Article – Nodule Count, End of Solidification Cooling Rate, and Shrinkage Porosity Correlations in High Silicon Spheroidal Graphite Iron


Nodule Count, End of Solidification Cooling Rate, and Shrinkage Porosity Correlations in High Silicon Spheroidal Graphite Iron

Gorka Alonso, Doru Michael Stefanescu, Beñat Bravo, Gorka Zarrabeitia and Ramon Suarez



High-silicon spheroidal graphite (SG) irons present higher changes of density during the solidification process when compared to normal SG irons. This special behavior is particularly significant in the last stages of solidification, where the graphite expansion may become insufficient to compensate the contraction of the austenite and the risk of microporosity formation increases. The goal of this laboratory research was to establish correlations between the different levels of nodule count obtained using five commercial inoculants, the cooling rate at the end of solidification, and the shrinkage porosity propensity. The analysis was conducted on thermal analysis cups that were sectioned and evaluated for microstructure by optical metallography and by 2D analysis with the Image J software to quantify the size of the microporosity region. It was found that a higher nodule count, associated with higher cooling rate at the end of solidification, generates lower porosity. SEM analysis was conducted to study the nature of nuclei. Complex (MgSiAl)N nitrides were found as the main nucleation sites for graphite.




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