Dual-phase stainless steel and dual-phase stainless steel seamless pipe

A dual-phase stainless steel seamless pipe having a composition that consists of, in mass %, C:

• 0.002 to 0.03%, Si:
• 0.05 to 1.0%, Mn:
• 0.10 to 1.5%, P:
• 0.040% or less, S:
• 0.0005 to 0.020%, Cr:
• 20.0 to 28.0%, Ni:
• 4.0 to 10.0%, Mo:
• 2.0 to 5.0%, Al:
• 0.001 to 0.05%, N:
• 0.06 to 0.35%, and optionally, W:
• 1.5% or less, Cu:
• 2.0% or less, Zr:
• 0.50% or less, B:
• 0.010% or less, Nb:
• 0.50% or less, REM:
• 0.005% or less, Ca:
• 0.010% or less, Sn:
• 0.20% or less, Mg:
• 0.01% or less, Ta:
• 0.10% or less, Co:
• 1.0% or less, and Sb:
• 1.0% or less, and in which the balance is Fe and incidental impurities,
• the dual-phase stainless steel seamless pipe having a microstructure containing 20 to 70% austenitic phase and 30 to 80% ferritic phase by volume,
• the dual-phase stainless steel seamless pipe having a yield strength, YS, of 448 MPa or more, and containing oxide inclusions of which oxide inclusions having an average particle diameter of 1 μm or more have a number density of 15/mm2 or less, and at most 50% of the oxide inclusions having an average particle diameter of 1 μm or more are oxide inclusions containing aluminum.