Font Size: 

Due to its proved effectiveness shot peening is one of the most widely used surface treatments to alleviate fatigue, rolling contact fatigue, fretting, stress corrosion cracking mechanical components. Generally, shot peening is applied as last treatment and follows the application of some surface hardening process, most of times carburizing. Less investigated is the application of nitriding followed by shot peening. In this paper the fatigue crack growth properties of a nitrided shot-peened steel is dealt with: different peening intensities were considered and the resulting residual stresses measured by means of an X-ray diffractometer. Rotating bending fatigue tests were executed on specimens including a micro blind hole, acting as a pre-existent crack. The broken specimens were observed with a SEM to detect the crack growth initiation point. The run-out specimens were broken after the test and the presence of nonpropagating cracks detected. The results allowed determining the threshold of propagation of the nitrided and of nitrided and shot peened material. It was also possible to put into relation the crack initiation point with the applied and the residual stresses.