COLD-ROLLED MARTENSITIC STEEL AND METHOD FOR PRODUCING MARTENSITIC STEEL Russian patent published in 2022 - IPC C21D1/22 C21D8/02 C22C38/28 C22C38/44 C22C38/50 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely, to cold-rolled steel sheets for use in the automotive industry. Cold rolled martensitic steel sheet contains the following elements, expressed in wt.%: 0.3 ≤ C ≤ 0.4, 0.5 ≤ Mn ≤ 1, 0.2 ≤ Si ≤ 0.6, 0.1 ≤ Cr ≤ 1, 0.01 ≤ Al ≤ 1, 0.01 ≤ Mo ≤ 0.5, 0.001 ≤ Ti ≤ 0.1, 0 ≤ S ≤ 0.09, 0 ≤ P ≤ 0.09, 0 ≤ N ≤ 0.09, and may contain one or several of the following optional elements: 0 ≤ Nb ≤ 0.1, 0 ≤ V ≤ 0.1, 0 ≤ Ni ≤ 1, 0 ≤ Cu ≤ 1, 0 ≤ B ≤ 0.05, 0.001% ≤ Ca ≤ 0.01, 0% ≤ Sn ≤ 0.1, 0 ≤ Pb ≤ 0.1, 0 ≤ Sb ≤ 0.1, the rest being iron and unavoidable impurities. The microstructure of the steel includes, in area percentages, at least 95% martensite, a sum amount of ferrite and bainite between 1 and 5%, and an optional amount of residual austenite between 0 and 2%.

EFFECT: sheet is characterised by high values of strength and hole expansion coefficient, making the sheet suitable for moulding and rolling with good welding and coating capacity.

19 cl, 4 tbl, 6 ex