Hardness is a very important property of the metals and has a wide variety of meanings. It embraces many different properties such as resistance to wear, scratching, deformation and machinability etc. It also means the ability of the metal to cut another metal.
The hardness is usually expressed in numbers which are dependent on the method of making the test.

Ferrous Metals The Ferrous metals are those which have the iron as their main constituent, such as cast iron, wrought iron and steel.

Non-ferrous metals The non-ferrous metals are those which have a metal other than iron as their main constituent, such as copper, aluminium, brass, tin, zinc etc.