Fatigue crack growth is a major subject of fracture mechanics analysis, and constitutes a key issue in the fields of applied engineering as well as materials science. During recent years extensive fatigue testing of Austempered Ductile Iron (ADI) has been performed at INTEMA. Experiments have been used to examine mechanisms of fatigue initiation, crack growth and coalescence. Interaction of propagating cracks with graphite nodules and microcracks were found to be issues of fundamental importance to understand fatigue crack propagation mechanisms. The aim of this work is to set up a numerical tool based on the Boundary Element Method (BEM) to study the mechanics of fatigue crack propagation in ADI in order to explain the low propagation rates and high effective threshold values measured in this material, when compared with those of steels. Crack propagation is modelled using an incremental crack extension analysis, with crack extensions calculated using a propagation law that accounts for the near-threshold regime. Fracture parameters are computed via the so-called one point displacement formulae using special crack-tip elements. The minimum strain energy criterion is used to determine the direction of the propagation. The methodology proves to be versatile and accurate to account for the interaction effects between cracks, microcraks and nodules. Obtained results allowed to validate fracture mechanics models proposed in the literature as well as give a better insight of the phenomena.