PRODUCTION OF SOUR RESISTANT STEEL SHEET FOR LINE PIPE EXCELLENT IN CO2 CORROSION RESISTANCE AND LOW TEMPERATURE TOUGHNESS

摘要

PURPOSE: To produce a sour resistant steel sheet for a line pipe excellent in CO₂ corrosion resistance and low temp. toughness by casting a steel having a specified componental compsn., subjecting the same to rolling treatment under specified conditions and executing cooling. ;CONSTITUTION: A steel having a compsn. contg., by weight, 0.01 to 0.07% C, 0.05 to 0.5% Si, 0.7 to 1.5% Mn, ≤0.015% P, ≤0.001% S, 0.01 to 0.06% Nb, 0.4 to 1.2% Cr, 0.05 to 0.4% Cu, 0.005 to 0.03% Ti, ≤0.05% Al, 0.001 to 0.005% Ca, 0.001 to 0.005% N and 0.001 to 0.005% O, furthermore satisfying the inequality, and the balance iron is cast. Next, without forming it into a cooled slab, rolling it started and is once stopped at a point of ≥900°C surface temp. After that, it is water-cooled to ≤700°C surface temp. at 5 to 40°C/s cooling rate, is air-cooled to ≤Ac₃ surface temp. and ≤950°C temp. in the central part of the sheet thickness and is thereafter applied with rolling reduction at 60% comulative draft so as to regulate rolling true strain per pass on the average to ≤0.2. Then, the rolling is finished at a point of ≥Ar₃ average temp. of the sheet thickness, and cooling is executed.;COPYRIGHT: (C)1996,JPO