PRODUCTION OF HIGH WORKABILITY COLD ROLLED STEEL SHEET EXCELLENT IN PRESS FORMABILITY AND ALSO SMALL IN FLUCTUATION OF PRESS FORMABILITY

摘要

PROBLEM TO BE SOLVED: To provide a method for producing a high workability cold rolled steel sheet excellent in press formability, also small in the fluctuation of the press formability in a coil and suitable for use to an automotive outside sheet or the like. SOLUTION: A steel slab contg., by weight, <=0.02% C, <=0.6% Si, <=2.5% Mn, <=0.10% P, <=0.05% S, <=0.01 O and 0.01 to 0.10% sol. Al and moreover contg. one or more kinds among Ti, Nb, V and Zr by 0.01 to 0.20% is subjected to rough rolling to 25 to 85 mm and is subjected to rolling in such a manner that the draft of the rough bar is controlled to >=85%, and the finishing temp. is controlled to the range of the Ar3 to the Ar3+50 deg.C from the tip end part to the tail end part. The schedule of rolling reduction is set in such a manner that, in the case the draft in a finish rolling final stand is >=10%, the effective draft is controlled to >=30%, and in the case of <10%, it is controlled to >=35%, cooling in a runout is started within 1.5 sec after the completion of the finish rolling, the average cooling rate at the finishing temp. to 750 deg.C is controlled to >=20%/sec, and, after that, at <=720 deg.C, cooling, pickling, cold rolling, final annealing and skinpass rolling are executed.