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

The metallurgical quality of a ductile iron is determined by the components of the metallic charge, as well as by the liquid treatment (spheroidization, inoculation) and the holding temperature and time. All these factors directly affect the nucleation potential of the melt, and consequently the formation of undesired carbides and microshrinkage. The goal of this industrial research was to investigate the effect of holding times in the heating/pouring unit on the microstructure and nucleation propensity of a 3.73% C, 2.53% Si spheroidal graphite iron. Thermal analysis was conducted at different processing times, and metallographic analysis was performed on the thermal analysis cups to evaluate the graphite particle count, the graphite shape parameters, and their size distribution. As expected, longer holding times produced higher amounts of carbides. SEM examination revealed that sulfides and Mg–Si–Al nitrides were the main nuclei. Their evolution in time was evaluated. The improvement of the metallurgical quality by inoculation even after prolonged holding times was demonstrated.