| 摘要 |
PROBLEM TO BE SOLVED: To provide a hot-rolled steel sheet superior in characteristics required for press working, specifically, all of shape freezing property, hole expansibility and bending property, although it has a high strength of 980 MPa or higher tensile strength. SOLUTION: In the steel sheet containing C, Si, Mn, Al, Ti, N and S, and balance Fe with inevitable impurities; the contents of the C, Ti, N and S satisfy the following formula (1); the contents of the Si and Mn satisfy the following formula (2); and in the microstructure of the steel sheet, bainitic ferrite is made to occupy 90 area%, martensite is made to occupy 0-5 area%, and bainite is made to occupy 0-5 area%. The formula (1) is represented by [C]-ä[Ti]-(48/14)×[N]-(48/32)×[S]}/4≤0.01 and the formula (2) is represented by 0.20≤([Si]/[Mn])≤0.85, wherein [] shows content (mass%) of each of elements. COPYRIGHT: (C)2009,JPO&INPIT
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