Development of Control Technology of Austempered Ductile Iron with High Strength and High Toughness for Gear Parts.

In this study, it was examined the relationship between the microstructure, fatigue properties, mechanical properties and retained austenite volume of Mo-Ni ADI corresponding to various austempering temperatures. When the austempering temperature is increased to , acicular bainite structure was found to be transformed to feathery bainite structure. But at the austempering temperature of , the dissolved bainite lath was showned. Up to the austempering temperature of , the volume of retained austenite was increased. However at the austempering temperature of a large amount of retained austenite was decreased. In this study, the retained austenite volume was determined by XRD(X-ray diffraction). It was observed that the optimum fatigue properties can be obtained at the condition of austempering temperature . Under the such conditions, fatigue limit determined as the value of 290 MPa, tensile strength 877MPa elongation 6%, hardness 285(BHN), impact values(CVN) 9.2J and retained austenite volume 30.3%, respectively.