	US 12,006,994 B2
	Valve spring
Shinya Teramoto, Tokyo (JP); Yutaka Neishi, Tokyo (JP); Michimasa Aono, Tokyo (JP); Shuji Kozawa, Tokyo (JP); Fumio Takahashi, Yokohama (JP); Shigekazu Nishimoto, Yokohama (JP); Mitsuhiro Kondo, Yokohama (JP); Tatsuro Ochi, Tokyo (JP); and Shoichi Suzuki, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP); NHK SPRING CO., LTD., Kanagawa (JP); and NIPPON STEEL SG WIRE CO., LTD., Tokyo (JP)
Appl. No. 17/754,667
Filed by NIPPON STEEL CORPORATION, Tokyo (JP); NHK SPRING CO., LTD., Yokohama (JP); and NIPPON STEEL SG WIRE CO., LTD., Tokyo (JP)
PCT Filed Oct. 15, 2020, PCT No. PCT/JP2020/038932 § 371(c)(1), (2) Date Apr. 8, 2022, PCT Pub. No. WO2021/075501, PCT Pub. Date Apr. 22, 2021.
Claims priority of application No. 2019-189245 (JP), filed on Oct. 16, 2019.
Prior Publication US 2024/0077123 A1, Mar. 7, 2024
Int. Cl. F16F 1/02 (2006.01); C21D 1/18 (2006.01); C21D 1/30 (2006.01); C21D 6/00 (2006.01); C21D 8/00 (2006.01); C21D 9/02 (2006.01); C22C 38/00 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/34 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/46 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C23C 8/26 (2006.01)

CPC F16F 1/021 (2013.01) [C21D 1/18 (2013.01); C21D 1/30 (2013.01); C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/005 (2013.01); C21D 9/02 (2013.01); C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/34 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/46 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C23C 8/26 (2013.01); C22C 2202/02 (2013.01); F16F 2224/02 (2013.01)]

2 Claims

1. A valve spring, comprising:

a nitrided layer formed in an outer layer, and

a core portion that is further inward than the nitrided layer;

wherein:

a chemical composition of the core portion consists of, in mass %,

C: 0.53 to 0.59%,

Si: 2.51 to 2.90%,

Mn: 0.70 to 0.85%,

P: 0.020% or less,

S: 0.020% or less,

Cr: 1.40 to 1.70%,

Mo: 0.17 to 0.53%,

V: 0.23 to 0.33%,

Ca: 0.0001 to 0.0050%,

Cu: 0.050% or less,

Ni: 0.050% or less,

Al: 0.0050% or less,

Ti: 0.050% or less,

N: 0.0070% or less, and

Nb: 0 to 0.020%,

with the balance being Fe and impurities;

in the core portion, a number density of V-based precipitates having a maximum diameter ranging from 2 to 10 nm is 500 to 8000 pieces/μm²; and

when, among inclusions in the core portion,

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,

in the core portion, 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.