Alloy material and oil-well seamless pipe

An alloy material, having:

• a chemical composition consisting of, in mass %,
• C:
• 0.030% or less,
• Si:
• 0.01 to 1.0%,
• Mn:
• 0.01 to 2.0%,
• P:
• 0.030% or less,
• S:
• 0.0050% or less,
• Cr:
• 28.0 to 40.0%,
• Ni:
• 32.0 to 55.0%,
• sol. Al:
• 0.010 to 0.30%,
• N:
• more than 0.30% and not more than Nmax that is defined by formula (i) below,
• O:
• 0.010% or less,
• Mo:
• 0 to 6.0%,
• W:
• 0 to 12.0%,
• Ca:
• 0 to 0.010%,
• Mg:
• 0 to 0.010%,
• V:
• 0 to 0.50%,
• Ti:
• 0 to 0.50%,
• Nb:
• 0 to 0.50%,
• Co:
• 0 to 2.0%,
• Cu:
• 0 to 2.0%,
• REM:
• 0 to 0.10%, and
• the balance:
• Fe and impurities,
• wherein:
• Fn1 defined by formula (ii) below is 1.0 to 6.0, and
• a yield strength at a 0.2% proof stress is 1103 MPa or more;
• Nmax=0.000214×Ni2−0.03012×Ni+0.00215×Cr2−0.08567×Cr+1.927 (i)
• Fn1=Mo+(½)W (ii)
• where, each symbol of an element in the above formulas represents a content (mass %) of the corresponding element contained in the alloy material, with 0 being substituted when the corresponding element is not contained,
• wherein a grain size number of austenite grains in a cross section parallel to a rolling direction and a thickness direction is 1.0 or more.