| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength steel sheet which has both of high strength and superior bend formability and has a tensile strength of 980 MPa or higher. SOLUTION: The steel sheet has a composition comprising, by mass%, 0.12 to 0.5% C, 2.0% or less Si, 1.0 to 5.0% Mn, 0.1% or less P, 0.07% or less S, 1.0% or less Al, 0.008% or less N and the balance Fe with unavoidable impurities; and has a steel structure in which martensite occupies 60% or more, ferrite occupies 40% or less, bainite occupies 10% or less and retained austenite occupies 5% or less each by an area rate. Among blocks of the martensite, blocks in which iron-based carbides with sizes of 5 to 500 nm precipitate at a density of 1×10<SP>4</SP>pieces or more per 1 mm<SP>2</SP>occupy 90% or more by an area rate with respect to the total martensite. COPYRIGHT: (C)2010,JPO&INPIT
|
