Abstract
The low strength and the brittleness of cast iron are commonly believed to depend fully upon the notch effect of the graphite, however the graphite in cast iron can be considered also to reduce the effective sectional area of cast iron. In this paper, the authors investigated the influence of graphite-carbon content and the graphite shape on the effective sectional area and the static strength of cast iron.
The effective sectional area of flake graphite cast iron is closely correlated with its graphite-carbon content, and can be estimated by the regression equation between them. Also, it is slightly influenced by the type of graphite distribution. It is far smaller than what is estimated from the volume percentage of its graphite-carbon content, and is only between 15% and 40%. As the graphite shape changes from spheroid to semi-spheroid and to flake, the effective sectional area is influenced largely, and is approximately 80% in case of a spheroidal graphite cast iron, and decreases greatly with the decrease in the degree of graphite spheroidization.
The static strength of cast iron is determined by the product of the effective sectional area and the strength of matrix. The results of the experiment with several holed plates and others showed that the notch effect of graphite hardly influences the static strength of cast iron, and furthermore, possibly enhances the static strength because of the plasticity restriction. Brinell hardness is correlated to the effective sectional area and it increases with the increase of the effective sectional area under the condition in which the hardness of matrix is constant.
