Effect of coverage and double peening treatments on the fatigue life of a quenched and tempered structural steel

The effects of shot peening treatments comprising different degrees of coverage and also the influence of double treatments applied to a quenched and tempered medium-carbon alloyed steel were analyzed. The latter consisted, in one case, of high intensity peening followed by a lower intensity peening treatment and, in the other, of the removal of the damaged surface layer. Surface roughness, subsurface hardening and the residual stress profiles were determined and compared. Furthermore, the fatigue life corresponding to the different shot peening treatments was assessed on a rotating beam machine under alternative stresses of 50% of the tensile strength of the steel. The full coverage peening treatment gave rise to the best fatigue behavior, as under-coverage produces a heterogeneous surface stress field, while overlong shot peening treatments probably lead to surface damage. On the other hand, double surface treatments are at least partially able to mitigate the surface damage produced by a first high intensity peening treatment. Nevertheless, none of the applied double treatments was able to exceed the fatigue life of the optimal single shot peening.