STUDY OF MICRO STRUCTURE OF HEAT TREATED EN8 STEEL

STUDY OF MICRO STRUCTURE OF HEAT TREATED EN8 STEEL
Dept. of Mechanical engineering, VAST-TC, Kilimanoor Page 1
CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION TO HEAT TREATMENT?
Heat treating (or heat treatment) is a group of
industrial and metalworking processes used to alter the
physical, and sometimes chemical, properties of a
material. The most common application is metallurgical.
Heat treatments are also used in the manufacture of many
other materials, such as glass. Heat treatment involves the
use of heating or chilling, normally to extreme
temperatures, to achieve a desired result such as
hardening or softening of a material. Heat treatment techniques include annealing, case
hardening, precipitation strengthening, tempering, normalizing and quenching. It is
noteworthy that while the term heat treatment applies only to processes where the heating
and cooling are done for the specific purpose of altering properties intentionally, heating
and cooling often occur incidentally during other manufacturing processes such as hot
forming or welding.
Physical processes
1.2 PHYSICAL PROCESSES
Metallic materials consist of a microstructure of small crystals called "grains" or
crystallites. The nature of the grains (i.e. grain size and composition) is one of the most
effective factors that can determine the overall mechanical behavior of the metal. Heat
treatment provides an efficient way to manipulate the properties of the metal by
controlling the rate of diffusion and the rate of cooling within the microstructure. Heat
treating is often used to alter the mechanical properties of a metallic alloy, manipulating
properties such as the hardness, strength, toughness, ductility, and elasticity.
There are two mechanisms that may change an alloy's properties during heat
treatment: the formation of martensite causes the crystals to deform intrinsically, and the
diffusion mechanism causes changes in the homogeneity of the alloy.
Figure 1
Heat treating furnace at 1,800 °F
(980 °C)

The crystal structure consists of atoms that are grouped in a very specific
arrangement, called a lattice. In most elements, this order will rearrange itself, depending
on conditions like temperature and pressure. This rearrangement, called allotropy or
polymorphism, may occur several times, at many different temperatures for a particular
metal. In alloys, this rearrangement may cause an element that will not normally dissolve
into the base metal to suddenly become soluble, while a reversal of the allotropy will
make the elements either partially or completely insoluble.
When in the soluble state, the process of diffusion
causes the atoms of the dissolved element to spread
out, attempting to form a homogenous distribution
within the crystals of the base metal. If the alloy is
cooled to an insoluble state, the atoms of the dissolved
constituents (solutes) may migrate out of the solution.
This type of diffusion, called precipitation, leads to
nucleation, where the migrating atoms group together
at the grain-boundaries. This forms a microstructure
generally consisting of two or more distinct phases.
Steel that has been cooled slowly, for instance, forms a
laminated structure composed of alternating layers of
ferrite and cementite, becoming soft pearlite. After heating the steel to the austenite
phase and then quenching it in water, the microstructure will be in the martensitic phase.
This is due to the fact that the steel will change from the austenite phase to the martensite
phase after quenching. It should be noted that some pearlite or ferrite may be present if
the quench did not rapidly cool off all the steel.
Unlike iron-based alloys, most heat treatable alloys do not experience a ferrite
transformation. In these alloys, the nucleation at the grain-boundaries often reinforces the
structure of the crystal matrix. These metals harden by precipitation. Typically a slow
process, depending on temperature, this is often referred to as "age hardening".
Many metals and non-metals exhibit a martensite transformation when cooled
quickly(with external media like oil,polymer,water etc.). When a metal is cooled very
quickly, the insoluble atoms may not be able to migrate out of the solution in time. This
Figure 2
Allotropes of iron, showing the
differences in lattice structures
between alpha iron (low temperature)
and gamma iron (high temperature).
The alpha iron has no spaces for carbon
atoms to reside, while the gamma iron
is open to free movement of small
carbon atoms.

is called a "diffusionless transformation." When the crystal matrix changes to its low
temperature arrangement, the atoms of the solute become trapped within the lattice. The
trapped atoms prevent the crystal matrix from completely changing into its low
temperature allotrope, creating shearing stresses within the lattice. When some alloys are
cooled quickly, such as steel, the martensite transformation hardens the metal, while in
others, like aluminum, the alloy becomes softer.
1.3 EFFECTS OF COMPOSITION
The specific composition of
an alloy system will usually
have a great effect on the
results of heat treating. If the
percentage of each constituent
is just right, the alloy will form
a single, continuous
microstructure upon cooling.
Such a mixture is said to be
eutectoid. However, If the
percentage of the solutes varies
from the eutectoid mixture,
two or more different microstructures will usually form simultaneously. A hypoeutectoid
solution contains less of the solute than the eutectoid mix, while a hypereutectoid
solution contains more.
Figure 4
A - pearlite (eutectoid)
B - ledeburite (eutectic)
a - α + pearlite
b- Fe3C + ledeburite + pearlite
c - Fe3C + ledeburite
d - cementite Fe3C + graphite
e - ferrite α
f - α + γ
g - austenite γ
h - γ + Fe3C + ledeburite
i - Fe3C + ledeburite
j - γ + liquid
k - liquid
l - liquid + Fe3C
Figure 3

1.3.1 Eutectoid alloys
A eutectoid (eutectic-like) alloy is similar in behavior to a eutectic alloy. A eutectic
alloy is characterized by having a single melting point. This melting point is lower than
that of any of the constituents, and no change in the mixture will lower the melting point
any further. When a molten eutectic alloy is cooled, all of the constituents will crystallize
into their respective phases at the same temperature.
A eutectoid alloy is similar, but the phase change occurs, not from a liquid, but from a
solid solution. Upon cooling a eutectoid alloy from the solution temperature, the
constituents will separate into different crystal phases, forming a single microstructure. A
eutectoid steel, for example, contains 0.77% carbon. Upon cooling slowly, the solution of
iron and carbon (a single phase called austenite) will separate into platelets of the phases
ferrite and cementite. This forms a layered microstructure called pearlite.
Since pearlite is harder than iron, the degree of softness achievable is typically limited to
that produced by the pearlite. Similarly, the hardenability is limited by the continuous
martensitic microstructure formed when cooled very fast
1.3.2 Hypoeutectoid alloys
A hypoeutectic alloy has two separate melting points. Both are above the eutectic
melting point for the system, but are below the melting points of any constituent forming
the system. Between these two melting points, the alloy will exist as part solid and part
liquid. The constituent with the lower melting point will solidify first. When completely
solidified, a hypoeutectic alloy will often be in solid solution.
Similarly, a hypoeutectoid alloy has two critical temperatures, called "arrests." Between
these two temperatures, the alloy will exist partly as the solution and partly as a separate
crystallizing phase, called the "proeutectoid phase." These two temperatures are called
the upper (A3) and lower (A1) transformation temperatures. As the solution cools from
the upper transformation temperature toward an insoluble state, the excess base metal
will often be forced to "crystallize-out," becoming the proeutectoid. This will occur until
the remaining concentration of solutes reaches the eutectoid level, which will then
crystallize as a separate microstructure.

Figure 5
A hypoeutectoid steel contains less than 0.77% carbon. Upon cooling a hypoeutectoid
steel from the austenite transformation temperature, small islands of proeutectoid-ferrite
will form. These will continue to grow and the carbon will recede until the eutectoid
concentration in the rest of the steel is reached. This eutectoid mixture will then
crystallize as a microstructure of pearlite. Since ferrite is softer than pearlite, the two
microstructures combine to increase the ductility of the alloy. Consequently, the
hardenability of the alloy is lowered.
1.3.3 Hypereutectoid alloy
A hypereutectic alloy also has different melting points. However, between these
points, it is the constituent with the higher melting point that will be solid. Similarly, a
hypereutectoid alloy has two critical temperatures. When cooling a hypereutectoid alloy
from the upper transformation temperature, it will usually be the excess solutes that
crystallize-out first, forming the proeutectoid. This continues until the concentration in
the remaining alloy becomes eutectoid, which then crystallizes into a separate
microstructure.
A hypereutectoid steel contains more than 0.77% carbon. When slowly cooling a
hypereutectoid steel, the cementite will begin to crystallize first. When the remaining
steel becomes eutectoid in composition, it will crystallize into pearlite. Since cementite
is much harder than pearlite, the alloy has greater hardenability at a cost in the ductility.
1.4 Effects of time and temperature
Proper heat treating requires precise control
over temperature, time held at a certain
temperature and cooling rate.
With the exception of stress-relieving,
tempering, and aging, most heat treatments
begin by heating an alloy beyond the upper
transformation (A3) temperature. This
temperature is referred to as an "arrest"
because at the A3 temperature the metal
experiences a period of hysteresis. At this
point, all of the heat energy is used to cause the
crystal change, so the temperature stops rising

for a short time (arrests) and then continues climbing once the change is complete.
Therefore, the alloy must be heated above the critical temperature for a transformation to
occur. The alloy will usually be held at this temperature long enough for the heat to
completely penetrate the alloy, thereby bringing it into a complete solid solution.
Because a smaller grain size usually enhances mechanical properties, such as
toughness, shear strength and tensile strength, these metals are often heated to a
temperature that is just above the upper critical-temperature, in order to prevent the
grains of solution from growing too large. For instance, when steel is heated above the
upper critical-temperature, small grains of austenite form. These grow larger as
temperature is increased. When cooled very quickly, during a martensite transformation,
the austenite grain-size directly affects the martensitic grain-size. Larger grains have
large grain-boundaries, which serve as weak spots in the structure. The grain size is
usually controlled to reduce the probability of breakage.
The diffusion transformation is very time-dependent. Cooling a metal will usually
suppress the precipitation to a much lower temperature. Austenite, for example, usually
only exists above the upper critical temperature. However, if the austenite is cooled
quickly enough, the transformation may be suppressed for hundreds of degrees below the
lower critical temperature. Such austenite is highly unstable and, if given enough time,
will precipitate into various microstructures of ferrite and cementite. The cooling rate can
be used to control the rate of grain growth or can even be used to produce partially
martensitic microstructures. However, the martensite transformation is time-independent.
If the alloy is cooled to the martensite transformation (Ms) temperature before other
microstructures can fully form, the transformation will usually occur at just under the
speed of sound.
When austenite is cooled slow enough that a martensite transformation does not
occur, the austenite grain size will have an effect on the rate of nucleation, but it is
generally temperature and the rate of cooling that controls the grain size and
microstructure. When austenite is cooled extremely slow, it will form large ferrite
crystals filled with spherical inclusions of cementite. This microstructure is referred to as
"sphereoidite." If cooled a little faster, then coarse pearlite will form. Even faster, and
fine pearlite will form. If cooled even faster, bainite will form. Similarly, these

microstructures will also form if cooled to a specific temperature and then held there for
a certain time.
Most non-ferrous alloys are also heated in order to form a solution. Most often, these
are then cooled very quickly to produce a martensite transformation, putting the solution
into a supersaturated state. The alloy, being in a much softer state, may then be cold
worked. This cold working increases the strength and hardness of the alloy, and the
defects caused by plastic deformation tend to speed up precipitation, increasing the
hardness beyond what is normal for the alloy. Even if not cold worked, the solutes in
these alloys will usually precipitate, although the process may take much longer.
Sometimes these metals are then heated to a temperature that is below the lower critical
(A1) temperature, preventing recrystallization, in order to speed-up the precipitation
1.5 TECHNIQUES
Complex heat treating schedules, or "cycles," are often devised by metallurgists to
optimize an alloy's mechanical properties. In the aerospace industry, a superalloy may
undergo five or more different heat treating operations to develop the desired properties.
This can lead to quality problems depending on the accuracy of the furnace's temperature
controls and timer. These operations can usually be divided into several basic techniques
1.5.1 Annealing
Annealing, in metallurgy and materials science, is a heat treatment that alters the
physical and sometimes chemical properties of a material to increase its ductility and
reduce its hardness, making it more workable. It involves heating a material above its
recrystallization temperature, maintaining a suitable temperature for a suitable amount of
time, and then cooling.
In annealing, atoms migrate in the crystal lattice and the number of dislocations
decreases, leading to a change in ductility and hardness. As the material cools it
recrystallizes. For many alloys, including carbon steel, the crystal grain size and phase
composition, which ultimately determine the material properties, are dependent on the
heating, and cooling rate. Hot working or cold working after the annealing process alter
the metal structure, so further heat treatments may be used to achieve the properties

required. With knowledge of the composition and phase diagram, heat treatment can be
used to adjust between harder and more brittle, to softer and more ductile.
In the cases of copper, steel, silver, and brass, this process is performed by heating the
material (generally until glowing) for a while and then slowly letting it cool to room
temperature in still air. Copper, silver[1] and brass can be cooled slowly in air, or
quickly by quenching in water, unlike ferrous metals, such as steel, which must be
cooled slowly to anneal. In this fashion, the metal is softened and prepared for further
work—such as shaping, stamping, or forming.
Annealing consists of heating a metal to a specific temperature and then cooling at a rate
that will produce a refined microstructure, either fully or partially separating the
constituents. The rate of cooling is generally slow. Annealing is most often used to
soften a metal for cold working, to improve machinability, or to enhance properties like
electrical conductivity.
In ferrous alloys, annealing is usually accomplished by heating the metal beyond the
upper critical temperature and then cooling very slowly, resulting in the formation of
pearlite. In both pure metals and many alloys that cannot be heat treated, annealing is
used to remove the hardness caused by cold working. The metal is heated to a
temperature where recrystallization can occur, thereby repairing the defects caused by
plastic deformation. In these metals, the rate of cooling will usually have little effect.
Most non-ferrous alloys that are heat-treatable are also annealed to relieve the hardness
of cold working. These may be slowly cooled to allow full precipitation of the
constituents and produce a refined microstructure.
Ferrous alloys are usually either "full annealed" or "process annealed." Full annealing
requires very slow cooling rates, in order to form coarse pearlite. In process annealing,
the cooling rate may be faster; up to, and including normalizing. The main goal of
process annealing is to produce a uniform microstructure. Non-ferrous alloys are often
subjected to a variety of annealing techniques, including "recrystallization annealing,"
"partial annealing," "full annealing," and "final annealing." Not all annealing techniques
involve recrystallization, such as stress relieving.
Annealing occurs by the diffusion of atoms within a solid material, so that the material
progresses towards its equilibrium state. Heat increases the rate of diffusion by providing

the energy needed to break bonds. The movement of atoms has the effect of
redistributing and eradicating the dislocations in metals and (to a lesser extent) in
ceramics. This alteration to existing dislocations allows a metal object to deform more
easily, increasing its ductility.[citation needed]
The amount of process-initiating Gibbs free energy in a deformed metal is also reduced
by the annealing process. In practice and industry, this reduction of Gibbs free energy is
termed stress relief.
The relief of internal stresses is a thermodynamically spontaneous process; however,
at room temperatures, it is a very slow process. The high temperature at which annealing
occurs serve to accelerate this process.
1.5.1.1 Stages
The three stages of the annealing process that proceed as the temperature of the
material is increased are: recovery, recrystallization, and grain growth. The first stage is
recovery, and it results in softening of the metal through removal of primarily linear
defects called dislocations and the internal stresses they cause. Recovery occurs at the
lower temperature stage of all annealing processes and before the appearance of new
strain-free grains. The grain size and shape do not change.The second stage is
recrystallization, where new strain-free grains nucleate and grow to replace those
deformed by internal stresses.If annealing is allowed to continue once recrystallization
has completed, then grain growth (the third stage) occurs. In grain growth, the
microstructure starts to coarsen and may cause the metal to lose a substantial part of its
original strength. This can however be regained with hardening
1.5.1.2 Controlled atmospheres
The high temperature of annealing may result in oxidation of the metal‘s surface,
resulting in scale. If scale must be avoided, annealing is carried out in a special
atmosphere, such as with endothermic gas (a mixture of carbon monoxide, hydrogen gas,
and nitrogen gas). Annealing is also done in forming gas, a mixture of hydrogen and
nitrogen.
The magnetic properties of mu-metal (Espey cores) are introduced by annealing the alloy
in a hydrogen atmosphere.

1.5.1.3 Setup and equipment
Typically, large ovens are used for the annealing process. The inside of the oven is
large enough to place the workpiece in a position to receive maximum exposure to the
circulating heated air. For high volume process annealing, gas fired conveyor furnaces
are often used. For large workpieces or high quantity parts, car-bottom furnaces are used
so workers can easily move the parts in and out. Once the annealing process is
successfully completed, workpieces are sometimes left in the oven so the parts cool in a
controllable way. While some workpieces are left in the oven to cool in a controlled
fashion, other materials and alloys are removed from the oven. Once removed from the
oven, the workpieces are often quickly cooled off in a process known as quench
hardening. Typical methods of quench hardening materials involve media such as air,
water, oil, or salt. Salt is used as a medium for quenching usually in the form of brine
(salt water). Brine provides faster cooling rates than water. This is because when an
object is quenched in water steam bubbles form on the surface of the object reducing the
surface area the water is in contact with. The salt in the brine reduces the formation of
steam bubbles on the object's surface, meaning there is a larger surface area of the object
in contact with the water, providing faster cooling rates. Quench hardening is generally
applicable to some ferrous alloys, but not copper alloys.
1.5.2 Normalizing
Normalizing heat treatment is a process applied to ferrous materials. The objective of
the normalizing heat treatment is to enhance the mechanical properties of the material by
refining the microstructure.
The ferrous metal is heated to the austenite phase, above the transformation range,
and is subsequently cooled in still air at room temperature. The normalizing heat
treatment balances the structural irregularities and makes the material soft for further
working.
The cold working operations such as forging, bending, hammering hardens the
materials and make it less ductile. Same goes for heat affected area near welded portion.

The normalizing heat treatment can re-gain the ductility and softness of this material.
This treatment is also used as before any subsequent surface hardening to improve
response to the desired hardening.
1.5.2.1 Normalizing Heat Treatment & Process
The metal is heated in a furnace for normalizing heat
treatment process. The temperature of the furnace is kept
between 750-980 °C (1320-1796 °F), depending upon the
carbon content in the material.
The material is kept at the temperature above austenite
temperature for 1-2 hours, until all the ferrite converts into austenite, and then cooled to
room temperature in still air or Nitrogen, if run in the vacuum furnace at less than 1 bar
pressure.
The solubility of carbon in iron is higher in the austenite phase. Normalizing heat
treatment produces a more uniform carbide size which aids further heat treatment
operations and results in a more consistent final product.
The process of normalizing is explained in following. The metal is heated from
temperature ―a‖ to ―b‖ and kept in this condition for some time. It is then cooled to
ambient temperature ―d‖ in still air.
1.5.2.2 Carbon Steel Normalizing
Carbon steel contains carbon in the range
of 0.12 to 2%. As the percentage of
carbon content increases, the steel
becomes harder, tougher and less ductile.
Low carbon steels usually do not need
normalizing. However, they can be
normalized on the requirement.
In normalizing heat treatment of carbon
steel, it is heated to a temperature of 55
Figure 6
Figure 7

°C (131 °F) above the austenitic temperature, Ac3, (Lies between 750-980 °C / 1320-
1796 °F) also known as ―holding temperature‖ as shown in the following figure.
The period of holding temperature is one hour per 25 mm (0.984 in) thickness. The
process ensures that all the steel transforms into austenite. Steel is then cooled down to
ambient temperature in still air.
This process produces fine pearlite structure which is more uniform. Pearlite is a layered
structure of two phases i.e. cementite (iron carbide) and α-ferrite. This process is
different from annealing because in the annealing the heated metal is cooled slowly at a
specified rate inside the furnace.
Normalized steel has greater strength and hardness than annealed steel, and the process
is more economical due to cooling directly with air.
1.5.2.3 Microstructure in Normalizing
The thickness of carbon steel can have a significant effect on the cooling rate and
thus the resulting microstructure. The thicker pieces cool down slower and become more
ductile after normalizing than thinner pieces.
After normalizing the portions of steel containing 0.80% of carbon are pearlite
while the areas having low carbon are ferrites. The redistribution of carbon atoms takes
place between ferrite (0.022 % by wt.) and cementite (6.7% by wt.) by the process of
atomic diffusion.
The amount of pearlite is more than that in annealed steel with same carbon
content. This is because of shifting of the eutectoid composition to lower value and
formation of cementite.
The fine-grained pearlite microstructure is tougher than coarse-grained ones.
Normalizing reduces the internal stresses of the carbon steel. It also improves
microstructural homogeneity, enhances thermal stability and response to heat treatment.

1.5.2.4 Normalizing Equipment
The equipment in use for normalizing comes in both batch and continuous operations.
Bell furnace offers an economical method of heat treatment and different bell lifting
mechanisms.
Continuous furnaces heat treats the metal in the continuous fashion. The conveyor runs
at constant speed, and the product is carried to desired conditions after heat treatment.
1.5.2.5 Application of Normalizing
The low cost of the normalizing process makes it one of the most extensively used
industrial process when compared to annealing. The furnace is available for the next
batch as soon as heating and holding periods are over. Normalizing is used to:
 Improve the grain size refinement and machinability of cast structures of castings
 Recover the original mechanical properties of forged or cold worked steel
 Ease the forging operations for high carbon steel
 Stress relieve of castings
1.5.3 Quenching
In materials science, quenching is the rapid cooling of a workpiece in water, oil or air
to obtain certain material properties. A type of heat treating, quenching prevents
undesired low-temperature processes, such as phase transformations, from occurring. It
does this by reducing the window of time during which these undesired reactions are
both thermodynamically favorable, and kinetically accessible; for instance, quenching
can reduce the crystal grain size of both metallic and plastic materials, increasing their
hardness.
In metallurgy, quenching is most commonly used to harden steel by introducing
martensite, in which case the steel must be rapidly cooled through its eutectoid point, the
temperature at which austenite becomes unstable. In steel alloyed with metals such as
nickel and manganese, the eutectoid temperature becomes much lower, but the kinetic
barriers to phase transformation remain the same. This allows quenching to start at a
lower temperature, making the process much easier. High speed steel also has added

tungsten, which serves to raise kinetic barriers and give the illusion that the material has
been cooled more rapidly than it really has. Even cooling such alloys slowly in air has
most of the desired effects of quenching.
Extremely rapid cooling can prevent the formation of all crystal structure, resulting in
amorphous metal or "metallic glass".
1.5.3.1 Quench hardening
Quench hardening is a mechanical process in which steel and cast iron alloys are
strengthened and hardened. These metals consist of ferrous metals and alloys. This is
done by heating the material to a certain temperature, depending on the material. This
produces a harder material by either surface hardening or through-hardening varying on
the rate at which the material is cooled. The material is then often tempered to reduce the
brittleness that may increase from the quench hardening process. Items that may be
quenched include gears, shafts, and wear blocks.
1.5.3.1.1 Purpose
Before hardening, cast steels and iron are of a uniform and lammelar (or layered)
pearlitic grain structure. This is a mixture of ferrite and cementite formed when steel or
cast iron are manufactured and cooled at a slow rate. Pearlite is not an ideal material for
many common applications of steel alloys as it is quite soft. By heating pearlite past its
eutectoid transition temperature of 727 °C and then rapidly cooling, some of the
material‘s crystal structure can be transformed into a much harder structure known as
martensite. Steels with this martensitic structure are often used in applications when the
workpiece must be highly resistant to deformation, such as the cutting edge of blades.
This is very efficient.
1.5.3.1.2 Process
The process of quenching is a progression, beginning with heating the sample. Most
materials are heated to between 815 and 900 °C (1,500 to 1,650 °F), with careful
attention paid to keeping temperatures throughout the workpiece uniform. Minimizing
uneven heating and overheating is key to imparting desired material properties.

The second step in the quenching process is soaking. Workpieces can be soaked in air
(air furnace), a liquid bath, or a vacuum. The recommended time allocation in salt or
lead baths is up to 6 minutes. Soaking times can range a little higher within a vacuum.
As in the heating step, it is important that the temperature throughout the sample remains
as uniform as possible during soaking.
Once the workpiece has finished soaking, it moves on to the cooling step. During this
step, the part is submerged into some kind of quenching fluid; different quenching fluids
can have a significant effect on the final characteristics of a quenched part. Water is one
of the most efficient quenching media where maximum hardness is desired, but there is a
small chance that it may cause distortion and tiny cracking. When hardness can be
sacrificed, mineral oils are often used. These oil based fluids often oxidize and form a
sludge during quenching, which consequently lowers the efficiency of the process. The
quenching velocity (cooling rate) of oil is much less than water. Intermediate rates
between water and oil can be obtained with a purpose formulated quenchant, a substance
with an inverse solubility which therefore deposits on the object to slow the rate of
cooling.
Quenching can also be accomplished using inert gases, such as nitrogen and noble
gasses. Nitrogen is commonly used at greater than atmospheric pressure ranging up to 20
bar absolute. Helium is also used because its thermal capacity is greater than nitrogen.
Alternatively argon can be used; however, its density requires significantly more energy
to move, and its thermal capacity is less than the alternatives. To minimize distortion in
the workpiece, long cylindrical workpieces are quenched vertically; flat work pieces are
quenched on edge; and thick sections should enter the bath first. To prevent steam
bubbles the bath is agitated.
Often, after quenching, an iron or steel alloy will be excessively hard and brittle due to
an overabundance of Martensite. In these cases, another heat treatment technique known
as tempering is performed on the quenched material in order to increase the toughness of
iron-based alloys. Tempering is usually performed after hardening, to reduce some of the
excess hardness, and is done by heating the metal to some temperature below the critical
point for a certain period of time, then allowing it to cool in still air.

1.5.3.2 Water Quenching
Liquid quenching, with water is the most popular type of cooling. Water is
flexible in its characteristics and composition, so that it can be changed by the varying
temperature of the water. Water also provides rapid speeds of cooling necessary for
different alloys. Water is best use to quench steels because of the ability to absorb huge
amounts of atmospheric gases. The bubbles hide in holes and are normally on the surface
of metals. Water is fairly good quenching medium.it is cheap, readily available, easily
stored nontoxic nonflammable smokeless and easy to filer and pump but with water
quench the formation of bubbles may cause soft spots in the metal. Agitation is
recommended with use of water quench. Still other problems with water quench
included its oxidizing nature, its corrosivity and the tendency to excessive distortion and
cracking although this bad properties for plain carbon steels.The cooling rate of the
object depends upon the size, composition, and initial temperature of the product being
cooled .Water quenching tanks should be changed daily. Water quench tanks should be
larger than the material need to be quenched. The temperature of water should not
exceed 65°F. This is about the ambient temperature of a room. Once the object is placed
in the water, the quench tank water should not raise higher than 20°F during the process.
Some heavy parts, or wrought products a higher temperature may occur above 20°.
Two types of cold water cooling are still-bath and flush quenching. Bath
quenching, cools material in a metal tank of liquid. The coolant medium flows through
canals that are integrated within the tank. The tank is colder than the material to be
quenched, and allows for the temperature of material to drop. Flush quenching occurs
when a liquid is sprayed onto the surface. This process is used for parts that have
hollows that cannot be cooled via still-bath quenching.
(a) (b)
Figure 8: (a)still-bath (b) flush quenching

1.5.3.3 Brine Quenching
This process was used quite early in the history of processing steel. In fact, it was
believed that biological fluids made the best quenching liquids and urine was sometimes
used. In some ancient civilizations, the red hot sword blades were sometimes plunged
into the bodies of hapless prisoners! Today metals are quenched in water or oil. Actually,
quenching in salt water solutions is faster, so the ancients were not entirely wrong.
Molten salts have been used for quenching for more than 50 years. Their wide operating
temperature range makes them ideal for many quenching processes aimed at minimizing
distortion of iron and steel parts. Their unique characteristics coupled with recent
advances in salt quality, pollution abatement, and material handling make salt bath
quenching more efficient and economical than ever before.
Distortion control: In interrupted quenching, parts are cooled rapidly from the
austeitizing temperature to a point above the martensite start temperature (Ms), where
they are held for a specified time and then cooled to room temperature. Thermal stresses
and the potential for distortion are considerably reduced during the hold above Ms.
Processes that make use of an interrupted quench include martempering, austempering
and variations of them.
For most steel and alloys, the temperature at which the quench is interrupted is usually in
the 175 to 370°C (350 to 700°F) range. Water, brine, polymer solutions and most
quench oils cannot be used at these temperatures. Attempts at using molten lead and
fluidized beds do not appear to have met with much success. Some oils can be used at
temperatures up to 230°C (450°F), but for higher temperatures, molten salt is the natural,
practical choice.
Advantages of salt over oil
The most distinct advantages of salt over oil is its wide operating temperature
range- 150 to 595°C (300 to 1100°F) for a typical composition. Thus, salt can be used
for any interrupted quenching process. Oil, however, cannot be used above 230°C
(450°F), which restricts its use to low temperature processes.
The quenching mechanism also is considerably different. Most of the heat extracted
during salt quenching is by convection (the third stage of liquid cooling), and is therefore

at a uniform rate. In oil quenching, heat is extracted during all three stages with varying
rates. As a result, salt quenching causes less distortion and produces more uniform and
consistent hardness.
Other important advantages of salt over oil include:
 Quench severity can be controlled to a greater degree by varying temperature,
agitation, and water content of the salt bath.
 Productivity is higher because parts attain temperature equalization faster.
 The excellent thermal and chemical stability of salt means that the only
replenishment required is due to dragout losses. A salt bath provides satisfactory
quenching performance for many years. In contrast, oil deteriorates with use,
requiring closer control and sometimes partial or complete replacement.
 Nonflammable salt poses no fire hazard, whereas oil at a comparable temperature
poses a serious hazard.
 Salt can be easily washed off with water and recovered for reuse, if desired.
Choosing to recover salt not only eliminates disposal but also reduces operating
costs. In contrast, washing of oil requires special cleaners and equipment; and its
recovery is not simple.
Limitations: There are relatively few limitations to salt as a quenching medium. It has
to be used above its melting point of about 150°C(300°F). And, because it is a strong
oxidizer, combustible or incompatible materials should definitely be kept out of the salt
bath to avoid the possibility of violent reactions.
Salt may appear to present safety and environmental problems, but the
technology for dealing with them is well developed and they are no longer viewed as a
deterrent to its use.
Required safety precautions
Although quenching salt is nonflammable and relatively nontoxic, concern for
personnel safety arises due to the temperature at which it is used. Adequate precautions
should therefore be taken to protect operating personnel from accidental burns.

Following these guidelines also will help ensure safe salt bath quenching:
 Although no toxic or hazardous fumes are given off by the quench bath, good
exhaust around the bath is highly recommended. This is particularly helpful
during charging with fresh salt and during the quenching operation.
 Parts, fixtures and conveyors entering a quench bath should be absolutely dry and
free of any moisture, oil or other liquid. Otherwise, rapid vaporization of the
liquid may cause sudden expulsion of molten salt, which could result in injury or
damage.
 Water sprinklers should not be installed in and around any molten salt system.
There should be a clearly visible sign saying not to use water or any liquid-type
extinguisher in case of fire. Carbon dioxide-type extinguishers and sand are the
best means of fight and contain fires surrounding molten salt baths.
 The salt bath should be protected from accidental overheating by installing
audio/visual alarms that go off when bath temperature exceeds a preset limit. If
the temperature continues to rise beyond 595°C (1100°F), the salt may break
down, and reactions between the products of the breakdown and the bath
container could result in leakage of salt.
 Combustible and incompatible materials like cyanide salt should never be
introduced into a quench bath to avoid possible violent reactions which may
result in an explosion.
 Salt should be stored in well marked, closed containers, which should be kept in
a dry location segregated from incompatible materials such as cyanide salts.
Recovery and disposal
After quenching, parts are immersed in an agitated hot water bath, where most
of the salt is dissolved, and then rinsed in hot water spray. Salt from wash water can be
recovered by evaporation of its water content. What results is molten salt that is
transferred to box-type metal containers, where it is allowed to freeze into blocks.
Following the recovery and reuse route eliminates disposal of wash water.
The drawback is that it causes build up of undesirable contaminants. Periodic

adjustment of salt chemistry is required to maintain uniform quenching performance.
This helps explain why many heat treaters still prefer to dispose of their wash water.
Although neither highly toxic nor flammable, quenching salt is classified as a
hazardous material because of its oxidizing nature. When salt is contained in wash
water, the hazard is reduced considerably, and many local waste treatment authorities
permit discharge of wash water into their drainage systems. If permission cannot be
obtained, the handling of wash water can be delegated to a waste disposal company.
Sludge can be used as chemical land fill, where permitted. Otherwise, it can be dissolved
in water and treated the same way as wash water.
1.5.3.4 Oil quenching
Quenching oil and heat treatment fluids are designed for rapid or controlled
cooling of steel or other metals as part of a hardening, tempering or other heat-treating
process. Quenching oil serves two primary functions. It facilitates hardening of steel by
controlling heat transfer during quenching, and it enhances wetting of steel during
quenching to minimize the formation of undesirable thermal and transformational
gradients which may lead to increased distortion and cracking.
Oil has a major advantage over water due to its higher boiling range. A typical
oil has a boiling range between 450ºF (230ºC) and 900ºF (480ºC). This causes the slower
convective cooling stage to start sooner, enabling the release of transformation stresses
which is the major problem with rapid water cooling. Oil is, therefore, able to quench
intricate shapes and high-hardenability alloys successfully.
1.5.3.4.1 The Quenching Process
When heat treatment fluids are used to quench metals, cooling occurs in three
distinct stages: film boiling, nucleate boiling and convective heat transfer
Film Boiling
Film boiling, also known as the "vapor blanket" stage, occurs upon initial
immersion. Contact between the hot metal surface and quenchant creates a layer of vapor
(known as the Leidenfrost phenomenon) due to the supply of heat being greater than that
which is carried off. The stability of the vapor layer, and thus the ability of the oil to

harden steel, is dependent on the metal's surface irregularities, oxides present, surface-
wetting additives (which accelerate wetting and destabilize the layer), and the quench
oil's molecular composition (including the presence of more volatile oil degradation by-
products). Cooling in this stage is a function of conduction through the vapor envelope
and is relatively slow since the vapor blanket acts as an insulator.
Nucleate Boiling
As the part cools, the vapor blanket collapses at points and nucleate boiling
(violent boiling of the quenchant) results. Heat transfer is fastest during this stage, with
heat transfer coefficients sometimes over two orders of magnitude higher than during
film boiling, largely due to the heat of vaporization. The boiling point of the quenchant
determines the conclusion of this stage. The points at which this transition occurs and the
rate of heat transfer in this region depend on the oil's overall molecular composition.
Convective Heat Transfer
When the part has cooled below the boiling point of the quenchant, slow
cooling occurs by convection and conduction (also called the "liquid" stage). Cooling
rate during this stage is slow, and is exponentially dependent on the oil's viscosity, which
varies with the degree of oil decomposition. Heat-transfer rates increase with lower
viscosities and decrease with increasing viscosity.
Figure 9: Typical cooling curves and cooling-rate curves for new oils

The ideal quenchant is one that exhibits little or no vapor stage, a rapid
nucleated boiling stage and a slow rate during convective cooling. The high initial
cooling rates allow for the development of full hardness by quenching faster than the so-
called critical transformation rate and then cooling at a slower rate as the metal continues
to cool. This allows stress equalization, reducing distortion and cracking in the
workpiece.
1.5.3.4.2 Oil Selection
When selecting quenching oils, industrial buyers will need to consider the chemistry,
properties, and features of the fluid that are needed for the application
Straight oils are non-emulsifiable products used in machining operations in an undiluted
form. They are composed of base mineral or petroleum oils, and often contain polar
lubricantslike fats, vegetable oils, and esters, as well as extreme pressure additives such
as chlorine, sulfur, and phosphorus. Straight oils provide the best lubrication and the
poorest cooling characteristics among quenching fluids. They are also generally the most
economical.
Water soluble and emulsion fluids are highly diluted oils, also known ashigh-water
content fluids (HWCF). Soluble oil fluids form an emulsion when mixed with water. The
concentrate consists of a base mineral oil and emulsifiers to help produce a stable
emulsion. These fluidsare used in a diluted form with concentrationsranging from 3% to
10%, and provide good lubrication and heat transfer performance. They are used widely
in industry and are the least expensive among all quenching fluids. Water-soluble fluids
are used as water-oil emulsions or oil-water emulsions. Water-in-oil emulsions have a
continuous phase of oil, and superior lubricating and friction reduction qualities (i.e.
metal forming and drawing). Oil-water emulsions consist of droplets of oil in a
continuous water phase and have better cooling characteristics (i.e. metal cutting fluids
and grinding coolants).
Synthetic or semi-synthetic fluids or greases arebased on synthetic compoundslike
silicone, polyglycol, esters, diesters,chlorofluorocarbons (CFCs),and mixtures of
synthetic fluids and water.Synthetic fluids tend to have the highest fire resistance and
cost.They contain no petroleum or mineral oil base, but are instead formulated
fromorganic and inorganic alkaline compoundswith additives for corrosion inhibition.

Synthetic fluidsare generally used in a diluted form with concentrations ranging from 3%
to 10%. They often provide the best cooling performance among all heat treatment
fluids. Some synthetics, such as phosphate esters, react or dissolve paint, pipe thread
compounds, and electrical insulation. Semi-synthetic fluids are essentially a combination
of synthetic and soluble petroleum or mineral oil fluids.The characteristics, cost, and
heat transfer performance of semi-synthetic fluids fall between those of synthetic and
soluble oil fluids.
Micro-dispersion oils contain a dispersion of solid lubricant particles such asPTFE
(Teflon®), graphite, and molybdenum disulfide or boron nitride in a mineral, petroleum,
or synthetic oil base. Teflon® is a registered trademark of DuPont.
1.5.3.4.3 Properties
Properties for describing heat treating fluids can be classified as either primary or
secondary.
Primary
Primary properties are those which describe the performance of the fluid. These
include cooling rate, thermal conductivity, viscosity, water content, and sludge formation
 Cooling rate / quenching speed - the rate at which a quenching fluid can
cool a workpiece. This specification is given either as a ratio in
comparison to water or as a number based on the GM quenchometer test.
The GM test (also called the "nickel ball" test) measures how long it takes
for a nickel ball to be cooled to the point at which it becomes magnetic.
The figure below gives an example of the setup for such a test.
Figure 10: GM quenchometer test apparatus

This property does not give any information about the cooling pathway,
however (as demonstrated in figure 11); it merely gives the time required to cool to a
certain temperature.
Figure 11: Cooling curves for 3 different quenching oils with the same GM results
 Thermal conductivity - the measure of a fluid's ability to transfer heat.
Quenching fluids with higher thermal conductivity will cool metals faster
than those with low thermal conductivity.
 Viscosity - the thickness of a fluid, commonly measured in centistokes
(cSt). Heat transfer during the convective stage is exponentially dependent
on the oil's viscosity, which will vary with the degree of oil
decomposition. Oil decomposition (formation of sludge and varnish) will
result initially in a reduction of oil viscosity followed by continually
increasing viscosity as the degradation continues. Heat transfer rates
increase with lower viscosities and decrease with increasing viscosity.
Figure 12 shows viscosity change over time.
Figure 12: Viscosity of a Martempering Oil as a Function of Time

 Water content - the amount of water in the quenching fluid. Water,
because it is not compatible with oil and possesses different physical
properties such as viscosity and boiling point, will cause increases in
thermal gradients and may cause soft spots, uneven hardness, or staining
on the workpiece. When water-contaminated oil is heated, a crackling
sound may be heard; the basis of a qualitative field test for water in quench
oil. Many automated moisture detectors typically measure as low as 0.5
percent, which is inadequate for the moisture content levels allowed for
quench oils (typically less than 0.1 percent).
 Sludge content - the amount of sludge and varnish in the quenching fluid
as a result of thermal and oxidative degradation. These by-products
typically do not adsorb uniformly on the metal's surface as it is being
quenched, resulting in non-uniform heat transfer, increased thermal
gradients, cracking, and distortion. Sludge may also plug filters and foul
heat-exchanger surfaces, causing overheating, excessive foaming, and
fires. The relative amount of sludge in quench oil may be quantified by the
precipitation number. This number can be used to estimate the remaining
life of used oil by comparing it to the levels in new oil.
Secondary
Secondary properties are those which describe a fluid's operating parameters. They
include operating temperature, pour point, and flash point.
 Operating temperature - the normal range of temperatures for which the fluid
is designed, or the maximum temperature of material the fluid can cool safely or
effectively.
 Pour point - the lowest temperature at which fluid or oil flows. The pour point
is typically 15°F to 20°F below the system's lowest end-use temperature to
prevent pump damage through cavitation.
 Flash point - the temperature at which the fluid produces sufficient vapors to
form an ignitable mixture in air near the surface. The lower the flash point, the
easier it is to ignite the material. Operating temperatures and procedures need to
be considered along with an oil's flash point to ensure a safe quenching process.

1.5.3.4.4 Features
Quenching oils and heat treatment fluids can include a number of additional features
which add versatility and functionality. Among these are biodegradable, low foaming,
and water displacement characteristics.
• Biodegradable - fluids are designed or suitable to decompose or break down into
harmless chemicals when released into the environment. This is useful for high
volume operations where disposal costs for degraded oils could otherwise be very
high.
• Low foaming - fluidsdo not produce foam or produce onlysmall amounts of foam.
Non-foaming characteristics areachieved through the use of additives that break
out entrained air. Leaks which introduce air into a system can cause pump damage
due to cavitation.Foaming can also reduce the cooling ability and the bulk
modulus (or stiffness) of the fluid.
• Water displacement - fluids have the ability to displace water from a surface
based on wetting or surface energy characteristics. Fluids with low surface energy
or interfacial tension compared to water will flow under the water or moisture on a
surface.
1.5.3.4.5 Additional Things to Consider when Quenching with Oil
 Always have on the proper safety equipment. Safety glasses, gloves, leathers, etc.
 Always have a fire extinguisher and a bucket of sand on hand for emergency fires.
 Make sure oil is in a metal container. Plastic can melt and cause an accident. Use a
turkey fryer for larger projects. A metal container that will hold around 2 gallons
is ideal for smaller projects.
 Oil can flash fire when you first place the blade in it. Long pliers or blacksmith
tongs work good to get your hands out of the way. Never have your face directly
over the oil quenchant container.
 Always heat the oil up prior to quenching your project. Quenchants should be at
room temperature or slightly above. Never quench in cold oil. Heat an old bolt or
scrap steel and use it to bring the solution up to temp

1.6 INTRODUCTION TO EN8
EN8 carbon steel is a common medium carbon and medium tensile steel, with
improved strength over mild steel, through-hardening medium carbon steel. EN8 carbon
steel is also readily machinable in any condition.EN means European Normative, and
mainly invented during World War 2. So its known as EMERGENCY NUMBER steel.
and its series like EN8,EN24,EN31 etc. That's pretty much the equivalent of
ASME/ASNT and other American standards. EN8 steels are generally used in the as
supplied untreated condition. But EN8 steels can be further surface-hardened by
induction processes, producing components with enhanced wear resistance. A steel EN8
material in its heat treated forms possesses good homogenous metallurgical structures,
giving consistent machining properties.Good heat treatment results on sections larger
than 65mm may still be achievable, but it should be noted that a fall-off in mechanical
properties would be apparent approaching the centre of the bar. It is therefore
recommended that larger sizes of EN8 steel materials are supplied in the untreated
condition, and that any heat treatment is carried out after initial stock removal. This
should achieve better mechanical properties towards the core.
1.6.1 MECHANICAL PROPERTIES OF EN8 STEEL
 EN8 carbon steel is a common medium carbon and medium tensile steel,
withimproved strength over mild steel, through-hardening medium carbon steel.
 Readily machinable in any condition (with proper tool).
 It can be further surface-hardened by induction processes, producing components
with enhanced wear resistance.
 In its heat treated forms possesses good homogenous metallurgical structures,
giving consistent machining properties
 Suitable for the manufacture of parts such as general-purpose axles and
shafts,gears, bolts and studs.
 Good heat treatment results on sections be achievable

Max Stress -700-850N/mm2

Yield stress - 465N/mm^2 min

Max Elongation - 16% min

Impact KCV - 28 Joules min

Hardness - 201-255 Brinell

1.6.2 Applications of EN8 Carbon Steel
EN8 steel material is suitable for the all general engineering applications requiring a
higher strength than mild steel such as:
 general-purpose axles
 shafts,
 gears,
 bolts and studs.
 spindles,
 automotive and general engineering components,
 other general engineering parts etc.
1.7 OBJECTIVES
 Keeping EN8 steel in furnace for 3 hours in 940⁰C
 To treat the En 8 steel by Annealing, Normalizing and 3 Quenching
Medium(Water, Oil,Brine) .
 To compare the hardness of En8 steel after treatment
 To compare the micro-structure of the specimen after different heat treatment
process.
1.8 APPROACH
Today, steel is one of the most common materials in the world, with more than 1.3
billion tons produced annually. It is a major component in buildings, infrastructure, tools,
ships, automobiles, machines, appliances and weapons. Modern steel is generally
identified by various grades defined by assorted standards organizations. The EN8 grade
steel is chosen for heat treatment to increase the hardness of the steel. In heat treatment
we are applying different types quenching medium and compare which quenching
medium is best for EN8 steel to improve the hardness. Also we are compare
microstructure of different quenched materials. The objective of this study is to improve
the hardness of EN8 steel by using heat treatment

1.9 REPORT OUTLINE
Chapter fabrication in brief in as follows; Initially, Chapter 2 deals with study of EN8
and various heat treatment techniques using various journal papers. It also includes an
exhaustive literature review. Chapter 3 is the Methodology section; it deals with the how
the experiment is done. Then result and analysis of the experiments that are showed in
chapter 3 is described in Chapter 4, concludes in chapter 5 which highlights the main
contributions of this project and ends with chapter 6 showing future scope that outlines
potential direction for further work.

Chapter 2
LITERATURE REVIEW
2.1. INTRODUCTION
Literature has been collected from various journals, books, papers etc. & has been
reviewed as followsSteels are particularly suitable for heat treatment, since they respond well
to heat treatment and the commercial use of steels exceeds that of any other material.
2.2 BASIC PRINCIPLE
Steels are heat treated for one of the following reasons:
1. Softening
2. Hardening
3. Material Modification
1. Softening: Softening is done to reduce strength or hardness, remove residual stresses,
improve toughness, restore ductility, refine grain size or change the electromagnetic
properties of the steel. Restoring ductility or removing residual stresses is a necessary
operation when a large amount of cold working is to be performed, such as in a cold-
rolling operation or wiredrawing. Annealing — full Process, Spheroidizing,
Normalizing and tempering, Austempering, Martempering are the principal ways by
which steel is softened.
2. Hardening: Hardening of steels is done to increase the strength and wear properties.
One of the pre-requisites for hardening is sufficient carbon and alloy content. If there
is sufficient Carbon content then the steel can be directly hardened. Otherwise the
surface of the part has to be Carbon enriched using some diffusion treatment
hardening techniques.
3. Material Modification: Heat treatment is used to modify properties of materials in
addition to hardening and softening. These processes modify the behavior of the steels
in a beneficial manner to maximize service life, e.g., stress relieving, or strength
properties, e.g., cryogenic treatment, or some other desirable properties, e.g., spring
aging.

Heat treatment is a combination of timed heating and cooling applied to a particular
metal or alloy in the solid state in such ways as to produce certain microstructure and desired
mechanical properties (hardness, toughness, yield strength, ultimate tensile strength, Young‘s
modulus, percentage elongation and percentage reduction). Annealing, normalising,
hardening and tempering are the most important heat treatments often used to modify the
microstructure and mechanical properties of engineering materials particularly steels.
Hardening is the most common heat treatment applied to tool steels. It consists of three
operations:
1. Heating
2. Quenching
3. Tempering.
Heating is carried out by preheating the work piece until its temperature is equalized
throughout, and then holding or soaking it at the processing temperature to dissolve its
carbides (compounds of carbon and alloying elements) into the matrix (the surrounding
material in which they are embedded). This makes the matrix richer in carbon and alloying
elements, with the hardness finally achieved depending primarily on the amount of carbon
dissolved. The alloying elements mostly determine the speed at which the steel must be
quenched and the depth of hardness attained in it.
Quenching consists of cooling the heated work piece rapidly by immersing it in a liquid (oil,
water, and molten salt), surrounding it with gas or air, or submerging it in a fluidized bed to
keep the carbon in solid solution in the steel.
Tempering consists of reheating the quenched steel one or more times to a lower
temperature, 150 to 650 °C., and cooling it again to develop the desired levels of ductility and
toughness.
 Steel in the annealed condition is soft and ductile and has low tensile strength.
Structure: Ferrite + Pearlite + Carbides of various compositions.
 At hardening temperature the steel is very soft and has very low tensile strength.
Structure: Austenite+ residual Carbides
 After quenching the steel is hard and brittle.
Structure: Martensite (highly stressed) + other transformation products + soft retained
Austenite + residual Carbides.

2.3 REFERENCE JOURNALS
2.3.1 Journal 1
Study the Effect on the Hardness of three Sample Grades of Tool Steel i.e.EN-31,
EN-8, and D3 after Heat Treatment Processes Such As Annealing, Normalizing, and
Hardening & Tempering by, Ashish Bhateja
This Study is based upon the empirical study which means it is derived from
experiment and observation rather than theory. Main Objective is to Study the Effect on the
Hardness of three Sample Grades of Tool Steel i.e. EN-31, EN-8, and D3 after Heat
Treatment Processes Such As Annealing, Normalizing, and Hardening & Tempering. This
survey also h elps to find out the place of the work to be carried out i.e. availability of set up,
techniques used for such, estimated time & cost requires for such study to be carried out for
such industrial survey to be carried out we designed a Survey questioner and selects various
places who offers heat treatment services Ludhiana based. After literature review and
industrial survey aims to prepare heat treatment performance Index HTPI 2012 which is
supposed to be very effective tool for defining the objective funct ion. After selection of
material & heat treatment processes further aims to perform mechanical & chemical analysis
i.e. composition testing of the three tool steel EN-31, EN-8, and D3 before treatment. After
composition testing aims to do heat treatment processes i.e. Annealing, Normalizing, and
Hardening & Tempering to be carried on such material & after treatment aims to perform
harness testing on the treated and untreated work samples.
2.3.2 Journal 2
Evaluation of en8 steel in different quenching medium - by N.Prithiviraj
The heat treatment and quenching process offer enormous advantages to the steels by
changing the mechanical properties, phase changes in structure of the steel in the present
scenario. So, we undergo this heat treatment process for the evaluation of the En8 steels in
different quenching medium. Samples of EN8 medium carbon steel were examined after
heating between 900ºC-930ºC in the Gas Carburizing Furnace and quenched in different
quenching medium. The different quenching mediums used like Oil, Water, and Air. The
mechanical properties such as hardness are determined using the Rockwell hardness
equipment and the hardness of the quenched material is higher than the parent material. The

hardness of the water quenched material is higher than the other quenched materials. The heat
treated materials are cut into the required specification using wire cutting machine. And the
microstructure of the quenched samples was taken using optical microscope. The water
quenched material has more hardness, suggesting improved mechanical properties.
2.3.3 Journal 3
Effect of water quenching process on the microstructure of cold rolled dual
phase steel – by L. Gao
The effects of water quenching process on the microstructure and magnetic property
of cold rolled dual phase steel are investigated. Correlations of microstructure, magnetic
properties and water quenching parameters are established. The results show that the
microstructure of the dual phase steels mainly consists of the ferrite and martensite phase, the
martensite volume fraction increases gradually on increasing the holding and quenching
temperature. It is found that magnetic properties of dual phase steel are very sensitive to the
quenching process. Based on the minor hysteresis loop results, the coercivity and hysteresis
loss increase obviously with the increase of quenching temperature, while the remanent
induction and the maximum permeability tend to decrease. Furthermore, the magnetic
domain structure of the ferrite phase in the presented dual phase steel is observed by
magnetic force microscopy. The mechanism of the magnetic property varying with the
quenching process is also discussed..
2.3.4 Journal 4
The effect of heat treatment on the hardness and impact properties of medium
carbon steel – by Noor Mazni Ismail
This paper covers the effect of heat treatment on the mechanical properties of medium
carbon steel. The main objective of this project is to investigate the hardness and impact
properties of medium carbon steel treated at different heat treatment processes. Three types of
heat treatment were performed in this project which are annealing, quenching and tempering.
During annealing process, the specimens were heated at 900oC and soaked for 1 hour in the
furnace. The specimens were then quenched in a medium of water and open air, respectively.
The treatment was followed by tempering processes which were done at 300oC, 450oC, and
600oC with a soaking time of 2 hours for each temperature. After the heat treatment process

completed, Rockwell hardness test and Charpy impact test were performed. The results
collected from the Rockwell hardness test and Charpy impact test on the samples after
quenching and tempering were compared and analysed. The fractured surfaces of the samples
were also been examined by using Scanning Electron Microscope. It was observed that
different heat treatment processes gave different hardness value and impact property to the
steel. The specimen with the highest hardness was found in samples quenched in water.
Besides, the microstructure obtained after tempering provided a good combination of
mechanical properties due to the process reduce brittleness by increasing ductility and
toughness.
2.3.5 Journal 5
Study the effect of hardness of steel by Annealing and Normalizing during hot
Rolling Processes - by Pradip A.Dahiwade, Sudhir Shrivastava & N.K.Sagar
Annealing is a heat treatment operation applied to steel for reliving internal stresses,
which may be developed during cold working, casting, quenching. The term annealing is
understood to mean the heating of steel above the temperature of phase transformation
followed by slow cooling. The annealing temperature may be 20-500C above AC3 for
hypereutectoid steel and in between AC1&ACm for hypereutectoid steel. The holding time
for the part at the annealing temperature should be heated uniformly from the surface to the
center and the temperature must be uniform from the surface to the center of the mass. The
part may be cooled in the furnace or by dumping it in ash, sand or lime. After annealing value
of hardness of specimen is 55 HRC as compared to untreated specimen annealed specimen
becomes softer. Therefore specimen machinability properties increase. We used HRA scale
because after annealing EN-31 becomes soft and below 20 HR value HRC scale is not gives
the accurate value and also value is not valid. The sample , after machining were heated to
9500C a temperature in the region of 30 – 500C above the A1 line of the Fe – Fe3C phase
diagram. At 9500C the sample was held for 1 hour to ensure through homogeneity, then the
furnace was switched off, so that the furnace and sample temperature gradually decrease to
room temp. The specimen was taken out of the furnace after 48 hours of gradual loss of heat
when the furnace temps. would have attain the normal room temperature. To improve the
machinability of steel annealing hypereutetoid spheroidize applied. This process will produce
a round shape or a ball l of carbide in the ferritic matrix which makes the machine easy. At

the high temperature will break pearl tic structure and cementite network, this structure is
called spheroid tie. This structure is desirable for the violence acquired a minimum with
maximum ductility and maximum machinability. Low carbon steel spheroid zed rare for
machines, because they are too soft and sickly in spheoridized conditions. Cutting tools will
tend to push the material rather than cut causing excessive heat and wear on the cutting edge.
Recrystallization annealing is frequently applied in the production of cold-rolled steel strip, in
deep drawing and in wir3 drawing operations as an intermediate process with the aim of
increasing the plasticity of the steel
2.3.6 Journal 6
Effect of normalizing and tempering temperatures on microstructure and
mechanical properties of P92 steel – by Dipika R. Barbadikar a , G.S. Deshmukh a , L. Maddi
a , K. Laha b , P. Parameswaran c , A.R. Ballal a , D.R. Peshwe a , R.K. Paretkar a , M.
Nandagopal b , M.D. Mathew
In the present investigation, systematic studies on microstructure and mechanical properties
of P92 steel subjected to various normalizing (1313e1353 K) and tempering (1013e1053 K)
temperatures were carried out. The effect of heat treatment on microstructural parameters revealed an
increase in grain size, lath width and decrease in the area fraction of the precipitates with an increase
in normalizing temperature. The precipitate size has not changed significantly with increase in the
normalizing temperature; rather it increased with increase in tempering temperature. Activation
energy calculations confirmed the two fold mechanisms that dominate the tempering behavior. As a
consequence, yield stress (YS) and ultimate tensile strength (UTS) were found to change with
normalizing and tempering temperatures. P92 steel normalized at 1353 K and tempered at 1013 K was
found to have the best combination of strength and ductility. Ferritic/martensitic steel has been
considered as a candidate material for power plant applications over austenitic stainless steel because
of its excellent thermal conductivity, low coefficient of thermal expansion, good weldability
accompanied with resistance to stress corrosion cracking and oxidation. They are widely used in the
fabrication of high temperature components of fossil fired and steam generators of nuclear power
plants. In order to increase the efficiency of the power plants operating at temperatures above 873 K
and pressure of 250e300 bar [1], there is a need to develop materials in accordance with increased
strength at particular service conditions. The development of 9Cr steels started few decades before,
starting from P9, P91 and P92. P92 steel [2,3] is the next version of modified P91 steels, where Mo
content is brought down to 0.5 wt.% from 1 wt.% and 1.8 wt.% tungsten is added. These steels derive
their strength from tempered martensite lath structure which is stabilized by M23C6 type of carbide,
intra-lath MX type carbide/nitride and martensite phase transformation induced high dislocation

density. P92 posses improved creep strength than P91 steel due to the solid solution strengthening and
increased hardenability offered by tungsten addition. Enhancement in strength of P92 steel has been
well explained by Ennis et al. [1] and has shown that the high degree of transient hardening in 9Cr
steels is due to the presence of very high dislocation density obtained during normalization of the
steel. The mechanical properties of these steels are found to be sensitive to normalizing and tempering
temperatures as well as time, which alter the microstructural constituents

CHAPTER 3
METHODOLOGY
3.1. SELECTION OF MATERIAL
EN8 is a very popular grade of through-hardening medium carbon steel, which
is readily machinable in any condition. EN8 is suitable for the manufacture of parts such
as general-purpose axles and shafts, gears, bolts and studs. It can be further surface-
hardened typically to 50-55 HRC by induction processes, producing components with
enhanced wear resistance. EN8 in its heat treated forms possesses good homogenous
metallurgical structures, giving consistent machining properties. EN8 is suitable for
shafts, Medium torque shafts, Typical applications include shafts, studs, bolts, connecting
rods, screws, rollers, Hydraulic rams (chromed). Key steel and machinery parts. It is
mostly used in Automobile parts and machine building industry. En8 has higher % of
Carbon (0.35–0.45) than Mild steel (0.05–0.25), which means En 8 has higher tensile
strength. It is normally supplied in the cold drawn or as rolled condition. Tensile
properties can vary but are usually between 500-800 N/mm². EN8 is widely used for
applications which require better properties than mild steel but does not justify the costs
of an alloy steel. EN8 can be flame or induction hardened to produce a good surface
hardness with moderate wear resistance. EN8 is available from stock in bar and can be cut
to our requirements It is also fairly straightforward to weld compared to many high alloy
steels and has good machinability plus the fact that being a cold drawn grade it has better
dimensional accuracy than black steels and so will tend to need lass machining.
It tends to be a good choice for medium duty applications where moderate strength and
accuracy is required but ease of manufacture is a priority.
3.2. SPECIMEN PREPARATION
For analyzing the properties of en8, we have to ensure that each specimen is
identical in size and structure. Since en8 is a medium carbon steel and we wanted to
analyze the micro-structure analysis normal cutting methods cannot be employed. So
lathe machine is used for specimen cutting.

3.2.1 Cutting
Figure 13: Cutting Operation In Lathe Machine
Cutting of en8 rod into required specimen is performed by a lathe machine. This
process involve cutting a small piece of the work piece by a parting tool. Carbide tool is
used for cutting since hardness is more than usual steel.
SAMPLE CUTTING
The sample was received as a one inch round bar. Later on it was cut to desired
specified measurement as per our requirement. Later the specimens were undergone
through various heat treatment processes.
Figure 14: 1"x1" specimen

3.2.2 Specimen Numbering
 Prepared 20 specimen of size 1‖x1‖ for the study
 Out of 20 , 15 are numbered numerically from 1-15 and others are
numbered A,B,C,D,E
 5 different heat treatment processes are conducting
 So from the numerically numbered specimens 3 pieces are selected for
each processes
 Other 5 are taken for finding hardness, checking chemical composition and
for replacing
Figure 15: Numbering of specimens
3.3 FINDING CHEMICAL COMPOSITION
1,2,3 FOR OIL QUENCH
4,5,6 FOR WATER QUENCHING
7,8,9 BRINE SOLUTION
10,11,12 FOR ANNEALING
13,14,15 FOR NORMALIZING
A For spectrometer analysis
B Rockwell hardness
C For brinell hardness
D & E
For replacing if any damage
occur

Chemical Composition is Important Testing for making sure that the Chemical
Composition of the Purchased Material Matches with that of the International Standards
of Materials.
3.3.1 Spectroscope
Mass spectrometry is a powerful analytical technique used to quantify known
materials, to identify unknown compounds within a sample, and to elucidate the
structure and chemical properties of different molecules. The complete process involves
the conversion of the sample into gaseous ions, with or without fragmentation, which
are then characterized by their mass to charge ratios (m/z) and relative abundances.
This technique basically studies the effect of ionizing energy on molecules. It depends
upon chemical reactions in the gas phase in which sample molecules are consumed
during the formation of ionic and neutral species.
Basic Principle
A mass spectrometer generates multiple ions from the sample under
investigation, it then separates them according to their specific mass-to-charge ratio
(m/z), and then records the relative abundance of each ion type.
The first step in the mass spectrometric analysis of compounds is the
production of gas phase ions of the compound, basically by electron ionization. This
molecular ion undergoes fragmentation. Each primary product ion derived from the
Figure 16: Mass spectrometer

molecular ion, in turn, undergoes fragmentation, and so on. The ions are separated in
the mass spectrometer according to their mass-to-charge ratio, and are detected in
proportion to their abundance. A mass spectrum of the molecule is thus produced. It
displays the result in the form of a plot of ion abundance versus mass-to-charge ratio.
Ions provide information concerning the nature and the structure of their precursor
molecule. In the spectrum of a pure compound, the molecular ion, if present, appears at
the highest value of m/z (followed by ions containing heavier isotopes) and gives the
molecular mass of the compound.
Components
The instrument consists of three major components:
Ion Source: For producing gaseous ions from the substance being studied.
Analyzer: For resolving the ions into their characteristics mass components according
to their mass-to-charge ratio.
Detector System: For detecting the ions and recording the relative abundance of each
of the resolved ionic species.
In addition, a sample introduction system is necessary to admit the samples to be
studied to the ion source while maintaining the high vacuum requirements (~10-6 to 10-
8 mm of mercury) of the technique; and a computer is required to control the
instrument, acquire and manipulate data, and compare spectra to reference libraries.
Figure 17 : Mass spectrometer components
With all the above components, a mass spectrometer should always perform the
following processes:

 Produce ions from the sample in the ionization source.
 Separate these ions according to their mass-to-charge ratio in the mass analyzer.
 Eventually, fragment the selected ions and analyze the fragments in a second
analyzer.
 Detect the ions emerging from the last analyzer and measure their abundance with the
detector that converts the ions into electrical signals.
 Process the signals from the detector that are transmitted to the computer and control
the instrument using feedback.
Figure 18: Spectrometer
principle
3.4 FURNACE
3.4.1 Induction furnace
Figure 19: After spectrometry

An Induction Furnace is an
electrical furnace in which the heat is
applied by induction heating of
metal. Induction furnace capacities
range from less than one kilogram to
one hundred tonnes, and are used to
melt iron and steel, copper,
aluminium, and precious metals.
The advantage of the induction furnace is a clean, energy-efficient and well-
controllable melting process compared to most other means of metal melting.
Most modern foundries use this type of furnace, and now also more iron foundries
are replacing cupolas with induction furnaces to melt cast iron, as the former emit
lots of dust and other pollutants.
Since no arc or combustion is used, the temperature of the material is no higher
than required to melt it; this can prevent loss of valuable alloying elements.
Principle of induction furnace
The induction heating power supply sends alternating current through the induction
coil, which generates a magnetic field. Induction furnaces work on the principle of
a transformer. An alternative electromagnetic field induces eddy currents in the
metal which converts the electric energy to heat without any physical contact
between the induction coil and the work piece.. The furnace contains a crucible
surrounded by a water cooled copper coil. The coil is called primary coil to which
a high frequency current is supplied. By induction secondary currents, called eddy
currents are produced in the crucible. High temperature can be obtained by this
method
3.4.2 Keeping specimen in the furnace
Figure 20: Induction furnace

 Out of 20 specimens 15 are used for heat treating
 Made 5 batches of 3 specimens are kept it in the furnace as in the figure 21
 Room temperature was 30⁰C
 Taken 2.5 hours to reach (preheating) 940⁰C
 Kept in the furnace for 3 hours at 940⁰C
3.5 HEAT TREATMENT AND QUENCHING
Figure 21: Placing specimen in the furnace
Figure 22: Specimen in the furnace

3.5.1 Annealing
After holding for 3hrs at 940⁰C, switch off furnace. Leave samples inside the
furnace for cooling down to 400⁰C, when it reaches opening furnace door and
cooling it to room temperature
3.5.2 Normalizing
Normalizing process for steels is defined as heating the steel to austenite phase
and cooling it in the air. It is carried out by heating the steel approximately 500C
above the upper critical temperature followed by cooling in air to room
temperature, or at no greater than 1 bar pressure. Normalizing temperature is
940⁰C
3.5.3 Water Quenching
Figure 23: Specimen at 400⁰C (Annealing)
Figure 24: After Annealing
Figure 25: After Normalizing

With the help of tongs, the specimens at 940⁰C were put into water
3.5.4 Oil Quenching
 When hardness can be sacrificed, mineral oils are often used.
 These oil based fluids often oxidize and form a sludge during quenching, which
consequently lowers the efficiency of the process.
 The quenching velocity (cooling rate) of oil is much less than water.
 Oil used SAE 120
 With the help of tongs, the specimens at 940⁰C were put into oil



3.5.5 Brine Solution
Figure 26: After Water quenching
Figure 27: After OIl Quenching

 Increasing the concentration of salt decreases the specific heat capacity of the water
 Brine solution also increase the speed of cooling
 Saturated solution is used for quenching
 The concentration of brine solution is 363 gm per 1 litre at room temperature (30⁰C)
 With the help of tongs, the specimens at 940⁰C were put into brine solution.
Figure 28: After Quenchng in Brine solution
3.6 Sample Preparation For Metallographic Observation
 Proper preparation of metallographic specimens to determine microstructure and
content requires that a rigid step-by-step process be followed.
 In sequence, the steps included cutting, mounting, course grinding, fine
grinding, polishing, etching and microscopic examination. Specimens must be
kept clean and preparation procedure carefully followed in order to reveal
accurate microstructures
3.6.1 Grinding
Coarse Grinding
For a perfect observation sample, it must :
 Be free from scratches, stains and others imperfections which tend to mark
the surface.
 Retain non-metallic inclusions.
 Reveal no evidence of chipping due to brittle intermetallic compounds and
phases. Be free from all traces of disturbed metal.
The purpose of the coarse grinding stage is to generate the initial flat surface
necessary for the subsequent grinding and polishing steps.

 Course grinding can be accomplished either wet or dry using 80 to
180 grit electrically powered disks or belts.
 Care must be taken to avoid significant heating of the sample.
 Grinding belt material is usually made of SiC paper.
 Rotate the specimen by 90⁰ on every grade- change
Fine Grinding
 Each grinding stage removes the scratches from the previous coarser paper.
 This is more easily achieved by orienting the specimen perpendicular to the
previous scratches, and watching for
these previously oriented scratches to be
obliterated.
 Between each grade the specimen is
washed thoroughly with soapy water to
prevent contamination from coarser grit
present on the specimen surface.
 In general, successive steps are 220,
400grit SiC and the grinding rate should steadily decrease from one stage to
the next.
3.6.2 Polishing
Polishing involves the use of abrasives, suspended in a water solution.
 In intermediate polishing, SiC paper of different grades are used.
 Again, the specimen is rotated
while switching from one grade to
another.
 The operation is carried out on a
disc with the sandpaper stretched across
it.
 Following the final stages 800,
1200grit fine-grinding stage, the sample must be washed and carefully dried
before proceeding to the first polishing stage.

 Before using a finer polishing wheel the specimen should be washed
thoroughly with warm soapy water followed by alcohol to prevent
contamination of the disc
 The final polishing stage with diamond paste of 1-micron particles
should be carried out on a separate polishing wheel at a slower speed of 100 -
150 rpm using a woven cloth (velvet)with aerosol as lubricant. After 1 or 2
minutes a properly polished specimen should have a mirror-like surface free of
scratches
Figure 30:
Polishing
3.6.3 Etching
1) The specimen was placed on the table with the polished surface up.
2) A few drops of etchant were applied to the specimen surface covering the entire
metallic surface of the specimen using the eye dropper.
3) The concentration of etchant is 5% nitric acid and 95% ethanl
4) After 20 to 30 seconds. The etchant was rinsed into the sink with the water
5) The sample was dried again.
Etching is used to reveal the microstructure of the metal through selective
chemical attack. In alloys with more than one phase etching creates contrast
between different regions through differences in topography or the reflectivity of
the different phases. The rate of etching is affected by crystallographic orientation,
so contrast is formed between grains, for example in pure metals. The reagent will
Figure 29: Diamond lubricant

also preferentially etch high energy sites such as grain boundaries. This results in
a surface relief that enables different crystal orientations, grain boundaries, phases
and precipitates to be easily distinguished.
Figure 31: a) Polished but unetched surface gives a clean image but no details about the microstructure of the
specimen
b) Etched surface: When the specimen
has grains with same orientations,
only the grain boundaries are visible.
c) Etched surface: When the specimen
has grains oriented differently, each
grain reacts differently to give
varying colours.
3.6.4 Final step
 After etching process, the specimen needs to be washed again in distilled water to
remove any excess reagent present on it.
 If not washed, under microscopic observation, there might be aberrations in the
color of the sample.
 Also, slow and continuous reaction for a long time may take place because of
which we cannot use the sample for proper microscopic observation.
 Cleaning can also be done by placing a drop of spirit and drying it.
 After washing, it can be dried using a low power blower.
 Finally, the specimen is ready for observation under microscope
3.7 Using Electro Optical Microscope For Metallographic Observation

 The sample was examined in the optical microscope. In the specimen, grains were
differentiated and impurity particles could be seen clearly.
 Metallurgical microscope was used to view the specimen at various magnifications
and the microstructural aspect of the material was noted.
 The microstructure of the specimen was snapped on 10x,100x zooming lenses.
Figure 32: Electro optical microscope
3.8 Finding Hardness Using Rockwell Hardness Machine
1. Check - Level of Machine should be proper.
2. Check - Machine should be in unload condition.
3. Check - Indenter Placement.
4. Check - Dial‘s hands should be stationary.
5. Select Diamond indenter
6. Since the scale is in HRC selecting the dwell load as 150kgf
7. Put Specimen on Specimen Table.
8. Bring Specimen in contact of indenter and keep moving up till small pointer in
dial comes up to Red Dot.
9. Switch Load Lever in Load Position.
10. Wait till pointer becomes steady, after 2 sec. switch Load lever in Unload
Position.
11. Read reading on dial for given scale .

CHAPTER 4
RESULT AND ANALYSIS
4.1. RESULT OF MASS SPECTROMETER
Figure 33: Spectro Analysis Test Report Of Specimen

The result of spectrometer confirms that the tested specimen is EN8 according to the
chemical composition
4.2. EFFECT OF HEAT TREATMENT IN MICROSTRUCTURE
The figure depicts microstructure of ‗As received material‘ (which is EN-8 steel prior to
heat treatment) at 10x & 100X zoom, from our objective point of view we consider this
microstructure as our reference for further analysis. We can observe from this
microstructure the pearlite and ferrite structure clearly. We can also observe non
uniformity of the grain size and its coarse nature, the ferrite and pearlite microstructure
are also non uniform. The material does not possess good wear resistance.
4.1.1 EN8 as received
4.1.2 Annealing
Figure 37: ANNEALED 10x
Figure 34: EN8 100X MAGNIFICATIONFigure 35: EN8 10X MAGNIFICATION
Figure 36: ANNEALING 100X

4.1.3 Normalizing
Figure 38: Normalizing 10x Figure 39: Normalizing 100x
4.1.4 Oil Quenching
Figure 40: Oil Quenching 10x Figure 41: Oil Quenching 100x
4.1.5 Water Quenching
Figure 43: Water quenched 10x Figure 42: Water Quenched 100x

4.1.6 Brine Quenching
4.2 ROCKWELL HARDNESS TESTING RESULTS
Heat treatment
Rockwell hardness
type C
As received 11
Annealed 02 (52 HRA)
Normalized 08
Oil quench 15
Water quench 22
Brine solution quenching 42
Figure 45: Brine Quenched 10x Figure 44: Brine Quenched 100x

4.3 ANALYSIS
As Received:Before treatment EN-8 hardness value is 11 HRC .Hardness of untreated
material is less due to low carbon % in EN-8. The pearlite and ferrite have been seen
clearly in the image. The composition of pearlite and ferrite was found to be equal
After done five treatments:
Annealing: After annealing value of hardness of specimen is 52HRA (about 02HRC)
as compared to untreated specimen annealed specimen becomes softer. So machine-
ability properties of specimen increase due to annealing we used HRA scale because
after annealing EN-8 becomes soft and below 20 HRC. Value HRC scale is not gives
the accurate value and also value is not valid.
Normalizing: After normalizing hardness is 08 HRC given on Rockwell testing
machine. It shows after the normalizing the specimen becomes harder than annealing
specimen .this is due to formation of pearlite is more as compared to ferrite.
Oil Quenching: After oil quenching hardness is 15 HRC given on Rockwell testing
machine. It shows after the oil quenching the specimen becomes harder than annealed
and normalized specimens. This produces abundance of martensitic microstructure
Water Quenching: After water quenching hardness is 22 HRC given on Rockwell
testing machine. It shows after the water quenching the specimen becomes harder than
annealed, normalized and oil quenched specimens. The faster the cooling rate the
higher the hardness. Water-quenched steels will generally be harder than oil-quenched
steels. This is mainly because the thermal conductivity of water is higher than the
thermal conductivity of most of the oils; consequently, the rates of cooling will be less
rapid (or lower) in oils compared with water. The microstructure consists of martensite
and retained austenite. Water quenched samples showed intermediate martensite
percentage
Brine Solution Quenching: After brine solution quenching hardness is 42 HRC given
on Rockwell testing machine. It shows after the brine solution quenching the specimen
becomes harder than annealed, normalized, oil quenched and water quenched
specimens. Brine quenched samples showed highest percentage of martensite

CHAPTER 5
CONCLUSION
 The following conclusion has been drawn from the experimental result and
discussion is made. The EN8 steel are subjected to different heat treatment
sequences: annealing, normalizing and 3 quenching temperatures at 940⁰C. Heat
treated specimens were mechanically tested for finding hardness.
 Quenching results in transformation of pearlite structure to martensite and retained
austenite.. Brine quenched samples showed highest percentage of martensite.
Water quenched samples showed intermediate martensite percentage while oil
quenched samples showed the least percentage of martensite.
 Based on the hardness number and the amount of martensite obtained we can
predict the quench severities of the subject quenchants. It can be observed that
brine quenching gives the highest hardness value and martensite phase and hence
can be predicted that it has the highest quench severity. Water gave intermediate
hardness value and martensite phase and hence we can predict its quench severity
also to be intermediate while oil gave the least hardness and martensite phase and
hence has the lowest quench severity. Therefore based on the hardness number as
well as the amount of martensite phase we can predict the quench severity of the
subject quenchant in the descending order as Brine solution > Water > Oil.

CHAPTER 6
SCOPE OF FUTURE WORK
 Engineering of microstructures requires wise choices based upon knowledge on the
one hand of the relation between processing and the microstructural states that may be
developed and, on the other hand, of the relation between microstructural states that
may be achieved and their properties. This project has focused on the tools that are
needed to choose a material and design a process to achieve a target microstructural
state.
 Quenching in brine and water will higher the hardness and lower the machinability.
Therefore they should only be used for attaining high hardness by sacrificing the
machinability. They were also brittle. So they can‘t be used in thin metals
 Oil quenched specimen shows the best results. They have intermediate hardness
compared to received en8 and specimens that quenched in water and oil. So they can
be used for many applications
 Annealing reduces the hardness of the material. So we can conclude that annealed
materials will improve machinability. By this finding we can assume that annealing is
a method for increasing machinability in hard metals.

STUDY OF MICRO STRUCTURE OF HEAT TREATED EN8 STEEL

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