METHOD FOR PRODUCING HIGH-STRENGTH STEEL SHEET Russian patent published in 2024 - IPC C21D8/02 C21D9/46 C22C38/22 C22C38/24 C22C38/26 C22C38/28 C22C38/32 

FIELD: metallurgy.

SUBSTANCE: invention relates namely to the production of high-strength steel sheets, and can be used for the manufacture of cutting tools and critical elements of agricultural earth-moving equipment. A method for producing a high-strength steel sheet with a tensile yield strength of at least 1350 MPa, a tensile strength of at least 1700 MPa and an elongation of at least 18% from steel containing, wt.%: carbon 0.30-0.46, silicon 1.50-2.0, manganese 1.00-1.40, chromium 0.80-1.20, molybdenum 0.20-0.50, if necessary at least one component: niobium up to 0.10, vanadium up to 0.20, titanium up to 0.04 and boron up to 0.005, iron and inevitable impurities. The rest is characterized by the fact that the steel billet is heated to a temperature of 1100-1080°C and kept at this temperature for at least 1 hour for homogenization. Rolling is carried out from a temperature of 1100-1080°C to a temperature of at least 900°C with a degree of compression of at least 60% and subsequent cooling in air. Then reheated to temperature A_C3+(30-50)°C, but not lower than 900°C, until complete austenitization. Cooling to the temperature of quenching is carried out into molten salt, preheated to a temperature of 70-130°C below the temperature of the onset of martensitic transformation Ms, with a cooling rate of 210-250°C per second in the range 900-300°C for 30-180 seconds, ensuring that no more than 40% retained austenite is obtained in the structure. Then the sheet is heated in molten salt to a temperature that is higher than the temperature of the onset of martensitic transformation M_S and is 350-410°C, carbon is distributed between martensite and retained austenite for 60-300 seconds to prevent the formation of bainite in an amount of more than 15%, and the sheet is cooled in water.

EFFECT: obtaining steel sheet with high strength and ductility.

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