Method of producing high-strength cold-rolled steel sheet suitable for

Abstract

A method of producing a high-strength cold-rolled steel sheet suitable for working uses which utilizes a steel material having the following composition: not more than 0.006 wt % of C, not more than 0.5 wt % of Si, not more than 2.0 wt % of Mn, and not less than 0.01 wt % but not more than 0.10 wt % of Ti, the Ti, C and N contents being determined to meet the condition of Ti>(48/12) C wt %+(48/14) N wt %, the steel also consisting essentially of not less than 0.0010 wt % but not more than 0.0100 wt % of Nb, not less than 0.0002 wt % but not more than 0.0020 wt % of B, not less than 0.03 wt % but not more than 0.20 wt % of P, not more than 0.03 wt % of S, not less than 0.010 wt % but not more than 0.100 wt % of Al, not more than 0.008 wt % of N, not more than 0.0045 wt % of O, and the balance substantially Fe and incidental inclusions. The steel material is cast and hot-rolled and then subjected to a cold rolling conducted at a sheet temperature not higher than 300.degree. C. under such a condition that the sum of the rolling reductions of passes which meet the following condition between said sheet temperature (T .degree.C.) and the strain rate .epsilon. (S-1) is 50% or greater: