SUPER-HIGH-STRENGTH AUSTENITIC AGEING STEEL OF HIGH TOUGHNESS AT CRYOGENIC TEMPERATURE Russian patent published in 2003 - IPC

FIELD: production of steel super-high-strength low-alloy steel sheets. SUBSTANCE: super-high-strength weldable low-alloy steel possesses high toughness at cryogenic temperatures both in main sheet and in heat- affected area during welding; tensile strength is higher than 830 MPa 9120 kfeet/sq. inch); steel has laminar microstructure containing fine layers of austenite and plates of finely-dispersed martensite/lower bainite; it is made by heating the steel slab containing iron and some or all additives: carbon, manganese, nickel, nitrogen, copper, chromium, molybdenum, silicon, niobium, vanadium, titanium, aluminum and boron at preset mass content: cogging of slab for obtaining sheet per pass or several passes at interval of temperatures where recrystallization of austenite takes place, final cogging of sheet per pass or several passes at interval of temperatures below austenite recrystallization temperature and above Ar₃; phase transformation temperature, hardening finished rolled sheet to adequate hardening transformation temperature or practically isothermal time lag or slow cooling of sheet before cooling in air or cooling in air to room temperature. EFFECT: enhanced tensile strength; high weldability; homogeneous structure; enhanced toughness at cryogenic temperatures. 22 cl, 6 dwg, 1 tbl, 4 ex