EP-4737608-A1 - GRAIN-ORIENTED ELECTRICAL STEEL SHEET

Abstract

In a grain oriented electrical steel sheet, a magnetic flux density B 8 in a rolling direction is 1.940T or more, an iron loss W 17/50 is 0.670 W/kg or less, and a magnetostriction velocity level Lva200@1.7T is 46.0 dB or less.

Inventors

• NAKAMURA, SHUICHI
• KAWAMURA, YUSUKE

Assignees

• Nippon Steel Corporation

Dates

Publication Date

20260506

Application Date

20240627

Claims (1)

1. A grain oriented electrical steel sheet whose magnetic domain is refined comprising a base steel sheet and an insulation coating, wherein when a magnetic flux density in a rolling direction under a condition of being excited at 800 A/m is defined as B 8 in units of T, when an iron loss under a condition of 50 Hz of frequency and 1.7 T of excited magnetic flux density is defined as W 17/50 in units of W/kg, and when a magnetostriction velocity level obtained from a magnetostriction composed of 200Hz in a magnetostrictive waveform under a condition of 50 Hz of frequency and 1.7 T of excited magnetic flux density is defined as Lva200@1.7T in units of dB, the B 8 satisfies B 8 ≥ 1.940, the W 17/50 satisfies W 17/50 ≤ 0.670, and the Lva200@1.7T satisfies Lva200@1.7T ≤ 46.0.

Description

TECHNICAL FIELD The present invention relates to a grain oriented electrical steel sheet. Priority is claimed on Japanese Patent Application No. 2023-106861, 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. Important magnetic characteristics of the grain oriented electrical steel sheet are, for instance, magnetic flux density, iron loss, and noise characteristics. 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 addition, an iron loss W17/50 is generally used as an index representing the iron loss. The iron loss W17/50 is an iron loss when the grain oriented electrical steel sheet is excited by alternating current so as to be a maximum magnetic flux density of 1.7 T under the condition of a frequency of 50 Hz. The grain oriented electrical steel sheet having a smaller value of the iron loss W17/50 has a lower energy loss and is suitable for a transformer. In addition, a magnetostriction velocity level (Lva) is used as an index representing the noise characteristics. The magnetostriction velocity level (Lva) is the value applied A-weighting with respect to frequency characteristics of human hearing in which the magnetostrictive waveform excited by alternating current is time-differentiated and converted into velocity. The sound characteristics which humans can perceive are not always constant at all frequencies, and can be expressed by the aural characteristics called A-weighting. The actual magnetostrictive waveform is not a sine wave, but a waveform in which various frequencies are overlapped. Thus, the magnetostrictive waveform is fourier-transformed, the amplitude at each frequency is obtained and multiplied by the A-weighting, and thereby, it is possible to obtain the magnetostriction velocity level (Lva) which is an index close to the aural characteristics of the actual human. When the above magnetostriction velocity level (Lva) is decreased, it is possible to suppress the iron core vibration caused by the frequency which humans perceive among the transformer noise. Thus, the transformer noise can be effectively reduced. With respect to the magnetic characteristics, for instance, the patent documents 1 and 2 disclose a method in which the secondary recrystallization is proceeded while giving a thermal gradient to the steel sheet in order to improve the magnetic flux density. The patent document 3 discloses a method in which strain is introduced into the steel sheet by scanning and irradiating extremely finely focused laser beam in order to reduce the iron loss. The patent document 4 discloses a method in which plural grooves are formed on a surface of the steel sheet in order to reduce the iron loss. Citation List Patent Document Patent Document 1: Japanese Unexamined Patent Application, First Publication No. S57-002839Patent Document 2: Japanese Unexamined Patent Application, First Publication No. S61-190017Patent Document 3: PCT International Publication No. WO 2004/083465Patent Document 4: PCT International Publication No. WO 2016/171129 SUMMARY OF INVENTION Technical Problem As described above, the magnetic characteristics of the grain oriented electrical steel sheet have been tried to be improved until today. However, it is difficult to simultaneously improve all of the magnetic flux density, the iron loss, and the noise characteristics by the conventional techniques. For instance, in the techniques of the patent documents 1 and 2, although the magnetic flux density increases, the secondary recrystallized grain grows coarsely in a case where a magnetic domain control technique is not applied, and thus, the iron loss is not excellent. Moreover, in the technique of the patent document 3, although the iron lo