METHOD FOR PRODUCING STRIP ROLLED PRODUCTS WITH A THICKNESS OF 10 TO 40 mm FOR MANUFACTURING LARGE-DIAMETER LONGITUDINALLY WELDED PIPES OPERATED UNDER EXTREMELY LOW TEMPERATURES Russian patent published in 2021 - IPC C21D8/02 C22C38/14 B21B1/26 

FIELD: metallurgy.

SUBSTANCE: invention relates to production of strip rolled products with a thickness of 10 to 40 mm from low-alloy steel for manufacturing large-diameter longitudinally welded pipes. The method includes austenisation of continuously cast workpieces, rough rolling with regulated reduction per pass, cooling-down of the rolls, finishing rolling, still-air cooling followed by accelerated cooling in a controlled cooling unit. The continuously cast workpieces are produced from steel with the following ratio of components, wt.%: carbon 0.04 to 0.07, silicon 0.10 to 0.30, manganese 1.40 to 1.80, aluminium 0.020 to 0.050, chromium no more than 0.10, nickel 0.10 to 0.50, copper no more than 0.15, titanium 0.010 to 0.030, vanadium no more than 0.01, niobium 0.02 to 0.06, molybdenum 0.01 to 0.35, nitrogen no more than 0.008, sulphur 0.005, phosphorus less than 0.015, iron and impurities the rest, wherein the carbon equivalent C_eq does not exceed 0.43%. Austenisation of the continuously cast workpieces is performed to a temperature of 1,180 to 1,210°C. Rough rolling begins at a temperature of no less than 950°C when performing austenisation in chamber-type heating furnaces and no less than 960°C when performing austenisation in continuous-type heating furnaces. Finishing rolling for strip rolled products with a final thickness of up to and including 20 mm begins at a temperature of 810 to 880°C and is completed at a temperature of 760 to 830°C, and for strip rolled products with a final thickness greater than 20 mm, begins at a temperature of 740 to 810°C and is completed at a temperature of 740 to 820°C. The strip rolled products are still-air cooled to the temperature of the beginning of accelerated cooling of 670 to 750°, and then subjected to accelerated cooling in a controlled cooling unit to a temperature of 20 to 250°C.

EFFECT: production of strip rolled products with the strength class K60 with a guarantee of impact strength on samples with a sharp notch and a falling load test at a temperature of up to and including minus 62°C, crack resistance CTOD of up to minus 20°C.

3 cl, 3 tbl