Computational Modeling of Shrinkage Porosity Formation in Spheroidal Graphite Iron: a Proof of Concept and Experimental Validation

Abstract

Prediction of microporosity (microshrinkage) formation in casting alloys continues to be a subject of high interest to metalcasters because failure to avoid this defect results in many instances in rejection of the casting with associated financial loss. It is a complex problem involving multiple material and process variables. Spheroidal graphite (SG) iron castings are particularly vulnerable to this type of defects because of the low mushy zone permeability associated with the late phases of solidification of this iron. A previously developed model that captures some important elements of the physics of the problem, including gas evolution in the melt with increasing fraction of solid and decreasing mushy zone permeability during solidification, was used to calculate the porosity distribution in L-shaped SG iron castings. The calculation results compared well with experimental observation on L-shaped castings. Some disagreements between calculations and experiments are attributed to gas pore migration during solidification, a phenomenon that is not included in the physics described by the model.