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