For environmental and economical reasons, most vehicles need weight reductions. A useful method to make lighter vehicles is to increase the fatigue limits of vehicle parts. On the previous paper, to prevent the decrease in the fatigue limits of carburized or carbonitrided gears for vehicles by accidental temperature rise while using the gears, a new method, which is treated with the middle temperature tempering before shot peening, was proposed. Based on this consideration, the authors conducted a study by using carburized and carbonitrided specimens on the new method, and evaluated their surface characteristics and bending fatigue limits. The result of the study showed that the fatigue limits of the carburized and carbonitrided specimens processed by the new method achieved 30% and 49% better than those of the specimens assumed accidental temperature rise respectively.
