METHOD OF PRODUCTION OF SUPERSTRENGTH WELDABLE STEELS Russian patent published in 2003 - IPC

FIELD: production of superstrength weldable steels for manufacture of pipe lines. SUBSTANCE: steel contains iron, carbon, silicon, manganese, copper, nickel, niobium, vanadium molybdenum, chromium, titanium, aluminum, calcium, rare-earth metals and magnesium. Steel slab is heated temperature sufficient for dissolving of all carbides and carbo-nitrides of vanadium and niobium. Then slab is swaged for forming steel sheet per pass or several passes of hot rolling within temperature range when recrystallization of austenite takes place. Steel sheet is additionally swaged per pass or several passes of hot rolling within range of temperatures below first range and above temperature at which austenite is transformed into ferrite during cooling, after which hardening of steel sheet is performed . Then, sheet is cooled in air to ambient temperature. Fine-grained lower bainite, fine-grained martensite or their mixtures prevail in microstructure of steel. Tensile strength of steel is no less than 900 Mpa and ductility is sufficient for operation of pipe lines at low temperatures. EFFECT: enhanced strength. 20 cl, 10 dwg, 2 tbl