Potential of sintered high speed steels in antifretting applications

The increased market for high speed steels (HSSs) is increasingly associate d with their use as wear resistant materials. The tribological properties c an be enhanced by incorporating into the HSS further ceramic particles to i ncrease wear resistance and solid lubricants to minimise friction, either a t the surface, or by powder metallurgy into the steel matrix, already conta ining some 15% of 'natural', predominately MC and M6C, carbides. The diffic ulty of relating engineering performance of a component in reciprocating mo tion to a simple tribological test, such as pin on disc, is well recognised . The present paper will present a methodology of fretting testing, where t he eventual failure is comparable to service damage of autoengine valve tra in parts, for which modified HSSs are prospective materials. Wear induced b y 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 p lane specimens underwent reciprocating movements against an AISI 52100 chro mium steel ball. Test parameters were normal load (100-1000 N), sliding dis placement (+/-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 condit ion fretting and materials response fretting maps. These results are interp reted in the light of damage observed and related to details of the microst ructure of the two high speed steels.