STEEL FOR LINE PIPE WITH SUPERIOR CORROSION RESISTANCE TO WET GASEOUS CARBON DIOXIDE AND SUPERIOR WELDABILITY

摘要

PURPOSE:To obtain the titled steel for a line pipe by adding Co and Ti to a steel having a specified composition and by restricting the ratio of B/N, the amounts of S and Cu, and the weld crack sensitivity index. CONSTITUTION:This steel consists of, by weight, =0.10% C, 0.10-1.00% Si, 0.10-1.20% Mn, 1.0-3.0% Cr, 0.01-0.08% Nb, 0.01-0.10% Al, 0.0002-0.0050% B, 0.0010-0.015% N (B/N=0.1-0.6), 0.5-2.0% Co and/or 0.005-0.10% Ti and the balance Fe with inevitable impurities including =0.010% S and =0.04% Cu. The steel may further contain 0.02-0.20% Mo and/or 0.01-0.10% V, and/or one or more among 0.005-0.10% Zr, 0.0005-0.01% Ca and 0.0005-0.05% rare earth element. The weld crack sensitivity index PCM of the steel represented by the equation is =0.23%. A line pipe made of the steel has superior corrosion resistance to CO2 and superior weldability as well as superior mechanical properties.