Patent ID: 11959177
Assignee: JFE STEEL CORPORATION
Field: Materials, metallurgy (Chemistry)
Classification: CPC C | IPC C

Claim 0:
1. A component comprising a core part and a surface layer, wherein
the core part comprises a chemical composition that consists of, in mass %,
C: 0.01% or more and less than 0.20%,
Si: 1.0% or less,
Mn: 1.5% or more and 3.0% or less,
P: 0.02% or less,
S: 0.06% or less,
Cr: 0.30% or more and 3.0% or less,
Mo: 0.005% or more and 0.40% or less,
V: 0.02% or more and 0.5% or less,
Nb: 0.003% or more and 0.20% or less,
Al: 0.010% or more and 2.0% or less,
Ti: more than 0.005% and less than 0.025%,
N: 0.0200% or less,
Sb: 0.0005% or more and 0.02% or less, and
optionally one or more selected from the group consisting of
B: 0.0100% or less,
Cu: 0.3% or less,
Ni: 0.3% or less,
W: 0.3% or less,
Co: 0.3% or less,
Hf: 0.2% or less,
Pb: 0.2% or less,
Bi: 0.2% or less,
Zn: 0.2% or less, and
Sn: 0.2% or less, and

the balance consisting of Fe and incidental impurities, with the chemical composition satisfying either one of following relations:

in a case where the C content is 0.01% or more and 0.10% or less,
(S/32)/(Ti/48)+(N/14)/(Ti/48)≤13.0, wherein each of S, Ti and N represents respectively S content, Ti content and N content expressed as mass %, and

in a case where the C content is more than 0.10% and less than 0.20%,
2(S/32)/(Ti/48)+3(N/14)/(Ti/48)≤35.0, wherein each of S, Ti and N represents respectively S content, Ti content and N content expressed as mass %,

the core part comprises a steel microstructure that contains bainite phase in an area ratio of more than 50%, and
the surface layer comprises a chemical composition with high nitrogen and carbon contents relative to the chemical composition of the core part.