Abstract
To reveal the role of graphite nodules in the pearlitic spheroidal graphite cast iron at impact and fatigue fracture, samples with varied graphite nodule number (Nm) but with a constant carbon content were tested and compared to see the difference between normalized and unnormalized conditions. As to the samples of unnormalized condition, with increasing Nm, the upper shelf absorbed energy of impact test became lower and transition temperature of absorbed energy became higher. It was shown from the measurement of graphite nodule number on the fracture surface (Nf) and Nf/Nm ratio that the effects observed in impact test were ascribed to the role of graphite nodules serving as the origin of ductile fracture and to the presence of eutectic cell boundaries which correspond to Nm. It was also found that there is a good correlation between the value of energy for crack propagation and the Nf/Nm ratio and that the crack path in fatigue fracture is related to the intensity of cyclic stress.
