Patent ID: 11891680
Assignee: NIPPON STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C | IPC C

Claim 0:
1. A steel material 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: 0.0050% or less,
Al: 0.005 to 0.100%,
Cr: 0.55 to 1.10%,
Mo: 0.70 to 1.00%,
Ti: 0.002 to 0.020%,
V: 0.05 to 0.30%,
Nb: 0.002 to 0.100%,
B: 0.0005 to 0.0040%,
N: 0.0100% or less,
O: less than 0.0020%,
Ca: 0 to 0.0100%,
Mg: 0 to 0.0100%,
Zr: 0 to 0.0100%,
rare earth metal: 0 to 0.0100%,
Cu: 0 to 0.50%,
Ni: 0 to 0.50%,
Co: 0 to 0.50%, and
W: 0 to 0.50%,
with the balance being Fe and impurities,
and satisfying Formula (1),
wherein
in the steel material, a grain diameter of a prior-austenite grain is 15.0 μm or less,
an average area of precipitate which is precipitated in a prior-austenite grain boundary is 12.5×10−3 μm2 or less, and
a yield strength is 758 to 862 MPa:

Mo/Cr≥1.90  (1)

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