EP-4741523-A1 - GRAIN-ORIENTED ELECTROMAGNETIC STEEL SHEET AND METHOD FOR MANUFACTURING SAME

EP4741523A1EP 4741523 A1EP4741523 A1EP 4741523A1EP-4741523-A1

Abstract

This grain-oriented electrical steel sheet includes a base steel sheet, a forsterite film optionally formed on the base steel sheet, and an insulating coating formed on the base steel sheet or the forsterite film. In a case where the base steel sheet has a plurality of grooves extending in a direction intersecting a rolling direction, a direction in which the plurality of grooves extend is defined as a longitudinal groove direction, a distance in the groove from an imaginary line that is an extension of a surface of the base steel sheet to the groove, along a straight line from the imaginary line in the sheet thickness direction of the base steel sheet, is defined as a groove depth, a width of the groove in the rolling direction is defined as a groove width, a position where the groove depth is 0.0 µm is defined as an end of the groove, and a 5 mm region from the end of the groove toward a center portion in the longitudinal groove direction is defined as an end portion of the groove, depths of the groove and widths of the groove at a plurality of positions in the end portion of the groove satisfy a predetermined relationship.

Inventors

WADA NAOKI
HAMAMURA HIDEYUKI
TAKAHASHI MASARU

Assignees

Nippon Steel Corporation

Dates

Publication Date: 20260513
Application Date: 20240704

Claims (12)

A grain-oriented electrical steel sheet comprising: a base steel sheet; a forsterite film optionally formed on the base steel sheet; and an insulating coating 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 a rolling direction, in a case where a direction in which the plurality of grooves extend is defined as a longitudinal groove direction, a distance in the groove from an imaginary line that is an extension of a surface of the base steel sheet to the groove, along a straight line from the imaginary line in the sheet thickness direction of the base steel sheet, is defined as a groove depth, a width of the groove in the rolling direction is defined as a groove width, a position where the groove depth is 0.0 µm is defined as an end of the groove, and a 5 mm region extending from the end of the groove toward a center portion in the longitudinal groove direction is defined as an end portion of the groove, in the longitudinal groove direction of the end portion of the groove, in units of µm, a groove depth at a position 1 mm from the end of the groove is defined as D1 and a groove width at the position 1 mm from the end of the groove is defined as W1, a groove depth at a position 2 mm from the end of the groove is defined as D2 and a groove width at the position 2 mm from the end of the groove is defined as W2, a groove depth at a position 3 mm from the end of the groove is defined as D3 and a groove width at the position 3 mm from the end of the groove is defined as W3, a groove depth at a position 4 mm from the end of the groove is defined as D4 and a groove width at the position 4 mm from the end of the groove is defined as W4, and a groove depth at a position 5 mm from the end of the groove is defined as D5 and a groove width at the position 5 mm from the end of the groove is defined as W5, an average groove width of the groove at the center portion in the longitudinal groove direction is defined as Wc, and an average groove depth of the groove at the center portion in the longitudinal groove direction is defined as Dc, the D1, the D2, the D3, the D4, the D5, the W1, the W2, the W3, the W4, and the W5 satisfy Formulae (1) and (2), and in the end portion of the groove, in a case where a width of the groove at a portion where a depth of the groove is 0.05 × Dc is defined as W0.05, and a width of the groove at a portion where a depth of the groove is 0.50 × Dc is defined as W0.50, W0.05 and W0.50 satisfy Formulae (3) and (4), D 5 ≥ D 4 ≥ D 3 ≥ D 2 ≥ D 1 W 5 ≥ W 4 ≥ W 3 ≥ W 2 ≥ W 1 0.004 ≤ W 0.05 / Wc ≤ 0.210 0.180 ≤ W 0.50 / Wc ≤ 0.810
The grain-oriented electrical steel sheet according to claim 1, wherein the W0.05 and the W0.50 satisfy Formulae (5) and (6), 0.008 ≤ W 0.05 / Wc ≤ 0.160 0.380 ≤ W 0.50 / Wc ≤ 0.710
The grain-oriented electrical steel sheet according to claim 1, wherein the D1, the D2, the D3, the D4, and the D5 satisfy Formula (1'), D 5 > D 4 > D 3 > D 2 > D 1
The grain-oriented electrical steel sheet according to claim 2, wherein the D1, the D2, the D3, the D4, and the D5 satisfy Formula (1'), D 5 > D 4 > D 3 > D 2 > D 1
The grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the Dc is 5.0 to 40.0 µm and the Wc is 10.0 to 200.0 µm.
The grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein an interval between the plurality of grooves in the rolling direction is 2 to 10 mm, and an angle between the longitudinal groove direction and the rolling direction is 60 to 120 degrees.
The grain-oriented electrical steel sheet according to claim 5, wherein an interval between the plurality of grooves in the rolling direction is 2 to 10 mm, and an angle between the longitudinal groove direction and the rolling direction is 60 to 120 degrees.
A method for manufacturing a grain-oriented electrical steel sheet comprising: a groove forming step of irradiating a steel sheet with a laser beam while scanning the steel sheet in a direction intersecting a rolling direction to form a groove extending in the rolling direction; a decarburization annealing step of performing decarburization annealing on the steel sheet after the groove forming step; a final annealing step of performing final annealing on the steel sheet after the decarburization annealing step; and an insulating coating forming step of forming an insulating coating on the steel sheet that serves as a base steel sheet and is obtained after the final annealing step, to obtain a grain-oriented electrical steel sheet having the base steel sheet, a forsterite film optionally formed on the base steel sheet, and the insulating coating formed on the base steel sheet or on the forsterite film, wherein in the groove forming step, in a case where a direction along which the groove extends is defined as a longitudinal groove direction, a distance in the groove from an imaginary line that is an extension of a surface of the base steel sheet to the groove, along a straight line from the imaginary line in the sheet thickness direction of the base steel sheet, is defined as a groove depth, a width of the groove in the rolling direction is defined as a groove width, a position where the groove depth is 0.0 µm is defined as an end of the groove, and a 5 mm region extending from the end of the groove toward a center portion in the longitudinal groove direction is defined as an end portion of the groove, in the longitudinal groove direction of the end portion of the groove, in units of µm, a groove depth at a position 1 mm from the end of the groove is defined as D1 and a groove width at the position 1 mm from the end of the groove is defined as W1, a groove depth at a position 2 mm from the end of the groove is defined as D2 and a groove width at the position 2 mm from the end of the groove is defined as W2, a groove depth at a position 3 mm from the end of the groove is defined as D3 and a groove width at the position 3 mm from the end of the groove is defined as W3, a groove depth at a position 4 mm from the end of the groove is defined as D4 and a groove width at the position 4 mm from the end of the groove is defined as W4, and a groove depth at a position 5 mm from the end of the groove is defined as D5 and a groove width at the position 5 mm from the end of the groove is defined as W5, an average groove width of the groove at the center portion in the longitudinal groove direction is defined as Wc, and an average groove depth of the groove at the center portion in the longitudinal groove direction is defined as Dc, the groove is formed by irradiation with the laser beam in such a manner that the D1, the D2, the D3, the D4, the D5, the W1, the W2, the W3, the W4, and the W5 satisfy Formulae (1) and (2) and in the end portion of the groove, in a case where a width of the groove at a portion where a depth of the groove is 0.05 × Dc is defined as W0.05, and a width of the groove at a portion where a depth of the groove is 0.50 × Dc is defined as W0.50, W0.05 and W0.50 satisfy Formulae (3) and (4), by changing a distance between a focal point of the laser beam and the surface of the base steel sheet in accordance with a distance from the end of the groove at the end portion of the groove, D 5 ≥ D 4 ≥ D 3 ≥ D 2 ≥ D 1 W 5 ≥ W 4 ≥ W 3 ≥ W 2 ≥ W 1 0.004 ≤ W 0.05 / Wc ≤ 0.210 0.180 ≤ W 0.50 / Wc ≤ 0.810
The method for manufacturing a grain-oriented electrical steel sheet according to claim 8, wherein in the groove forming step, the groove is formed in such a manner that the W0.05 and the W0.50 satisfy Formulae (5) and (6), 0.008 ≤ W 0.05 / Wc ≤ 0.160 0.380 ≤ W 0.50 / Wc ≤ 0.710
The method for manufacturing a grain-oriented electrical steel sheet according to claim 8 or 9, wherein in the groove forming step, the groove in which the Dc is 5.0 to 40.0 µm and the Wc is 10.0 to 200.0 µm is formed under irradiation conditions of the laser beam that a power of the laser beam is set to 200 to 3000 W, a focused spot diameter of the laser beam defined as a diameter in the rolling direction that contains 86% of the power is set to 10 to 1000 µm, the focused spot diameter of the laser beam in a sheet width direction is 10 to 1000 µm, and a scanning speed is set to 2 to 50 m/s.
The method for manufacturing a grain-oriented electrical steel sheet according to claim 8 or 9, wherein in the groove forming step, the groove is formed in such a manner that an interval between a plurality of the grooves in the rolling direction is 2 to 10 mm, and an angle between the longitudinal groove direction and the rolling direction is 60 to 120 degrees.
The method for manufacturing a grain-oriented electrical steel sheet according to claim 10, wherein in the groove forming step, the groove is formed in such a manner that an interval between a plurality of the grooves in the rolling direction is 2 to 10 mm, and an angle between the longitudinal groove direction and the rolling direction is 60 to 120 degrees.

Description

TECHNICAL FIELD The present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the same. Priority is claimed on Japanese Patent Application No. 2023-111726, filed July 06, 2023, the content of which is incorporated herein by reference. BACKGROUND ART A grain-oriented electrical steel sheet is a soft magnetic material and is mainly used as a core material of a transformer. Thus, the grain-oriented electrical steel sheet is desired so as to have magnetic characteristics such as a high magnetic flux density and a low iron loss. The iron loss is a loss due to thermal energy consumption that occurs when a core is excited by an AC magnetic field, and the iron loss should be as low as possible from the viewpoint of energy saving. The level of the iron loss is affected by magnetic susceptibility, a sheet thickness, a coating tension, an impurity amount, an electric resistivity, a crystal grain size, a magnetic domain width, and the like. Even at present when various techniques have been developed regarding the grain-oriented electrical steel sheet, research and development for reducing the iron loss is being continued in order to increase energy conversion efficiency. A technique for irradiating a steel sheet with a laser has been proposed as one method for reducing the iron loss. In this technique, strain is introduced to the surface of the steel sheet by the laser irradiation, and the magnetic domain width is refined. As a result, the eddy-current loss that is part of the iron loss can be reduced. For example, Patent Document 1 discloses a method for manufacturing a grain-oriented electrical steel sheet in which a magnetic domain is controlled by irradiation with a laser beam. The method includes a step of irradiating a surface of the grain-oriented electrical steel sheet with a focused continuous wave laser beam while scanning the surface in a direction inclined from a rolling direction of the grain-oriented electrical steel sheet and a step of repeating a portion scanned with the continuous wave laser beam while shifting the portion at a predetermined interval. When the average power of the continuous wave laser beam is represented as P (W), the scanning speed is represented as Vc (mm/s), the predetermined interval is represented as PL (mm), and an input energy Ua is defined as Ua = P/(Vc × PL) (mJ/mm2), 1.0 mm ≤ PL ≤ 3.0 mm, and 0.8 mJ/mm2 ≤ Ua ≤ 2.0 mJ/mm2 are satisfied. Patent Document 1 discloses that iron losses in both directions of an L direction and a C direction of the grain-oriented electrical steel sheet can be reduced easily while ensuring high productivity. However, for example, when a wound core is manufactured, stress-relief annealing is preferable because the grain-oriented electrical steel sheet is bent and formed. Accordingly, in such an above-described method of introducing strain into the surface by the laser irradiation, the strain introduced into the grain-oriented electrical steel sheet is released by the stress-relief annealing. Thus, an effect of magnetic domain refinement by the laser irradiation disappears. Thus, it has been proposed that the magnetic domain width is refined to reduce the eddy-current loss by forming a groove in a sheet surface as in the case of strain introduction. In such a case, since the groove remains even though the stress-relief annealing is performed, the effect of magnetic domain refinement does not disappear. Examples of the method for forming a groove in a steel sheet include an electrolytic etching method for forming a groove on a sheet surface of a grain-oriented electrical steel sheet by electrolytic etching, a gear pressing method for forming a groove on a sheet surface of a grain-oriented electrical steel sheet by mechanically pressing a gear on the sheet surface, and a laser irradiation method for melting and evaporating a steel sheet by laser irradiation (area irradiated with a laser beam) to form a groove. For example, Patent Document 2 discloses a method for improving iron loss characteristics of grain-oriented electrical steel sheets that can withstand stress-relief annealing, in which irradiation is performed by controlling a laser beam and a recessed portion having a width of 0.5 mm or less and a depth of 10 µm or more is formed in a rolling direction. Here, in general, an insulating coating is formed on a surface of the grain-oriented electrical steel sheet, in order to impart electrical insulation properties, tensile strength, heat resistance, and the like to the steel sheet. As described in Patent Document 2, in the grain-oriented electrical steel sheet, a groove is formed on a steel sheet approximately parallel to the width direction, so that the magnetic domain width is refined, and the iron loss is reduced. On the other hand, the width or depth of end portions (in the vicinity of the leading end and trailing end) of the formed groove in the longitudinal direction changes as compared with the center