Very high cycle fatigue behavior of shot-peened 3Cr13 high strength spring steel

The effect of shot peening (SP) on the very high cycle fatigue behavior of 3Cr13 high strength spring steel was investigated. The samples that underwent electro-polishing (EP) and SP treatments were analyzed at 20. kHz by ultrasonic fatigue tests. The results showed that subsurface crack initiation occurred in both types of specimens at low stress amplitude. A fine granular area (FGA) was also observed in the vicinity of the inclusion. The stress intensity factor range at the front of the FGA was regarded as the threshold value that controls the stable internal crack propagation. The S-. N curve decreased in very high cycle regime for both types of specimens, and the fatigue life for the subsurface initiation of the SP specimens was reduced compared with that of the EP specimens. Furthermore, the fatigue life of the internal crack in the FGA was estimated based on the crack propagation rate assuming Paris' law. Considering the tensile residual stress in the interior of the SP specimens, the prediction of the S-. N curves on the mean size of the non-metallic inclusions were consistent with the experimental results.