METHOD FOR PRODUCING CARBON STEEL OR LOW-ALLOY STEEL FOR ELECTRIC-WELDED PIPES OF INCREASED CORROSION RESISTANCE Russian patent published in 2002 - IPC

FIELD: metallurgy. SUBSTANCE: method involves melting steel and providing processing thereof outside furnace; effecting continuous casting of steel in slabs, hot sheet or strip rolling and cooling. Resultant steel contains, wt. %: carbon, 0.05-0.25; manganese, 0.20-1.70; silicon, 0.20-0.80; chromium, 0.01-1.00; nickel, 0.01-0.60; copper, 0.01-0.50; phosphor, less than 0.035; sulfur, not more 0.025; aluminum, 0.01- 0.06; iron and bound contaminants, the balance. Sulfur and manganese content meets the requirement of (Mn)x(S) <0.015, (1), where (Mn) and (S) is content of manganese and sulfur, respectively, expressed in wt.%. Processing outside furnace is conducted at temperature above 1.580 C. Rolling of slabs into strips or sheets is terminated within temperature range of 800-950 C. During outside furnace steel processing, steel is blown with powder containing calcium, or alternatively wire containing calcium is introduced for providing calcium content in ready rolled product in an amount of 0.0001-0.008%. Also bottom blowing with inert gas is provided for time depending upon amount of calcium introduced into steel in accordance with ratio: T>(18 Ca+7.5) plus and minus 20, (2), where T is blowing time, min; Ca is amount of calcium introduced into steel during outside furnace steel processing, t. Rolled strips are cooled in accelerated mode to temperature below 650 C at cooling rate exceeding 2 C/s, with following winding of strips into rolls. Cooled strips or sheets are subjected to thermal treatment. Method is used for producing steel for constructing pipelines adapted for conveyance of corrosive media, in particular, aqueous media containing chloride ions, hydrogen sulfide, carbon dioxide, mechanical contaminants and other components. EFFECT: increased corrosive resistance of steel and strength, toughness, weldability and reduced production cost. 5 cl, 1 tbl