| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high-strength steel plate having superior ductility and stretch flangeability and a tensile strength (TS) of 980 MPa or higher. <P>SOLUTION: The steel plate comprises, by mass, 0.17 to 0.73% C, ≤3.0% Si, 0.5 to 3.0% Mn, ≤0.1% P, ≤0.07% S, ≤3.0% Al and ≤0.010% N, wherein Si+Al: ≥0.7%, an area ratio of martensite of 10 to 90% with respect to the entire steel plate structure, a residual austenite amount of 5 to 50%, and an area ratio of bainitic ferrite in the upper bainite of 5% or more with respect to the entire steel plate structure. The martensite of 25% or more is made to be tempered martensite, and the total of the area ratio of the martensite with respect to the entire steel plate structure, the residual austenite amount and the area ratio of the bainitic ferrite in the upper bainite with respect to the entire steel plate composition is 65% or more. The area ratio of polygonal ferrite with respect to the entire steel plate structure is 10% or less (including 0%). <P>COPYRIGHT: (C)2010,JPO&INPIT |
