The high intensity steel sheet and its production mannered null mass which are superior in

摘要

PROBLEM TO BE SOLVED: To provide a high-strength steel sheet which satisfies the expressions of 500 MPa≤TS, 1.2≤r value and 1.0≤r₉₀, and to provide a manufacturing method therefor.;SOLUTION: The high-strength steel sheet which has such a superior deep drawability as to satisfy 1.2≤r value and 1.0≤r₉₀ comprises: by mass%, 0.030 to 0.050 C, 1.0 or less Si, 2.0 to 3.0 Mn, 0.005 to 0.1 P, 0.01 or less S, 0.005 to 0.5 Al, 0.01 or less N, 0.010 to 0.30 Nb while satisfying the expression (1): (Nb/93)/(C/12)=0.2 to 0.7 and the balance Fe with unavoidable impurities. The steel sheet has also a structure including, a ferrite phase of 50% or more and a martensite phase of 3% or more, by an area rate; and has such a crystal orientation distribution in a sheet thickness direction as to satisfy the expressions (2) to (5); where (2): f^{sur to 1/4}_{111}≥40% (3): f^{sur to 1/4}_{110}≤5% (4): Δf_{111}≥10% and (5): Δf_{110}≤3%, wherein f^{sur to 1/4}_{111} and f^{sur to 1/4}_{110} represent average area rates of crystal grains of which the {111} and {110} faces are parallel to the surface of the sheet, and which are determined at four positions that are 1/4 deep from the surface layer in the sheet thickness direction; f^1/2_{111} and f^1/2_{110} represent average area rates of crystal grains of which the {111} and {110} faces are parallel to the surface of the sheet, and which are determined at two positions in the vicinity of a 1/2 deep portion from the surface in the sheet thickness direction; and Δf_{111} is equal to f^{sur to 1/4}_{111}-f^1/2_{111}, and Δf_{110} is equal to f^{sur to 1/4}_{110}-f^1/2_{110}.;COPYRIGHT: (C)2009,JPO&INPIT