Evolution of the Metallurgical Quality of Spheroidal Graphite Iron during the Thermal Cycle of the Melt: Furnace – Ladle – Heating/Pouring Unit

The final properties of a ductile iron and its nucleation potential are determined by the different processes undergone by the melt from the melting in furnaces until the mold filling. The goal of this industrial research was to investigate the evolution of the metallurgical quality for a spheroidal graphite iron during its thermal cycle: furnace – ladle – heating/pouring unit (HPU). Cooling curves were recorded, and metallographic analysis was conducted on thermal analysis cups not inoculated, to evaluate the nodule count, the shape parameters of graphite and their size distribution. A clear loss of metallurgical quality was found during the whole manufacturing process. Extreme conditions on the HPU produces an evident degeneration of graphite. Ti carbonitrides and sulfides were detected as the main nuclei through SEM study. A significant decrease in the number of oxides was observed with holding times. Vaporization and oxidation of Mg seem to be the origin.