Cast Iron and Grey Cast Iron: 

Cast iron has the carbon content more than the carbon content in steel. Making it very hard and abrasion resistant.

Grey cast iron is very similar in composition and properties to the crude pig iron produced by the blast furnace. It does not require the complex and costly refinement processes of steels and, therefore, pro­vides a useful low-cost engineering material Cast irons contain substantially more than the 1.7 % carbon that forms the upper limit for plain carbon steels. In fact, the distinguishing characteristic of cast irons is their uncombined or 'free' carbon content. In grey cast iron the free carbon appears as flakes of graphite as shown in Figure  . It is these flakes of graphite which give grey cast iron its characteristic colour when fractured, its `dirtiness' when machined and its weakness when subjected to a tensile load. The graphite also promotes good machining characteristics by acting as an internal lubri­cant and also producing an easily disposable discontinuous chip. The cavities containing the flake graphite have a dampening effect upon vibrations - cast iron is non-resonant - and this property makes it particularly suitable for machine tool frames and beds.