Mechanism of Damage of Ferritic Ductile Iron, Influence of Matrix Heterogeneity

Ferritic ductile cast iron (FDI) microstructure is composed by graphite nodules embedded in a ferritic matrix. It is usual to assume that the ferritic matrix is homogeneous. However, the experimental analysis shows impurities and in some cases a high degree of heterogeneity. It is necessary to investigate the influence of these heterogeneities on the mechanical properties of FDI.This work focusses on the characterization of the elastoplastic properties of different zones of the ferritic matrix of FDI and the identification of the sequence and extent of the damage mechanisms at the micro-scale under uniaxial tensile loading.The methodologies for the characterization of the material micro constituents and micro-segregated zones involve nano-indentation and atomic force microscopy techniques in combination with computational modelling. The analysis is performed by applying inverse analysis algorithms proposed in the literature. The microsegregated zones are identified by using color etching. The assessment of the micro-scale damage mechanisms was performed by in-situ optical microscopy observation of tensile tests of very small specimens.The results led to the quantification of the differences in mechanical properties along the metallic matrix as a result of the existing heterogeneities and allow for a better understanding of the ductile iron damage mechanism.