High toughness ultra-high strength stainless steel tube and a method of manufacturing the same for oil well excellent corrosion resistance

摘要

PROBLEM TO BE SOLVED: To provide a high-toughness ultrahigh-strength stainless steel pipe for an oil well having excellent corrosion resistance, and to provide its production method.;SOLUTION: A steel stock having a composition comprising, by mass, ≤0.05% C, 0.20 to 1.80% Mn, 14.0 to 18.0% Cr, 5.0 to 8.0% Ni, 1.5 to 3.5% Mo, 0.5 to 3.5% Cu, 0.005 to 0.15% N and ≤0.006% O, also satisfying Cr+2Ni+1.1Mo+0.7Cu≤32.5, and further comprising one or two selected from ≤0.20% Nb and ≤0.20% V so as to satisfy the condition of Nb+V≥0.05% is made into a pipe. The pipe is cooled to ≤150°C, and is thereafter subjected to tempering treatment where heating temperature T is 500 to 580°C, and also, T(20+logt) satisfies 15,200 to 16,800. In this way, a steel pipe having a YS of ≥965 MPa and vE_-40 of ≥50 J, and having excellent corrosion resistance in a CO₂-containing high-temperature corrosive environment heated at ≥200°C can be obtained. It is also possible that, before the tempering treatment, the pipe is subjected to quenching treatment so as to be heated to an Ac₃ transformation point or above, and, successively, to be cooled at a cooling rate of air cooling or above.;COPYRIGHT: (C)2008,JPO&INPIT