Abstract
In order to investigate the infiuence of graphite nodule on impact fracture characteristics of ferritic spheroidal graphite iron, Charpy impact test and fractographical study of the fracture surface were carried out on irons with varried carbon content and constant nodule size. On conducting the Charpy impact test, total absorbed energy was divided into two absorbed energies by using an instrumented impact tester, that is, crack initiation energy and propagation energy were determined from load-time curves. On fractographical study, the ductile and brittle fracture surfaces were observed with a scanning electron microscope.
Void nucleation occurs at the graphite structures of the ductile cast iron that failed in a ductile manner at high temperature, and the graphite nodules facilitate the growth and coalescence of voids. Therefore, increasing the number of graphite nodules lowers the ductile impact value in all cases. Under the condition of brittle fracture at low temperature, cleavage crack initiates at the eutectic cell boundary. Graphite structures arrest the continuous propagation of a crack and causes the crack to branch.
