Notch Effects on Impact and Bending Characteristics of Ferritic Spheroidal Graphite and Compacted Vermicular Graphite Cast Irons

This study aims to clarify the effects of external notch on the impact and bending characteristics of spheroidal graphite cast iron (FDI) and compacted vermicular graphite cast iron (FCV) whose matrix was fully-ferritized by annealing. From each sample we produced five kinds of Charpy-type specimens by adding five kinds of notches whose stress concentration factor (α) varied from 1 (un-notched) to 4.8. They were applied for instrumented Charpy impact testing at the temperature range between 98 K to 423 K and also for three-point-bend testing under a slow loading speed at room temperature. The test results of the Charpy impact testing and bend testing showed that the absorbed energy decreases greatly in the range of α from 1 to 2.3 but decreases slightly in the range of α larger than 2.3 in both samples. The results of energy analysis showed that the decreasing tendency of the absorbed energy by adding notches is mainly caused by the decreasing tendency of crack-initiation energy. The degree of influence of the external notches on toughness was found to be larger in the case of FDI than in the case FCV, and also larger in impact testing than in bend testing.