The high intensity cold rolling steel sheet null mass which is superior in extension and extension flange

摘要

PROBLEM TO BE SOLVED: To provide a high strength cold rolled steel sheet in which a balance of elongation and stretch flange properties is improved, and which has more excellent formability.;SOLUTION: The cold rolled steel sheet has a componential composition comprising, by mass, 0.05 to 0.30% C, ≤3.0% Si, 0.1 to 5.0% Mn, ≤0.1% P, ≤0.010% S, 0.001 to 0.10% Al, 0.10 to 0.50% V, and the balance mainly iron, and has a structure composed of, by area ratio, α: 10 to 80% and retained γ+M:5%, and the balance hard second phase, and in which an α grain size is ≤2 μm, also, the number of θ grains of ≥0.1 μm present in the hard second phase in contact with the α in the boundary is ≤3 pieces/μm², among V-containing precipitates in the α, the ratio of the grains of 8 to 20 nm occupies ≥60% by a number base to the whole number of the V-containing precipitates, and also, among the V-containing precipitates in the α and the hard second phase, the number of the grains of ≥20 nm is ≤3 pieces per μm².;COPYRIGHT: (C)2011,JPO&INPIT