malleable cast iron

Malleable cast iron is a type of cast iron that has been heat-treated to increase its ductility. Standard cast iron, while strong, is brittle. Malleable cast iron is produced by annealing white cast iron, a process that converts hard cementite into graphite in a nodular form. This transformation results in a material that is more ductile than white iron or ordinary gray iron, which contains graphite in flake form.1

White cast iron, a precursor to malleable cast iron, has a high carbon content and all its carbon exists as cementite (Fe₃C), giving it a bright fracture surface. It is too hard to be machined and must be ground to shape, limiting its applications to areas requiring wear resistance. The primary use of white iron is as the starting material for malleable cast irons.2

Malleable cast iron is widely used in agricultural and engineering machinery. More recently, ductile irons, also known as spheroidal graphite (SG) irons, have been developed. These irons have graphite in spherical nodules, making them strong and malleable, and are often preferred over steel castings and forgings for parts like gears and crankshafts.23