Effect of austempering parameters on microstructure and mechanical properties of heavy section Machinable Austempered Ductile Cast Iron (MADI)

Abstract

The first important limitation of ADI usage in industries is the machinability of the parts. Machinable Austempered Ductile Cast Iron (MADI) is a novel kind of ADI with improved properties such as better machinability compared to ADI and similar to as cast ductile iron. Furthermore, MADI has a higher strength than ductile iron at the same hardness value. The present work aimed to investigate into the impact of the austempering time and temperature on microstructure and mechanical properties of ductile iron samples prepared from Y-block with 75 mm thickness. In order to achieve the microstructure of the continuous matrix of equiaxed ferrite with islands of austenite, samples were partially austenitized (intercritical austenitization) at 850 °C for 2 hours. The austempering process was carried out at 350 °C and 390 °C for 1, 2, 3, 4 hours. The result of this study indicated that austempering at 390 °C, results in lower strength and hardness and higher ductility and toughness compared to austempering at 350 °C. It was also noticed that the minimum hardness was achieved by austempering at 390 °C for 2 hours.