LOW-ALLOYED PRACTICALLY BORON-FREE STEEL Russian patent published in 2003 - IPC

FIELD: metallurgy. SUBSTANCE: invention relates to the search of super- -strength weldable thick-plate steel that is used for making pipelines. Invention proposes low-alloyed, practically boron-free steel with tensile-strength at least 900 MPa, impact viscosity measured of samples with V-incisions by Charpy method at 40 C, at least 120 J and microstructure containing mainly small-grained bainite, small-grained martensite or their mixture formed from practically non-recrystallized grains of austenite. Steel comprises components taken in the following ratio, wt.-%: carbon, 0.03-0.10; manganese, 1.6- 2,1; niobium, 0.01-0.10; vanadium, 0.01-0.1; molybdenum, 0.3-0.6; titanium, 0.005-0.003; iron, the balance being carbon equivalent C_e-steel is in the range 0,5≤C_e≤0,7 and index of weldability P_cm≤ 0.35. Invention provides the enhancement of steel strength without tempering carrying out to provide the secondary strengthening. The ratio of limit of fluidity to tensile strength is 0.93, not above. EFFECT: enhanced and valuable properties of steel. 14 cl, 10 deg, 2 tbl