Duplex stainless steel pipe

A duplex stainless steel pipe that has a chemical composition consisting of, in mass %,

• C:
• 0.030% or less,
• Si:
• 0.20 to 1.00%,
• Mn:
• 0.5 to 7.0%,
• P:
• 0.040% or less,
• S:
• 0.020% or less,
• Al:
• 0.100% or less,
• Ni:
• 4.0 to 9.0%,
• Cr:
• 20.0 to 30.0%,
• Mo:
• 0.5 to 2.0%,
• Cu:
• 1.5 to 3.0%,
• N:
• 0.15 to 0.30%,
• V:
• 0.01 to 0.50%,
• Nb:
• 0.030 to 0.300%,
• Co:
• 0.10 to 0.50%,
• Sn:
• 0.001 to 0.050%,
• Ta:
• 0 to 0.100%,
• Ti:
• 0 to 0.100%,
• Zr:
• 0 to 0.100%,
• Hf:
• 0 to 0.100%,
• W:
• 0 to 0.200%,
• Sb:
• 0 to 0.100%,
• Ca:
• 0 to 0.020%,
• Mg:
• 0 to 0.020%,
• B:
• 0 to 0.020%, and
• rare earth metal:
• 0 to 0.200%,
• with the balance being Fe and impurities, and
• has a microstructure that is composed of, in volume ratio, ferrite in an amount of 35.0 to 65.0% and σ phase in an amount of 0 to less than 1.0%, with the balance being austenite;
• wherein
• a content of undissolved Nb is 0.008% by mass or more, and a ratio of the content of undissolved Nb to a content of undissolved Al is 1.0 or more, and
• a yield strength is 655 MPa or more.