| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a high-strength steel sheet which is superior in workability and has a tensile strength (TS) of 980 MPa or more. <P>SOLUTION: This steel sheet has a composition comprising, by mass%, 0.17% to 0.73% C, 3.0% or less Si, 0.5% to 3.0% Mn, 0.1% or less P, 0.07% or less S, 3.0% or less Al, 0.010% or less N and the balance Fe with unavoidable impurities, while Si+Al is controlled to satisfy 0.7% or more; and has a metallurgical structure in which lower bainite and a total martensite are controlled to occupy 10% to 90% by an area rate in total with respect to the whole metallurgical structure, retained austenite is controlled to occupy 5% to 50% by an amount and bainitic ferrite in upper bainite is controlled to occupy 5% or more by an area rate with respect to the whole metallurgical structure, and in which an amount of martensite in as-quenched state out of the total amount of the lower bainite and the total martensite is controlled to satisfy 75% or less, the area rate of polygonal ferrite with respect to the whole metallurgical structure is controlled to satisfy 10% or less (including 0%) and an average C content in the retained austenite is controlled to 0.70% or more. <P>COPYRIGHT: (C)2010,JPO&INPIT</p> |
