EN8 is a very popular grade of through-hardening medium carbon steel, which is readily machined able in any condition. EN8 is suitable for the manufacture of parts such as general-purpose axles and shafts, gears, bolts and studs

1. Sakib Ali
Saqueeb Ali
Anis Haider
Md Javed Raja Ansari
Muddasir Ali Mondal
Sourav Kumar Mahato
130207075
130207079
140307132
140307136
140307137
140307145

2. 1. Abstract
2. Introduction
3. Objective
4. Introduction To En-8 Steel
5. Properties Of En-8 Steel
6. Heat Treatment Process
7. Universal Testing Machine
8. Sample Preparation
9. Optical Microscope
10.Comparison Of Microstructures
11.Inference
12.Reference

3. Steels are generally heat treated in order to achieve desired changes in
their microstructure and mechanical properties. The effect of heat
treatment cycle on the microstructure and some mechanical properties of
EN8 steel have been studied and presented in this presentation. The
heat treatment cycles given are Annealing, normalizing, hardening and
tempering are the most important heat treatments often used to modify
the microstructure and mechanical properties of engineering materials
particularly steels.
Sample of steel is purchased and various specimens are prepared for
tests of mechanical properties, the changes in properties are examined
and studied. Finally the heat treated sample was examined in the
microscope. In the specimen, grains were differentiated and impurity
particle could be seen clearly. The microstructure of the specimen was
snapped on 100X, 200X, 500X, and 1000X. Then, analysis and
comparison of the microstructure is done.

4.  Heat treatment and microstructure studies have always been
a wide area of research for mechanical engineers
 We come across steel in our life on an everyday basis. We
can find its influence in our life in almost everything we do,
we use or we look at. The steel used for this research
however is a medium carbon EN-8 steel AISI 1040. It is
alloyed and it is used to make things like shafts, keys,
stressed pins. The steel with its immense practical
applications are an important component in everybody's life.
 EN8 is a very popular grade of through-hardening medium
carbon steel, which is readily machined able in any
condition. EN8 is suitable for the manufacture of parts such
as general-purpose axles and shafts, gears, bolts and studs.

5.  To treat the En 8 steel in quenching annealing and normalizing.
 To treat the En 8 steel in single tempering after quenching annealing
and normalizing .
 To measured tensile strength by universal testing machine (UTM) .
 To compare the hardness of En8 steel after quenching annealing and
normalizing.
 To compare the micro-structure of the specimen after different heat
treatment process.

6.  EN8 is an alloyed medium carbon steel grade with
reasonable 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.

7.  EN8 carbon steel is a common medium carbon and medium tensile steel, with
improved strength over mild steel, through-hardening medium carbon steel.
 Readily machinable in any condition.
 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.

8. Max Stress 700-850N/mm^2
Yield stress 465N/mm^2 min
Max Elongation 16% min
Impact KCV 28 Joules min
Hardness 201-255 Brinell
MECHANICAL PROPERTIES

9. En8 specification chemical composition
carbon 0.36-0.44%
silicon 0.10-0.40%
manganese 0.60-1.00%
Sulphur 0.050Max
phosphorus 0.050Max

10. The sample was received as a 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.
 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. The heat treatment of steel was done at
different temperatures of 950OC, 975OC, 1000OC, 1025OC by
using muffle furnace. At each temperature 6 samples were kept to
be heated.

11.  A furnace is a device used for high-
temperature heating.
 A furnace used for many things, such
as the extraction of metal from ore or
in oil refineries and other chemical
plants.
 The heat energy to fuel a furnace may
be supplied directly by
fuel combustion, by electricity such as
the electric arc furnace, or
through induction heating in induction
furnaces.
 It serves as a reactor to provide heats to
the reaction. The design of the furnaces
varies, however the basic features are
most common among all of them.

12. Specimen of EN-8 steel rod was first preheated at 15OC per minute to 950OC
in a furnace and then held there for 30 minutes such that the temperature
homogeneity occurs at all section of the specimens for austentization. After
holding for 30 minutes, switch off the furnace and open the furnace door to
allow the samples to cool inside the furnace until red heat is gone. Take out the
samples and air cool to 65OC in air take out the samples which are at the
austenitizing temperature, submerge in oil bath, and water quenched to the
room temperature.

13. To remove any preexisting anomalies of material properties, the sample were
first subject to a careful annealing cycle: preheating to 950OC, hold for 15
min. slow (stepwise) heating to 950OC; 200-400-600-800-950OC; hold for 15
min at each step. Holding for ½ hrs at 950OC, slow cooling and switch off
furnace. Leave samples inside until cooled to 480OC. brisk cooling open
furnace door, cool to room temperature.

14. 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 using nitrogen if the process is
being run in a vacuum furnace. Normalizing temperatures usually
vary from 8100c to 9300C.

15. Temper the EN8 component immediately after quenching whilst tools are still
hand warm. Re-heat the EN8 component to the tempering temperature then
soak for one hour per 25 millimeter of total thickness (2 hours minimum) Cool
in air. For most applications tempering of EN8 will be between 550-660°C.

16. Sl.
No.
Heat Treated Sample Force (KN)
1.
Quenching
(Without Tempering) 251
2.
Annealing
(Without Tempering) 152
3.
Normalizing
(Without Tempering) 168
4.
Quenching
(With Tempering) 207
5.
Annealing
(With Tempering) 118
6.
Normalizing
(With Tempering) 165
Heat treated samples were
tested for various mechanical
properties. Average HRC
readings were determined by
taking several readings at
different positions on the
samples, using Rockwell
hardness tester. For tensile
properties, standard tensile
specimens were loaded into
400-KN Universal Testing
Machine hooked up to a data
logger.

17. A machine used to test specimens for tensile strength,
compressive strength, shear strength and to perform bend test
along other important laboratory tests. The primary use of the
testing machine is to create the stress strain diagram.
Once the diagram is generated, a pencil and straight edge or
computer algorithm can be
used to calculate
yield strength,
Young's Modulus,
tensile strength
or total elongation.

18. Tool Steel
Material
Sample Mark Rockwell
Hardness
C-HRC
Rockwell
Hardness
B-HRB
Brinell
Hardness
HB
EN-8
Annealing
12 91 187
Annealing with
Tempering
1 82 155
Quenching
42 113 392
Quenching
with Tempering
63 - 685
Normalizing
47 115 446
Normalizing
with Tempering
22 99 234
Hardness of EN-8 Steel was determined using Brinell and Rockwell

19. 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.
This operation was performed using a power hacksaw. this process is involve
cutting a small piece of the work piece by a tool consisting of a series of
narrowly spaced teeth, called a saw blade. Sawing is used to separate work
parts into two or more pieces, or to cut off an unwanted section of a part.

20. Grinding is the most common form of abrasive machining. It is a material cutting
process which engages an abrasive tool whose cutting elements are grains of
abrasive material known as grit. These grits are characterized by sharp cutting
points, high hot hardness, chemical stability and wear resistance. The grits are
held together by a suitable bonding material to give shape of an abrasive tool.
Metal Polishing sometimes known as Finishing or Buffing is the process of
removing scratches and abrasions from a surface, and creating the desired
brightness of finish on that surface. Polishing, like using sand paper, consists of
procedures each of which is less abrasive than the previous. A combination of
polishing buffing wheels and compounds are used with a buffing machine or a
household electric drill (pneumatic tools may also be used but only at relatively
low speeds of 4000 rpm max.)

21. The specimen was placed on the table under the fume hood with the polished
surface up.
1. The surface was cleaned with alcohol and let dried.
2. A few drops of nital solution (2%) were applied to the specimen surface
covering the entire metallic surface of the specimen using the eye dropper.
3. After 20 to 30 seconds. The etchant was rinsed into the sink with the water and
it is quickly rinsed with alcohol.
4. The sample was dried again.
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 100X, 200X, 500X, 1000X
zooming lenses.

22. The optical microscope, often referred to as light
microscope, is a type of microscope which
uses visible light and a system of lenses to
magnify images of small samples.
The image from an optical microscope can be
captured by normal light-sensitive cameras to
generate a micrograph.
Compound optical microscopes are typically used
to examine a smear, a squash preparation, or a
thinly sectioned slice of some material.
A common use of non-transmitted lighting is to
study the thin structure of metals and minerals,
where the light is reflected from the examined
surface.
It can produce a magnified image of a specimen
up to 1000X and, at high magnifications, are used
to study thin specimens as they have a very
limited depth of field.

23. The figure depicts microstructure of ‘As received material’ (which is
EN-8 steel prior to heat treatment) at 200X 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.

24. The quenched specimens would have their austenites transformed to
martensites. These are fine, needle-like structures which are very strong and
hard, but very brittle. The transformation of austenite to martensite by a
diffusion less shear type transformation in quenching is also responsible for
higher hardness obtained and this property is attributed to the effectiveness of
the interstitial carbon in hindering the dislocation motion. After the hardened
steel tempered the prevalent martensite is an unstable structure and the carbon
atoms diffuse from martensite to form a carbide precipitate and the concurrent
formation of ferrite and cementite.
Fig. Quenching with tempering Fig. Quenching without tempering

25. If we now observed the microstructure of normalized with tempering steel we can
see the coarse grains are produced. The grain size diameter is increased.
Because of tempering the heating temp is low and cooling rate is low so nuclei
formation will be less. The grain boundary is less than the normalized steel, void
also decreases. It increases the dislocation movement because of this ductility of
the material will also increase.
Fig. Normalizing (200X) Fig. Normalizing with
tempering (200X)

26. If we observe the microstructure of annealing with that of annealing along with
tempering we can see the fine grains are transformed into coarsened grains due
to which void is decreased. The grain size diameter is increased .Because in
tempering the heating temp.is low and cooling rate is low so nuclei formation will
be less. The grain boundary is less than the annealed steel. As a result of
tempering the martensite gets transformed into tempered martensite and thus as
a result hardness of the sample decreases.
Fig. Annealing (200X) Fig. Annealing With
Tempering (200X)

27. 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, quenching and tempering at different temperatures at 2000C,
4000C, 6000C, 8000C, 9500C. Heat treated specimens were mechanically tested for
tensile properties, ductility, and hardness.
 After quenching the tensile strength and hardness was increased due the formation
of martensitic structure. The crystal grain size was reduced.
 After annealing it is observed that the hardness is reduced which softens the
specimen, the grain size is refined which in turns improves the machinability of EN8
steel.
 After normalizing it is observed that uniform ferrite plus pearlite microstructure is
established and uniform grain size obtained.
 Tempering the specimen after undergoing above process was found to have many
changes like the ductility and toughness was increased with some loss of strength,
hardness and ultimate tensile strength, it also possess good corrosion resistance.

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