Fatigue crack tip damaging micromechanisms in pearlitic ductile cast irons

In the last years, damaging micromechanisms in ductile cast irons (DCIs) were widely investigated: DCI microstructure (ranging from ferritic–pearlitic DCIs to austempered ones), graphite elements morphology (shape, dimension and distributions) and loading conditions were the main investigated parameters. Focusing on the role played by the graphite nodules, they were considered merely as voids embedded in a metal matrix. Recent analysis underlined that the nodules role in the DCIs damage evolution is more complicated and is influenced by the matrix microstructure. In this work, the crack tip damaging micromechanisms in a pearlitic DCI is investigated considering both fatigue loading conditions and the effects of overloads, focusing the interaction between the crack and the investigated DCI microstructure (pearlitic matrix and graphite nodules). On the basis of experimental results, the applicability of ASTM E399 standard on the characterization of fatigue crack propagation resistance in pearlitic DCIs is critically re-analyzed.