Kawasaki Steel Corporation

Hidetaka Kawabe

Kei Sakata

Saiji Matsuoka

Toshiyuki Kato

Eiko Yasuhara

In a method of producing a high-strength cold-rolled steel 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.ltoreq.Nb/C.ltoreq.30, 10.ltoreq.Al/N.ltoreq.80, and 16.ltoreq.(3.times.Si/28+200 .times.P/31)/(Mn/55).ltoreq.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 Ar.sub.3 transformation temperature and not lower than 500.degree. 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 .degree. to 950.degree. C.

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Chiba, Japan

Hidetaka Kawabe