Abstract: Austempered ductile iron (ADI) is a heat treated ductile Iron or S.G. iron with a unique micro-structure, which consists of retained austenite and bainitic ferrite with graphite nodules dispersed in it. Due to this excellent microstructure it possesses high yield strength with good ductility, good fatigue strength, fracture toughness and wear resistance. ADI has emerged as a major engineering material in recent years because of its many attractive properties. The properties can be achieved upon adequate heat treatment which yields optimum microstructure for a given chemical composition. But this type of heat treatment is bit tricky, since it requires controlled heating and isothermal holding of the material. The wear properties of ADI not only depends upon the hardness but also depends on the microstructure of the material. Present investigation was carried out to assess the influence of cryogenic processing on the microstructure and wear properties of ADI. Experiment was carried out on two categories of ADI, one is austempered at 400ºC and other is at 340ºC with austempering time of 2.5, 3 and 3.5 hours respectively. These specimens were then cryogenically processed. The morphological changes, hardness values and wear rate of these samples were evaluated and compared with the noncryogenically treated samples. Test results indicates that the cryogenic processing can improve the wear properties, the lowest wear rate is observed for cryotreated ADI austempered at 400ºC for 2.5hour.

Keywords: Austempered Ductile Iron (ADI), Cryogenic Treatment, Austenite, Martensitic Transformation.