Quantitative characterization of ferritic ductile iron damaging micromechanisms: Fatigue loadings

摘要

Due to the peculiar graphite elements shape, Ductile Cast Irons (DCIs) are able to combine the high castability of gray irons with the toughness of steels. This result is obtained by means of a chemical composition control and not by means of an extended, and expensive, annealing treatment of white irons (that is necessary to obtain malleable irons). Focusing ferritic DCIs, different damaging micromechanisms should be investigated considering both ferritic matrix and the role played by graphite nodules: according to the observed micromechanisms, it is evident that graphite nodules role can't be summarized with a simple "debonding", usually considered as the only effective in numerical simulations. In this work, damaging micromechanisms in fatigue loaded ferritic DCI specimens were investigated by means of Scanning Electron Microscope (SEM) during the fatigue test ("in situ" tests). Focusing graphite nodules, customized image processing procedures were optimized in order to quantify the evolution of damaging micromechanisms with the loading cycles number.