Optimizing the Microstructure and Mechanical Properties of Austempered Ductile Iron for Automobile Differential Gear

Austempered ductile iron (ADI) has been proved to be an excellent material as it possesses attractive properties: high strength, ductility and toughness combined with good wear resistance and machinability. These properties can be achieved upon adequate heat treatment which yields the optimum microstructure for a given chemical composition. The heat treating of the ductile cast iron produces the austempered ductile iron with outstanding mechanical properties that can be varied over a wide range by changing the heat treatment parameters. ADI has excellent combination of strength, fracture toughness and wear resistance and are used for a wide variety of applications in automotive, rail and heavy industries. In the present study, the effect of austenitizing temperature and austempering time on the microstructure and mechanical properties of low-alloyed Ni-Mo-Cu ductile iron for automobile differential gear have been investigated. Samples were austenitized at 850C, 900C and 950C for 1.5 hr and then austempered at 350C in the interval from 0.5 to 2 hr. The digital metallurgical polarizing microscope attached with imaging software was used to analyze the microstructure and investigate the bainitic transformation, while hardness, tensile and fatigue tests were performed for determination of mechanical properties.