Study on Chemical Composition and Heat Treatment Cycle of Austempered Ductile Iron for Improved Machinability and Fatigue Properties

For long years, Austempered Ductile Iron (ADI) has found widespread application in different fields such as transportation, agriculture and other heavy industries due to its high strength and hardness coupled with reasonably good ductility. However, it’s low machinability and hence high machining costs limits further exploration of this material in certain areas. In the present work, a new engineering material having desirable properties and higher machinability, called machinable austempered ductile iron has been designed and studied. This new material has a specific composition with low alloying elements and the heat treatment cycle consisted of austenitizing at 850°C for one hour followed by austempering at 390°C for an hour, Subsequently the material has been evaluated for hardness, tensile and fatigue properties. A hardness of 235 HB has been obtained in the material with yield strength of 705 N/mm2 and a tensile strength of 900 N/mm2. The corresponding percent elongation in the material was %15 with fatigue strength of 370 N/mm2. The results indicate significant improvement in machinability and endurance limit compared to regular austempered ductile iron. Thus, this new machinable austempered ductile iron can become a substitute for regular ADI in many applications to improve production and/or performance efficiency.