FATIGUE BEHAVIOR OF NITRIDED STEELS

The fatigue behaviour of surface strengthened steels can be explained by the concept of local fatigue limit. A damage parameter proposed by Smith, Watson and Topper allows the characterization of the influence of residual stresses on the fatigue limit of notched specimens. The de fect model of Kogaev and Serensen, which is based upon the statistic s trength theory of Weibull, can also be applied to surface strengthened materials, enabling the description of the influences of load, compon ent cross-section and component size on the fatigue strength. Based on the extended concept of the local fatigue limit, the relationship bet ween the structure of nitrided cases and fatigue strength is illustrat ed, and recommendations for materials selection and nitriding conditio ns are derived.