STAINLESS STEEL FOR OIL WELL, STAINLESS STEEL PIPE FOR OIL WELL, AND PROCESS FOR PRODUCTION OF STAINLESS STEEL FOR OIL WELL

摘要

Disclosed is a stainless steel having the following chemical composition: C: 0.05% or less, Si: 0.5% or less, Mn: 0.01 to 0.5%, P: 0.04% or less, S: 0.01% or less, Cr: more than 16.0% and not more than 18.0%, Ni: more than 4.0% and not more than 5.6%, Mo: 1.6 to 4.0%, Cu: 1.5 to 3.0%, Al: 0.001 to 0.10%, and N: 0.050% or less, with the remainder being Fe and impurities, wherein the components meet the requirements represented by formulae (1) and (2). The structure of the stainless steel contains a martensite phase and 10 to 40% by volume of a ferrite phase, wherein the percentage of distribution of the ferrite phase is greater than 85%. Cr + Cu + Ni + Mo = 25.5 (1) -8 = 30(C+N) + 0.5Mn + Ni + Cu/2 + 8.2 - 1.1(Cr+Mo) = -4 (2)