MATERIAL SCIENCE LECTURE NOTES.pptx

MATERIAL SCIENCE
BY-
SAMEER VISHWAKARMA
BHUPENDRA KUMAR SARASWAT
UNIVERSITY POLYTECHNIC

SYLLABUS
MODULE 1
 Introduction: Material, History of Material Origin, Scope of Material Science, Overview
of different engineering materials and applications, Classification of materials,
Thermal, Chemical, Electrical, Mechanical properties of various materials, Present and
future needs of materials, Overview of Biomaterials and semi conducting materials,
Various issues of Material Usage- Economical, Environment and Social.
 Crystallography Fundamentals: Crystal, Unit Cell, Space Lattice, Arrangement of
atoms in Simple Cubic Crystals, BCC, FCC and HCP Crystals, Number of atoms per
unit Cell, Atomic Packing Factor. Metals And Alloys
 Introduction: History and development of iron and steel, Different iron ores, Raw
Materials in Production of Iron and Steel, Basic Process of iron-making and steel-
making, Classification of iron and steel,
 Cast Iron: Different types of Cast Iron, manufacture and their usage.

SYLLABUS
MODULE 2
 Steels
Steels and alloy steel, Classification of plain carbon steels, Availability, Properties and usage of
different types of Plain Carbon Steels, Effect of various alloys on properties of steel, Uses of
alloy steels (high speed steel, stainless steel, spring steel, silicon steel) Spring materials,
Iron –carbon diagram, TTT Diagram.
 Concepts and effects of Heat Treatment
Purpose of heat treatment, Cooling Curves various heaT treatment processes hardening,
tempering, nnealing, normalizing, Case hardening and surface hardening.
 Non Ferrous
Materials: Properties and uses of Light Metals and their alloys, properties and uses of White
Metals and their alloys.
 Engineering Plastics
Important sources of plastics, Classification-thermoplastic and thermo set and their uses,
Various Trade names of engg. Plastics, Plastic Coatings
 Ceramics: Classification, properties, applications
 Heat insulating materials Miscellaneous Materials
 Properties and uses of Asbestos, Glass wool, thermocole, cork, mica. Overview of tool and die
materials, Materials for bearing metals, Materials for Nuclear Energy, Refractory materials.
 Composites
 Classification, properties, applications

WHY TO STUDY MATERIAL SCIENCE
 To understand how materials are made
 To know how materials behave under load and on environmental
conditions
 To know the effect of mixing and how mixing (alloying) changes the
material properties
 To know about structure of material
 To select a material for different engineering vapplications
 To optimize the overall cost of a product
 For research
 To become multidisiplinary engineer

CHAPTER 1
HISTORY, CLASSIFICATION AND PROPERTIES
OF MATERIALS
https://www.youtube.com/watch?v=qShgQd6a
AEc&t=409s

HISTORY OF MATERIAL ORIGIN
TIME DURATION EXAMPLES
PRE-HISTORY 300,000 BCE FLINT
STONE AGE 30,000 BCE–10,000
BCE
STONE AXE
BRONZE AGE 5,500 BCE-3000 BCE GOLD, SILVER, COPPER , COOPER –TIN ALLOYS
IRON AGE 1,200 BCE- 2ND
CENTURY
IRON, GLASS, STEELS , PAPER
ROMAN AGE
(ANTIQUITY)
31 BC – 5TH CENTURY CEMENT, WOOD, BONE, STONES, CRYSTALLINE
MATERIALS, ASBESTOS, CORK, OXIDES
MIDDLE AGE A.D. 476 -A.D. 1450 DEMASCUS STEEL, LEATHER, LINEN, SILK, FUR,
STEEL UTENSILS
EARLY MODERN
PERIOD
A.D. 1450-A.D. 1750 RUBBER, MICROSCOPE, TELESCOPE, ZINC,
P.O.P.,
ZINC-ACID BATTERY, ALUMINUM
MODERN AGE A.D. 1750-Present ALLOYS, CERAMICS, SILICON CHIPS, POLYMERS,

ENGINEERING MATERIALS
 Engineering materials refers to the
group of materials that are used in
the construction of manmade
structures and components.
 The primary function of an
engineering material is to withstand
applied loading without breaking and
without exhibiting excessive
deflection.

PROPERTIES OF MATERIALS
 PHYSICAL PROPERTIES
 CHEMICAL PROPERTIES
 MECHANICAL PROPERTIES
 ELECTRICAL PROPERTIES
 THERMAL PROPETIES
https://www.youtube.com/watch?v=B15xoj3b4eo
https://www.youtube.com/watch?v=E5uc4Brkivc&t=1643s

PHYSICAL PROPERTIES OF MATERIAL
HTTPS://WWW.YOUTUBE.COM/WATCH?V=B15XOJ3B4EO
The physical properties of a material
are those which can be observed
without any change of the identity of
material.
 Density
 Specific gravity
 State Change temperatures
 Coefficients of thermal expansion
 Specific Heat
 Latent heat
 Fluidity
 Weld ability
 Elasticity
 Plasticity
 Porosity
 Thermal conductivity
 Electrical Conductivity

CHEMICAL PROPERTIES OF MATERIAL
HTTPS://WWW.YOUTUBE.COM/WATCH?V=B15XOJ3B4EO
 Chemical composition
 Atomic bonding
 Corrosion resistance
 Acidity or Alkalinity

MECHANICAL PROPERTIES OF MATERIAL
 Strength
 Elasticity
 Plasticity
 Hardness
 Toughness
 Brittleness
 Stiffness
 Ductility
 Malleability
 Cohesion
 Impact strength
 Fatigue
 Creep
https://www.youtube.com/watch?v=E5uc4Brkivc&t=1643s

STRENGTH
 Strength is the mechanical property that enables a metal to resist
deformation load.
 The strength of a material is its capacity to withstand destruction
under the action of external loads.
 The stronger the materials the greater the load it can withstand.

ELASTICITY
 According to dictionary elasticity is the ability
of an object or material to resume its normal
shape after being stretched or compressed.
 When a material has a load applied to it, the
load causes the material to deform.
 The elasticity of a material is its power of
coming back to its original position after
deformation when the stress or load is
released.
 Heat-treated springs, rubber etc are good
examples of elastic materials.

PLASTICITY
 The plasticity of a material is its
ability to undergo some permanent
deformation without rupture(brittle).
 Plastic deformation will take place
only after the elastic range has been
exceeded.
 Pieces of evidence of plastic action in
structural materials are called yield,
plastic flow and creep.
 Materials such as clay, lead etc are
plastic at room temperature, and steel
plastic when at bright red-heat.


HARDNESS
 The resistance of a material to force
penetration or bending is hardness.
 The hardness is the ability of a
material to resist scratching,
abrasion, cutting or penetration.
 Hardness indicates the degree of
hardness of a material that can be
imparted particularly steel by the
process of hardening.
 It determines the depth and
distribution of hardness is introduce by
the quenching process.

TOUGHNESS
 It is the property of a material which enables it to withstand shock or
impact.
 Toughness is the opposite condition of brittleness.
 The toughness is may be considering the combination of strength and
plasticity.
 Manganese steel, wrought iron, mild steel etc are examples of toughness
materials.

BRITTLENESS
 The brittleness of a property of a
material which enables it to
withstand permanent deformation.
 Cast iron, glass are examples of
brittle materials.
 They will break rather than bend
under shock or impact.
 Generally, the brittle metals have high
compressive strength but low in
tensile strength.

STIFFNESS
 It is a mechanical property.
 The stiffness is the resistance of a
material to elastic deformation or
deflection.
 In stiffness, a material which suffers light
deformation under load has a high degree
of stiffness.
 The stiffness of a structure is important in
many engineering applications, so the
modulus of elasticity is often one of the
primary properties when selecting a
material.

DUCTILITY
 The ductility is a property of
a material which enables it to
be drawn out into a thin wire.
 Mild steel, copper, aluminium
are the good examples of a
ductile material.

MALLEABILITY
 The malleability is a property of a material which permits it to
be hammered or rolled into sheets of other sizes and shapes.
 Aluminium, copper, tin, lead etc are examples of malleable
metals.

COHESION
 It is a mechanical property.
 The cohesion is a property of a solid body by virtue of which they
resist from being broken into a fragment.

IMPACT STRENGTH
 The impact strength is the ability of a metal to resist suddenly
applied loads.

FATIGUE
 The fatigue is the long effect of repeated straining action which
causes the strain or break of the material.
 It is the term 'fatigue' use to describe the fatigue of material
under repeatedly applied forces.

CREEP
 The creep is a slow and
progressive deformation of a material
with time at a constant force.
 The simplest type of creep
deformation is viscous flow.
 Some metals are generally exhibiting
creep at high temperature, whereas
plastic, rubber, and similar amorphous
material are very temperature
sensitive to creep.
 The force for a specified rate of strain at
constant temperature is called creep
strength.

ELECTRICAL PROPERTIES OF MATERIAL
 Resistivity
 Conductivity
 Permittivity
 Thermoelectricity

THERMAL PROPERTIES OF MATERIAL
 Specific Heat
 Heat capacity
 Thermal Expansion
 Thermal conductivity
 Melting point
 Boiling point
 Freezing point
 Dew point

 Specific Heat
 the quantity of heat required to raise the temperature of one gram of a
substance by one Celsius degree.
 Heat capacity
 the amount of heat required to raise the temperature of an object by 1 degree
Celcius.
 Thermal Expansion
 Thermal expansion is the tendency of matter to change its shape, area, volume,
and density in response to a change in temperature.
 Thermal conductivity
 The rate at which heat is transferred by conduction through a unit cross-section
area of a material.

 Melting point
 The temperature at which it changes state from solid to liquid.
 Boiling point
 The temperature at which the liquid boils and changes into gaseous state at the
atmospheric pressure is called boiling point.
 Freezing point
 Liquids have a characteristic temperature at which they turn into solids, known as
their freezing point.
 Dew point
 The temperature at which the air is completely saturated and can't hold any more
moisture.

BIOMATERIALS
 Polymers, synthetic and natural
 Metals
 Ceramics
 Composites

CHAPTER 3
CONDUCTOR, SEMICONDUCTOR AND INSULATORS

CONDUCTOR, SEMI CONDUCTORS AND INSULATORS
 Insulators An insulator is a material that does not conduct electrical current
under normal conditions. Most good insulators are compounds rather than single-
element materials and have very high resistivities. Valence electrons are tightly
bound to the atoms; therefore, there are very few free electrons in an insulator.
Examples of insulators are rubber, plastics, glass, and quartz.
 Conductors A conductor is a material that easily conducts electrical current.
Most metals are good conductors. The best conductors are single-element
materials, such as copper (Cu), silver (Ag), gold (Au), and aluminum (Al), which
are characterized by atoms with only one valence electron very loosely bound to
the atom. These loosely bound valence electrons become free electrons.
Therefore, in a conductive material the free electrons are valence electrons.

CONDUCTOR, SEMI CONDUCTORS AND INSULATORS
 Semiconductors A semiconductor is a material that is between conductors and
insulators in its ability to conduct electrical current. A semiconductor in its pure
(intrinsic) state is neither a good conductor nor a good insulator. Single element
semiconductors are antimony (Sb), arsenic (As), boron (B), silicon (Si), and
germanium (Ge). Compound semiconductors such as gallium arsenide, are also
commonly used. The single-element semiconductors are characterized by atoms
with four valence electrons. Silicon is the most commonly used semiconductor.

INSULATORS, CONDUCTORS, SEMICONDUCTORS
FROM ENERGY BAND STRUCTURES
E
valence band
filled
conduction band
empty
Forbidden
region Eg > 5eV
Band
gap
E
conduction
band
Eg < 5eV
Band
gap
+
-
electron
hole
E
valence
band
partially-filled
band
Insulator Semiconductor Conductor

CHAPTER 4
CRYTALLOGRAPHY
https://www.youtube.com/watch?v=zuR2wnJlrOk&t=998
s

CRYSTALLOGRAPHY
 CRYSTAL: A crystal is a solid whose atoms are arranged in a "highly
ordered" repeating pattern. These patterns are called crystal systems. If a
mineral has its atoms arranged in one of them, then that mineral is a
crystal.
 UNIT CELL: A unit cell is the smallest representation of an entire crystal.
 The unit cell is the simplest repeating unit in the crystal.
 Opposite faces of a unit cell are parallel.
 SPACE LATTICE: A space lattice is an array of points showing how
particles (atoms, ions or molecules) are arranged at different sites in three
dimensional spaces.

SIMPLE CUBIC CELL
 The simple cubic unit cell is delineated by eight atoms, which mark the
actual cube. These are corner atoms, so each one only contributes one
eighth of an atom to the unit cell, thus giving us only one net atom.

BODY CENTRED CUBIC (BCC) CELL
 A BCC unit cell has atoms at each corner
of the cube and an atom at the centre of
the structure. The diagram shown below is
an open structure. According to this
structure, the atom at the body centre
wholly belongs to the unit cell in which it is
present.
 In BCC unit cell every corner has atoms.
 There is one atom present at the centre of the
structure
 Below diagram is an open structure
 According to this structure atom at the body
centres wholly belongs to the unit cell in which
it is present.

FACE CENTRED CUBIC (FCC) CELL
 An FCC unit cell contains atoms at all the
corners of the crystal lattice and at the centre
of all the faces of the cube. The atom
present at the face-centered is shared
between 2 adjacent unit cells and only 1/2 of
each atom belongs to an individual cell.
 In FCC unit cell atoms are present in all the
corners of the crystal lattice
 Also, there is an atom present at the centre of
every face of the cube
 This face-centre atom is shared between two
adjacent unit cells
 Only 12 of each atom belongs to a unit cell

HEXAGONAL CLOSE PACKED (HCP) CELL
 The Hexagonal Close-
Packed (HCP) crystal
structure is one of the most
common ways for atoms to
arrange themselves in
metals.
 HCP is one of the most
stable crystal structures and
has the highest packing
density.

ATOMIC PACKING FACTOR (APF)
Atomic packing is the ratio of total volume of atoms and total volume of the
unit cell.
APF =
APF =
Where Ne = Effective number of atoms = Ni + (Nf /2) + (Nc / No of corners)
here, Ni = Number of atoms inside the cell
Nf = Number of atoms on the face
Nc = Number of corners

CHAPTER 5
INTRODUCTION TO IRON AND STEEL

IRON ORES
HEMATITE MAGNETITE
SIDERITE
LIMONITE

MAKING PIG IRON (BLAST FURNACE)
Go throu the video:
https://www.youtube.com/shorts/18dVw06bJ0g
MAKING CAST IRON (CUPOLA FURNACE)
Go throu the video:
https://www.youtube.com/watch?v=znL8sqK1-sQ

TYPES OF CASTE IRON
 There are primarily 4 different types of cast iron. Different processing
techniques can be used to produce the desired type, which include:
 Grey Cast Iron
 White Cast Iron
 Ductile Cast Iron
 Malleable Cast Iron

Grey Cast Iron
 Grey Cast iron refers to a type of cast iron that has been processed to
produce free graphite (carbon) molecules in the metal. The size and
structure of the graphite can be controlled by moderating the cooling rate of
the iron and by adding silicon to stabilize the graphite. When Grey Cast Iron
fractures, it fractures along the graphite flakes and has a grey appearance
at the fracture site.
 Grey Cast Iron is not as ductile as other cast irons, however it has an
excellent thermal conductivity and the best damping capacity of all cast
irons. It is also hard wearing making it a popular material to work with.
 The high wear resistance, high thermal conductivity, and the excellent
damping capacity of Grey Cast Iron makes it ideal for engine blocks, fly
wheels, manifolds, and cookware.
 It has Good machinability
 It has Good resistance to galling and wear
 It has high compressive strength
 It is brittle

White Cast Iron
 White Cast Iron is named based on the appearance of fractures. By
tightly controlling the carbon content, reducing the silicon content, and
controlling the cooling rate of iron, it is possible to consume all carbon in
the iron in the generation of iron carbide. This ensures there are no free
graphite molecules and creates an iron that is hard, brittle, extremely
wear resistant and has a high compressive strength. As there are no free
graphite molecules, any fracture site appears white, giving White Cast
Iron its name.
 White Cast Iron is used primarily for its wear resistant properties in pump
housings, mill linings and rods, crushers and brake shoes.
 It has High compressive strength
 It is difficult to machine
 It has Good hardness
 It has Resistance to wear

Ductile Cast Iron
 Ductile Cast Iron is produced by adding a small amount of magnesium,
approximately 0.2%, which makes the graphite form spherical inclusions
that give a more ductile cast iron. It can also withstand thermal cycling
better than other cast iron products.
 Ductile Cast Iron is predominantly used for its relative ductility and can be
found extensively in water and sewerage infrastructure. The thermal
cycling resistance also makes it a popular choice for crankshafts, gears,
heavy duty suspensions and brakes.
 It has High ductility
 It has High strength

Malleable Cast Iron
 Malleable Cast Iron is a type of cast iron that is manufactured by heat
treating White Cast Iron to break down the iron carbide back into free
graphite. This produces a malleable and ductile product that has good
fracture toughness at low temperatures.
 Malleable Cast Iron is used for electrical fittings, mining equipment and
machine parts.
 Its properties are
 They have High ductility
 They are tougher than gray cast iron
 They can be twisted or bent without fracture
 They have excellent machining capabilities

ADVANTAGES OF CAST IRON
 It has Good casting properties
 It is available in large quantities,
hence produced in mass scale.
Tools required for casting process
are relatively cheap and
inexpensive. This results into low
cost of its products.
 It can be given any complex shape
and size without using
costly machining operations
 It has three to five times more
compression strength compared to
steel
 It has Good machinability (gray
cast iron)
 It has excellent anti-vibration (or
damping) properties hence it is
used to make machine frames
 It has good Sensibility
 It has excellent resistance to wear
 It has constant Mechanical
properties between 20 to 350
degree Celsius
 It has very low notch sensitivity
 It has Low stress concentration
 It bears Low cost
 It has Durability
 It has Resistance to deformation

DISADVANTAGES OF CAST IRON
 It is Prone to rusting
 It has poor tensile strength
 Its parts are section sensitive, this is due to slow cooling of thick sections.
 failure of Its parts is sudden and total, it does not exhibit yield point.
 It has poor impact resistance
 Compared to steel it has poor machinability
 It has High weight to strength ratio
 It has High brittleness
 It is Non machinable (white cast iron)

APPLICATIONS OF CAST IRON
 It is used in making pipes, to carry suitable fluids
 It is used in making different machines
 It is used in making automotive parts
 It is used in making pots pans and utensils
 It is used in making anchor for ships.

CHAPTER 1
 TYPES OF STEEL
 EFFECT OF VARIOUS ELEMENTS ON STEEL
 APPLICATIONS OF STEEL

 Tantalum (TA)
 Used as stabilizing elements in stainless steels. Each has a high affinity for carbon
and forms carbides, which are uniformly dispersed throughout the steel. Thus,
localized precipitation of carbides at grain boundaries is prevented.
 Titanium (TI)
 Used as stabilizing elements in stainless steels. Each has a high affinity for carbon
and forms carbides, which are uniformly dispersed throughout the steel. Thus,
localized precipitation of carbides at grain boundaries is prevented.
 Tungsten (W)
 Increases strength, wear resistance, hardness and toughness. Tungsten steels
have superior hot-working and greater cutting efficiency at elevated temperatures.
 Vanadium (V)
 Increases strength, hardness, wear resistance and resistance to shock impact. It
retards grain growth, permitting higher quenching temperatures. It also enhances
the red-hardness properties of high-speed metal cutting tools.

TYPES OF STEEL
1. CARBON STEEL
 Carbon steel looks dull, matte-like, and is known to be vulnerable to
corrosion.
 Overall, there are three subtypes to this one: low, medium, and high
carbon steel, with low containing about .30% of carbon, medium .60%,
and high 1.5%.
 The name itself actually comes from the reality that they contain a very
small amount of other alloying elements.
 They are exceptionally strong, which is why they are often used to make
things like knives, high-tension wires, automotive parts, and other similar
items.

2. ALLOY STEEL
 Next up is alloy steel, which is a mixture of several different metals, like
nickel, copper, and aluminum.
 These tend to be more on the cheaper side, more resistant to corrosion
and are favored for some car parts, pipelines, ship hulls, and mechanical
projects.
 For this one, the strength depends on the concentration of the elements
that it contains.

3. TOOL STEEL
 Tool steel is famous for being hard and both heat and scrape resistant.
 The name is derived from the fact that they are very commonly used to
make metal tools, like hammers
 For these, they are made up of things like cobalt, molybdenum, and
tungsten, and that is the underlying reason why tool steel has such
advanced durability and heat resistance features.

4. STAINLESS STEEL
 Last but not least, stainless steels are probably the most well-known type
on the market.
 This type is shiny and generally has around 10 to 20% chromium, which
is their main alloying element. With this combination, it allows the steel to
be resistant to corrosion and very easily molded into varying shapes.
 Because of their easy manipulation, flexibility, and quality, stainless steel
can be found in surgical equipment, home applications, silverware, and
even implemented as exterior cladding for commercial/industrial buildings.

EFFECTS OF COMMON ALLOYING ELEMENTS IN STEEL
Carbon (C)
 The most important constituent of steel. It raises tensile strength, hardness,
and resistance to wear and abrasion. It lowers ductility, toughness and
machinability.
Chromium (CR)
 Increases tensile strength, hardness, hardenability, toughness, resistance to
wear and abrasion, resistance to corrosion, and scaling at elevated
temperatures.
Cobalt (CO)
 Increases strength and hardness and permits higher quenching
temperatures and increases the red hardness of high speed steel. It also
intensifies the individual effects of other major elements in more complex
steels.
Columbium (CB)
 Used as stabilizing elements in stainless steels. Each has a high affinity for
carbon and forms carbides, which are uniformly dispersed throughout the
steel. Thus, localized precipitation of carbides at grain boundaries is
prevented.

Copper (CU)
 In significant amounts is detrimental to hot-working steels. Copper negatively
affects forge welding, but does not seriously affect arc or oxyacetylene welding.
Copper can be detrimental to surface quality. Copper is beneficial to atmospheric
corrosion resistance when present in amounts exceeding 0.20%. Weathering
steels are sold having greater than 0.20% Copper.
Manganese (MN)
 A deoxidizer and degasifier and reacts with sulfur to improve forgeability. It
increases tensile strength, hardness, hardenability and resistance to wear. It
decreases tendency toward scaling and distortion. It increases the rate of carbon-
penetration in carburizing.
Molybdenum (MO)
 Increases strength, hardness, hardenability, and toughness, as well as creep
resistance and strength at elevated temperatures. It improves machinability and
resistance to corrosion and it intensifies the effects of other alloying elements. In
hot-work steels and high speed steels, it increases red-hardness properties.

Phosphorus (P)
 Increases strength and hardness and improves machinability. However, it
adds marked brittleness or cold-shortness to steel.
Silicon (SI)
 A deoxidizer and degasifier. It increases tensile and yield strength,
hardness, forgeability and magnetic permeability.
Sulfur (S)
 Improves machinability in free-cutting steels, but without sufficient
manganese it produces brittleness at red heat. It decreases weldability,
impact toughness and ductility.
Nickel (NI)
 Increases strength and hardness without sacrificing ductility and toughness.
It also increases resistance to corrosion and scaling at elevated
temperatures when introduced in suitable quantities in high-chromium
(stainless) steels.

APPLICATIONS OF STEEL
Long
 A steel bridge
 A steel pylon suspending overhead power lines
 As reinforcing bars and mesh in reinforced concrete
 Railroad tracks
 Structural steel in modern buildings and bridges
 Wires
 Input to reforging applications

Flat carbon
 Major appliances
 Magnetic cores
 The inside and outside body of automobiles, trains, and ships.
Weathering (COR-TEN)
 Intermodal containers
 Outdoor sculptures
 Architecture
 Highliner train cars

Stainless Steel
 A stainless steel gravy boat
 Cutlery
 Rulers
 Surgical instruments
 Watches
 Guns
 Rail passenger vehicles
 Tablets
 Trash Cans
 Body piercing jewellery
 Inexpensive rings
 Components of spacecraft and space stations

CHAPTER 2
 IRON-CARBON DIAGRAM
 TTT DIAGRAM
 HEAT TREATMENT
REFER-
https://www.youtube.com/watch?v=4F6ANK6fIUA

ALLOTROPIC TRANSFORMATIONS IN IRON
 Iron is an allotropic metal,
which means that it can exist in
more than one type of lattice
 structure depending upon
temperature. A cooling curve
for pure iron is shown in fig:

THE IRON–IRON CARBIDE (FE–FE3C) PHASE DIAGRAM
 The Fe-C (or more precisely the Fe-Fe3C) diagram is an important one.
Cementite is a metastable phase and ‘strictly speaking’ should not be
included in a phase diagram. But the decomposition rate of cementite is
small and hence can be thought of as ‘stable enough’ to be included in a
phase diagram. Hence, we typically consider the Fe-Fe3C part of the Fe-C
phase diagram.
 C is an interstitial impurity in Fe. It forms a solid solution with α, γ, δ
phases of iron

 In their simplest form,
steels are alloys of
Iron (Fe) and Carbon
(C). The Fe-C phase
diagram is a fairly
complex one, but we
will only consider the
steel part of the
diagram, up to around
7% Carbon.
 Carbon Solubility in
Iron
Solubility of carbon in Fe
is function of structure
and temperature.

PHASES APPEARED IN FE–FE3C PHASE DIAGRAM
1. α-ferrite ( solid solution of C in BCC Fe)
 It is an interstitial solid solution of a small
amount of carbon dissolved in α iron.
 BCC has relatively small interstitial positions
 The maximum solubility is 0.022%C at 723 °
C and it dissolves only 0.008%C at room
temperature. BCC has relatively small
interstitial positions
 It is the softest structure that appears on the
diagram
• Transforms to FCC γ-austenite at 912 °C

2. Γ-AUSTENITE –(SOLID SOLUTION OF C IN FCC FE)
• The maximum solubility of C is
2.14 wt %. at 1147 ° C. FCC has
larger interstitial positions.
• Transforms to BCC δ-ferrite at
1395 °C
• Is not stable below the eutectic
temperature(727°C) unless cooled
rapidly (discuss later in unit4)

solid solution of carbon in α-iron.
α-ferrite BCC crystal structure
low solubility of carbon – up to 0.25%
at 1333 ºF (723ºC). α-ferrite exists at RT
γ(Austenite)
 Interstitial solid solution of carbon in γ iron.
Austenite has FCC crystal structure,
high solubility of carbon up to 2.14% at
(1147ºC).
Soft, ductile, malleable and non-magnetic
γ

3. δ-ferrite (solid solution of C in BCC Fe)
• The same structure as α-ferrite
• Stable only at high T, above 1394 °C. The stability of the phase
ranges between 1394-1539°C.
 Melts at 1538 °C
4. Fe-C liquid solution

δ-(FERRRITE)
Solid solution of carbon in δ-iron.
The crystal structure of δ-ferrite is BCC
(cubic body centered).
δ

5. FE3C (IRON CARBIDE OR CEMENTITE)
• This intermetallic compound is metastable, it remains as a compound
indefinitely at room T, but decomposes (very slowly, within several years)
into α-Fe and C (graphite) at 650 - 700 °C
 It is typically hard and brittle interstitial compound of low tensile strength
(approx. 5000psi) but high compressive strength.
 It is the hardest structure that appears on the diagram.

Fe3C-(Cementite)
 Intermetallic compound, having fixed composition
Fe3C.
Orthorhombic crystal structure,12-iron .4- carbon
Hard and brittle
Ferromagnetic upto 210 C
Fe3C

Peritectic Reaction:
L + δ → γ
(0.55%C) (0.10%C) (0.18%C)
S1 + L S2
δ =
0.55
0.55-0.18
0.55-0.1
X 100
= 82.2 %
0.18-0.1
0.55-0.1
L = X 100
= 17.8%
1492 ºC

EUTECTIC AND EUTECTOID REACTIONS IN FE–FE3C
γ(0.76 wt% C) ↔ α (0.022 wt% C) +
Fe3C

Eutectoid Reaction:
γ → α + Fe3C
S1 S2 + S3
727 ºC
α =
6.67-0.8
6.67-0.008
x 100
= 88.1%
Fe3C =
0.8- 0.025
6.67-0.008
100
x
= 11.09 %
(0.80%C) (0.025%C) (6.67%C)
Fe3C
Fe3C
Pearlite

Eutectic Reaction (at)
Liquid → γ + Fe3C
(4.30%C) (2.00%C) (6.67%C)
L1 S1 + S2
Ledeburite
1147 ºC

TTT DIAGRAMS
TTT diagram stands for “time-temperature-
transformation” diagram. It is also called
isothermal transformation diagram
Definition: TTT diagrams give the kinetics of
isothermal transformations.

T (Time) T(Temperature) T(Transformation) diagram is a plot of temperature versus the
logarithm of time for a steel alloy of definite composition. It is used to determine when
transformations begin and end for an isothermal (constant temperature) heat treatment of a
previously austenitized alloy. When austenite is cooled slowly to a temperature below LCT
(Lower Critical Temperature), the structure that is formed is Pearlite. As the cooling rate
increases, the pearlite transformation temperature gets lower. The microstructure of the
material is significantly altered as the cooling rate increases. By heating and cooling a
series of samples, the history of the austenite transformation may be recorded. TTT
diagram indicates when a specific transformation starts and ends and it also shows what
percentage of transformation of austenite at a particular temperature is achieved.
TTT DIAGRAM

Stable Austenite
Unstable Austenite
Transformation
starts/begins
Transformation ends
Coarse Pearlite
Fine Pearlite
Unstable Austenite
Feathery Bainite
Acicular Bainite
Ms
Mf
Austenite + Martensite
Martensite Time-Temperature Transformation Curves

STABLE AUSTENITE
Bianite in feather
shaped patches
Degree of under
cooling high
Sluggish
transformation
Austenite to
Coarse Pearlite
Greater time for
diffusion
Slow rate of diffusion of
Carbon atoms retards
increased tendency of
Austenite transformation,
550
550-220
Near A1

Austenite is stable at temperatures above LCT but unstable below LCT. Left curve
indicates the start of a transformation and right curve represents the finish of a
transformation. The area between the two curves indicates the transformation of austenite
to different types of crystal structures. (Austenite to pearlite, austenite to martensite,
austenite to bainite transformation.) Isothermal Transform Diagram shows that γ to
transformation (a) is rapid! at speed of sound; (b) the percentage of transformation depends
on Temperature only:

Upper half of TTT Diagram
(Austenite-Pearlite Transformation Area)

As indicated when is cooled to temperatures below LCT, it transforms to other
crystal structures due to its unstable nature. A specific cooling rate may be chosen
so that the transformation of austenite can be 50 %, 100 % etc. If the cooling rate is
very slow such as annealing process, the cooling curve passes through the entire
transformation area and the end product of this the cooling process becomes 100%
Pearlite. In other words, when slow cooling is applied, all the Austenite will
transform to Pearlite. If the cooling curve passes through the middle of the
transformation area, the end product is 50 % Austenite and 50 % Pearlite, which
means that at certain cooling rates we can retain part of the Austenite, without
transforming it into Pearlite.

Lower half of TTT Diagram
(Austenite-Martensite and Bainite Transformation Areas)

If a cooling rate is very high, the cooling curve will remain
on the left hand side of the Transformation Start curve. In
this case all Austenite will transform to Martensite. If there
is no interruption in cooling the end product will be
martensite.

TTT DIAGRAM GIVES
- Nature of transformation-isothermal or athermal
(time independent) or mixed
- Type of transformation-reconstructive, or displacive
- Rate of transformation
- Stability of phases under isothermal transformation
conditions
- Temperature or time required to start or finish
transformation
- Qualitative information about size scale of product
- Hardness of transformed products

FACTORS AFFECTING TTT DIAGRAM
Composition of steel-
(a) carbon wt%,
(b) alloying element wt%
Grain size of austenite
Heterogeneity of austenite

HEAT TREATMENT
 Heat treatment is a method used to alter the physical, and sometimes
chemical properties of a material. The most common application is
metallurgical
  It involves the use of heating or chilling, normally to extreme
temperatures, to achieve a desired result such as hardening or softening
of a material
 It applies only to processes where the heating and cooling are done for
the specific purpose of altering properties intentionally
 Generally, heat treatment uses phase transformation during heating and
cooling to change a microstructure in a solid state.

 Hardening: When a metal is hardened, it’s heated to a point where the
elements in the material transform into a solution. Defects in the
structure are then transformed by creating a reliable solution and
strengthening the metal. This increases the hardness of the metal or
alloy, making it less malleable.
 Annealing: This process is used on metals like copper, aluminum,
silver, steel, and brass. These materials are heated to a certain
temperature, are held at that temperature until transformation occurs,
and then are slowly air-dried. This process softens the metal, making it
more workable and less likely to fracture or crack.
HEAT TREATMENT : TYPES

 Tempering: Some materials like iron-based alloys are very hard, making
them brittle. Tempering can reduce brittleness and strengthen the metal. In
the tempering process, the metal is heated to a temperature lower than
the critical point to reduce brittleness and maintain hardness.
 Case Hardening: The outside of the material is hardened while the inside
remains soft. Since hardening can cause materials to become brittle, case
hardening is used for materials that require flexibility while maintaining a
durable wear layer.
 Normalization: Similar to annealing, this process makes the steel more
tough and ductile by heating the material to critical temperatures and
keeping it at this temperature until transformation occurs.

CHAPTER 3
NON-FERROUS METALS
 Aluminium and its alloys
 Copper and its alloys
 Tin and its alloys
 Zinc and its alloys

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