1) The document studies the effect of flame hardening speed on the fatigue properties of medium carbon steel. 2) Samples of medium carbon steel were flame hardened at different speeds and then subjected to fatigue testing. It was found that as the flame hardening speed increased, the fatigue strength of the material decreased. 3) The number of cycles to failure increased as the flame hardening speed decreased, indicating that slower flame hardening leads to higher fatigue strength of the medium carbon steel.

1. ISSN (e): 2250 – 3005 || Volume, 06 || Issue, 08|| August – 2016 ||
International Journal of Computational Engineering Research (IJCER)
www.ijceronline.com Open Access Journal Page 9
Studying the Fatigue Properties Of Hardened For Carbon Steel
Dr. Mohammed Abdulraoof Abdulrazzaq
Materials Eng. Dept. /University of Mustansiriyah, Baghdad, Iraq
mohammedraof415@yahoo.com
I. INTRODUCTION
The medium carbon steels have a normal content of carbon carbon (0.45 – 0.8)that means that they are not as
hard as high carbon steel neither are as strong as the Mild carbon steel. The mechanical properties of medium
carbon steel were investigated in two different quenching media (water and palm oil). The properties are
hardness, impact and strength of the material. Result indicated that water quenched steel produce best properties
in strength and hardness; while palm oil quenched steel has its best properties in impact strength [1-3]. Some
mechanical properties of medium carbon steel [4]: (1) Machinability is 60%-70%; therefore cut slightly better
than low carbon steels. It is less machinable than high carbon steel since that is very hard steel. (2) Good
toughness and ductility. Enough carbon to be quenched to form martensite and bainite (if the section size is
small). (3) Responds to heat treatment but is often used in the natural condition. (4) The hardenability is low. (5)
The loss of strength and embrittlement are decreased by both low and high temperature. (6) Subject to corrosion
in most environments. All heat treating operators consist of subjecting a metal or steel to a definite time-
temperature cycle which may be divided into three parts: (1) Heating the metal or alloy. (2) Holding at certain
temperature (soaking). (3) Cooling [5-6]. Medium carbon steel is steel where the major interstitial alloying
component is carbon. It is usually treated by using high temperatures so as to enhance ductility and strength. A
0.8% carbon steel (medium carbon steel) will begin to solidify at approximately 1470 0
C. And when
solidification is complete, the structure will consist of crystals of austenite of composition 0.8% carbon. As the
steel cools slowly, the structure becomes uniform and no further structural change will take place. The upper
and lower critical temperatures coincide and the austenitic structure transform at this temperature to pearlite.
The treatment of medium carbon steel with heat significantly changes the mechanical properties, such as
ductility, hardness and strength. Heat treatment of steel slightly affects other properties such as its ability to
conduct heat and electricity as well. A variety of methods exist for treating steel with heat [7].
The uses for medium-carbon steel are defined by the requirement for a high tensile strength and ductility that,
despite its brittleness when compared to other forms of steel, make it the preferred choice.
Medium carbon steels is used for making car components such as crankshafts, gears, axles, tool shanks and heat
treated machine elements. it is also used to make lead screws bright drawn bar , railway wheels , tracks , turbine
discs , connecting rods , tram axles , gun parts shells rifle barrels , forging dies and spindles . Medium-carbon
steels have good wear resistance, so they are often used for automobile parts and similar applications. They are
also used in forging and for large parts [8]. Surface hardening is a process which is used to improve the wear
resistance of parts without affecting the softer, tough interior of the part. This combination of hard surface and
resistance and breakage upon impact is useful in parts such as a cam or ring gear, bearing or shafts, turbine
applications. Most surface treatments result in compressive residual stresses at the surface that reduce the
ABSTRACT
In this study, Medium carbon steel is one of the most important materials used in
industrial applications especially it is used in applications exposed to fatigue stresses such
as airplanes, automotive components and electrical engines industries. Medium carbon
steels were prepared and the effect of hardening on hardening strength of medium carbon
steel was studied, the flame hardening method was used at different speeds then fatigue
test was done. The following results were obtained, first sample (none), second sample
(3.5 mm/s), and third sample (1.75 mm /s) and forth sample (1.165 mm/s). It has been
found that as the flaming speed increases, the fatigue strength of the material decreases.
The fatigue test result at stress (407.44 N/mm2
) was as follow: for the first sample the no.
of cycles to failure was at (67511 rpm), for the second sample (95832 rpm), for the third
sample (122565rpm) and for the fourth sample it was (134585 rpm).
Keywords: Medium carbon steel, flame hardening, fatigue test.

2. Studying The Fatigue Properties Of Hardened For Carbon Steel
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probability of crack initiation. Further, the surface hardening of steels has an advantage over through hardening
because less expensive low-carbon and medium-carbon steels can be surface hardened without the problems of
distortion and cracking associated with the through hardening of thick sections [9]. Plain- carbon and low alloy
steels are used for surface hardening. Manganese may be present in amounts up to 1.4% since it stabilizes
cementite and increases the depth of hardening .unfortunately it increases the tendency of steel to crack during
quenching [10].
Types of surface hardening (thermal treatments) are Flame hardening, Induction hardening, Electron beam
hardening. Flame hardening is a method for hardening of surfaces of components, usually in selected areas by a
short time application of heating followed by quenching. Flame hardening rely on the presence of an adequate
carbon content in the material to achieve the hardness level required .Flame hardening is the process of selective
hardening with a combustible gas flame as the source of heat. The heating media may be oxygen-acetylene,
propane or any other combination of fuel gases that will allow reasonable heating rates .the hardening
temperatures are the same as those required for furnace hardening [11, 12]. Flame hardening is a heat treating
process in which a thin surface shell of a steel part is heated rapidly to a temp., above the critical point of the
steel. After the grain structure has become austenitic the part is quickly quenched, transforming the austenite to
martensite. Flame hardening is mainly used to develop high levels of hardness for wear resistance. The process
also improves bending and torsional strength and fatigue life [13, 14]. The success of many flame hardening
applications depends largely on the skill of the operator. This is especially true when the volume of work is so
small. The principle operating variables are distance from inner core of oxy-fuel gas flame to work surface,
flame velocities and oxygen to fuel ratios, rate of travel of flame head or work and type of quenching [15].
Flame hardenings have the following benefits: (1) Flame hardening imparts a hard, wear resistance surface to
the component improving its fatigue strength, (2) Flame hardening offer options for the treatment of
exceptionally large components, where only localized surface hardening is required, (3) Flame hardening can be
automated for reproducible results once the process parameters have been set [4].
S.K. Akay et al.(2008) presented the effect of heat treatment on the fatigue life of low carbon steel sheet with
dual-phase microstructure. The steel sheets were heat treated with two different procedures; intermediate
quenching, intermediate quenching and tempering. The properties of tensile strength, fatigue life, hardness,
micro hardness and microstructure were evaluated by the mechanical tests and metallographic analysis,
respectively. The results showed that dual-phase steel (DPS) microstructures, composed by ferrite and
martensite had higher fully reversed plane bending fatigue strength when compared with as-received steel and
tempered martensite (TM) steel. The experimental results showed that fatigue life of the heat-treated steel sheets
enhanced with increasing amount of martensite in the microstructure. The highest fatigue strength was observed
on the intermediately annealed steel sheets at 870 ◦C. internal microstructures, fatigue crack initiation and
propagation of the heat-treated steel were analyzed by scanning electron microscopy (SEM) [16]. Vytautas et al.
(2010) investigated the influence of various kinds of surface treatments (hardening with high frequency electric
current, rolling by rollers, tempering) on fatigue strength of carbon steel specimens. Analyzed technology of
surface hardening greatly increases the fatigue strength and durability of specimens. They estimated that
hardening effect depends on the residual stresses introduced applying deformation and thermal treatment
regimes. The optimal treatment of the analyzed carbon steel is deformation up to 1 mm depth, hardening with
high-frequency electric current and tempering for 2 hours at 200 ºC. Conditions of machine elements during
exploitation, also durability and security of all construction depends a lot on the state of metals surface layer.
Hardening of metals surface allows changing expensive metals to cheap ones. Improvement of surface quality
allows increasing the durability of all construction [17]. Sweta Rani Biswal (2013) studied fatigue of medium
carbon steel (EN9 grade) and investigated the effect of various heat treatment operations (like annealing,
normalizing, tempering) on fatigue life since the mechanical properties are greatly influenced by heat-treatment
techniques. He also studied The change in the value of endurance limit of the material concerned as a result of
various heat-treatment operations and found that the specimens tempered at low temperature (2000C) exhibits
the best results as far as fatigue strength is concerned [18].
II. EXPERIMENTAL WORK
Substrate material used in this study was medium carbon steel which contains (0.390) %C, with chemical
composition illustrate in table (1). The specimen as shown in figure (1) according ASTM G99. Figure (1)
explains the experimental for this research.
Table (1) Chemical composition of specimen used in research
Element wt % C Si S P Mn Fe
Standard: 1039 ASTM value 0.36-0.44 0.4 ≤ 0.05 ≤ 0.04 0.7-1 0.057
Measured value 0.39 0.173 0.022 0.009 0.796 remain

3. Studying The Fatigue Properties Of Hardened For Carbon Steel
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Fig. (1) Fatigue sample with dimensions
Flame hardenings processes were used in this research which consists of the following steps: Step1: examine the
chemical composition of the metal used in the test conclusion in State Company for Inspection and Engineering
Rehabilitation (SIER). Step2: five samples of medium carbon steel are prepared according to standard
specifications for fatigue testing using turning machine. This step was done in Public Company for Electrical
Industry. Step3: sample no.2 was hardened by oxy acetylene torch (in the Mechanical workshop, College of
Engineering, Al-Mustansiriya University). This process is called flame hardening, the sample is first subjected
to heat of the torch for certain time and then is cooled directly by water after hardening. The heat used was at
temperature (7500
C) and hardening time was (5sec.) this means that the hardening speed was (3.5mm/sec).
Sample number 2 after being hardened by oxy acetylene torch is shown in figure (2).
Fig.(2): Sample number 2 after hardening
Step4: sample no.3 is hardened by oxy acetylene torch (in the Mechanical workshop, College of Engineering,
Al-Mustansiriya University). For hardening the sample by flame hardening method, then direct cooling by
water. The heat of the torch was at (7500
C) and hardening time (10sec). The hardening speed was at
(1.75mm/s). Step5: sample no.4 is hardened by oxy acetylene torch (in the Mechanical workshop, College of
Engineering, Al-Mustansiriya University). For hardening the sample by flame hardening method , then direct
cooling by water. The heat of the torch was at (7500
C) and hardening time (15sec.). The hardening speed was at
(1.165mm/s). Step 6: A sample was tested in material testing laboratory (in the Department of Production and
Metallurgy, Engineering University of technology). In this test, the ultimate strength was at 1000 Maps. Step7:
fatigue test is achieved in material testing laboratory in material engineering, college of engineering, Al-
Mustansiriya University. Sample No.1 was not hardened by flame hardening method. All the samples were
fatigue tested. In this test, the applied stress was constant at (407.44N/mm2
) and the applied load was at (20N)
and the number of cycles at which the samples failed was calculated.
III. RESULTS AND DISCUSSION
Table (2) explains the relationship between the flame hardening speed and the number of samples.
Table (2) Relationship between hardening speed and number of samples.
No. of Sample Time of Flame Hardening (sec) Hardening Speed (mm/s)
1 non non
2 5 3.5
3 10 1.75
4 15 1.165

4. Studying The Fatigue Properties Of Hardened For Carbon Steel
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Table (3) explains the relationship between the flame hardening speed and number of cycles to failure.
Table (3): Relationship between flame hardening speed and number of cycles.
No. of
Samples
Applied
Load (N)
Applied Bending
Stress (N/mm2
)
Number of Test
Cycles (rpm)
Flame Hardening
speed (mm/s)
1 20 407.44 67511 non
2 20 407.44 95832 3.5
3 20 407.44 122565 1.75
4 20 407.44 134585 1.165
Figure (3) shows the relationship between No. of samples and flame hardening speed
Fig.(3): Relationship between No. of samples and flame hardening speed.
Figure (4) shows the relationship between the No. of samples and number of cycles:
Fig.(4) relationship between the No. of samples and number of cycles
Figure (5) shows stress and strain of a tensile test sample.
Fig.(5): stress-strain curve of a tensile test sample

5. Studying The Fatigue Properties Of Hardened For Carbon Steel
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Flame hardening process didn't do on sample no.1 to compare it with other samples that have been hardened by
oxy acetylene torch in order to understand the effect of flame hardening speed on fatigue strength of the
material. From table (2) it is clear that sample no.2 was subjected to oxy acetylene torch for (5 sec.) at flame
hardening speed of (3.5mm/s), sample no. 3 subjected to oxy acetylene torch for (10 sec.) at speed of (1.75
mm/s) and sample no. 4 was subjected to oxy acetylene torch for (15 sec.) at speed of (1.165 mm/s), so in this
case flame hardening speed decreases as the no. of samples increases.
Table (3) shows the relationship between flame hardening speed and no. of cycles. Sample no.1 failed at no. of
cycles (67511 rpm), sample no.2 failed at (95832 rpm) at flame hardening speed of (3.5 mm/s), sample no.3
failed at (122565 rpm) at flame speed of (1.75 mm/s) and finally sample no.4 failed at (134585rpm) at flame
speed of 1.165 mm/s).
From information above we notice that there is a reverse relationship between flame hardening speed and no. of
cycles. With increasing no. of samples, no. of cycle's increases and flame hardening speed decreases. As the no.
of cycle's increases and flame hardening speed decreases, the fatigue strength of the material increases. So the
fatigue strength of sample no.4 is more than sample no.3 and fatigue strength of sample no.3 is more than
sample no.2 and fatigue strength of sample no.2 is more than sample no.1 because the no. of cycles to failure is
more and flame hardening speed is less.
IV. CONCLUSIONS
Regarding the effect of hardening speed by oxy acetylene torch on medium carbon steel we can conclude that as
the flame hardening speed increases, the fatigue strength of the material decreases. Tables (2) and (3) from
chapter four shows the effect of flame hardening speed and no. of cycles to failure on fatigue strength. Conclude
that as the no. of cycle's increases and flame hardening speed decreases, the fatigue strength of the material
increases. So there is a straight relationship between the no. of cycles to failure and fatigue strength and there is
a reverse relationship between flame hardening speed and fatigue strength.
In order to enhance the capability of medium carbon steel to withstand the fatigue crack the following
recommendations can be suggested:
1- Increasing the number of the samples in order to get more precise result.
2- Changing the value of the stress greater or less than the stress used.
3- Apply other methods of surface hardening such as carburizing, coating and nitriding in order to know which
method is the best.
4- It is possible to use flat samples instead of circular samples which were used in this project so that to know
the difference between them.
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