| 摘要 |
<p>Disclosed is a high-strength steel plate having superior ductility and stretch flangeability and a tensile strength (TS) of 980 MPa or higher, and having 0.17-0.73% C, 3.0% or less Si, 0.5-3.0 or less Mn, 0.1% or less P, 0.07% S, 3.0% or less Al, 0.010% or less N, and 0.7% or more Si + Al, an area ratio of martensite of 10-90% with respect to the entire steel plate composition, a residual austenite amount of 5-50%, and an area ratio of bainitic ferrite in the upper bainite of 5% or less with respect to the entire steel plate composition. Twenty-five percent or more of the aforementioned martensite is tempered martensite, and the total of the area ratio of the aforementioned martensite with respect to the entire steel plate composition, the aforementioned residual austenite amount and the area ratio of the aforementioned 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 composition is 10% or less (including 0%), and the average amount of C in the aforementioned residual austenite is 0.70% or more.</p> |
