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Ductile iron discovery in 1948 gave a new lease on life to the cast ironfamily. In fact these cast irons are characterised both by a high castability and by hightoughness values, combining cast irons and steel good properties. Ductile cast ironsare also characterised by high fatigue crack propagation resistance, although thisproperty is still not widely investigated.In the present work we considered three different ferritic-pearlitic ductile cast irons,characterised by different ferrite/pearlite volume fractions, and an austempered ductilecast iron. Their fatigue crack propagation resistance was investigated in air by meansof fatigue crack propagation tests according to ASTM E647 standard, considering threedifferent stress ratios (R = Kmin/Kmax = 0.1; 0.5; 0.75). Crack surfaces were extensivelyanalysed by means of a scanning electron microscope both considering a traditionalprocedure and performing a quantitative analysis of 3D reconstructed surfaces, mainlyfocusing graphite nodules debonding mechanisms and considering the microstructureinfluence.