High-strength cold-rolled steel sheet excelling in deep drawability and method of producing the same.

摘要

In a method of producing a high-strength cold-rolled steal sheet excelling in deep drawability, a steel material is used which consists of: a basic composition including 0.01% or less of C, 0.1 to 2.0% of Si, 0.5 to 3.0% of Mn, 0.02 to 0.2% of P, 0.05% or less of S, 0.03 to 0.2% of Al, 0.01% or less of N, 0.001 to 0.2% of Nb, and 0.0001 to 0.008% of B in such a way that the respective contents of C, Nb, Al, N, Si, Mn and P satisfy the following formulae: 5 </= Nb/C </= 30, 10 </= Al/N </= 80, and 16 </= (3 x Si/28 + 200 x P/31)/(Mn/55) </= 40; Fe remnant; and inevitable impurities, the method including the steps of: performing rolling on the steel material with a total reduction of 50% or more and 95% or less while effecting lubrication thereon in a temperature range of not higher than the Ar3 transformation temperature and not lower than 500 DEG C; performing a hot-rolled sheet recrystallization treatment on the steel material by a coiling or annealing process; performing cold rolling on the steel material with a reduction of 50 to 95%, and then effecting recrystallization annealing on the steel material in a temperature range of 700 to 950 DEG C. <IMAGE>