Microscopic approach to micromechanism of damage in spheroidal cast iron.

In this work, the observations of the fracture surface after standard tensile tests of several kinds of spheroidal cast irons, ferritic and austempered ductile irons, have been carried out by means of scanning electron microscopy. The local crack path in the area of graphite (G)/matrix (M) interface has been analyzed as affected by a matrix phase composition and the austempering treatment parameters. The obtained results allowed identifying some determination factors for debonding mode at the G/M interface and their role in a final damage mechanism. Some microstructural details in the microregions composed of graphite and matrix showed that the G-M debonding mode in the separation area of the G/M interface seems to be controlled by macroscopic properties of the alloy and by the morphology of G/M interface. On the other hand, the internal destruction of graphite nodule has been mainly determined by a structure and anisotropy of graphite crystal lattice.