HIGH STRENGTH MARTENSITIC STAINLESS STEEL FOR OIL WELL PIPE, EXCELLENT IN STRESS CORROSION CRACKING RESISTANCE AND HIGH TEMPERATURE TENSILE CHARACTERISTIC

摘要

PROBLEM TO BE SOLVED: To provide a martensitic stainless steel for oil well pipe, having superior resistance to corrosion, pitting corrosion, and stress corrosion cracking even under a severe corrosive environment containing CO₂, Cl^-, and further H₂S, etc., and also having excellent high temp. tensile characteristics. ;SOLUTION: This steel has a composition consisting of, by mass, ≤0.05% C, ≤0.50% Si, 0.30-1.50% Mn, ≤0.03% P, ≤0.005% S, 11.0-17.0% Cr, 3.0-7.0% Ni. 0.5-5.0% Mo, ≤0.05% Al, 0.01-0.15% N, ≤0.005% O, at least either of ≤0.20% Nb and ≤0.20% V, and the balance essentially Fe and satisfying the following inequalities I to III: inequality I, 0.02≤0.8(Nb%)+(V%)≤0.20; inequality II, (Cr%)+3.2(Mo%)+16(N%)+0.5(Ni%)-5(C%)≥17; inequality III, 1.1[(Cr%)+1.5(Si%)+(Mo%)]-(Ni%)-0.5(Mn%)-30[(C%)+(N%)]≤6.;COPYRIGHT: (C)1998,JPO