| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength steel sheet which has excellent workability represented by elongation and stretch-flanging properties and is suitable to an automobile member, the steel sheet being a dual-phase steel sheet containing retained austenite high in ductility. SOLUTION: The high tensile strength hot rolled steel sheet comprises, by weight, 0.1 to 0.2% C, 0.5 to 2.0% Si, 0.5 to 1.7% Mn,≤0.06% P,≤0.01% S,≤0.06% Al,≤0.006% N, 0.1 to 0.5% Mo and 0.05 to 0.2% Ti, and the balance substantially Fe. The steel sheet has a composite structure consisting of three phases of ferrite, bainite and retained austenite, or four phases partially containing martensite in addition to these three phases. Carbides containing Ti and Mo in the ranges satisfying, by weight, (Mo/96)/ä(Ti/48)+(Mo/96)}≥0.25 are dispersedly precipitated into the ferrite. COPYRIGHT: (C)2004,JPO
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