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|1. (WO2018043474) HIGH-STRENGTH STEEL PLATE AND PRODUCTION METHOD THEREOF|
|Applicants:||JFE STEEL CORPORATION
|Title:||HIGH-STRENGTH STEEL PLATE AND PRODUCTION METHOD THEREOF|
The component composition of this high-strength steel plate contains, in mass%, C: 0.08-0.35%, Si: 0.50-2.50%, Mn: 1.50-3.00%, P: 0.001-0.100%, S: 0.0001-0.0200%, and N: 0.0005-0.0100%, the remainder being Fe and unavoidable impurities; the steel composition comprises, by area percent, 20-50% ferrite, 5-40% lower bainite, 1-20% martensite and no more than 20% tempered martensite, and, by volume percent, 5% or more retained austenite; the average crystal grain diameter of the retained austenite is less than or equal to 2 μm; and further, the aggregate composition of the steel plate is a microstructure in which the inverse strength ratio of γ-fibers to α-fibers is less than or equal to 3.0. Thereby, a high-strength steel plate is provided which has a 780 MPa or higher TS, excellent stretch flangeability, and also excellent in-plane anisotropy of TS.