This slide contains different manufacturing processes. Covering maximum syllabus of b-tech first year in subject of manufacturing processes.

1. SUBMITTED TO- Dr. Amit Sharma
1
SUBMITTED BY- MAYANK GUPTA
SHABHAM GOEL
B-tech 1st YEAR
D.C.R.U.S.T

2. TOPIC -1
A. General Properties of Engineering Materials.
B. Explain cast iron, types, microstructures properties,
applications.
C. Difference between mild steel, medium carbon steel, high
carbon steel & effect of percentage of carbon.
D. Give composition, properties, applications of high speed
steel & high temperature materials.
2

3. Property of a material is a factor that influences
quantitatively or qualitatively the response of a
given material to impose stimuli and constraints.
Different material properties are:
1. Mechanical properties
2. Physical properties
3. Electrical properties
4. Magnetic properties
5. Chemical properties
6. Thermal properties
7. Optical properties
3

4. MECHANICAL PROPERTIES
It define the behaviour of materials under the action of external
forces.
Some important mechanical properties are:
1. Strength –Strength of a material may be defined as the ability
of a material to sustain loads without distortion.
2. Stiffness –It is the ability of material to resist deformation.
3. Elasticity –It is that property of a material by virtue of which
deformation caused by applied loads disappear completely on
removal of load.
4. Ductility –It is the ability of metal to withstand elongation.
5. Mallaebilty – It is the ability of metal to withstand
deformation under compression and elongation without
rupture.
6. Toughness –It is a measure of amount of energy of a material
can absorb before takes place.
7. Brittleness –Lack of Ductility is brittleness.
8. Hardness –It is usually defined as resistance of material to
penetration. 4

5. PHYSICAL PROPERTIES
 Colour –It relates to quality of light reflected from metal.
 Density –Mass per unit volume is termed as density.
 Dimension –It means shape and size of material.
 Porosity –A material is said to be porous within it.
 Specific gravity-It is the ratio of the mass of a given volume of
metal to the mass of same volume of water at specified
temperature usually 4degree Celsius.
ELECTRICAL PROPERTIES
Various electrical properties are:
1.Conductivity –It is the ability of the material to pass electric
current through it easily.
2.Resistivity –It is the property of material due to which it resist
the flow of electrify through it.
3.Dielectric strength –It means insulating capacity of material at
high voltage.
4.Thermoelectricity –If two dissimilar metals are joined and this
junction is heated, a small voltage is produced and this is known
as thermoelectric effect. 5

6. MAGNETIC PROPERTIES
Various magnetic properties are:
 Permeability –It is the ratio of flux density in a material to
magnetising force producing that flux density.
 Coercive force-It may be defined as the magnetising force
which is necessary to neutralize completely the magnetism in
an electromagnet after the value of magnetising force
becomes zero.
 Magnetic hysteresis –Below Curie temperature all magnetic
materials exhibit the phenomenon called hysteria.
CHEMICAL PROPERTIES
A study of Chemical properties of material is necessary because
most of the engineering materials. When they come in contact
with other substances with which they can react, tend to suffer
from Chemical deterioration. Some of Chemical properties are:
 Corrosion resistance
 Chemical composition
6

7. THERMAL PROPERTIES
The study of thermal properties is essential in order to
know their response to thermal changes.
Various thermal properties are:
1. Thermal conductivity –It is rate of heat flow.
2. Thermal expansion – It arises arises from the addition
of heat energy in the atoms.
3. Specific heat –It is defined as the amount of heat
required for unit mass of solid to raise it’s temperature
by one degree.
4. Melting point – It is the temperature at which a pure
metal or compound changes from solid to liquid.
5. Thermal diffusivity –It is defined as conductivity
divided by heat capacity multiplied by density.
7

8. INTRODUCTION OF CAST IRON
 Cast iron is the name given to those ferrous
metals containing more than1.7 % carbon.
 It is similar in composition to crude pig iron as
produced by the blast furnace.
 Its structure is crystalline and relatively brittle
and weak in tension.
8

9. COMPOSTION OF CAST IRON
 Carbon - 2.5 to 3.7%
 Silicon - 1.0 to 3.0%
 Manganese - 0.5 to 1.0%
 Phosphorus - 0.1 to 0.9%
 Sulphur - 0.07 to 0.10%
9

10. CLASSIFICATIONS OF CAST
IRON
1. WHITE CAST IRON
2. GRAY CAST IRON
3. DUCTILE (NODULAR) CAST IRON
4. MALLEABLE CAST IRON
10
There are Four Types Of Cast Iron . They are:-

11. WHITE CAST IRON :-
 These are iron-carbon alloys having more than 2.11%
carbon.
 All the carbon is present in the combined cementite
form, which makes the fracture of these alloys to have
dull and white colour, and that is the reason of their
name as white irons.
 Composition:
C=2.5%,Mn=0.4%,
Cr=17%,Si=1.3%,
Ni + Cu %,P=0.15%,
S=0.15%,Mo=0.5%
11

12. GREY CAST IRON :-
Iron-carbon alloys containing flakes of graphite
embedded in steel matrix, which show a gray -blackish
coloured fracture due to graphite’—the free foam of
carbon, are called gray cast irons.
The strength of gray iron depends on the strength of steel
matrix and the size and character of graphite flakes in it.
COMPOSITION:
Total carbon : 2.4—3.8%
Silicon : 1.2—3.5%
Manganese : 0.5—1.0%
Sulphur :0.06—0.12%
Phosphorus :0.1—0.9%
12

13. MALLEABLE CAST IRON :-
 Malleable iron is cast as White iron, the structure being a
metastable carbide in a pearlitic matrix.
Graphite in nodular form
Produced by heat treatment of white cast iron
Graphite nodules are irregular clusters
Similar properties to ductile iron.
Composition of Malleable Iron :-
13

14. DUCTILE(NODULE) CAST IRON:-
In ductile irons, the graphite is in the form
of spherical nodules rather than flakes (as in grey iron), thus
inhibiting the creation of cracks and providing the enhanced
ductility.
Also known as spheroidal graphite (SG), and nodular graphite iron
COMPOSITION:
 A typical chemical analysis of this material
 Iron carbon 3.3 to 3.4%
 Silicon 2.2 to 2.8%
 Manganese 0.1 to 0.5%
 Magnesium 0.03 to 0.05%
 Phosphorus 0.005 to 0.04%
 Sulphur 0.005 to 0.02%
14

15. APPLICATIONS OF CAST IRON:
 Cast iron is used in a wide variety of structural and decorative
applications, because it is relatively , inexpensive, durable &
easily cast into a variety of shapes.
 Construction of machines and structures (High Tensile Strength)
 As Columns , balusters & Arches (High Compressive Strength)
 Machine and car parts like
 Cylinder heads
 blocks
 gearbox cases
 cookware
 pipes etc.
15

16. Mild steel
1.It is having carbon
0.15 to 3%.
2.It is having fibrous
structure.
3.It can be hardened
and tempered but not
easily.
4.Mallaeble and
ductile.
5.Rust readily.
6.It absorbs shock.
7.It is used for all kind
of structure work in
bridges and buildings.
Medium carbon steel
1.It contains carbon
0.3 to 0.8%.
2.It is having
structure like semi
killed state.
3.Hardenability is
limited to thin
sections.
4.Ductilite
5.Not get easily rust
readily.
6.It absorbs shock
7.It is used for making
axles and shafts
High carbon steel
1.It contains 0.55 to
1.3%.
2.It has fine granular
structure.
3.Can be hardened
and tempered easily.
4.Brittle and less
ductile.
5.Rust rapidly.
6.It absorbs shock.
7.It is used for dies,
cutlery and edge
tools.
16

17. PERCENTAGE OF CARBON
 Low Carbon Steel – Composition of 0.05%-0.25% carbon and
up to 0.4% manganese. Also known as mild steel, it is a low-
cost material that is easy to shape. While not as hard as higher-
carbon steels, carburizing can increase its surface hardness.
 Medium Carbon Steel – Composition of 0.29%-0.54%
carbon, with 0.60%-1.65% manganese. Medium carbon steel is
ductile and strong, with long-wearing properties.
 High Carbon Steel – Composition of 0.55%-0.95% carbon,
with 0.30%-0.90% manganese. It is very strong and holds
shape memory well, making it ideal for springs and wire.
17

18. COMPOSITION
High Speed Steel is a high carbon tool steel, containing a large
dose of tungsten. A typical HSS composition is: 18%tungsten,
4% Chromium, 1% Vanadium, 0.7% carbon and the rest,
Iron. HSS tools have a harness of 62-64 Rc. The addition of 5
to 8% cobalt to HSS imparts higher strength and wear
resistance.
18

19. PROPERTIES
 High working hardness.
 High wear resistance.
 Excellent toughness.
 Compressive strength.
 High retention of hardness and red hardness.
 Strength to prevent breakage on the cutting edge. The
influence of alloying elements on steel properties: Carbon.
19

20. APPLICATION
 High Speed Steel is a cutting tool material used in
drilling, milling, turning, threading, boring, broaching,
gear cutting and many other machining operations.
 High Speed Steel is used for form tools, slitter knives,
guillotine knives, parting tools and many other types of
cutting tools.
20

21. TOPIC -2
A. Differentiate between hot working and cold working processes.
B. Explain following cold working processes with diagram
1. Shearing
2. Punching
3. Blanking
4. Pearcing
5. Forming
6. Bending
7. Joining
C. Explain following cold working processes with diagram
1. Forging
2. Rolling
3. Extrusion
4. Wire drying
21

22. HOT WORKING
 It is carried out above the
recrystaline temperature so
deformation of metal and
recovery takes place
simultaneously.
 Cracks and blowholes are
welded up.
 Force required for deformation
is less.
 Surface finish is poor.
 Handling of material is difficult
because of high temperature.
 Due to recrystalisation, no
hardening of metal takes place.
COLD WORKING
 It is carried out below
recrystalisation temperature so
no recovery takes place during
deformation.
 Possibility of new crack
formation and it’s propagation is
less.
 Force required for deformation is
more.
 Better surface finish is obtained.
 Handling of material is easy
because of low working
temperature.
 Metals get hardened.
22

23. COLD WORKING PROCESSES
PUNCHING
 Punching is a metal forming process that
uses a punch press to force a tool, called a
punch, through the workpiece to create a
hole via shearing. The punch often passes
through the work into a die. A scrap slug
from the hole is deposited into the die in
the process. Depending on the material
being punched this slug may be recycled
and reused or discarded. Punching is
often the cheapest method for creating
holes in sheet metal in medium to high
production volumes. When a specially
shaped punch is used to create multiple
usable parts from a sheet of material the
process is known as blanking. In forging
applications the work is often punched
while hot, and this is called hot punching.
23

24. BENDING Bending is a manufacturing
process that produces a V-shape,
U-shape, or channel shape along
a straight axis in ductile
materials, most commonly sheet
metal. Commonly used
equipment include box and pan
brakes, brake presses, and other
specialized machine presses.
Typical products that are made
like this are boxes such as
electrical enclosures and
rectangular ductwork.
24

25. FORMING
 These processes are known as cold working or cold
forming processes. They are characterized by
shaping the workpiece at a temperature below its
recrystallization temperature, usually at ambient
temperature. Cold forming techniques are usually
classified into four major groups: squeezing, bending,
drawing, and shearing.
25

26. • Rolling is usually first process used to convert material into a finished
wrought product.
• Stock can be rolled into blooms, billets, slabs, or these shapes can be
obtained directly from continuous casting.
– A bloom has a square or rectangular cross section, with a thickness
greater than 6 inches and a width no greater than twice the thickness.
– A billet is usually smaller than a bloom and has a square or circular
cross section. Billets are usually produced by some form of
deformation process, such as rolling or extrusion.
– A slab is a rectangular solid where the width is greater than twice the
thickness. Slabs can be further rolled to produce plate, sheet, and
strip
26
HOT WORKING PROCESSES

27. • These hot-worked products use for subsequent processing techniques
such as cold forming or for machining.
– Sheet and strip fabricated into products or cold rolled into
thinner, stronger material even into foil.
– Blooms and billets rolled into finished products, such as
structural shapes or railroad rail, or processed into semi-finished
shapes, such as bar, rod, tube, or pipe
• Hot Rolling :-
– is prominent among all manufacturing processes
– equipment and practices are sufficiently advanced
– is standardized
– produce uniform-quality products at relatively low cost
– products are normally obtained in standard shapes and sizes
27

28. 28

29. • Forging is term applied to a family of processes where
deformation is induced by localized compressive forces.
• The equipment can be manual or power hammers, presses, or
special forging machines. The term forging usually implies hot
forging done above the recrystaIlization temperature.
• The forging material may be
– Drawn out to increase its length and decrease its cross section
– Upset to decrease the length and increase the cross section
– Squeezed in closed impression dies to produce multidirectional
flow.
29

30. • Common forging processes include:
– Open-die drop-hammer forging
– Impression-die drop forging
– Press forging
– Upset forging
– Automatic hot forging
– Roll forging
– Swaging
30

31. Operation on a Rectangular Bar
31
Blacksmiths use this process to reduce the thickness of bars by hammering the part on an
anvil. Reduction in thickness is accompanied by barreling, as in Fig. 14.3c. (b) Reducing the
diameter of a bar by open-die forging; note the movements of the dies and the workpiece. (c)
The thickness of a ring being reduced by open-die forging.

32. • In the extrusion process, metal is compressed and forced to flow through
a suitably shaped die to form a product with reduced but constant cross
section.
• Extrusion may be performed either hot or cold, hot extrusion is
commonly employed for many metals to reduce the forces required.
• Extrusion process is like squeezing toothpaste out of a tube. In the case
of metals, a common arrangement is to have a heated billet placed inside
a confining chamber. As ram continues to advance, pressure builds until
material flows plastically through the die.
• Lead, copper, aluminum, magnesium, and alloys of these metals are
commonly extruded, because of relatively low yield strengths and low
hot-working temperatures.
• Steels, stainless steels, and nickel-based alloys are far more difficult to
extrude.
32

33. 33

34. • Almost any cross-sectional shape can be extruded from
nonferrous metals..
34

35. TOPIC-3
Neat labeled diagram & specifications of following machine tools
1. Lathe
2. Planner
3. Shaper
4. Miller
5. Driller
6. Slotter
B. Nomenclature of single point Cutting tool
35

36. Introduction
Lathe is a machine, which removes the metal
from a piece of work to the required shape &size
36

37. Types of Lathe
Engine Lathe
The most common form of lathe, motor driven and comes
in large variety of sizes and shapes.
Bench Lathe
A bench top model usually of low power used to make
precision machine small work pieces.
Tracer Lathe
A lathe that has the ability to follow a template to copy a
shape or contour.
37

38. Automatic Lathe
A lathe in which the work piece is automatically fed and
removed without use of an operator. Cutting operations are
automatically controlled by a sequencer of some form
Turret Lathe
lathe which have multiple tools mounted on turret either
attached to the tailstock or the cross-slide, which allows for
quick changes in tooling and cutting operations.
Computer Controlled Lathe
A highly automated lathe, where both cutting, loading, tool
changing, and part unloading are automatically controlled by
computer coding.
38

39. 39
COMPONENT DESCRIPTION

40. Lathe Operations
Turning: Produce straight, conical, curved, or grooved work pieces.
Facing: to produce a flat surface at the end of the part or for making
face grooves.
Boring: to enlarge a hole or cylindrical cavity made by a previous
process or to produce circular internal grooves.
Drilling: to produce a hole by fixing a drill in the tailstock
Threading: to produce external or internal threads
Knurling: to produce a regularly shaped roughness on cylindrical
surfaces
40

41. 41
LATHE OPERATIONS

42. Introduction
 A shaping machine is used to machine surfaces. It can cut curves, angles and
many other shapes. It is a popular machine in a factory workshop because its
movement is very simple although it can produce a variety of work. They are
less common in school workshops, perhaps because of their moving parts
which present a high risk.
42
SHAPER

43. SHAPING MACHINE DESCRIPTION
43

44.  The major components of a shaper are the ram, which has the tool post with
cutting tool mounted on its face, and a worktable, which holds the part and
accomplishes the feed motion.
44

45. SHAPING MACHINE OPERATION
 The tool feed handle can be turned to slowly feed the cutting tool into the
material as the 'ram' moves forwards and backwards. The strong machine vice
holds the material securely. A small vice would not be suitable as the work
could quite easily be pulled out of position and be damaged. The vice rests on
a steel table which can be adjusted so that it can be moved up and down and
then locked in position. Pulling back on the clutch handle starts the 'ram'
moving forwards and backwards.
45
The tool post has been turned at an
angle so that side of the material can
be machined
The tool post is not angled so that the
tool can be used to level a surface.

46. PLANNING MACHINE
 The machine tool for planning is a planer. Cutting speed is achieved by a
reciprocating worktable that moves the part past the single-point cutting tool.
Construction and motion capability of a planer permit much larger parts to be
machined than on a shaper.
46

47. Planers can be classified as either open side planers or double-
column planers.
 The open side planer, also known as a single-column planer has a
single column supporting the cross rail on which a tool head is
mounted. The configuration of the open side planer permits very wide
work parts to be machined.
 A double-column planer has two columns, one on either side of the
bed and worktable. The columns support the cross rail on which one or
more tool heads are mounted. The two columns provide a more rigid
structure for the operation but limit the width of the work that can be
handled.
47

48. PLANNING MACHINE DESCRIPTION
48

49. SLOTTING MACHINE
 Slotting machines can simply be considered as vertical shaping machine.
Unlike shaping and planning machines, slotting machines are generally used
to machine internal surfaces (flat, formed grooves and cylindrical).
49

50. SLOTTING MACHINE DESCRIPTION
50

51. DRILLING
 Drilling is the operation of producing circular hole in
the work-piece by using a rotating cutter called
DRILL.
 The machine used for drilling is called drilling
machine.
 The drilling operation can also be accomplished in
lathe, in which the drill is held in tailstock and the
work is held by the chuck.
 The most common drill used is the twist drill.
51

52. DRILLING MACHINE
 It is the simplest and accurate machine used in
production shop.
 The work piece is held stationary ie. Clamped in
position and the drill rotates to make a hole.
 Types :-
a) Based on construction:
Portable, Sensitive,Radial, up-right, Gang,
Multi-spindle
b)Based on Feed:
Hand and Power driven
52

53. SENSITIVE DRILLING MACHINE
 Drill holes
from 1.5 to
15mm
 Operator
senses the
cutting action
so sensitive
drilling
machine
53

54. UP-RIGHT DRILLING MACHINE
 Drill holes
up to 50mm
 Table can
move
vertically
and radially.
54

55. RADIAL DRILLING MACHINE
 It the largest
and most
versatile used
fro drilling
medium to
large and heavy
work pieces.
55

56. SINGLE POINT CUTTING
TOOL
 As its name indicates, a tool that has a single point for
cutting purpose is called single point cutting tool. It is
generally used in the lathe machine, shaper machine
etc. It is used to remove the materials from the
workpiece.
56

57. GEOMETRY
57

58. TOPIC -4
A. Explain the construction and working of cupola
furnace.
B. Give the comparison between soldering, brazing and
welding.
C. Briefly explain various heat treatment processes
58

59.  Cupola was made by Rene-Antoine around 1720.
 Cupola is a melting device.
 Used in foundries for production of cast iron.
 Used for making bronzes.
 Its charge is Coke , Metal , Flux.
 Scrap of blast furnace is re melted in cupola.
 Large cupolas may produce up to 100 tons/hour of
hot iron.
59

60. CONSTRUCTION
 Cupola is a cylindrical in shape and placed vertical.
 Its shell is made of steel.
 Its size is expressed in diameters and can range from 0.5
to 4.0 m.
 It supported by four legs.
 Internal walls are lined with refectory bricks.
 Its lining is temporary.
60

61. Parts of Cupola
 Spark arrester.
 Charging door.
 Air box.
 Tuyeres.
 Tap hole.
 Slag hole.
61

62. Zones
WELL
 The space between the bottom
of the Tuyeres and the sand
bed.
 Molten metal collected in this
portion.
COMBUSTION ZONE
 Also known as oxidizing zone .
 Combustion take place in this
zone.
 It is located between well and
melting zone.
 Height of this zone is normally
15cm to 30cm.
62

63. Zones
 In this zone the temperature is
1540°C to 1870°C.
 The exothermic reactions takes
place in this zone these are
following .
 C + O2 → CO2 + Heat
 Si + O2 → SiO2 + Heat
 2Mn + O2 → 2MnO + Heat
Reducing zone
 Locate between upper level of
combustion zone and upper
level of coke bed.
63

64. Zones
 In this zone temperature is about
1200°C.
 In this zone CO2 change in to
CO.
CO2 + C (coke) → 2CO
Melting zone
 In this zone the melting is done.
 It is located between preheating
zone and combustion zone.
 The following reaction take place
in this zone.
 3Fe + 2CO → Fe3C + CO2 .
64

65. Zones
PREHEATING ZONE
 This zone is starts from the upper
end of the melting zone and
continues up to the bottom level of
the charging door .
 Objective of this zone is preheat
the charges from room temperature
to about 1090°C before entering the
metal charge to the melting zone.
STACK
 The empty portion of cupola above
the preheating zone is called as
stack. It provides the passage to hot
gases to go to atmosphere from the
cupola furnace.
65

66. Charging of Cupola Furnace
 Before the blower is started, the furnace is uniformly pre-
heated and the metal, flux and coke charges, lying in
alternate layers, are sufficiently heated up.
 The cover plates are positioned suitably and the blower is
started.
 The height of coke charge in the cupola in each layer
varies generally from 10 to 15 cm . The requirement of flux
to the metal charge depends upon the quality of the
charged metal and scarp, the composition of the coke and
the amount of ash content present in the coke.
66

67. Working of Cupola Furnace
 Its charge consist of scrap,
coke and flux.
 The charge is placed layer by
layer.
 The first layer is coke, second
is flux and third metal.
 Air enter through the bottom
tuyeres.
 This increases the energy
efficiency of the furnace.
 Coke is consumed.
67

68. Working of Cupola Furnace
 The hot exhaust gases rise up
through the charge, preheating
it.
 The charge is melted.
 As the material is consumed,
additional charges can be added
to the furnace.
 A continuous flow of iron
emerges from the bottom of the
furnace.
 The slag is removed from slag
hole.
 The molten metal achieved by
tap hole.
68

69. ADVANTAGES
 It is simple and economical to operate .
 Cupolas can refine the metal charge, removing impurities
out of the slag.
 High melt rates .
 Ease of operation .
 Adequate temperature control .
 Chemical composition control .
 Efficiency of cupola varies from 30 to 50%.
 Less floor space requirements.
69

70. DISADVANTAGES
 Since molten iron and coke are in contact with each
other, certain elements like Silicon , Magnese are lost
and others like sulphur are picked up. This changes the
final analysis of molten metal.
 Close temperature control is difficult to maintain
70

71. S no WELDING SOLDERING BRAZING
1
Welding joints are strongest
joints used to bear the load.
Strength of the welded
portion of joint is usually
more than the strength of
base metal.
Soldering joints are weakest
joints out of three. Not meant
to bear the load. Use to make
electrical contacts generally.
Brazing joints are weaker than
welding joints but stronger
than soldering joints. This can
be used to bear the load up to
some extent.
2
Temperature required is
3800°C in welding joints.
Temperature requirement is
up to 450°C in soldering
joints.
Temperature may go to 600°C
in brazing joints.
3
To join work pieces need to be
heated till their melting point.
Heating of the work pieces is
not required.
Work pieces are heated but
below their melting point.
4
Mechanical properties of base
metal may change at the joint
due to heating and cooling.
No change in mechanical
properties after joining.
May change in mechanical
properties of joint but it is
almost negligible.
5
Heat treatment is generally
required to eliminate
undesirable effects of welding.
No heat treatment is required.
No heat treatment is required
after brazing.
6
No preheating of work piece is
required before welding as it
is carried out at high
temperature.
Preheating of work pieces
before soldering is good for
making good quality joint.
Preheating is desirable to
make strong joint as brazing is
carried out at relatively low
temperature. 71

72. Heat Treatment Processes
 Annealing involves heating the material to a predetermined temperature
and hold the material at the temperature and cool the material to the room
temperature slowly. The process involves:
Annealing: Annealing
1) Heating of the material at the
elevated or predetermined
temperature
2) Holding the material (Soaking) at
the temperature for longer time.
3) Very slowly cooling the material
to the room temperature.
72

73. Heat Treatment Processes
 The various purpose of these heat treatments is to:
Annealing: Annealing
1) Relieve Internal stresses developed during solidification,
machining, forging, rolling or welding,
2) Improve or restore ductility and toughness,
3) Enhance Machinability,
4) Eliminate chemical non-uniformity,
5) Refrain grain size, &
6) Reduce the gaseous contents in steel.
73

74. Heat Treatment Processes
 Hardening and Hardness are two very different things. One is a process
of heat treatment and other is a extrinsic property of a material.
Hardening:
 Hardening is a heat treatment
process in which steel is rapidly cooled
from austenitising temperature. As a
result of hardening, the hardness and
wear resistance of steel are improved.
 Hardening treatment generally
consists of heating to hardening
temperature, holding at that
temperature, followed by rapid cooling
such as quenching in oil or water or salt
baths.
74

75. Heat Treatment Processes
 The high hardness developed by this process is due to the phase
transformation accompanying rapid cooling. Rapid cooling results in the
transformation of austenite at considerably low temperature into non-
equilibrium products.
Hardening:
 The hardening temperature depends on chemical composition. For plain
carbon steels, it depends on the carbon content alone. Hypoeutectoid steels
are heated to about 30 – 50 oC above the upper critical temperature, whereas
eutectoid and hyper eutectoid steels are heated to about 30 – 50 oC above
lower critical temperature.
 Ferrite and pearlite transform to austenite at hardening temperature for
hypoectectoid steel. This austenite transforms to martensite on rapid
quenching from hardening temperature. The presence of martensite
accounts for high hardness of quenched steel.
75

76. Heat Treatment Processes
 Hardening is applied to cutting tools and machine parts where high hardness and
wear resistance are important.
Hardening:
 The Process Variables:
Hardening Temperature: The steel should be heat treated to optimum austenitising
temperature. A lower temperature results lower hardness due to incomplete
transformation t austenite. If this temperature is too high will also results lower
hardness due to a coarse grained structure.
Soaking Time: Soaking time at hardening temperature should be long enough to
transform homogenous austenite structure. Soaking time increases with increase in
section thickness and the amount of alloying element.
Delay in quenching: After soaking, the steel is immediately quenched. Delay in
quenching may reduce hardness due to partial transformation of austenite.
Type of quenching medium also has a profound effect, which will be discussed briefly.76

77. Heat Treatment Processes
 The main purpose of hardening tool steel is to develop high hardness.
This enables tool steel to cut other metals. High hardness developed by
this process also improves wear resistance. Gears, shafts and bearings.
Tensile strength and yield strength are improved considerably y hardening
structural steels.
Hardening:
 Because of rapid cooling, high
internal stresses are developed in
the hardened steel. Hence these
steels are generally brittle.
Hardening in general is followed
by another treatment known as
tempering which reduces internal
stresses and makes the hardened
steel relatively stable,
77

78. Heat Treatment Processes
 Hardened steels are so brittle that even a small impact will cause
fracture. Toughness of such a steel can be improved by tempering.
However there is small reduction in strength and hardness.
Tempering:
 Tempering is a sub-critical heat
treatment process used to improve
the toughness of hardened steel.
 Tempering consists of reheating
of hardened steel to a temperature
below Lower critical temperature
and is held for a period of time, and
then slowly cooled in air to room
temperature.
78

79. Heat Treatment Processes
 At tempering temperature, carbon atoms diffuses out and form fine
cementite and softer ferrite structure left behind. Thus the structure of
tempered steel consists of ferrite and fine cementite.
Tempering:
Thus tempering allows to precipitate
carbon as very fine carbide and allow the
microstructure to return to BCC
 The temperatures are related to the
function of the parts. Cutting tools are
tempered between 230 – 300 oC. If greater
ductility and toughness are desired as in case
of shafts and high strength bolts, the steel is
tempered in the range of 300 – 600 oC.
79

80. Heat Treatment Processes
 Tempering temperatures are usually identified by the colour. Tempering
temperatures for tools and shafts along with temper colors.
Tempering:
 Depending on temperatures, tempering processes can be classified as:
1) Low- temperature tempering
(150 – 250 oC),
2) Medium – temperature
tempering (350 – 450 oC),
3) High – temperature tempering
(500 – 650 oC).
80

81. Heat Treatment Processes
 Quenching is a process of rapid cooling of materials from high
temperature to room temperature or even lower. In steels quenching
results in transformation of austenite to martensite (a non-equilibrium
constituent).
Quenching:
 During cooling, heat must be extracted at
a very fast rate from the steel piece. This is
possible only when a steel piece is allowed
to come in contact with some medium which
can absorb heat from the steel piece with in a
short period.
 Under ideal conditions, all the heat
absorbed by the medium should be rejected
to the surroundings immediately.
81

82. Heat Treatment Processes
 The removal of heat during quenching is complex in the sense that heat
is removed in three stages.
Quenching:
1) Vapor Blanket,
2) Nucleate Boiling,
3) Convection.
82

83. Heat Treatment Processes
 In many situations hard and wear resistance surface is required with the
tough core. Because of tough core the components can withstand impact
load. The typical applications requiring these conditions include gear
teeth, cams shafts, bearings, crank pins, clutch plate, tools and dies.
 The combination of the these properties can be achieved by the
following methods:
Surface Hardening:
 1. Hardening and tempering the surface layers (surface hardening)
(i) Flame Hardening (ii) Induction Hardening
 2. Changing the composition at surface layers (chemical heat
treatment or case hardening)
(i) Carburising (ii) Nitriding (iii) Carburising and Cyaniding
83

84. Heat Treatment Processes
 The flame hardening involves heating the surface of a steel to a
temperature above upper critical point (850 oC) with a oxyacetylene flame
and then immediately quenched the surface with cold water.
 Heating transforms the structure of surface layers to austenite, and the
quenching changes it to martensite.
Surface Hardening:
84

85. Heat Treatment Processes
 The surface layers are hardened to about 50 – 60 HRC. It is less expensive
and can be easily adopted for large and complex shapes.
Flame hardened parts must be tempered after hardening. The tempering
temperature depends on the alloy composition and desired hardness.
Surface Hardening:
 The flame hardening methods are suitable for the steels with carbon
contents ranging from 0.40 to 0.95% and low alloy steels. 85

86. SOURCES
 Workshop technology by S. K Garg.
 www.slidesshare.com
 www.powershow.com
 www.qualmetservice.com
 www.scribd.com
 www.google.co.in
 www.americanmachinetools.com
 www.quora.com
 www.wikipedia.com
 www.drive.google.com
 www.dropbox.com
 http://bigthink.com
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