Solidification front

Front side of the crystallization area that shifts towards the thermal center of the casting during the progress of solidification. The solidification front may be either smooth- or coarse-walled (s. Solidification type). That area of the solidification front that comprises both solid and liquid phases is referred to as solidification band.

Formation of the solidification front depends on solidification conditions and the content quantity of dissolved elements. In the proximity of the solidification front, the melt does not have a consistent chemical composition. 

Solidification front in cast iron
The areas solidifying first contain less carbon and other alloying elements. The interdendritic spaces are enriched with carbon and alloying elements. The resulting slight differences in concentration are referred to as primary segregation, crystal segregation (micro segregation).