Stainless steel seamless pipe and method for manufacturing the same

A stainless steel seamless pipe having a chemical composition comprising, in mass %,

• C:
• 0.06% or less,
• Si:
• 1.0% or less,
• Mn:
• 0.01 to 1.0%,
• P:
• 0.05% or less,
• S:
• 0.005% or less,
• Cr:
• 15.2 to 18.0%,
• Mo:
• 1.5 to 4.3%,
• Cu:
• 0.5 to 3.5%,
• Ni:
• 3.5 to 5.2%,
• V:
• 0.5% or less,
• Al:
• 0.10% or less,
• N:
• 0.10% or less, and
• O:
• 0.010% or less,
• with the balance being Fe and incidental impurities,
• wherein the stainless steel seamless pipe has a microstructure including a martensite phase at a volume fraction of 40% or more, a ferrite phase at a volume fraction of 15 to 55%, and a retained austenite phase at a volume fraction of 40% or less,
• with an average of ferrite filling factors being 0.80 or less,
• wherein the stainless steel seamless pipe has a yield strength of 758 MPa or more, and
• wherein each ferrite filling factor is a value defined by the following formula for one ferrite grain:
• Ferrite filling factor=(actual area of one ferrite grain)/(area of convex hull surrounding the one ferrite grain).