HIGH YIELD RATIO TYPE HIGH STRENGTH STEEL SHEET, HIGH YIELD RATIO TYPE HIGH STRENGTH COLD ROLLED STEEL SHEET, HIGH YIELD RATIO TYPE HIGH STRENGTH GALVANIZED STEEL SHEET, HIGH YIELD RATIO TYPE HIGH STRENGTH HOT DIP GALVANIZED STEEL SHEET, HIGH YIELD RATIO TYPE HIGH STRENGTH HOT DIP GALVANNEALED STEEL SHEET, METHOD FOR PRODUCING HIGH YIELD RATIO TYPE HIGH STRENGTH COLD ROLLED STEEL SHEET, METHOD FOR PRODUCING HIGH YIELD RATIO TYPE HIGH STRENGTH HOT DIP GALVANIZED STEEL SHEET AND METHOD FOR PRODUCING HIGH YIELD RATIO TYPE HIGH STRENGTH HOT DIP GALVANNEALED STEEL SHEET

摘要

FIELD: metallurgy.;SUBSTANCE: invention relates to metallurgy, namely to high-strength steel sheet with the proof/ultimate factor 0.6 and more. The sheet is made from steel of the following composition, wt %: C - 0.03-0.20, Si - 1.0 or less, Mn - 1.5-3.0, P - 0.10 or less, S - 0.05 or less, Al - 0.10 or less, N - 0.010 or less, one or several elements from Ti, Nb and V, the total content of which amounts 0.010-1.000%, 0.001-0.01 Ta, the rest is Fe and background impurities. The sheet composition includes ferrite and secondary phase including martensite. The share of the ferrite area amounts 50% or more, and average size of the crystalline grain amounts 18 microns or less. The fraction of the martensite area in the secondary phase amounts 1-7%.;EFFECT: required strength and mouldability with decrease of sheet weight are provided.;20 cl, 6 tbl, 1 ex