Whereas sharp graphite flakes create stress concentration points within the metal matrix, rounded nodules inhibit the creation of cracks, thus providing the enhanced ductility that gives the alloy its name. In ductile irons, graphite is in the form of nodules rather than flakes as in grey iron. The common defining characteristic of this group of materials is the shape of the graphite. Another micrograph showing the carbon islanding effect, with nodules surrounded by areas depleted of carbonĭuctile iron is not a single material but part of a group of materials which can be produced with a wide range of properties through control of their microstructure. Metallurgy Ductile iron microstructure at 100× magnification, showing carbon islanding effect around nodules. Meehan was awarded a patent in January 1931 for inoculating iron with calcium silicide to produce ductile iron subsequently licensed as Meehanite, still produced as of 2017. On October 25, 1949, Keith Dwight Millis, Albert Paul Gagnebin and Norman Boden Pilling received US patent 2,485,760 on a cast ferrous alloy for ductile iron production via magnesium treatment. While most varieties of cast iron are weak in tension and brittle, ductile iron has much more impact and fatigue resistance, due to its nodular graphite inclusions. Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron and SG iron, is a type of graphite-rich cast iron discovered in 1943 by Keith Millis.
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