Engineering Materials And Their Properties Hours – 06 Marks - 12
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Engineering Materials
And
Their Properties
Hours – 06
Marks - 12
Introduction
• There are more than 50,000 materials available
to the engineers, in designing structure or
device, how is the engineer to choose from this
vast menu of the materials which is best suited
for the purpose.
• More recently three comet aircraft were lost
before it was realized that the design called for
fatigue strength that given the design of the
window frames was greater than that
possessed by the material.
• You yourself will be familiar with poorly
designed appliances made of plastics, their
excessive give is because the designer did not
allow for the low modulus of the polymer.
• The bulk properties along with their common
classes of property that the designer must
consider when choosing a material.
Classification and application of
engineering materials
A) Metals –
1) Ferrous
2) Non-Ferrous
B) Non –Metals –
1) Organic
2) Inorganic
C) Composites
1) Ferrous – These materials contain iron as their main constituent. Ex- Iron and Steel.
2) Non-ferrous - These materials contain substances other than iron as their main constituent. Ex- Aluminium, lead and zinc.
3) Organic – These materials are made from animal or vegetable cells or organic compounds. Ex – Polymers, plastics, leather, wood & paper.
4) Inorganic – These materials contain elements other than animal or vegetable cells and carbon compounds. Ex - Ceramic, cement, glass and minerals.
5) Composites – These materials are formed by
combining two or more materials that have
quite different properties.
The different materials work together to give
the composite unique properties, but within the
composite you can easily tell different
materials apart. They do not dissolve or blend
into each other.
•What is polymorphism?
• It is the ability of a solid
material to exists in
more than one form or
crystal structure.
I.S. Specification of Materials • The is a very large number of different types of
steels manufactured and available in the market.
They differ from one another in their
1) Chemical composition
2) Properties
3) Applications
The most commonly used methods known as
1) AISI – American iron and steel institute
2) SAE – Society of automotive engineers
3) EN – English number series
4) IS – Indian standard designation
• Designers and purchasers have to specify their
requirement according to these designations.
• It is therefore necessary to understand these
designation system.
Indian Standard Designation • Indian standard code for designation of steel
was adopted bi ISI in 1762.
• In 1974 this standard was revised in two parts.
• As per ISI 1762-1974 steels have been
classified on the basis of
1. Mechanical properties i.e. part 1 – it covers
the designation of steel based on letter
symbol.
2. Chemical composition i.e. part 2 – it covers
the designation of steel based on numerals.
Designation on the basis of mechanical
properties
• It is based upon the tensile strength or yield
strength.
• Symbol Fe is used to designate minimum tensile
strength and FeE is used to designate minimum
yield strength in N/mm2.
• It is followed by a special characteristics covering
method of deoxidation, steel quality, degree of
purity, surface condition, weldability, heat
treatment and low and high temperature
properties.
Designation on the basis of chemical
composition
• It consists of a numerical figure indicating 100
times the average % of carbon .
• Letter C is used for plain carbon steel and letter T
is used for tool steel.
• Letter C & T is followed by a figure indicating 10
times average % of manganese content.
• Symbols S, Se, Te, Pb or P are used to indicate
free cutting steels followed by a figure indicating
100 times the % of respective element.
• Alloy steels are designated in the symbolic form
on the basis of their alloy content by first
specifying the average content of carbon in 100
times of %, followed by chemical symbol of the
significant element in the descending order of %
content, the nominal and average % of each
alloying element is indicated by an index number
just after its chemical symbol.
IS designation of Low & Medium Alloy Steel
• Figure indicting 100 times the average %.
• Chemical symbol for alloying elements each
followed by the figure for its average % content
multiplied by a factor given below.
Element Multiplying
Factor
Cr, Co, Ni, Mn, Si and W 4
Al, Be, V, Pb, Cu, Nb, Ti, Ta, Zr and Mo 10
P, S and N 100
• For Example 40Cr4Mo2 means alloy steel having
average 0.4% carbon, 4% chromium and 0.2%
molybdenum.
• Note –
1) The figure after multiplying shall be rounded off to
the nearest integer.
2) Symbol ‘Mn’ for manganese shall be included in
case manganese content is equal to or greater than
1%.
3) The chemical symbols and their figures shall be
listed in the designation and the order of decreasing
content.
IS designation of high alloy steels
( stainless steel & heat resisting steel)
• Letter X
• Figure indicating 100 times the % of carbon
content.
• Chemical symbol for alloying elements each
followed by a figure for its average % content
rounded off to the nearest integer,
• Chemical symbol to indicate specially added
element to allow the desired properties.
• For example X 10 Cr 18 Ni 9 means high alloy
steel with average carbon 0.10 %, chromium
18 % and nickel 9%.
IS designation of high speed tool steel
• Letter XT
• Figure indicating 100 times the % of carbon
content.
• Chemical symbol for alloying elements each
followed by the figure for its average % content
rounded off to the nearest integer.
• Chemical symbol to indicate specially added
element to attain the desired properties.
• XT 75 W 18 Cr 4 V 1 means a tool steel with
average carbon 0.75%, tungsten 18%, chromium
4% and vanadium 1%.
Free cutting steel • These steels contain sulphur and phosphorus.
• These steels have higher sulphur content than
other carbon steel.
• In general, the carbon content of such steels vary
from 0.1 to 0.45% and sulphur from 0.08 to
o.3%.
• These steels are used where rapid machining is
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 machine.
• Now-a-days, lead is used from 0.05 to 0.2%
instead of sulphur because lead also greatly
improves machinability of steel without the
loss of toughness.
• According to IS designation carbon and carbon-
manganese steels are designated in following
order
• Figure indicating 100 times average % of carbon.
• Letter ‘C’
• Figure indicating 10 times average % of
manganese.
• Symbol ‘S’ followed by the figure indicating 100
times average % of sulphur.
• Instead of sulphur lead (Pb) is added to make the
steel free cutting.
Sr.
No.
Designation Special Characteristics and Composition
1 Fe 410 K Killed steel with min tensile strength 410 N/mm2
2 FeE 300 P
35
Semi –killed steel with min yield strength 300 N/mm2 and
containing P as 0.035 max.
3 Fe 470 W Killed steel with min tensile strength 470 N/mm2 and
guaranteed fusion welding quality.
4 Fe 00 R Rimming quality steel with no guarantee of min tensile or
yield strength
5 FeE 590 F7 Sheet steel of plating finish and min yield strength 590
N/mm2
6 Fe 600 T4 Semi-killed steel in controlled rolled condition with a min
tensile strength 600 N/mm2
7 Fe 510 Ba Steel in annealed condition with a min tensile strength 510
N/mm2 and resistance to brittle fracture.
8 40 C 8 Unalloyed steel 0.4% C and 0.8% Mn
Sr.
No.
Designation Special Characteristics and Composition
9 45 C 10 S 18 0.45% C, 1.0% Mn, 0.18% S
10 20 c 12 Pb 15 T 14 0.20% C, 1.2% Mn, 0.15 Pb hardened and
tempered
11 40 Cr 4 0.4% C, 0.8% Mn and 1.0% Cr
12 35 Mn 6 Mo 3 0.35% C, 1.5% Mn, 0.3% Mo
13 40 Cr 4 Mo 3 0.4% C, 1.0% Cr, 0.3% Mo
14 40 Cr 13 Mo 10 V 2 0.4% C, 3.3% Cr, 1.0% Mo and 0.2 V
15 40 Cr 7 Al 10 Mo 2 0.4% C, 1.7% Cr, 1.0% Al and 0.2% Mo
16 35 Ni 5 Cr 2 0.35% C, 1.2% Ni and 0.5% Cr
17 40 Ni 6 Cr 4 Mo2 0.4% C, 1.5% Ni, 1.0% Cr and 0.2%% Mo
18 T 7 Tool Steel containing 0.7% C
19 10 T4 Mould steel containing 0.1% C and 0.4% Mn
20 T 15 Cr 3 Tool steel containing 0.15% C, 0.7% Cr
21 T 90 Mn 6 W Cr 2 Tool steel containing 0.9% C, 1.5% Mn, 0.5%
W and 0.5% Cr
Sr.
No.
Designation Special Characteristics and Composition
22 T 55 Ni 6 Cr Mo 3 Tool steel containing 0.55% C, 1.5% Ni, 0.7%
Cr and 0.3% Mo
23 T10 Cr 20 Mo8 V 2 Tool steel containing 0.1% C, 5.0% Cr, 0.8%
Mo and 0.2% V
24 X 10 Cr 18 Ni 9 High alloy steel containing 0.1% C, !8.0% Cr,
9.0% Ni
25 X 15 Cr 25 Ni 12 High alloy steel containing 0.15% C, 25.0%
Cr, 12.0% Ni
26 XT 75 W 18 Cr 4 V 1 High alloy Tool Steel containing 0.75% C,
18.0% W, 4.0% Cr and 1.0% V
27 XT 98 W 6 Mo 5 Cr 4
V 1
High alloy Tool Steel containing 0.98% C,
6.0% W, 5.0% Mo, 4.0% Cr and 1.0% V
28 XT 215 Cr 12 High alloy Tool Steel containing 2.15% C and
12.0% Cr
Factors for selecting materials
1) Easiness in fabrication
2) Service condition
3) Dimensional stability
4) Operational needs, process control and
durability.
5) Material cost
6) Resistance to corrosion
7) Resistance to moisture
8) Resistance to impact and shock.
Properties of Metals
1) Density –
• Density of a material is defined as its mass per unit
volume.
• Density = (Mass / Volume)
• Different materials have different density at the same
temperature.
• In general, density can be changed by changing
either the pressure or the temperature. Increasing
the pressure always increases the density of a
material. Increasing the temperature generally
decreases the density.
• Density plays a significant role in determining
the strength of a material to its density.
2) Melting Point –
It is defined as the fixed or constant temperature at which
pure metals or non-metals change from solid to liquid form.
The melting point of a material depends on the energy
required to separate its atoms.
The melting point of materials such as alloys that are made
from two or more metals varies on the basis of their
composition.
Zinc, lead and tin have low melting point.
Aluminium alloys have medium melting point.
Copper alloys have high melting point
Ceramics have the highest melting point.
3) Specific heat –
The amount of heat required to raise the
temperature of material by 10C is called the
heat capacity or specific heat.
Metals have lower specific heat than plastics.
Therefore they require less heat to reach a
particular temperature than plastics.
The specific heat of water is 1 calories/gram0C
i.e. 4.187 J/g0K.
Mechanical Properties • Mechanical properties determine the behavior
of materials when mechanical force is applied
to them.
• The study of mechanical properties is essential
for designing and manufacturing purpose.
1) Strain –
It is measured as the deformation caused per unit
length in the direction of force applied.
Strain is divided into two types elastic and
plastic.
Some materials such as rubber return to their
original shape after the applied force is removed.
This property of material is called elastic strain.
Plastic stain results in permanent deformation.
2) Stress –
When an external load is applied to a material,
the material resists deforming effect. This
resistance is called as stress.
a) Tensile stress
b) Compressive stress
c) Shear stress
d) Bending stress
3) Strength –
It is the ability of material to withstand
external forces applied on it during a test of
when it is in use.
These forces cause distortion. The resistance to
this distortion is called as strength.
a) Tensile strength –
It is defined as the ability of material to
withstand distortion caused by pulling forces.
Ex – bags, rigging sailboats.
b) Compressive strength –
It is defined as the ability of material to
withstand distortion caused by compressive
forces.
Ex- Bricks, concretes
c) Yield strength –
The strength of a material at a particular
temperature is known as yield strength.
The yield strength of a material is the point at
which a material deforms and does not retain
its original shape even after force is removed.
4) Stiffness –
It is defined as the resistance of a material to
elastic deformation. It is also known as
Young’s modulus of elasticity.
Stiffness & plastic deformation are inversely
proportional.
For Ex - spring, airplane wings which are
required to maintain their shape in turbulent
air.
Bicycle is an another example where the frame
does not deform permanently.
5) Hardness –
Hardness is the ability of a material to resist
penetration and wear by another material.
The hardness of a metal is directly related to its machinability, since toughness decreases as hardness increases.
The tensile strength is directly proportional to
hardness. Tensile strength increases with
hardness.
The hardness of a material must be considered
while making objects such as knifes.
A knife can be made of stainless steel or
carbon steel.
Carbon steel has high hardness. Therefore
knifes are made from carbon steel.
Diamond is the hardest material and is used to
cut hard materials.
Talc is the softest material.
Ceramics have high hardness, metals have
medium and plastics have low hardness.
6) Toughness –
It is defined as the ability of a material to
absorb sudden external pressure that exerts
force.
It is measured as the energy absorbed per unit
volume of material
It is the amount of energy absorbed by material
before it develops a fracture.
It is also the ability of a material to resist
propagation of cracks in the material.
7) Elasticity –
The ability of a material to return to its original
shape after the applied load is removed is
called elasticity.
This is measured as the modulus of elasticity.
It is the ratio of stress and strain.
Temperature lowers the modulus of elasticity.
Elasticity is an important when selecting
materials for high load application, such as
bridges.
8) Ductility –
It is defined as the ability of a material to resist a
high plastic deformation before breaking under
tension.
Ductility is denoted by percentage elongation,
which is defined as the maximum elongation.
100%
lengthOriginal
materialoflengthinchangeelongation
9) Malleability –
It is defined as the ability of a material to
exhibit deformation when compressive force is
applied.
Malleability can be considered as an example
of plastic deformation.
Malleable materials can be rolled into thin
sheets.
If the temperature of material increases
malleability increases.
Plastic is an example of malleable material.
10) Fatigue –
It is defined as the behavior of a material when
exposed to fluctuating or periodic loads.
This results in stress, which causes the material to
fracture.
Fatigue strength is the property of a material to
withstand continuously varying and alternating
loads.
The level at which the fracture occurs when
fluctuating load is applied is lower than the level
at which fracture occurs when static load is
applied.
11) Creep –
It is defined as the permanent plastic deformation
of materials when subjected to constant stress or
prolonged loading usually at high temperatures.
Creep leads to a fracture in the material at static
stresses.
Creep at room temperature is known as low
temperature creep.
Some materials in which a low temperature creep
may occur are load pipes, roofing and glass.
The creep at high temperature is known as
high temperature creep.
Creep is nothing but a deformation that occurs
over a period of time when a material is
subjected to constant stress at constant
temperature.
In metals, creep usually occurs at elevated
temperatures.
Creep at room temperature is more common in
plastic material and is called cold flow or
deformation under load.
The creep of a material can be divided into three
stages.
1) In the initial stage, or primary creep, the
strain rate is relatively high, but slows with
increasing time. This is due to work
hardening.
2) Secondary creep has a relatively uniform rate.
3) Tertiary creep has an accelerating creep rate
and terminates by failure of material at time
for rupture.
12) Plasticity –
It is defined as the property of material, such
as gold, silver or lead which retains the
deformation produced under load permanently.
This property of material is important for
forging and in ornamental work.
This property is opposite to strength.
Electrical Properties
Electrical properties of a material refer to the
ability of a material to permit or resist the flow
of electricity through it.
Materials to be used in electrical equipment
can be selected on the basis of their electrical
properties. Such as
Resistivity
Conductivity
Dielectric strength
1) Resistivity –
It is the property of a material to resist the
flow of electricity through it.
conductortheofLengthL
conductorofsCA
conductoraofcesisR
L
RAsistivity
/
tanRe
Re
2) Conductivity –
Electrical conductivity is the electrical
property of a material due to which electric
current flows through the material.
It is the reciprocal of resistivity.
It is an important factor to consider when
selecting materials for electric wiring.
RA
LtyConductivi
1)(
3) Dielectric strength –
Dielectric strength of a material refers to the
insulating capacity of a material against high
voltage.
A material with high dielectric strength can
withstand high voltage field.
Ceramics have high dielectric strength.
Chemical Properties
Chemical properties of a material are the
manner in which the material reacts with
substances such as air, water and acids.
A study of the chemical properties of a
material is necessary because most of the
engineering materials, when combined with
other substances, may react with their
characteristics such as corrosion, relativities
and solubilities.
1) Oxidation –
It is the process in which metal react with
oxygen to form layers of metallic oxides on
its surface.
The rate of oxidation increases with the
increase in temperature.
Oxidation also takes place due to the presence
of sulphur and chlorine in air, which form an
oxidation film.
Metals such as silver, gold and platinum do
not react with oxygen.
2) Corrosion –
Corrosion of metals is the process of metals
being destroyed when exposed to atmosphere.
In addition to destruction of metals, further
contact of these metals with atmosphere or
moisture leads to formation of harmful
compounds.
Thermal Properties
The thermal properties of a material measure
the change caused in the material due to
application of heat.
The thermal properties determine the amount
by which a material expands for a given
change in temperature.
In addition, the temperature change of material
when heat is applied is also determined by the
thermal properties of materials.
These properties also determine the extent to
which a material can conduct heat.
1) Thermal conductivity –
It can be defined as the ability of a material to
allow heat to pass through it.
Polymers are usually poor conductors of heat.
Copper is good conductor of heat and is used
to make equipment for transferring heat.
Materials such as plastic and felt are poor
conductors and have low thermal
conductivity.
These materials are used as insulators in
water coolers and oven gloves.
2) Thermal expansion –
Thermal expansion is the amount by which the
length of a material changes when the
temperature increases.
It is inversely proportional to the change in
temperature and is referred to as coefficient of
linear expansion.
3) Heat capacity –
If a solid material is heated, there will be rise
in temperature.
This rise in temperature will be noted that,
some energy has been absorbed.
4) Specific heat –
It is defined as the amount of heat required to
rise the temp. of unit mass of a substance
through 10C or the amount of heat added to
unit mass of a solid to raise its temperature by
10C.
5) Melting point –
The temperature at which the metals starts to
change its state from solid to liquid.
Always the melting point mostly depends upon
the bonds between the atoms.
Stronger the bonds, the higher the melting
point and weaker the bonds lower the melting
points.
Rubber – 2570F, steel – 2250 to 22700F,
copper – 10800C
6) Thermal Stability –
Mostly the surrounding to the materials may
always effect their properties.
The surrounding effects are generally of
reaction which will affect the phase and micro
structural change in it.
It is the ability of material to stable at the
surrounding effects.
•End of Part I of Unit No.1
Related Documents
