| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet having excellent stretch-flange formability, high fatigue properties and a low yield ratio. SOLUTION: Disclosed is a steel sheet having a composition comprising, by mass, >0.03 to 0.20% C, 0.08 to 1.5% Si, 1.0 to 3.0% Mn,≤0.05% P, 0.0005 to 0.02% S, 0.0005 to 0.01% N,≤0.01% acid soluble Al, 0.08 to 0.2% acid soluble Ti, one or two kinds selected from Ce and La by 0.0005 to 0.04% in total, and the balance iron with inevitable impurities, and in which the piece ratio of extended inclusions with a circle equivalent diameter of≥1μm and in which the major axis/minor axis is≥5 is≤20%. COPYRIGHT: (C)2009,JPO&INPIT
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