Recently, the demands for developing a new mechanical parts and materials which are not only lighter but stronger are expended because of the trends for higher efficiencies and better performances with light weight. For this reason, many studies have been made for the fatigue strength enhancement by using surface treatment. The laser heat treatment is a good candidate because it uses a controllable heat source and can locally apply the high dense heat energy on the surface and make small heat affected zone (HAZ). However, it changes the material to brittle and it is not allowed in some applications. In this study, the development of new process which is the combination of laser heat treatment and vibration peening is proposed to increase the fatigue strength without changing the material characteristics. The SCM440H is used for the experiments and the specimens were tested until giga cycles with ultrasonic fatigue tester to examine how the material behaves in very high cycles. The results show that the combination of two processes increased the fatigue strength and the different fracture types observed in low and high cycles.
