Ductile Iron is also known as Nodular Cast Iron or Spheroidal Graphite Iron. Rich as graphite cast iron, it throws a wide range of applications. Keith Dwight Millis is credited for the discovery of this product in 1943. The US patent for its commercial production was obtained by Keith Dwight Millis, Albert Paul Gagnebin and Norman Boden Pilling jointly on a Cast Ferrous Alloy through magnesium treatment.
In 1931 Augustus F Meehan received a patent for inoculating iron with calcium silicide, nothing but an inorganic compound, a silicide of calcium that is either dark greyish or whitish prone to decomposition on contact with moisture particularly hot water though insoluble in water. Extremely inflammable, it is capable of igniting at regular atmospheric temperature to turn out ductile iron licensed in the name of ‘Meehanite’.
The applications of ductile iron are now recognized internationally. In India, it has been used commercially for the last five decades, the manufacturing of which began in the early 90’s.
Ductile Iron isn’t a single material as the name may indicate, but a group of materials having a range of properties depending on the micro-structure. The most important feature of ductile iron is the nodular shape of graphite molecules like in the case of cast iron, also termed as grey iron; however, the graphite’s shape is nodular compared to the flake form as in the case of grey iron or cast iron. Because cast iron possesses sharp graphite flakes within the metal matrix, it results in crack formation in the metal unlike nodular graphite which does not.
When it comes to ductile iron, because the graphite is nodular in shape, the stress is eliminated such that the end product becomes elastic or ductile in nature. Thus, ductile iron is not vulnerable to damage and cracks and highly resistant. This characteristic of ductile iron is due to magnesium treatment: magnesium functions only as a catalyst; this makes ductile iron as a non-corrosive and unbreakable product. Although Mild Steel (MS) is also unbreakable, it is extremely corrosive when exposed to natural oxidation and galvanic corrosion, and hence its overall life is less than that of ductile iron and cast iron. Therefore, ductile iron has a competitive edge over mild steel as well as cast iron. The chemical composition of ductile iron, as a material, is Carbon (C), Silicon (Si), Manganese (Mn), Magnesium (Mg), Phosphorous (P), Sulphur (S), Copper (Cu) and Iron (Fe).