Cold-rolled high-tension steel sheet having superior deep drawability

Abstract

A high-tension steel sheet suitable for deep drawing and having superior surface treatment characteristics is made of a steel consisting essentially of, by weight: 0.001 to 0.05% of C; not more than 1.0% of Si; not more than 2.5% of Mn; 0.05 to 1.0% of Mo; one or both of 0.001 to 0.2% of Nb and not more than 0.3% of Ti, wherein Ti*%+(48/93)Nb%.gtoreq.(48/12)C% in which Ti*%=Ti%-(48/32) S%-(48/14)N%, wherein, when Ti*%<0, Ti*% is regarded as being 0; 0.0005 to 0.01% of B; 0.01 to 0.10% of Al; not more than 0.15% of P; not more than 0.010% of S; not more than 0.006% of N; Si, Mn and P meeting the condition of 0.2<(Si%+10P%)/Mn%<3.3; and the balance substantially Fe and incidental impurities. This steel sheet is produced by a process which includes: hot-rolling the steel slab to obtain a hot rolled steel strip at a final hot-rolling temperature not lower than the Ar.sub.3 transformation temperature; coiling the steel strip at a temperature not lower than 300.degree. C. but not higher than 615.degree. C. when Nb is not contained and not lower than 500.degree. C. but not higher than 700.degree. C. when Nb is contained; cold-rolling the steel strip to obtain a cold rolled steel strip at a rolling reduction not smaller than 65%; and recrystallization-annealing the cold rolled strip at a temperature not lower than the recrystallization temperature but below the Ac.sub.3 transformation temperature.