Relation between microstructural heterogeneities and damage mechanisms of a ferritic spheroidal graphite cast iron during tensile loading

In this work, the influence of the metallic matrix heterogeneities and the spheroidal graphite nodules distribution on both crack initiation and propagation and damage evolution during tensile loading of ferritic spheroidal graphite cast iron is examined. The experimental methodology involves specialized metallographic techniques, step by step tensile loading, microscopic observation by using optical and scanning electron microscopy and three-dimensional (3D) reconstruction of the graphite nodules distribution. The results show that the graphite nodules are the major heterogeneities responsible for inducing the development of cracks in the metallic matrix. Crack initiation is preferentially located at the irregular contour of graphite nodule cavities, ferritic grain boundaries and internodular areas highly strained. The final fracture involves cracks mainly propagating through the internodular ligaments of matrix-nodule debonded areas belonging to the first-to-freeze zones resulting from the solidification process.