Pearlitic Ductile Cast Irons: Fatigue Initiation Micromechanisms

Damaging micromechanisms in Ductile Cast Irons (DCIs) are strongly affected both by the matrix microstructure and by the graphite nodules morphology peculiarities (e.g., nodularity level, dimension, distribution etc.). The role played by the graphite nodules depends on the matrix microstructure and by the loading conditions (e.g., static, quasi-static or cyclic loadings): although,in the past, matrix – graphite nodules debonding was considered as the unique damaging micromechanism and graphite nodules were considered analogously to mere voids embedded in metal matrix, recent experimental results showed the presence of an internal mechanical properties gradient inside the graphite nodules and other damaging micromechanisms have been identified (e.g., “onion-like mechanism). In this work, the fatigue damaging micromechanisms in a pearlitic DCI have been investigated by means of scanning electron microscope and digital microscope observationsof the lateral surfaces of notched specimens during a fatigue tests.