| 摘要 |
PURPOSE:To produce a cold rolled steel sheet having high strength and excellent in deep drawability. CONSTITUTION:At the time of hot-rolling a steel which has a composition consisting of <=0.005% C, <=1.0% Si, 0.6-2.5% Mn, 0.05-0.15% P, <=0.010% S, 0.005-0.10% Al, (R)0.0035% N, 0.010-0.10% Ti and/or 0.005-0.03% Nb, further 0.0004-0.0020% B, and the balance Fe with inevitable impurities, finish rolling is completed at >=930 deg.C finishing temp. and cooling is done, without delay, while regulating the average cooling rate before coiling to 50-200 deg.C/sec and then coiling is performed at <=600 deg.C, by which a structure consisting of acicular ferrite and/or bainite is obtained. Subsequently, the hot rolled steel plate is pickled, cold-rolled at >=50% draft, and continuously annealed at a temp. between the recrystallization temp. and the Ac3 point, by which the cold rolled steel sheet excellent in deep drawability and having a strength as high as >=40 kgf/mm<2> can be obtained. |
