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F. Iacoviello et alii, Frattura ed Integrità Strutturale, 34 (2015) 406-414; DOI: 10.3221/IGF-ESIS.34.45 406 Focussed on Crack Paths Degenerated graphite nodules influence on fatigue crack paths in a ferritic ductile cast iron Francesco Iacoviello, Vittorio Di Cocco Università di Cassino e del Lazio Meridionale, DiCeM, via G. Di Biasio 43, 03043 Cassino (FR), Italy iacoviello@unicas.it , v.dicocco@unicas.it A BSTRACT . Focusing on ferritic-pearlitic DCIs, these alloys are characterized by a microstructure that ranges from a fully ferritic to a completely pearlitic matrix, and they are widely used for many applications (e.g. wheels, gears, crankshafts in cars, exhaust manifolds, valves, flywheels, boxes bearings, hubs, shafts, valves, flanges, pipelines ...). Considering the graphite elements, their morphology can be considered as degenerated when its nodularity is too low and this can be due to different causes (e.g., a partially failed nodularization process or a wrong inoculant). In this work, a ferritic DCI with degenerated nodules was obtained by means of an annealing treatment and the fatigue crack propagation resistance was investigated by means of fatigue crack propagation tests performed according to ASTM E647, focusing on the influence of degenerated graphite nodules on the fatigue crack paths. This analysis was performed both analysing the crack path profile by means of a scanning electron microscope (SEM) and by means of a SEM fracture surfaces analysis. K EYWORDS . Ferritic-pearlitic ductile cast irons; Fatigue damaging mechanism; Degenerated graphite elements. I NTRODUCTION ue to their interesting mechanical properties and good castability, DCIs are widely used in the automotive parts (e.g., crankshafts, truck axles, etc.), and in many other application, like pumps, pipes or turbine components [1, 2]. DCIs can be considered as natural composites, with graphite nodules embedded in a metal matrix. The DCIs performances are strongly affected by the graphite elements morphological peculiarities (e.g., graphite elements nodularity, volume fraction, density, distribution, dimension). The most common metallurgical defects in DCIs can be classified as follows [3]:  Exploded graphite, mainly due to an excess of rare earth additions, Fig. 1;  Chunky graphite, due to an excess of rare earth additions, Fig. 2;  Compacted graphite, mainly due to low residual magnesium and/or rare earth (high temperatures or long holding time), Fig. 3;  Spiky graphite, due to very small amounts of lead which have not been neutralised by rare earth;  Graphite flotation, which potential causes can be high carbon equivalent, excess of pouring temperature, slow cooling rate in thicker sections or an insufficient inoculation;  Surface structure, due to a sulphur excess in moulding sand;  Nodule alignment, due to the presence of large dendrites, with nodules aligned between arms of dendrite; D