METHOD FOR PRODUCING A ULTRA HIGH STRENGTH COATED OR NOT COATED STEEL SHEET AND OBTAINED SHEET Russian patent published in 2019 - IPC C21D8/02 C21D9/46 C21D1/18 C22C38/02 C22C38/04 C22C38/06 C22C38/22 C22C38/26 

FIELD: chemistry.

SUBSTANCE: invention relates to a steel sheet with a coating made from steel, having a chemical composition, containing, in % by weight: 0.34 % ≤ C ≤ 0.40 %, 1.50 % ≤ Mn ≤ 2.30 %, 1.50 ≤ Si ≤ 2.40 %, 0.35 % ≤ Cr ≤ 0.45 %, 0.07 % ≤ Mo ≤ 0.20 %, 0.01 % ≤ Al ≤ 0.08 % and 0 % ≤ Nb ≤ 0.05 %, the balance of Fe and unavoidable impurities, wherein the coated steel sheet has a structure which includes at least 60 % martensite and 12–15 % residual austenite, wherein the coated steel sheet is zinc-plated, as well as the coated steel sheet has a tensile strength of at least 1470 MPa and a total elongation of at least 16 %. Also disclosed is a method of making a coated steel sheet having a tensile strength TS of at least 1470 MPa and a total TE elongation of at least 16 %, at that, the method includes the following successive stages: heating to temperature AT of cold-rolled steel sheet made from steel of the above composition, wherein temperature of AT is higher than that of steel Ac3, cooling of heated steel sheet to temperature QT lower than temperature of conversion of steel Ms, and is in range from 200 to 230 °C, and redistribution of treatment by reheating of steel sheet to temperature of redistribution PT 350–450 °C with holding of steel sheet at this temperature during time of redistribution Pt 25–55 s, wherein after redistribution, steel plate is galvanized and cooled down to room temperature to produce coated steel sheet. Also disclosed is a variant of the above steel sheet and a variant of its production.

EFFECT: technical result is production of heavy-duty steel sheet with improved tensile strength and improved overall elongation.

19 cl, 6 tbl, 44 ex