| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high strength cold rolled steel sheet satisfying a tensile strength of ≥440 MPa, and having excellent deep drawability and shape fixability. <P>SOLUTION: The high strength cold rolled steel sheet has a composition comprising, by mass, 0.015 to 0.050% C, ≤1.0% Si, 1.0 to 3.0% Mn, 0.005 to 0.1% P, ≤0.01% S, 0.005 to 0.5% Al, ≤0.01% N and 0.01 to 0.3% Nb, and the balance Fe with inevitable impurities, and in which the Nb content and the C content satisfy inequality (1), and has a structure comprising a ferritic phase of ≥50%, by area, and a martensitic phase of 1 to 15%, and in which δdefined by formulae (2) and (3) is ≤0.3: [C]-(12×[Nb]/93)≥0.01 (1), δ=(σc/ρ)/TS (2), and σc=äE/(1-ν<SP>2</SP>)}×t×(1/D<SB>0</SB>-1/D<SB>1</SB>) (3); wherein [M] denotes the content of the element M; E denotes a Young's modulus (MPa); ν denotes a Poisson's ratio; t denotes a sheet thickness (mm); D<SB>0</SB>denotes a cup outer diameter (mm) after cup forming at a drawing ratio ρ; and D<SB>1</SB>is a ring outer diameter (mm) in a direction orthogonal to the rolling direction when a ring sample is cut out from the cut side face, and a cut is made in the rolling direction, so as to open the sample. <P>COPYRIGHT: (C)2007,JPO&INPIT |
