Granted Patent B2

US 12,742,476 · App. 17/043,583 · Granted Sep 22, 2026

Inventors: Chikara Ohki (Kuwana, JP); Masahiro Yamada (Kuwana, JP)

Assignee: NTN Corporation

F16C33/121C21D1/18C21D6/004C21D9/40C21D2211/008

Abstract

Claims (15)

1 . A bearing part composed of a steel, the bearing part comprising a quench-hardened layer in a surface of the bearing part, wherein

the quench-hardened layer includes a plurality of martensite crystal grains and a plurality of austenite crystal grains,

each martensite crystal grain of the plurality of martensite crystal grains is determined such that a crystal orientation deviation between adjacent martensite crystal grains is more than or equal to 15°,

a ratio of a total area of the plurality of martensite crystal grains in the quench-hardened layer is more than or equal to 70%,

a ratio of a total area of the plurality of austenite crystal grains in the quench-hardened layer is less than or equal to 20%,

the quench-hardened layer contains nitrogen,

an average nitrogen concentration of the quench-hardened layer is more than equal to 0.15 mass % between the surface and a position at a distance of 10 μm from the surface of the bearing part,

the plurality of martensite crystal grains are classified into a first group and a second group,

all of crystal grain sizes belonging to the first group martensite is larger than all of crystal grain sizes belonging to the second group martensite,

a value obtained by dividing a total area of the martensite crystal grains belonging to the first group by the total area of the plurality of martensite crystal grains is more than or equal to 0.5,

a value obtained by dividing, by the total area of the plurality of martensite crystal grains, a total area of the martensite crystal grains belonging to the first group, except for a martensite crystal grain that has a minimum crystal grain size in the first group, is less than 0.5,

an average grain size of the martensite crystal grains belonging to the first group is less than or equal to 0.97 μm, and

an average aspect ratio of the martensite crystal grains belonging to the first group is less than or equal to 2.57.

2 . The bearing part according to claim 1 , wherein the steel is a high carbon chromium bearing steel SUJ2 defined in JIS.

3 . The bearing part according to claim 2 , wherein a hardness of the quench-hardened layer in the surface is more than or equal to 730 Hv.

Assignments (2)

Priority Claims (1)

Continuity (1)

References Cited (148)