Dual Phase Austempered Ductile Iron - The Material Revolution and Its Engineering Applications

Abstract

During the last few years, there has been an increased interest in improving the strength of ductile iron by means of heat-treating to obtain dual phase microstructures that enhance the properties found in the Austempered Ductile Irons (ADI). Therefore, additional research int this field is well motivated. An example of this is the innovative dual phase austempered irons - DP-ADI, that has a greater ductility than the conventionally heat treated ADI, due to its microstructure composed of ausferrite (regular ADI microstructure) and free (proeutectoid) allotriomorphic ferrite. Additionally, dual phase ADI could provide a wide range of mechanical properties as a function of the relative proportion of proeutectoid ferrite and ausferrite constituents, thereby replacing conventional ductile iron. Hence, dual phase ADI will be appropriate for new applications in the critical parts, where a combination of high strength and ductility is a pressing requirement. Furthermore, with the introduction of free ferrite into the matrix increased machinability of ADI could be achieved. The aim of this paper was to review works that have been published over the past years on the effects of process variables, mechanical properties, microstructure and applications of Dual phase Austempered Ductile Iron and to present some own results. This review is an attempt to assemble the results of the worldwide sudden increase in research and development that followed the announcement of the first production of the DP-ADI material.