抄録
Various kinds of cast iron containing flaky or spheroidal graphites were subjected to usual tension testing and fracture toughness testing, and their fracture surfaces were examined with a scanning electron microscope. From a viewpoint of fractography, microscopic fracture mechanism of cast iron was discussed.
Most of the fracture surfaces of pearlitic spheroidal graphite cast iron exhibit a river pattern, and the initiating points of microcracks are found in the middle of the matrix away from graphites.
In the case of ferritic or austenitic spheroidal graphite cast iron, their fracture surfaces generally show a dimple pattern formed by coalescence of voids of graphites.
Such distinctly different features in the fractographs can be interpreted based on the correlation between the elastic-plastic stress distribution around graphites and the fracture stress level of matrix material. Furthermore, it was attempted to correlate fracture toughness to the appearance of the fracture surfaces.
