| 摘要 |
A steel composition contains: 0.05% or less of C; 0.5% or less of Si; 0.20% to 1.80% of Mn; 0.03% or less of P; 0.005% or less of S; 14.0% to 18.0% of Cr; 5.0% to 8.0% of Ni; 1.5% to 3.5% of Mo; 0.5% to 3.5% of Cu; 0.05% or less of Al; 0.20% or less of V; 0.01% to 0.15% of N; and 0.006% or less of O on a mass basis, and satisfies the following expressions: Cr+0.65Ni+0.6Mo+0.55Cu-20C>=18.5 and Cr+Mo+0.3Si-43.5C-0.4Mn-Ni-0.3Cu-9N<=11 (where Cr, Ni, Mo, Cu, C, Si, Mn, and N represent their respective contents (mass %)). After such a steel pipe material is formed into a steel pipe, the steel pipe is quenched by cooling after heating to a temperature of the AC3 transformation point or more and tempered at a temperature of the AC1 transformation point or less. The composition may further contain at least one element of Nb and Ti; at least one element selected from the group consisting of Zr, B, and W; or Ca, singly or in combination. Preferably, the steel pipe has a martensitic structure containing 5 to 25 percent by volume of a residual austenite phase, or further containing 5% percent by volume or less of a ferrite phase. Thus, the resulting stainless steel pipe for oil country tubular goods exhibits a superior corrosion resistance even in extremely severe, corrosive environments containing carbon dioxide gas (CO2), chloride ions (Cl<->), or the like.
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