Potential of sintered high speed steels in antifretting applications

The increased market for high speed steels (HSSs) is increasingly associated with their use as wear resistant materials. The tribological properties can be enhanced by incorporating into the HSS further ceramic particles to increase wear resistance and solid lubricants lo minimise friction, either at the surface, or by powder metallurgy into the steel matrix, already containing some 15% of ʹnaturalʹ, predominately MC and M6C, carbides. The difficulty of relating engineering performance of a component in reciprocating motion to a simple tribological test, such as pin on disc, is well recognised. The present paper will present a methodology of fretting testing, where the eventual failure is comparable to service damage of autoengine valve train parts, for which modified HSSs are prospective materials. Wear induced by fretting and microcracking of the surface and bulk material were studied in M3 class 2 and T42 HSSs in a newly developed fretting machine. The HSS plane specimens underwent reciprocating movements against an AISI 52100 chromium steel ball. Test parameters were normal load (100-1000 N), sliding displacement (+ -4 to + -100(mu)m), frequency (1 25 Hz) of reciprocation, and number of test cycles (1-10^6). The results were plotted on running condition fretting and materials response fretting maps. These results are interpreted in the light of damage observed and related to details of the microstructure of the two high speed steels.