The cast iron is obtained by re-melting pig iron with coke and limestone in a furnace known as a cupola. It is an alloy of iron and carbon. The carbon contents in cast iron differ from 1.7% to 4.5%. Also, it contains a very small amount of silicon, sulfur, manganese, and phosphorus.

Carbon is present in the following two forms:

Free carbon or graphite
Combined carbon or cementite

Following are the important properties of cast iron that make it a valuable material for engineering purposes.

Low cost.
Good casting characteristics.
High compressive strength.
Wear resistance.
Excellent machinability.

The cast iron compressive strength is greater than tensile strength.

Following are the values of the ultimate strengths of cast iron.

Tensile – 100 to 200 N/mm2
Compressive – 400 to 100 N/mm2
Shear – 120 N/mm2

Types of Cast Iron
The following are types of cast iron used for engineering purposes:

Grey cast iron
White cast iron
Chilled cast iron
Mottled cast iron
Malleable cast iron
Nodular cast iron
Alloy cast iron

#1 Grey Cast Iron
Grey cast iron is commercial iron has the following compositions:

It consists of Carbon – 3 to 3.5%, Silicon – 1 to 2.75%, Manganese – 0.40 to 1%, Phosphorus – 0.15 to 1%, Sulphur – 0.02 to 0.15% and the remaining is iron.

The grey color is due to the fact that carbon is present as free graphite. Grey cast iron can be easily machined because it has high compressive strength, low tensile strength, and no ductility.

A good property of grey cast iron is that free graphite in its structure acts as a lubricant. For this reason, it is highly suitable for parts where sliding action is desired. The grey iron castings are broadly used for machine tool bodies, pipes and pipe fittings, automobile cylinder blocks, and agricultural implements.

Read more: TYPES OF CAST IRON [EXPLAINED WITH MATERIAL COMPOSITION]