Quantitative Analysis of Solidification of Compacted Graphite Irons – A Modelling Approach

Several X-ray topography studies which have appeared recently in the literature show compacted graphite in cast iron consisting of coarse interconnected graphite lamellas. This suggested that solidification of these alloys could be described as done for irregular eutectics by accounting for limited branching of graphite lamellas. The corresponding growth law has been inserted in appropriate mass balances for describing the successive solidification stages. Predictions of the model thus obtained have been compared to quantitative experimental information previously gained on solidification of a series of hyper-eutectic alloys. The deep undercooling and marked recalescence which are so characteristic of the solidification of compacted graphite cast irons in the stable system are reproduced and appear to be closely related to the limited branching of graphite lamellas in the compacted graphite cells. The competition between stable and metastable solidification could be described and leads to a decrease of the recalescence amplitude that was properly reproduced.