Cast irons differ from each other in their graphite particles shape. Grey iron castings have graphite flakes that are randomly oriented, while ductile iron graphite particles are individual spheres. Compacted graphite iron has graphite particles that are elongated and randomly oriented similar to grey iron, however they are thicker and shorter with rounded edges.
For a more striking differentiation of the three graphite types, viewing can be done using a deep-etch three-dimensional scanning electron micrograph. In comparing the ductile iron or grey iron, the compacted entangled cluster of graphite interlock into the iron matrix providing a strong adhesion. The graphite shape allows for the suppression of crack propagation and initiation and is the origin of enhanced mechanical properties with regard to grey iron as well as better thermal conductivity with regard to the ductile iron.
The development of dependable production methods enabled CGI to be commercially available. The graphite has blunt flakes interconnected within individual cell. The graphite structure and the final iron properties are intermediate between the ductile and gray irons. The compacted shape of the graphite is also known as aggregated flake, quasiflake, vermicular, and semi-nodular graphite.
The CGI production is the same as that of ductile iron in its requirement of close metallurgical control as well as additions of rare earth element. It also requires an additional alloying element like titanium for the minimization of spheroidal graphite formation. CGI retains most of the gray iron castability but with a more enhanced tensile strength and ductility. The matrix structure is adjusted through heat treatment or by alloying.
For a more striking differentiation of the three graphite types, viewing can be done using a deep-etch three-dimensional scanning electron micrograph. In comparing the ductile iron or grey iron, the compacted entangled cluster of graphite interlock into the iron matrix providing a strong adhesion. The graphite shape allows for the suppression of crack propagation and initiation and is the origin of enhanced mechanical properties with regard to grey iron as well as better thermal conductivity with regard to the ductile iron.
The development of dependable production methods enabled CGI to be commercially available. The graphite has blunt flakes interconnected within individual cell. The graphite structure and the final iron properties are intermediate between the ductile and gray irons. The compacted shape of the graphite is also known as aggregated flake, quasiflake, vermicular, and semi-nodular graphite.
The CGI production is the same as that of ductile iron in its requirement of close metallurgical control as well as additions of rare earth element. It also requires an additional alloying element like titanium for the minimization of spheroidal graphite formation. CGI retains most of the gray iron castability but with a more enhanced tensile strength and ductility. The matrix structure is adjusted through heat treatment or by alloying.

