US 12,338,518 B2
Valve spring
Shinya Teramoto, Tokyo (JP); Yutaka Neishi, Tokyo (JP); Michimasa Aono, Tokyo (JP); Satoru Mineta, Tokyo (JP); Shoichi Suzuki, Tokyo (JP); and Tatsuro Ochi, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP); and NIPPON STEEL SG WIRE CO., LTD., Tokyo (JP)
Appl. No. 17/904,448
Filed by NIPPON STEEL CORPORATION, Tokyo (JP); and NIPPON STEEL SG WIRE CO., LTD., Tokyo (JP)
PCT Filed Feb. 19, 2021, PCT No. PCT/JP2021/006386
§ 371(c)(1), (2) Date Aug. 17, 2022,
PCT Pub. No. WO2021/167070, PCT Pub. Date Aug. 26, 2021.
Claims priority of application No. 2020-027778 (JP), filed on Feb. 21, 2020.
Prior Publication US 2023/0087453 A1, Mar. 23, 2023
Int. Cl. C22C 38/54 (2006.01); C22C 38/00 (2006.01); C22C 38/04 (2006.01); C22C 38/34 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/52 (2006.01)
CPC C22C 38/54 (2013.01) [C22C 38/002 (2013.01); C22C 38/04 (2013.01); C22C 38/34 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/52 (2013.01)] 4 Claims
OG exemplary drawing
 
1. A valve spring, wherein:
when a wire diameter is defined as d (mm), a chemical composition at a d/4 depth position from a surface contains, in mass %,
C: 0.50 to 0.80%,
Si: 1.20 to less than 2.50%,
Mn: 0.25 to 1.00%,
P: 0.020% or less,
S: 0.020% or less,
Cr: 0.40 to 1.90%,
V: 0.05 to 0.60%,
Ca: 0.0001 to 0.0050%,
N: 0.0100% or less,
Mo: 0 to 0.50%,
Nb: 0 to 0.050%,
W: 0 to 0.60%,
Ni: 0 to 0.500%,
Co: 0 to 0.30%
B: 0 to 0.0050%,
Cu: 0 to 0.050%,
Al: 0 to 0.0050%, and
Ti: 0 to 0.050%,
with the balance being Fe and impurities,
and wherein:
in a microstructure of the valve spring, an area fraction of martensite is 90.0% or more,
a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 5000 to 80000 pieces/μm3, and
wherein, among inclusions,
inclusions in which, in mass %, an O content is 10.0% or more are defined as oxide-based inclusions,
inclusions in which, in mass %, an S content is 10.0% or more and the O content is less than 10.0% are defined as sulfide-based inclusions, and
among the sulfide-based inclusions, inclusions in which, in mass %, a Ca content is 10.0% or more, the S content is 10.0% or more, and the O content is less than 10.0% are defined as Ca sulfides,
a numerical proportion of the Ca sulfides with respect to a total number of the oxide-based inclusions and the sulfide-based inclusions is 0.20% or less.