Inroduction to Engineering materials

ENGINEERING MATERIALS AND
METALLURGY
AUTONOMOUS

For fourth SEMESTER(II YEAR)
PREPARED BY
S.ARAVINDHA BALAJI
ASSISTANT PROFESSOR
DEPARTMENT OF MECHANICAL
ENGINEERING
SONA COLLEGE OF TECHNOLOGY
SALEM:636005

METALLURGY

1/5/2013
Application of EMAM(In Industry):
 Steel industry( e.g. steel plants, (SAIL) Essar

SAB-AP/MECH SONACT
steels, jindal steel ltd.(JSW))
 Pipe maufacturing industry, Plastic

industry.
 Some jewelry industry(Grades of the gold)

 Manufacturing industry.

2

METALLURGY

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OBJECTIVE

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 Knowledge on the structure
 Properties of the materials
 Treatment
 Testing and applications of metals and non-metallic
materials
 Suitable materials for various engineering application

3

METALLURGY

Review (Not for Exam)
 Crystal structure
 BCC, (Body cubic centre) structure
 FCC, (Face cubic centre) structure and
 HCP, (Hexagonal close packing)structure
 Unit cell
 Crystallographic planes and directions
 Miller indices
 Crystal imperfections for point, line, planar and
volume defects.

METALLURGY

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Review (Not for Exam)
 Grain size

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 ASTM grain size number

5

METALLURGY

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UNIT:I CONSTITUTION OF ALLOYS AND
PHASE DIAGRAMS
Constitution of alloys-Solid solution,

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
substitutional and interstitial-Phase
diagrams, Isomorphous, eutectic,
peritectic, and peritectroid reactions,
Iron-Iron carbon equilibrium diagram.

 Classification of steel and cast Iron,
Microstructure, Properties and
applications. 6

METALLURGY

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UNIT:II HEAT TREATMENT
Definition-Full annealing, stress relief,
recrystallisation and spheroidizing-

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normalising, hardening and tempering of
steel. Isothermal transformation
diagrams-cooling curves superimposed on
I.T.diagram, CCR-Hardenability, Jominy
and quench test- Austempering,
Martempering-case hardening-
carburising, nitriding, cyaniding,
carbonitriding, flame and induction
hardening . 7

METALLURGY

1/5/2013
UNIT:III
MECHANICAL PROPERTIES AND TESTING

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Mechanism of plastic deformation, slip and
twinning-types of fracture-testing of materials
under tension, compression and shear loads-
Hardness tests (Brinell, Vickers and Rockwell),
Impact test-Izod and charpy, Fatigue and creep
tests, fracture toughness tests.

8

METALLURGY

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UNIT:IV
FERROUS AND NON FERROUS METALS

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Effect of alloying elements on steel(Mn, Si,
Cr, Mo, V, Ti & W) –Stainless and tool steels
–HSLA-maraging steels-Cast irons-Grey,
White malleable, spheroidal-Graphite, Alloy
cast irons,
Copper and copper alloys-Brass, Bronze and
Cupronickel-Aluminum and Al-Cu alloy-
Precipitation hardening-Bearing alloys.
9

METALLURGY

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UNIT V
NON-METALLIC MATERIALS

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Polymers-Types of polymer, commodity and
Engineering polymers-properties and
applications of PE, PP, PS, PVC, PMMA, PET,
PC, PA, ABS, PI, PAI, PPO, PPS, PEEK, PTFE
Polymer-Urea and Phenol formaldehydes-
Engineering ceramics-Introduction to fiber
reinforced plastics.

10

METALLURGY
Each category of engineering application requires material from any or all of

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these three group of materials
Ceramics and Polymers
Metals and alloys

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glasses

Engineering Materials

Application

Structures Machines Devices
11

METALLURGY

Metals and alloys
Steels, aluminum,
copper, silver
reinforced steel

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d plastics
reinforce
Metal-
,gold, Brasses,,
Si, Ge, GaAs,

bronze s, maganin
invar, super alloys
Boride-

boron rare earth
magnetic alloys

Ceramic and Organic polymers
Plastics,
glasses Pvc,PTFE,
Mgo, cds, polyethylene
Fibers:Terylene,nylo
Al2O3, n,cotton,
S iC, BaTio3,Silica, natural, and
soda-time-glass, synthetic
rubbers ,
Concrete, cement leathers
ferrites and garnets
ceramic
superconductors

Glass fiber- reinforced
12
plastics
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METALLURGY

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Structure:
The internal structure of a material,

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simply called the structure.

13

NON-METALLIC MATERIALS:

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 PE (polyethylene)
 PP (Polypropylene)

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 PS(Polystyrene)
 PMMA(Polymethyl methacrylate)
 PET(Polyethylene teraphthalate)
 PC(Polycarbonates)
 PA(Polyamides)
 ABS(Acryknitrile-Butadiene-styrene)
 PI(Polyimide)
14

NON-METALLIC MATERIALS:

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 PAI( Polyamideimide)
 PPO(Polyphenylene oxide)

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 PPS(Polyphenylene sulphide)
 PEEK(Polyether ether ketone)
 PTFE(Polytetra fluoro ethylene)

15

METALLURGY

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UNIT:I CONSTITUTION OF ALLOYS AND
PHASE DIAGRAMS

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Constitution of alloys-Solid solution, substitutional
and interstitial-Phase diagrams Isomorphous,
eutectic, peritectic, and peritectroid reactions,
Iron-Iron carbon equilibrium diagram.
Classification of steel and cast Iron,
Microstructure, Properties and applications.

16

UNIT:I
CONSTITUTION OF ALLOYS
AND PHASE DIAGRAMS

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 CONSTITUTION- establishment, foundation,

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creation, formation, structure, organization,

charter, bill.

17

UNIT:I
AND PHASE DIAGRAMS

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SOME TECHNICAL TERMS AND

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DEFINITIONS:
1.SYSTEM: It is a combination of phases of one or
more components.

2.PHASE: It is a Physically and chemically
homogenous part of a system under study, one
phase is different from the other in structure or
composition 18

UNIT:I
CONSTITUTION OF ALLOYS AND
PHASE DIAGRAMS

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3.COMPONENTS:

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The elements present in the

system are called component. A system may

consist of two or more components.

19

AND PHASE DIAGRAMS

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CONSTITUTION OF ALLOYS:
4.ALLOY:

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 An alloy is defined as a combination of two or

more elements, of which one of the element should be

a metal in major proportion.

 The others could be metals or non-metals, for eg:

Brass (CU-Zn), Steel (Fe-C)
20

UNIT:I
PHASE DIAGRAMS

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 Alloy find very wide application in the industry than pure metals.

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 Uses of pure metals

1. High electrical conductivity

2. High ductility

3. Corrosion resistance are required.

These properties are generally at a maximum value in pure metals.

21

UNIT:I
PHASE DIAGRAMS

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 Mechanical properties

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1. Tensile strength

2. Yield point

3. Hardness are

improved by alloying.
22

UNIT:I
CONSTITUTION OF ALLOYS AND PHASE
DIAGRAMS

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CLASSIFICATION OF ALLOYS
CLASSIFICATION OF

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ALLOYS

Solid Intermedia
Pure metals
Solution te phase

23

UNIT:I
PHASE DIAGRAMS

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 Alloy can be either a single phase or a mixture

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of phases.

 A phases is anything which is homogeneous and

physically distinct.

 In solid state alloys of three are three possible

phase. 24

UNIT:I
PHASE DIAGRAMS

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 If an alloy has a single phase, it could be either
a solid solution or an intermediate phase.

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 If the alloy is a mixture it could be composed of
any combination of the above three phases.

25

UNIT:I
PHASE DIAGRAMS

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 Themajor element which is large in
amount is called base metal or parent

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metal or solvent.
 The other element that is lesser in
amount is called the alloying element or
solute, it is the minor part (such as salt or
sugar which is less in amount, being
mixed in water- solvent).

26

UNIT:I
PHASE DIAGRAMS

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5. MIXTURE:
It is a material more than one phase.

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27

UNIT:I
PHASE DIAGRAMS

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SOLID SOLUTION

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Substitutinal Interstitial
Solid solution solid solution

Disordered Ordered
(or) Random (or) regular
28

UNIT:I
PHASE DIAGRAMS

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 Solid solutions:

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 A solid solution is the simplest type of alloys.

 A Solution can be defined as a homogeneous mixture

in which the atoms or molecules of one substance are

dispersed at random into another substance.

29

UNIT:I
PHASE DIAGRAMS

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 A solid solution may be defined as a solid
that consist of two or more elements

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atomically dispersed in a single-phase
structure.
 A solid solution is composed of two parts.

1 . Solute: A solute is the minor part of
the solution or the material which is
dissolved.

30

UNIT:I
PHASE DIAGRAMS

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2. Solvent: Solvent constitutes the major portion of

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the solution.

Both the solute and the solvent can be solid,

liquid or gas.

31

UNIT:I
PHASE DIAGRAMS

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 Solid solution:
Simply a solution in the solid state.

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Solid solution may be defined as a
solution In the solid state which consists of two
kinds of atoms combined in one type of space
lattice.

32

UNIT:I
PHASE DIAGRAMS

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 space lattice:

Space lattice is defined as an array of

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points in three dimensions in which every point

has surroundings identical to that every other

point in the array.

33

SOLID SOLUTION

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 Case:
 In certain cases, the solidification of an

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alloy results in the formation of one kind of
crystal.
 In which both metals are present, but they
cannot be detected by the microscope
 Although properties of the crystals are
profoundly( deeply,strongly) changed.

34

SOLID SOLUTION

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 In such a case we have a solid metal in which the

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interatomic state which existed in the liquid solution

has been persevered after solidification, and it is

known as a solid solution.

 In a solid solution the atom occur in a definite

geometrical pattern, which is usually a slightly
35
distorted form of one of the constituent metals.

SOLID SOLUTION

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 Soildsolution are conductors, but not so good as
the pure metals on which they are based.

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Some examples of solid solutions are:
 Cu-Zn alloys (Brasses)

 Ni-Cu alloys (Monel metal)

 Au-Ag alloys(Sterling silver)
 Fe-Cr-Ni alloys (Certain stainless steels)

 Fe-C alloys (Steels)

36

SUBSTITUTIONAL SOLID SOLUTION
Solute Atoms

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SOLVENT OR

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MATRIX ATOMS

solute-Atom of Metal-B Solvent-Atoms of zinc Metal-A
37
zinc(Solute) Copper(Solvent)
Disordered substitutinal solid solution(random,)

Ordered subsitutional solid solution

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
SOLVENT OR
MATRIX ATOMS

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Solute
Atoms

38


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 In substitutional solid solution, there is a direct

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substitution of one type of atom for another.

 so that solute atoms(cu) enter the crystal to take

positions normally occupied by solvent atoms (e.g.,

Nickel atoms);

39


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 The alloy is said to be in a disordered condition if

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in the formation of a substitutional solid

solution, the solute atoms do not occupy any

specific position but are distributed at random in

the lattice structure of the solvent.

40


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 An ordered subsititutional solid solution is shown

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fig Cu-Zn, Al-Cu, α-Brass are some examples of

ordered structures.

41

INTERSTITIAL SOLID SOLUTION

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 The four elements hydrogen, carbon, nitrogen,

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and boron have such small diameters that they

can occupy the empty spaces (Interstices) in the

crystal lattices of many metals.

42

Solvent or

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matrix atoms Solute atoms

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CARBON
(solute)

IRON
( SOLVENT)

43


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 Interstitial solid solution usually have a limited

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composition range and are generally considered

of secondary importance, but there are a few

instances worthy of special attention.

44


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 The interstitial solution of carbon in iron

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constitutes the basis of steel hardening.

 Very small amount of hydrogen introduced into

steels during acid pickling(cleaning), plating, or

welding operations causes a Sharpe decrease in

ductility, known as hydrogen embrittlement. 45


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 Interstitial nitrogen is useful not only in

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nirtriding process but also as an important factor

in maintaining 18Cr-8Ni

Stainless steel in the austenitic condition.

46

HUME - ROTHERY’S RULES OF SOLID
SOLUBILITY

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SAB-AP/MECH SONACT
Hume - Rothery’s Rules of solid solubility
47

HUME - ROTHERY’S RULES OF
SOLID SOLUBILITY

1/5/2013
SAB-AP/MECH SONACT
Hume - Rothery’s Rules of solid solubility 48


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HUME –ROTHERY’S RULES OF SOLID SOLUBILITY

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The solubility limit of solute in solvents depends on

various factors. These were stated by Hume-rothery

and are as follows:

1. Critical structure factor (or) Crystal structure:

Metals that have the same crystal stucture (Lattice

structure) have a greater solubility. 49

2. Relative atomic size factor(or) size factor:

1/5/2013
 The solid solution will tend to form if the

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difference in size of solute and solvent is less than

15%.

 If the difference is greater than 15% formation of

solid solution will be limited.

 For good solid solubility the difference should be less
50
than 8%

3. Chemical affinity factor (or) Electronegativity:

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 Formulation of solid solution is

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favoured for metals that have less chemical affinity

is more, then a compound is formed instead of a solid

solution.

 The metal which are separated in widely in the

periodic table are not suitable for making alloys

because of their high affinity. 51


1/5/2013
4. Relative valency factor(or)valence:

A metal that has a higher valency will

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disslove only a small amount of a lower valency

metal, where as the metal with low valency

will have good solubility for the higher valency

metal.
52


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 In some alloys both interstitial and

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substitutional solid solution are formed to an

appreciable extent.

 For Eg: A Cr-Ni steel contains interstitially

dissolved carbon and substitution ally dissolved

chromium, nickel, and minor elements. 53

POSSIBILITIES OF SOLID SOLUTIONS

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• There are three possible solid solutions based on

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the amount of their elements. They are:

1.Unsaturated solid solution: In the solvent is

dissolving small amount of solute as well as at a

given temperature and pressure, it is called

unsaturated solid solution. 54


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2. Saturated solid solution:

If the solvent is dissolving

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limiting amount of solute, it is called saturated

solid solution.

55


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3. Supersaturated solid solution:

If the solvent is dissolving more of solute that it

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should, under equilibrium, it is called

supersaturated solid solution.

56

PHASE DIAGRAM

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Types of phase diagram

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1. Isomorphous

2. Eutectoid system

3. Eutectic system

4.Peritectic system

57
5. Peritectroid reactions

PHASE DIAGRAM

1/5/2013
 Phase Diagrams

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Phase diagrams are graphical

representation of what phases are present in an

alloy system at various

Temperatures, pressures, and compositions.

58

PHASE DIAGRAM

1/5/2013
(or)
A phase diagram is a map showing the

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structure or phase present as the
temperature and overall composition of
the material are varied.
 Phase diagrams are also known as equilibrium

diagrams or constitutional diagrams.

59

WHY SHOULD PHASE DIAGRAMS BE
STUDIED?

1/5/2013
 The phase diagrams can answer the following

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important questions:

 What condition is the material in?

 Is the composition uniform throughout?

If not, how much of each component is present?

60

STUDIED?

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 Is something present that may give undesired

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properties?

 What will happen if temperature is increased or

decreased; pressure is changed or composition is

varied?

61

STUDIED?

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 Phase diagrams are used by engineers and

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scientists to understand and to predict many

aspects of the behavior of materials.

62

TERMINOLOGY USED IN PHASE DIAGRAMS

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1. Components

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2. System

3. Alloy

4. Solid solution

5. Solute Solution

63


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6. Solvent

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7. Phase

8. Equilibrium

9. Solubility limit

10.Degrees of freedom

64


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 The various terms used in the study of phase

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diagrams have been explained below:

1. COMPONENT: Component are pure metals

and or compounds of which an alloy is composed.

Eg: In a copper-zinc brass, the components are

CU and Zn. 65


1/5/2013
2. SYSTEM: The system has two meanings in this
context

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i. System: May refer to a specific body of

material under consideration. For Eg: A

ladle of molten steel is referred as a system.

66


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 (ii)system: May also refer to the series of possible

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alloys consisting of the same components. For

example, the Iron-Carbon system.

67


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 A system having one components is called a

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Unary system, and the system having two, three

and four components are known as Binary,

ternary and quaternary systems, respectively.

68


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3. ALLOY:

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An alloy is a mixture of two or more metals

or a metal (metals) and a non-metal (non-metals).

69


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4.SOLID SOLUTION:

It is a solid that consist of two or

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more elements atomically dispersed in a single-

phase structure.

70


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5. SOLUTE SOLUTION:

It is the minor part of the

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solution or the material which is dissolved.

71


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6. SOLVENT:

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The material which contributes the

major portion of the solution.

72


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7. PHASE:

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A phase may be defined as a homogenous

portion of a system that has uniform physical

and chemical characteristics.

73


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8. EQUILIBRIUM:

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Equilibrium is said to exit when

enough time is allowed for all possible reactions

to be completed.

74


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 The equilibrium state refers to the

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characteristics of the system that remain

constant indefinitely. Equilibrium occurs when

the free energy of the system is at its minimum

value.

75


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 The term phase equilibrium refers to

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equilibrium as it applies to systems in which

more than one phase may exist.

76


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9. SOLUBILITY LIMIT:

It is the maximum concentration of

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

solute that may be added without forming a new

phase.

77


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 NOTE: The addition of solution in excess

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of the solubility limit results in the formation of

another solid solution or compound.

78


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10. DEGREES OF FREEDOM:

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It is the number of

independent variables ( such as temperature,

pressure, and composition).

That can be changed independently without

changing the phase or phases of the system.

79

WHAT IS MEANT BY THE TERM PHASE?

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 A phase may be a portion of matter which is

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homogenous

 A phase may be defined as any physical distinct

homogenous and mechanically separable portion

of a substance.

80


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 In Layman’s term, a phase requires a unique

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structure, uniform composition, and well-defined

boundaries or interfaces

Examples: A pure substance such as water is a

single phase.

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 The pure substance water can exist in solid,

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liquid and vapour, each of these states being a

single phase, as shown in fig (a)

 Now consider the effect of adding salt(Nacl) to

water. Salt will dissolve in water to give a

homogeneous solution. 82


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 Thus the salt- water solution forms a single

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phase as shown if fig(b)

 If more salt is added into water, then we have

two different phases as shown if fig(c)

83


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 A Single phase system is also termed as

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“homogeneous system”

84


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 System composed of two or more phases are

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termed as mixtures or heterogeneous systems’.

Fig (d)

 Most metallic alloys, ceramic, polymers, and

composite are heterogenous.

85

ILLUSTRATION OF PHASES
WATER VAPOUR(3)

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SAB-AP/MECH SONACT
ICE (1) WATER(2)

WATER

ILLUSTRATION OF PHASES:
(A) Three
forms of water: 1) Ice 2)water 3)
water vapour are each a phase. 86


1/5/2013
salt

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•

(b) Salt and water have unlimited solubility
(Homogeneous solution)- from a single phase

87


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Saturated brine

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Excess salt

(C) Salt and water have limited solubility
(Heterogenous solution)-from two distinct phases

88


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SAB-AP/MECH SONACT
OIL

WATER

OIL AND WATER HAVE VIRTUALLY NO SOLUBILITY FROM TWO 89
DISTINCT PHASES

PHASE DIAGRAM OF PURE
SUBSTANCE

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 One- Component Phase diagram

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90

SUBSTANCE

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SAB-AP/MECH SONACT
91

SUBSTANCE

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 A pure substance such as water can exist in

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solid, liquid, or vapour phases, depending on the

condition of temperature and pressure

92

SUBSTANCE

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 The phase relationships may be represented on

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a pressure- temperature (PT) diagram, known as

a one-component (or unary) phase diagram, for

the H2O System.

93

SUBSTANCE

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 The phase diagram is composed of regions of

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pressure and temperature where only a single

phase is stable.

 The line OA indicates the vapourisation line

and the line OB indicates the freezing line.

94

SUBSTANCE

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 Liquid and vapour phase exist along the

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vapourisation line and liquid and solid phases

along the freezing line, shows in figure. These

lines are also known as Two phase equilibrium

lines.

95

SUBSTANCE

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 The point “O” is know as Triple point.

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Triple point is the point at which three phases

(Solid, liquid, and vapour phases(gas)).

of a single material coexit. This triple point of

water exists at temperature 0.00980C

and at pressure 4.58 mm of Hg. 96

PHASE DIAGRAMS

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 The properties of an alloy depend on nature,

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amount, size, distribution and orientation of the

phases.

 A phase is the chemically and structurally

homogeneous portion of the microstructure.

97

PHASE DIAGRAMS

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 It has the following characteristics
1. Same structure throughout.

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2. Roughly the same composition and

properties throughout.

3. Definite interface between the phase

and surrounding.

98

J.W. GIBBS
( JOSIAH WILLARD GIBBS)

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SAB-AP/MECH SONACT
99

J.W. GIBBS( JOSIAH WILLARD
GIBBS)
JOSIAH WILLARD GIBBS PROPOSAL

1/5/2013
(OR)

SAB-AP/MECH SONACT
J.W. GIBBS LAW
(OR)
GIBB’S PHASE RULE
(or)
PHASE RULE

100

GIBBS PHASE RULE

1/5/2013
 J.W. Gibbs, American physicist derived an

SAB-AP/MECH SONACT
equation which established relationship in a

system between the number of phases,

 The number of degree of freedom and the

number of components.

101

GIBB’S PHASE RULE

1/5/2013
 The phase rule indicates the phases that exists

SAB-AP/MECH SONACT
at equilibrium.

 The Gibb’s phase rule satisfies the following

relation:

P+F=C+n

102

GIBB’S PHASE RULE

1/5/2013
 P- Number of phases that exist in a

SAB-AP/MECH SONACT
system under certain conditions.

C-Number of components in the system.

n- It represents the number of variables,

examples: Temperature, pressure and

concentration. 103

GIBB’S PHASE RULE

1/5/2013
F- Degree of freedom. It is the number of

SAB-AP/MECH SONACT
variables such as temperature or

pressure or concentration which can

be change independently without

changing the number of phases that

are present in the system.
104

GIBB’S PHASE RULE

1/5/2013
 In most studies the pressure is constant

SAB-AP/MECH SONACT
 i.e., 1 atmospheric pressure and hence pressure
is not considered a variable.

 Usually the only variable under consideration is
temperature and hence the Gibb’s phase rule
becomes;

P+F=C+1
105

USES OF PHASE RULE

1/5/2013
 The phase rule predicts maximum number of
phases present in the alloy under equilibrium

SAB-AP/MECH SONACT
conditions at any point of diagram.

 If the number of phases are known, one can
determine the degree of freedom using phase
rule.

106

USES OF PHASE RULE

1/5/2013
 Thus the phase rule is useful to know whether

SAB-AP/MECH SONACT
the temperature or pressure or both variables

can be changed without changing the structure of

the alloy.

107

ILLUSTRATION OF THE USE OF THE
PHASE RULE

1/5/2013
 Let us consider the application of gibbs phase rule
to the phase diagram of water system

SAB-AP/MECH SONACT
 Case 1 : Consider a triple point in the diagram.
At the triple point, three phases coexist in
equilibrium .

 P=3. Since there is one component (water) in the
system C= 1

108

THE USE OF THE PHASE RULE

1/5/2013
 The number of degree of freedom can be

SAB-AP/MECH SONACT
calculated using the Gibbs phase rule as,

 F=1- 3+2

F=0 (Zero degree of freedom)

 This means that one of the variables
(Temperature or pressure) can be changed
at the triple point. 109


1/5/2013
 Note: Since the variables temperature or

SAB-AP/MECH SONACT
pressure cannot be changed and still keep the

three phases of coexistence.

 The triple point is called an invariant point.

110


1/5/2013
Case 2: Next consider a point along liquid-
solid freezing curve

SAB-AP/MECH SONACT
P=2
Then for water system
C=1
Applying the phase rule, we get:
F=1- 2+ 2
F=1 (one degree of freedom)

111


1/5/2013
 This means that one variable

SAB-AP/MECH SONACT
 ( Temperature or pressure) can be changed

independently and still maintain a system

with two coexisting phases.

112


1/5/2013
 Case:3
Now consider a point on the phase

SAB-AP/MECH SONACT
diagram of water inside a single phase in this
case there will be only one phase present.
P=1 ,
Then for water system, C=1
Now the phase rule gives

113


1/5/2013
 F=1-1+2

SAB-AP/MECH SONACT
F=2 ( two degree of freedom)

This means that two variables ( Temperature

and pressure) can be varied independently and

the system will still remain in a single phase.

114


1/5/2013
 Note: In many application (especially for most

SAB-AP/MECH SONACT
binary alloy) the pressure is kept constant at 1

atmosphere.

 In this case Gibbs phase rule is modified as

F=C-P+1

115


1/5/2013
 The above equation is known as condensed phase

SAB-AP/MECH SONACT
rule.

 This equation can be applied to most of

the binary phase diagram.

116

OBJECTIVE TYPE QUESTIONS

1/5/2013
1. -----------May be visualized as forming from a

SAB-AP/MECH SONACT
centre of freezing, or nucleus, which is composed

of a small group of atoms oriented into one of the

common crystal patterns.

Crystal

117

OBJECTIVE TYPE QUESTIONS

1/5/2013
2.Perfect crystal of proper external shape can be

SAB-AP/MECH SONACT
obtained only if crystallisation develops under

conditions

when degree of ----------------is very slight and the

metal has a very high purity.

118

MICRO-CONSTITUENTS OF IRON-CARBON
ALLOYS

1/5/2013
 There are different micorscope constituents of

SAB-AP/MECH SONACT
Iron-Carbon alloys exit.

 The study of these micro-constituents is

essential in order to understand iron-iron

carbide (Fe-Fe3C) equilibrium phase diagram.

119

VARIOUS MICRO-CONSTITUENTS OF IRON-
CARBON ALLOYS ARE:

1/5/2013
1.Ferrite

SAB-AP/MECH SONACT
2.Austenite

3.Cementite

4.Pearlite

5.Ledeburite

120
6.Martensite

CARBON ALLOYS ARE:

1/5/2013
7. Troosite

SAB-AP/MECH SONACT
8. Sorbite, and

9.Bainite

121

CARBON ALLOYS ARE:

1/5/2013
1. Ferrite (or α-Iron)

SAB-AP/MECH SONACT
 Ferrite is a primary solid solution based on α iron

having BCC structure.

 It is Nothing but the interstitial solid solution of

carbon in iron.

122

1/5/2013 SAB-AP/MECH SONACT
123
FERRITE

CARBON ALLOYS ARE:

1/5/2013
 Maximum solubility of carbon in iron is 0.025% carbon

SAB-AP/MECH SONACT
at 723°C, While its solubility at room temperature is

only 0.008%.

 Ferrite is soft, ductile, and highly

Magnetic.

 It can undergo extensive cold working 124

CARBON ALLOYS ARE:

1/5/2013
2. Austenite(or γ-Iron)

SAB-AP/MECH SONACT
 Austenite is a primary solid solution based on γ

iron having FCC structure.

 This is also an interstitial solid solution of

carbon in iron

125

126
AUSTENITE

AUSTENITE

1/5/2013
 It is also a non-magnetic (paramagnetic)

SAB-AP/MECH SONACT
 Austentite has a greater electrical resistance

and coefficient of expansion than ferrite.

127

CEMENTITE

1/5/2013
 Cementite is the name given to the carbide of

SAB-AP/MECH SONACT
iron(Fe3c).

 It is the hard, brittle, intermetallic compound of

iron with 6.69% of carbon.

128

CEMENTITE

1/5/2013
 The hardness and brittleness of cast iron is

SAB-AP/MECH SONACT
believed to be due to the presence of the

cementite.

 It is Magnetic below 250°c

129

130
CEMENTITE

PEARLITE

1/5/2013
 Pearlite is the eutectoid mixture of ferrite

SAB-AP/MECH SONACT
(87.5%) and cementite (12.5%).

 It is formed when austenite decomposes

during cooling. It contains 0.8% of carbon

131

132
PEARLITE

PEARLITE
LAMELLAR-PEARLITE BEADED BAG

1/5/2013
SAB-AP/MECH SONACT
133

PEARLITE

1/5/2013
 It consist of alternate thin layers (or lamellae) of

SAB-AP/MECH SONACT
ferrite and cementite shown in fig.

 The name derives from its lustrous apperance

(similar to mother of pearl) when viewed in

white light under a microscope.

134

PEARLITE

1/5/2013
 The properties of pearlite is midway between

SAB-AP/MECH SONACT
ferrite and cementite. It is relatively strong, hard

and ductile.

135

LEDEBURITE

1/5/2013
 Ledeburite is the eutectic mixture of austenite(γ-Iron) and

SAB-AP/MECH SONACT
cementite (Fe3C) Containing 4.3% carbon.

 In pure iron-carbon alloy, it forms at 1140 °C.

Most of the engineering alloy materials belong to

this range of alloy.

136

LEDEBURITE

1/5/2013
 Pig iron, the most important engineering

SAB-AP/MECH SONACT
material, is ledeburite.

137

138
LEDEBURITE

139
LEDEBURITE

MARTENSITE

1/5/2013
 Martensite is the super saturated solid solution

SAB-AP/MECH SONACT
of carbon in α-Iron.

 It is formed when steel is very rapidly cooled from the

austenitic state.

 It exhibits a characteristic acicular or needle like

structure. 140

MARTENSITE

1/5/2013
 It is very hard more brittle and low ductility

SAB-AP/MECH SONACT
properties.

 There is an increase in specific volume during

formation of martensite from austenite.

141

MARTENSITE

1/5/2013
 As a result internal stresses are set up in the

SAB-AP/MECH SONACT
materials leading to the formation of minute

cracks.

142

MARTENSITE (RED AND YELLOW
MARTENSITE. GREEN: AUSTENITE)

1/5/2013
SAB-AP/MECH SONACT
143

TROOSTITE

1/5/2013
 Troosite is the mixture of radial lamella of

SAB-AP/MECH SONACT
ferrite and cementite. In fact, it differs from

pearlite only in the degree of fitness.

 This constituents is also known as troostite

pearlite.

144

TROOSTITE

1/5/2013
 It is the microstructure consisting ferrite and

SAB-AP/MECH SONACT
finely divided cementite, produced on tempering

martensite below 450 °C

145

TROOSTITE

1/5/2013
 It is formed by the decomposition of austenite

SAB-AP/MECH SONACT
when cooled at a rate slower than that which

will yield a martensitic structure and faster than

that which will produce a sorbitic structure.

146

TROOSTITE

1/5/2013
 It has hardness intermediate between

SAB-AP/MECH SONACT
martensite and sorbite.

147

148
TROOSTITE

SORBITE

1/5/2013
 Sorbite is the microstructure consisting ferrite,

SAB-AP/MECH SONACT
and finely divided cementite, produced on

tempering martensite above 450°C

149

SORBITE

1/5/2013
 This constituents is also known as sorbitic

SAB-AP/MECH SONACT
pearlite.

 It is formed by the decomposition of austenite

when cooled at a rate slower than that which

will produce a pearlitic structure

150

SORBITE

1/5/2013
 Though sorbitic steel is slightly less ductile than

SAB-AP/MECH SONACT
pearlite steel, its tensile and yield strength are

high.

 The sorbite steels are often known as Toughened

steels.

151

152
SORBITE

SORBITE

1/5/2013
Note:

SAB-AP/MECH SONACT
 All the pearlite, troosite and sorbite are ferrite-

cementite mixtures having lamellar structure.

 However they are distinguished by their degree of

dispersion.

 Pearlite has corase pearlite.
153

SORBITE

1/5/2013
 Troosite has fine pearlite

SAB-AP/MECH SONACT
 And sorbite has medium pearlite

154

BAINITE

1/5/2013
 Bainite is a decomposition product of austenite,

SAB-AP/MECH SONACT
consisting of an aggregate of ferrite and carbide.

 Bainite is obtained by transformation of pearlite

higher temperature ( has a feathery structure) is

called upper bainite.

155

BAINITE

1/5/2013
 Lower bainite provides high mechanical

SAB-AP/MECH SONACT
properties and that is why it is extensively

used for components of machine and structures.

 Bainite has hardness in between the hardness

of pearlite and martensite.

156

157
BAINITE

IRON/CARBON ALLOY PHASE DIAGRAM

1/5/2013
SAB-AP/MECH SONACT
158

159

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