High-cycle and very high-cycle bending fatigue strength of shot peened spring steel

This paper examined bending fatigue strength of shot-peened spring steel under the high cycle fatigue (HCF) and very high cycle fatigue (VHCF), and analyzed the effects of shot-peening on the high strength spring steel through service life. Hourglass shape specimens made of spring steel (Si-Cr alloys) were prepared for the rotary bending fatigue test. Actual local stresses were quantitatively calculated to compensate for the applied stress amplitudes, through which it was clarified that the shot-peening had strongly positive effects on the HCF strength, but rather negative effect on the VHCF strength. The fracturing process examination confirmed that most fish-eye fractures arose at sites deeper than the compressive residual stress zone, which did not prevent the creation of the fish-eye. The fatigue strength improvement in the VHCF range was scarcely expected as a result of the shot-peening treatment.