| The goal of this dissertation was to develop a comprehensive 3-D fluid flow and solidification numerical model applicable to the production of spheroidal graphite (SG) cast iron. A further goal was to provide the experimental data required to validate the model.; A numerical model was developed to describe the solidification phenomena. The model is divided into macro and micro phenomena stages. The macro phenomenon stage includes solution of the macrotransport equations, namely energy, momentum, and mass conservation equations. This stage includes solid particle movement and macrosegregation calculations and it is coupled with the micro stage through the latent heat evolution from kinetic solidification. Two steps are considered in the model; the first one, before grain coalescence, the austenitic grains, the graphite nodules, and the remained liquid are moving; the second one, after grain coalescence, when only the interdendritic liquid is moving. The micro phenomenon stage covers micromodeling of solidification kinetic, which is intended to describe the present understanding of the solidification process of SC cast iron. It includes graphite particle growing from the liquid, before the eutectic reaction, and through the austenite shell, during eutectic reaction. Austenite dendrites nucleate and grow independently of the graphite and its influence on the solidification is quantified. Carbide formation is also presented. To the author's best knowledge, carbide formation through inverse segregation is predicted for the first time. Microsegregation of carbon and silicon is calculated and their influence on the whole solidification process is accounted for.; Extensive experimental work was performed to develop the database required for model validation. Experimental results are presented from an instrumented thin-wall casting with plate thickness varying from 2 to 7 mm produced with hypereutectic ductile iron alloy. Cooling curves are presented along with maps for each plate containing distribution of nodule diameter, nodule count, sphericity, and ferrite, and carbide percent. Experimental results are suitable to be used as benchmark to study solidification process using thin-wall castings.; Reasonable agreement between the simulation and the experimental results was demonstrated. The developed model is suitable for hypereutectic, hypoeutectic and eutectic SG cast iron alloys. |
