Evaluation of Toughness of Austempered Ductile Iron by Instrumented Impact Testing

The impact toughness of ductile iron with two graphite nodularity levels (25% and 95% ) was determined in the as cast and in the austempered conditions. impact tests were conducted on unnotched Charpy specimens using an instrumented impact testing machine in the test temperature range:-150 to 300 C. specimens with higher graphite nodularity level exhibited higher impact fracture energy along the entire testing temperature range in both the as cas and he austempered conditions. the effect of graphite nodularity on the fracture energy was more pronounced at high test - temperatures, i.e. within the ductile fracture range. the impact energy values of the austempered specimens were less than those of the as cast specimens, at room temperature, but they exceeded them at higher-test temperatures. load-time traces obtained from instrumented impact tests showed that none of the rest-specimens failed in a complete ductile manner at all test-temperatures and that most of the impact energy was expended in the fracture initiation process. scanning electron microscopy examination of specimens fractured at room temperature reveled cleavage and quasicleavage morphology for the s cast and the austempered conditions, respectively