TWO-PHASE STEEL AND METHOD FOR MAKING THEREOF Russian patent published in 2000 - IPC

FIELD: steel industry. SUBSTANCE: steel is composed of ferrite and martensite-bainite phases. The former contains reinforcing particles, mainly vanadium and niobium carbides and carbonitrides. Steel is made by one-sheet rolling, the first rolling passage being carried out at temperature superior to austenite recrystallization temperature, the second at temperature below austenite recrystallization temperature, and the third within a temperature range between conversion points Ar3 and Ar1, after which sheet is cooled to temperature approximately below 400 C. Steel can contains following components, wt %: carbon 0.05-0.12, silicon 0.01-0.50, manganese 0.4- 2.0, niobium 0.03-0.12, vanadium 0.05-0.15, molybdenum 0.2-0.8, titanium 0.015-0.03, aluminum 0.01-0.03, iron - the balance. Hardenability parameter of steel is <or = 0.24. If steel contains welding thermal effect zone, its strength in this zone is at least 95% that of the major part of metal. EFFECT: enabled formation of essentially homogeneous microstructure all over the thickness of sheet, which is at least 15 mm. 25 cl, 5 dwg, 5 tbl