Classification Of Engineering Materials

A large numbers of engineering materials exists in the universe such as metals and non metals (leather, rubber, asbestos, plastic, ceramics, organic polymers, composites and semi conductor). Some commonly used engineering materials are broadly classified as shown in Fig. 4.1. Leather is generally used for shoes, belt drives, packing, washers etc. It is highly flexible and can easily withstand against considerable wear under suitable conditions. Rubber is commonly employed as packing material, belt drive as an electric insulator. Asbestos is basically utilized for lagging round steam pipes and steam pipe and steam boilers because it is poor conductor of heat, so avoids loss of heat to the surroundings. Engineering materials may also be categorized into metals and alloys, ceramic materials, organic polymers, composites and semiconductors. The metal and alloys have tremendous applications for manufacturing the products required by the customers.

Metals and Alloys

Metals are polycrystalline bodies consisting of a great number of fine crystals. Pure metals possess low strength and do not have the required properties. So, alloys are produced by melting or sintering two or more metals or metals and a non-metal, together. Alloys may consist of two more components. Metals and alloys are further classified into two major kind namely ferrous metals and non-ferrous metals.

(a) Ferrous metals are those which have the iron as their main constituent, such as pig iron, cast iron, wrought iron and steels.

(b) Non-ferrous metals are those which have a metal other than iron as their main constituent, such as copper, aluminium, brass, bronze, tin, silver zinc, invar etc.

Ferrous Metals

Ferrous metals are iron base metals which include all variety of pig iron, cast iron wrought iron and steels. The ferrous metals are those which have iron as their main constituents. The ferrous metals commonly used in engineering practice are cast iron, wrought iron, steel and alloy steels. The basic principal raw material for all ferrous metals is pig iron which is obtained by smelting iron ore, coke and limestone, in the blast furnace. The principal iron ores with their metallic contents are shown in Table 4.1

Main Types of Iron

1. Pig iron

2. Cast iron

(A) White cast iron

(B) Gray cast iron

(D) Ductile cast iron

(E) Meehanite cast iron

(F) Alloy cast iron

3. Wrought iron

4. Steel

(A) Plain carbon steels

1. Dead Carbon steels

2. Low Carbon steels

3. Medium Carbon steels

4. High Carbon steels

(B) Alloy steels

1. High speed steel

2. Stainless steel