The Effect of Heat Treatment Parameters on Microstructure and Toughness of Austempered Ductile Iron (ADI)

Abstract

In this investigation, the effect of heat treatment parameters on the microstructure and impact energy as a measure of toughness of the austempered ductile cast iron (ADI) was studied. Yblocks were casted from ductile cast iron with following composition: 3.2% C, 2.5% Si, 1.09% Ni, 0.87% Cu, 0.5% Mo and 0.16%Mn. Charpy specimens (un-notched) were machined from the straight part of Y-blocks. All of specimens were heat treated with different conditions. Some of them were austenitized at 900°C for 60 min and then austempered at 250, 300, 350 and 400°C for various durations. Then, hardness test, impact test, optical microscopy and X-ray diffraction (XRD) were performed on the heat treated ductile iron samples. The results reveal the highest impact energy (105 J) for the sample austenitized at 900°C and austempered at 350°C for 150 min. The microstructure of this sample consisted of 28% austenite and broad ferrite needles.