Thrust roller bearing and method of manufacturing the same

1 . A thrust roller bearing comprising:

a race; and

a cage that retains a plurality of rollers and is disposed on the race,

wherein the race comprises:

an annular plate portion defining a raceway for the plurality of rollers,

a flange that is extended in an axial direction thereof and provided at a radially outer ide or a radially inner side of the annular plate portion, and

an annular locking portion that is provided at an entire periphery on a front end of the flange and is projected in a radial direction thereof in such a manner that the annular locking portion catches a radially outer side or a radially inner side of the cage in the axial direction, and

wherein an entire circumference of the flange and an entire circumference of the annular locking portion are softer than the annular plate portion.

2 . The thrust roller bearing according to claim 1 , wherein the annular plate portion, the flange and the annular locking portion are integrally formed.

3 . The thrust roller bearing according to claim 1 , wherein the flange and the annular locking portion are continuously tapered toward a front end of the annular locking portion.

4 . The thrust roller bearing according to claim 1 , wherein only the annular plate portion is subjected to a hardening heat treatment to make the entire circumference of the flange and the entire circumference of the annular locking portion softer than the annular plate portion.

5 . The thrust roller bearing according to claim 1 , wherein an inner diameter of the annular locking portion is smaller than an outer diameter of the cage.

6 . A method of manufacturing a thrust roller bearing, the method comprising:

providing a cage which retains a plurality of rollers;

providing an annular base material to be a race comprising an annular plate portion defining a raceway, a flange and an annular locking portion;

bending the base material to form the flange which is extended in an axial direction thereof from the annular plate portion;

subjecting only the annular plate portion to a hardening heat treatment;

after the bending and subjecting steps, assembling the cage which retains the plurality of rollers into the race; and

bending an entire periphery of a front end of the flange to form the annular locking portion which is projected in a radial direction thereof in such a manner that the annular locking portion catches a radially outer side or a radially inner side of the cage in the axial direction.

7 . The method according to claim 6 , wherein the hardening heat treatment is locally carried out by a high frequency induction heating coil.

8 . A thrust roller bearing manufactured by a method, the method comprising:

providing a cage which retains a plurality of rollers;

providing an annular base material to be a race comprising an annular plate portion defining a raceway, a flange and an annular locking portion;

bending the base material to form the flange which is extended in an axial direction thereof from the annular plate portion;

subjecting only the annular plate portion to a hardening heat treatment;

after the bending and subjecting steps, assembling the cage which retains the plurality of rollers into the race; and

bending an entire periphery of a front end of the flange to form the annular locking portion which is projected in a radial direction thereof in such a manner that the annular locking portion catches a radially outer side or a radially inner side of the cage in the axial direction.