US-20260124704-A1 - GRAIN-ORIENTED ELECTRICAL STEEL SHEET AND METHOD OF PRODUCTION OF SAME

Abstract

The present invention has as its object to provide grain-oriented electrical steel sheet further improved in core loss in control of magnetic domains by forming laser grooves in steel sheet after decarburization annealing and before finish annealing. The grain-oriented electrical steel sheet according to the present invention is a grain-oriented electrical steel sheet having a plurality of grooves on the surface of the steel sheet and provided with a glass coating on that surface, which grain-oriented electrical steel sheet characterized in that an absolute value of an angle θ formed by a direction perpendicular to both a rolling direction and sheet thickness direction of the steel sheet and a longitudinal direction of the grooves is 0 to 40°, a width W of the grooves is 20 to 300 μm, a depth D of the grooves is 10 to 40 μm, and a pitch P of the grooves in the rolling direction is 1.0 to 30 mm and in that the relationship of formula (1) is satisfied when a thickness of the glass coating of flat parts of the steel sheet surface (parts other than grooves) is t1 and the thickness of the glass coating at the deepest parts of the grooves is t2: t 2/ t 1<1.00  formula (1)

Inventors

• Masato Yasuda
• Hideyuki Hamamura
• Kimihiko Sugiyama
• Nobusato Morishige

Assignees

• NIPPON STEEL CORPORATION

Dates

Publication Date

20260507

Application Date

20231004

Priority Date

20221004

Claims (3)

1. 1 . A grain-oriented electrical steel sheet having a plurality of grooves on a surface of the steel sheet and provided with a glass coating on that surface, which grain-oriented electrical steel sheet characterized in that an absolute value of an angle θ formed by a direction perpendicular to both a rolling direction and sheet thickness direction of the steel sheet and a longitudinal direction of the grooves is 0 to 40°, a width W of the grooves is 20 to 300 μm, a depth D of the grooves is 10 to 40 μm, and a pitch P of the grooves in the rolling direction is 1.0 to 30 mm, and when a thickness of the glass coating of flat parts being parts other than grooves of the steel sheet is t1 and the thickness of the glass coating at the deepest parts of the grooves is t2, the relationship of formula (1) is satisfied: t ⁢ 2 / t ⁢ 1 < 1. . formula ⁢ ( 1 )
2. 2 . The grain-oriented electrical steel sheet according to claim 1 , characterized in that, in that grain-oriented electrical steel sheet, the relationship of formula (2) is satisfied when a thickness of anchoring parts of the glass coating of flat parts is s1 and a thickness of anchoring parts of the glass coating at the deepest parts of the grooves is s2: s ⁢ 2 / s ⁢ 1 < 1. . formula ⁢ ( 2 )
3. 3 . A method of production of grain-oriented electrical steel sheet according to claim 1 , which method of producing the grain-oriented electrical steel sheet characterized by including a groove forming step of forming grooves by lasering the surface of steel sheet after decarburization annealing and before finish annealing, in which a focused spot diameter dL of the laser beam in a rolling direction of the steel sheet and a focused spot diameter dC of the laser beam in a sheet width direction satisfy formula (3): 0.1 ≤ d ⁢ L / dC < 1. . formula ⁢ ( 3 )

Description

FIELD The present invention relates to grain-oriented electrical steel sheet. BACKGROUND Grain-oriented electrical steel sheet is steel sheet controlled in crystal orientation by a combination of cold rolling and annealing so that the easy magnetization axes of crystal grains and the rolling direction match. The crystal orientation is controlled by building in a primary recrystallization texture in annealing treatment after cold rolling treatment and further annealing at a high temperature to thereby cause preferential growth of an orientation preferable for the magnetic properties, that is, so-called secondary recrystallization. This control of the crystal orientation enables the hysteresis loss of the grain-oriented electrical steel sheet to be reduced. As art for reducing eddy current loss, one type of core loss, of grain-oriented electrical steel sheet, grain-oriented electrical steel sheet comprised of a base steel sheet controlled in crystal orientation and an insulating coating formed on the surface is known. The insulating coating performs a role of not only providing electrical insulation, but also tension and rust resistance etc. to the base steel sheet. Further, as another method for reducing abnormal eddy current loss, the method of control of magnetic domains forming distorted regions or grooves in a direction crossing the rolling direction at a predetermined pitch along the rolling direction to narrow the widths of the 180° magnetic domains (the 180° magnetic domain refining) is known. Methods for control of magnetic domains are classified into methods imparting distortion to a base steel sheet of grain-oriented electrical steel sheet and methods forming grooves in the surface of a base steel sheet having a coating giving tension at the base steel sheet. By using grain-oriented electrical steel sheet controlled in magnetic domains by grooves, even if producing iron cores (wound cores) of transformers and applying straightening annealing, the grooves will not disappear, so the effects of magnetic domain refining can be maintained. For this reason, the method for control of magnetic domains using formation of grooves as the method for reducing abnormal eddy current loss is sometimes employed for wound cores. FIG. 1 is a view showing an outline of electrical steel sheet formed with grooves. In FIG. 1, the state is shown where the surface of the base steel sheet 1 is formed with a plurality of grooves 2 at a pitch in the rolling direction of the base steel sheet 1. In FIG. 1, the notation e shows the angle formed by the direction perpendicular to the rolling direction and sheet thickness direction (sheet width direction) of the base steel sheet 1 and the longitudinal direction of the grooves 2. The notation W shows the width of the grooves, the notation D shows the depth of the grooves, and the notation P shows the pitch of the grooves 2 adjoining each other in the rolling direction. Various methods for forming grooves in electrical steel sheet have been proposed. For example, PTL 1 discloses an electrolytic etching method of using electrolytic etching to form grooves in the steel sheet surface of grain-oriented electrical steel sheet. PTL 2 discloses a gear press method of mechanically pressing a gear against the steel sheet surface of grain-oriented electrical steel sheet to thereby form grooves in the steel sheet surface. However, the gear press method suffers from wear of the gear teeth in a short period of time due to the high hardness of electrical steel sheet. Further, from the viewpoint of high speed processing, it is difficult to realize a line speed of 100 mpm or more like demanded in general ferrous metal manufacturing processes. The method using electrolytic etching is free from the problem of wear of the gear teeth, but steps of masking, etching, and mask removal are required. Compared with mechanical methods, there is the problem that the process becomes complicated. PTL 3 discloses a lasering method of using lasering to melt and evaporate lasered parts of the steel sheet surface of grain-oriented electrical steel sheet. The lasering method has no problem of wear of gear teeth or a complicated process and also enables high speed processing. Further, even in the lasering method, there have been several proposals for the groove-forming step. For example, PTL 4 is also a lasering method. Lasering a final product sheet coated with a tension insulating coating is disclosed. However, in that case, it is necessary to again coat an insulating tension coating. There is the problem of poor productivity. On the other hand, PTL 5 discloses formation of grooves in cold rolled steel sheet. This method does not require recoating of an insulating tension coating and is excellent in productivity. However, there is the problem that in the subsequent decarburization annealing, the primary recrystallization texture degrades and the secondary recrystallization in the subsequent high temperature annealing