Some observations on the structure of Spheroidal graphite in Nodular cast irons

Graphite nodules in cast irons are found to exist in two different forms. One form, called spherulitic, is believed to occur in annealed white irons in which sulphur exists predominantly as iron sulphide(FeS); the other, called flake-aggregate type, is believed to occur when sulphur in these white irons exits predominantly as manganese sulphide (MnS) and when no irons sulphide (Fes) is present. The graphite in nodular cast irons is observed to be of the spherulitic type. It is of flake-aggregate type nodules in these irons. In cerium-treated irons, however, the occurrence of “quasi-flake” graphite has been reported.