UNIT TWO: CLASSIFICATION AND PROPERTIES OF METALS AND THEIR ALLOYS
The knowledge of materials and their properties is of great significance for design and manufacturing.
The machine elements should be made of such a material which has properties suitable for the
conditions of operation. In addition to this, a design engineer must be familiar with the effects which the
manufacturing processes and heat treatment have on the properties of the materials. In this chapter, we
shall discuss the commonly used engineering materials and their properties in manufacturing and design.
2.2 CLASSIFICATIONS OF ENGINEERING MATERIALS
The engineering materials are mainly classified as
Metals and their alloys, such as iron, steel, copper, aluminum, etc.
Non-metals, such as glass, rubber, plastic etc.
The metals may be further classified as:
Ferrous metals, and
The ferrous metals are those which have the iron as their main constituent, such as cast iron, wrought
iron and steel.
The non-ferrous metals are those which have a metal other than iron as their main constituent, such
as copper, aluminum, brass, tin, zinc, etc.
We have already discussed that the ferrous metals are those which have iron as their main constituent.
The ferrous metals commonly used in engineering practice are cast iron, wrought iron, steels and alloy
steels. The principal raw material for all ferrous metals is pig iron which is obtained by smelting iron ore
with coke and limestone, in the blast furnace.
The cast iron is obtained by re-melting pig iron with coke and limestone in a furnace known as cupola. It
is primarily an alloy of iron and carbon. The carbon content in cast iron varies from 1.7 per cent to 4.5
per cent. It also contains small amounts of silicon, manganese, phosphorous and sulphur. The carbon in
a cast iron is present in either of the following two forms:
Free carbon or graphite, and
Combined carbon or cementite.