Page 126 - WCS - Electrical

WORKSHOP CALCULATION & SCIENCE - CITS

EXERCISE 11 : Engineering Materials

Types of metals
The metals is of two types:
1 Ferrous metal 2 Non-ferrous metal
1 Ferrous metals : The metals that contains major part of iron and contain carbon sre called ferrous metals
such as pig iron, mild steel, nickel etc., they have iron properties such as rusting, magnetisations etc.
2 Non-ferrous metals : The metals that do not contains iron or carbon and do not have the property of iron are
called non-ferrous metals such as copper, aluminum etc.
Ferrous and Non ferrous alloys
Alloying metals and ferrous alloys
An alloy is formed by mixing two or more metals together by melting.
For ferrous metals and alloys, iron is the main constituent metal. Depending on the type and percentage of the
alloying metal added, the property of the alloy steel will vary.
Metals commonly used for making alloy steels
Nickel (Ni)

This is a hard metal and is resistant to many types of corrosion rust.
It is used in industrial applications like nickel, cadmium batteries, boiler tubes, valves of internal combustion
engines), engine spark plugs etc. The melting point of nickel is 1450°C. Nickel can be magnetised. In the
manufacture of permanent magnets a special nickel steel alloy is used. Nickel is also used for electroplating.
Invar steel contains about 36% nickel. It is tough and corrosion resistant. Precision instruments are made of Invar
steel because it has the least coefficient of expansion.
Nickel-steel alloys are available containing nickel from 2% to 50%.
Chromium (Cr)

Chromium, when added to steel, improves the corrosion resistance, toughness and hardenability of steel.
Chromium steels are available which may contain chromium up to 30%.
Chromium, nickel, tungsten and molybdenum are alloyed for making automobile components and cutting tools.
Chromium is also used for electroplating components. Cylinder liners are chrome-plated inside so as to have
wear resistance properties. Stainless steel contains about 13% chromium. Chromium-nickel steel is used for
bearings. Chrome-vanadium steel is used for making hand tools like spanners and wrenches.

Manganese (Mn)
Addition of manganese to steel increases hardness and strength but decreases the cooling rate.
Manganese steel can be used to harden the outer surface for providing a wear resisting surface with a tough core.
Manganese steel containing about 14% manganese is used for making agricultural equipment like ploughs and
blades.
Silicon (Si)
Addition of silicon for alloying with steel improves resis-tance to high temperature oxidation.

This also improves elasticity, and resistance against corrosion. Silicon alloyed steels are used in manufacturing
springs and certain types of steel, due to its resistance to corrosion. Cast iron contains silicon about 2.5%. It
helps in the formation of free graphite which promotes the machineability of cast iron.

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