Cast Iron and Ductile Iron: Cheap, Castable, Capable

Cast iron - Fe-C-Si with more than 2.1 percent C - is the largest tonnage of all ferrous cast metals because it is cheap, fluid and readily cast into complex shapes. Its properties hinge on how carbon appears: as flakes (grey iron, good damping, poor toughness), as nodules (ductile/spheroidal-graphite iron, good strength and ductility) or as carbides (white iron, hard and wear-resistant).

Morrogh (1948) first produced nodular graphite by adding cerium/magnesium, creating ductile iron with tensile strengths of 400-900 MPa and real elongation - enabling crankshafts, pipes and wind components. The physical metallurgy of cast iron (solidification of the stable Fe-C and metastable Fe-Fe3C systems, the "iron-carbon double diagram") was systematised by Lacaze and Nestor (1997). Malleable and compacted-graphite (CG) irons fill intermediate needs.

Selection: grey iron (for example GG25/HT250) for machine beds; ductile iron (for example GGG40/QT450) for fatigue-loaded parts; wear irons for liners. JLHSteel supplies cast-iron bar and finished castings and can advise grade-to-load matching.

References
1. Morrogh, H. (1948). The production of nodular graphite structures in cast iron. Journal of the Iron and Steel Institute 158: 306-327.
2. Lacaze, J., Nestor, J. (1997). The physical metallurgy of cast iron. Materials Characterization 39(2-5): 1-9.
3. ASM Handbook, Volume 1 (1990). ASM International.