Abstract
Austempered Ductile Iron (ADI), which has much the same strength and toughness as usual steels, have been developed. ADI has many advantages in mechanical properties and manufacturing, of example, weight reduction due to smaller density than that of steel, good properties of vibration and noise, low cost in machining and heat treatment of blanks due to near-net-shape casting. It has been reported that ADI can be sufficiently applied as a medium hardness gear material. In medium hardness gears, tooth surface failure of steel gear is usually pitting, which occurs in all teeth and gradually progresses. However, in the case of ADI gear that is medium hardness, tooth surface failure is spalling, which occurs suddenly on a few teeth. On the spalling of ADI gear, the situation of generation and progress of the crack has not been clarified well. In this paper, the damages occurred on ADI gear tooth were observed in detail, and the mechanism in which spalling is occurred is investigated.
