Method of making cold rolled dual-phase structure steel sheet having an excellent deep drawability

Abstract

Abstract A cold rolled dual-phase structure steel sheet having an excellent deep drawability is disclosed, which consists of ferrite phase and low temperature transformation product phase and comprises 0.001-0.008 wt % of C, not more than 1.0 wt % of Si, 0.05-1.8 wt % of Mn, not more than 0.15 wt % of P, 0.01-0.10 wt % of Al, 0.002-0.050 wt % of Nb and 0.0005-0.0050 wt % of B provided that the value of Nb(%)+10B(%) is in a range of 0.010-0.080%, and, if necessary, 0.05-1.00 wt % of Cr and the balance being substantially Fe with inevitable impurities. This steel sheet is manufactured by hot and cold rolling a steel slab with the above chemical composition and continuously annealing the resulting steel sheet in such a manner than the steel sheet is heated and soaked at a temperature from α→γ transformation point to 1,000° C. and then cooled at an average cooling rate of not less than 0.5° C./sec but less than 20° C./sec in a temperature range of from the soaking temperature to 750° C., and subsequently at an average cooling rate of not less than 20° C./sec in a temperature range of from 750° C. to not more than 300° C.

Inventors

• 👤 Susumu Satoh
• 👤 Hideo Suzuki
• 👤 Takashi Obara
• 👤 Minoru Nishida
• 👤 Osamu Hashimoto

Bibliographic Details