Patent Number: 7,101,445

Title: Cold rolled steel sheet and galvanized steel sheet having strain age hardenability and method of producing the same

Abstract: An object of the present invention is to provide a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet in which tensile strength is effectively increased by press forming and heat treatment while maintaining excellent deep drawability in press forming. Specifically, a steel composition contains less than 0.01% of C, 0.005 to 1.0% of Si, 0.01 to 1.0% of Mn, 0.005 to 0.050% of Nb, 0.005 to 0.030% of Al, 0.005 to 0.040% of N, 0.0005 to 0.0015% of B, 0.05% or less of P, and 0.01% or less of S, the balance substantially composed of Fe, in which the following equations (1) and (2) are satisfied: N %.gtoreq.0.0015+14/93Nb %+14/27Al %+14/11B % (1) C %.ltoreq.(12/93)Nb %. (2)

Inventors: Kami; Chikara (Chiba, JP), Tosaka; Akio (Chiba, JP), Yamazaki; Takuya (Chiba, JP)

Assignee: JFE Steel Corporation

International Classification: C22C 38/06 (20060101); C22C 38/02 (20060101); C22C 38/04 (20060101)

Expiration Date: 9/05/02018