| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet whose stretch-flanging properties are remarkably increased in a high strength-ultrahigh strength region of an about 500 to 1,400 MPa class. SOLUTION: In the high strength steel sheet, the contents of C, Si+Al, Mn, P, S, Ca and rare earth metals are prescribed, the selective incorporation of one or more kinds of metals selected from Mo, Ni, Cu and Cr and one or more kinds of metals selected from Ti, Nb and V are allowed, also the space factor of tempered martensite or tempered bainite or ferrite in a base phase structure to the whole structure is prescribed, and the space factor of retained austenite in a second phase structure to the whole structure, the C concentration (C<SB>γR</SB>) in the retained austenite and the ratio of lath-shaped retained austenite occupied in the whole of the retained austenite are prescribed. The high strength steel sheet can further comprise bainite/martensite. COPYRIGHT: (C)2004,JPO
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