A Comparative Study of Graphite Growth in Cast Iron and in Analogous Systems

Crystallization of graphite during the solidification and cooling of cast iron to room temperature has been the object of relentless, yet often inconclusive research. The importance of the subject cannot be underestimated, as graphite morphology is a major player in establishing the mechanical and physical properties of cast iron. Graphite crystallization is a complex phenomenon controlled by melt composition, local melt supersaturation, melt temperature and temperature gradient (cooling rate). All these are wide-ranging variables in the casting process. The results of a major effort to understand the complexity of graphite crystallization in cast iron is presented in this comparative study of crystal growth in materials with crystal morphologies similar to that of graphite. The analysis includes that of analogous materials such as eutectic aluminum–silicon and nickel carbon alloys, growth of other hexagonal or tetragonal crystals such as ice crystals and Al3Ti in aluminum–titanium alloys, growth of graphite through other processing routes such as chemical vapor deposition (a gas-to-solid transformation), and heat treatment of carbon steel (a solid-to-solid transformation), and the previous information on the crystallization of carbon in cast irons. An exhaustive analysis of the most widely accepted models for graphite growth is also presented.