Inocculation treatment:
A most significant and very new inocculation treatment is that of adding up small quantities of magnesium to cast iron to generated ductile iron. The addition of as little as 0.04 % residual magnesium alters the graphite flakes to almost ideal spheroids with incredible improvement in mechanical properties of the alloy. A metallurgically same phenomenon to the magnesium treatment of ductile iron is the sodium inocculation of aluminium-silicon alloys. In this minute quantities of sodium alter a needle as Al2Si precipitate to a finely divided eutectic structure. This treatment has been in use for various years. It substantially developed the ductility of aluminium silicon alloys having more than approximate 8 to10 % silicon.
This is known that the action of these inocculants is because of more than just alloying effect. Two melts along analytically identical final chemical composition might produce extremely different microstructures based on the time, temperature and kind of inocculating additions. Distinctive of this is the graphitization inoculation of cast iron; a ferrosilicon addition created late in the melting operation is a far more influence graphitizer than a same addition made previous. The influence of inocculants seem to be because of more subtle causes than chemistry; for instance, grain refiners and graphitizers possibly promote nucleation in the melt by introducing "foreign" nuclei into the liquid metal.
Other inocculants such like those that manufacture ductile iron might change the surface tension of solidifying particles and so alter nucleation and/or growth.