HIGH-STRENGTH AND HIGHLY-FORMABLE COLD-ROLLED AND HEAT-TREATED STEEL SHEET AND METHOD OF PRODUCTION THEREOF Russian patent published in 2020 - IPC C22C38/12 C22C38/38 C22C38/06 C22C38/04 C21D8/02 

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to cold-rolled and thermally treated steel sheet used for production of parts of body structure and body panels for mechanical vehicles. Sheet has a composition containing the following, wt. %: 0.10 ≤ C ≤ 0.40; 3.5 ≤ Mn ≤ 8.0; 0.5 ≤ Si ≤ 2.5; 0.003 ≤ Al ≤ 3.0; wherein Si + Al ≥ 0.8; 0.001 ≤ Mo ≤ 0.5; S ≤ 0.010; P ≤ 0.020; N ≤ 0.008; optionally one or more elements of: 0.01 ≤ Cr ≤ 2.0; 0.010 ≤ Ti ≤ 0.080; 0.010 ≤ Nb ≤ 0.080; 0.010 ≤ V ≤ 0.30 and 0.0005 ≤ B ≤ 0.003; balance is iron and unavoidable impurities. Value of carbon equivalent of steel sheet C_eq is not more than 1.3 %. Sheet has a microstructure consisting of surface proportions of 10–50 % residual austenite, tempered martensite and at most 8 % fresh martensite. Said residual austenite contains Mn-enriched austenite characterized by Mn content in excess of 1.3⋅Mn %, and Mn-depleted austenite, characterized by content of Mn ranging from 0.5⋅Mn % to 1.3⋅Mn %, where Mn % is the content of Mn in the steel sheet, wherein the surface fraction of said Mn-rich austenite with respect to the entire microstructure is in range from 2 % to 12 %.

EFFECT: produced sheets have required high level of mechanical properties.

24 cl, 6 tbl