Effect of Shot-Peening Process on Fatigue Strength of Austenite Stainless Steel.

It is well known that the shot peening process is often used industrially for the purpose of improvement of the fatigue strength of many kinds of steels. Generally the surface of these steels subjected to this process is hardened and addition to it, the compressive residual stress is also induced on the surface layer. In this study, the fatigue tests of shot-peened steel SUS 304 were conducted using the rotating-bending fatigue test machine, and residual stresses were detected by X-ray stress measurement. And surface characteristics related to residual stress σR, hardness and microstructure are also investigated to clarify the influential factors on the bending fatigue strength of stainless steel SUS 304 by shot peening. As a result, the surface layer was hardened by the shot peening process and the strain-induced transformation was ascertained by X-ray analysis. And residual stresses were almost released at the initial time during fatigue cycles. Concerned about work hardening, it is also studied precisely. We found that the increments of hardness was attributed to both martensitic transformation and hardness of austenite itself, and then the bending fatigue strength of austenitic stainless steel with shot peening process was improved by twenty percents. Consequently, it is found that the increments of hardness by the shot peening are mainly due to hardness of austenite structure itself, and it affects the improvement of the fatigue strength of the shot peened austenite stainless steel.