Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths

Urko de La Torre (1) , Jacques Lacaze (2) , Jon Sertucha (1)

1 Azterlan - Centro de Investigación Metalúrgica
2 CIRIMAT - Centre interuniversitaire de recherche et d'ingenierie des matériaux

Use of rare earths, high silicon and carbon contents, and low cooling rates are reported as possible reasons for formation of chunky graphite in ductile iron castings. The understanding of this graphite degeneration is however limited, and the above conclusions are still controversial. To get further insight into this topic, ductile cast iron melts have been prepared with various carbon and silicon contents and using nodularizing alloys with various rare earth levels. These melts have been cast in blocks with different sizes to include also the effect of cooling rate on graphite degeneration. Metallographic investigation revealed that the chunky-affected areas enlarge when decreasing the cooling rate, when increasing the silicon content and without low-level addition of rare earth. In the discussion, a schematic based on change of liquid/graphite interfacial energy with alloying elements is proposed which describes the conditions for the formation of chunky graphite instead of nodular graphite.

Mots clés: Ductile cast iron; Heavy section casting; Chunky graphite; Rare earth; Silicon

Domaines: Matériaux; Science des matériaux [cond-mat.mtrl-sci]; Génie des procédés; Matériaux

Urko de La Torre, Jacques Lacaze, Jon Sertucha. Chunky graphite formation in ductile cast irons: effect of silicon, carbon and rare earths. International Journal of Materials Research, 2016, 107 (11), pp.1041-1050. ⟨10.3139/146.111434⟩. ⟨hal-01581076⟩