Abstract
Cavitation Shotless Peening (CSP) is a new method of surface modification. Cavitation impacts induced by collapses of cavitation bubbles produce compressive residual stress and work hardening on the material surface. In the case of CSP, shots were not required and that is why we call it Cavitation Shotless Peening. At CSP, cavitation was induced by high-speed submerged water jet with cavitation, i.e., a cavitating jet, whose intensity and occurring region of cavitation impacts could be controlled by parameters such as upstream pressure and nozzle size. The authors have already revealed that lifetime of forging die treated by CSP was extended by about 50% compared with the non-peened forging die. In this paper, in order to make clear the mechanism of increase of lifetime of forging die, alloy tool steel (JIS SKD61) was tested both in non-peened and peened conditions. Compressive residual stress was measured by an X-ray diffraction method. Comparison between the non-peened specimen and cavitation shotless peened specimen revealed that improved mechanical properties leading to longer life-time of the forging die were favourable in CSP.
