Effect of antimony on primary graphite growth in cast iron - From Ab-initio calculations to experimental observations

Chunky graphite - interconnected strings of graphite - is a common degenerate form of nodular graphite associated with the use of rare-earth for melt treatment. Being rare-earth scavenger, antimony is used to eliminate chunky graphite in large castings while it leads to other degenerate forms in small castings. In the present work, both theoretical and experimental approaches of the effect of antimony on graphite growth were attempted. Ab initio calculations of graphite layers and of 11 21 twin boundary showed the graphite structure is modified by Sb absorption, with the twin angle being smoothed and the graphite curved. Experiments were performed with carbon saturated Fe-C-Sb alloys where primary graphite precipitates appeared as long thin curved lamellae contrasting with the thick and straight plates obtained in Fe-C alloys. This similarity in curving effect of Sb at both scales is quite striking as there are four orders of magnitude separating the calculations from the metallographic observations