Effect of the duration of austempering on particle erosion wear resistance of ADI was studied. In short duration (Stage I) region, a fair amount of martensite phase can be recognized, and hence deterioration of erosion wear resistance. In initial Stage II, the austempering region (0.5 hr duration) is free of carbide. If prolonged the austempering duration, the retained austenite amount tend to decrease and hence carbide formation. Even if slightly increase of carbide amount that still can play an important role on debasing wear resistance, resulted from the alternation of erosion behavior. Erosion-induced phase transformation of retained austenite also can be determined that is generality transformed to "-carbide.