COLD-ROLLED THICK SHEET STEEL WITH GOOD DEEP DRAWABILITY, AND METHOD FOR PRODUCING IT

摘要

A steel slab having a composition that comprises at most 0.008 % by weight of C, at most 0.5 % by weight of Si, at most 1.0 % by weight of Mn, at most 0.15 % by weight of P, at most 0.02 % by weight of S, from 0.01 to 0.10 % by weight of Al, at most 0.008 % by weight of N, from 0.035 to 0.20 % by weight of Ti, and from 0.001 to 0.015 % by weight of Nb, with a balance of Fe and inevitable impurities, in which those C, S, N, Ti and Nb satisfy the following condition: 1.2(C/12 + N/14 + S/32) < (Ti/48 + Nb/93), is subjected to rough hot-rolling to a reduction ratio of not lower than 85 %, at a temperature falling between the Ar3 transformation point of the steel and 950.degree.C, then to finishing hot-rolling to a reduction ratio of not lower than 65 %, at a temperature falling between 600.degree.C and the Ar3 transformation point of the steel, while being lubricated, to thereby have a mean shear strain of not larger than 0.06, then pickled, pre-annealed at a temperature falling between 700 and 920.degree.C, cold-rolled to a reduction ratio of not lower than 65 %, and thereafter further annealed for recrystallization at a temperature falling between 700 and 920.degree.C. The method of the invention provides thick cold-rolled sheet steel having a thickness of not smaller than 1.2 mm and having an r value of not smaller than 2.9.