Grain-oriented electromagnetic steel sheet and method for manufacturing same

Abstract

This grain-oriented electromagnetic steel sheet comprises a base material steel sheet, a forsterite film that is optionally formed on the base material steel sheet, and an insulating film that is formed on the base material steel sheet or the forsterite film. The base material steel sheet has a plurality of grooves extending in a direction intersecting a rolling direction. A groove depth and a groove width at a plurality of positions on groove edge parts satisfy a prescribed relationship, where: the groove depth is a distance within the grooves, on a straight line that extends along a plate thickness direction of the base material steel sheet from a virtual line obtained by extending the surface of the base material steel sheet, from the virtual line to the grooves; the groove width is the rolling-direction width of the grooves; and the groove edge parts are regions within 5 mm from groove edges toward groove-longitudinal-direction central parts, the groove longitudinal direction being the direction in which the grooves extend, and the groove edges being positions at which the groove depth is 0.0 μm.

Description

Grain-oriented electrical steel sheet and its manufacturing method

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof. This application claims priority to Japanese Patent Application No. 2023-111726, filed on July 6, 2023, the contents of which are incorporated herein by reference.

[0002] Grain-oriented electrical steel sheets are soft magnetic materials primarily used as iron core materials in transformers. Therefore, grain-oriented electrical steel sheets are required to have magnetic properties such as high magnetic flux density and low iron loss. Iron loss is the loss of thermal energy consumed when an iron core is excited by an alternating current magnetic field. From the perspective of energy conservation, iron loss should be as low as possible. The level of iron loss is influenced by factors such as magnetic susceptibility, sheet thickness, film tension, impurity content, electrical resistivity, grain size, and magnetic domain width. Even though various technologies for grain-oriented electrical steel sheets have been developed, research and development continues to reduce iron loss in order to improve energy conversion efficiency. One method for reducing iron loss is laser irradiation of steel sheets. This technique introduces strain into the surface of the steel sheet by laser irradiation, which reduces the magnetic domain width and is believed to reduce eddy current loss, a part of iron loss.

[0003] For example, Patent Document 1 discloses a method for producing a steel sheet having a surface irradiated with a focused continuous wave laser beam while scanning the surface in a direction inclined from the rolling direction of the steel sheet, and a method for repeating the process while shifting the area scanned with the continuous wave laser beam at predetermined intervals, in which the average power of the continuous wave laser beam is represented as P (W), the scanning speed as Vc (mm / s), the predetermined interval as PL (mm), and the input energy Ua as Ua = P / (Vc × PL) (mJ / mm ２ ), 1.0 mm ≦ PL ≦ 3.0 mm, and 0.8 mJ / mm ２ ≦Ua≦2.0mJ / mm ２ Patent Document 1 discloses a method for manufacturing a grain-oriented electrical steel sheet in which magnetic domains are controlled by irradiation with laser light, which method is characterized by satisfying the following: Patent Document 1 shows that it is possible to easily reduce iron loss in both the L direction and the C direction of a grain-oriented electrical steel sheet while ensuring high productivity.

[0004] However, for example, when manufacturing wound cores, grain-oriented electrical steel sheets are bent and shaped, requiring stress relief annealing. Therefore, in the above-mentioned method of introducing strain into the surface by laser irradiation, the strain introduced into the grain-oriented electrical steel sheet is released by stress relief annealing. This eliminates the effect of magnetic domain refinement achieved by laser irradiation. For this reason, it has been proposed to form grooves on the steel sheet surface to refine the magnetic domain width and reduce eddy current loss, similar to strain introduction. In such cases, the grooves do not disappear even after stress relief annealing, so the effect of magnetic domain refinement is not lost. Methods for forming grooves in steel sheets include, for example, electrolytic etching, which forms grooves on the surface of grain-oriented electrical steel sheets by electrolytic etching; gear pressing, which forms grooves on the surface of grain-oriented electrical steel sheets by mechanically pressing a gear onto the surface of the grain-oriented electrical steel sheet; and laser irradiation, which forms grooves by melting and evaporating the steel sheet (laser-irradiated portion) with laser irradiation. For example, Patent Document 2 discloses a method for improving the iron loss characteristics of a grain-oriented electrical steel sheet that can withstand stress relief annealing, in which a laser beam is controlled and irradiated to form recesses having a width of 0.5 mm or less in the rolling direction and a depth of 10 μm or more.

[0005] Generally, grain-oriented electrical steel sheets have an insulating coating formed on their surfaces to provide electrical insulation, tensile strength, heat resistance, and other properties. As disclosed in Patent Document 2, grain-oriented electrical steel sheets have grooves formed substantially parallel to the width of the steel sheet, thereby dividing the magnetic domain width and reducing iron loss. Meanwhile, the width and depth of the longitudinal ends (near the beginning and end) of the formed grooves vary compared to the center. This makes it difficult to apply a coating solution to every corner of the groove ends, resulting in insufficient adhesion of the insulating coating at the groove ends. Because the length of the region where the width and depth change at the groove ends is a relatively small proportion of the overall length of the groove, poor adhesion of the insulating coating in this region is not thought to have a significant impact on magnetic properties. However, poor adhesion of the insulating coating at the groove ends may expose the steel substrate to the surface, potentially causing rust. Furthermore, when grain-oriented electrical steel sheets are stacked, significant interlaminar currents may flow in such exposed steel substrate regions, potentially increasing iron loss. However, Patent Document 2 does not consider such exposure of the base steel or the occurrence of rust.

[0006] As a technique for controlling the shape of the groove ends, for example, Patent Document 3 discloses a technique for suppressing etching of the widthwise ends of a steel strip in a method for manufacturing grain-oriented silicon steel sheet in which linear or dotted grooves are formed on the surface of the steel strip, so that the groove depth at the widthwise ends is 70% or less of the groove depth at the widthwise center.

[0007] Furthermore, as a technique for improving the adhesion and rust resistance of an insulating coating or the like at the groove ends, for example, Patent Document 4 discloses a grain-oriented electrical steel sheet in which a first angle θ formed between the steel sheet surface and the groove end straight line and an aspect ratio A obtained by dividing the average groove depth D by the average groove width W satisfy the relationship θ<−21×A+77.

[0008] Furthermore, Patent Document 5 discloses a grain-oriented electrical steel sheet which includes linear grooves formed on one or both surfaces of the electrical steel sheet in a direction intersecting the rolling direction, the grooves including a sloping portion (GS) and a flat portion (US) in a cross section including the longitudinal direction of the groove and the normal direction to the rolling surface of the steel sheet, and the lengths of the sloping portion and the flat portion satisfy a predetermined relationship.

[0009] Japanese Patent No. 4669565 Japanese Patent Application Publication No. 6-57335 Japanese Patent Application Publication No. 4016431 Japanese Patent Application Publication No. 6418322 Japanese Patent Application Publication No. 2022-503782

[0010] However, in Patent Document 3, the purpose of suppressing etching of the widthwise ends of the steel strip and making the groove depth at the widthwise ends 70% or less of the groove depth at the widthwise center is to prevent breakage of the steel strip in subsequent processes when linear grooves are introduced by electrolytic etching, but there is no mention of the adhesion or rust resistance of the insulating coating at the groove ends. Furthermore, Patent Document 4 does not mention the width or depth of the groove at the groove ends, and as a result of the inventors' investigation, it was found that it does not necessarily improve the adhesion or rust resistance of the insulating coating at the groove ends. Furthermore, Patent Document 5 does not mention the width of the groove at the groove ends, and as a result of the inventors' investigation, it was found that it does not necessarily improve the adhesion or rust resistance of the insulating coating at the groove ends. Furthermore, it was found that the reduction in magnetic flux density due to the formation of grooves does not necessarily occur.

[0011] As described above, in the past, in grain-oriented electrical steel sheets in which magnetic domain refinement is performed by forming grooves, techniques for improving the adhesion and rust resistance of the insulating coating at the groove ends have been proposed, but it cannot be said that sufficient research has been conducted on these techniques. Therefore, an object of the present invention is to provide a grain-oriented electrical steel sheet that has high adhesion of the insulating coating and excellent rust resistance even at the groove ends.

[0012] The inventors have investigated methods for improving the adhesion of insulating coatings at the groove ends, and have found that the adhesion and rust resistance of insulating coatings and the like can be improved by shaping the grooves so that the depth and width become shallower and narrower toward the end in the longitudinal direction of the groove (groove longitudinal direction), and by shaping the grooves so that the depth and width satisfy a certain relationship.

[0013] The present invention has been made based on the above findings. The gist of the present invention is as follows. [1] A grain-oriented electrical steel sheet according to one aspect of the present invention comprises a base steel sheet, and optionally a forsterite film formed on the base steel sheet, and an insulating film formed on the base steel sheet or the forsterite film, wherein the base steel sheet has a plurality of grooves extending in a direction intersecting the rolling direction, the direction in which the grooves extend is defined as the groove longitudinal direction, the distance from an imaginary line extending across the surface of the base steel sheet to the groove in the thickness direction of the base steel sheet is defined as the groove depth, the width of the groove in the rolling direction is defined as the groove width, the position where the groove depth is 0.0 μm is defined as the groove end, a region 5 mm from the groove end towards the center in the groove longitudinal direction is defined as the groove end, the groove depth in the groove longitudinal direction of the groove at a position 1 mm from the groove end is defined as D1 and the groove width in μm is defined as W1, When the groove depth at a position 2 mm from the end of the groove is D2 and the groove width is W2, the groove depth at a position 3 mm from the end of the groove is D3 and the groove width is W3, the groove depth at a position 4 mm from the end of the groove is D4 and the groove width is W4, the groove depth at a position 5 mm from the end of the groove is D5 and the groove width is W5, and the average groove width at the center of the groove in the longitudinal direction of the groove is Wc and the average groove depth is Dc, 1. When D2, D3, D4, D5, W1, W2, W3, W4, and W5 satisfy the following formula (1) and formula (2), and when the width of the groove at the portion where the groove depth is 0.05×Dc at the groove end is W0.05, and the width of the groove at the portion where the groove depth is 0.50×Dc is W0.50, W0.05 and W0.50 satisfy the following formula (3) and formula (4). D5≧D4≧D3≧D2≧D1 (1) W5≧W4≧W3≧W2≧W1 (2) 0.004≦W0.05 / Wc≦0.210 (3) 0.180≦W0.50 / Wc≦0.810 (4) [2] In the grain-oriented electrical steel sheet according to [1], W0.05 and W0.50 may satisfy the following formulas (5) and (6):0.008≦W0.05 / Wc≦0.160 (5) 0.380≦W0.50 / Wc≦0.710 (6) [3] In the grain-oriented electrical steel sheet according to [1], the D1, the D2, the D3, the D4, and the D5 may satisfy the following formula (1′): D5>D4>D3>D2>D1 (1′) [4] In the grain-oriented electrical steel sheet according to [2], the D1, the D2, the D3, the D4, and the D5 may satisfy the following formula (1′): D5>D4>D3>D2>D1 (1′) [5] In the grain-oriented electrical steel sheet according to any one of [1] to [4], the Dc may be 5.0 to 40.0 μm and the Wc may be 10.0 to 200.0 μm. [6] In the grain-oriented electrical steel sheet according to any one of [1] to [4], the grooves may be spaced apart in the rolling direction by 2 to 10 mm, and the groove longitudinal direction and the rolling direction may form an angle of 60 to 120 degrees. [7] In the grain-oriented electrical steel sheet according to [5], the grooves may be spaced apart in the rolling direction by 2 to 10 mm, and the groove longitudinal direction and the rolling direction may form an angle of 60 to 120 degrees.[8] A method for producing a grain-oriented electrical steel sheet according to one aspect of the present invention includes a groove forming step of irradiating a steel sheet with a laser while scanning the steel sheet in a direction intersecting the rolling direction to form grooves extending in the rolling direction, a decarburization annealing step of decarburization annealing the steel sheet after the groove forming step, a finish annealing step of finish annealing the steel sheet after the decarburization annealing step, and a process of forming an insulating film on the steel sheet after the finish annealing step to become a base steel sheet, thereby forming an insulating film on the base steel sheet, a forsterite film arbitrarily formed on the base steel sheet, and an insulating film on or above the base steel sheet. and an insulating coating forming step of obtaining a grain-oriented electrical steel sheet having the insulating coating formed on the coating, wherein in the groove forming step, the direction in which the groove extends is defined as the groove longitudinal direction, the distance from an imaginary line extending from the surface of the base steel sheet to the groove along a straight line extending in the thickness direction of the base steel sheet from the imaginary line to the groove is defined as the groove depth, the width of the groove in the rolling direction is defined as the groove width, the position where the groove depth is 0.0 μm is defined as the groove end, a region 5 mm from the groove end toward the center in the groove longitudinal direction is defined as the groove end, and the length of the groove end in the groove longitudinal direction is defined as the length in μ. m, the groove depth at a position 1 mm from the end of the groove is D1, the groove width is W1, the groove depth at a position 2 mm from the end of the groove is D2, the groove width is W2, the groove depth at a position 3 mm from the end of the groove is D3, the groove width is W3, the groove depth at a position 4 mm from the end of the groove is D4, the groove width is W4, the groove depth at a position 5 mm from the end of the groove is D5, the groove width is W5, and the average groove width at the center of the groove in the longitudinal direction is Wc and the average groove depth is Dc, at the groove end, The laser is irradiated to form the groove by changing the distance between the focus of the laser and the surface of the base steel plate so that D1, D2, D3, D4, D5, W1, W2, W3, W4, and W5 satisfy the following formulas (1) and (2), and also so that, when the width of the groove at the groove end portion where the groove depth is 0.05 × Dc is W0.05 and the width of the groove at the groove end portion where the groove depth is 0.50 × Dc is W0.50, W0.05 and W0.50 satisfy the following formulas (3) and (4).D5≧D4≧D3≧D2≧D1 (1) W5≧W4≧W3≧W2≧W1 (2) 0.004≦W0.05 / Wc≦0.210 (3) 0.180≦W0.50 / Wc≦0.810 (4) [9] In the method for producing a grain-oriented electrical steel sheet according to [8], in the groove forming step, the grooves may be formed so that W0.05 and W0.50 satisfy the following formulas (5) and (6): 0.008≦W0.05 / Wc≦0.160 (5) 0.380≦W0.50 / Wc≦0.710 (6)

[10] In the method for producing a grain-oriented electrical steel sheet according to [8] or [9], in the groove forming step, the laser irradiation conditions may be such that the laser output is 200 to 3000 W, the focused spot diameter, which is a diameter including 86% of the laser output in the rolling direction, is 10 to 1000 μm, the focused spot diameter in the sheet width direction of the laser is 10 to 1000 μm, and a scanning speed is 2 to 50 m / s, and the grooves are formed such that the Dc is 5.0 to 40.0 μm and the Wc is 10.0 to 200.0 μm.

[11] In the method for producing a grain-oriented electrical steel sheet according to [8] or [9], in the groove forming step, the grooves may be formed so that the intervals between the plurality of grooves in the rolling direction are each 2 to 10 mm and the angle between the groove longitudinal direction and the rolling direction is 60 to 120 degrees.

[12] In the method for producing a grain-oriented electrical steel sheet according to

[10] , in the groove forming step, the grooves may be formed so that the intervals between the plurality of grooves in the rolling direction are each 2 to 10 mm and the angle between the groove longitudinal direction and the rolling direction is 60 to 120 degrees.

[0014] According to the above aspect of the present invention, a grain-oriented electrical steel sheet having high adhesion of the insulating coating even at the groove ends and excellent rust resistance can be obtained.

[0015] FIG. 1 is a diagram showing an example of groove formation in a grain-oriented electrical steel sheet according to an embodiment; FIG. 2 is a schematic diagram of a range including a groove in a cross section parallel to the rolling direction and sheet thickness direction of the grain-oriented electrical steel sheet according to an embodiment; FIG. 3 is a schematic diagram of a cross section parallel to the sheet thickness direction and the groove extension direction and passing through the center of the groove width of the grain-oriented electrical steel sheet according to an embodiment; FIG. 4 is a schematic diagram of a range including a groove in a cross section parallel to the rolling direction and sheet thickness direction of the grain-oriented electrical steel sheet according to an embodiment after the insulating coating has been removed in order to measure the groove width and depth; FIG. 5 is a schematic diagram of a cross section parallel to the sheet thickness direction and the groove extension direction and passing through the center of the groove width of the grain-oriented electrical steel sheet according to an embodiment after the insulating coating has been removed in order to measure the groove width and depth.

[0016] A grain-oriented electrical steel sheet according to one embodiment of the present invention (grain-oriented electrical steel sheet according to this embodiment) and a method for manufacturing the same will be described.

[0017] As shown in Figures 1, 2A, and 2B, the grain-oriented electrical steel sheet 1 according to this embodiment includes a base steel sheet 2 and an insulating coating 3 formed on the base steel sheet 2. Alternatively, although not shown in the figures, a forsterite coating may be present between the base steel sheet 2 and the insulating coating 3. That is, the grain-oriented electrical steel sheet 1 may include a base steel sheet 2, a forsterite coating formed on the base steel sheet 2, and an insulating coating 3 formed on the forsterite coating. In the grain-oriented electrical steel sheet 1 according to this embodiment, the base steel sheet 2 has a plurality of grooves extending in a direction intersecting the rolling direction. Furthermore, each of the plurality of grooves has a predetermined shape, which will be described later, at the groove end portions, which are regions extending 5 mm from the groove end E toward the center in the longitudinal direction of the groove. This will be described in detail below.

[0018] For the purposes of explanation, in this embodiment, the direction in which the groove extends is referred to as the groove longitudinal direction. The groove depth is the distance from a virtual line extending from the surface of the base steel sheet to the groove (groove bottom) in the thickness direction of the base steel sheet, and the groove width is the width of the groove in the rolling direction. The position where the groove depth is 0.0 μm is referred to as the groove end, and the region 5 mm from the groove end toward the center in the groove longitudinal direction is referred to as the groove end. Furthermore, the groove depth at a position 1 mm from the groove end in the groove longitudinal direction at the groove end is referred to as D1, the groove width is referred to as W1, the groove depth at a position 2 mm from the groove end is referred to as D2, the groove width is referred to as W2, the groove depth at a position 3 mm from the groove end is referred to as D3, the groove width is referred to as W3, the groove depth at a position 4 mm from the groove end is referred to as D4, the groove width is referred to as W4, and the groove depth at a position 5 mm from the groove end is referred to as D5, the groove width is referred to as W5. The average width of the groove at the center in the longitudinal direction of the groove is Wc, and the average depth of the groove is Dc.

[0019] <Grain-oriented electrical steel sheet> [Base steel sheet] (Grooves) In grain-oriented electrical steel sheets, grooves are formed substantially parallel to the sheet width direction to reduce iron loss. Conventionally, grooves have different widths and depths at the longitudinal ends (near the start and end) of the grooves compared to the center, resulting in insufficient adhesion of the insulating coating to the grooves. In contrast, in the grain-oriented electrical steel sheet 1 according to this embodiment, the groove G formed in the base steel sheet 2 has groove ends, which are regions extending 5 mm from the groove end E (where the groove depth is 0.0 μm) toward the center in the longitudinal direction of the groove. The groove depth and width become shallower and narrower toward the end E in the longitudinal direction of the groove, satisfying a predetermined relationship between the groove depth and groove width, thereby improving the adhesion of the insulating coating to the grooves. More specifically, when groove depths D1 to D5 and groove widths W1 to W5 at positions 1 to 5 mm from the groove end at the groove end satisfy the following formulas (1) and (2) (where D5≠D1 and W5≠W1), and when the groove width at the groove end where the groove depth is 0.05×Dc is W0.05 and the groove width at the groove end where the groove depth is 0.50×Dc is W0.50, adhesion of an insulating coating or the like is improved when W0.05 and W0.50 satisfy the following formulas (3) and (4): D5≧D4≧D3≧D2≧D1 (1) W5≧W4≧W3≧W2≧W1 (2) 0.004≦W0.05 / Wc≦0.210 (3) 0.180≦W0.50 / Wc≦0.810 (4)

[0020] Although it is not clear why the adhesion of the insulating coating improves when the groove shape satisfies formulas (1) to (4) at the groove ends, it is thought that this is because when formulas (1) to (4) are satisfied, the groove width and depth at the groove ends change gradually, making it easier to apply the coating solution to every corner of the groove. Furthermore, when the above conditions are satisfied, the amount of base steel lost by the grooves is reduced, which also has the effect of increasing magnetic flux density.

[0021] As described above, in the base steel sheet 2 of the grain-oriented electrical steel sheet 1 according to this embodiment, the groove depth becomes shallower and the groove width becomes narrower toward the longitudinal end of the groove. As can be seen from formulas (1) and (2), the groove depth and groove width may change continuously (D5 > D4 > D3 > D2 > D1), but there may also be a region where they do not change within a certain range (for example, D5 = D4 ≥ D3 = D2 ≥ D1). If formula (1) and / or formula (2) are not satisfied, the groove depth and width will change abruptly at the longitudinal end of the groove, making it difficult to apply a coating solution in that region, which is thought to result in reduced adhesion of the insulating coating.

[0022] Furthermore, as shown in formulas (3) and (4), in the base steel sheet 2 of the grain-oriented electrical steel sheet 1 according to this embodiment, the groove width is narrower in areas where the groove depth is shallow. If formula (3) and / or formula (4) are not satisfied, that is, if the degree of change in groove depth and the degree of change in groove width at the groove ends are significantly different, there will be areas where the groove width is narrow but the groove depth is deep, and it will be difficult to apply a coating solution to these areas, which is thought to result in reduced adhesion of the insulating coating.

[0023] W0.05 and W0.50 preferably satisfy formulas (3') and (4'), more preferably formulas (5) and (6), and even more preferably formulas (5') and (6'). 0.005≦W0.05 / Wc≦0.200 (3') 0.200≦W0.50 / Wc≦0.800 (4') 0.008≦W0.05 / Wc≦0.160 (5) 0.380≦W0.50 / Wc≦0.710 (6) 0.010≦W0.05 / Wc≦0.150 (5') 0.400≦W0.50 / Wc≦0.700 (6') In this case, the effect of further improving the adhesion of the insulating coating can be obtained.

[0024] The shape of the grooves other than the groove ends is not limited, but it is preferable that the average groove depth Dc at the center in the longitudinal direction of the groove is 5.0 to 40.0 μm and the average groove width Wc is 10.0 to 200.0 μm. By setting the ranges within these ranges, the iron loss reduction effect due to magnetic domain refinement is increased.

[0025] The spacing S between the multiple grooves G in the rolling direction RD is preferably 2 to 10 mm. The groove spacing S is the distance from the center of one groove in the width direction to the center of the adjacent groove in the width direction. The spacing between the multiple grooves G does not need to be equal as long as it is within the above range, but it is preferable that the spacing be equal. Furthermore, the angle between the direction in which the grooves extend (the groove longitudinal direction) and the rolling direction is preferably 60 to 120 degrees. Since a direction closer to a perpendicular direction to the rolling direction is preferable, the angle is more preferably 75 to 115 degrees with respect to the rolling direction. The multiple grooves are preferably approximately parallel to each other. When the groove extension direction and spacing are within the above ranges, the iron loss reduction effect is increased. The shape of the groove is not limited, and for example, the cross section may be approximately rectangular or approximately triangular. The cross section may also be arch-shaped, forming a part of a circle.

[0026] The grooves are linear and extend in the width direction of the grain-oriented electrical steel sheet. The grooves may be formed over the entire width direction of the grain-oriented electrical steel sheet, or may be formed only in a part of the width direction.

[0027] The groove depths (D1 to D5) and widths (W1 to W5) at the groove ends are measured using a laser microscope (a 3D laser microscope using a pinhole confocal optical system). When the grain-oriented electrical steel sheet has an insulating coating, the groove depth and width are measured on the surface of the base steel sheet excluding the insulating coating. Specifically, the insulating coating of the grain-oriented electrical steel sheet can be first removed, for example, by the following method. The grain-oriented electrical steel sheet having the insulating coating is washed with NaOH: 30 mass % + H ２The specimen was immersed in an aqueous sodium hydroxide solution containing 70% by mass of SiO at 80°C for 20 minutes, followed by rinsing with water. Finally, the specimen was dried with a hot air blower for 1 minute. After removing the insulating coating in the above manner, a measured profile curve defining the groove contour was obtained by measurement using a laser microscope in a cross section parallel to the plate thickness direction and the groove extension direction and passing through the center of the groove width. A low-pass filter with a cutoff value λs was applied to the measured profile curve to obtain a profile curve, and bandpass filters with cutoff values ​​λf and λc were then applied to the profile curve to remove long and short wavelength components from the profile curve. As a result, a waviness curve WCL defining the groove contour in a cross section parallel to the plate thickness direction and the groove extension direction and passing through the center of the groove width was obtained, as shown in FIG. 3B. A waviness curve is a type of profile curve suitable for simplifying the contour shape itself with a smooth line. In the waviness curve WCL, an imaginary line IL is drawn in the groove extension direction (left-right direction on the paper) extending from the surface of the base steel sheet, and the start point of the imaginary line IL, i.e., the position where the groove depth is 0.0 μm, is defined as the groove end E. At a position 1 mm from the groove end E in the groove extension direction (rightward on the paper), the linear distance between the imaginary line IL and the base steel sheet 2 is determined, and this is defined as the groove depth D1. Furthermore, at the position where the groove depth D1 is determined, a measured profile curve forming the groove outline in a cross section parallel to the rolling direction and the sheet thickness direction is obtained by measurement using a laser microscope. A low-pass filter with a cutoff value λs is applied to this measured profile curve to obtain a profile, and then bandpass filters with cutoff values ​​λf and λc are applied to the profile curve to remove long wavelength components and short wavelength components from the profile, resulting in a waviness curve WCT forming the groove outline in a cross section parallel to the rolling direction and the sheet thickness direction, as shown in FIG. 3A. In the waviness curve WCT, the length of an imaginary line IL extending from the surface of the base steel plate in the rolling direction is determined, and this is defined as the groove width W1. In a similar manner, the groove depths D2, D3, D4, and D5 and the groove widths W2, W3, W4, and W5 are determined at positions 2 mm, 3 mm, 4 mm, and 5 mm from the groove end E in the groove extension direction, respectively.

[0028] The average groove depth Dc and average groove width Wc at the center in the longitudinal direction of the groove are measured using a laser microscope in the same manner as the groove depth and groove width at the groove ends. The groove depth and groove width are measured at five arbitrary locations in the center in the longitudinal direction of one groove (within a range of ±10 mm from the center), and the average values ​​are taken as the average groove depth Dc and the average groove width Wc.

[0029] Furthermore, the groove width W0.05 at the groove end where the groove depth is 0.05 × Dc and the groove width W0.50 at the groove depth 0.50 × Dc are measured using a laser microscope. As shown in Figure 3B, the waviness curve WCL defining the groove profile in a cross section parallel to the thickness direction and the groove extension direction and passing through the center of the groove width is used to determine the linear distances from the groove end E to positions where the groove depth is 0.05 × Dc and 0.50 × Dc. At each position, a measured profile curve defining the groove profile is obtained in a cross section parallel to the rolling direction and the thickness direction by measurement using a laser microscope. A low-pass filter with a cutoff value λs is applied to this measured profile curve to obtain a profile, and then bandpass filters with cutoff values ​​λf and λc are applied to the profile curve to remove long-wavelength and short-wavelength components from the profile, thereby obtaining a waviness curve WCT of a cross section parallel to the rolling direction and the thickness direction. On each waviness curve WCT, the lengths of the imaginary lines IL extending in the rolling direction on the surface of the base steel sheet are determined, and these are designated as W0.05 and W0.50.

[0030] When multiple grooves are formed in the base steel plate, it is preferable that all grooves satisfy formulas (1) to (4). Furthermore, it is more preferable that formulas (3') and (4'), or formulas (5 and (6), or formulas (5') and (6'), are satisfied. When grooves are repeatedly formed at equal intervals in the rolling direction under the same conditions, if one groove satisfies formulas (1) to (4), it is considered that the other grooves also satisfy formulas (1) to (4). However, when grooves are formed to the end of the plate width of the base steel plate, the groove end E does not exist at the end of the groove, and therefore the above-mentioned measurement is not performed (the groove is not considered to be the target of measurement).

[0031] (Chemical Composition) The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet is not limited as long as it is the same as that of the base steel sheet of a known grain-oriented electrical steel sheet. For example, the chemical composition may be, in mass %, Si: 2.50 to 4.50%, Mn: 0.010 to 0.150%, C: 0 to 0.085%, acid-soluble Al: 0 to 0.065%, N: 0 to 0.012%, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Sn: 0 to 0.30%, and Sb: 0 to 0. 30%, Ni: 0-1.00%, S: 0-0.015%, Se: 0-0.015%, Bi: 0-0.10%, Nb: 0-0.10%, V: 0-0.10%, Mo: 0-0.10%, Ta: 0-0.10%, W: 0-0.10%, B: 0-0.080%, Ti: 0-0.10%. Alternatively, the alloy may contain the above, with the balance being Fe and impurities.

[0032] The chemical composition of the grain-oriented electrical steel sheet (base steel sheet) may be measured by a general steel analysis method. For example, the chemical composition may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). When a forsterite film and an insulating film (described later) are formed, the chemical composition of the base steel sheet may be analyzed by removing the insulating film from the grain-oriented electrical steel sheet using the method described above, and then removing the forsterite film using a known method such as pickling. Specifically, for example, a 35 mm square (35 mm × 35 mm) test piece may be obtained from the center of the base steel sheet after removing the film as needed, and the analysis may be performed using a Shimadzu ICPS-8100 (measuring device) or the like under conditions based on a previously prepared calibration curve. C and S, which are difficult to measure by ICP-AES, can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas fusion-thermal conductivity method.

[0033] (Thickness) The thickness of the base steel sheet of the grain-oriented electrical steel sheet is not limited, but is preferably 0.15 to 0.30 mm. If the thickness of the base steel sheet exceeds 0.30 mm, classical eddy current loss increases, and iron loss increases. On the other hand, if the thickness is less than 0.15 mm, rolling efficiency decreases, which is disadvantageous in terms of productivity and cost.

[0034] [Forsterite film] [Insulating film] The grain-oriented electrical steel sheet according to this embodiment may comprise a base steel sheet and an insulating film formed on the surface of the base steel sheet, or a forsterite film may be formed on the surface of the base steel sheet. In that case, the insulating film may be formed on the surface of the forsterite film. That is, the grain-oriented electrical steel sheet according to this embodiment may comprise a base steel sheet, a forsterite film formed on the base steel sheet, and an insulating film formed on the forsterite film. The forsterite film and the insulating film may be formed on one side or both sides. The forsterite film is an inorganic film containing magnesium silicate as its main component. The forsterite film is formed during finish annealing by a reaction between an annealing separator containing magnesia (MgO) applied to the surface of the base steel sheet and the components of the surface of the base steel sheet, and has a composition derived from the components of the annealing separator and the base steel sheet (more specifically, Mg ２ SiO ４ On the other hand, in the final annealing, Al ２ O ３ When an annealing separator mainly containing phosphate and colloidal silica is used, a forsterite film may not be formed. The insulating film has the function of imparting electrical insulation and tension to the grain-oriented electrical steel sheet. By applying tension to the grain-oriented electrical steel sheet and facilitating domain wall movement in the grain-oriented electrical steel sheet, iron loss in the grain-oriented electrical steel sheet can be reduced. Furthermore, in addition to the electrical insulation and tension described above, the insulating film can also provide various other properties such as rust resistance, heat resistance, and slip resistance. In the grain-oriented electrical steel sheet according to this embodiment, the insulating film may be a known film formed by, for example, applying a coating solution mainly composed of phosphate and colloidal silica to the surface of the base steel sheet or the forsterite film and baking it (a process for forming an insulating film).

[0035] <Manufacturing Method> The grain-oriented electrical steel sheet according to this embodiment can achieve the effects described above as long as it has the characteristics described above, regardless of the manufacturing method, but a manufacturing method including the following steps is preferred because it can be manufactured stably: (I) a groove forming step of forming a plurality of grooves in a steel sheet extending in a direction intersecting the rolling direction at predetermined intervals in the rolling direction, (II) a decarburization annealing step of performing decarburization annealing on the steel sheet after the groove forming step, (III) a finish annealing step of performing finish annealing on the steel sheet after the decarburization annealing step, and (IV) an insulating film forming step of performing a process of forming an insulating film on the steel sheet after the finish annealing step (which may have a forsterite film formed on the base steel sheet) to form a base steel sheet, thereby obtaining a grain-oriented electrical steel sheet having the base steel sheet, any forsterite film formed on the base steel sheet, and the insulating film formed on the base steel sheet or on the forsterite film. Furthermore, when the steel sheet to be subjected to the groove forming step is a cold-rolled steel sheet, it can be produced by a production method including the following steps: (V) a hot rolling step of heating and hot-rolling a slab to form a hot-rolled steel sheet, (VI) a hot-rolled steel sheet annealing step of annealing the hot-rolled steel sheet after the hot-rolling step, and (VII) a cold rolling step of pickling and cold-rolling the hot-rolled steel sheet after the hot-rolled steel sheet annealing step to form a cold-rolled steel sheet.

[0036] The groove forming process, which is characteristic for obtaining the grain-oriented electrical steel sheet according to this embodiment, will be described below. Other processes can be performed by setting known conditions according to the target magnetic flux density before groove formation, so descriptions will be omitted. However, in the final annealing process, generally, the main components are MgO and Al. ２ O ３ For example, when an annealing separator containing MgO as the main component is used, forsterite (Mg ２ SiO ４ ) A coating layer is formed. ２ O ３ When an annealing separator containing the above as a main component is used, a forsterite film may not be formed. Therefore, the annealing separator may be selected depending on whether or not the formation of a forsterite film is required.

[0037] The chemical composition of the slab to be subjected to hot rolling may be determined in accordance with the desired chemical composition of the grain-oriented electrical steel sheet, taking into consideration changes in the chemical composition in each process. For example, when obtaining the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to the preferred embodiment described above, it is preferable to use a slab having the following chemical composition. That is, the slab has the following chemical composition, in mass %, Si: 2.50 to 4.50%, Mn: 0.010 to 0.150%, C: 0.020 to 0.100%, acid-soluble Al: 0 to 0.065%, N: 0.002 to 0.030%, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Sn: 0 to 0.30%, Sb: 0.50 to 0.30%, and Sb: 0.50 to 0.30%. It may contain: 0 to 0.30%, Ni: 0 to 1.00%, S: 0.001 to 0.050%, Se: 0 to 0.050%, Bi: 0 to 0.10%, Nb: 0 to 0.10%, V: 0 to 0.10%, Mo: 0 to 0.10%, Ta: 0 to 0.10%, W: 0 to 0.10%, B: 0 to 0.080%, and Ti: 0 to 0.10%. It may also contain the above, with the balance being Fe and impurities.

[0038] (Groove Forming Process) In the groove forming process, a plurality of grooves extending in a direction intersecting the rolling direction are formed in a steel plate such as a hot-rolled steel plate or a cold-rolled steel plate at predetermined intervals in the rolling direction. The grooves extending in a direction intersecting the rolling direction can be formed by irradiating the surface with a laser while scanning in a direction intersecting the rolling direction. Furthermore, by repeatedly shifting the area scanned with the laser light at predetermined intervals in the rolling direction, a plurality of grooves are formed at predetermined intervals in the rolling direction. When forming the groove, the laser is irradiated to form the groove by changing the distance between the focal point of the laser and the surface of the base steel sheet at the groove end depending on the distance from the end of the groove so that D1, D2, D3, D4, D5, W1, W2, W3, W4, and W5 satisfy the following formulas (1) and (2), and also so that W0.05 and W0.50 satisfy the following formulas (3) and (4), where W0.05 is the groove width at the groove end where the groove depth is 0.05 × Dc and W0.50 is the groove width at the groove end where the groove depth is 0.50 × Dc. Preferably, the groove is formed so that W0.05 and W0.50 satisfy the following formulas (3') and (4'), (5) and (6), or (5') and (6'). Forming grooves that satisfy formulas (1) to (4) improves the adhesion of the insulating coating formed in a subsequent process, making it possible to produce a grain-oriented electrical steel sheet with excellent adhesion of the insulating coating. D5≧D4≧D3≧D2≧D1 (1) W5≧W4≧W3≧W2≧W1 (2) 0.004≦W0.05 / Wc≦0.210 (3) 0.180≦W0.50 / Wc≦0.810 (4) 0.005≦W0.05 / Wc≦0.200 (3') 0.200≦W0.50 / Wc≦0.800 (4') 0.008≦W0.05 / Wc≦0.160 (5) 0.380≦W0.50 / Wc≦0.710 (6) 0.010≦W0.05 / Wc≦0.150 (5') 0.400≦W0.50 / Wc≦0.700 (6')

[0039] When forming grooves by laser irradiation, by shifting the laser focus away from the surface of the steel sheet, the laser energy at the surface of the steel sheet is reduced, resulting in a shallower groove depth and a narrower groove width. Therefore, the distance between the laser focus and the surface of the base steel sheet is changed depending on the distance from the edge of the groove. That is, at the start of laser irradiation of one groove, the laser focus is set at a position away from the surface of the steel sheet, and the focus is gradually moved to the surface of the steel sheet as the scanning progresses. This allows the groove depth and width to be changed within a certain range from the start point of the groove. Similarly, at the end of laser irradiation of one groove, the laser focus is moved to a position away from the surface of the steel sheet, allowing the groove depth and width to be changed within a certain range from the end point of the groove. Groove depth and width can also be changed by changing the laser output, focal spot diameter, and scanning speed. Since the groove depth and groove width can be changed independently depending on the conditions to be changed, the conditions are set in combination so that the groove depth and groove width satisfy the formulas (1) to (4). Methods for moving the laser focus include displacing the position of an optical component.

[0040] In the groove forming process, from the viewpoint of magnetic domain refinement, it is preferable to form grooves having an average groove depth Dc of 5.0 to 40.0 μm and an average groove width Wc of 10.0 to 200.0 μm at the center of the groove longitudinal direction. In the groove forming process, the laser irradiation conditions are not limited, but in regions other than the groove ends, it is preferable to set the laser output to 200 to 3000 W, the focused spot diameter, which is the diameter including 86% of the laser output in the rolling direction, to 10 to 1000 μm, the focused spot diameter in the laser plate width direction to 10 to 1000 μm, and the scanning speed to 2 to 50 m / s. In this case, it is easy to form grooves with Dc and Wc in the preferred ranges.

[0041] In the groove forming step, it is preferable to form the grooves so that the intervals between the grooves in the rolling direction are 2 to 10 mm and the angle between the groove longitudinal direction and the rolling direction is 60 to 120 degrees (°). In this case, the iron loss reduction effect is increased.

[0042] A slab having a chemical composition containing, in mass%, Si: 3.30%, Mn: 0.120%, C: 0.060%, acid-soluble Al: 0.028%, N: 0.008%, Cr: 0.050%, Cu: 0.040%, P: 0.010%, Sn: 0.020%, Ni: 0.005%, S: 0.007%, with the balance being Fe and impurities, was hot-rolled to obtain a hot-rolled steel sheet having a thickness of 2.6 mm. This hot-rolled steel sheet was annealed under the conditions of heating to 1100 ° C and holding for 1 minute. The hot-rolled steel sheet after annealing was pickled and cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.22 mm. The obtained cold-rolled steel sheet was subjected to a hot-rolling process. For each sample, laser irradiation was performed under various conditions shown in Table 1 to form multiple grooves (the laser irradiation conditions were the same within a single cold-rolled steel sheet). The groove ends were gradually changed in depth and width by displacing the position of the polygon mirror. The cold-rolled steel sheets after groove formation were subjected to decarburization annealing by heating to 850°C and holding for 2 minutes. An annealing separator primarily composed of magnesia (MgO) was applied to the cold-rolled steel sheets after decarburization annealing, and then the cold-rolled steel sheets were subjected to finish annealing by heating to 1200°C and holding for 20 hours. As a result, a steel sheet having a forsterite film formed on the surface of the cold-rolled steel sheet (base steel sheet) was obtained. Next, a coating solution containing colloidal silica and aluminum phosphate was applied to the forsterite film, and heat treatment was performed by heating to 850°C and holding for 1 minute to form an insulating film. The insulating film had a thickness of 5 μm. A sample measuring 60 mm in the width direction and 300 mm in the rolling direction was taken from the obtained grain-oriented electrical steel sheet, and a single sheet magnetic property test (SST test) was performed on this sample in accordance with JIS C2556 (2015), and the magnetic flux density B8 generated when magnetized at 800 A / m was measured.

[0043] A 30 mm x 30 mm test piece was taken from the resulting grain-oriented electrical steel sheet, including the groove end portion. The insulating coating was removed using the method described above. For one representative groove, the average groove depth Dc at the center of the groove longitudinal direction, the average groove width Wc, and the groove depths D1 to D5 and groove widths W1 to W5 at positions 1 mm to 5 mm from the groove end were measured using the method described above. For the same groove, the groove width W0.05 at the groove end portion where the groove depth was 0.05 x Dc, and the groove width W0.05 at the groove end portion where the groove depth was 0.50 x Dc were also measured using the method described above. The results are shown in Table 2.

[0044] The adhesion of the insulating film and the rust resistance of the obtained grain-oriented electrical steel sheets were evaluated by the following methods. The results are shown in Table 3.

[0045] <Adhesion of Insulation Coating> A test piece measuring 80 mm x 80 mm was cut out from a portion of the obtained grain-oriented electrical steel sheet, including the end of the groove, and wrapped around a round bar with a diameter of 20 mm. The test piece was then flattened. The surface of the flattened test piece was observed, and the area of ​​the insulation coating that had not peeled off from the steel sheet relative to the area of ​​the bent part was measured to calculate the remaining coating area ratio (%). The insulation coating adhesion of test pieces with a remaining coating area ratio of 95% or more was evaluated as "excellent (Ex)." The insulation coating adhesion of test pieces with a remaining coating area ratio of 90% or more but less than 95% was evaluated as "good (G)." The insulation coating adhesion of test pieces with a remaining coating area ratio of less than 90% was evaluated as "poor (P)."

[0046] <Rust Resistance> A 30 mm x 30 mm test piece was taken from a portion including the end of the groove of the obtained grain-oriented electrical steel sheet, and the test piece was left in an atmosphere of a temperature of 50°C and a humidity of 91% for one week, and the test piece was evaluated based on the weight change of the test piece before and after the period. Since the weight of the test piece increases when rust occurs, it was determined that the smaller the weight increase, the better the rust resistance. Specifically, a weight increase of 1.0 mg / m ２ The rust resistance of the following test pieces was evaluated as "excellent (Ex)" and the weight gain was 5.0 mg / m ２ The rust resistance of the following test pieces was evaluated as "good (G)" and the weight increase was 5.0 mg / m ２ The rust resistance of over 100 test pieces was rated as "poor (P)".

[0047]

[0048]

[0049]

[0050] As can be seen from Tables 1 to 3, it was confirmed that the rust resistance and insulating coating adhesion of grain-oriented electrical steel sheets were improved by forming grooves that satisfied formulas (1) to (4). Furthermore, by forming grooves that satisfied formulas (3') and (4'), (5) and (6), or (5') and (6'), grain-oriented electrical steel sheets with further improved rust resistance and insulating coating adhesion were obtained.

[0051] 1 Grain-oriented electrical steel sheet 2 Base steel sheet 3 Insulation coating G Groove E Groove edge D Groove depth (general term for D1, D2, D3, D4, D5, Dc) W Groove width (general term for W1, W2, W3, W4, W5, Wc) IL Imaginary line extending the surface of the base steel sheet S Groove spacing RD Rolling direction TD Sheet width direction ND Sheet thickness direction of the base steel sheet

[0052] According to the present invention, it is possible to improve the rust resistance and insulating coating adhesion of a grain-oriented electrical steel sheet having grooves formed on the surface for the purpose of reducing iron loss. Therefore, by using the grain-oriented electrical steel sheet of the present invention, it is possible to prevent an increase in iron loss due to the generation of interlaminar current when steel sheets are stacked, and to prevent poor appearance.

Claims

1. A steel sheet comprising: a base steel plate; optionally, a forsterite film formed on the base steel plate; and an insulating film formed on the base steel plate or on the forsterite film; the base steel plate has a plurality of grooves extending in a direction intersecting the rolling direction, the direction in which the grooves extend is defined as the groove longitudinal direction, the distance from an imaginary line extending along the surface of the base steel plate to the groove in the thickness direction of the base steel plate is defined as the groove depth, the width of the groove in the rolling direction is defined as the groove width, the position where the groove depth is 0.0 μm is defined as the groove end, and a region 5 mm from the groove end toward the center in the groove longitudinal direction is defined as the groove end, When the groove depth at a position 1 mm from the groove end in the groove longitudinal direction of the groove end portion is D1 and the groove width is W1, the groove depth at a position 2 mm from the groove end is D2 and the groove width is W2, the groove depth at a position 3 mm from the groove end is D3 and the groove width is W3, the groove depth at a position 4 mm from the groove end is D4 and the groove width is W4, and the groove depth at a position 5 mm from the groove end is D5 and the groove width is W5, and the average groove width at the center of the groove in the groove longitudinal direction is Wc and the average groove depth is Dc, the D1, D2, D3, D4, D5, W1, W2, W3, W4 and W5 satisfy the following formula (1) and the following formula (2), A grain-oriented electrical steel sheet, characterized in that, when the groove width at a portion where the groove depth is 0.05×Dc at the groove end is W0.05 and the groove width at a portion where the groove depth is 0.50×Dc is W0.50, W0.05 and W0.50 satisfy the following formulas (3) and (4): D5≧D4≧D3≧D2≧D1 (1) W5≧W4≧W3≧W2≧W1 (2) 0.004≦W0.05 / Wc≦0.210 (3) 0.180≦W0.50 / Wc≦0.810 (4) 2. The grain-oriented electrical steel sheet according to claim 1, wherein the W0.05 and the W0.50 satisfy the following formulas (5) and (6): 0.008≦W0.05 / Wc≦0.160 (5) 0.380≦W0.50 / Wc≦0.710 (6) 3. The grain-oriented electrical steel sheet according to claim 1, wherein D1, D2, D3, D4, and D5 satisfy the following formula (1'): D5>D4>D3>D2>D1... (1') 4. The grain-oriented electrical steel sheet according to claim 2, wherein D1, D2, D3, D4, and D5 satisfy the following formula (1'): D5>D4>D3>D2>D1... (1') 5. A grain-oriented electrical steel sheet according to any one of claims 1 to 4, characterized in that Dc is 5.0 to 40.0 μm and Wc is 10.0 to 200.0 μm.

6. The grain-oriented electrical steel sheet according to any one of claims 1 to 4, characterized in that the intervals between the multiple grooves in the rolling direction are each 2 to 10 mm, and the angle between the longitudinal direction of the groove and the rolling direction is 60 to 120 degrees.

7. The grain-oriented electrical steel sheet according to claim 5, wherein the intervals between the plurality of grooves in the rolling direction are each 2 to 10 mm, and the angle between the longitudinal direction of the groove and the rolling direction is 60 to 120 degrees.

8. A method for manufacturing a steel sheet comprising: a groove forming step of irradiating a laser onto a steel sheet while scanning in a direction intersecting the rolling direction to form grooves extending in the rolling direction; a decarburization annealing step of decarburization annealing the steel sheet after the groove forming step; a finish annealing step of finish annealing the steel sheet after the decarburization annealing step; and an insulating film forming step of performing a process of forming an insulating film on the steel sheet after the finish annealing step to become a base steel sheet, to obtain a grain-oriented electrical steel sheet having the base steel sheet, a forsterite film arbitrarily formed on the base steel sheet, and the insulating film formed on the base steel sheet or on the forsterite film, wherein in the groove forming step, the direction in which the groove extends is defined as the groove longitudinal direction, the distance from an imaginary line extending from the surface of the base steel sheet to the groove in the thickness direction of the base steel sheet is defined as the groove depth, and the width of the groove in the rolling direction is defined as the groove width, The position where the groove depth is 0.0 μm is defined as the groove end, and a region 5 mm from the groove end toward the center in the groove longitudinal direction is defined as the groove end, and the groove depth in the groove longitudinal direction of the groove end is defined as D1, the groove width in the groove longitudinal direction of the groove end is defined as W1, the groove depth in the groove longitudinal direction of the groove end is defined as D2, the groove width in the groove longitudinal direction of the groove end is defined as W2, the groove depth in the groove longitudinal direction of the groove end is defined as D3, the groove width in the groove longitudinal direction of the groove end is defined as W3, the groove depth in the groove longitudinal direction of the groove end is defined as D4, the groove width in the groove longitudinal direction of the groove end is defined as W4, and the groove depth in the groove longitudinal direction of the groove end is defined as D5, and the groove width in the groove longitudinal direction of the groove end is defined as W5, and The groove is formed by irradiating the laser so that, at the groove end, the distance between the focus of the laser and the surface of the base steel sheet is changed according to the distance from the end of the groove, so that D1, D2, D3, D4, D5, W1, W2, W3, W4, and W5 satisfy the following formula (1) and formula (2), and, when the groove width at a portion where the groove depth is 0.05×Dc at the groove end is W0.05 and the groove width at a portion where the groove depth is 0.50×Dc is W0.50, W0.05 and W0.50 satisfy the following formula (3) and formula (4).A method for producing a grain-oriented electrical steel sheet, characterized in that D5≧D4≧D3≧D2≧D1 (1) W5≧W4≧W3≧W2≧W1 (2) 0.004≦W0.05 / Wc≦0.210 (3) 0.180≦W0.50 / Wc≦0.810 (4) 9. The method for producing a grain-oriented electrical steel sheet according to claim 8, wherein in the groove forming step, the grooves are formed so that the W0.05 and the W0.50 satisfy the following formulas (5) and (6): 0.008≦W0.05 / Wc≦0.160 (5) 0.380≦W0.50 / Wc≦0.710 (6) 10. A method for producing a grain-oriented electrical steel sheet as claimed in claim 8 or 9, characterized in that in the groove forming process, the laser irradiation conditions are a laser output of 200 to 3000 W, a focused spot diameter which is a diameter including 86% of the laser output in the rolling direction of the laser of 10 to 1000 μm, a focused spot diameter of the laser in the sheet width direction of the laser of 10 to 1000 μm, and a scanning speed of 2 to 50 m / s, and grooves are formed such that Dc is 5.0 to 40.0 μm and Wc is 10.0 to 200.0 μm.

11. A method for manufacturing grain-oriented electrical steel sheet as claimed in claim 8 or 9, characterized in that in the groove forming step, the grooves are formed so that the intervals between the multiple grooves in the rolling direction are each 2 to 10 mm, and the angle between the longitudinal direction of the groove and the rolling direction is 60 to 120 degrees.

12. A method for manufacturing grain-oriented electrical steel sheet as set forth in claim 10, characterized in that in the groove forming step, the grooves are formed so that the intervals between the multiple grooves in the rolling direction are each 2 to 10 mm, and the angle between the longitudinal direction of the groove and the rolling direction is 60 to 120 degrees.

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