EP-4737606-A1 - GRAIN-ORIENTED ELECTRICAL STEEL SHEET

Abstract

In a grain oriented electrical steel sheet, aveϕ L which is an average of the angular deviation ϕ obtained from plural measurement points with spacing of 1 mm in the rolling direction L is 3.5° or less, D L 10 which is a grain size at 10% by number base from largest in a case where the grain sizes D L obtained in the rolling direction L are sorted from largest to smallest is (100 - 15 × aveϕ L ) or less in units of mm, and aveD C which is an average of the grain size D C obtained in the transverse direction C is 50 mm or more.

Inventors

• NAKAMURA, SHUICHI
• USHIGAMI, YOSHIYUKI

Assignees

• Nippon Steel Corporation

Dates

Publication Date

20260506

Application Date

20240627

Claims (1)

1. A grain oriented electrical steel sheet, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction Z is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction C is defined as β, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a rolling direction L is defined as y, when a deviation angle of a crystal orientation measured at one measurement point on a sheet surface is represented as (α β γ), when an angular deviation at the measurement point is defined as ϕ = (α 2 + β 2 ) 1/2 , and when an average of the angular deviation ϕ obtained from plural measurement points with spacing of 1 mm in the rolling direction L is defined as aveϕ L , the aveϕ L satisfies aveϕ L ≤ 3.5°, when deviation angles of crystal orientations measured at two measurement points which are adjacent on the sheet surface and which have spacing of 1 mm are represented as (α 1 β 1 γ 1 ) and (α 2 β 2 γ 2 ), when a midpoint of two measurement points which satisfy [(α 2 - α 1 ) 2 + (β 2 - β 1 ) 2 + (γ 2 - γ 1 ) 2 ] 1/2 ≥ 1.0° is defined as a grain boundary GB, when a grain size in the rolling direction L obtained based on the grain boundary GB is defined as D L in units of mm, and when a grain size which is at 10% by number base from largest in a case where the grain sizes D L obtained in the rolling direction L are sorted from largest to smallest is defined as D L 10 in units of mm, the D L 10 satisfies D L 10 ≤ 100 - 15 × aveϕ L , and when a grain size in the transverse direction C obtained based on the grain boundary GB is defined as D C in units of mm, and when an average of the grain size D C obtained in the transverse direction C is defined as aveD C , the aveD C satisfies aveD C ≥ 50.

Description

TECHNICAL FIELD The present invention relates to a grain oriented electrical steel sheet. Priority is claimed on Japanese Patent Application No. 2023-106860, filed June 29, 2023, the content of which is incorporated herein by reference. BACKGROUND ART A grain oriented electrical steel sheet includes Si, the crystal orientation of the grains thereof closely aligns in the Goss orientation (cubic crystal {110}<001>), and the <001> orientation, which is a magnetization easy axis, is substantially aligned in the rolling direction in the steel sheet manufacturing process. Such a grain oriented electrical steel sheet is very desirable as a material for an iron core and the like of a transformer. One of important magnetic characteristics of the grain oriented electrical steel sheet is, for instance, magnetic flux density. The magnetic flux density of the grain oriented electrical steel sheet when a predetermined magnetizing force is applied tends to increase as the degree to which the magnetization easy axes of the grains are aligned in the rolling direction of the steel sheet, that is, the orientation of the grains is higher. A magnetic flux density B8 is generally used as an index representing the magnetic flux density. The magnetic flux density B8 is a value of the magnetic flux density of the grain oriented electrical steel sheet excited at a magnetizing force of 800 A/m in the rolling direction. That is, the grain oriented electrical steel sheet having a larger value of the magnetic flux density B8 is more easily magnetized with a certain magnetizing force, the magnetic flux density becomes high, and thus it is suitable for a small-sized and highly efficient transformer. In the past, it has been proposed to control the grain growth in secondary recrystallization in order to obtain the steel sheet showing high magnetic flux density, as a method and the like. For instance, the patent documents 1 and 2 disclose a method in which the secondary recrystallization is proceeded while a thermal gradient is given to the steel sheet in a tip area of secondary recrystallized grain which is encroaching primary recrystallized grains in final annealing process. When the secondary recrystallized grain is grown while the thermal gradient is given, the secondary recrystallized grain having the orientation close to the ideal Goss orientation is nucleated from the region where the secondary recrystallization is likely to start antecedently in the steel sheet, and the secondary recrystallized grain grows preferentially due to the thermal gradient. As a result, alignment degree to the Goss orientation increases and the magnetic flux density B8 is improved. However, when the secondary recrystallized grain is grown while the thermal gradient is given, the grain having the orientation close to the ideal Goss orientation may grow preferentially, but the secondary recrystallized grain may be excessively large. When the secondary recrystallized grain grows excessively, a deviation from the ideal Goss orientation increases in a tip area of growth of the secondary recrystallized grain, and the effect of improving the magnetic flux density may be restricted. For instance, the secondary recrystallization in the steel sheet proceeds in a state of being coiled. In other words, the secondary recrystallized grain grows in a state where the steel sheet is under the condition with curvature. However, the secondary recrystallized grain while maintaining the linearity of the crystal orientation. When the secondary recrystallized grain grows larger, the deviation from the ideal Goss orientation increases in the tip area of growth of the secondary recrystallized grain due to the curvature of coil. It is possible to represent the deviation between the actual crystal orientation and the ideal Goss orientation by a deviation angle α, a deviation angle β, and a deviation angle γ. The deviation angle α is an angle formed by the <001> direction of crystal projected on the rolled surface and the rolling direction L when viewing from the normal direction Z. The deviation angle β is an angle formed by the <001> direction of crystal projected on L cross section (cross section whose normal direction is the transverse direction) and the rolling direction L when viewing from the transverse direction C (width direction of sheet). The deviation angle γ is an angle formed by the <110> direction of crystal projected on C cross section (cross section whose normal direction is the rolling direction) and the normal direction Z when viewing from the rolling direction L. It is known that, among these deviation angles α, β and γ, the deviation angles α and β affect the magnetic flux density. When the values of the deviation angles α and β are small, the magnetic flux density B8 is improved. In addition, it is known that, among the deviation angles α, β and γ, the deviation angle β affects magnetostriction. When the value of the deviation angle β is small, the magnetostricti