Inocculation:
It is the addition made to a melt that modify the solidification structure of gray iron. It involves the utilization of certain materials that, while added to molten iron previous to casting, make higher quality, more predictable, gray and ductile iron castings. Its primary reasons are to develop the mechanical properties and the machinability of iron castings. Most commonly Inocculants are 70-90% ferrosilicon blended along calcium (0.50% minimum) and aluminum (1.0-1.4%). At times, the molten metal might be inocculated with graphite to adjust carbon content or treated along calcium carbide to drop off the sulphur content.
In grain-refining aluminium alloys less than 0.2 %, titanium or 0.02 % boron is enough to drop off the cast grain size of the alloy from as much as 0.10 in diameters to as short as 0.005 in diameter. Magnesium aluminium alloys are rather anomalous; most other cast metals tend to exhibit a coarser grain structure while they are superheated high above their melting point. Magnesium alloys that usually do not have aluminum are grain refined along little additions of zirconium. Magnesium-aluminium alloys are grain refined through small additions of carbon to the melt, or by superheating the metal to approximate 165oF.
A slight different kind of inocculation treatment is the graphitizing inocculation of gray cast iron. Here the inocculant promotes graphite formation and it is utilized to prevent "chilling" (formation of white iron in thin sections) and to ignore the unwanted "interdendritic graphite" structure that sometimes forms on quick cooling. Common graphitizers working are nickelsilicon, ferrosilicon, silicon-manganese-zirconium and calcium-manganese-silicon. These inocculants ought to be added late in the melting operation or their efficiency is diminished.