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|1. (WO2018221307) HIGH-STRENGTH STEEL SHEET AND METHOD FOR PRODUCING SAME|
|Applicants:||KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.)
|Title:||HIGH-STRENGTH STEEL SHEET AND METHOD FOR PRODUCING SAME|
This high-strength steel sheet contains 0.15% to 0.35% by mass of C, 0.5% to 3.0% by mass of the total of Si and Al, at least 0.01% by mass of Al, no more than 0.01% by mass of N, 1.0% to 4.0% of Mn, no more than 0.05% by mass of P, and no more than 0.01% by mass of S, with the remainder being made up of Fe and unavoidable impurities. The steel structure is such that the ferrite fraction is no more than 5%, the total fraction of tempered martensite and tempered bainite is at least 60%, the quantity of retained austenite is at least 10%, the average size of MA is does not exceed 1.0 µm, the average size of retained austenite does not exceed 1.0 µm, retained austenite having a size of at least 1.5 µm accounts for at least 2% of total retained austenite content, and the solute nitrogen content of the steel plate does not exceed 0.002% by mass.