Development of austenite free ADI (austempered ductile cast iron)

The primary goal of this investigation was to create austempered ductile cast iron (ADI) with a fully ferritic microstructure without compromising its mechanical properties. This was achieved by applying a novel heat treatment process. This process consists of austempering and subsequent isothermal tempering below the inter critical (A1) temperature of ductile cast iron. Ductile cast iron samples were initially austenitized at 927 °C (1700 °F) for 2 h and then austempered at three different temperatures 260 °C (500 °F), 316 °C (600 °F) and 385 °C (725 °F) and finally isothermally tempered at 484 °C (900 °F) for 2 h. This resulted in a fully ferritic microstructure. The effect of this tempering on the physical and mechanical properties of the material was examined and compared with conventionally processed ADI. Tests results show that when ADI is austempered at 260 °C (500 °F) and subsequently tempered at 484 °C (900 °F) it has significantly better mechanical properties than the samples initially austempered at other two temperatures (i.e. 316 °C (600 °F) and 385 °C (725 °F)).