| 摘要 |
Provided is an ultra-high-strength steel plate having a component composition that comprises specific amounts of each of C, Si, Mn, and Al and a remainder of iron and unavoidable impurities, and in which the amounts of each of P, S, and N among the unavoidable impurities are limited to a specific amount. The ultra-high-strength steel plate comprises 1 area% or more of a region in which martensite constitutes 90 area% or more, residual austentite constitutes 0.5 area% or more, and the local Mn concentration is at least 1.2 times that of the Mn content of the entire steel plate. The ultra-high-strength steel plate has a tensile strength of 1470 MPa or more, a yield ratio of 0.75 or more, and a total elongation of 10% or more. |
