement rate after the strain-relieving annealing process for the winding core according to the disclosed example and the winding core according to the comparative example was then compared with that of the winding core according to the standard example.

[0067] In this experiment, each wound core was a 20 kVA single-phase wound core. The strain relief annealing process involved annealing at 800°C for 3 hours in a 100% nitrogen atmosphere. Then, a primary winding (excitation winding) and a secondary winding (search coil) were wound onto each wound core, and the iron loss of each core was measured using a power meter.

[0068] Figure 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 of the steel plate according to the disclosed example compared to the steel plate according to the reference example. Bar graph G2 shows the iron loss improvement rate of the wound core according to the disclosed example after the strain-relieving annealing process compared to the wound core according to the reference example. Bar graph G3 shows the iron loss improvement rate of the steel plate according to the comparative example compared to the steel plate according to the reference example. Bar graph G4 shows the iron loss improvement rate of the wound core according to the comparative example after the strain-relieving annealing process compared to the wound core according to the reference example.

[0069] In this experimental example, when comparing the steel plate according to the disclosed example with the steel plate according to the comparative example, there was no difference in the rate of iron loss improvement after the groove formation process. However, when comparing the wound iron core according to the disclosed example with the wound iron core according to the comparative example, the wound iron core according to the disclosed example showed a rate of iron loss improvement after the strain-relieving annealing process that was 3% or more better than that of the wound iron core according to the comparative example.

[0070] Figure 6 shows a schematic diagram comparing the cross-sections around the groove 32 of a wound core after the strain-relieving annealing process in the present disclosure and the comparative example. Figure 6(A) shows the comparative example, and Figure 6(B) shows the present disclosure. As shown in Figure 6(A), subgrain boundaries were generated around the groove 32 in the wound core of the comparative example, while as shown in Figure 6(B), no subgrain boundaries were generated around the groove 32 in the wound core of the present disclosure.

[0071] Thus, this experiment confirmed that if heat treatment is not performed on the strain generation region 38, subgrain boundaries are generated around the groove 32 during the strain-relieving annealing process, and when subgrain boundaries are generated around the groove 32, iron loss deteriorates during the strain-relieving annealing process.

[0072] Furthermore, this experimental example revealed that the region where subgrain boundaries occur is in the range from 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. The region where subgrain boundaries occur is considered to be approximately the same as the strain generation region 38 described above. Therefore, in order to suppress the generation of subgrain boundaries around the groove 32, it is considered that the strain present in this range should be eliminated by performing heat treatment (i.e., high-temperature strain-relieving annealing heat treatment) with the second laser beam L2 in a range from the surface of the groove 32, such as 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. In other words, it was found that the heat treatment region 36 should be 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 at least 10 μm.

[0073] It should be noted that the above irradiation conditions for the second laser beam L2 in this experimental example are merely an example, and other irradiation conditions are acceptable as long as they satisfy the irradiation conditions corresponding to the heat treatment conditions that eliminate the strain. Here, we would like to define the predetermined conditions for heat treatment in the area from the opening edge 32A, the side surface 32B, and the bottom surface 32C of the groove 32 up to 10 μm by heating temperature, but in this experimental example, it is difficult to directly measure the temperature in the area from the opening edge 32A, the side surface 32B, and the bottom surface 32C of the groove 32 up to 10 μm. Therefore, we will use heat transfer calculations to define the predetermined conditions for heat treatment in the area from the opening edge 32A, the side surface 32B, and the bottom surface 32C of the groove 32 up to 10 μm.

[0074] In the heat transfer calculations, the irradiation conditions for the second laser beam L2 were set to the same conditions as those in the disclosed example that suppress the degradation of iron loss. Specifically, the irradiation conditions for the second laser beam L2 were set to the following conditions. Output: 2000W, Movement speed in the plate width direction: 30m / s, Irradiation pitch in the transport direction: 3mm, Beam diameter: 0.15mm (transport direction) x 15mm (plate width direction) Furthermore, in the heat transfer calculations, the laser beam absorption rate of steel plate 30 was assumed to be 60%.

[0075] Figure 8 shows an example of the results obtained by heat transfer calculation of the temperature distribution in the width direction of the steel plate 30, with respect to an arbitrary point on the surface of the steel plate 30. In Figure 8, the horizontal axis represents the time [msec] with respect to the moment when the second laser beam L2 passes over the arbitrary point. Specifically, it represents the elapsed time, with 0.00 seconds set to the time when the center of the second focused spot S2 in the transport direction coincides with the arbitrary point. The vertical axis represents the position [mm] of the steel plate 30 in the width direction, with the position on the optical axis of the second laser beam L2 set to 0 mm. As shown in Figure 8, under the above irradiation conditions of the second laser beam L2 (i.e., irradiation conditions that can suppress the deterioration of iron loss), the calculation result was obtained that the surface temperature of the steel plate 30 on the optical axis of the second laser beam L2 is 1600°C or less, which is the melting temperature of the steel plate 30. If the surface temperature of the steel plate 30 exceeds 1600°C, the surface of the steel plate 30 will melt, so it is considered that the surface temperature of the steel plate 30 needs to be 1600°C or less.

[0076] Furthermore, calculations revealed that the range in the transport direction where the surface temperature of the steel plate 30 exceeds 1000°C is within ±40 μm (80 μm 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 transport direction). In other words, calculations revealed that the range in the transport direction where the surface temperature of the steel plate 30 exceeds 1000°C includes the range from the opening edge 32A of the groove 32 to 10 μm.

[0077] Figure 9 shows an example of the results obtained by heat transfer calculation of the temperature distribution in the thickness direction of the steel plate 30. In Figure 9, the horizontal axis shows the time [msec] relative to the moment the second laser beam L2 passes over an arbitrary point, and the vertical axis shows the position [μm] in the thickness direction of the steel plate 30, with the surface of the steel plate 30 being 0 μm. As shown in Figure 9, under the above irradiation conditions of the second laser beam L2 (i.e., irradiation conditions that can suppress the deterioration of iron loss), calculation results were obtained showing that, for example, the temperature in the thickness direction range from the surface of the steel plate 30 to 10 μm remains at least 1000°C for 0.1 msec. Therefore, in order to suppress the deterioration of iron loss, it is considered 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 longer.

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

[0079] Figure 10 shows an example of irradiation conditions for the second laser beam L2 that satisfy the heat treatment conditions obtained from heat transfer calculations (i.e., conditions that can suppress the deterioration of iron loss). The example shown in Figure 10 is an example of irradiation conditions for the second laser beam L2 when heat transfer calculations are performed with the following conditions for the irradiation conditions of the second laser beam L2. Beam diameter of the second laser beam L2 in the transport direction: 0.15 mm, movement speed of the second laser beam L2 in the plate width direction: 30 m / s, laser beam absorption rate of steel plate 30: 60%

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

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

[0082] The range that satisfies the heat treatment conditions, as shown in Figure 10, can be expressed by the following formula: 0.0105 × P-6.5 ≤ dc ≤ 0.0155 × P-12.0 However, P is the output power [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 for the second laser beam L2 within the "range that satisfies the heat treatment conditions" shown in Figure 10, and irradiating with the second laser beam L2, the KAM value around the groove 32 can be made between 0.1 and 3.0. This suppresses the generation of subgrain boundaries, thereby suppressing the deterioration of iron loss. Note that while etching can reduce the KAM value to 0, in principle, laser beam irradiation cannot reduce the KAM value to below 0.1.

[0084] Figure 11 shows a first example of the cross-sectional structure of a grain-oriented electrical steel sheet according to one embodiment of the present disclosure. The steel sheet 30 shown in Figure 11 was manufactured by the first example of the method for manufacturing a grain-oriented electrical steel sheet shown in Figure 3. The steel sheet 30 comprises a glass coating 40, an insulating coating 42 formed by an insulating coating formation process, and a re-insulating coating 44 formed by a re-insulating coating formation process. In the example shown in Figure 11(A), a modified portion 42A is formed in a part of the insulating coating 42 (i.e., the part irradiated with the second laser beam L2). In the example shown in Figure 11(B), the modified portion 42B is a region in which a part of the insulating coating 42 (i.e., the part irradiated with the second laser beam L2) is thinned or missing. In the example shown in Figure 11(A), the modified portion 42A is limited to the insulating coating 42, but there may be cases where a modified portion 42A is formed in both the insulating coating 42 and the glass coating 40. In other words, although the altered portion 42A occurs only in the insulating film 42, the altered portion 42A may also be present in the insulating film 42 and the insulating film 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 Figure 11(B).

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

[0086] Figure 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 Figure 13(A) was manufactured by a manufacturing method that omits the second laser beam irradiation step compared to the first example of the manufacturing method of grain-oriented electrical steel sheet shown in Figure 3. The steel sheet 130 shown in Figure 13(A) is similar to the steel sheet 30 shown in Figure 11 in that it comprises a glass coating 40, an insulating coating 42 formed by an insulating coating formation step, and a re-insulating coating 44 formed by a re-insulating coating formation step. However, it differs from the steel sheet 30 shown in Figure 11 in that it does not have the characteristic of having altered portions 42A or 42B in a part of the insulating coating 42. In other words, the steel sheet 130 according to the comparative example shown in Figure 13(A) does not have altered portions 42A or 42B, but in the example shown in Figure 11, the coating covering the surface of a predetermined range of the steel sheet portion 30A from the groove 32 (more specifically, the opening edge 32A of the groove 32) has altered portions 42A or 42B.

[0087] The steel sheet 130 shown in Figure 13(B) was manufactured by a manufacturing method that omits the second laser beam irradiation step compared to the second example of the manufacturing method for grain-oriented electrical steel sheet shown in Figure 4. The steel sheet 130 shown in Figure 13(B) is similar to the steel sheet 30 shown in Figure 12 in that it comprises a glass coating 40 and an insulating coating 46 formed by an insulating coating formation step performed after the groove formation step, but it differs from the steel sheet 30 shown in Figure 12 in that it does not have the characteristic of having altered portions 40A or 40B in a part of the glass coating 40. In other words, the steel sheet 130 in the comparative example shown in Figure 13(B) does not have altered portions 40A or 40B, but in the example shown in Figure 12, the coating covering the surface of a predetermined range of steel sheet portion 30A from the groove 32 (more specifically, the opening edge 32A of the groove 32) has altered portions 40A or 40B.

[0088] Thus, the steel sheet 30 manufactured by the first example of the manufacturing method for grain-oriented electrical steel sheets shown in Figure 3 or the second example of the manufacturing method for grain-oriented electrical steel sheets shown in Figure 4 has a different cross-sectional structure from the steel sheet 130 of the comparative example manufactured by a manufacturing method that omits the second laser beam irradiation step.

[0089] As described in detail above, in this embodiment, in the groove formation process, the second laser beam L2 is irradiated from the second laser beam irradiation unit 14 along the groove 32 under irradiation conditions corresponding to the heat treatment conditions that relieve the strain generated when the groove 32 was formed, thereby relieving the strain generated around the groove 32 when the groove 32 was formed. Therefore, even when manufacturing the wound core of a transformer from grain-oriented electrical steel sheets, the generation of subgrain boundaries around the groove 32 can be suppressed in the strain-relieving annealing process performed after winding the grain-oriented electrical steel sheets, thereby suppressing the deterioration of iron loss.

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

[0091] In the above embodiment, a first laser beam L1 and a second laser beam L2 are used in the groove formation process, but 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 a first laser beam irradiation unit 12 that irradiates the first laser beam L1, the first electron beam irradiation unit is an example of the "first irradiation unit" in this disclosure. Also, when a second electron beam irradiation unit that irradiates an electron beam is used instead of a second laser beam irradiation unit 14 that irradiates the second laser beam L2, the second electron beam irradiation unit is an example of the "second irradiation unit" in this disclosure. As for the electron beam irradiation unit, any type of irradiation device capable of irradiating an electron beam is acceptable, such as a thermionic emission type, a field emission type, or a Schottky type.

[0092] Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above, and it is of course possible to implement it in various modified forms without departing from its spirit.

[0093] All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually incorporated by reference. In addition, the disclosure of Japanese application number 2024-031639, filed on March 1, 2024, is incorporated in its entirety by reference herein. [Explanation of Symbols]

[0094] 10 Grooving equipment 12. First laser beam irradiation section 14. Second laser beam irradiation section 16 Control Unit 18 First Control Unit 20 Second Control Unit 30 steel plate 30A steel plate part 32 Groove 34. Second laser beam irradiation area 36 Heat Treatment Area 38. Distortion generation region L1 First laser beam L2 Second laser beam

Claims

1. A method for grooving grain-oriented electrical steel sheets, which involves grooving the surface of the grain-oriented electrical steel sheet, A first irradiation step involves irradiating the surface of the grain-oriented electrical steel sheet with a first beam under first irradiation conditions that enable the formation of linear grooves extending in a direction corresponding to the width direction of the grain-oriented electrical steel sheet, A second irradiation step involves irradiating the surface of the grain-oriented electrical steel sheet with a second beam along the groove under second irradiation conditions different from the first irradiation conditions, Equipped with, The aforementioned grain-oriented electrical steel sheet has undergone final finish annealing. The second irradiation condition is an irradiation condition corresponding to a heat treatment condition that applies a predetermined heat treatment to a portion of the steel sheet within a predetermined range from the surface of the groove in the grain-oriented electrical steel sheet to eliminate strain within that portion of the steel sheet. The second irradiation step involves irradiating the groove with the second beam such that the irradiation area to which the second beam is irradiated overlaps with at least a portion of the surface of the groove. A method for processing grooves in grain-oriented electrical steel sheets.

2. The second beam has a lower power density than the first beam. A method for grooving a grain-oriented electrical steel sheet according to claim 1.

3. The center of the second beam corresponds to the center of the first beam, A method for grooving a grain-oriented electrical steel sheet according to claim 1 or claim 2.

4. The first irradiation step is performed using a fiber laser device, The second irradiation step uses a semiconductor laser device that outputs a laser beam with a higher steel plate absorption rate and shorter wavelength than the fiber laser device. A method for grooving a grain-oriented electrical steel sheet according to claim 1 or claim 2.

5. The heat treatment conditions are such that the temperature of the opening edge of the groove, the side surface of the groove, and the area up to 10 μm from the bottom surface of the groove is 1000°C or higher for 0.1 msec or longer, and the temperature in the area is maintained at 1600°C or lower. A method for grooving a grain-oriented electrical steel sheet according to claim 1 or claim 2.

6. The first irradiation step and the second irradiation step are performed when transporting the grain-oriented electrical steel sheet. A method for grooving a grain-oriented electrical steel sheet according to claim 1 or claim 2.

7. A grooving apparatus for grain-oriented electrical steel sheets, which performs groove processing on the surface of grain-oriented electrical steel sheets, A first irradiation unit that irradiates the surface of the grain-oriented electrical steel sheet with a first beam under first irradiation conditions that enable the formation of linear grooves on the surface of the grain-oriented electrical steel sheet in a direction corresponding to the width direction of the sheet, A second irradiation section is provided on the surface of the grain-oriented electrical steel sheet, which irradiates a second beam along the groove with a second irradiation condition different from the first irradiation condition, Equipped with, The aforementioned grain-oriented electrical steel sheet has undergone final finish annealing. The second irradiation condition is an irradiation condition corresponding to a heat treatment condition that applies a predetermined heat treatment to a portion of the steel sheet within a predetermined range from the surface of the groove in the grain-oriented electrical steel sheet to eliminate strain within that portion of the steel sheet. The second irradiation unit irradiates the second beam such that the irradiation area to which the second beam is irradiated overlaps with at least a portion of the surface of the groove. Grooving machine for grain-oriented electrical steel sheets.

8. The first irradiation unit and the second irradiation unit operate when transporting the grain-oriented electrical steel sheet, The grooving apparatus for grain-oriented electrical steel sheets according to claim 7.

9. 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 groove. A grooving apparatus for grain-oriented electrical steel sheets according to claim 7 or claim 8.

10. A process for manufacturing grain-oriented electrical steel sheets, A winding core forming step in which a winding core is formed from the aforementioned grain-oriented electrical steel sheet, A strain-relieving annealing step is performed on the wound iron core, Equipped with, The aforementioned grain-oriented electrical steel sheet manufacturing process includes a grooving process for grooving the surface of the grain-oriented electrical steel sheet, The groove machining process described above is: A first irradiation step involves irradiating the surface of the grain-oriented electrical steel sheet with a first beam under first irradiation conditions that form linear grooves extending in a direction corresponding to the width direction of the grain-oriented electrical steel sheet, A second irradiation step involves irradiating the surface of the grain-oriented electrical steel sheet with a second beam along the groove under second irradiation conditions different from the first irradiation conditions, Equipped with, The aforementioned grain-oriented electrical steel sheet has undergone final finish annealing. The second irradiation condition is an irradiation condition corresponding to a heat treatment condition that applies a predetermined heat treatment to a portion of the steel sheet within a predetermined range from the surface of the groove in the grain-oriented electrical steel sheet to eliminate strain within that portion of the steel sheet. The second irradiation step involves irradiating the groove with the second beam such that the irradiation area to which the second beam is irradiated overlaps with at least a portion of the surface of the groove. A method for manufacturing a wound iron core.

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