Ductile iron

Steels
Phases
Ferrite Austenite Cementite Martensite Graphite
Microstructures
Spheroidite Pearlite Bainite Ledeburite Tempered martensite Widmanstätten structures
Classes
Crucible steel Carbon steel Spring steel Alloy steel Maraging steel Stainless steel High-speed steel Weathering steel Tool steel
Other iron-based materials
Cast iron Gray iron White iron Ductile iron Malleable iron Wrought iron

Ductile iron, also known as ductile cast iron, nodular cast iron, spheroidal graphite iron, spheroidal graphite cast iron^[1] and SG iron, is a type of graphite-rich cast iron discovered in 1943 by Keith Millis.^[2] 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.

Augustus F. Meehan was awarded U.S. patent 1,790,552 in January 1931 for inoculating iron with calcium silicide to produce ductile iron subsequently licensed as Meehanite, still produced as of 2024^[update]. In October 1949 Keith Dwight Millis, Albert Paul Gagnebin and Norman Boden Pilling, all working for INCO, received U.S. patent 2,485,760 on a cast ferrous alloy using magnesium for ductile iron production.^[3]