GROOVING PROCESSING METHOD, GROOVING PROCESSING APPARATUS AND GRAIN-ORIENTED ELECTRIC STEEL SHEET

Abstract

Provided is a grooving method for forming grooves on a grain-oriented electrical steel sheet, wherein: the method includes a grooving step for forming, by scanning a laser beam, linear grooves at constant intervals or non-constant intervals in a rolling direction of the grain-oriented electrical steel sheet, such that the grooves have a maximum depth of 10 to 50 µm and extend in the scanning direction, which is a direction parallel to a width direction of the grain-oriented electrical steel sheet, the width direction being perpendicular to the rolling direction, or a direction tilted by a prescribed angle from the width direction; the laser beam has a center irradiation section, which is a region including a center of an optical path of the laser beam through which the laser beam is irradiated, and a peripheral irradiation section, which is a region in the periphery of the center irradiation section irradiated with the laser beam; and the energy density [J / cm2] of the center irradiation section is set to be greater than the energy density [J / cm2] of the peripheral irradiation section.

Description

60 GROOVING PROCESSING METHOD, GROOVING PROCESSING APPARATUS AND GRAIN-ORIENTED ELECTRIC STEEL SHEET TECHNICAL FIELD

[001] The present invention relates to a groove processing method, a groove processing apparatus and an electrically oriented grain steel sheet.

[002] Priority is claimed in Japanese Patent Application No. 2023-022958, filed on February 16, 2023, the contents of which are incorporated herein by reference. FUNDAMENTALS OF THE TECHNIQUE

[003] As a measure to reduce iron loss in a grain-oriented electrical steel sheet used for an iron core of a transformer, a magnetic domain control process, in which a sheet surface is scanned with a laser beam, has been put into practical use (see, for example, Patent Document 1). In this magnetic domain control process, linear deformations or linear grooves are formed on the sheet surface by scanning the steel sheet with a laser beam along a direction parallel to a direction perpendicular to a rolling direction (the width direction of the grain-oriented electrical steel sheet) at regular intervals in a sheet passage direction (rolling direction) of the grain-oriented electrical steel sheet or a direction inclined at a predetermined angle relative to the width direction.

[004] Here, various techniques using laser processing are considered in order to reduce iron loss and, for example, a technique for applying the “deformations” described above, described in Patent Document 2, may be exemplified, and a technique for forming the “grooves” described above, described in Patent Documents 3 and 4, may be Petition 870250070654, dated 11 / 08 / 2025, p. 92 / 164 / 60 exemplified.

[005] In a case where the technique of applying “deformations” and the technique of forming “grooves” are compared, the latter, which performs magnetic domain control by forming grooves on the sheet surface, can exhibit excellent performance, such that the effect of magnetic domain control is not lost, even if stress-relief annealing is performed after the iron core is formed using the grain-oriented electrical steel sheet processed with grooves. Furthermore, since the grooves are formed on the sheet surface, there is also the advantage of being able to easily and clearly identify the steel sheet on which magnetic domain control is being performed. Considering this advantage, the following description will focus on the technique of forming a “groove” and performing magnetic domain control.

[006] In a laser processing method for forming a groove by irradiating the surface of a grain-oriented electrical steel sheet with a laser beam, the surface of the grain-oriented electrical steel sheet is instantly melted and evaporated by local thermal processing with the laser beam to form a groove having a depth of, for example, about 20 to 30 μm. Any molten material that remains unevaporated and scattered can be pushed onto the sheet surface and solidified, or molten droplets (splatters) can adhere to the periphery of the groove, and the molten material can remain as elevations on the sheet surface.

[007] In the case where an iron core of a transformer is manufactured by stacking grain-oriented electrical steel sheets, a certain pressure (also called interlayer pressure) is generated between the stacked grain-oriented electrical steel sheets. If elevations occur on the sheet surface during stacking, Petition 870250070654, dated 11 / 08 / 2025, page 93 / 164 / 60 local deformations in grain-oriented electrical steel sheets due to pressure between layers, thus causing an increase in iron loss. Furthermore, the elevations can be a factor causing the breakdown of electrical insulation between grain-oriented electrical steel sheets. Therefore, in the magnetic domain control process for groove processing in a grain-oriented electrical steel sheet using a laser beam, it is necessary to minimize the formation of elevations.

[008] For example, Patent Document 3 describes a method for forming a groove in a sheet metal surface using a continuous wave laser beam, in which the height of an elevation is controlled to 5 [μm] or less by specifying a laser beam irradiation condition, and describes, as an example, the use of a laser having a laser beam intensity profile in the basic Gaussian mode. Furthermore, Patent Document 4 describes that the elevations are removed by a brush roller after the grooves have been processed by a laser. List of Citations Patent Document

[009] Patent Document 1: Japanese Patent Application No. Examined, First Publication No. H6-57335

[0010] Patent Document 2: International Publication PCT No. WO 2022 / 045265

[0011] Patent Document 3: Japanese Patent No. 5234222

[0012] Patent Document 4: Japanese Patent No. 6826606 SUMMARY OF THE INVENTION Technical Problem

[0013] However, as described in Patent Document 3, even if the laser beam irradiation condition is specified, it is difficult to completely avoid the formation of the elevations. Furthermore, although it is possible to remove the elevations with a brush roller or similar. Petition 870250070654, dated 11 / 08 / 2025, page 94 / 164 / 60 after processing, in this case, additional equipment is required. Therefore, in a magnetic domain control technique to reduce iron loss by irradiating a surface of an electrically oriented grain steel sheet with a laser beam to form a groove having a depth of, for example, 20 μm or more, it is desired to reduce iron loss without forming an elevation on the sheet surface around the groove.

[0014] One objective of the present invention is to provide a groove processing method, a groove processing apparatus and a grain-oriented electrical steel sheet, which allow for the reduction of iron loss without forming a raised area around a groove, compared with the conventional technique. Solution to the Problem

[0015] The present invention was made in view of the above circumstances and adopts the following aspects.

[0016] A groove processing method according to one aspect of the present invention is a groove processing method for forming a groove in a grain-oriented electrical steel sheet, and the method includes a groove processing step of performing a scan with a laser beam to form a groove having a linear shape and a maximum depth of 10 [pm] or more and 50 [pm] or less and extending in a scan direction serving as a direction parallel to a width direction of the grain-oriented electrical steel sheet perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction, the grooves being formed at regular intervals in the rolling direction of the grain-oriented electrical steel sheet, wherein the laser beam includes a central irradiation portion serving as a region including the center of an optical path of the laser beam where the laser beam is emitted,and a peripheral radiation portion serving as a region surrounding the part of, Petition 870250070654, dated 11 / 08 / 2025, p. 95 / 164 / 60 central irradiation where the laser beam is emitted, and an energy density [J / cm2] of the central irradiation part is defined as greater than an energy density [J / cm2] of the peripheral irradiation part.

[0017] A groove processing method according to another aspect of the present invention is a groove processing method for forming a groove in a grain-oriented electrical steel sheet, and the method includes a groove processing step of performing a scan with a laser beam to form a groove having a linear shape and a maximum depth of 10 [μm] or more and 50 [μm] or less and extending in a scan direction serving as a direction parallel to a width direction of the grain-oriented electrical steel sheet perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction, the grooves being formed at irregular intervals in the rolling direction of the grain-oriented electrical steel sheet, wherein the laser beam includes a central irradiation portion serving as a region including the center of an optical path of the laser beam where the laser beam is emitted,and a peripheral irradiation zone serving as a region around the central irradiation zone where the laser beam is emitted, and an energy density [J / cm2] of the central irradiation zone is defined as greater than an energy density [J / cm2] of the peripheral irradiation zone.

[0018] Furthermore, a groove processing apparatus according to an aspect of the present invention is a groove processing apparatus configured to form a groove in a grain-oriented electrical steel sheet, in which the groove processing apparatus performs a scan with a laser beam to form a groove having a linear shape and a maximum depth of 10 μm or more and 50 μm or less and extending in a scan direction that serves as a direction parallel to a width direction of the steel sheet. Petition 870250070654, dated 11 / 08 / 2025, page 96 / 164 / 60 electrically oriented grain perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction, the grooves being formed at regular intervals in the rolling direction of the electrically oriented grain steel sheet, the laser beam includes a central irradiation portion that serves as a region that includes the center of an optical path of the laser beam where the laser beam is emitted, and a peripheral irradiation portion that serves as a region surrounding the central irradiation portion where the laser beam is emitted, and an energy density [J / cm2] of the central irradiation portion is defined as greater than an energy density [J / cm2] of the peripheral irradiation portion.

[0019] Furthermore, a groove processing apparatus according to another aspect of the present invention is a groove processing apparatus configured to form a groove in a grain-oriented electrical steel sheet, wherein the groove processing apparatus performs a scan with a laser beam to form a groove having a linear shape and a maximum depth of 10 [μm] or more and 50 [µm] or less and extending in a scan direction that serves as a direction parallel to a width direction of the grain-oriented electrical steel sheet perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction, the grooves being formed at irregular intervals in the rolling direction of the grain-oriented electrical steel sheet,The laser beam includes a central irradiation portion, which serves as the region encompassing the center of the laser beam's optical path where the laser beam is emitted, and a peripheral irradiation portion, which serves as the region surrounding the central irradiation portion where the laser beam is emitted. The energy density [J / cm²] of the central irradiation portion is defined as greater than the energy density [J / cm²] of the peripheral irradiation portion.

[0020] In addition, a grain-oriented electrical steel sheet of Petition 870250070654, dated 11 / 08 / 2025, page 97 / 164 / 60 according to one aspect of the present invention is a grain-oriented electrical steel sheet, in which a groove having a linear shape and a maximum depth of 10 [μm] or more and 50 [pm] or less and extending in a direction parallel to a width direction perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction is formed, the grooves being formed at regular intervals in the rolling direction, and the groove having a multi-stage shape including a deep groove portion with a deeper point and a groove edge portion with a smoother gradient than a gradient of a wall surface of the deep groove portion as seen in the direction in which the groove extends.

[0021] Furthermore, a grain-oriented electrical steel sheet according to another aspect of the present invention is a grain-oriented electrical steel sheet in which a groove having a linear shape and a maximum depth of 10 [pm] or more and 50 [pm] or less and extending in a direction parallel to a width direction perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction is formed, the grooves being formed at irregular intervals in the rolling direction, and the groove having a multi-stage shape including a deep groove portion with a deeper point and a groove edge portion with a smoother gradient than a gradient of a wall surface of the deep groove portion as seen in the direction in which the groove extends. Advantageous Effects of the Invention

[0022] In accordance with each of the aspects described above of the present invention, when the aim is to minimize iron loss from grain-oriented electrical steel sheet by groove formation using a laser beam, it is possible to minimize an elevation around the groove compared Petition 870250070654, dated 11 / 08 / 2025, page 98 / 164 / 60 with the conventional technique and reduce iron loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] [Figure 1] A perspective view showing a configuration of a groove processing apparatus according to an embodiment of the present invention.

[0024] [Figure 2] A schematic diagram showing a focused shape of a laser beam emitted by the slot processing apparatus. Here, (2A) shows a top view relative to the surface of a sheet, (2B) shows a focused shape of the laser beam when (2A) is viewed in a cross-section along the T direction, and (2C) shows a focused shape of the laser beam when (2A) is viewed in a cross-section along the S direction.

[0025] [Figure 3] A schematic diagram showing a relationship between a focused shape of a laser beam emitted by the groove processing apparatus and a groove formed by this laser beam. Here, (3A) shows a focused shape of the laser beam when viewed from above relative to a sheet metal surface, and (3B) shows a focused shape of the laser beam when (3A) is viewed in a cross-section along a direction T. In addition, (3C) is a plan view of a groove formed in the sheet metal surface, and (3D) is a longitudinal cross-sectional view of (3C) as seen along line A-A'.

[0026] [Figure 4] A schematic diagram showing a relationship between a focused shape of a conventional laser beam and a groove formed by the conventional laser beam. Here, (4A) shows a focused shape of the laser beam when viewed from above relative to a sheet metal surface, and (4B) shows a focused shape of the laser beam when (4A) is viewed in a cross-section along a direction T. In addition, (4C) is a plan view of the groove formed in the sheet metal surface, and (4D) is a longitudinal cross-sectional view of (4C) as seen along line B-B'. Petition 870250070654, dated 11 / 08 / 2025, page 99 / 164 / 60

[0027] [Figure 5] A schematic diagram showing individual production steps after a grain-oriented electrical steel sheet in the modality is subjected to a cold rolling step.

[0028] [Figure 6] Cross-sectional views of a product in which a groove is processed using the groove processing apparatus according to the embodiment. Here, (LP1a) and (LP1b) are cross-sectional views showing a cross-sectional constitution of a product A subjected to a laser processing step LP1 after the cold rolling step in step S1 shown in Figure 5. Furthermore, (LP2a) and (LP2b) are cross-sectional views showing a cross-sectional constitution of product A subjected to a laser processing step LP2 after a primary recrystallization annealing step in step S2 shown in Figure 5. Furthermore, (LP3a) and (LP3b) are cross-sectional views showing a cross-sectional constitution of product A subjected to a laser processing step LP3 after a secondary recrystallization annealing step in step S3 shown in Figure 5.

[0029] [Figure 7] Cross-sectional views of a product in which a groove is processed using the groove processing apparatus according to the embodiment. Here, (LP4a-1) and (LP4b-1) are seen in cross-section showing a cross-sectional constitution of a product B subjected to a laser processing step LP4 after an insulation coating step in step S4 shown in Figure 5. In addition, (LP4a-2) and (LP4b-2) are seen in cross-section showing a cross-sectional constitution of a product C subjected to laser processing step LP4 after the insulation coating step in step S4 shown in Figure 5 and subsequently subjected to a new coating step.

[0030] [Figure 8] A schematic diagram showing a constitution of a laser beam according to another embodiment of the present Petition 870250070654, dated 11 / 08 / 2025, p. 100 / 164 / 60 invention. Here, (8A) shows a view when viewed from above with respect to a sheet metal surface, (8B) shows a view of (8A) when viewed in a cross-section along a T direction, and (8C) shows a view of (8A) when viewed in a cross-section along the S direction.

[0031] [Figure 9] A schematic diagram showing a constitution of a laser beam according to yet another embodiment of the present invention. Here, (9A) shows a view when viewed from above with respect to a sheet metal surface, (9B) shows a view of (9A) when viewed in a cross-section along a direction T, and (9C) shows a view of (9A) when viewed in a cross-section along the direction S.

[0032] [Figure 10] A schematic diagram showing the constitution of a laser beam according to yet another embodiment of the present invention. Here, (10A) shows a view when viewed from above with respect to a sheet metal surface, (10B) shows a view of (10A) when viewed in a cross-section along a direction T, and (10C) shows a view of (10A) when viewed in a cross-section along the direction S.

[0033] [Figure 11] A schematic diagram showing the constitution of a laser beam according to yet another embodiment of the present invention. Here, (11A) shows a view when viewed from above with respect to a sheet metal surface, (11B) shows a view of (11A) when viewed in a cross-section along a direction T, and (11C) shows a view of (11A) when viewed in a cross-section along the direction S.

[0034] [Figure 12] A schematic diagram showing the constitution of a laser beam according to yet another embodiment of the present invention. Here, (12A) shows a view when viewed from above with respect to a sheet metal surface, (12B) shows a view of (12A) when viewed in a cross-section along a direction T, and (12C) shows Petition 870250070654, dated 11 / 08 / 2025, page 101 / 164 / 60 a view of (12A) when viewed in a cross section along the S direction.

[0035] [Figure 13] A schematic diagram showing a sheet surface of a grain-oriented electrical steel sheet in which a plurality of grooves is formed by a laser beam in a verification test.

[0036] [Figure 14] A perspective view showing the construction of a simulated transformer used in the verification test. DESCRIPTION OF THE MODALITIES

[0037] The following will describe in detail embodiments and various examples of modifications of the present invention with reference to the drawings. In the following description, the same components are indicated by the same reference numbers and redundant descriptions will be omitted. (1) <Constituição do Aparelho de Processamento de Ranhura de Acordo Com a Presente Modalidade>

[0038] Figure 1 is a perspective view showing an embodiment of a groove processing apparatus 1 according to the present embodiment. The groove processing apparatus 1 irradiates a surface (hereinafter referred to as the “sheet surface”) of a grain-oriented electrical steel sheet 100, which is the object to be processed, with a laser beam LB to form a U-groove extending in a direction parallel to a width direction of the grain-oriented electrical steel sheet 100 or in a direction inclined at a predetermined angle relative to the width direction, the U-grooves being formed at regular intervals or irregular intervals along a rolling direction. The position of the groove processing apparatus 1 relative to the grain-oriented electrical steel sheet 100 is defined based, for example, on the length and position of the U-groove formed on the sheet surface.The 100 grain-oriented electrical steel sheet is passed in the direction of... Petition 870250070654, dated 11 / 08 / 2025, page 102 / 164 / 60 lamination by a sheet passage device (not shown).

[0039] In Figure 1, a Y direction is a rolling direction of the 100 grain-oriented electrical steel sheet, an X direction is a width direction of the 100 grain-oriented electrical steel sheet, and an S direction is a scanning direction (hereinafter, it may also be called the laser scanning direction S or simply the scanning direction S) of the LB laser beam to form the U groove. A T direction is a direction perpendicular to the laser scanning direction S on the sheet surface and is also a width direction (groove width direction) of the U groove. Note that the laser scanning direction S (direction S) and a groove extension direction U (also called the groove extension direction S) are the same direction.Furthermore, in the following description, a geometric axis X, a geometric axis Y, a geometric axis S, and a geometric axis T mean geometric axes that pass through the center (i.e., the center of a central irradiation portion) of an optical path of the laser beam LB condensed on the sheet surface of the grain-oriented electrical steel sheet 100 and are parallel to the X direction, the Y direction, the S direction, and the T direction, respectively.

[0040] The slot processing device 1 includes a laser oscillator 2 and a laser irradiation device 3. The laser irradiation device 3 includes a collimator, a polygonal mirror, a condenser lens, and the like.Laser oscillator 2 emits a laser beam emitted by a predetermined irradiation method (e.g., a continuous irradiation method or a pulsed irradiation method) to laser irradiation device 3 via a fiber optic cable 4 having a dual structure including a central core and a peripheral core. Because the fiber optic cable 4 has a dual structure, including the central core and the peripheral core, the fiber optic cable 4 transmits a laser beam, including a central irradiation portion and a peripheral irradiation portion described below, to laser irradiation device 3. Petition 870250070654, dated 11 / 08 / 2025, p. 103 / 164 / 60

[0041] The laser oscillator 2 includes a power division adjustment device and, during the scanning of the laser beam LB, the laser power of the laser beam transmitted to each of the central and peripheral cores of the optical fiber cable 4 is adjusted by the power division adjustment device. Thus, the laser beam LB having different energy densities in the central irradiation part and in the peripheral irradiation part is generated.

[0042] For example, the laser irradiation device 3 transforms a divergent beam output from the fiber optic cable 4 into a collimated beam having an appropriate diameter and irradiates the polygonal mirror with the transformed laser beam. The laser irradiation device 3 rotates the polygonal mirror incorporated in it to change an angle of the polygonal mirror relative to the emitted laser beam, thus altering the direction of displacement of the laser beam reflected by the polygonal mirror. Thus, the laser beam LB is scanned along the scan direction S, which is either a direction parallel to the width direction of the oriented grain 100 electrical steel sheet or a direction inclined at a predetermined angle relative to the width direction.

[0043] The scanned laser beam LB is condensed onto the sheet surface by, for example, a lens 10 incorporated into the laser irradiation device 3. As a result, the laser beam LB is condensed and focused onto the sheet surface of the grain-oriented electrical steel sheet 100 and scanned in the S direction, with increased energy density, so that the groove U is formed on the sheet surface of the grain-oriented electrical steel sheet 100.

[0044] In a case where the U-groove is formed on the surface of 100-grain oriented electrical steel sheet by the LB laser beam to reduce iron loss from the 100-grain oriented electrical steel sheet, the formation of the U-groove extending parallel to the width direction of the Petition 870250070654, dated 11 / 08 / 2025, page 104 / 164 / 60 100 grain-oriented electrical steel sheet maximizes iron loss reduction efficiency. However, for example, in a case where 100 grain-oriented electrical steel sheet is used for an iron core of a transformer or similar, the 100 grain-oriented electrical steel sheet is subjected to a bending step, and the 100 grain-oriented electrical steel sheet is more likely to fracture from the U-groove parallel to the width direction during the bending step when the extension direction of the U-groove is parallel to the width direction of the 100 grain-oriented electrical steel sheet. Therefore, the direction of the U-groove (i.e., the sweep direction S) can be slightly inclined from the direction parallel to the width direction, allowing a slight decrease in reduction efficiency.Note that, in a case where the direction (i.e., the sweep direction S) of the U-groove is inclined relative to the width direction, the U-groove can be inclined by appropriately determining an angle according to the required performance of iron loss or similar and, for example, from the point of view of sufficiently ensuring the amount of iron loss reduction, it is conceivable to incline the U-groove within a range of more than 0° and 30° or less relative to the width direction of the oriented grain 100 electrical steel sheet.

[0045] In this case, the groove processing apparatus 1 scans the surface of the grain-oriented electrical steel sheet 100 with the laser beam LB to form a plurality of U-grooves, each having a linear shape and a maximum depth of 10 [μm] or more and 50 [μm] or less, and extending in the scanning direction S parallel to the width direction of the grain-oriented electrical steel sheet 100 perpendicular to the rolling direction or inclined at a predetermined angle relative to the width direction, the plurality of U-grooves being formed at regular intervals in the rolling direction of the grain-oriented electrical steel sheet 100. Note that, as required, the intervals at which the U-grooves Petition 870250070654, dated 11 / 08 / 2025, page 105 / 164 / 60 are formed and can be altered to irregular intervals along the rolling direction of the grain-oriented electrical steel sheet 100. (2)<Constituição do Feixe de Laser de Acordo com a Presente Modalidade>

[0046] Figure 2 is a schematic diagram showing the constitution of a focused laser beam shape LB according to the present embodiment. (2A) of Figure 2 is a schematic diagram showing a focused shape of the laser beam LB emitted by the laser irradiation device 3 towards the grain-oriented electrical steel plate 100. (2B) of Figure 2 is a schematic diagram showing an intensity profile of the laser beam LB on the surface of the grain-oriented electrical steel plate 100 along the geometric axis T, i.e., a spatial distribution of power [W] for the focused shape shown in (2A) of Figure 2. Furthermore, (2C) of Figure 2 is a schematic diagram showing a spatial distribution of the power [W] of the laser beam LB on the surface of the grain-oriented electrical steel plate 100 along the geometric axis S.

[0047] As shown in (2A) of Figure 2, the power distribution of the laser beam LB has a circular shape in the ST plane (the plate surface including both the S and T directions) and, specifically, includes a central irradiation portion M1 serving as a region including the center of an optical path of the laser beam LB, and a peripheral irradiation portion N1 formed in an annular shape around the central irradiation portion M1 so as to encircle the central irradiation portion M1. In addition, the power distribution of the laser beam LB includes a non-irradiation portion R1 between the central irradiation portion M1 and the peripheral irradiation portion N1, the non-irradiation portion R1 serving as a region where the power is relatively small and can be considered as substantially no irradiation with the laser beam LB.

[0048] As shown in (2B) of Figure 2, the power distribution of the central radiating part M1 is a Gaussian type distribution, Petition 870250070654, dated 11 / 08 / 2025, page 106 / 164 / 60, in which a maximum power Pm [W] is achieved at a position corresponding to the center of an optical path of the laser beam LB, where the power is highest and the beam intensity profile attenuates in a radial direction outward from the position of maximum power Pm [W]. The power distribution of the peripheral irradiation portion N1 is a Gaussian type distribution, in which a maximum power Pn [W] is achieved at a position in the central portion (central diameter) in a width direction of an annular ring between the inner circumferential portion and the outer circumferential portion within the annular portion, where the power is highest, and the power attenuates from the position of maximum power Pn [W] towards the inner circumferential portion and the outer circumferential portion.Note that the “Gaussian-type distribution” indicates a ridge-shaped power distribution in which the power [W] gradually decreases as the distance from the center where the power [W] of the LB laser beam reaches its absolute maximum value increases. This “Gaussian-type distribution” includes both a Gaussian distribution defined by a mathematical formula and a ridge-shaped distribution that cannot be represented by a mathematical formula.

[0049] Note that (2B) of Figure 2 shows the diameters of the central radiating part M1 and the peripheral radiating part N1 along a direction of the geometric axis T. The diameter of the central radiating part M1 in the direction of the geometric axis T is defined by a position on the geometric axis T where the central radiating part M1 reaches 1 / e2 times the maximum power Pm. Furthermore, the inner diameter and outer diameter of the peripheral radiating part N1 in the direction of the geometric axis T are defined by a position on the geometric axis T where the peripheral radiating part N1 reaches 1 / e2 times the maximum power Pn. In (2B) of Figure 2, 1 / e2 times the maximum power Pm of the central radiating part M1 is denoted by Pme, and the diameter of the central radiating part M1 in the direction Petition 870250070654, dated 11 / 08 / 2025, p. 107 / 164 / 60 of the geometric axis T is denoted by dmt [cm]. 1 / e2 times the maximum power Pn of the annular peripheral irradiation part N1 is denoted by Pne, the diameter of the inner circumferential portion of the peripheral irradiation part N1 in the direction of the geometric axis T is denoted by dnit [cm], and the diameter of the outer circumferential portion is denoted by dnot [cm]. Furthermore, an annular strip from the diameter dmt of the central irradiation part M1 to the diameter dnit of the inner circumferential portion of the peripheral irradiation part N1 is the non-irradiated part R1 which can be considered as not being substantially irradiated with the laser beam LB, since the power of the laser beam LB is small.

[0050] (2C) of Figure 2 shows the diameters of the central radiating part M1 and the peripheral radiating part N1 along a direction of the geometric axis S. Similar to the direction of the geometric axis T, the diameter of the central radiating part M1 in the direction of the geometric axis S is defined based on a position in the direction of the geometric axis S where the central radiating part M1 reaches 1 / e2 times the maximum power Pm. Furthermore, similarly to the direction of the geometric axis T, the inner and outer diameters of the peripheral radiating part N1 are also defined based on a position in the direction of the geometric axis S where the peripheral radiating part N1 reaches 1 / e2 times the maximum power Pn. The diameter of the central radiating part M1 in the direction of the geometric axis T is denoted by dms[cm].The diameter of the inner circumferential portion of the annular peripheral irradiation zone N1 in the direction of the geometric axis S is denoted by dnis [cm], and the diameter of the outer circumferential portion is denoted by dnos [cm]. Furthermore, an annular strip from the diameter dms of the central irradiation zone M1 to the diameter dnis of the inner circumferential portion of the peripheral irradiation zone N1 is the non-irradiated zone R1 in the direction of the geometric axis S.

[0051] In the case where metal processing (formation of Petition 870250070654, dated 11 / 08 / 2025, page 108 / 164 / 60 (U-shaped groove in steel plate) is performed by scanning with the LB laser beam; the phenomena that lead to the increase in temperature, melting, and evaporation of the metal depend mainly on the energy density of the emitted LB laser beam. The energy density is the product of the power density of the emitted LB laser beam and the irradiation time. The power density is defined by a value obtained by dividing the maximum powers Pm and Pn of the central irradiation part M1 and the peripheral irradiation part N1 by an area of ​​the LB laser beam.

[0052] In the present embodiment shown in Figure 2, a power density Pdm [MW / cm2] of the central radiating part M1 and a power density Pdn [MW / cm2] of the peripheral radiating part N1 can be represented by (Equation 1) and (Equation 2), respectively. The power density Pdm of the central radiating part M1 can exemplify a range of 5.0 [MW / cm2] or more and 600 [MW / cm2] or less. Furthermore, the power density Pdn of the peripheral radiating part N1 can exemplify a range of 1.0 [MW / cm2] or more and less than 5.0 [MW / cm2]. Pdm = Pm / (n / 4 x dmt x dms) ·· · (Equation 1) Pdn = Pn / (n / 4 x (dnot x dnos - dnit x dnis)) ··· (Equation 2)

[0053] The irradiation time, when scanning with the LB laser beam, is a value obtained by dividing the diameter of the LB laser beam in the scanning direction S by a scanning rate Vs [cm / s]. In the present embodiment, the irradiation times Tm [s] and Tn [s] of the central irradiation part M1 and the peripheral irradiation part N1 can be represented by (Equation 3) and (Equation 4), respectively. Tm = dms / Vs ··· (Equation 3) Tn = 2 x (dnos - dnis) / Vs ··· (Equation 4)

[0054] Therefore, an energy density Edm [J / cm2] of the central irradiation part M1 and an energy density Edn [J / cm2] of the part of Petition 870250070654, dated 11 / 08 / 2025, page 109 / 164 / 60 peripheral irradiation N1 can be represented by (Equation 5) and (Equation 6), respectively. Edm = Pdm x Tm ··· (Equation 5) Edn = Pdn x Tn ··· (Equation 6)

[0055] Although Figure 2 shows an example where the central irradiation part M1 has a perfect circular shape and the peripheral irradiation part N1 has a perfect annular shape, the present invention is not limited to this example. In a case where the central irradiation part M1 is elliptical and the peripheral irradiation part N1 has an elliptical ring shape, i.e., dmt and dms may be different from each other, or dnit and dnis, and dnot and dnos may be different from each other.

[0056] In the present embodiment, the U-groove is formed in the grain-oriented electrical steel plate 100 by the central irradiation portion M1 by scanning with the LB laser beam. However, in a case where the scanning is performed with a laser beam including only the central irradiation portion M1, the irradiated portion in the grain-oriented electrical steel plate 100 is melted and evaporated due to the relatively large energy density Edm. The molten metal is pushed upwards around the U-groove by the high-pressure metal vapor generated at this time, so that the molten metal is lifted from the surface of the grain-oriented electrical steel plate 100 and then solidified by rapid cooling to remain as an elevation. On the other hand, in the present embodiment, the scanning is performed not only on the central irradiation portion M1, but also on the peripheral irradiation portion N1 at once.Therefore, the molten metal pushed upwards around the U-groove is immediately heated due to the peripheral radiation N1. Thus, the cooling rate of the molten metal is reduced or the temperature of the molten metal is maintained at a high temperature, so that the viscosity of the molten metal decreases and the fluidity increases. As a result, the molten metal is... Petition 870250070654, dated 11 / 08 / 2025, p. 110 / 164 / 60 flattened before solidification or flows towards the deep portion of the U-groove, so that no elevation is formed on the sheet surface.

[0057] It is desirable to define the energy density Edn of the peripheral irradiation part N1 less than the energy density Edm of the central irradiation part M1. More specifically, the surface of the oriented grain electrical steel sheet 100 is locally melted and evaporated by the central irradiation part M1 to form the U-groove, but in order to form the U-groove having a depth of 10 [μm] or more, necessary to obtain the effect of reducing iron loss by magnetic domain control, the energy density Edm of the central irradiation part M1 is preferably, for example, 50 [J / cm2] or more.On the other hand, in a case where the energy density Edm of the central radiating part M1 is greater than 1000 [J / cm2] and excessively large, a deep groove with a depth greater than 50 [μm] is formed, resulting in significant inhibition of the generation of magnetic flux density, which is an important performance of the electrical steel sheet, and in a decrease in iron loss reduction. Therefore, the energy density Edm of the central radiating part M1 is desirably 1000 [J / cm2] or less. Furthermore, the peripheral radiating part N1 requires an appropriate energy density Edn in order to obtain a metal heating effect, and a specific numerical value is preferably, for example, 1 [J / cm2] or more. In contrast, in a case where the energy density Edn is too large, the molten metal may rise excessively, and the formation of elevations is promoted, so the energy density Edn is desirably, for example, less than 50 [J / cm2].For the reason described above, the energy density range of the central irradiation portion M1 can be exemplified as 50 [J / cm2] or more and 1000 [J / cm2] or less, and the energy density range of the peripheral irradiation portion N1 can be exemplified as 1 [J / cm2] or less. Petition 870250070654, dated 11 / 08 / 2025, p. 111 / 164 / 60 plus and minus 50 [J / cm2].

[0058] When the energy density Edm of the central irradiating part M1 and the energy density Edn of the peripheral irradiating part N1 satisfy the above ranges, favorable processing can be performed, and furthermore, the ratio between Edm and Edn can be defined as follows with these ranges satisfied. That is, a ratio obtained by dividing the energy density Edn of the peripheral irradiating part N1 by the energy density Edm of the central irradiating part M1 can be defined within a range of 0.1 to 0.3. Here, in a case where the ratio is less than the lower limit value, the heating effect of the peripheral portion is relatively small in relation to the amount of melt generated in the central irradiating part, and the effect of minimizing melt elevations may be insufficient. In contrast, in a case where the ratio is greater than the lower limit value of the ratio, the effect of reducing iron loss may decrease.This is considered to occur because a recessed part having a depth equivalent to the groove depth of the central part is also formed in the peripheral irradiation part, and a wide groove is formed. For this reason, the Edn / Edm ratio is preferably defined within the range described above. In this respect, the Edn / Edm ratio defined here is an example; it is sufficient that each of the energy densities Edm and Edn satisfies the range described above, and it is not necessary to define Edn / Edm for 0.1 to 0.3.

[0059] The laser irradiation device 3 irradiates the surface of the grain-oriented electrical steel sheet 100 having the laser beam LB having a multi-stage beam intensity profile, including the central irradiation part M1 and the peripheral irradiation part N1, the laser beam LB being inserted using, for example, a fiber transmission type laser having an annular refractive index distribution. Note that, in the present embodiment, for example, a case where a laser beam is transmitted and emitted by the laser irradiation device 3 using the cable of Petition 870250070654, dated 11 / 08 / 2025, p. 112 / 164 / 60 optical fiber 4 including a central core having a propagation core diameter of a Gaussian beam type and additionally including a concentric transmission core around the central core. However, the present invention is not limited to this example, and the laser irradiation device 3 may emit the laser beam LB including the central irradiation part M1 and the peripheral irradiation part N1 described above, combining two fiber transmission type lasers having different beam intensity profiles using a coaxial coupling optical system.

[0060] Next, the U-groove formed on the surface of the grain-oriented electrical steel sheet 100 by irradiation with the LB laser beam according to the present embodiment will be described. Figure 3 shows a relationship between a focused shape of the LB laser beam and the U-groove formed by the LB laser beam in the present embodiment. More specifically, (3A) of Figure 3 shows a focused shape when the LB laser beam according to the present embodiment is viewed in a cross-section perpendicular to an optical axis. (3B) of Figure 3 shows a beam intensity profile of the LB laser beam shown in (3A) of Figure 3 along the geometric axis T direction on the surface of the grain-oriented electrical steel sheet 100. (3C) of Figure 3 shows the U-groove seen in the vertical direction when the U-groove is formed by irradiation with the LB laser beam according to the present embodiment.(3D) of Figure 3 shows a cross-sectional shape when the U-groove shown in (3C) of Figure 3 is viewed in a cross-section along the groove width direction (direction T).

[0061] The focused shape and beam intensity profile shown in (3A) and (3B) of Figure 3 are used to adjust the power density and scan rate of this LB laser beam, and the energy densities Edm and Edn are set accordingly. Then, scanning with the LB laser beam is performed at high speed along the scan direction. Petition 870250070654, dated 11 / 08 / 2025, page 113 / 164 / 60 laser S to form the U groove shown in (3C) and (3D) of Figure 3.

[0062] The LB laser beam forms a deep groove portion U1 of the groove U on the surface of the grain-oriented electrical steel sheet 100 by the central irradiation part M1 with a high energy density and simultaneously heats the periphery of the central irradiation part M1 by the peripheral irradiation part N1 with a low energy density.

[0063] As described above, the laser beam LB simultaneously heats a position next to the central irradiation part M1 along the laser scanning direction S of the central irradiation part M1 and at least one of the positions on either side of the slot U along the direction T perpendicular to the laser scanning direction S by the peripheral irradiation part N1.

[0064] This heating prevents the molten material generated when the deep groove portion U1 is formed in the central irradiation part M1 from being lifted around the deep groove portion U1 or from re-adhering to the surface of the grain-oriented electrical steel sheet 100 after dispersion and solidifying in a raised shape. Therefore, it is possible to minimize the molten material that remains as a raised area on the surface of the grain-oriented electrical steel sheet 100. Furthermore, as the molten metal that can cause the raised area is heated by the peripheral irradiation part N1, the fluidity increases as the viscosity decreases, and the molten metal moves towards the center of the deep groove portion U1.Thus, a shape is formed in which the end portions of the U-groove in the T-groove width direction are inclined towards the center of the deep groove portion U1, and it is possible to minimize the generation of a rise rising from the sheet surface of the grain-oriented electrical steel sheet 100.

[0065] In a case where scanning with the LB laser beam is Petition 870250070654, dated 11 / 08 / 2025, page 114 / 164 / 60, carried out along the laser scanning direction S, a main portion of the peripheral irradiation part N1 having a low energy density relative to the central irradiation part M1 advances before the scanning of the central irradiation part M1 having a high energy density. Therefore, a position where the deep groove portion U1 should be formed by the central irradiation part M1 is preliminarily heated by the peripheral irradiation part N1. As a result, there is an effect of improving the efficiency of groove processing at high power intensity by the central irradiation part M1.

[0066] The U-shaped groove formed by scanning processing with the LB laser beam according to the present embodiment has a multi-stage shape, including a deep groove portion U1 having a U-shaped cross-sectional shape or a V-shaped cross-sectional shape having the deepest point and a groove edge portion U2 having a smoother gradient than a gradient of a wall surface of the deep groove portion U1 as seen in the cross-section in the groove width direction, which is a cross-section in the T direction perpendicular to the groove extension direction S. That is, in a case where the U-shaped groove is formed by the LB laser beam, the rapid cooling and solidification of the molten material generated when heated by the central irradiation part M1 is avoided by heating by the peripheral irradiation part N1.As a result, it is possible to minimize the solidification of the molten material in a state of being elevated as an elevation. Furthermore, the viscosity of the molten metal, through heating by the central irradiation portion M1, is reduced by heating by the peripheral irradiation portion N1. Therefore, the molten metal flows towards the side of the deep groove portion U1 and flows into the groove U. As a result, once the groove edge portion U2 has a smooth gradient, it is formed along the side of the groove portion. Petition 870250070654, dated 11 / 08 / 2025, page 115 / 164 / 60 deep U1 in the portion of the U-shaped groove irradiated in the peripheral irradiation part N1, it is possible to reduce the occurrence of a rising elevation (higher than the sheet surface) from the sheet surface of the grain-oriented electrical steel sheet 100.

[0067] Here, a straight line extending along the surface of the grain-oriented 100 electrical steel sheet is defined as a surface reference line, and when the groove U is viewed in a cross-section along the groove width direction T perpendicular to the groove extension direction S and the normal direction Z, the maximum depth D, which is a distance from the surface reference line to the deepest point of the groove U, is preferably 10 [μm] or more and 50 [pm] or less. In a case where the maximum depth D is less than 10 pm, the iron loss reduction effect is hardly achieved, and in a case where the maximum depth D is greater than 50 pm, the magnetic flux density capable of being generated is significantly reduced, so that the performance of a transformer iron core is considerably reduced.Note that the surface reference line can be obtained, for example, by obtaining a surface roughness curve of the sheet surface of the 100 grain-oriented electrical steel sheet at a position where U-grooves are not formed and averaging the surface roughness curve. In the present embodiment, in a case where the U-groove is processed by scanning with the LB laser beam, no elevations are formed on both adjacent sides of the U-groove, so that the sheet surface of the 100 grain-oriented electrical steel sheet follows the surface reference line.

[0068] Note that the maximum depth D of the groove U is obtained, for example, by performing an image analysis on a cross-sectional image along the groove width direction T obtained by a scanning electron microscope (SEM), by determining a line Petition 870250070654, dated 11 / 08 / 2025, page 116 / 164 / 60 of surface reference or similar from the cross-sectional shape of the U-groove in this cross-sectional image and the cross-sectional shape of the surface of the oriented grain electrical steel sheet 100 and, similarly, by measuring the maximum depth D of the U-groove based on the surface reference line as a limit by image analysis.

[0069] Figure 4 shows a relationship between a focused shape of a conventional LB100 laser beam and a U100 groove formed by the conventional LB100 laser beam. More specifically, (4A) and (4B) of Figure 4 show a constitution of the conventional LB100 laser beam. Here, (4A) of Figure 4 is a schematic diagram showing a focused shape of the LB100 laser beam, and (4B) of Figure 4 is a schematic diagram showing a beam intensity profile of the LB100 laser beam in the vertical direction of the sheet surface. (4C) of Figure 4 is a schematic diagram of a surface of the U100 groove formed by scanning with the conventional laser beam, and (4D) of Figure 4 is a schematic diagram of a cross-section of the U100 groove along the T direction.

[0070] The conventional LB100 laser beam has, for example, a circular energy density portion on the surface of the grain-oriented electrical steel sheet 100, a beam intensity profile of the energy density portion follows a Gaussian-type distribution, and the energy density portion has a single peak. In this case, as shown in (4C) and (4D) of Figure 4, the U100 groove formed by the LB100 laser beam is formed along the laser scanning direction S of the finely condensed LB100 laser beam according to the Gaussian-type distribution. However, due to heating by the high energy density portion in the center of the LB100 laser beam, the metal melts on the sheet surface of the grain-oriented electrical steel sheet 100, leading to evaporation. Thus, the molten metal is pushed out of the U100 groove by a large Petition 870250070654, dated 11 / 08 / 2025, page 117 / 164 / 60 pressure generated when the molten metal evaporates, and the molten metal adheres in a state in which it is lifted from the sheet surface of the grain-oriented electrical steel sheet 100 at a position of one edge of the groove U100. Subsequently, as the molten metal is solidified while being lifted by rapid cooling, an elevation 101 is formed on the sheet surface of the grain-oriented electrical steel sheet 100.

[0071] The principle of U100 groove formation on the surface of grain-oriented 100 electrical steel sheet by processing with the finely condensed LB100 laser beam lies in the temperature increase and melting of the metal constituting the grain-oriented 100 electrical steel sheet due to absorption by the LB100 laser beam, followed by flow, evaporation, and spreading of the molten metal. In particular, in processing performed by scanning with the LB100 laser beam having a high energy density only at the center, a keyway filled with high-temperature metal vapor exceeding the boiling point is formed locally at the irradiation point. Then, the molten metal is pushed onto the sheet surface around the U100 groove by the vapor pressure of the metal.

[0072] In scanning processing with the finely condensed LB100 laser beam, a region in which the temperature reaches a high temperature equal to or greater than the melting point by irradiation with this LB100 laser beam is very limited, and the surface temperature around the U100 groove is relatively low. As a result, the molten metal pushed out of the U100 groove is rapidly cooled on the surrounding surface, and surface tension acts in the molten state, so that the molten metal solidifies while being elevated to be the elevation 101.

[0073] Furthermore, in a case where scanning with the LB100 laser beam is performed at high speed, the molten metal is pushed out and flows at high speed towards the next side along the Petition 870250070654, dated 11 / 08 / 2025, page 118 / 164 / 60 laser scanning direction S, since the molten metal is pressed between the keyway and a solid layer immediately below the molten portion due to the pressure within the keyway. The molten metal flowing at high speed is solidified by rapid cooling after being pushed upwards. As a result, an elevation having a height greater than the sheet surface of the oriented grain 100 electrical steel sheet can be formed in the center of the U100 groove.

[0074] In contrast, in the present embodiment, the LB laser beam is used, the LB laser beam including, in addition to the central irradiation part M1 which has a high power intensity to melt and evaporate the metal, the peripheral irradiation part N1 which has a low power intensity to raise the temperature close to the melting point of the metal and which is also arranged on the next side relative to the central irradiation part M1 in the scanning direction S. Thus, in the present embodiment, in a case where the U-shaped groove is formed by heating by the central irradiation part M1, the periphery of this U-shaped groove is heated by the peripheral irradiation part N1 which has a low energy density, and the temperature is raised to the melting point or to a temperature close to the melting point.Therefore, the rapid cooling and solidification of the molten metal pushed upwards on the opposite side relative to the S-sweep direction, which occurs during the sweep of the central irradiation section M1, is attenuated, and the high temperature of the molten metal is maintained. In this way, the viscosity of the molten metal decreases, and the phenomenon of solidification in the form of an elevation can be minimized. As a result, the formation of an elevation in the center of the U-groove can be minimized.

[0075] Furthermore, the high-temperature state of the molten metal on the surrounding surface of the deep groove portion U1 formed by heating from the central radiating portion M1 is maintained for a relatively long time without generating a large evaporation pressure, by Petition 870250070654, dated 11 / 08 / 2025, page 119 / 164 / 60 reduction of the energy density Edn of the peripheral irradiation part N1 to an energy density at which the metal on the surface of the grain-oriented electrical steel sheet 100 does not reach its boiling point. The molten metal in the portion heated by the peripheral irradiation part N1 melts with the molten metal pushed out of the interior of the deep groove portion U1, and the molten metal passes through the peripheral irradiation part N1, followed by solidification as it flows towards a groove bottom portion of the deep groove portion U1.As a result, the depth of the deep groove portion U1 in the central part is slightly smaller, and the shallow groove edge portion U2 is formed around the deep groove portion U1, so that it is possible to prevent an elevation from occurring between the groove U and the surface of the oriented grain 100 electrical steel sheet in the X direction that intersects the laser scanning direction Y.

[0076] Furthermore, a position where a groove is to be formed is preheated by the peripheral irradiation section N1 having a low power intensity, before heating at the main position relative to the laser scanning direction S of the laser beam LB (forward in the direction of travel when scanning is performed with the laser beam LB) by the central irradiation section M1 having a high power intensity. Since heating by the peripheral irradiation section N1 has a preheating effect at the position where the groove is to be formed, an effect of improving the efficiency of groove processing is obtained with the central irradiation section M1.Furthermore, since heating by the peripheral irradiation section N1 has the effect of mitigating the rapid cooling of the molten metal in the next position relative to the laser scanning direction S of the laser beam LB, it is possible to reduce a phenomenon in which the molten metal in the groove U solidifies into an elevation shape when lifted to become higher than the sheet surface. Petition 870250070654, dated 11 / 08 / 2025, page 120 / 164 / 60 With the effect described above, in the present embodiment, it is possible to minimize the formation of the elevation around the U-groove. (3) <Momento de Implementação da Etapa de Processamento a Laser da Ranhura de Processamento de Varredura>

[0077] Next, a production step of scanning a plurality of U-grooves in grain-oriented electrical steel sheet 100 using groove processing apparatus 1 according to the present embodiment will be described. Figure 5 is a schematic diagram showing the individual production steps after the cold rolling step in the production procedure of grain-oriented electrical steel sheet 100. In the present production step, firstly, a hot-rolled electrical steel sheet coil containing Si in an amount of 2 to 8% is rolled to a sheet thickness of about 0.2 to 0.3 mm by cold rolling (step S1). Subsequently, primary recrystallization annealing is performed to form a SiO2 coating on the sheet surface (step S2).

[0078] Next, an annealing separator containing mainly MgO is applied to the sheet surface, and secondary recrystallization annealing is performed, thus allowing the so-called Goss grains, in which the rolling direction coincides with the easily magnetized geometric axis, to be preferentially grown into crystals (secondary recrystallization occurs). In addition, SiO2 and MgO react with each other to form a glass-like coating (called a vitreous coating) on ​​the sheet surface (step S3). It is known that the iron loss of oriented grain 100 electrical steel sheet is reduced by the addition of surface tension. Therefore, after secondary recrystallization annealing, an insulating coating is applied to the sheet surface for annealing purposes to flatten the steel sheet deformed due to annealing and, in addition, to impart surface tension and ensure properties Petition 870250070654, dated 11 / 08 / 2025, page 121 / 164 / 60 of electrical insulation (step S4). The resulting 100 grain-oriented electrical steel sheets are used as final products A and B. Furthermore, in a case where the moment of performing the groove processing with a laser described later is after step S4 (LP4), a new coating is applied to the surface of the insulation coating layer after step S4 (step S5), and the resulting 100 grain-oriented electrical steel sheet is used as a final product C.

[0079] Here, at any point from LP1 to LP4 shown in Figure 5, it is possible to perform a laser processing step (groove processing step) to scan a U-groove on the sheet surface using the groove processing apparatus 1 according to the present embodiment.

[0080] Figure 6 shows cross-sectional views of a product when the U-groove is processed using the groove processing apparatus 1 according to the present embodiment. More specifically, (LP1a) and (LP1b) of Figure 6 are cross-sectional views showing a cross-sectional constitution of product A obtained in a case where a laser processing step LP1 is performed after the cold rolling step in step S1. SiO2 is formed in product A in step S2 after the U-groove is processed with the laser, a reaction with MgO occurs in step S3, and the insulating coating is performed in step S4. Therefore, a vitreous coating 105 is formed within the U-groove, and an insulating coating layer 106 is additionally formed on the vitreous coating 105.

[0081] Because the insulation coating layer 106 has a different elemental component than that of the steel material that serves as a processed base metal 100b, the processed base metal 100b can be distinguished from the vitreous coating 105 by secondary electron beam analysis using an electron microscope or X-ray analysis. Petition 870250070654, dated 11 / 08 / 2025, page 122 / 164 / 60 characteristic in the observation of the cross-section, in addition to the observation of the optical microscope. On the other hand, although an extremely thin fused and resolidified layer is formed in the U-groove and its periphery immediately after laser processing, the fused and resolidified layer is almost lost by the secondary recrystallization annealing in the subsequent S3 step, so that it is difficult to observe the fused and resolidified layer in the final product.

[0082] Here, in a case where the U groove is processed on the surface of the grain-oriented electrical steel sheet 100 using the groove processing apparatus 1 according to the present embodiment, the beam intensity of the laser beam LB in the peripheral irradiation part N1 can be adjusted to form the U groove having only the deep groove portion U1 without any elevation formed around the U groove, as shown in (LP1a) of Figure 6, or the U groove having a multi-stage shape wherein the groove edge portion U2 having a smooth gradient is formed in addition to the deep groove portion U1, as shown in (LP1b) of Figure 6.

[0083] The U-groove shown in (LP1a) of Figure 6 is obtained in a case where the beam intensity of the peripheral irradiation portion N1 is relatively low and includes only the deep groove portion U1 formed in the U-groove, but a groove edge portion with a smooth gradient is not formed. However, no elevation is formed around the U-groove. The U-groove shown in (LP1b) of Figure 6 is obtained in a case where the beam intensity of the peripheral irradiation portion N1 is relatively high, and constant melting occurs around the deep groove portion U1 when the deep groove portion U1 is formed. Thus, the U-groove has a multi-stage shape in which the groove edge portion U2, having a smoother gradient than the gradient of a wall surface of the deep groove portion U1, is formed along the groove portion. Petition 870250070654, dated 11 / 08 / 2025, page 123 / 164 / 60 deep U1. Also in this case, no elevation forms around groove U.

[0084] (LP2a) and (LP2b) of Figure 6 are seen in cross-section of product A obtained in a case where a laser processing step LP2 is performed after the primary recrystallization annealing step in step S2. In this case, as the laser processing step LP2 is performed on the sheet surface of the grain-oriented electrical steel sheet 100 that has undergone primary recrystallization annealing, the SiO2 formed by primary recrystallization is removed when groove processing is performed with the laser beam LB. As a result, the vitreous coating 105 formed by the reaction between MgO and SiO2 applied subsequently is not formed within the groove U. Therefore, in this case, only the insulating coating layer 106 is formed in the groove U of product A.Furthermore, the fused-resolidified layer produced on the surface of the U-slot immediately after laser processing is removed by high-temperature secondary recrystallization annealing (step S3), which is the subsequent step.

[0085] The U-slot shown in (LP2a) of Figure 6 is obtained with a relatively low beam intensity from the peripheral irradiation portion N1. The U-slot shown in (LP2b) of Figure 6 is obtained with a relatively high beam intensity from the peripheral irradiation portion N1. In both (LP2a) and (LP2b), no elevation is formed around the U-slot when the deep groove portion U1 is formed by heating from the peripheral irradiation portion N1.

[0086] (LP3a) and (LP3b) of Figure 6 are seen in cross-section of product A obtained in a case where a laser processing step LP3 is performed after the secondary recrystallization annealing step in step S3. In this case, as the laser processing step LP3 is performed on the sheet surface that has undergone recrystallization annealing Petition 870250070654, dated 11 / 08 / 2025, page 124 / 164 / 60 secondary, the vitreous coating 105 formed in the U-groove during the secondary recrystallization annealing step is removed by the LB laser beam. Furthermore, since a high-temperature annealing step to remove the molten-resolidified layer is not provided after the LP3 laser processing step, the molten-resolidified layer 108 formed in the U-groove is not removed and remains as is, and the insulating coating layer 106 is formed on the molten-resolidified layer 108. Note that, for the molten-resolidified layer 108, the average grain size of columnar crystal grains and grains formed during rapid cooling can be determined by transverse microscopic observation.

[0087] The U-slot shown in (LP3a) of Figure 6 is obtained with a relatively low beam intensity from the peripheral irradiation portion N1. The U-slot shown in (LP3b) of Figure 6 is obtained with a relatively high beam intensity from the peripheral irradiation portion N1. In both (LP3a) and (LP3b), no elevation is formed around the U-slot when the deep groove portion U1 is formed by heating from the peripheral irradiation portion N1.

[0088] Figure 7 shows cross-sectional views of a product in which the U-groove is processed using groove processing apparatus 1 according to the present embodiment. More specifically, (LP4a-1) and (LP4b-1) of Figure 7 are cross-sectional views of product B obtained in a case where a laser processing step LP4 is performed after the insulation coating step in step S4. The U-groove shown in (LP4a-1) of Figure 7 is obtained with a relatively low beam intensity from the peripheral irradiation part N1. The U-groove shown in (LP4b-1) of Figure 7 is obtained with a relatively high beam intensity from the peripheral irradiation part N1. In both (LP4a-1) and (LP4b-1), no elevation is formed around the U-groove. Petition 870250070654, dated 11 / 08 / 2025, page 125 / 164 / 60 when the deep groove portion U1 is formed by heating from the peripheral irradiation part N1. In this case, as the laser processing step LP4 is performed after the completion of a tension coating step, the vitreous coating 105 and the insulating coating layer 106 formed in the groove U on the sheet surface at the time of the secondary recrystallization annealing step are removed by the laser beam LB, and only the fused-resolidified layer 108 remains.

[0089] (LP4a-2) and (LP4b-2) of Figure 7 are seen in cross-section of product C obtained in a case where the laser processing step LP4 is performed after the insulation coating step in step S4 and subsequently a re-coating step is performed. The U-groove shown in (LP4a-2) of Figure 7 is obtained with a relatively low beam intensity from the peripheral irradiation part N1. The U-groove shown in LP4b-2 of Figure 7 is obtained with a relatively high beam intensity from the peripheral irradiation part N1. In both (LP4a-2) and (LP4b-2), no elevation is formed around the U-groove when the deep groove portion U1 is formed by heating from the peripheral irradiation part N1.

[0090] In this case, once the re-coating step has been carried out, the insulation coating layer 106 is also formed on the fused-resolidified layer 108 that remains in the U-groove after the re-coating step. Furthermore, the thickness of the insulation coating layer 106 on the sheet surface, which is formed by the insulation coating step in step S4, is increased by carrying out the re-coating step. (4)<Operações e Efeitos>

[0091] The slot processing apparatus 1, having the constitution described above, performs a scan with the LB laser beam. Petition 870250070654, dated 11 / 08 / 2025, page. 126 / 164 / 60 to form U-grooves at regular or irregular intervals in the Y-rolling direction of the 100-grain oriented electrical steel sheet. The U-groove has a maximum depth of 10 [μm] or more and 50 [μm] or less, and has a linear shape extending in the laser scanning direction S, which is either a direction parallel to the X-width direction of the 100-grain oriented electrical steel sheet perpendicular to the Y-rolling direction or a direction inclined at a predetermined angle relative to the X-width direction. In this case, the LB laser beam, including the central irradiating part M1 and the peripheral irradiating part N1, in which the periphery of the central irradiating part M1 is heated, is used, and the energy density Edm of the central irradiating part M1 is defined as being greater than the energy density Edn of the peripheral irradiating part N1.

[0092] As a result, the groove processing apparatus 1 can mitigate the rapid cooling and solidification of the generated molten material when the deep groove portion U1 is formed by the central irradiation part M1 by heating the periphery of the central irradiation part M1 by the peripheral irradiation part N1, and minimize a raised surface on the sheet due to the flow of molten metal into the deep groove portion U1. Therefore, the groove U can be formed by scanning processing with the laser beam LB without forming a raised surface on the sheet. As a result, since no raised surface is generated, it is possible to reduce iron loss deterioration compared to the conventional technique in a case where 100 oriented grain electrical steel sheets are stacked to produce a transformer iron core.As described above, when the aim is to minimize iron loss from 100-grain oriented electrical steel sheet by forming a U-groove using the LB laser beam, it is possible to minimize elevation around the U-groove compared to the related technique and reduce iron loss. Petition 870250070654, dated 11 / 08 / 2025, page 127 / 164 / 60

[0093] Iron loss deterioration will be described in more detail. First, consider a pair of adjacent U-grooves among the plurality of U-grooves formed on the sheet surface.

[0094] Conventionally, in a case where the molten portion generated on the periphery of each of the U-grooves is solidified by rapid cooling, the molten and solidified portions pull each other in the portion of the sheet surface between the pair of U-grooves, so that the portion of the sheet surface between the pair of U-grooves undulates slightly in the direction of sheet thickness. This waviness of the sheet surface occurs on the sheet surface between all the U-grooves, i.e., on almost the entire sheet surface. Therefore, in a case where grain-oriented electrical steel sheets are stacked to produce a transformer iron core, the grain-oriented electrical steel sheets are deformed in a direction of reducing the irregularity that occurs due to the waviness, so that the occurrence of deformations cannot be avoided.Due to deformation during stacking, the iron loss from grain-oriented electrical steel sheets increases after stacking compared to before stacking.

[0095] On the other hand, according to the groove processing method using the groove processing apparatus of the present embodiment, since the formation of the molten and solidified portion is minimized in all U grooves, the resulting 100 oriented grain electrical steel sheet can have a flat shape with less waviness. Therefore, since the waviness before stacking is small, the deformation generated at the time of stacking is also small. Here, in a case where the amount of iron loss increased before and after stacking is evaluated as a construction factor, the iron loss after stacking greatly increased compared to the iron loss before stacking in Petition 870250070654, dated 11 / 08 / 2025, page 128 / 164 / 60 a conventional grain-oriented electrical steel plate, resulting in a poor construction factor. In contrast, as the 100 grain-oriented electrical steel plate of the present embodiment exhibits almost no waviness due to the fused and solidified portion, the iron loss after stacking is almost the same as the iron loss before stacking, resulting in an excellent construction factor.

[0096] Furthermore, with respect to the groove processing apparatus 1 of the present embodiment, the groove processing apparatus 1 employs a constitution in which irradiation and heating are carried out by the peripheral irradiation part N1 in the position next to the central irradiation part M1 along the laser scanning direction S and at least one of the positions on both sides of the groove U along the direction perpendicular to the laser scanning direction S. According to this constitution, it is possible to mitigate the rapid cooling and solidification of the molten material generated by heating the surface of the grain-oriented electrical steel sheet 100 by the central irradiation part M1 and to minimize the elevations generated around the groove U and in the center of the groove U.

[0097] Furthermore, the groove processing apparatus 1 employs a design in which the main position relative to the central irradiation part M1 along the laser scanning direction S is irradiated and heated by the peripheral irradiation part N1, thus preheating the surface of the grain-oriented electrical steel sheet 100 before it is heated by the central irradiation part M1. According to this design, it is possible to improve the efficiency of groove processing at high power intensity by the central irradiation part M1. (5)<Outras Modalidades>

[0098] Note that, in the embodiment described above, it has been described as the case where the laser beam LB includes the central irradiation portion M1 having a focused shape of a circle or an ellipse, in which a profile of Petition 870250070654, dated 11 / 08 / 2025, p. 129 / 164 / 60 beam intensity in a vertical cross-section with respect to the laser scanning direction S follows a Gaussian type distribution, and the peripheral irradiation section N1 having a focused shape of an annular or annular elliptical shape, wherein a beam intensity profile of a vertical cross-section with respect to the laser scanning direction S is strongest in the center of the annular shape, and the beam intensity profile attenuates towards the inner circumferential portion and the outer circumferential portion, but the present invention is not limited to the present example.

[0099] Figure 8 is a schematic diagram showing a constitution of an LB2 laser beam according to another embodiment. (8A) of Figure 8 is a schematic diagram showing a focused shape of the LB2 laser beam emitted by the laser irradiation device 3 towards the surface of the grain-oriented electrical steel sheet 100, and (8B) of Figure 8 is a schematic diagram showing an intensity profile of the LB2 laser beam on the geometric axis T of the surface of the grain-oriented electrical steel sheet 100, i.e., a spatial distribution of power [W] for the focused shape shown in (8A) of Figure 8. Furthermore, (8C) of Figure 8 is a schematic diagram showing a spatial distribution of the power [W] of the LB2 laser beam on the surface of the grain-oriented electrical steel sheet 100 on the geometric axis S.

[00100] More specifically, for example, as shown in Figure 8, a laser beam LB2 can be applied, the laser beam LB2 including a central irradiation portion M2 having a focused circular shape and a flat-top distribution in which a beam intensity profile in the vertical cross-section with respect to the laser scanning direction S is columnar, and a peripheral irradiation portion N2 having an annular shape focused on the plate surface and a flat-top distribution in which a beam intensity profile in the vertical cross-section with respect to the laser scanning direction S is constant from a portion Petition 870250070654, dated 11 / 08 / 2025, p. 130 / 164 / 60 internal circumferential portion to an external circumferential portion. In this case, the laser beam LB2 includes a non-irradiated annular portion R2 between the central irradiating portion M2 and the peripheral irradiating portion N2 surrounding the periphery of the central irradiating portion M2.

[00101] The LB2 laser beam having such a flat top distribution as the beam intensity profile also has a peripheral irradiation portion N2 through which the periphery of the central irradiation portion M2 is heated. The energy density of the central irradiation portion M2 is also defined as being greater than the energy density of the peripheral irradiation portion N2, and the same effect of the modality described above can be obtained.

[00102] The energy densities of the central radiating part M2 and the peripheral radiating part N2 are denoted by Pdm and Pdn, respectively. Note that although Figure 8 shows the case where the central radiating part M2 is a perfect circle and the peripheral radiating part N2 is a perfect annular shape, the central radiating part M2 can be elliptical and the peripheral radiating part N2 can have an elliptical ring shape. That is, dmt and dms can be different from each other. Furthermore, dnit and dnis can be different from each other. Alternatively, dnot and dnos can be different from each other.

[00103] The power density Pdm [MW / cm2] of the central irradiating section M2, the power density Pdn [MW / cm2] of the peripheral irradiating section N2, the irradiation times Tm and Tn [s] of the central irradiating section M2 and the peripheral irradiating section N2 by scanning with the LB laser beam, the energy density Edm [J / cm2] of the central irradiating section M2 and the energy density Edn [J / cm2] of the peripheral irradiating section N2 are represented by the following (Equation 7) to (Equation 12), respectively. The power density Pdm of the central irradiating section M1 can exemplify a range of 5.0 [MW / cm2] or more. Petition 870250070654, dated 11 / 08 / 2025, pp. 131 / 164 / 60 and 600 [MW / cm2] or less. Furthermore, the power density Pdn of the peripheral irradiation part N1 can exemplify a range of 1.0 [MW / cm2] or more and less than 5.0 [MW / cm2]. Additionally, as described above, the energy density range Edm of the central irradiation part M1 can be exemplified as 50 [J / cm2] or more and 1000 [J / cm2] or less, and the energy density range Edn of the peripheral irradiation part N1 can be exemplified as 1 [J / cm2] or more and less than 50 [J / cm2]. Pdm = Pm / (n / 4 χ dmt χ dms) ·· · (Equation 7) Pdn = Pn / (n / 4 χ (dnotχdnos - dnitχdnis)) ··· (Equation 8) Tm = dms / Vs ··· (Equation 9) Tn = 2 χ (dnos - dnis) / Vs ··· (Equation 10) Edm = Pdm χ Tm ··· (Equation 11) Edn = Pdn χ Tn ··· (Equation 12)

[00104] Furthermore, as a laser beam having a peripheral irradiation portion through which the periphery of the central irradiation portion is heated, for example, as shown in Figure 9, a laser beam LB3 can be applied, the laser beam LB3 having a continuously connected beam intensity profile without providing a portion in which the power is substantially 0 (a portion that can be considered as 0) at a boundary between the central irradiation portion M3 and the peripheral irradiation portion N3 surrounding the periphery of the central irradiation portion M3. (9A) of Figure 9 is a schematic diagram showing a focused shape of the laser beam LB3 emitted by the laser irradiation device 3 towards the grain-oriented electrical steel plate 100.(9B) of Figure 9 is a schematic diagram showing an intensity profile of the LB3 laser beam on the surface of the 100 grain-oriented electrical steel sheet along the geometric T-axis, i.e., a spatial distribution of power [W] for the focused shape shown in (9A) of Figure 9. Furthermore, (9C) of Figure 9 is a schematic diagram showing a spatial distribution of power. Petition 870250070654, dated 11 / 08 / 2025, pages 132 / 164 / 60 [W] of the LB3 laser beam on the surface of the grain-oriented electrical steel sheet 100 on the geometric axis S.

[00105] In this case, the diameter dmt of the central irradiating part M3 in the T direction and the diameter dnit of the inner circumferential portion of the peripheral irradiating part N3 coincide with each other at a position where the intensity is 1 / e2 times the maximum power of the central irradiating part M3 with the irradiated surface using the laser beam LB3 as a reference point, and regions of the diameters dmt and dms of the central irradiating part M3 have a high power intensity. In contrast, a region of the diameters dmt and dms of the central irradiating part M3 to the diameters dnot and dnos of the outer circumferential portion of the peripheral irradiating part N3 has a low power intensity. Note that dnot and dnos are diameters at positions where the intensity is 1 / e2 times the maximum power Pn of the peripheral irradiating part N3.

[00106] Such an LB3 laser beam also has the peripheral irradiation portion N3, whereby the periphery of the central irradiation portion M3 is heated. Since the energy density Edm [J / cm2] of the central irradiation portion M3 is also defined as being greater than the energy density Edn [J / cm2] of the peripheral irradiation portion N3, the same effect as that of the modality described above can be obtained.

[00107] In (9B) of Figure 9, although the central irradiation part M3 is a perfect circle, and the peripheral irradiation part N3 is a perfect circle, the present invention is not limited to this example, and the central irradiation part M3 and the peripheral irradiation part N3 may be elliptical, i.e., dmt and dms may be different from each other, and dnot and dnos may be different from each other.

[00108] The power density Pdm [MW / cm2] of the central irradiation section M3, the power density Pdn [MW / cm2] of the peripheral irradiation section N3, the irradiation times Tm and Tn [s] of the section Petition 870250070654, dated 11 / 08 / 2025, page 133 / 164 / 60 central irradiation M3 and peripheral irradiation N3 by scanning with the LB3 laser beam, the energy density Edm [J / cm2] of the central irradiation M3 and the energy density Edn [J / cm2] of the peripheral irradiation N3 are represented by the following (Equation 13) to (Equation 18), respectively. Pdm = Pm / (n / 4 χ dmt χ dms) ·· · (Equation 13) Pdn = Pn / (n / 4 χ (dnotχdnos)) · ·· (Equation 14) Tm = dms / Vs ··· (Equation 15) Tn = 2 χ (dnos - dnis) / Vs ··· (Equation 16) Edm = Pdm χ Tm ··· (Equation 17) Edn = Pdn χ Tn ··· (Equation 18)

[00109] Furthermore, as shown in Figure 10, for example, a total of four peripheral irradiation parts N4, two in the direction of the geometric axis S serving as a laser scanning direction and two in the direction of the geometric axis T serving as a direction perpendicular to the direction of the geometric axis S, can be arranged independently in positions separate from the central irradiation part M4. (10A) of Figure 10 is a schematic diagram showing a focused shape of the laser beam LB4 emitted by the laser irradiation device 3 towards the grain-oriented electrical steel plate 100. (10B) of Figure 10 is a schematic diagram showing an intensity profile of the laser beam LB4 on the plate surface of the grain-oriented electrical steel plate 100 on the geometric axis T, i.e., a spatial distribution of power [W] for the focused shape shown in (10A) of Figure 10.Furthermore, (10C) of Figure 10 is a schematic diagram showing a spatial distribution of the power [W] of the LB4 laser beam on the surface of the grain-oriented electrical steel plate 100 on the geometric axis S.

[00110] Figure 10 shows an example where the peripheral irradiation portion N4 has a beam intensity profile following a distribution Petition 870250070654, dated 11 / 08 / 2025, page 134 / 164 / 60 Gaussian type in the cross-section perpendicular to the geometric axis S or to the geometric axis T, but the peripheral irradiation part N4 may have a rectangular distribution (top-flat distribution), as shown in Figure 8, for example. Furthermore, in Figure 10, the central irradiation part M4 and the peripheral irradiation part N4 are formed in a perfect circular shape, but they may be formed in an elliptical shape having different diameters in the S direction and in the T direction.

[00111] Furthermore, a peripheral irradiation part N4 is arranged on the main side, and a peripheral irradiation part N4 is arranged on the next side relative to the central irradiation part along the geometric axis direction S in the geometric axis direction T, and peripheral irradiation parts N4 are arranged on the left and right sides in the geometric axis direction T, but the number of peripheral irradiation parts N4 is not limited to this example, and the number of peripheral irradiation parts can be appropriately altered, as shown by a laser beam LB5 in Figure 11 and a laser beam LB6 in Figure 12. (11A) of Figure 11 and (12A) of Figure 12 are schematic diagrams showing focused shapes of the laser beams LB5 and LB6 emitted by the laser irradiation device 3 towards the grain-oriented electrical steel plate 100.(11B) of Figure 11 and (12B) of Figure 12 are schematic diagrams showing intensity profiles of laser beams LB5 and LB6 on the surface of the grain-oriented electrical steel sheet 100 on the geometric axis T, i.e., spatial distributions of power [W] for the focused shapes shown in (11A) of Figure 11 and (12A) of Figure 12. In addition, (11C) of Figure 11 and (12C) of Figure 12 are schematic diagrams showing spatial distributions of power [W] of laser beams LB5 and LB6 on the surface of the grain-oriented electrical steel sheet 100 on the geometric axis S.

[00112] Even with such LB4 to LB6 laser beams, it is possible to prevent the molten material generated when the U-slots are formed by Petition 870250070654, dated 11 / 08 / 2025, page 135 / 164 / 60 central irradiation parts M4 to M6 should be raised above the sheet surface and solidified around the U grooves, minimizing the occurrence of a lift.

[00113] Note that, in the groove processing method for the surface of the oriented grain 100 electrical steel sheet according to the present embodiment, it is sufficient to use a laser beam having an intensity profile that includes the central irradiation portion having high energy density to form the U-shaped groove and the peripheral irradiation portion having low energy density to minimize elevation at the periphery thereof and, additionally, improve the efficiency of groove processing. Therefore, since the intensity profile of the laser beam has such an effect, the shapes and intensity profiles of the central irradiation portions M1 to M6 and the peripheral irradiation portions N1 to N6 shown in Figures 2 and 8 to 12 can be appropriately combined and applied. In this combination, the energy distribution can be a combination of a Gaussian type distribution and a flat-top distribution.Furthermore, the focused shape of each central irradiation part and the peripheral irradiation part can be a polygonal shape, such as a rectangular shape. The focused shape of the peripheral irradiation part can be a rectangular annular shape, a semi-annular shape, or similar. Additionally, in Figures 2 and 8, the peripheral irradiation parts N1 and N2 are formed in a single annular shape, but they can be formed in a plurality of annular shapes, such as double or triple rings.

[00114] As a method for obtaining a laser beam having multiple intensity profiles, as described above, using fiber beam transmission fibers in which a plurality of optical fibers are bundled together, each laser power is transmitted from a plurality of laser devices to each optical fiber corresponding to each central irradiation portion and the peripheral irradiation portion, so that the profiles of Petition 870250070654, dated 11 / 08 / 2025, page 136 / 164 / 60 desired intensities can be formed in the irradiation areas.

[00115] In addition, a diffractive optical element (DOE) can be used that converts an intensity profile of the laser output into a plurality of intensity profiles using a light diffraction phenomenon.

[00116] Furthermore, as in the laser beam scanning method described with reference to Figure 1, a galvanometer mirror which is a vibrating mirror can be used in addition to a rotating polygonal mirror. Additionally, a parabolic mirror can be used as a condenser element. (6)<Teste deVeriflçação>

[00117] Next, a verification test was performed to confirm whether or not an elevation was formed around the groove when it was scanned with a laser beam including a peripheral irradiation portion to heat the periphery of the central irradiation portion. The 100-grain oriented electrical steel sheet used in this verification test was produced by sequentially performing a hot rolling step, a cold rolling step, a primary recrystallization step, a MgO application step, a secondary recrystallization annealing step, a flattening step, and a surface coating step on a sheet containing Si as a major component in an amount of 3%. The groove was scanned on the sheet surface after the cold rolling step, altering the laser processing conditions of the laser beam from the groove processing apparatus.

[00118] Figure 13 is a schematic diagram showing a grain-oriented electrical steel sheet 100 in which a plurality of U-grooves is formed by an LB laser beam in a verification test. The U-groove is scanned with the LB laser beam such that the plurality of U-grooves extends in an inclined direction in a Petition 870250070654, dated 11 / 08 / 2025, page 137 / 164 / 60 predetermined angle in relation to the width direction of the grain-oriented electrical steel sheet 100 at regular intervals PL in the rolling direction of the grain-oriented electrical steel sheet 100. The interval PL between the grooves U in the rolling direction was 3 [mm], and the angle formed by the laser scan direction S and the width direction of the grain-oriented electrical steel sheet 100 was 10 [degrees].

[00119] A coil was prepared by winding 100-grain oriented electrical steel sheet after the cold rolling stage (stage S1). The U-groove was then processed by changing the laser processing conditions every 100 mm in the rolling direction to form a portion having different laser conditions every 100 m in the rolling direction, and then this coil was subjected to an add-on treatment stage performed after the primary recrystallization annealing stage, thus producing 100-grain oriented electrical steel sheet as a final product. The sheet thickness of the final product 100-grain oriented electrical steel sheet is 0.23 [mm].

[00120] Next, the iron loss-related performance of each end product was compared depending on the laser processing conditions. Specifically, from the 100 grain-oriented electrical steel sheet coil produced by altering the laser processing conditions, rectangular 100 grain-oriented electrical steel sheets of 30 [mm] in the sheet width direction x 320 [mm] in the rolling direction were cut as samples for each region in which the laser processing conditions were altered, and 36 sheets were defined as a set, and 10 sets were prepared. Then, as shown in Figure 14, in each set, 9 100 grain-oriented electrical steel sheets were stacked to prepare 4 stacked blocks, and these stacked blocks were assembled into a square shape to prepare a simulated transformer iron core 200 to simulate the iron core. Petition 870250070654, dated 11 / 08 / 2025, page 138 / 164 / 60 of the transformer for each sample with a different laser processing condition.

[00121] Next, the iron loss of the simulated transformer iron core 200 prepared for each sample with a different laser processing condition was measured according to the Epstein method (JIS C2550-2011) for measuring iron loss. Then, the stacked block of simulated transformer iron core 200 was pressurized to 5 kgf / cm2, and the iron loss was measured in the same way to evaluate the iron loss. An iron loss value was obtained as a W17 / 50 iron loss in an AC magnetic field having a magnetizing force of 1.7 [T] and a frequency of 50 [Hz]. The number of stacked blocks under each laser condition was 10 sets, and a measurement value was the average value of these 10 sets.

[00122] A groove depth and an average height H of the elevations were obtained by measuring the groove depths and elevation heights with microscopic observation in 20 randomly extracted cross-sections to obtain the average value of the same. The laser processing conditions, the groove processing results and the iron loss characteristics in the verification test are shown in Tables 1 and 2. Petition 870250070654, dated 11 / 08 / 2025, page 139 / 164 / 60 Radiation area (outer diameter) cm 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.008 Peripheral part shape (diameter) 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.008 Peripheral irradiation part shape (inner diameter) cm 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004 Central irradiation part format dms cm 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 dmt 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 0.0028 Maximum power of the peripheral irradiation part Pn W 400 100 400 O 700 04 009 04 009 Maximum power of the central irradiation part Pm W 1000 1000 250 0009 1000 1000 270 5500 1000 1000 Type Reference Example Comparative 1 Example of the Invention 1 Example Comparative 2 Example Comparative 3 Example Comparative 4 Example Comparative 5 Example of the Invention 2 Example of the Invention 3 Example of the Invention 4 Example of the Invention 5 [Table 11 o Condition n 04 CO -f- O- oo CF o Petition 870250070654, dated 11 / 08 / 2025, pages 140 / 164 / 60 Iron loss during pressurization W17 / 50 W / kg 0.85 0.78 o Iron loss W17 / 50 W / kg 0.85 O o Average elevation height μm -f- o Average groove depth Q μm 25 24 Energy density of the peripheral irradiation part Edn J / cm2 34.0 Energy density of the central irradiation part Edm J / cm2 182.0 182.0 Irradiation time of the peripheral irradiation part Tn t / i 3.2 (M [Table 21] Petition 870250070654, dated 11 / 08 / 2025, pages 141 / 164 / 60

[00123] In the verification test, the slot processing apparatus 1 shown in Figure 1 was used. In the verification test, a fiber laser having a wavelength of approximately 1.07 [μm] was used. The output of the fiber laser is transmitted by the optical fiber cable 4. As the optical fiber cable 4, an optical fiber cable is used, the optical fiber cable having a core with a double structure for light transmission and including a central circular core and a peripheral annular core around the central circular core. Each laser power of the central irradiation part M1 and the peripheral irradiation part N1 of the laser beam was adjusted by changing the laser power transmitted in the central core and the peripheral core of the fiber with a power division adjustment device in the laser irradiation device 3.Laser irradiation device 3 includes a rotating polygonal mirror for scanning with a laser beam, a lens f9 serving as an element that condenses the scanned laser beam, and similar components. The shape and intensity profile of the condensed laser beam emitted to irradiate the steel plate were such that the central irradiation portion M1 shown in Figure 2 had a Gaussian-type circular distribution, and the peripheral irradiation portion N1 had a distribution in which the intensity was maximized at the center of the annular shape and decreased towards the periphery.

[00124] Condition No. 1 (reference) is a simulated transformer iron core 200 manufactured using a portion of the verification coil that is not subjected to laser slot processing. On the other hand, an iron loss value measured by the Epstein method, an iron loss value when pressurization was performed, and similar values ​​were obtained and used as reference values ​​for this verification test.

[00125] Condition No. 2 (Comparative Example 1) is a simulated transformer iron core 200 manufactured using a portion of the check coil that is subjected to a conventional processing method. Petition 870250070654, dated 11 / 08 / 2025, page 142 / 164 / 60 of laser groove. Here, as a condition of laser groove processing, a processing condition was used in which the maximum power of the central irradiation part M1 is 1000 W and the power of the peripheral irradiation part is 0 W, i.e., a laser processing condition when a single Gaussian beam is used as a conventional technique. In the present Condition No. 2, the average groove depth and the average elevation height were also obtained as the results of the groove processing, and an iron loss value measured by the Epstein method and an iron loss value when pressurization was performed were obtained as the iron loss characteristics. As shown in Table 2, in Condition No. 2, the average groove depth D was 25 [pm] and the average elevation height H of elevations 101 was 4 [pm].Since the groove depth is formed at an appropriate depth, the iron loss is less than that in the reference example of Condition #1. However, since the 101 elevations were generated with an average height of 4 pm, the iron loss during pressurization increased. Therefore, there was a problem in terms of the construction factor.

[00126] Condition No. 3 (Invention Example 1) is an example of the embodiment described above. This Condition No. 3 is a simulated transformer iron core 200 manufactured using a portion of the verification coil that is subjected to the laser slot processing method of the embodiment described above. Here, the beam intensity profile of the central irradiation part M1, the power, the focused shape, the scan rate and the like of the central irradiation part M1 are the same as Condition No. 2 described above (Comparative Example 1), but one condition of the laser slot processing is different, since the peripheral irradiation part N1, having an annular shape and low intensity profile with a maximum power of 400 W, is provided around the central irradiation part M1. In this Condition No. 3, the energy density Edm of Petition 870250070654, dated 11 / 08 / 2025, page 143 / 164 / 60 central irradiation part Ml was 182.0 [J / cm2], and the energy density Edn of the peripheral irradiation part N1 was 34.0 [J / cm2].

[00127] In this Condition No. 3, the average groove depth D was 24 μm, which was almost equal to the average groove depth of Condition No. 2 of 25 μm. Furthermore, the iron loss before pressurization was also approximately the same as in Condition No. 2. However, in this Condition No. 3, since elevations 101 did not occur around groove U, the iron loss after pressurization also remained at a low value and did not increase. Therefore, it was confirmed that the construction factor was excellent.

[00128] In Condition No. 4 (Comparative Example 2), the power of the central irradiation section M1 and the peripheral irradiation section N1 was reduced to proportionally decrease the energy density, and the other conditions are the same as in Condition No. 3. Since the energy density Edn of the peripheral irradiation section N1 was of a certain value or more, it was confirmed that no elevation was formed and there was no increase in iron loss after pressurization. However, since the energy density Edm of the central irradiation section M1 was significantly reduced, the average groove depth D was 8 pm, which was less than 10 pm, and the reduction in iron loss was also small.

[00129] In Condition #5 (Comparative Example 3), the laser power of the central irradiation section M1 was increased to increase the energy density Edm. The other conditions were the same as in Condition #3. In Condition #5, since the average groove depth D was 60 pm, which was greater than 50 pm, it was confirmed that the decrease in iron loss was small, and large elevations 101 were generated around the groove. It was assumed that this occurred because a large amount of molten material was generated in the central irradiation section M1, and the evaporation pressure of the metal increased. In this state, as a large amount Petition 870250070654, dated 11 / 08 / 2025, page 144 / 164 / 60 of molten metal is also pushed out on the T-direction side, crossing the S-sweep laser direction and in the S-sweep laser direction, even heating by the N1 peripheral irradiation part is not able to minimize the elevations. Therefore, large elevations 101 were generated. As a result, the iron loss reduction effect was reduced. Furthermore, an increase in iron loss during pressurization was also noticeable due to the elevations 101, and it was also verified that there is a problem in terms of the construction factor.

[00130] In Condition No. 6 (Comparative Example 4), the power of the peripheral irradiation section N1 was decreased to reduce the energy density Edn to 0.8 [J / cm2], which was less than 1.0 [J / cm2]. Other conditions were the same as in the example of Condition No. 3. In this case, since an appropriate average groove depth D can be obtained by the central irradiation section M1, a low iron loss can be achieved. However, it was confirmed that, since the effect of minimizing elevation by the peripheral irradiation section N1 was small, elevations 101 were generated and the iron loss after pressurization increased. That is, it was found that there is a problem in terms of the construction factor.

[00131] In Condition No. 7 (Comparative Example 5), the power of the peripheral irradiation section N1 was increased to raise the energy density Edn to 59.4 [J / cm2], which was greater than 50.0 [J / cm2]. Other conditions were the same as in the example of Condition No. 3. In this case, as an appropriate average groove depth D can be obtained by the central irradiation section M1, a low iron loss can be achieved. However, the melting by the peripheral irradiation section N1 was excessive, and elevations 101 were formed around the groove. As a result, it was confirmed that the iron loss after pressurization increased. That is, it was found that there is a problem in terms of the construction factor.

[00132] In Condition No. 8 (Invention Example 2), the power of Petition 870250070654, dated 11 / 08 / 2025, page 145 / 164 / 60. The energy density of the central irradiation part M1 and the peripheral irradiation part N1 was reduced, the energy density Edm of the central irradiation part M1 was adjusted to 49.1 [J / cm2], which was slightly less than 50 [J / cm2], and the energy density of the peripheral irradiation part was adjusted to 1.0 [J / cm2]. Other conditions were the same as in invention example 1 of Condition No. 3. In this Condition No. 8 (Invention Example 2), although the energy density Edm of the central irradiation part M1 was small, an average groove depth D of 10 μm was obtained, so that a relatively low iron loss was achieved. Furthermore, since no elevation 101 was generated around the U-groove, the iron loss after pressurization was also kept at a low value and did not increase. Therefore, it was confirmed that the construction factor was excellent.

[00133] In Condition No. 9 (Invention Example 3), the power of the central irradiation part M1 and the peripheral irradiation part N1 was increased, the energy density Edm of the central irradiation part M1 was adjusted to 1000.9 [J / cm2], which was slightly higher than 1000 [J / cm2], and the energy density Edn of the peripheral irradiation part N1 was adjusted to 51.0 [J / cm2], which was slightly higher than 50 [J / cm2]. Other conditions were the same as in invention example 1 of Condition No. 3. In this Condition No. 9 (Invention Example 3), since the energy density Edm of the central irradiation part M1 was large, an average groove depth D of 49 μm was obtained, so that a low iron loss was achieved.Furthermore, although molten metal is likely generated in a case where a relatively deep groove is formed, no elevation 101 was generated around the groove U, since the energy density Edn of the peripheral irradiation part N1 was also increased. Therefore, the iron loss after pressurization was also kept at a low value and did not increase. Therefore, it was confirmed that the construction factor was excellent. Petition 870250070654, dated 11 / 08 / 2025, pages 146 / 164 / 60

[00134] In Condition No. 10 (Invention Example 4), the power of the peripheral irradiation part N1 was increased compared to Condition No. 6 (Comparative Example 4), and the energy density Edn of the peripheral irradiation part N1 was set to 1.0 [J / cm2]. The other conditions were the same as in Condition No. 6. In this Condition No. 10 (Invention Example 4), the groove depth was 25 μm, which was the same as in Condition No. 6, and a low iron loss was obtained. Furthermore, no elevation 101 was generated around the groove U due to the increase in the energy density Edn of the peripheral irradiation part N1, and the iron loss after pressurization was also maintained at a low value and did not increase. Therefore, it was confirmed that the construction factor was excellent.

[00135] In Condition No. 11 (Invention Example 5), the power of the peripheral irradiation part N1 was further increased compared to Condition No. 6 (Comparative Example 4), and the energy density Edn of the peripheral irradiation part N1 was set at 51.0 [J / cm2]. Other conditions were the same as in the example of Condition No. 6. In this Condition No. 11 (Invention Example 5), the groove depth was 27 μm, which was equal to or greater than that of Condition No. 6, and a low iron loss was obtained. Furthermore, no elevation 101 was generated around the groove U due to the energy density Edn of the peripheral irradiation part N1, and the iron loss after pressurization was also maintained at a low value and did not increase. Therefore, it was confirmed that the construction factor was excellent.

[00136] With the verification test described above, according to the groove processing method and the groove processing apparatus of the modality described above, in the scanning processing with the LB laser beam, it was confirmed that, by properly setting the energy density Edm of the central irradiation part M1 and the energy density Edn of the peripheral irradiation part N1, the U groove having an appropriate depth to reduce iron loss can be formed, and the generation of Petition 870250070654, dated 11 / 08 / 2025, page 147 / 164 / 60 elevations 101 raised from the sheet surface around the groove can be minimized and, as a result, the grain-oriented electrical steel sheet 100, particularly excellent in construction factor, can be obtained.

[00137] Next, an example will be described in a case where the groove processing intervals are irregular intervals, but before that, the groove intervals will be described first.

[00138] As described above, it is known that a magnetic domain is refined by forming grooves in grain-oriented electrical steel sheet; iron loss is reduced while the magnetic flux density generated at a constant magnetizing force is reduced. In a case where grain-oriented electrical steel sheet is used for an iron core of a transformer, there is an advantage that the transformer can be reduced in size, since the magnetic flux density that can be generated is higher. Therefore, it is desirable to reduce iron loss and maintain magnetic flux density at a high level.

[00139] Magnetic flux density is correlated with slot formation gap, and the reduction in magnetic flux density is smaller when the distance between slot gaps is as wide as possible. Conversely, when the distance between slot gaps is too large, the iron loss reduction effect also decreases. In order to effectively control magnetic domain by slot formation, a portion having a wide magnetic domain width is selected to form slots and refine the magnetic domain. In contrast, a sufficient iron loss reduction effect can be obtained even when a slot is not formed in a portion where the original magnetic domain width is narrow, or the slot gaps are widened.

[00140] The magnetic domain width can be measured using a Petition 870250070654, dated 11 / 08 / 2025, pp. 148 / 164 / 60 magneto-optical sensor. The magneto-optical sensor is a sensor that irradiates a steel plate with a polarized laser beam and rotates the polarized laser beam in a direction of self-magnetization of the plate surface when the light is reflected. That is, as the polarized laser beam rotates depending on the direction of magnetization of the magnetic domain, the transmittance of a polarizing plate provided in a light-receiving element changes, and the distribution of the magnetic domain appears as light and dark on a light-receiving surface of the sensor. The magnetic domain width can be specified by image analysis of the width of the light and dark areas.

[00141] Using the principle described above, a portion having a wide magnetic domain width and a portion having a narrow magnetic domain width were specified, and a processing embodiment case, in which the groove formation interval was altered in correlation with the magnetic domain width, was verified. Here, a steel plate was prepared, the steel plate including a region having a magnetic domain width of 500 μm or more in which a groove formation interval PL was defined as 2 mm, a region having a magnetic domain width of less than 500 μm and 200 μm or more in which the groove formation interval PL was defined as 5 mm, a region having a magnetic domain width of less than 200 μm and 50 μm or more in which the groove formation interval PL was defined as 10 mm, and a region having a magnetic domain width of less than 50 μm in which no groove was formed.As a result, the PL groove formation interval was not constant and varied depending on the location, with a minimum of 2 mm and a maximum of 30 mm. The results of the evaluation of the magnetic characteristics of this steel plate are shown in Table 3 in comparison with other examples. Petition 870250070654, dated 11 / 08 / 2025, pp. 149 / 164 / 60 'Table 3' Condition No. Type Slot Interval Irradiation Interval Maximum Power of Central Irradiation Part Iron Loss Iron Loss During Pressurization Magnetic Flux Density PL Pm W17 / 50 W17 / 50 B8 mm WW / kg W / kg T 1 Reference Reference (without slot processing) - - 0.85 0.85 1.920 3 Example of the Invention 1 Regular 3 1000 0.71 0.71 1.907 12 Example of the Invention 6 Non-regular 2 to 30 1000 0.72 0.72 1.915

[00142] For the magnetic characteristics, in addition to the iron loss W17 / 50 shown in Table 2, a magnetic flux density B8 was also measured. The magnetic flux density B8 is a magnetic flux density (Unit: T, Tesla) generated with a magnetizing force of 0.8 A / m.

[00143] Condition No. 1 (reference) is the same as shown in Tables 1 and 2 and displays the magnetic characteristics of the steel sheet in which the groove is not processed.

[00144] Condition No. 3 (Invention Example 1) is the same as shown in Tables 1 and 2 and includes the groove formation interval PL, which is constant at 3 mm in the rolling direction.

[00145] Condition No. 12 (Invention Example 6) includes an outcome in which grooves are formed under the same ring-mode laser condition as Condition No. 3 (Invention Example 1), but the grooves are formed at irregular intervals according to the magnetic domain width described above. In this Condition No. 12 (Invention Example 6), iron loss characteristics equivalent to those of Condition No. 3 (Invention Example 1) are obtained. However, as a region in which the PL groove formation interval is wide is included, the effect of the decrease Petition 870250070654, dated 11 / 08 / 2025, pages 150 / 164 / 60, confirming that the magnetic flux density is small.

[00146] Note that, in the present example, the magnetic domain width is measured by the magneto-optical sensor to change the groove width, but the present invention is not limited to this method of alteration. As another example, the iron loss value and the magnetic flux density can be measured, and the groove formation interval PL can be appropriately altered according to the measured value to define irregular intervals. That is, the condition for making the groove formation interval PL constant or non-constant is not limited to a specific condition. INDUSTRIAL APPLICABILITY

[00147] According to the embodiments described above of the present invention and various examples of modification, it is possible to provide the groove processing method, the groove processing apparatus and the grain-oriented electrical steel sheet, which allow for the reduction of iron loss without forming a raised area around a groove, compared with the related technique. Therefore, the industrial applicability is significant. LIST OF REFERENCE SIGNS

[00148] 1 Groove processing apparatus Laser irradiation device LB, LB2, LB3, LB4, LB6 Laser Beam M1, M2, M3, M4 Central part of irradiation N1, N2, N3, N4 Peripheral irradiation portion U Groove U1 Deep groove portion U2 Groove edge portion Petition 870250070654, dated 11 / 08 / 2025, pages 151 / 164

Claims

1 / 6 CLAIMS 1. A groove processing method for forming a groove in a grain-oriented electrical steel sheet, the method characterized in that it comprises: a groove processing step for performing scanning with a laser beam to form a groove having a linear shape and a maximum depth of 10 [μm] or more and 50 [μm] or less and extending in a scanning direction serving as a direction parallel to a width direction of the grain-oriented electrical steel sheet perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction, the grooves being formed at regular intervals in the rolling direction of the grain-oriented electrical steel sheet, wherein the laser beam includes a central irradiation portion serving as a region that includes the center of an optical path of the laser beam where the laser beam is emitted,and a peripheral irradiation zone serving as a region surrounding the central irradiation zone where the laser beam is emitted, and an energy density [J / cm2] of the central irradiation zone is defined above an energy density [J / cm2] of the peripheral irradiation zone.

2. Groove processing method according to claim 1, characterized in that, by the peripheral irradiation part, one position next to the central irradiation part along the sweep direction and at least one position on both sides of the groove along a direction perpendicular to the sweep direction are heated to minimize the solidification of a molten material as a rise generated when the groove is formed in the grain-oriented electrical steel sheet by the central irradiation part. Petition 870250070654, dated 11 / 08 / 2025, p. 71 / 164 2 / 6 3. Groove processing method according to claim 1, characterized in that, by the peripheral irradiation part, an advancing position relative to the central irradiation part along the scanning direction is heated, and a surface of the grain-oriented electrical steel sheet is preheated before being heated by the central irradiation part.

4. A groove processing method according to claim 1, characterized in that a beam intensity profile of the peripheral irradiation portion, as seen in the scanning direction, follows a Gaussian-type distribution or a flat-top distribution.

5. Groove processing method according to claim 1, characterized in that a focused shape of the peripheral irradiation part is an annular shape surrounding the central irradiation part on a grain-oriented electrical steel sheet surface.

6. Groove processing method according to claim 1, characterized in that a focused shape of the central radiating part is an elliptical shape having a principal geometric axis in the scanning direction on a surface of grain-oriented electrical steel sheet.

7. Groove processing method according to claim 1, characterized in that the energy density of the central irradiation part is 50 [J / cm2] or more and 1000 [J / cm2] or less, and the energy density of the peripheral irradiation part is 1 [J / cm2] or more and less than 50 [J / cm2].

8. Groove processing apparatus configured to form a groove in a grain-oriented electrical steel sheet, the groove processing apparatus characterized by the fact that it performs a scan with a laser beam to form a groove having a Petition 870250070654, dated 11 / 08 / 2025, page.72 / 164 3 / 6 linear shape and a maximum depth of 10 [μm] or more and 50 [μm] or less and extending in a scanning direction serving as a direction parallel to a width direction of the grain-oriented electrical steel sheet perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction, the grooves being formed at regular intervals in the rolling direction of the grain-oriented electrical steel sheet, the laser beam includes a central irradiation portion serving as a region that includes the center of an optical path of the laser beam where the laser beam is emitted, and a peripheral irradiation portion serving as a region surrounding the central irradiation portion where the laser beam is emitted, and an energy density [J / cm2] of the central irradiation portion is defined above an energy density [J / cm2] of the peripheral irradiation portion.

9. Grain-oriented electrical steel sheet, characterized in that a groove having a linear shape and a maximum depth of 10 [pm] or more and 50 [pm] or less and extending in a direction parallel to a width direction perpendicular to a rolling direction or in a direction inclined at a predetermined angle relative to the width direction is formed, the grooves being formed at regular intervals in the rolling direction, and the groove having a multi-stage shape, including a deep groove portion with a deeper point and a groove edge portion with a smoother gradient than the gradient of a wall surface of the deep groove portion, as seen in the direction in which the groove extends.

10. Groove processing method for forming a groove in a grain-oriented electrical steel sheet, the method characterized in that it comprises: a groove processing step to perform scanning with a laser beam to form a groove having a specific shape. Petition 870250070654, dated 11 / 08 / 2025, page 10.73 / 164 4 / 6 linear and a maximum depth of 10 [μm] or more and 50 [μm] or less and extending in a scanning direction serving as a direction parallel to a width direction of the grain-oriented electrical steel sheet perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction, the grooves being formed at irregular intervals in the rolling direction of the grain-oriented electrical steel sheet, wherein the laser beam includes a central irradiation portion serving as a region that includes the center of an optical path of the laser beam where the laser beam is emitted, and a peripheral irradiation portion serving as a region surrounding the central irradiation portion where the laser beam is emitted, and an energy density [J / cm2] of the central irradiation portion is defined above an energy density [J / cm2] of the peripheral irradiation portion.

11. Groove processing method according to claim 10, characterized in that, by the peripheral irradiation part, one position next to the central irradiation part along the sweep direction and at least one of the positions on both sides of the groove along a direction perpendicular to the sweep direction are heated to minimize the solidification of a molten material as an elevation generated when the groove is formed in the grain-oriented electrical steel sheet by the central irradiation part.

12. Groove processing method according to claim 10, characterized in that, by the peripheral irradiation part, an advance position relative to the central irradiation part along the sweep direction is heated, and a surface of the grain-oriented electrical steel sheet is preheated before being heated by the central irradiation part. Petition 870250070654, dated 11 / 08 / 2025, p. 74 / 164 5 / 6 13. A groove processing method according to claim 10, characterized in that a beam intensity profile of the peripheral irradiation portion, as seen in the scanning direction, follows a Gaussian-type distribution or a flat-top distribution.

14. Groove processing method according to claim 10, characterized in that a focused shape of the peripheral irradiation part is an annular shape surrounding the central irradiation part on a grain-oriented electrical steel sheet surface.

15. Groove processing method according to claim 10, characterized in that a focused shape of the central radiating part is an elliptical shape having a principal geometric axis in the scanning direction on a surface of grain-oriented electrical steel sheet.

16. Groove processing method according to claim 10, characterized in that the energy density of the central irradiating part is 50 [J / cm2] or more and 1000 [J / cm2] or less, and the energy density of the peripheral irradiating part is 1 [J / cm2] or more and less than 50 [J / cm2].

17. Groove processing apparatus configured to form a groove in a grain-oriented electrical steel sheet, the groove processing apparatus characterized in that it performs a scan with a laser beam to form a groove having a linear shape and a maximum depth of 10 [μm] or more and 50 [μm] or less and that extends in a scan direction serving as a direction parallel to a width direction of the grain-oriented electrical steel sheet perpendicular to a rolling direction or a direction inclined at a predetermined angle relative to the width direction, the grooves Petition 870250070654, dated 11 / 08 / 2025, page.75 / 164 6 / 6 being formed at irregular intervals in the lamination direction of the grain-oriented electrical steel sheet, the laser beam includes a central irradiation portion serving as a region that includes the center of an optical path of the laser beam where the laser beam is emitted, and a peripheral irradiation portion serving as a region surrounding the central irradiation portion where the laser beam is emitted, and an energy density [J / cm2] of the central irradiation portion is defined above an energy density [J / cm2] of the peripheral irradiation portion.

18. Grain-oriented electrical steel sheet, characterized in that a groove having a linear shape and a maximum depth of 10 μm or more and 50 μm or less, and extending in a direction parallel to a width direction perpendicular to a rolling direction or in a direction inclined at a predetermined angle to the width direction, is formed, the grooves being formed at irregular intervals in the rolling direction, and the groove having a multi-stage shape, including a deep groove portion with a deeper point and a groove edge portion with a smoother gradient than the gradient of a wall surface of the deep groove portion, as seen in the direction in which the groove extends. Petition 870250070654, dated 11 / 08 / 2025, p. 76 / 164

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