Surface treatment of rolling element bearing steel

Details Surface treatment of rolling element bearing steel Surface treatment of rolling element bearing steel

1999-05-17

2001-01-30

Jenkins, Daniel J. (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

Carburizing or nitriding using externally supplied carbon or...

C148S225000, C148S230000

Reexamination Certificate

active

06179933

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates in general to a process of manufacturing a rolling element bearing component and more particularly to a final surface treatment of the bearing component.
BACKGROUND
It is well known to subject steels to thermo-chemical treatments to create a hardened surface layer or case. Such treatments can involve several heating cycles to achieve the desired properties and post-machining is often necessary to compensate for dimensional changes and unwanted surface features. It is also known to subject steel to ion nitriding but in the case of conventionally nitrided bearing components additional steps are needed after nitriding to remove the friable compound layer which forms on the surface.
SUMMARY OF THE INVENTION
The present invention relates in general to a process applied to rolling element bearing components made in pre-hardened steel in the fully machined condition.
Rolling element bearing components for use in aircraft engines in particular are made from M50, M50 NiL, RBD and Pyrowear 675 steels. It has now been found that such components can exhibit superior properties if, as a final step in the manufacturing process, the component is subjected to a plasma (ion) nitriding treatment designed to increase the hardness of the outer surface to between 800 to 1200 HV0.3 up to a depth of 150 &mgr;m and the surface case is devoid of any compound layer.
The nitriding treatment can involve exposing the component to a plasma established by subjecting a gaseous atmosphere, principally composed of N
2
and preferably N
2
and H
2
to electrical energy and maintaining the exposure at a temperature in the range of 375° C. to 592° C. By careful control of the plasma (ion) nitriding conditions the formation of a compound layer is prevented and the distortion minimised thereby negating the need for subsequent machining.


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