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 (A(1)) temperature of ductile cast iron. Ductile cast iron samples were initially austenitized at 927 degrees C (1700 degrees F) for 2 h and then austempered at three different temperatures 260 degrees C (500 degrees F), 316 degrees C (600 degrees F) and 385 degrees C (725 degrees F) and finally isothermally tempered at 484 degrees C (900 degrees F) for 2h. 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 degrees C (500 degrees F) and subsequently tempered at 484 degrees C (900 degrees F) it has significantly better mechanical properties than the samples initially austempered at other two temperatures (i.e. 316 degrees C (600 degrees F) and 385 degrees C (725 degrees F)). (c) 2006 Elsevier B.V. All rights reserved.