Thermal Fatigue Behavior Evaluation of Shot-Peened JIS SKD61 Hot-Work Mold Steel

Abstract

Thermal fatigue cracking is one of the most important failure mechanisms in hot work die steels. Shot-peening can be used in a much wider field to obtain higher static strength, as well as better fatigue resistance. This study investigates the shot-peening effect on the microstructure and mechanical properties of hardened JIS SKD61 hot-work steel. The thermal fatigue test is based on cyclic induction heating and water cooling. A non-peened specimen with a hardness of 510 HV_0.05 was used as the reference material. The scanning electron microscopic observations showed craters on the surface and a severely worked hardened area in the shot-peened specimen subsurface. The microhardness values of the shot-peened surface are about 720 and 750 HV_0.05 for the Almen intensity of 15 A (typical shot-peened specimen) and 18 A (severe shot-peened specimen), respectively. The work hardening depths of typical shot-peened and severe shot-peened specimens are about 20 and 30 µm, respectively. The thermal fatigue properties of shot-peened specimens, including the mean crack length and crack distribution density, are better than those of non-peened specimens. Only a slight improvement in thermal fatigue properties occurred for the severe shot-peened specimen compared with typical shot-peened specimen.