Notch Effects on Impact and Bending Characteristics of Spheroidal Graphite and Compacted Vermicular Graphite Cast Irons with Various Matrices

The object of this study is to find out and evaluate systematically how the basic factors such as graphite-shape, external notch and matrix-characteristic affect the impact and bending characteristics of cast irons. The Spheroidal Graphite (SG) and Compacted Vermicular graphite (CV) cast iron samples were prepared, and their matrixes were modified into ferritic, pearlitic and bainitic in order to make the various kinds of samples whose graphite-shape and matrix vary widely. From each sample we produced five kinds of Charpy-type specimens by adding five kinds of notches whose stress concentration factor (a) varied from 1.0 (un-notched) to 4.8. The Charpy impact value decreases greatly in the range of a from 1 to 2.3 but decreases slightly in the range of a larger than 2.3. No influence to the fracture energy in the range of a larger than 2.3. Increasing of a results in moderate elevation of transition temperature of Charpy impact value and the transition temperature of CV cast ion is lower than that of SG one. The impact value in brittle fracture region of the cast iron samples were recognized to be a little bit larger than that of cast steel sample, and it was considered to be caused by graphite which act as a kind of buffer effect against crack growth in brittle fracture.