Fatigue strength of shot-peened nitrided steel: Optimization of process parameters by means of design of the experiment

There is a general interest in increasing the fatigue strength of materials. Shot-peening and nitriding are the two processes commonly used in order to increase the fatigue strength of steel-notched components. These two processes are often used separately. The effect of a combination of both processes has not been thoroughly investigated so far. The purpose of the present investigation was two-fold: first, the authors verified whether further improvements can be achieved by a combination of the two treatments; second, the optimal process parameters were determined in order to obtain the maximal increase in fatigue strength. Fatigue tests were conducted on unnotched and notched nitrided and shot-peened 32CrMoV13 steel specimens. Several process variables were tested. Tests were designed based on the criteria of the Design of the Experiment (DOE). Three-level experiments were used in order to determine the optimal set of process parameters. It was found that the combination of nitriding and shot-peening could be applied successfully in order to increase the fatigue limit when extreme performance is sought in notched components.