Patent ID: 11905580
Assignee: NIPPON STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C | IPC C

Claim 0:
1. A seamless steel pipe comprising:
a chemical composition consisting of, in mass %,
C: 0.15 to 0.45%,
Si: 0.05 to 1.00%,
Mn: 0.01 to 1.00%,
P: 0.030% or less,
S: 0.0001 to 0.0050%,
Al: 0.005 to 0.070%,
Cr: 0.30 to 1.50%,
Mo: 0.25 to 2.00%,
Ti: 0.002 to 0.020%,
Nb: 0.002 to 0.100%,
B: 0.0005 to 0.0040%,
rare earth metal: 0.0001 to 0.0015%,
Ca: 0.0001 to 0.0100%,
N: 0.0100% or less,
O: 0.0001 to 0.0020%,
V: 0 to 0.30%,
Mg: 0 to 0.0100%,
Zr: 0 to 0.0100%,
Co: 0 to 1.00%,
W: 0 to 1.00%,
Ni: 0 to 0.50%,
Cu: 0 to 0.50%, and
with the balance being Fe and impurities,
and satisfying Formula (1),
wherein
a maximum major axis of inclusions in the seamless steel pipe is 150 μm or less, the maximum major axis being predicted by means of extreme value statistical processing, and
a yield strength is within a range of 758 to 862 MPa:

(Ca/O+Ca/S+0.285×REM/O+0.285×REM/S)×(Al/Ca)≥40.0  (1)

where, a content (mass %) of a corresponding element is substituted for each symbol of an element in Formula (1).