Case-hardened stainless steel bearing component and process and

Abstract

A stainless steel bearing component containing in excess of 11% chromium and between 0.05% and 0.50% carbon is case-hardened by introducing carbon or nitrogen into the surface of the race using a plasma process. The component is heated in a chamber from which air is evacuated. There it is bombarded with hydrogen ions to clean its surface. Next, while the component remains at an elevated temperature, a gas containing carbon or nitrogen or both is introduced into the chamber where it exists at a relatively low pressure on the order of 2-9 torr. A plasma is produced intermittently, and it causes carbon or nitrogen or both to diffuse intio the surface of the component and create a case containing a greater proportion of carbon or nitrogen than the underlying core. Thereafter, the component is cooled and with most stainless steels this may be acheived by quenching in oil. Where the case is enriched in carbon, the component is thereafter reheated to a temperature where its core exists as single phase austenite and held at that temperature to effect a soak. An oil quench follows and it converts much of the austenite to martensite. The quench in turn may be followed by cryogenic cooling to convert retained sustenite into martensite. After assuming ambient temperature, the component is again heated to temper the hardened case.