Abstract
Austempered Ductile Iron (ADI), which has much the same strength and toughness as usual steels, has been developed. ADI has many advantages in mechanical properties and manufacturing, for 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. Recently, two steps bending phenomenon of S-N curve for the bending fatigue strength of ADI is reported, and the fatigue phenomenon in long life region over 10,000,000 time number of cycles is discussed. However, the surface durability in long life region has not been clarified until now. In this paper, surface durability of ADI rollers in long life region is investigated using a disk machine which simulates the rolling and sliding action of gears. Furthermore, fatigue limit for surface durability of ADI is estimated by observations with crack initiation and propagation.
