Examples of Chunky Graphite Formation in Production of Ductile Iron Castings and Effective Countermeasures

Papers since 1956 on chunky graphite (CHG) formation in the production of ductile iron castings were reviewed by authors. On the topic of spheroidal graphite nucleation in liquid iron, many theories have been reported to date. The most prevailing are divided into two groups. One is the heterogeneous nucleus theory, and the other is the gas bubble theory. The focus of this paper is the evaluation of papers based upon what the auditors have previously called “the site theory” which proposes that graphite nucleates and grows in a magnesium gas bubble. Based upon that theory, the causes of CHG were summarized, and the countermeasures were designed. The site theory was found to not only explain the mechanism for graphite spheroidization but also its degeneration. The results reviewed were applied in foundry practice. In this paper, the examples of CHG formation and the effective countermeasures are introduced. The site theory helped to understand complex phenomena of CHG formation.