HOT ROLLED STEEL SHEET AND ITS PRODUCTION METHOD

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PROBLEM TO BE SOLVED : To provide a hot rolled steel sheet combining high ductility and stretch flange properties, and to provide its production method. SOLUTION : The hot rolled steel sheet has a composition comprising, by mass, 0.02 to 0.25% C, ≤2.0% Si, 0.3 to 2.5% Mn, ≤0.2% P, ≤0.05% S, 0.005 to 0.5% Al and ≤0.01% N, and the balance Fe with impurities and a structure composed of, by volume, a 40 to 95% bainite phase, and a ferrite phase, and in which the average crystal grain size of the ferrite is ≥1.2 to 600°C to ≤640°C is controlled to ≤25 s, and coiling is performed at ≤600°C and ≥350°C. COPYRIGHT : (C)2006, JPO&NCIPI