Deep drawability and stretch flange formability in excellent complex tissue-type high-strength cold-rolled steel sheet and method of manufacturing the same

摘要

PROBLEM TO BE SOLVED: To provide a dual-phase high-tensile cold rolled steel sheet excellent in deep drawability and stretch-flangeability and its production method. ;SOLUTION: The dual-phase high-tensile cold rolled steel sheet comprises 0.01-0.05 mass% C, 0.1-1.5 mass% Si, 1.0-3.0 mass% Mn, 0.10 mass% or less P, 0.02 mass% or less S, 0.005-0.1 mass% Al, 0.02 mass% or lower N, 0.01-0.2 mass% V, 0.005-0.2 mass% Nb, and the balance substantially being Fe and unavoidable impurities provided that the contents of V, Nb, and C satisfy the relation represented by 0.5×C/12≤(V/51+Nb/93)≤2×C/12). The steel sheet has such a steel structure that the main phase is a ferrite phase comprising a polygonal ferrite phase and a bainitic ferrite phase and the second phase contains a martensite phase in an areal ratio of 1% or higher.;COPYRIGHT: (C)2004,JPO