Font Size: 

Short fatigue crack nuclei in austempered ductile cast iron have been studiedusing optical microscopy, scanning electron microscopy, electron backscatter diffractionanalysis and X-ray microtomography. The aim of the investigation was to determine themechanisms of crack initiation, propagation and arrest, with the objective of developing amicrostructure fracture mechanics model for the statistical distribution of the fatigueendurance limit.Short fatigue cracks nucleate at graphite nodules in rising load fatigue tests. The cracknuclei are arrested and retarded by barriers in the microstructure, by either blocking ofslip at phase boundaries or the requirement for tilt and twist of the {111} crystallographiccrack at the prior austenite grain boundaries. The most significant barriers are the prioraustenite grain boundaries. The size of the defects such as graphite nodules and porosityand the size of the prior austenite grains control the largest crack nucleus that can develop,and hence determine the fatigue limit.