Influence of the Holding Time in the Heating/Pouring Unit on the Metallurgical Quality of Spheroidal Graphite Iron

The final metallurgical quality of a ductile iron is determined by the components of the metallic charge, as well as by the liquid treatment, the melting temperature, and the holding time. All these factors directly affect the nucleation potential of the melt, and therefore the formation of carbides and microshrinkage. The goal of this industrial research was to investigate the effect of different holding times in the heating/pouring unit, on the microstructure and nucleation propensity for a 3.73% C, 2,53% Si spheroidal graphite iron. Cooling curves were recorded, and metallographic analysis was conducted on TA cups to evaluate the nodule count, the shape parameters of graphite and their size distribution. As expected, longer holding times produced higher amounts of carbides. Sulfides and Mg-Si-Al nitrides were detected as the main nuclei through SEM study. Their evolution in time was evaluated. The improvement of the metallurgical quality by inoculation was demonstrated.