Ductile irons damaging micromechanisms: graphite nodules role investigated by means of image processing procedures

Ductile cast irons (DCIs) combine the good castability of gray irons and the toughness of steels. This is due to their peculiar graphite elements shape, obtained by means of a chemical composition control and not by means of extended annealing treatment of white irons (as in malleable irons). Focusing ferritic matrix, different damaging micromechanisms were identified: graphite nodules role seemed to be more complex than the simple “debonding” micromechanism usually considered in numerical simulations. In this work, a scanning electron microscope (SEM) analysis of metallographically prepared ferritic ductile iron specimens was performed by means of customized image processing procedures, and results were compared with the observed damaging micromechanisms, considering the different graphite nodules solidification mechanisms.