High cycle fatigue of ion nitrided 40Cr steel specimens

In order to investigate the effect of ion nitration in glow discharge on the high cycle fatigue lives, ion nitrided specimens of Cr-alloyed steel were tested in uniaxial fatigue. The influence of depth of nitration on the fatigue strength is investigated. The experimental investigations were carried out on a bending testing machine in constant amplitude cyclic loading and R=-1 stress condition. X-ray analysis and strain gage approach were used in order to evaluate the residual stresses in the depth and on the surface of the layer. Both approaches are in good agreement. Significant possibilities for increasing the fatigue strength, with about 80%, were observed.