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Mechanical Characterization of Heat Treated EN 9 Steel
Conference Paper · March 2017
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International Conference on Engineering and Information Technology Held on 17th - 18th March
2017, in Kuala Lampur, Malaysia ISBN: 9788193137314
MECHANICAL CHARACTERIZATION OF
HEAT TREATED EN 9 STEEL
U Achutha Kini,
Sathya Shankara Sharma,
Department of Mechanical & Manufacturing
Department of Mechanical & Manufacturing
Engineering, Manipal Institute of Technology,
Engineering, Manipal Institute of Technology,
Manipal University, Manipal, India.
Manipal University, Manipal, India.
Suhas Yeshwant Nayak,
Srinivas Shenoy Heckadka
Department of Mechanical & Manufacturing
Department of Mechanical & Manufacturing
Engineering, Manipal Institute of Technology,
Engineering, Manipal Institute of Technology,
Manipal University, Manipal, India.
Manipal University, Manipal, India.
Abstract- EN 9 (AISI 1015) is a low carbon steel
specimen. Impact strength increases in the order:
having
Normalizing > Annealing > Hardening treatments.
general
engineering
applications
that
includes blades for axes, knives, and sickles as well
Keywords- Medium carbon Steel, Hardness Test,
as shafts, bushes, crankshafts, screws and wood
Tensile Test, Heat Treatment
working drills. In normalised condition, it can be
I. INTRODUCTION
used for gears, sprockets and cams. The purpose of
Plain carbon steels are alloys of iron with carbon and
heat treatment is to soften the metal, to change the
other elements, primarily tungsten, molybdenum,
grain size, to modify the structure of the material
manganese, sulfur, chromium, vanadium, nickel etc. as
and relive the stresses set up in the material during
traces and widely used in construction and other
manufacturing. In the present work, annealing,
applications because of high tensile strengths and low
normalizing and hardening treatments are given to
cost. Carbon, alloying elements, and inclusions in steel
EN 9 steel. The mechanical properties (Hardness,
act as hardening agents that prevent the movement of
Tensile and Impact strengths) are determined and
dislocations
compared in untreated and heat treated conditions.
considerable strain hardening [1]. The carbon in
Microstructure study is also performed on as
conventional steel alloys may contribute up to 1.5% of
bought and heat treated specimens. It is found that
its weight.
hardness increases substantially with hardening
Steel, has properties similar to iron when its carbon
treatment and decreases marginally with annealing
content is low. As the percentage of carbon increases
and normalizing treatments compared to as bought
the metal becomes stronger and harder but less ductile
condition. An increase of more than two fold is
and more difficult to machine and weld [2]. Generally
observed in tensile strength of hardened specimen
in order to increase the strength and incorporate other
and three fold increase in % elongation for
special properties of steel other alloying elements are
annealed specimen in comparison with as bought
25
during
deformation
to
undergo
International Conference on Engineering and Information Technology Held on 17th - 18th March
2017, in Kuala Lampur, Malaysia ISBN: 9788193137314
added which generally increase the strength while
of heating the steel 30 – 50ºC above the upper critical
retaining the toughness and ductility.
temperature (temperature where high temperature
EN 9 is low carbon constructional steel usually
austenite phase is stable) followed by furnace cooling.
supplied in black condition untreated or annealed. It is
Furnace cooling forms coarse or medium pearlite
low strength, low hardness steel. Surface hardness can
phase at room temperature which is very close to
be further improved by inculcating high level of
equilibrium phase. This pearlite is two phase structure
toughness with excellent wear resistance. EN 9 has
and consists of well defined ferrite and cementite
general engineering applications that includes case
lamellar phase mixture. The coarser structure has got
hardened shafts, bushes and wood working drills, light
higher plasticity property suitable for deformation
duty spanners etc. In normalised condition. EN 9 can
induced fabrication [8]. This heat treatment is also
be used for gears, sprocket and cams.
performed to soften steel after cold rolling, before
In
the
present
work,
an
effort
is
made
to
surface coating to relieve internal stresses developed
conventionally heat treat the steel with different heat
[4].
treatment cycles. Study also compares hardness related
Normalizing process consists of heating the metal to a
properties of steel in hardened and different related
temperature of 30 - 50°C above the upper critical
treatments.
temperature similar to annealing. It is held at that
A. Heat Treatment
temperature for a considerable time till the high
The purpose of heat treatment is in many fold i e., to
temperature austenite formation is complete and
soften the metal, to refine the grain size, to modify the
cooled in still air. The purpose of normalizing is to
structure of the material, relive the stress set up in the
refine
material, to improve the strength, hardness and
hardness. It also improves the machinability of low
toughness properties. The various heat treatment
carbon steels. Air cooling converts high temperature
processes include annealing, normalizing, hardening,
austenite into fine pearlite with small interlamellar
austempering, martempering, tempering and surface
spacing.
hardening.
Hardening process consists of heating the metal to a
The heat treatments used in the present work and their
temperature of 30-50°C above the upper critical point
purposes are:
for low carbon steels and held isothermally till
Annealing treatment is given to improve ductility and
complete phase transformation of room temperature
workability, to increase the weight percentage of
phase into austenite takes place, followed by
proeutectoid ferrite. Normalizing is done to improve
quenching in water to form diffusionless room
strength with grain refinement. Hardening treatment is
temperature phase known as martensite. The structure
given to increase hardness or to improve strength with
of this super saturated phase is body centered
higher proof stress ratio [3].
tetragonal (BCT) which is harder phase and hardness
The main purpose of annealing is to soften the
of this non equilibrium structure depends on height of
materials, or to alter material properties (such as
the BCT cell and is the measure of the weight
machinability, plasticity or electrical properties with
percentage of the carbon trapped in the volumetric
dimensional stability). The annealing process consists
space of BCT [5].
26
grain
structure,
improve
toughness
and
International Conference on Engineering and Information Technology Held on 17th - 18th March
2017, in Kuala Lampur, Malaysia ISBN: 9788193137314
TABLE II
II METHODOLOGY
A. Material
HEAT TREATMENT CONDITIONS USED
Table 1 presents the elemental level composition (wt
Heat
%) of EN 9 (AISI 1015) steel used in the study.
treatment
Normalizing
Hardening
910
910
910
90
90
120
Furnace
Air
Water
condition
TABLE I
Austenitising
COMPOSITION OF EN 9 (AISI 1015)
Element
Annealing
C
Mn
Cr
0.27
Mo
P
S
0.01
0.03
0.01
0.15
0.65
Element
Ni
% Wt
0.08
(˚C)
Si
0.11
% Wt
Temperature
Fe
Holding Time
(min)
Balance
Cooling
medium
Hardening treatment is performed by heating the
B. Specimen
specimen in muffle furnace for 2 h at
followed
by
rapid
quenching
in
910º C
cold
water.
Normalizing is carried out by heating steel for 2 h at
910ºC and then allowing the material to cool down to
room temperature outside of the oven i e., in still air.
Annealing heat treatment is performed similar to
hardening and normalizing. The difference is in the
cooling rate. After soaking for 2 hours, the specimen is
allowed to cool in the furnace itself. The cooling
process takes nearly 12 hours to reach room
Fig.1 Tensile test specimen (ASTM E8M)
temperature.
Specimens are prepared as per ASTM E8M and
D. Microstructure
ASTM E23-020 standard-Type A for tensile and
Emery papers of fine grades (120, 200, 400, 600 and
Charpy impact strength respectively (Fig. 1 & 2).
1000) are initially used for polishing in series. Further
polishing is done on a polishing machine. When
mirror like finish is obtained during fine polishing
with velvet cloth, the specimen is subjected to etching
for preferential chemical attack using nital solution.
The polished surface is washed and dried before
applying nital solution. Few drops of nital are applied
on the surface and allowed for optimum etching
(optimal duration) and then washed away with water
and the surface is dried immediately using blower.
Fig. 2 Charpy test specimen (ASTM E23-020
III RESULTS AND DISCUSSIONS
standard-Type A) with its dimensional tolerances
A. Hardness Test
C. Heat Treatment
27
International Conference on Engineering and Information Technology Held on 17th - 18th March
2017, in Kuala Lampur, Malaysia ISBN: 9788193137314
The hardness of the pearlitic structure obtained by the
treatment depends upon the fineness of the two phases
present in the pearlitic colony [6]. Since normalizing
cooling rate is faster than annealing, results in fine
pearlitic structure which in turn increases hardness.
From Table 2 and Fig. 3, it is evident that hardness of
the
specimen
decreases
with
normalizing
and
annealing treatments continuously compared to as
bought specimen. Hardening treatment increases the
Fig. 3 Plot of hardness v/s type of treatment
hardness by approximately 25 % as compared to as
B. Tensile Test
bought material because of the martensitic structure.
The tensile test is performed on tensile testing machine
Hardness of as bought and normalized specimens are
of 50 kN capacity. The Ultimate Tensile Strength
close to each other. This indicates that as bought steel
(UTS) value is directly obtained by the computerized
is as cast.
system. UTS behaves in a similar fashion to hardness.
TABLE II
TABLE III
HARDNESS TEST RESULTS
TENSILE TEST RESULTS
Trial
Indent
er
diamet
er,
(mm)
d
Loa
d
(kg
f)
Trea
tmen
numb
Diam
er
eter
of the
t
indent
cond
ation
ition
(mm)
Brinell
Hardnes
s
Number
(BHN)
Aver
Treatment
Area
age
Condition
(mm2)
ht
Anne
N
As bought
20.1
710.05
20
16.9
597.59
48
Normalizing
17.8
629.42
25
Hardening
49
1732.6
6
182
2.20
180
1
2.32
165
2
2.33
166
3
2.33
166
1
2.27
175
2.28
177
2.27
175
An increase of above 100 % in UTS is observed for
1.91
255
hardened specimen in comparison to as bought
1.90
254
1.91
255
3
2
3
1
Hard
(%)
2.22
2
Nor
ing
Elongation
28.28
182
It is evident from Table 3 & Fig. 4 that tensile strength
increases with hardening treatment and decrease with
annealing and normalizing treatments. Normalized
165
specimen shows marginal improvement in UTS value
750
maliz
(KN/mm2)
182
aling
5
(KN)
Percentage
2.22
As
Boug
Load
UTS
BH
Annealing
1
Ultimate
2
ening
3
as compared to annealed. The improvement may be
due to finer pearlitic colony and enhancement of
176
weight fraction of pearlite over annealed pearlite [7].
specimen. This may be the result of enormous
254
improvement in the density of the crystal defects and
lattice deformation during martensite formation [8].
28
International Conference on Engineering and Information Technology Held on 17th - 18th March
2017, in Kuala Lampur, Malaysia ISBN: 9788193137314
The hardness and tensile strength are directly
C. Impact Test
proportional to each other [9]. Hence, considerable
Normalized specimen displays highest impact strength
improvement in UTS of hardened specimen is
when compared to as bought, annealed and hardened
observed in comparison with annealed and normalized
specimen (Table 4 and Fig, 6). An increase of
material.
approximately 100 % in impact energy is observed for
normalized
specimen
compared
to
as
bought
specimen. The fine pearlite has got highest impact
strength compared to other pearlitic and martensitic
structures [11]. As bought and hardened specimens
show similar impact strength values. Drastic reduction
in impact resistance of as bought condition reveals that
as bought condition is as cast. In as cast condition the
coarse dendrites exhibits such behaviour [12]
TABLE IV
IMPACT TEST RESULTS
Fig. 4 Plot of UTS v/s type of treatment
Treatment
Trial
Condition
Number
As bought
Annealing
Normalizing
Hardening
Impact
Average
load
Load
(kgf)
(kgf)
1
38
2
34
1
49
2
46
1
64
2
62
1
36
2
33
Energy
(J)
36
67
47.5
95
63
126
34.5
69
Fig. 5 Plot of percentage elongation v/s type of
treatment
Fig. 5 shows percentage elongation (measure of
ductility) with respect to heat treatment conditions.
The annealed structure gives excellent ductility over
other conditions [10]. As bought and normalized have
almost similar results. This is in good agreement with
Fig. 6 Plot of Impact Energy v/s Type of treatment
hardness and UTS results indicates that as the strength
D. Microstructure Analysis
increases ductility decreases.
29
International Conference on Engineering and Information Technology Held on 17th - 18th March
2017, in Kuala Lampur, Malaysia ISBN: 9788193137314
An Inverted Metallurgical Microscope is used for 
An increase of approximately 100 % in impact energy
microstructure observation. Fig. 7 shows the images of
is observed for normalized specimen compared to as
the different specimens at 500X magnification. Fig 7
bought specimen. As bought and hardened specimens
(a) shows microstructure of as bought specimen
show similar impact strength values.
reveals medium size phases. From the microstructure 
Annealed structure (coarse pearlite) is coarser in size
it is clear that annealed structure (coarse pearlite) is
compared to as bought and normalized. Hardened
coarser in size compared to as bought and normalized
shows lath type structure, which is the evidence for
(as shown in figure 7). Hardened condition shows lath
martensite formation.
type structure, which is the evidence for martensite
ACKNOWLEDGEMENT
formation [Morris].
The authors are grateful to Dr. K. Jagannath, Head of
the Department, Department of Mechanical and
Manufacturing Engineering for his encouragement
during the research work. The authors thankfully
acknowledge Manipal University, Manipal, India for
sponsoring our conference participation.
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International Conference on Engineering and Information Technology Held on 17th - 18th March
2017, in Kuala Lampur, Malaysia ISBN: 9788193137314
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31
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