| 摘要 |
PURPOSE:Steel for an oil well pipe having high strength and enhanced in CO2 corrosion resistance and sulfide cracking resistance, obtained by a method wherein steel of which the amounts of C, Si+Mn, Cr, Cu, Ni and N are specified is heated to a specific temp. and, after quenching, the treated steel is subsequently subjected to tempering treatment. CONSTITUTION:Steel which comprises, on a wt. basis, 0.22% or less C, 0.25% or less Si+Mn, 0.05% or less Cu, 0.10% or less Ni, 12.0-14.5% Cr, 0.01% or less Al, 0.0050-0.1% N, one or more of 0.02-0.15% Mo and 0.005-0.50% Nb and the remainder of Fe and inevitable impurities and contains, on the basis of impurities 0.015% or less P and 0.005% or less S is cast. In this composition, formula 100XC%+100XN%-2XCr%+9>=0 is satisfied. This steel is heated to 940-1,050 deg.C and quenched to sufficiently perform the solution heat-treatment of Cr-carbide with the substrate and, succeedingly, if the treated steel is tempered at a temp. of a AC1 point or less, steel for an oil well pipe having a martensite structure and excellent corrosion resistance is obtained.
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