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Although shot peening is an old technology, it has been revived in the Japanese automotive industry as a means to enhance the fatigue durability of steel components. Particular emphasis is on the application of “hard shot peening”. “Hard shot peening” is a high intensity peening technology which results in a higher magnitude of compressive residual stress and, therefore, greater fatigue resistance than conventional shot peening. The first area of development was in high performance carburizing steels suitable for hard shot peening. Desirable traits were enhanced by reducing the carburizing anomalies resulting from intergranular oxidation and by the enhancing case toughness. Further improvement of fatigue resistance has been accomplished by dual peening, first with hard shot followed by smaller diameter steel shot at a lower intensity. This paper also describes the development of long life shot media for hard shot peening.

Based on fundamental research about the influence of chemical composition on rolled bar hardness, hardenability, case hardenability, cold formability, and mechanical properties, a new case hardening steel has been developed which can be cold forged without spheroidizing annealing. The steel contains boron and the Si and Mn contents are less than conventional steels. The steel shows fatigue strength equivalent to the conventional steels and better toughness and machinability.