EFFECT OF MELT PRECONDITIONING INOCULATION TREATMENT ON DUC- TILE CAST IRON STRUCTURE FORMATION IN THIN-WALLED CASTINGS
DOI:
https://doi.org/10.15407/plit2026.03.048Keywords:
ductile cast iron, spheroidal graphite, microstructure, melt preconditioning, graphite powder, inoculation, cementite, thin-walled castingAbstract
Ductile cast iron chemical composition is one of the key factors governing its microstructure and the required level of mechanical properties. Ensuring a large number of spheroidal graphite nod- ules uniform distribution in cast iron microstructure is an essential aspect of the melt processing technology. The influence of melt preconditioning treatment as the inoculation enhancing factor on the microstructure formation at ductile cast iron castings producing – particularly thin-walled ones –manufactured with using a complex ferrosilicon-magnesium-calcium master alloy at ladle spheroidizing treatment of the melt was investigated in this article. Graphite powder, ferrosilicon FeSi75 and FeSi-based inoculants containing Ba and Ca were used as preconditioning reagents. It was established that the highest efficiency of melt preconditioning in furnace was achieved with graphite powder usage. Its adding to the melt in furnace suppresses the chilling tendency and reduces free cementite formation in ductile cast iron castings with wall thicknesses of 5 mm and above, and promotes metallic matrix ferritization. The results demonstrate that such precondition- ing intensifies formation of graphite nucleation sites (the number of graphite inclusions increases in 2-2.5 times) with a higher spheroidization degree and increased dispersion (its size reduces by 1.5-2 times) in castings with wall thicknesses ranging from 3 to 10 mm. Preconditioning of the base melt allows to form a more homogeneous microstructure with a uni- form distribution of spheroidal graphite nodules and is a basic condition for the ductile cast iron mechanical properties improving by 15-30 %. Furthermore, free cementite absence in microstruc- ture eliminates the graphitizing annealing process usage that makes it possible to save up to 150 kWh of energy per ton of castings, thereby improving the production process economic efficiency.
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