METHOD OF PRODUCTION OF SEAMLESS TUBES FROM CARBON STEEL OR LOW-ALLOY STEEL OF HIGH CORROSION RESISTANCE Russian patent published in 2004 - IPC

FIELD: metallurgy; methods of production of seamless tubes for lines working under pressure and in contact with aggressive media. SUBSTANCE: proposed method includes melting steel in electric furnace, tapping molten steel into ladle, refining in the course of tapping and treatment outside furnace at introduction of ferroalloys and blowing with argon, tapping for tubular blank, rolling tubes and heat treatment of these tubes; steel contains the following components, mass- %: carbon, 0.05-0.30; manganese, 0.35-1.50; silicon, 0.15-1.0; chromium, 0.005-0.50; nickel, 0.005-0.50; copper, 0.005-0.50; sulfur, no more than 0.010; phosphorus, no more than 0.020; aluminum, 0.01-0.05; the remainder being iron and unavoidable admixtures. Content of carbon and manganese satisfies the following condition: [C] = (0,29-0,15[Mn])±0,05, where [C] and [Mn] are contents of carbon and manganese in mass-%; in the course of treatment outside the furnace at content of aluminum no less than 0.015%, ferroalloys are introduced after which desulfurization is performed till required content of sulfur has been obtained and then teeming of steel is started. Niobium may be additionally introduced into steel at content not exceeding 0.01-0.06 mass-%. In the course of treatment outside the furnace, steel is modified with calcium at temperature not below 1600 C; content of calcium in steel ranges from 0.0008 to 0.0020 mass-%. Heat treatment of tubes is just hardening and tempering and normalizing. EFFECT: enhanced corrosion resistance at retained strength, toughness and cold resistance; low cost of process. 5 cl, 1 tbl, 6 ex