| 摘要 |
PROBLEM TO BE SOLVED: To provide an ultrahigh-strength cold-rolled steel sheet which has a tensile strength of 1,760 MPa or higher and is superior in formability for extension flange, and to provide a method for manufacturing the same. SOLUTION: The ultrahigh-strength cold-rolled steel sheet superior in formability for extension flange comprises, by mass%, 0.25-0.4% C, 1.0% or less Si, 1.5-2.5% Mn, 0.02% or less P, 0.003% or less S, 0.01-0.1% Al, 0.005% or less N, 0.0005-0.005% B, further one or two elements selected from 0.005-0.1% Ti and 0.005-0.1% Nb in total of 0.005-0.1%, and the balance Fe with unavoidable impurities; has a metallographic structure formed of a single-phase martensite structure (except a surface layer 20 μm deep from the surface); and further has the tensile strength of 1,760 MPa or higher. COPYRIGHT: (C)2011,JPO&INPIT |
