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The effect of a different type of microalloy material on the durability and processing of an existing pitman arm design was evaluated. The durability properties of a particular type microalloy material i.e. impact toughness, impact ductility, programmed fatigue life and high load fatigue life properties, were evaluated and compared to the current production conventional heat treated material. Metallurgical evaluation was performed and showed that the hardness and microstructure of the acicular ferrite - bainitic microalloy was nearly independent of the cooling rate from hot forging and could provide equivalent or better properties as compared to conventional quench and tempered forgings.

The effects of different shot peening parameters on the fatigue life of rear axle hypoid pinion gears were evaluated. Shot hardness, shot size, intensity, shot velocity and prior heat treatment were studied and compared to current production. Metallurgical analysis of the carburized SAE 4320 gears along with residual stress gradient analysis at tooth root fillets were performed. The results showed that significant fatigue life enhancement can be achieved by precision shot peening (directed, air nozzle type) and proper determination and tight tolerance of shot peening process parameters and heat treatment.