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16 ^ A Textbook of Machine Design
2.1 Introduction
The knowledge of materials and their properties is of
great significance for a design engineer. 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 Machine Design.
2.2 Classification of Engineering Materials
The engineering materials are mainly classified as :
1. Metals and their alloys, such as iron, steel,
copper, aluminium, etc.
2. Non-metals, such as glass, rubber, plastic, etc.
The metals may be further classified as :
( a ) Ferrous metals, and ( b ) Non-ferrous metals.
Engineering Materials and
their Properties
_1. Introduction.
- Classification of Engineering_ _Materials.
- Selection of Materials for_ _Engineering Purposes.
- Physical Properties of_ _Metals.
- Mechanical Properties of_ _Metals.
- Ferrous Metals.
- Cast Iron.
- Alloy Cast Iron.
- Effect of Impurities on Cast Iron.
- Wrought Iron.
- Steel.
- Effect of Impurities on Steel.
- Free Cutting Steels.
- Alloy Steels.
- Stainless Steel.
- Heat Resisting Steels.
- Indian Standard Designation of High Alloy Steels (Stainless Steel and Heat Resisting Steel).
- High Speed Tool Steels.
- Indian Standard Designation of High Speed Tool Steel.
- Spring Steels.
- Heat Treatment of Steels.
- Non-ferrous Metals.
- Aluminium.
- Aluminium Alloys.
- Copper.
- Copper Alloys.
- Gun Metal.
- Lead.
- Tin.
- Bearing Metals.
- Zinc Base Alloys.
- Nickel Base Alloys.
- Non-metallic Materials._
C H A P T E R
Engineering Materials and their Properties ^ 17
- The word ‘ferrous’ is derived from a latin word ‘ferrum’ which means iron.
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, aluminium, brass, tin, zinc, etc.
2.3 Selection of Materials for
Engineering Purposes
The selection of a proper material, for
engineering purposes, is one of the most difficult
problem for the designer. The best material is one
which serve the desired objective at the minimum
cost. The following factors should be considered
while selecting the material :
1. Availability of the materials,
2. Suitability of the materials for the work-
ing conditions in service, and
3. The cost of the materials.
The important properties, which determine the
utility of the material are physical, chemical and mechanical properties. We shall now discuss the
physical and mechanical properties of the material in the following articles.
2.4 Physical Properties of Metals
The physical properties of the metals include luster, colour, size and shape, density, electric and
thermal conductivity, and melting point. The following table shows the important physical properties
of some pure metals.
A filament of bulb needs a material like tungsten which can withstand high temperatures without undergoing deformation.
Copper
Aluminium
Zinc
Iron (^) Lead
Valuable Metals
Engineering Materials and their Properties ^ 19
6. Brittleness. It is the property of a material opposite to ductility. It is the property of breaking
of a material with little permanent distortion. Brittle materials when subjected to tensile loads, snap
off without giving any sensible elongation. Cast iron is a brittle material.
7. Malleability. It is a special case of ductility which permits materials to be rolled or hammered
into thin sheets. A malleable material should be plastic but it is not essential to be so strong. The
malleable materials commonly used in engineering practice (in order of diminishing malleability) are
lead, soft steel, wrought iron, copper and aluminium.
8. Toughness. It is the property of a material to resist fracture due to high impact loads like
hammer blows. The toughness of the material decreases when it is heated. It is measured by the
amount of energy that a unit volume of the
material has absorbed after being stressed upto
the point of fracture. This property is desirable
in parts subjected to shock and impact loads.
9. Machinability. It is the property of a
material which refers to a relative case with
which a material can be cut. The machinability
of a material can be measured in a number of
ways such as comparing the tool life for cutting
different materials or thrust required to remove
the material at some given rate or the energy
required to remove a unit volume of the
material. It may be noted that brass can be
easily machined than steel.
10. Resilience. It is the property of a
material to absorb energy and to resist shock
and impact loads. It is measured by the amount
of energy absorbed per unit volume within
elastic limit. This property is essential for
spring materials.
11. Creep. When a part is subjected to
a constant stress at high temperature for a long
period of time, it will undergo a slow and
permanent deformation called creep. This
property is considered in designing internal
combustion engines, boilers and turbines.
12. Fatigue. When a material is
subjected to repeated stresses, it fails at
stresses below the yield point stresses. Such
type of failure of a material is known as
* fatigue. The failure is caused by means of a
progressive crack formation which are usually
fine and of microscopic size. This property is
considered in designing shafts, connecting rods, springs, gears, etc.
13. Hardness. It 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 a metal to cut another metal. The hardness is usually
Gauge to show the pressure applied.
Ball is forced into the surface of the ordinary steel
Screw to position sample
Brinell Tester : Hardness can be defined as the resis- tance of a metal to attempts to deform it. This ma- chine invented by the Swedish metallurgist Johann August Brinell (1849-1925), measure hardness precisely.
- For further details, refer Chapter 6 (Art. 6.3) on Variable Stresses in Machine Parts.
20 ^ A Textbook of Machine Design
expressed in numbers which are dependent on the method of making the test. The hardness of a metal
may be determined by the following tests :
( a ) Brinell hardness test,
( b ) Rockwell hardness test,
( c ) Vickers hardness (also called Diamond Pyramid) test, and
( d ) Shore scleroscope.
2.6 Ferrous Metals
We have already discussed in Art. 2.2 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 principal iron ores
with their metallic contents are shown in the following table :
Table 2.2. Principal iron ores.
Iron ore Chemical formula Colour Iron content (%)
Magnetite Fe 2 O 3 Black 72 Haematite Fe 3 O 4 Red 70 Limonite FeCO 3 Brown 60–
Siderite Fe 2 O 3 (H 2 O) Brown 48
2.7 Cast Iron
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
contents 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:
1. Free carbon or graphite, and 2. Combined car-
bon or cementite.
Since the cast iron is a brittle material, therefore,
it cannot be used in those parts of machines which are
subjected to shocks. The properties of cast iron which
make it a valuable material for engineering purposes
are its low cost, good casting characteristics, high
compressive strength, wear resistance and excellent
machinability. The compressive strength of cast iron is
much greater than the tensile strength. Following are
the values of ultimate strength of cast iron :
Tensile strength = 100 to 200 MPa*
Compressive strength = 400 to 1000 MPa
Shear strength = 120 MPa
- 1MPa = 1MN/m^2 = 1 × 10^6 N/m^2 = 1 N/mm^2
Coke burns to carbon monoxide which releases the iron from the ore
Iron ore, coke and limestone are loaded into the furnace
Waste gas used as fuel
Waste gas used as fuel
Slag, or impurities, floats to the top of the iron Smelting : Ores consist of non-metallic elements like oxygen or sulphur combined with the wanted metal. Iron is separated from the oxygen in its ore heating it with carbon monoxide derived from coke (a form of carbon made from coal). Limestone is added to keep impurities liquid so that the iron can separate from them.
22 ^ A Textbook of Machine Design
are chilled at their outer skin by contact of the molten iron with the cool sand in the mould. But on
most castings, this hardness penetrates to a very small depth (less than 1 mm). Sometimes, a casting
is chilled intentionally and sometimes chilled becomes accidently to a considerable depth. The
intentional chilling is carried out by putting inserts of iron or steel (chills) into the mould. When the
molten metal comes into contact with the chill, its heat is readily conducted away and the hard surface
is formed. Chills are used on any faces of a casting which are required to be hard to withstand wear
and friction.
4. Mottled cast iron. It is a product in between grey and white cast iron in composition, colour
and general properties. It is obtained in castings where certain wearing surfaces have been chilled.
5. Malleable cast iron. The malleable iron is a cast iron-carbon alloy which solidifies in the
as-cast condition in a graphite free structure, i. e. total carbon content is present in its combined form
as cementite (Fe 3 C).
It is ductile and may be bent without breaking or fracturing the section. The tensile strength of
the malleable cast iron is usually higher than that of grey cast iron and has excellent machining
qualities. It is used for machine parts for which the steel forgings would be too expensive and in
which the metal should have a fair degree of accuracy, e. g. hubs of wagon wheels, small fittings for
railway rolling stock, brake supports, parts of agricultural machinery, pipe fittings, door hinges,
locks etc.
In order to obtain a malleable iron castings, it is first cast into moulds of white cast iron. Then
by a suitable heat treatment ( i. e. annealing), the combined carbon of the white cast iron is separated
into nodules of graphite. The following two methods are used for this purpose :
1. Whiteheart process, and 2. Blackheart process.
In a whiteheart process , the white iron castings are packed in iron or steel boxes surrounded by
a mixture of new and used haematite ore. The boxes are slowly heated to a temperature of 900 to
950°C and maintained at this temperature for several days. During this period, some of the carbon is
oxidised out of the castings and the remaining carbon is dispersed in small specks throughout the
structure. The heating process is followed by the cooling process which takes several more days. The
result of this heat treatment is a casting which is tough and will stand heat treatment without fracture.
In a blackheart process , the castings used contain less carbon and sulphur. They are packed in
a neutral substance like sand and the reduction of sulphur helps to accelerate the process. The castings
are heated to a temperature of 850 to 900°C and maintained at that temperature for 3 to 4 days. The
carbon in this process transforms into globules, unlike whiteheart process. The castings produced by
this process are more malleable.
Notes : ( a ) According to Indian standard specifications (*IS : 14329 – 1995), the malleable cast iron may be either whiteheart, blackheart or pearlitic, according to the chemical composition, temperature and time cycle of annealing process. ( b ) The whiteheart malleable cast iron obtained after annealing in a decarburizing atmosphere have a silvery-grey fracture with a heart dark grey to black. The microstructure developed in a section depends upon the size of the section. In castings of small sections, it is mainly ferritic with certain amount of pearlite. In large sections, microstructure varies from the surface to the core as follows : Core and intermediate zone : Pearlite + ferrite + temper carbon Surface zone : Ferrite. The microstructure shall not contain flake graphite.
- This standard (IS : 14329-1995) supersedes the previous three standards, i. e. ( a ) IS : 2107–1977 for white heart malleable iron casting, ( b ) IS : 2108–1977 for black heart malleable iron casting, and ( c ) IS : 2640–1977 for pearlitic malleable iron casting.
Engineering Materials and their Properties ^ 23
( c ) The blackheart malleable cast iron obtained after annealing in an inert atmosphere have a black fracture. The microstructure developed in the castings has a matrix essentially of ferrite with temper carbon and shall not contain flake graphite.
( d ) The pearlitic malleable cast iron obtained after heat-treatment have a homogeneous matrix essentially of pearlite or other transformation products of austenite. The graphite is present in the form of temper carbon nodules. The microstructure shall not contain flake graphite.
( e ) According to IS: 14329 – 1995, the whiteheart, blackheart and pearlitic malleable cast irons are designated by the alphabets WM, BM and PM respectively. These designations are followed by a figure indicating the minimum tensile strength in MPa or N/mm^2. For example ‘WM 350’ denotes whiteheart malleable cast iron with 350 MPa as minimum tensile strength. The following are the different grades of malleable cast iron :
Whiteheart malleable cast iron — WM 350 and WM 400 Blackheart malleable cast iron — BM 300 ; BM 320 and BM 350 Pearlitic malleable cast iron — PM 450 ; PM 500 ; PM 550 ; PM 600 and PM 700
6. Nodular or spheroidal graphite cast iron. The nodular or spheroidal graphite cast iron is
also called ductile cast iron or high strength cast iron. This type of cast iron is obtained by adding
small amounts of magnesium (0.1 to 0.8%) to the molten grey iron. The addition of magnesium
In a modern materials recovery plant, mixed waste (but no organic matter) is passed along a conveyor belt and sorted into reusable materials-steel, aluminium, paper, glass. Such recycling plants are expensive, but will become essential as vital resources become scarce.
Household mixed waste, containing steel (mainly food cans), paper, plastics aluminium and glass
Steel objects are carried away on conveyor belt for processing
Second conveyor belt made of chains
Electromagnet removes iron and steel
Magnetized drum holds aluminium
Glass falls through chains and is sorted by hand into three colour-brown, green and clear
Powerful fans blow paper into wire receptacles
Plastic waste is carried away for processing
Note : This picture is given as additional information and is not a direct example of the current chapter.
Engineering Materials and their Properties ^ 25
gears, automobile parts like cylinders, pistons, piston rings, crank cases, crankshafts, camshafts, sprock-
ets, wheels, pulleys, brake drums and shoes, parts of crushing and grinding machinery etc.
2.10 Effect of Impurities on Cast Iron
We have discussed in the previous articles that the cast iron contains
small percentages of silicon, sulphur, manganese and phosphorous. The
effect of these impurities on the cast iron are as follows:
1. Silicon. It may be present in cast iron upto 4%. It provides the
formation of free graphite which makes the iron soft and easily
machinable. It also produces sound castings free from blow-holes,
because of its high affinity for oxygen.
2. Sulphur. It makes the cast iron hard and brittle. Since too much
sulphur gives unsound casting, therefore, it should be kept well below
0.1% for most foundry purposes.
3. Manganese. It makes the cast iron white and hard. It is often
kept below 0.75%. It helps to exert a controlling influence over the
harmful effect of sulphur.
4. Phosphorus. It aids fusibility and fluidity in cast iron, but
induces brittleness. It is rarely allowed to exceed 1%. Phosphoric irons
are useful for casting of intricate design and for many light engineering
castings when cheapness is essential.
2.11 Wrought Iron
It is the purest iron which contains at least 99.5% iron but may contain upto 99.9% iron. The
typical composition of a wrought iron is
Carbon = 0.020%, Silicon = 0.120%, Sulphur = 0.018%, Phosphorus = 0.020%, Slag = 0.070%,
and the remaining is iron.
The wrought iron is produced from pig iron by remelting it in the puddling furnace of
reverberatory type. The molten metal free from impurities is removed from the furnace as a pasty
mass of iron and slag. The balls of this pasty mass, each about 45 to 65 kg are formed. These balls
are then mechanically worked both to squeeze out the slag and to form it into some commercial
shape.
The wrought iron is a tough, malleable and ductile material. It cannot stand sudden and excessive
shocks. Its ultimate tensile strength is 250 MPa to 500 MPa and the ultimate compressive strength is
300 MPa.
It can be easily forged or welded. It is used for chains, crane hooks, railway couplings, water
and steam pipes.
Phosphorus is a non-metallic element. It must be stored underwater (above), since it catches fire when exposed to air, forming a compound.
Wrought Iron
A close look at cast iron
Iron is hammered to remove impurities
Slabs of impure iron
Polarized light gives false-colour image.
26 ^ A Textbook of Machine Design
2.12 Steel
It is an alloy of iron and carbon, with carbon content up to a maximum of 1.5%. The carbon
occurs in the form of iron carbide, because of its ability to increase the hardness and strength of the
steel. Other elements e. g. silicon, sulphur, phosphorus and manganese are also present to greater or
lesser amount to impart certain desired properties to it. Most of the steel produced now-a-days is
plain carbon steel or simply carbon steel. A carbon steel is defined as a steel which has its properties
mainly due to its carbon content and does not contain more than 0.5% of silicon and 1.5% of manganese.
The plain carbon steels varying from 0.06% carbon to 1.5% carbon are divided into the following
types depending upon the carbon content.
1. Dead mild steel — up to 0.15% carbon
2. Low carbon or mild steel — 0.15% to 0.45% carbon
3. Medium carbon steel — 0.45% to 0.8% carbon
4. High carbon steel — 0.8% to 1.5% carbon
According to Indian standard *[IS : 1762 (Part-I)–1974], a new system of designating the
steel is recommended. According to this standard, steels are designated on the following two
basis :
( a ) On the basis of mechanical properties, and ( b ) On the basis of chemical composition.
We shall now discuss, in detail, the designation of steel on the above two basis, in the following
pages.
2.13 Steels Designated on the Basis of Mechanical Properties
These steels are carbon and low alloy steels where the main criterion in the selection and in-
spection of steel is the tensile strength or yield stress. According to Indian standard **IS: 1570 (Part–I)-
1978 (Reaffirmed 1993), these steels are designated by a symbol ‘Fe’ or ‘Fe E’ depending on whether
- This standard was reaffirmed in 1993 and covers the code designation of wrought steel based on letter symbols. ** The Indian standard IS : 1570-1978 (Reaffirmed 1993) on wrought steels for general engineering purposes has been revised on the basis of experience gained in the production and use of steels. This standard is now available in seven parts.
Á The ocean floor contains huge amounts of manga- nese (a metal used in steel and industrial processes). The manganese is in the form of round lumps called nodules, mixed with other elements, such as iron and nickel. The nodules are dredged up by ships fitted with hoselines which scrape and suck at the ocean floor.
Á Nodules look rather like hailstones. The minerals are washed into the sea by erosion of the land. About one-fifth of the nodule is manga- nese.
Note : This picture is given as additional information and is not a direct example of the current chapter.
Nodule Suction line (^) Dredging rake
28 ^ A Textbook of Machine Design
Notes : 1. The steels from grades Fe 290 to Fe 490 are general structural steels and are available in the form of bars, sections, tubes, plates, sheets and strips.
2. The steels of grades Fe 540 and Fe 620 are medium tensile structural steels. 3. The steels of grades Fe 690, Fe 770 and Fe 870 are high tensile steels.
2.14 Steels Designated on the Basis of Chemical Composition
According to Indian standard, IS : 1570 (Part II/Sec I)-1979 (Reaffirmed 1991), the carbon
steels are designated in the following order :
( a ) Figure indicating 100 times the average percentage of carbon content,
( b ) Letter ‘C’, and
( c ) Figure indicating 10 times the average percentage of manganese content. The figure after
multiplying shall be rounded off to the nearest integer.
For example 20C8 means a carbon steel containing 0.15 to 0.25 per cent (0.2 per cent on
an average) carbon and 0.60 to 0.90 per cent (0.75 per cent rounded off to 0.8 per cent on an average)
manganese.
Table 2.6 shows the Indian standard designation of carbon steel with composition and their uses.
Table 2.6. Indian standard designation of carbon steel according to
IS : 1570 (Part II/Sec 1) – 1979 (Reaffirmed 1991).
Indian standard Composition in percentages Uses as per IS : 1871 (Part II)– designation (Reaffirmed 1993) Carbon (C) Manganese (Mn)
4C2 0.08 Max. 0.40 Max.
5C4 0.10 Max. 0.50 Max. 7C4 0.12 Max. 0.50 Max. 10C4 0.15 Max. 0.30 – 0.
10C4 0.15 Max. 0.30 – 0. 14C6 0.10 – 0.18 0.40 – 0.
15C4 0.20 Max. 0.30 – 0.
It is a dead soft steel generally used in electrical industry. These steels are used where cold form- ability is the primary requirement. In the rimming quality, they are used as sheet, strip, rod and wire especially where excellent surface finish or good drawing qualities are required, such as automobile body, and fender stock, hoods, lamps, oil pans and a multiple of deep drawn and formed products. They are also used for cold heading wire and rivets and low carbon wire products. The killed steel is used for forging and heat treating applications.
The case hardening steels are used for making camshafts, cams, light duty gears, worms, gudgeon pins, spindles, pawls, ratchets, chain wheels, tappets, etc. It is used for lightly stressed parts. The material, although easily machinable, is not designed specifically for rapid cutting, but is suitable where cold web, such as bending and riveting may be necessary.
Engineering Materials and their Properties ^ 29
15C8 0.10 – 0.20 0.60 – 0.
20C8 0.15 – 0.25 0.60 – 0.
25C4 0.20 – 0.30 0.30 – 0.
25C8 0.20 – 0.30 0.60 – 0.
30C8 0.25 – 0.35 0.60 – 0.
35C4 0.30 – 0.40 0.30 – 0.
35C8 0.30 – 0.40 0.60 – 0.
40C8 0.35 – 0.45 0.60 – 0.
45C8 0.40 – 0.50 0.60 – 0.
50C4 0.45 – 0.55 0.30 – 0.
50C12 0.45 – 0.55 1.1 – 1.
55C4 0.50 – 0.60 0.30 – 0.
55C8 0.50 – 0.60 0.60 – 0.
60C4 0.55 – 0.65 0.30 – 0.
65C9 0.60 – 0.70 0.50 – 0.
These steels are general purposes steels used for low stressed components.
It is used for making cold formed parts such as shift and brake levers. After suitable case hardening or hardening and tempering, this steel is used for making sprockets, tie rods, shaft fork and rear hub, 2 and 3 wheeler scooter parts such as sprocket, lever, hubs for forks, cams, rocket arms and bushes. Tubes for aircraft, automobile, bicycle and furniture are also made of this steel. It is used for low stressed parts, automobile tubes and fasteners. It is used for low stressed parts in machine structures, cycle and motor cycle tubes, fish plates for rails and fasteners. It is used for crankshafts, shafts, spindles, push rods, automobile axle beams, connecting rods, studs, bolts, lightly stressed gears, chain parts, umbrella ribs, washers, etc. It is used for spindles of machine tools, bigger gears, bolts, lead screws, feed rods, shafts and rocks. It is used for keys, crankshafts, cylinders and machine parts requiring moderate wear resistance. In surface hardened condition, it is also suitable for large pitch worms and gears. It is a rail steel. It is also used for making spike bolts, gear shafts, rocking levers and cylinder liners. These steels are used for making gears, coil springs, cylinders, cams, keys, crankshafts, sprockets and machine parts requiring moderate wear resistance for which toughness is not of primary importance. It is also used for cycle and industrial chains, spring, can opener, umbrella ribs, parts of camera and typewriter. It is used for making clutch springs, hardened screws and nuts, machine tool spindles, couplings, crankshafts, axles and pinions. It is a high tensile structural steel used for making locomotive carriage and wagon tyres. It is also used for engine valve springs, small washers and thin stamped parts.
Indian standard Composition in percentages Uses as per IS : 1871 (Part II)–
designation (Reaffirmed 1993) Carbon (C) Manganese (Mn)
Engineering Materials and their Properties ^ 31
2.16 Free Cutting Steels
The free cutting steels contain sulphur and phosphorus. These steels have higher sulphur content
than other carbon steels. In general, the carbon content of such steels vary from 0.1 to 0.45 per cent
and sulphur from 0.08 to 0.3 per cent. These steels are used where rapid machining is the prime
requirement. It may be noted that the presence of sulphur and phosphorus causes long chips in machining
to be easily broken and thus prevent clogging of machines. Now a days, lead is used from 0.05 to 0.
per cent instead of sulphur, because lead also greatly improves the machinability of steel without the
loss of toughness.
According to Indian standard, IS : 1570 (Part III)-1979 (Reaffirmed 1993), carbon and carbon
manganese free cutting steels are designated in the following order :
1. Figure indicating 100 times the average percentage of carbon,
2. Letter ‘C’,
3. Figure indicating 10 times the average percentage of manganese, and
4. Symbol ‘S’ followed by the figure indicating the 100 times the average content of sulphur.
If instead of sulphur, lead (Pb) is added to make the steel free cutting, then symbol ‘Pb’
may be used.
Table 2.7 shows the composition and uses of carbon and carbon-manganese free cutting steels,
as per IS : 1570 (Part III)-1979 (Reaffirmed 1993).
2.17 Alloy Steel
An alloy steel may be defined as a steel to which elements other than carbon are added in
sufficient amount to produce an improvement in properties. The alloying is done for specific purposes
to increase wearing resistance, corrosion resistance and to improve electrical and magnetic properties,
which cannot be obtained in plain carbon steels. The chief alloying elements used in steel are nickel,
chromium, molybdenum, cobalt, vanadium, manganese, silicon and tungsten. Each of these elements
confer certain qualities upon the steel to which it is added. These elements may be used separately or
in combination to produce the desired characteristic in steel. Following are the effects of alloying
elements on steel:
1. Nickel. It increases the strength and toughness of the steel. These steels contain 2 to 5%
nickel and from 0.1 to 0.5% carbon. In this range, nickel contributes great strength and hardness with
high elastic limit, good ductility and good resistance to corrosion. An alloy containing 25% nickel
possesses maximum toughness and offers the greatest resistance to rusting, corrosion and burning at
high temperature. It has proved to be of advantage in the manufacture of boiler tubes, valves for use
with superheated steam, valves for I.C. engines and spark plugs for petrol engines. A nickel steel
alloy containing 36% of nickel is known as invar. It has nearly zero coefficient of expansion. So it is
in great demand for measuring instruments and standards of lengths for everyday use.
2. Chromium. It is used in steels as an alloying element to combine hardness with high strength
and high elastic limit. It also imparts corrosion-resisting properties to steel. The most common chrome
steels contains from 0.5 to 2% chromium and 0.1 to 1.5% carbon. The chrome steel is used for balls,
rollers and races for bearings. A nickel chrome steel containing 3.25% nickel, 1.5% chromium and
0.25% carbon is much used for armour plates. Chrome nickel steel is extensively used for motor car
crankshafts, axles and gears requiring great strength and hardness.
3. Tungsten. It prohibits grain growth, increases the depth of hardening of quenched steel and
confers the property of remaining hard even when heated to red colour. It is usually used in conjuction
with other elements. Steel containing 3 to 18% tungsten and 0.2 to 1.5% carbon is used for cutting
tools. The principal uses of tungsten steels are for cutting tools, dies, valves, taps and permanent
magnets.
32 ^ A Textbook of Machine Design
It is used for small parts to be cyanided orcarbonitrided.It is used for parts where good machinability and finishare important.It is used for bolts, studs and other heat treated parts ofsmall section. It is suitable in either cold drawn,normalised or heat treated condition for moderatelystressed parts requiring more strength than mildsteel.It is used for heat treated bolts, engine shafts,connecting rods, miscellaneous gun carriage, and smallarms parts not subjected to high stresses and severewear.It is used for lightly stressed components not subjectedto shock (nuts, studs, etc.) and suitable for productionon automatic lathes. It is not recommended for generalcase hardening work but should be used when ease ofmachining is the deciding factor.It is used for heat treated axles, shafts, small crankshaftsand other vehicle parts. It is not recommended forforgings in which transverse properties are important.
Table 2.7. Indian standard designation of carbon and carbon–manganese free cutting steels
according to
IS:1570 (Part III) – 1979 (Reaffirmed 1993).
Indian
Composition in percentages
standard
Uses as per IS : 1871 (Part III)–
designation
Carbon
Silicon
Manganese
Sulphur
Phosphorus
(Reaffirmed 1993)
(C)
(Si)
(Mn)
(S)
(P) Max
10C8S
0.15 Max.
14C14S
25C12S
0.25 Max.
40C10S
0.25 Max.
11C10S
0.10 Max.
40C15S
0.25 Max.
34 ^ A Textbook of Machine Design
Table 2.8. Composition and uses of alloy steels according to
IS : 1570-1961 (Reaffirmed 1993).
Indian
Composition in percentages
standard
Uses as per IS : 1871–
designation
Carbon
Silicon
Manganese
Nickel
Chromium
Molybdenum
(C)
(Si)
(Mn)
(Ni)
(Cr)
(Mo)
11Mn
0.16 Max.
–^
–^
20Mn
–^
–^
27Mn
–^
–^
37Mn
–^
–^
47Mn
–^
–^
40Cr
–^
50Cr
–^
35Mn2Mo
–^
–^
35Mn2Mo
–^
–^
40Cr1Mo
–^
It is a notch ductile steel forgeneral purposes. It is also usedin making filler rods, colliery cagesuspension gear tub, mine cardraw gear, couplings and ropesockets.These
are
used
for
welded
structures, crankshafts, steeringlevers, shafting spindles, etc.It is used for making axles, shafts,crankshafts, connecting rods, etc.It is used for tram rails and similarother structural purposes.It is used for making gears,connecting rods, stub axles,steering arms, wear resistant platesfor earth moving and concretehandling equipment, etc.It is spring steel. It is used in ahelical
automobile
front
suspension springs.These are used for making generalengineering components such ascrankshafts, bolts, wheel studs,axle shafts, levers and connectingrods.It is used for making axle shafts,crankshafts, connecting rods,gears, high tensile bolts and studs,propeller shaft joints, etc.
Contd..
Engineering Materials and their Properties ^ 35
15Cr3Mo
0.30 Max.
25Cr3Mo
0.30 Max.
40Ni
0.30 Max.
30Ni4Crl
35NilCr
40Ni2CrlMo
These are used for componentsrequiring medium to high tensileproperties. In the nitrided condition,it is used for crank-shafts, cylinderliners for aero and automobileengines, gears, and machine partsrequiring high surface hardness andwear resistance.It is used for parts requiringexcessively high toughness. Inparticular, it is used for componentsworking at low temperatures (inrefrigerators,
compressors,
locomotives and aircraft) and forheavy forgings, turbine blades,severely stressed screws, bolts andnuts.It is used for highly stressed gearsand other components requiringhigh tensile strength of the orderof 16 N/mm
2 and where minimum
distortion in heat treatment isessential.It is used in the construction ofaircraft and heavy vehicles forcrankshafts, connecting rods, gearshafts, chain parts, clutches, flexibleshafts for plenary gears, camshafts,etc.It is used for high strength machineparts collets, spindles, screws, hightensile bolts and studs, gears,pinions, axle shafts, tappets,crankshafts, connecting rods,boring bars, arbours, etc.
Indian
Composition in percentages
standard
Uses as per IS : 1871–
designation
Carbon
Silicon
Manganese
Nickel
Chromium
Molybdenum
(C)
(Si)
(Mn)
(Ni)
(Cr)
(Mo)
