Tribological enhancement of AISI 420 martensitic stainless steel through friction-stir processing

Friction Stir Processing (FSP) has been used to modify the microstructure and properties of AISI 420 stainless steel. The effects of FSP on the steel's microstructure, hardness and wear resistance have been measured and compared with the properties of a conventionally hardened AISI 420 and with D2 tool steel. Optical microscopy, X-ray diffraction and micro-hardness have been used to characterise the steel, and two types of wear tests; dry reciprocating ball-on-flat and micro-scale abrasive wear testing, have been used to determine the processed steel's wear performance under two quite different wear mechanisms. The results show that FSP of AISI 420 can produce higher hardness (maximum HV0.3=722) and better wear performance than conventional heat treatments and in some regions better hardness and tribological performance than D2 tool steel. FSP appears to induce the austenite to martensite transformation within the AISI 420, but the resulting microstructures appear to be significantly different from the conventionally heat treated material