Grain refinement during solidification

Grain refinement during solidification reportedly can also be obtained by additions of reactive elements like alkaline and rare earth elements, such as calcium, barium, yttrium, or nonmetals like Boron [12], In these cases, nuclei for crystallization from the melt are provided by formation of high melting compounds (sometimes intermetallic phases) of these reactive additions with other alloying elements or impurities, particularly oxygen. 

Grain refinement a liquid metal treatment made late in the melting operation to produce a finer and equiaxed grain during solidification. 

Formation of the rare earth compounds facilitates heterogeneous nucleation during solidification which leads to grain refinement. The inclusions are made finer and nearly spherical, and the rare earth additions make them disperse uniformly within the grains, unlike the film-like appearance of MnS along the grain boundary (Kepka et al. 1973, Rowntree et al. 1973). These changes in the microstructure lead to improvement in mechanical properties. 

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