Abstract
The effect of slit depth on the impact value of austempered spheroidal graphite cast iron was studied. The principal results and conclusions are as follows:
(1) The impact value could not be improved, though the tensile strength was raised by austempering treatment.
(2) The impact value decreased as the slit depth and the angle of the fall of a pendulum increased.
(3) Dimple rupture, which consists of both large dimples originating from graphites and small ones occurring from inclusions, was mainly observed on the impact fracture surface in ferrite structure. Also the cleavage facets were observed on the surface with an increase in slit depth.
(4) Quasi-cleavage pattern was observed on the surface of austempered or upper bainitic structure. The number of graphite particles on the fracture surface was less than that on the ferrite one.
