Subject: Engineering Materials and Metallurgy
Course Objective: The objectives of this course are to: (1) reinforce
fundamental concepts and introduce advanced topics in physical metallurgy, and
(2) develop literacy in major alloy systems, with emphasis on microstructural
evolution and structure-properties relations. From a foundation in modern
physical metallurgy, the student will understand the basis for optimization of the
structural metallic alloys that enable modern technology. Topics; including
equilibrium phase diagrams, thermodynamics, diffusional and martensitic
transformation kinetics, recrystallization, and grain growth; are discussed in
conjunction with transition-metal alloys based on iron, nickel and titanium, as well
as with thermomechanical processing methods.
Historical Perspective
Materials are so important in the development of civilization that we associate
Ages with them. In the origin of human life on Earth, the Stone Age, people used
only natural materials, like stone, clay, skins, and wood. When people found
copper and how to make it harder by alloying, the Bronze Age started about 3000
BC. The use of iron and steel, a stronger material that gave advantage in wars
started at about 1200 BC. The next big step was the discovery of a cheap
process to make steel around 1850, which enabled the railroads and the building
of the modern infrastructure of the industrial world.
Materials Science and Engineering
The combination of physics, chemistry, and the focus on the relationship
between the properties of a material and its microstructure is the domain of
Materials Science. The development of this science allowed designing materials
and provided a knowledge base for the engineering applications (Materials
Engineering).
Advantages of Studying Materials Science and Engineering
To be able to select a material for a given use based on considerations of cost
and performance.
To understand the limits of materials
To change the material properties based on the use.
To be able to create a new material that will have some desirable properties.
UNIT-I
Classification of Materials
According to the way the atoms bound together:
Metals: valence electrons are detached from atoms, and spread in an 'electron
sea' that "glues" the ions together. Metals are usually strong, conduct electricity
and heat well and are opaque to light (shiny if polished). Examples: aluminum,
steel, brass, gold.
Semiconductors: the bonding is covalent (electrons are shared between atoms).
Their electrical properties depend extremely strongly on minute proportions of
contaminants. They are opaque to visible light but transparent to the infrared.
Examples: Si, Ge, GaAs.
Ceramics: atoms behave mostly like either positive or negative ions, and are
bound by Coulomb forces between them. They are usually combinations of
metals or semiconductors with oxygen, nitrogen or carbon (oxides, nitrides, and
carbides). Examples: glass, porcelain, many minerals.
Polymers: are bound by covalent forces and also by weak van der Waals forces,
and usually based on H, C and other non-metallic elements. They decompose at
moderate temperatures (100 – 400 C), and are lightweight. Other properties vary
greatly. Examples: plastics (nylon, Teflon, polyester) and rubber.
Types of Bonding
Ionic Bonding
This is the bond when one of the atoms is negative (has an extra electron) and
another is positive (has lost an electron). Then there is a strong, direct Coulomb
attraction. An example is NaCl. In the molecule, there are more electrons around
Cl, forming Cl- and less around Na, forming Na+. Ionic bonds are the strongest
bonds.
Covalent Bonding
In covalent bonding, electrons are shared between the molecules, to saturate the
valency. The simplest example is the H2 molecule, where the electrons spend
more time in between the nuclei than outside, thus producing bonding.
Metallic Bonding
In the metallic bond encountered in pure metals and metallic alloys, the atoms
contribute their outer-shell electrons to a generally shared electron cloud for the
whole block of metal.




Secondary Bonding (Van der Waals)
Fluctuating Induced Dipole Bonds
Polar Molecule-Induced Dipole Bonds
Permanent Dipole Bonds
Crystal Structures
Atoms self-organize in crystals, most of the time. The crystalline lattice is a
periodic array of the atoms. When the solid is not crystalline, it is called
amorphous. Examples of crystalline solids are metals, diamond and other
precious stones, ice, graphite. Examples of amorphous solids are glass,
amorphous carbon (a-C), amorphous Si, most plastics
Unit Cells
The unit cell is the smallest structure that repeats itself by translation through the
crystal. The most common types of unit cells are the faced-centered cubic
(FCC), the body-centered cubic (FCC) and the hexagonal close-packed (HCP).
Other types exist, particularly among minerals.
Polymorphism and Allotropy
Some materials may exist in more than one crystal structure, this is called
polymorphism. If the material is an elemental solid, it is called allotropy. An
example of allotropy is carbon, which can exist as diamond, graphite, and
amorphous carbon.
Polycrystalline Materials
A solid can be composed of many crystalline grains, not aligned with each other.
It is called polycrystalline. The grains can be more or less aligned with respect to
each other. Where they meet is called a grain boundary.
Imperfection in solids
Materials are not stronger when they have defects. The study of defects is
divided according to their dimension:
0D (zero dimension) – point defects: vacancies and interstitials Impurities.
1D – linear defects: dislocations (edge, screw, mixed)
2D – grain boundaries, surfaces.
3D – extended defects: pores, cracks
Introduction to phase diagram
Component: pure metal or compound (e.g., Cu, Zn in Cu-Zn alloy, sugar, water,
in a syrup.)
Solvent: host or major component in solution.
Solute: dissolved, minor component in solution.
System: set of possible alloys from same component (e.g., iron-carbon system.)
Solubility Limit: Maximum solute concentration that can be dissolved at a given
temperature.
Phase: part with homogeneous physical and chemical characteristics
Solid Solutions
A solid solution occurs when we alloy two metals and they are completely soluble
in each other. If a solid solution alloy is viewed under a microscope only one type
of crystal can be seen just like a pure metal. Solid solution alloys have similar
properties to pure metals but with greater strength but are not as good as
electrical conductors.
The common types of solid solutions are
1) Substitutional solid solution 2) interstitial solid solutions
Substitutional solid solution :
The name of this solid solution tells you exactly
what happens as atoms of the parent metal ( or solvent metal) are replaced or
substituted by atoms of the alloying metal (solute metal) In this case, the atoms
of the two metals in the alloy, are of similar size.
Interstitial solid solutions: In interstitial solid solutions the atoms of the parent or
solvent metal are bigger than the atoms of the alloying or solute metal. In this
case, the smaller atoms fit into interstices i.e spaces between the larger atoms.
Phases
One-phase systems are homogeneous. Systems with two or more phases are
heterogeneous, or mixtures. This is the case of most metallic alloys, but also
happens in ceramics and polymers.
A two-component alloy is called binary. One with three components is called
ternary.
Microstructure
The properties of an alloy do not depend only on concentration of the phases but
how they are arranged structurally at the microscopy level. Thus, the
microstructure is specified by the number of phases, their proportions, and their
arrangement in space.
A binary alloy may be

a single solid solution



two separated, essentially pure components.
two separated solid solutions.
a chemical compound, together with a solid solution.
Phase diagram: A graph showing the phase or phases present for a given
composition as a function of temperature.
Polyphase material: A material in which two or more phases are present.
Eutectoid: Transforming from a solid phase to two other solid phases upon
cooling.
Peritectoid: Transforming from two solid phases to a third solid phase upon
cooling.
Peritectoid reaction: A reaction in which a solid goes to a new solid plus a liquid
on heating, and reverse occurs on cooling.
Iron-Iron Carbon diagram is essential to understand the basic differences among
iron alloys and control of properties
Iron is allotropic; at room temperature pure iron exists in the Body Centered
Cubic crystal form but on heating transforms to a Face Centered Cubic crystal.
The temperature that this first transformation takes place is known as a critical
point and it occurs at 910 degrees Celsius.
This change in crystal structure is accompanied by shrinkage in volume, sine the
atoms in the face centered crystal are more densely packed together than in the
body centered cubic crystal. At the second critical point the F.C.C crystal
changes back to a B.C.C crystal and this change occurs at 1390 degrees
Celsius.
Iron above 1390 degrees is known as delta iron
Iron between 1390 and 910 degrees is known as gamma iron
Iron below 910 degrees is known as alpha iron .
Iron carbon diagram
At 4.3% carbon composition, on cooling Liquid phase is converted in to two
solids hence forming Eutectic reaction.
L ↔ γ + Fe3C
Eutectoid: 0.76 wt%C, 727 °C
γ(0.76 wt% C) ↔ α (0.022 wt% C) + Fe3C
Shown below is the steel part of the iron carbon diagram containing up to 2%
Carbon. At the eutectoid point 0.83% Carbon, Austenite which is in a solid
solution changes directly into a solid known as Pearlite which is a layered
structure consisting of layers of Ferrite and Cementite
UNIT II
I. HEAT TREATMENT PROCESSES
A. The process of heating a metal workpiece to a high temperature to
change
it's properties, normally to make the workpiece harder or softer.
B. Basic heat treatment steps and equipment:
1. Heating to the correct temperature.
a. Equipment normally a heat-treating furnace, a blowtorch, gas welding torch, or
a forge.
2. Holding or soaking at this temperature for a certain length of time.
a. Equipment can be the same furnace or forge.
3. Cooling in a way that will produce the desired results.
a. Equipment can be container of water, tempering oil or brine.
C. Heat treatment processes and uses.
1. Hardening
a. The process:
(1). Heating and cooling steel to increase its hardness and tensile strength, to
reduce its
ductility.
(2). Requires a steel with a minimum of 0.20% carbon content.
b. Uses:
(1). To produce sharp-edged cutting tools.
(2). To make bearing surfaces wear better/longer.
(3). To put "spring" in a spring.
2. Tempering
a. The process
(1). Process of reducing the degree of hardness (removing brittleness) and
strength and
increasing toughness.
(2). If a part is too hard, it will chip; if it is not hard enough, it will bend. Tempering
achieves the balance between hardness and strength.
b. Uses:
(1). Knife blades, screw driver tip, cold chisel tip, axes, shears.
3. Annealing
a. The process:
(1). Process of softening metal to relieve internal strain and to make the metal
easier to
shape and cut.
b. Uses:
(1). Reusing old springs or files for other projects not requiring hardness.
(2). To relieve built up stresses and prevent cracking of manufactured metals.
II. HOT METAL FORMING PROCESSES
A. Techniques to give objects shape or form without adding or removing
any
materials from the part.
B. Metal forming operations.
1. Bending.
a. The process:
(1). Process by which metal is uniformly strained or stretched around a straight
axis
and results in a product having a linear or straight shape.
b. Uses:
(1). Decorative grillwork.
2. Forging (blacksmithing).
a. The process:
(1). Forming is achieved by hammering or applying steady pressure to a
workpiece,
forcing it to take the shape of a die. May be done with the workpiece either hot or
cold.
b. Uses:
(1). Making small tools (chisels and center punches), horseshoes, ornamental
ironwork.
I. CLASSIFICATION AND USES OF METALS
A. Ferrous metal types ("ferrous" = containing iron and alloys)
1.Iron.
a. Rare in the pure state; pure iron is not used commercially.
2. Wrought iron.
a. Contains:
(1). Iron, alloyed (combined) with,
(2). Less than 0.03% carbon.
b. True wrought iron is scarce and expensive.
c. True wrought iron forges well, can be easily bent hot or cold and can be
welded.
d. "Wrought iron" is currently used to refer to almost any malleable low carbon
steel.
3. Carbon steels, or "steel".
a. Contains:
(1). Iron, alloyed (combined) with,
(2). Carbon,
(3). Less than 1.65% manganese,
(4). Less than 0.60% copper, and
(5). Smaller amounts of silicon, sulfur and phosphorous.
b. Types:
(1). Low-carbon ("mild") steels
(a). Between 0.05% and 0.30% carbon.
(b). Tough and ductile. Easily formed, machined and welded.
(c). Most commonly used of the carbon steel types.
(2). Medium-carbon steels
(a). Between 0.30% and 0.45% carbon.
(b). Strong and hard, but less ductile.
(c). Not as easily welded, due to tendency to crack after welding.
(d). Used for gears.
(3). High-carbon steels
(a). Between 0.45% and 0.75% carbon.
(b). Very hard and strong, less ductile.
(c). Special electrodes and welding procedures are required, to prevent
brittleness
and cracking.
(d). Used for cold chisels and hammers.
(4). Very-high-carbon steels
(a). Between 0.75% and 1.5% carbon.
(b). Super hard and strong.
(c). Seldom welded; special electrodes and procedures used.
(d). Used for tools and springs.
(e). Can be used for items that must be hardened and tempered. (See paragraph
IV.
below for definition of these terms).
4. Rolled steels.
a. Bar, rod and structural steels produced by rolling the steel into shape, much
like an old
clothes wringer.
 Cold rolled steel.
 Steel formed when cold.
 Results in more accurately sized, better surface finished product.
 Hot rolled steel.
 Metal formed into shape while the metal is red hot.
 Produces a uniform quality, commonly used steel.
 Bluish scale on the surface formed when water sprayed on the steel as it
passes between rollers.
5. Galvanized steel.
a. Mild steel coated with zinc to prevent rusting.
b. Care should be taken not to inhale toxic fumes when welding this
material.
II. PROPERTIES OF METALS
A. Tensile Strength.
1. Ability to resist being pulled apart in tension. Metal failures are often caused by
forces
exceeding the tensile strength of the part.
B. Ductility.
1. Ability to be stretched or pulled through a die to form wire.
2. Copper is a very ductile metal.
C. Hardness.
1. Ability to resist penetration.
2. Hardness can be increased by heat treatment or work hardening.
III. IDENTIFICATION OF METALS
A. Numbering system for carbon and alloy steels.
1. Four digit (sometimes five digits) numbering system to identify carbon and
alloy steels:
a. First digit usually indicates the principle element in the steel as follows:
SERIES TYPES AND
DESIGNATION CLASSES
10XX Non-resulferized carbon steel grades (plain carbon steel)
13xx Manganese 1.75%
20xx Nickel steels
23xx Nickel 3.5%
30xx Nickel-chromium steels*
31xx Nickel 1.25% - chromium 0.65 or 0.80%
40xx Molybdenum 0.25%
41xx Chromium 0.50 – 0.95% - molybdenum 0.15 or 0.20%
43xx Nickel 1.80% - chromium 0.50 or 0.80% - molybdenum 0.25%*
50xx Chromium 0.28 or 0.40%
51xx Chromium 0.80, 0.90, 0.95, 1.00 or 1.05%
5xxxx Carbon 1.00% - chromium 0.50, 1.00 or 1.45%
60xx Chrome-vanadium steels
61xx Chromium 0.80 or 0.95% - vanadium 0.10 or 0.15% min.
70xx Heat resisting casting alloys
80xx Nickel – chrome – molybdenum steels*
86xx Nickel 0.55% - chromium 0.50 or 0.65% - molybdenum 0.20%
90xx Silicon – manganese steels
92xx Manganese 0.85% - silicon 2.00%
93xx Nickel 3.25% - chromium 1.20% - molybdenum 0.12%
*Stainless steels always have a high chromium content, often considerable
amounts of
nickel, and sometimes contain molybdenum and other elements. Stainless steels
are
identified by a three-digit number beginning with 2, 3, 4, or 5.
b. Second digit (in alloy steels) represents the approximate percentage of alloy
element.
c. Third and fourth digits show the carbon content in points (where a point
equals 100 times the percentage carbon).
d. Examples:
(1). 1095 steel is a carbon steel with 0.95% (95 points) carbon.
(2). 2511 steel is nickel steel with approximately 5% nickel and 0.11% carbon.
Austenite to Pearlite Transformation (a) Austenite-to-pearlite transformation of
iron-carbon alloy as a functionof time and temperature.
(b) Isothermal
transformation diagram obtained from (a) for a transformation temperature of 675
°C (1247 °F).
TTT Diagram
CCT Diagram Phase Transformations and Production of Microconstituents takes TIME.
 Higher Temperature = Less Time.
 If you don’t hold at one temperature and allow time to change, you are
“Continuously Cooling”.
 Therefore, a CCT diagram’s transition lines will be different than a TTT
diagram.
Tempering
 Martensite needs to be tempered to get better ductility. This happens
when Fe3C is allowed to precipitate from the supercooled Martensite.

Process Annealing — Eliminating Cold Work: A low-temperature heat
treatment used to eliminate all or part of the effect of cold working in steels.
Annealing and Normalizing — Dispersion Strengthening: Annealing - A heat
treatment used to produce a soft, coarse pearlite in steel by austenitizing, then
furnace cooling. Normalizing - A simple heat treatment obtained by austenitizing
and air cooling to produce a fine pearlitic structure.
Spheroidizing — Improving Machinability: Spheroidite - A microconstituent
containing coarse spheroidal cementite particles in a matrix of ferrite, permitting
excellent machining characteristics in high-carbon steels.
HOT METAL WORKING TECHNIQUES
A. Holding stock.
1. Select tongs to fit the work. Jaws should be parallel when clamped on the
stock. If
necessary, heat the jaws to a cherry red and bend them to fit and hold the stock
securely.
2. Keep the tongs cool by dipping them frequently in water.
B. Heating stock.
1. Forge.
a. Most economical for heating large pieces of metal.
b. Place the stock in the fire in a horizontal position so that the surface of
the metal will be heated uniformly.
c. Observe the piece periodically to ascertain that it is heating uniformly
(i.e., look at its color).
2. Oxy-acetylene torch flame.
a. Best for smaller pieces.
b. Move the flame over the entire surface to be worked to prevent
overheating in spots and to provide sufficient heat to last until the working
operation is completed.
C. Hardening stock.
1. Requires carbon steel with greater than 0.20% carbon, i.e. steels at
least at the high end percentage carbon of lo carbon steels.
2. Heat the steel to the critical temperature for the type of steel to be
hardened.
a. The color of the glow of the metal is a rough indicator of the
temperature:
Oxides on clean surface:
yellow 430.°F
straw 470.
brown 500.
purple 540.
blue 560.
Glow of metal:
black red 875.°F
dark red 975.
cherry red 1450. critical temperature for mild steel
yellow 2000.
white 2300.
sparks 2550.
drips 2800.
b. Carbon steel becomes nonmagnetic at the critical temperature and
could also be an indicator.or,
c. A thermometer in the furnace is the best method.
3. Remove the piece to be hardened and plunge it into the cooling solution and
move it about rapidly to cool the metal quickly and evenly. Do not drop the piece
into the coolant as it will not cool rapidly enough.
a. Fresh water is cheapest.
b. Brine (5 to 10% salt) in water.
c. Mineral oil allows for slower quenching and tends to decrease the
chances of cracking and warping.
4. Check the piece for hardness:
a. A new file run across the edge of the piece will not cut in or take hold.
D. Tempering - process of reducing the degree of hardness (removing
brittleness) and strength and increasing toughness.
1. Complete the hardening process as described above (remember that
the hardening process will not work on carbon steel with less than 0.20%
carbon).
2. Thoroughly clean (use wire wheel and/or emery paper) off the carbon
from the surface of
the metal in the location where the piece is to be tempered. The metal should be
"shiny"
clean in order to view the surface colors during the following tempering process.
3. Reheat the tool (or portion) of the tool to be tempered to the appropriate
tempering temperature.
Note: the color will appear on the surface of the metal part.
Note: the higher the tempering temperature used, the more hardness removed
Tempering temperatures are normally between 430 and 530 degrees Fahrenheit.
TEMPERING
TEMPERING TEMPERATURE IN TOOL COLOR DEGREES FARENHEIT
HAMMER FACE, PALE YELLOW 430 TO 450ºF
SCRAPER
CENTER PUNCH, FULL YELLOW 470ºF
DRILL
SCREWDRIVER, STRAW BROWN 490 TO 510ºF
COLD CHISEL
4. Quench that portion of the tool to be tempered.
or,
5. To simultaneously harden and temper a part (cold chisel for example):
a. Heat the piece of metal to a cherry red color (hardening color).
b. Hold the piece vertically and dip the end to be tempered (tip end of the
screwdriver) and
rapidly move the tip into and around in the water (or oil). This will harden the
working
end.
c. When the tip appears cool, remove the screwdriver tip from the water (or oil)
and
brighten the tip with a piece of emery cloth.
d. Observe the tip end and you will notice colors gradually move down from the
hot
portion to the tip end.
(1). You will first notice a light straw color
then,
(2). a dark straw color,
then,
(3). a light brown color,
then,
(4) a dark brown color.
e. When a dark brown color appears at the tip end, plunge the tip end into the
water (or oil)
and the tempering process will be achieved.
29
E. Annealing - the process of softening metal to relieve internal strain and
to
make the metal easier to shape and cut.
1. Heat the piece to the critical temperature (approximately 1450º F. for mild
steel, i.e., a
cherry red color).
2. Allow the piece to cool slowly (in the shut-down furnace, packed in sand,
clamped
between two pieces of hot metal or in a pile of fireplace bricks).
The effect of carbon and heat treatment on the properties of plain-carbon steels.
(a) White cast iron prior to heat treatment ( 100). (b) Ferritic malleable iron with
graphite nodules and small MnS inclusions in a ferrite matrix (  200). (c) Pearlitic
malleable iron drawn to produce a tempered martensite matrix (  500). (Images
(b) and (c) are from Metals Handbook, Vols. 7 and 8, (1972, 1973), ASM
International, Materials Park, OH 44073.) (d) Annealed ductile iron with a ferrite
matrix ( 250). (e) As-cast ductile iron with a matrix of ferrite (white) and pearlite
( 250). (f) Normalized ductile iron with a pearlite matrix ( 250).
Isothermal Heat Treatments
 Austempering - The isothermal heat treatment by which austenite
transforms to bainite.
 Isothermal annealing - Heat treatment of a steel by austenitizing,
cooling rapidly to a temperature between the A1 and the nose of the
TTT curve, and holding until the austenite transforms to pearlite.
Application of Hardenability
 Jominy test - The test used to evaluate hardenability. An austenitized
steel bar is quenched at one end only, thus producing a range of
cooling rates along the bar.
 Hardenability curves - Graphs showing the effect of the cooling rate on
the hardness of as-quenched steel.
 Jominy distance - The distance from the quenched end of a Jominy
bar. The Jominy distance is related to the cooling rate.
The setup for the Jominy test used for determining the hardenability of steel
Quench and Temper Heat Treatments
 Retained austenite - Austenite that is unable to transform into martensite
during quenching because of the volume expansion associated with the
reaction.
 Tempered martensite - The microconstituent of ferrite and cementite
formed when martensite is tempered.
 Quench cracks - Cracks that form at the surface of a steel during
quenching due to tensile residual stresses that are produced because of
the volume change that accompanies the austenite-to-martensite
transformation.
 Marquenching - Quenching austenite to a temperature just above the MS
and holding until the temperature is equalized throughout the steel before
further cooling to produce martensite.
The effect of tempering temperature on the mechanical properties of a 1050
steel.
Increasing carbon reduces the Ms and Mf temperatures in plain-carbon steels.
Effect of Alloying Elements
 Hardenability - Alloy steels have high hardenability.
 Effect on the Phase Stability - When alloying elements are added to
steel, the binary Fe-Fe3C stability is affected and the phase diagram is
altered.
 Shape of the TTT Diagram - Ausforming is a thermomechanical heat
treatment in which austenite is plastically deformed below the A1
temperature, then permitted to transform to bainite or martensite.
 Tempering - Alloying elements reduce the rate of tempering compared
with that of a plain-carbon steel.
Surface Treatments
 Selectively Heating the Surface - Rapidly heat the surface of a mediumcarbon steel above the A3 temperature and then quench the steel.
 Case depth - The depth below the surface of a steel at which hardening
occurs by surface hardening and carburizing processes.
 Carburizing - A group of surface-hardening techniques by which carbon
diffuses into steel.
 Cyaniding - Hardening the surface of steel with carbon and nitrogen
obtained from a bath of liquid cyanide solution.
 Carbonitriding - Hardening the surface of steel with carbon and nitrogen
obtained from a special gas atmosphere.
(a) Surface hardening by localized heating. (b) Only the surface heats above
the A1 temperature and is quenched to martensite.
Outline of Heat Treatment Processes for Surface Hardening
Proces
Metals
Elemen
Procedure
General
Typical
s
harden
t added
Characteristic applicatio
ed
to
s
ns
surface
Carburiz Lowing
C
Heat steel at 870– A hard, high- Gears,
carbon
950
°C
(1600– carbon surface cams,
steel
1750 °F) in an is
(0.2%
atmosphere
C), alloy
carbonaceous
steels
gases
(0.08–
carburizing)
0.2% C)
carbon-containing
<
solids
0.060
produced. shafts,
of Hardness
to
65
55 bearings,
HRC. piston pins,
(gas Case depth < sprockets,
or 0.5–1.5 mm ( clutch
0.020
to plates
in.).
(pack carburizing). Some
Then quench.
distortion
part
of
during
heat
treatment.
Carbonit Lowriding
C and N
Heat steel at 700– Surface
°C
Bolts, nuts,
carbon
800
(1300– hardness 55 to gears
steel
1600 °F) in an 62 HRC. Case
atmosphere
of depth 0.07 to
carbonaceous gas 0.5 mm (0.003
and
ammonia. to 0.020 in.).
Then
quench
in Less distortion
oil.
than in
carburizing.
Cyanidi
Low-
C and N
Heat steel at 760– Surface
ng
carbon
845
steel
1550
(0.2%
molten
C), alloy
solutions
steels
cyanide (e.g., 30% (0.001
(0.08–
sodium
0.2% C)
and other salts.
°C
Bolts, nuts,
(1400– hardness up to screws,
°F)
in
bath
a 65 HRC. Case small gears
of depth 0.025 to
of 0.25
mm
to
cyanide) 0.010
in.).
Some
distortion.
Nitriding
Steels
N
Heat steel at 500– Surface
Gears,
(1% Al,
600 °C (925–1100 hardness up to shafts,
1.5%
°F)
Cr,
atmosphere
0.3%
ammonia gas or 0.1 to 0.6 mm cutters,
Mo),
mixtures of molten (0.005
alloy
cyanide salts. No 0.030 in.) and bars,
steels
further treatment.
in
an 1100
of Case
HV. sprockets,
depth valves,
to boring
fuel-
0.02 to 0.07 injection
(Cr,
mm (0.001
pump parts
Mo),
to 0.003 in.)
stainles
for high speed
s steels,
steel.
highspeed
tool
steels
Boronizi
Steels
B
ng
Part
is
heated Extremely
using
Tool
and
boron- hard and wear die steels
containing gas or resistant
solid
in
contact surface. Case
with part.
depth
0.025–
0.075
mm
(0.001–
0.003 in.).
Flame
Medium
None
Surface is heated Surface
Gear
and
hardeni
-carbon
with
ng
steels,
oxyacetylene
cast
torch,
then depth 0.7 to 6 axles,
irons
quenched
with mm (0.030 to crankshafts
an hardness 50 to sprocket
60 HRC. Case teeth,
water
spray
or 0.25 in.). Little ,
other
quenching distortion.
methods.
piston
rods, lathe
beds
and
centers
Inductio
Same
n
hardeni
ng
None
Metal
part
is Same
as Same
as
placed in copper above
above
above
induction coils and
is heated by high
frequency current,
then quenched.
as
Induction Heating
Types of coils used in induction heating of various surfaces of parts
UNIT-III

The common alloying elements added to steel are
 Aluminium
 Boron
 Carbon
 Chromium
 Cobalt
 Copper
 Manganese
 Molybdeum
 Nickel
 Silicon
 Tungsten
 Vanadium
Alloy steel are the types of steel in which elements other than carbon an iron are
present in sufficient quantities to modify the properties of the materials.
Alloying elements added for the purpose are:
 To increase hardenability
 To improve strength
 To improve mechanical properties
 To increase wear resistance
 To increase corrosion resistance
 To improve magnetic properties
Classification of alloy steel
 Low alloy steel
 High alloy steel
Alloy steel can also be subdivided as follows:
 Tool steel
 Stainless steel
 Maraging steel
 HSLA steel
Copper and its alloys
Copper has a density of 8900Kg/m3 and melting point of 1083oc.
The properties of copper are:
High electrical conductivity
High thermal conductivity
Good corrosion resistance
Non-magnetic
In addition, copper can be subjected to welding, brazing and soldering.
Copper alloys:
 Brass
 Bronze
 Copper nickel alloys
 Precipitation harden able alloys
Aluminum and its alloys are:



Commercial aluminium
Cast aluminium
Wrought aluminium alloy
UNIT-IV
Polymers are materials of complex structure. Polymer consists of many units.
In polymer, molecules of ordinary sizes are combined in long chains.
Types of polymers
 Plastics
 Fibers
 Elastomers
Polymers with fillers, solvents, plasticers and pigments are known as plastic.
Types of plastics:
 Thermo plastic
 Thermoset plastic
Major Characteristics of plastics are:
 Non crystalline structure
 Low softening temperature
 Resistance to chemical reaction
 Visco- elastic behaviour
 Non-conductors
 Low thermal conductivity
Engineering thermoplastics are:
 Polythene
 Polyvinylchloride
 Polypropene
 Polystyrene
 Polymethyl Methacrylate
 Polyesters
 Polycarbonates
 Polyamides
 ABS
UNIT-V
When material is stressed below its elastic limit, the strain formed is temporary.
When a material is stressed above its elastic limit, the plastic deformation takes
place.
Plastic deformation may takes place by:
 Slip
 Twinning
Types of Mechanical tests:
 Tensile test
 Compressive test
 Shear test




Hardness test
Fatigue test
Creep test
Impact test