Effect of graphite morphology on decarburized cast iron

The decarburization of cast irons graphite has been studied as part of the process to make high-value-added cast iron. The aim is to develop new uses for cast irons. Once the graphite has been eliminated in a surface layer by high temperature oxidation in air, other materials conferring improved properties can be infiltrated into the resulting pores. The effects of holding time (3-48h), holding temperature (1023-1223K) and chemical composition (3.27-4.0%C, 2.0-4.0%Si) were investigated for each graphite morphology (flake graphite, compacted graphite, spheroidal graphite). As a result, it was found that the rate of formation of porosity (due to the decomposition of graphite) in cast iron obeyed the diffusion law. The rate of formation of porosity in flake graphite irons was faster than that for the other graphite morphologies, probably because flake graphite is continuous in the matrix, whereas spheroidal graphite exists as independent deposits. It has been found that the continuity of the graphite has a strong effect on the rate of formation of porosity.