한국주조공학회

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 $3370℃, acicular bainite structure was found to be transformed to feathery bainite structure. But at the austempering temperature of 420℃, the dissolved bainite lath was showned. Up to the austempering temperature of 370℃, the volume of retained austenite was increased. However at the austempering temperature of 420℃ 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 370℃. 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.