Mechanisms of Formation of Degenerated Graphite in Lamellar Graphite Cast Iron

The final morphology of graphite and its effect on the physical and mechanical properties of a cast iron, is highly influenced by the complex reactions which occur during the solidification process and its subsequent cooling. Factors such as chemical composition, melting, inoculation process, nodularization treatment or the melt handling techniques play a key role on the formation of graphite. In this research, the morphological changes of graphite in commercial gray irons produced by the involuntary addition of undesirable elements such as Te and Pb coming form charge materials were investigated. A great variety of degeneration graphite was found. Scanning electron microscopy on polished specimens was used to study the kinetics of nucleation and growth of graphite.

Unique features with relevant protuberances growing around the surface of the sheets of graphite were detected for the case of tellurium. Big and large flake graphite acting as central axis on whose sides many secondary nerves are born, were also found. Lamellas of graphite seem to end in a meshed-arborescent graphite favoring the connection between them. Sequential nucleation of graphite on Mn sulfides that have nucleated on complex Mg-Al-Te oxides was documented. These inclusions seem to be the responsible of the particular branching of graphite. The presence of Pb leads to the appearance of a graphite similar to Widmanstätten with multitude of needles and thorns growing around the plates of this degraded graphite.