COLD-ROLLED HIGH-TENSION STEEL SHEET HAVING SUPERIOR DEEP DRAWABILITY

摘要

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 % ? (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 Ar3 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 Ac3 transformation temperature.