Abstract
Although cavitation impacts normally cause damage in hydraulic machinery, the impacts can strengthen metallic materials as same as shot peening (SP). In case of peening by cavitation impacts, the shots are not required, thus the peening is called "cavitation shotless peening (CSP)". In older to figure out the mechanism of the improvement of life time of forging die treated by CSP, residual stress and hardness were measured with and without CSP. Tested materials were tool alloy steel SKD61. It was revealed that the residual stress of the surface treated by CSP was more compressive than that of not peened specimen and still kept compressive after heat treatment.
