FIELD: manufacture of sheets from superstrong weldable low-alloy steels with excellent ductility at cryogenic temperatures.
SUBSTANCE: method involves heating steel slab including iron and specific content of some or all of admixtures of group of admixtures consisting of carbon, nickel, manganese, nitrogen, copper, chromium, molybdenum, silicon, niobium, vanadium, titanium, aluminum and boron; reducing slab for forming of sheet in one or several passes within temperature range providing for recrystallization of austenite; providing finishing rolling of sheet in one or several passes in temperature range below austenite recrystallization temperature and above Ar3 transition temperature; quenching ready rolled steel sheet to specific quenching stopping temperature; terminating quenching process; cooling by holding sheet for predetermined time at quenching stopping temperature, or by slow cooling of sheet before air cooling, or by merely cooling of sheet in air to ambient temperature. Superstrong weldable low-alloy steel has excellent ductility at cryogenic temperatures in basic sheet and in temperature effect zone during welding. Steel of such structure has tensile strength exceeding 830 MPa and microstructure including fine-crystalline lower bainite, fine-crystalline lamellar martensite, fine-grain bainite or mixture thereof, and up to 10% of retained austenite. Method allows ductile-brittle transition temperature of basic steel in transverse direction and in weldable zone under temperature effect to be reduced to value below -620C.
EFFECT: improved quality and improved weldability of sheet steel.
30 cl, 5 dwg, 4 tbl
