Ductile Iron is a kind of cast iron. It has been known for its impact and fatigue resistance, elongation, and wear resistance due to the spherical (round) graphite structures in the metal. Ductile Iron can also be named as ductile cast iron, spheroidal graphite cast iron, or nodular cast iron.
Both ductile iron and cast iron have graphite in them. If you look closely (use high-power microscope with 100x magnification or more) at regular cast iron, you can see the graphite bits look like squiggly lines called “flakes.” When you look at the graphite in ductile cast iron, while, they look like little spheres or nodules (so the spheroidal graphite iron and nodular iron names).
We give Keith Millis credit for creating ductile iron back in 1943. He and his buddies Albert Gagnebin and Norman Pilling received US patent 2,485,760 and US Patent 2,485,761 for making ductile iron using magnesium (Mg) in the metallurgy (the metal composition or what was in the secret recipe) to get the graphite to line up into spheres.
Millis was not the first person to strengthen common cast iron. We still cast Meehanite® castings today. Augustus Meehan patented the Meehanite process back in January of 1931. Meehan used calcium silicide to also produce similar nodules to what is in ductile iron.
Ductile iron has become one of the most popular types of iron casting. Development of ductile iron continued into the 1950s, making the process of ductile iron casting better leading to acceptance of ductile iron, acceptance proven out by the nine-fold increase in use during the 1960s as an engineered material for commercial applications.