Grain-oriented electrical steel sheet and manufacturing method thereof
AssigneeNippon Steel & Sumitomo Metal Corporation
InventorsYoshiaki Natori, Shuichi Yamazaki, Fumiaki Takahashi, Seiki Takebayashi
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Abstract
Nitriding process of a steel strip is performed. Next, annealing is performed to form a forsterite based glass coating film at a surface of the steel strip. Heating is performed up to 1000° C. or more in a mixed gas atmosphere containing H2 gas and N2 gas, and a rate of N2 gas is 20 volume % or more, next, the atmosphere is switched into H2 gas atmosphere at the temperature of 1000° C. or more and 1100° C. or less, when the annealing is performed. An oxygen potential P (H2O)/P (H2) is set to be 0.05 to 0.3 when the temperature is 850° C. or less during the heating in the mixed gas atmosphere.
Claims9
A grain-oriented electrical steel sheet, comprising:
- a steel strip;
- and
- a forsterite based glass coating film formed at a surface of the steel strip,
- wherein when a portion of which thickness is continuously twice or more as thick as average thickness of the glass coating film, and of which size in a direction parallel to the surface of the steel strip is 3 μm or more is defined as an aggregated portion,
- a ratio of a total length of the aggregated portions crossed by a line segment relative to a length of the line segment is set to be 0.15 or less in an arbitrary line segment parallel to the surface of the steel strip.
A manufacturing method of a grain-oriented electrical steel sheet, comprising:
- performing nitriding process of a steel strip;
- and
- next performing annealing to form a forsterite based glass coating film at a surface of the steel strip,
- wherein the performing annealing comprises:
- performing heating up to 1000° C. or more in a mixed gas atmosphere containing H2 gas and N2 gas, and a rate of N2 gas is 20 volume % or more;
- and
- next switching the atmosphere into H2 gas atmosphere at the temperature of 1000° C. or more and 1100° C. or less,
- wherein an oxygen potential P (H2O)/P (H2) is set to be 0.05 to 0.3 when the temperature is 850° C. or less during the heating in a mixed gas atmosphere.
Dependencies are inferred from the claim text.