Cavitation shotless peening for surface modification of alloy tool steel

Cavitation Shotless Peening (CSP) is a new method of surface modification. Cavitation impacts induced by the collapse of cavitation bubbles produce compressive residual stress and work hardens the material surface. In the case of CSP, shots are not required and therefore we call it Cavitation Shotless Peening. In CSP, cavitation is induced by a submerged high-speed water jet, i.e., a cavitating jet, for which the intensity and region of cavitation impact can be controlled by parameters such as the upstream pressure and nozzle size. The authors have already shown that the lifetime of forging die treated by CSP can be extended by about 50% compared with non-peened forging die. In this paper, in order to make clear the mechanism by which the lifetime of forging die is increased, an alloy tool steel (JIS SKD61) was tested both in peened and non-peened conditions. Compressive residual stress was measured by an X-ray diffraction method. It was evident from a comparison between the non-peened specimen and the cavitation shotless peened specimen that CSP improved the mechanical properties of the forging die thus giving it a longer lifetime.