Study of Microsegregation Buildup during Solidification of Spheroidal Graphite Cast Iron

This work presents an attempt to describe the complex relationship between the development of the solidification microstructures and buildup of microsegregation in spheroidal graphite (SG) cast irons by coupling an experimental investigation and a modeling approach. Experimental characterization of microsegregation in cast iron was made by means of point counting microanalysis along a grid. With this method, the differences of silicon distribution in alloys solidified in the stable system, the metastable system, or in both systems were clearly evidenced. The distribution of manganese in alloy solidified in the stable system was also investigated. It has been, in particular, observed that alloys solidified in the stable (respectively, metastable) system present significant negative (respectively, positive) segregation of silicon, and that alloys solidified in both systems are much less segregated. The solidification path of these alloys has been conveniently reproduced by means of predictions made with a physical model accounting for the nature of the alloy, either hypoeutectic or hypereutectic, and for the sensitivity to temperature and composition of the partition coefficient of alloying elements.