Improvement in fatigue strength of silicon manganese steel SUP7 by using acavitating jet

It is possible to strengthen metallic materials by using a cavitating jet t o introduce compressive residual stress in the material surface, since the impact of collapsing cavitation bubbles peen the surface in the same way as shot peening. In order to demonstrate the improvement in the fatigue stren gth of a material by using a cavitating jet, an experimental study was carr ied out. Silicon manganese steel JIS SUP7 was chosen as a test material, si nce JIS SUP7 is used as a spring material after shot peening. The specimens were exposed to the cavitating jet with upstream pressure p(1) = 20 MPa, d ownstream pressure p(2) = 0.28 MPa, the cavitation number sigma congruent t o p(2)/p(1) = 0.014, the nozzle throat diameter d = 0.842 mm and the stando ff distance s = 31 mm. The scanning speed v at which the compressive residu al stress took the most significant value was 0.25 mm/s. The compressive re sidual stress was introduced in the entire surface peened by the cavitating jet under the above conditions. The fatigue strength of the specimen was i nvestigated by a four point bending test. The minimum bending stress sigma( min) was fixed at 123 MPa and the amplitude of the load was varied. The fat igue strength of material peened by the cavitating jet is shown to be about 440 MPa, which is about 10% stronger than the strength without peening.