Effects of heat treatment on hardness and dry wear properties of a semi-solid processed Fe-27 wt pct Cr-2.9 wt pct C cast iron

Abstract

Effects of heat treatments on hardness and dry wear properties of a semi-solid processed Fe-26.96 wt pct Cr-2.91 wt pct C cast iron were studied. Heat treatments included tempering at 500°C, destabilisation at 1075°C and destabilisation at 1075°C plus tempering at 500°C, all followed by air cooling. Electron microscopy revealed that, in the as-cast condition, the primary proeutectic austenite was round in shape while the eutectic M7C3 carbide was found as radiating clusters mixed with directional clusters. Tempering did not change the microstructure significantly when observed by scanning or transmission electron microscopy. Destabilisation followed by air cooling led to a precipitation of secondary M23C6 carbide and a transformation of the primary austenite to martensite. Precipitation behaviour is comparable to that observed in the conventionally cast iron. Tempering after destabilisation resulted in a higher amount of secondary carbide precipitation within the tempered martensite in the eutectic structure. Vickers macrohardness and microhardness in the proeutectic zones were measured. Dry wear properties were tested by using a pin-on-disc method. The maximum hardness and the lowest dry wear rate were obtained from the destabilisation-plus-tempering heat treatment due to the precipitation of secondary carbides within the martensite matrix and a possible reduction in the retained austenite.