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Engineering Materials and their Properties
2
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The machine elements should be made of such a material which has properties suitable for the
conditions of operation
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In this note, we shall discuss the commonly used engineering materials and their properties in
Machine Design

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2 Classification of Engineering Materials
The engineering materials are mainly classified as :
1
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2
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The metals may be further classified as :

(a) Ferrous metals, and (b) Non-ferrous metals
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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
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The best material is one which serve the desired objective at the
minimum cost
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Availability of the materials,
2
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The cost of the materials
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We shall now discuss
the physical and mechanical properties of the material in the following article
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4 Physical Properties of Metals
The physical properties of the metals include luster, colour, size and shape, density, electric and
thermal conductivity, and melting point
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These mechanical properties of the metal include
strength, stiffness, elasticity, plasticity, ductility, brittleness, malleability, toughness, resilience,
creep and hardness
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Strength
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The internal resistance offered by a part to an externally applied force is called
*stress
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Stiffness
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The modulus of
elasticity is the measure of stiffness
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Elasticity
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This property is desirable for materials used in tools and
machines
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4
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It is property of a material which retains the deformation produced under load
permanently
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5
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It is the property of a material enabling it to be drawn into wire with the

application of a tensile force
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The ductility is
usually measured by the terms, percentage elongation and percentage reduction in area
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Note : The ductility of a material is commonly measured by means of percentage elongation
and percentage reduction in area in a tensile test
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Brittleness
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It is the property of breaking
of a material with little permanent distortion
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These steels can be easily welded and machined
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are required in fabrication, steel having 0
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With increasing carbon, it is possible by hardening and
tempering to obtain tensile strength in the range of 600 to 900 N/mm2, combined with

reasonable toughness and ductility
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Also, with the higher carbon range in
the hardened and lightly tempered condition, tensile strength of about 1600 N/mm2 may be
developed with lowered ductility
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However, these
steels are not suitable for shafts and parts working in contact with non-ferrous metals (i
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brass, bronze or gun metal bearings) and with graphite packings, because electrolytic corrosion
is likely to occur
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Therefore, they are used for cutlery, springs, surgical and dental instruments
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In fact, creep resistance of these steels at this temperature is not superior
to that of mild steel
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2
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The steels containing greater amount of chromium (from 16 to 18

per cent) and about 0
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These steels have

better corrosion resistant property than martensitic stainless steels
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However, in the softened condition, they possess

good ductility and are mainly used as sheet or strip for cold forming and pressing operations
for purposes where moderate corrosion resistance is required
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They are ferro-magnetic, usually undergo excessive grain growth during prolonged

exposure to elevated temperatures, and may develop brittleness after electric arc resistance or

gas welding
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However, resistance to scaling and corrosion at elevated temperatures are usually better
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Note: When nickel from 1
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5 per cent is added to 16 to 18 per cent chromium steel, it not
only makes more

resistant to corrosion than martensitic steel but also makes it hardenable by heat treatment
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Thus, it is widely used for pump shafts, spindles and valves as
well as for many other fittings where a good combination of mechanical and corrosion
properties are required
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Austenitic stainless steel
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There are many variations in chemical composition of

these steels, but the most widely used steel contain 18 per cent chromium and 8 per cent nickel
with carbon content as low as possible
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These

steels cannot be hardened by quenching, in fact they are softened by rapid cooling from about
1000°C
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These steels are very tough and can be forged and rolled but offer great difficulty in machining
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This susceptibility to corrosion (called intercrystalline corrosion or weld
decay) may be removed by softening after welding by heating to about 1100°C and cooling
rapidly
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Since 18/8 steel provide excellent

resistance to attack by many chemicals, therefore, it is extensively used in chemical, food, paper
making and dyeing industries
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A number of heat resisting steels have been developed
as discussed below :

1
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These steels contain 0
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The main application of

these steels are for superheater tubes and pipes in steam plants, where service temperatures are
in the range of 400°C to 500°C
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Valve steels
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4% C, 8% Cr, 3
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5% C, 8% Cr, 3
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5% Mo) are used for automobile valves
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For aeroplane engines and marine diesel engine valves, 13/13/3 nickelchromium-tungsten valve steel is usually used
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Plain chromium steel
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These steels are very good for oxidation resistance at high temperatures as compared to their
strength which is not high at such conditions
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4
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These steels have good mechanical properties at high
temperatures with good scaling resistance
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Other carbide forming
elements such as molybdenum or tungsten may also be added in order to improve creep

strength
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2
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The carbon steel cutting tools do not retain their sharp cutting edges under heavier
loads and higher speeds
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This temperature would soften the carbon tool steel and thus the tool
will not work efficiently for a longer period
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Most of the high speed steels contain tungsten as the chief alloying element, but
other elements like cobalt, chromium, vanadium, etc
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Following are the different types of high speed steels:
1
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This steel, on an average, contains 18 per cent tungsten, 4 per cent
chromium and 1 per cent vanadium
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It is widely used for drills, lathe, planer and shaper tools, milling cutters, reamers,
broaches, threading dies, punches, etc
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Molybdenum high speed steel
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It has excellent toughness

and cutting ability
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It is particularly used for drilling and tapping operations
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Super high speed steel

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