Ductile Cast Iron Mechanical Properties

Ductile cast iron, which is also called nodular iron or spheroidal graphite (SG) cast iron, is not a single material but is part of a group of materials which can be produced to have a wide range of properties through control of the microstructure. Nodular cast iron obtains nodular graphite through spheroidization and inoculation treatment, which effectively improves the mechanical properties of the cast iron, especially the plasticity and toughness, so as to obtain higher strength than carbon steel. Nodular cast iron is a high-strength cast iron material. Its comprehensive properties are close to steel. Based on its excellent properties, the ductile iron has been successfully used for casting components of complex forces, strength, toughness and wear resistance. Nodular cast iron has rapidly developed into a cast iron material second only to gray cast iron and widely used. The so-called "substituting iron for steel" mainly refers to ductile iron. Ductile iron is often used to produce parts for crankshafts and camshafts for automobiles, tractors, and internal combustion engines, as well as medium-pressure valves for general machinery.

The common defining characteristic of ductile cast iron is the shape of the graphite. In ductile irons, the graphite is in the form of nodules rather than flakes as it is in grey iron. The sharp shape of the flakes of graphite create stress concentration points within the metal matrix and the rounded shape of the nodules less so, thus inhibiting the creation of cracks and providing the enhanced ductility that gives the alloy its name. The formation of nodules is achieved by the addition of nodulizing elements, most commonly magnesium (note magnesium boils at 1100°C and iron melts at 1500°C) and, less often now, cerium (usually in the form of Mischmetal). Tellurium has also been used. Yttrium, often a component of Misch metal, has also been studied as a possible nodulizer.