High-strength stainless steel seamless pipe for oil country tubular goods, and method for producing same

A high-strength stainless steel seamless pipe for oil country tubular goods, the high-strength stainless steel seamless pipe having a yield strength of 862 MPa or more with a composition that comprises, in mass %, C:

• 0.05% or less, Si:
• 0.5% or less, Mn:
• 0.15 to 1.0%, P:
• 0.030% or less, S:
• 0.005% or less, Cr:
• 14.5 to 17.5%, Ni:
• 3.0 to 6.0%, Mo:
• 2.7 to 5.0%, Cu:
• 0.3 to 4.0%, W:
• 0.1 to 2.5%, V:
• 0.02 to 0.20%, Al:
• 0.10% or less, N:
• 0.15% or less, B:
• 0.0005 to 0.0100%, and the balance Fe and unavoidable impurities, and in which the C, Si, Mn, Cr, Ni, Mo, Cu, and N satisfy the formula (1) below, and the Cu, Mo, W, Cr, and Ni satisfy the formula (2) below,
• wherein the stainless steel pipe has a structure that contains more than 45% martensite phase as a primary phase, 10 to 45% ferrite phase and 30% or less retained austenite phase as a secondary phase, by volume, and
• wherein the ferrite grains have a maximum crystal grain size of 500 μm or less as measured in an inspection of a 100 mm2 continuous region by assuming that grains having a crystal orientation difference of no greater than 15° represent the same grains in electron backscatter diffraction (EBSD):
• −5.9×(7.82+27C−0.91Si+0.21Mn−0.9Cr+Ni−1.1Mo+0.2Cu+11N)≥13.0, Formula (1)
• wherein C, Si, Mn, Cr, Ni, Mo, Cu, and N represent the content of each element (mass %);
• and
• Cu+Mo+W+Cr+2Ni≤34.5, Formula (2)
• wherein Cu, Mo, W, Cr, and Ni represent the content of each element (mass %).