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 a method for producing high-strength steel sheets, and is aimed at manufacturing from it particularly important elements of agricultural earth-moving equipment subject to combined loads. A method for producing high-strength steel sheets with a tensile yield strength of at least 1300 MPa, a tensile strength of at least 1700 MPa and an elongation of at least 21% 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, niobium up to 0.1, aluminium up to 0.02, if necessary, at least one component: titanium up to 0.04, vanadium up to 0.20 and boron up to 0.005, iron and inevitable impurities the rest, 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 at a temperature of 1100-1050°C with a reduction degree of at least 80% to the end of rolling temperature, defined as A_C3+10°C, but not lower than 870°C. The hot-rolled sheet is cooled into molten salt, heated to a temperature of 30-50°C below the temperature of the onset of martensitic transformation Ms, with a cooling rate of at least 210-250°C per second in the temperature range of 900-300°C for 30 to 180 seconds, ensuring that at least 60% of 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 Ms 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 then the sheet is cooled in the air to a temperature of 200°C at a speed of no more than 10°C per second for self-tempering of secondary martensite.

EFFECT: obtaining steel sheet with high strength and ductility.

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