440MPA CLASS HOT ROLLED STEEL PLATE EXCELLENT IN COLLISION SAFETY, AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To provide a 440MPa class hot rolled steel plate capable of attaining automobile weight reduction and stability improvement and excellent in collision safety, and its production. ;SOLUTION: This steel plate has a composition consisting of, by weight, 0.005-0.015% C, ≤1.5% Si, ≤2.0% Mn, ≤0.05% P, ≤0.01% S, 0.01-0.1% Al, and the balance Fe with inevitable impurities. In this case, the ratio between the maximum strength δS(MPa) when deformation is performed at 10^-3(s^-1) strain rate and the maximum strength δD(MPa) when deformation is performed at 10³(s^-1) strain rate after E(%) restrain is applied and treatment is carried out at T(°C) for (t)(min), δD/δS, satisfies δD/δS≥460/δS+0.35+571E(t^1/2) exp[-5000/(T+273)].A steel having the above composition is hot-rolled at ≥(Ar₃-50°C) hot rolling finishing temp. and then coiled at ≥600°C or ≤300°C.;COPYRIGHT: (C)1998,JPO