STAINLESS STEEL FOR OIL WELL, STAINLESS STEEL PIPE FOR OIL WELL, AND METHOD OF MANUFACTURING STAINLESS STEEL FOR OIL WELL

摘要

The chemical composition of a stainless steel in accordance with the present invention consists of C: not more than 0.05%, Si: not more than 0.5%, Mn: 0.01 to 0.5%, P: not more than 0.04%, S: not more than 0.01%, 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: not more than 0.050%, the balance being Fe and impurities, and satisfies Formulas (1) and (2). Also, the micro-structure thereof contains a martensitic phase and a ferritic phase having a volume ratio of 10 to 40%, and the ferritic phase distribution ratio is higher 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)