Abstract
Gray cast iron is used as structural materials for many machines. It has been assumed homogeneous when its strength was evaluated. But it has a composite structure of perlite and graphite. It is necessary to consider its microstructure for accurate strength evaluation of reliable products. In this study, the distribution of graphite was observed by SEM and its area ratio A_G was evaluated in equally divided areas of parallel part of specimen. It was found that high A_G region corresponded to the fracture surface of tensile test. This fact suggests that the position of fracture surface is predictable by the distribution of graphite.
