METHOD OF MANUFACTURING THICK-SHEET ROLLED STOCK FOR MANUFACTURING OF ELECTRICALLY WELDED GAS-AND-OIL PIPES OF LARGE DIAMETER CATEGORY X42-X56, RESISTANT AGAINST HYDROGEN-INDUCED CRACKING IN HS-CONTAINING MEDIA Russian patent published in 2018 - IPC C21D8/02 C22C38/00 

FIELD: metallurgy.

SUBSTANCE: steel is melted containing wt %: C 0.04-0.08, Si 0.10-0.35, Mn 0.8-1.3, Cr 0.015-0.5, Ni 0.01-0.5, Cu 0.1- 0.5, Ca 0.0005-0.005, Al 0.015-0.05, Nb 0.02-0.06, V 0.005-0.05, Mo 0.01-0.02, Ti 0.005-0.025, S≤0.002, P≤0.015, N 0.004-0.012, Fe and unavoidable impurities and H₂ is the rest, with the ratio Ca/S=1.0+2.0, the sum of Nb+Ti is not more than 0.06 wt %; Cr+Ni+Cu not more than 0.6 wt %, carbon equivalent C_eq not more than 0.38, parameter of crack resistance P_cm is not more than 0.21, steel is subjected to out-of-furnace treatment and evacuation with provision of H₂ not more than 2 ppm. Slab is produced and heated to 1150-1250°C and subjected to preliminary deformation at 1000-1150°C with total reduction of 50-70% in 3 stages: with total reduction of 10-25% in longitudinal direction, 20-35% in transverse direction, 40-70% at special reduction of not less than 15% in longitudinal direction. Final deformation is carried out with total reduction of 60-80% in the range from 950°C to A_r3+(30-50)°C, then cooled to 400-550°C at a rate of 15-35°C/s, further, sheets of up to 20 mm thickness are cooled at a rate of 0.05-0.15°C/s and 0.0015-0.0035°C/s in the stack in case the sheets are of greater thickness.

EFFECT: high resistance against destruction in acid gas medium, high strength, plasticity and viscosity.

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