	US 12,276,005 B2
	Steel shaft component
Kison Nishihara, Tokyo (JP); Hiroaki Tahira, Tokyo (JP); and Yoko Sueyasu, Tokyo (JP)
Assigned to NIPPON STEEL CORPORATION, Tokyo (JP)
Appl. No. 17/593,593
Filed by NIPPON STEEL CORPORATION, Tokyo (JP)
PCT Filed Apr. 9, 2020, PCT No. PCT/JP2020/015917 § 371(c)(1), (2) Date Sep. 21, 2021, PCT Pub. No. WO2020/209320, PCT Pub. Date Oct. 15, 2020.
Claims priority of application No. 2019-074788 (JP), filed on Apr. 10, 2019.
Prior Publication US 2022/0177991 A1, Jun. 9, 2022
Int. Cl. C21D 9/30 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/04 (2006.01); C22C 38/06 (2006.01); C22C 38/24 (2006.01); C22C 38/28 (2006.01)

CPC C21D 9/30 (2013.01) [C22C 38/001 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/04 (2013.01); C22C 38/06 (2013.01); C22C 38/24 (2013.01); C22C 38/28 (2013.01); C21D 2211/005 (2013.01); C21D 2211/009 (2013.01)]

4 Claims

1. A steel shaft component, comprising:

one or a plurality of shaft parts, each of the shaft part having a circular shape in a cross section perpendicular to an axial direction, and having a hardened layer having a Vickers hardness of 620 HV or more in an outer layer;

wherein:

a chemical composition of the steel shaft component consists of, by mass %,

C: 0.40 to 0.60%,

Si: 0.05 to 1.00%,

Mn: 1.00 to 2.00%,

P: 0.030% or less,

S: 0.005 to 0.100%,

Cr: 0.10 to 0.50%,

V: 0.10 to 0.30%,

Al: 0.005 to 0.050%,

N: 0.0050 to 0.0200%,

Ti: 0 to 0.050%, and

the balance: Fe and impurities;

a Vickers hardness Hs of a surface of the shaft part is 620 HV or more;

in the cross section perpendicular to the axial direction of the shaft part, a Vickers hardness Hb at an R/2 position that corresponds to a center position of a radius R of the shaft part satisfies Formula (1);

a microstructure at the R/2 position is composed of ferrite and pearlite;

a depth Hr (mm) of the hardened layer having a Vickers hardness of 620 HV or more satisfies Formula (2); and

in the hardened layer of the cross section perpendicular to the axial direction of the shaft part, a number of density of V-containing precipitates which contain V and which have an equivalent circular diameter of more than 100 nm is 10 particles/276 μm²or less:

Hs/2.3≤Hb≤350 (1)

0.05≤Hr/R≤0.40 (2)

where, R in Formula (2) represents a radius (mm) of the shaft part.