A review: phase transformation and wear mechanisms of single-step and dual-step austempered ductile irons

Austempered ductile iron (ADI) is a type of graphite cast iron produced by an isothermal heat treatment process. It is an alternative to traditional steel castings and forgings and even aluminum due to the exceptional mechanical properties such as high strength, good toughness and excellent machinability. In the matrix, the unique ausferritic structure consists of graphite nodules uniformly surrounded by acicular ferrite and carbon saturated austenite. In the automotive industry, ADI has been commonly applied in the manufacturing of camshafts, crankshafts, gears and engine valves. These components are frequently subjected to surface contact with relative motion and external load. Therefore, it is necessary to understand the wear behavior of ADI in order to solve the tribological issues in existing ADI applications and utilize ADI into future designs appropriately. This paper was aimed at reviewing the fabrication processes of single-step and dual-step ADIs. The corresponding microstructure and mechanical properties were also briefly discussed. The studies on wear performance of ADI and potential mechanisms have been systemically reviewed.