Grey Cast Iron: It is obtained by allowing the molten metal to cool and solidify slowly. On solidifying the iron contains the greater part of carbon in the form of graphite flakes. The grey colour is due to the fact that the carbon is present in the form of free graphite.
When filing or machining, cast iron makes our hand black, then it shows that free graphite is present in cast iron. It has a low tensile strength, high compressive strength and no ductility.
It can be easily machined. Avery good property of grey cast iron is that the fee graphite in its structure acts as a lubricant Due to this reason. it is very suitable for those parts where sliding action is desired.
The grey cast iron castings are widely used for machine tool bodies, automobile cylinder blocks, pipes and pipe fittings and agricultural implements. The main advantages in favour of its use are, (i) Its cheapness(ii) Its low melting temperature 1150C-1200C.