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Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.4, pp.323-337, 2011
jmmce.org Printed in the USA. All rights reserved
Influence of Material Condition on the Dry Sliding Wear Behavior of Spring
K. V. Arun* and K.V. Swetha
Department of studies in Industrial & Production Engineering, University BDT College of
Engineering, Davangere-577004, India
*Corresponding Author: firstname.lastname@example.org
During the past two decades, considerable efforts have been made in the development of high
performance spring steels to meet the needs for weight and savings in the automotive industry.
During the service the suspension system will be subjected to different environmental conditions,
at the same time it has to sustain a variety of loads acting on it. Among all the wear of spring
steel plays a vital role. In this experimental analysis an attempt has been made to investigate the
performance of spring steel (EN-47 / SUP 10) under the dry sliding condition. The specimen
preparation and the experimentations have been carried out according to the ASTM G99
standards. The effects of tempering and cryogenic treatments on the performance of the spring
steel have also been determined. The results have revealed that the material condition has got a
significant influence on the performance of the spring steel. In order to analyze the percentage
contribution of different wear parameter and the material condition, the DOE and ANOVA have
been made. The results have shown that the load (49.205%) has shown the highest influence and
the material condition has shown 22.56% of contribution on wear behavior.
Key Words: Dry Sliding Wear, Tempering, Cryogenic Treatment, ANOVA, Wear Loss.
Aggressive mass reduction trends in the automotive industry have spurred the development of
suspension springs that can withstand high stresses at a reduced section size . Major
applications of spring steel are in Railway coach axles, Crank pin on heavy machines, Crank
shafts, Spline Shafts, leaf spring likewise. New trends in development of automotive industry can
be formulated as follows: higher passenger’s safety, fuel consumption decrease and higher
324 K. V. Arun and K.V. Swetha Vol.10, No.4
comfort with better furnishing. During the last two decades, considerable efforts have been made
in the development of high-performance spring steels to meet the needs for the weight and cost
savings in the automotive industry .
Different heat treatment processes can be applied on the spring element of a force transducer in
order to obtain good and satisfactory performance. The manufacturers are generally focused on
the improvement of performance by applying different heat treatments on spring material .
Today, most coil springs for automotive applications are made of quenched and tempered,
medium carbon high-strength steels. In order to increase the harden ability of elements such as
chromium, manganese and silicon are added to these steels . The primary objective of the heat
treatment of steels is to improve wear resistance. The benefit of cryotreatment of steels has been
cited by several researchers. However, the mechanisms responsible for enhancing the wear
resistance by cryotreatment are yet to be clearly established. Recent work has also shed light on
the effects of cryogenic treatment on bearings, gears and engine components to reduce wear and
improve performance [5-6].
Spring steels are used in the quenched and tempered condition which gives optimum strength
and toughness, vibrational damping. The change in microstructure and strength after the heat
treatment process depends on the cooling rate obtained during quenching . Due to operational
safety, springs have to meet increasing performance requirements, which concern mechanical
properties, tribological properties as well as fatigue strength .
The improvement of the sag resistance has been achieved by changing prior austenite grain size,
the distribution of precipitated particles, and the chemical composition of the steel, as well as by
changing processing treatments such as magnitude of pre-strain and shot-peening . Some
mechanical properties such as elastic modulus, tensile strength, hardness, microstructure, strain
hardening and fracture strain also influence the wear of the materials. Hardness is a measure of
the wear resistance of a material. In other words it is the resistance of a material to permanent
deformation by indentation or scratching . Hardness of material depends upon the type of
bonding forces between atoms, ions or molecules. Furthermore for spring steels, the emphasis in
materials research has been focused on increasing the strength while maintaining good ductility,
toughness and fatigue properties .
Prevention of wear depends principally on design and operation of component, but can be
minimized by the correct choice of material. It is seen that most of the study has been focused on
the experimental work for wear behavior of steels, and a few mathematical models based on
statistical regression techniques has been reported[12-15]. The Taguchi’s design is a simple,
efficient and systematic approach to optimize designs for performance, quality and cost . In
the Taguchi method, Design of experiments approach enables to analyze successfully the wear
behavior of materials . The design of an experiment (DOE) technique is a optimized
Vol.10, No.4 Wear Behavior of Spring Steels 325
technique mainly employed in determining wear behavior of material, which must follow certain
sequence for the experiments to yield an improved understanding of product or process
From the literature survey it is clear that there is lot of scope for the study of wear behavior of
spring steel. Hence present study was focused on the dry sliding wear behavior of spring steel
and the effect of heat treatment on spring steel. The main aim was to investigate the effect of
applied load, sliding distance, sliding speed and material conditions which mainly influences the
dry sliding wear of the spring steel with the help of Taguchi technique under various testing
conditions. Furthermore, the analysis of variance (ANOVA) is employed to investigate the
testing characteristics of different steels. Tests were carried out using a pin-on-disc type of
apparatus under different conditions. A major step in the DOE process is the determination of the
combination of factors and levels which will provide the experimenter with the desired
2. MATERIAL AND EXPERIMENTATION
The experimentation has been carried out on spring steel material EN-47 (SAE 6150 Steel). The
specimen preparation and experimentation were carried out according to ASTM standards. The
mechanical properties of EN-47 spring steel material has a hardness of 99 HRC, yield strength
of 640Mpa, density of 7.85g/cc and modulus of elasticity 205Gpa. The chemical composition of
the materials used in the investigation is as follows.
Table 1 Chemical composition of EN 47
Components C Mn Si Cr V
Wt% 0.48-0.53 0.70-0.90 0.20-0.35 0.80-1.10 0.15-0.25
2.1. Material Condition
The specimens were tested under different conditions to analyze the influence of each condition
of the material fracture characterizing parameters. The conditions of the material are, Normal,
Tempered at 2500C and 3500C and Cryogenic.
Specimens are kept under procured condition and tested to evaluate characterizing parameters
like hardness and wear under normal condition. The specimens are heated to annealing
temperature (7000C) and are cooled by oil quenching. Then these specimens are tempered at
2500C and 3500C. The process of heat treatment for tempering is shown in Figure 1. Since the
specimens are annealed and quenched the quench cracks are developed in the specimens. These
quench cracks gets healed up after tempering at different tempering temperatures such as 2500C
326 K. V. Arun and K.V. Swetha Vol.10, No.4
Figure 1 Heat treatment Cycle for Tempering
Instead of tempering, the specimens are kept under cryogenic condition as shown in Figure 2.
The quench crack developed during annealing will increase further after cryogenic treatment.
Figure 2 Cycle of Cryogenic Treatment
Vol.10, No.4 Wear Behavior of Spring Steels 327
The experimentations were carried out in order to determine the wear property of the spring
steel. A pin-on-disc test apparatus was used to investigate the dry sliding wear characteristics of
the spring steel (EN-47) material as per ASTM standards. The disc used is En-32 steel hardened
to 62 HRC, 135mm track diameter and 8mm thick, with surface roughness of 10μm Ra.
Specimens are prepared from the standard bar of 12 mm diameter and turned to 10 mm diameter
and are cut to 25mm length. The tests were conducted by selecting test duration, load and
velocity and performed in a track of 115mm diameter. The specimen prepared are positioned
parallel using die holder and in same sliding direction. The test set up used for the
experimentation is as shown in the Figure 3. The difference in the weight measured before and
after test gives the sliding wear of spring steel specimen and then the volume loss was calculated.
Figure 3 Schematic Diagram of Pin on Disk Apparatus
2.3. Design of Experiments
The Taguchi approach to experimentation provides an orderly way to collect, analyze, and
interpret data to satisfy the objectives of the study. This design can optimize the performance
characteristics through the setting of design parameters and reduce the sensitivity of the system
performance to the source of variation. This technique is a powerful tool for acquiring the data in
a controlled way and to analyze the influence of process variable over some specific variable,
which is unknown function of these process variables. The most important stage in the plan of
experiments is selection of factors. Taguchi technique creates a standard orthogonal array to
accommodate the effect of several factors on the target value and defines the plan of
experiments. The experimental results are analyzed using analysis of means and variance to
328 K. V. Arun and K.V. Swetha Vol.10, No.4
study the influence of factors. The Experiments were conducted as per the standard orthogonal
array so as to investigate which design parameter significantly affects the dry sliding wear for the
selected combinations of load, sliding speed and sliding distance and material. The selection of
the orthogonal array was based on the condition that the degree of freedom for the orthogonal
array should be greater than or equal to sum of those wear parameters. In the present
investigation an L9 orthogonal array was chosen, this has 9 rows and 4 columns as shown in the
Table 2 L9 Orthogonal Array
Trial no. A B C D
1 1 1 1 1
2 1 2 2 2
3 1 3 3 3
4 2 1 2 3
5 2 2 3 1
6 2 3 1 2
7 3 1 3 2
8 3 2 1 3
9 3 3 2 1
Table 3 Process parameters and their levels
Levels Load (N) Speed (rpm) Sliding
1 7 900 5000 3500C
2 5 700 3000 2500C
3 3 500 1000 270C
The wear parameters chosen were (1) sliding speed (2) Load (3) sliding distance (4) material and
their levels indicated in table 3. The experiments consist of 9 tests (each row in the L9 orthogonal
array) and first column in table was assigned to load (L), second column was assigned to sliding
speed (S), third column was assigned to sliding distance (D) and fourth column was assigned to
Vol.10, No.4 Wear Behavior of Spring Steels 329
3. RESULTS AND DISCUSSIONS
The spring steel is characterized for its strength assessment. The experimentations were carried
out to determine the most significant parameters which influence on the wear behavior of the
springs in service. The results of the experimentation have been summarized and discussed in
3.1. Hardness Test
The hardness trials were taken at different regions of the specimen and the average value of
which is tabulated. Rockwell C hardness test is used to determine the hardness. The hardness of
material at different conditions is tabulated in Table 4. The maximum Hardness is obtained in the
cryogenic material (61.5 RHN.). The minimum Hardness obtained in normal untreated
specimens (26 RHN.). Due to the change in the structure of the material, the hardness has
increased. Since the cryogenic treatment has been done after quenching, the quench cracks get
widened further. This leads for increased hardness.
Table 4 Hardness of Spring Steel in Different Conditions
3.2. Influence of Sliding Distance on the Wear Behavior
Wear behavior of spring steel plotted as a function of sliding distance is shown in Figure 4. This
represents the variation of wear rate with sliding distance at a constant load of 5kg and speed 700
rpm for different material conditions like normal, 2500C, 3500C and cryogenic conditions. The
weight loss increased with increasing sliding distance for all condition. The wear rate increases
continuously in normal specimens. The wear is increasing gradually upto 3000m distance
beyond that wear is increased rapidly in 3500C heat treated specimens and in 2500C heat treated
specimens the wear is increasing with respect to distance. Theoretically cryogenic treated
SPECIMEN RHN-B RHN-C BHN VHN
Normal 98.6 26 258 272
Tempered 129 45 421 446
Tempered 124 51 487 528
Cryogenic 110.5 61.5 688 746
330 K. V. Arun and K.V. Swetha Vol.10, No.4
specimen must have less wear rate compared to normal specimen because of high hardness. Even
though it is showing high wear rate upto 3000m due to the crack widening in cryogenic treated
specimen, above 3000m the wear rate becomes stable because of formation of smeared layer
which heals the cracks. Finally from the distance 4000m to 5000m the wear rate gets increased
but less than normal specimen this is because the specimen reached unstable condition where the
smeared layer gets peeled off at that distance.
Figure 4 Shows Variations of Wear Rate of Spring Steel with Sliding Distance.
If all the specimens under different conditions at a distance of 3000m are compared then the
wear is more in cryogenically treated specimen and the wear rate is relatively less in 3500C
treated specimens. Similarly if the specimens at distance of 5000m are compared the wear is
more in normal specimens and it is less in 3500C treated specimens. Hence it is best to use the
3500C treated specimen compared to others. Wear rate of normal and cryogenic treated material
is increased compared to tempered materials at 2500C and 3500C as the sliding distance
increases. The wear rate for the normal, tempered 2500C and 3500C specimens increases
gradually. But the wear rate depends on the hardness of the material because as hardness
increases the wear rate decreases.
3.3. Influence of Load on the Wear Behavior
The load has a significant influence on the wear loss of the material. Figure 5 represents the
variations of wear rate of the spring steel as a function of applied load for a constant sliding
distance 3000m and speed 700rpm for different material conditions like normal, 2500C, 3500C
and cryogenic conditions. It may be noted that wear rate of spring steel metal increased with
increasing load. Also as hardness increases the wear rate is reduced. The wear rate of metal is
depended on the heat treated conditions of the metal and the applied load. The seizure event was
accompanied by a sudden increase in wear rate, heavy noise and vibration. During this process,
transfer of pin material to the disc was also observed. This type of seizure has been referred to as
Vol.10, No.4 Wear Behavior of Spring Steels 331
galling seizure which leads to further increase in wear rate. Wear rate of normal specimen
increases gradually with applied load. The tempered 2500C and 3500C the trend appeared to be
similar. But due to increase in the hardness the wear rate of 3500C tempered specimens is less
compared to 2500C tempered specimens. The wear rate of cryogenic specimens increased
gradually and becomes stable from 3 to 5 kg and again the wear rate increases suddenly.
Figure 5 Shows Variations of Wear Rate of Spring Steel with Load.
It is observed from the figure 5 that as the load increases the wear also increase for all conditions
because whenever applied load increases the friction at the contact surface of the material and
rotating disc increases. This leads to increase in temperature and the material becomes ductile.
So wear particles get adhered to the surface and leads to less wear rate. The wear rate is
increased gradually up to 5kg for tempered 3500C and 2500C specimens because the cracks
developed due to annealing get healed up after tempering. The wear particles get adhered to the
surface and layer called smeared layer is formed. Further there is sudden increase in wear rate
because the smeared layer formed earlier gets peeled off. But in cryogenically conditioned
specimens the cracks get widened further. The increase in temperature increases the ductility.
The wear becomes stable from 3kg to 5kg load. Beyond 5kg load the wear increases and
becomes unstable. The stable condition is obtained due to the formation of smeared layer on
surface of specimen which leads to reduced wear rates. This smeared layer gets peeled off leads
to instability. The wear is less at 5kg load for 3500C heat treated specimens and relatively wear is
more for normal conditioned specimen and at 7kg load the wear is less for cryogenically
conditioned specimens and it is more for 2500C treated specimens. Hence it is best to use
cryogenically conditioned specimens under the above context.
3.4. Influence of Speed on the Wear Behavior
The wear rate of the pin increases with increasing speed. As the speed increases the temperature
increases which leads to plastic deformation of the material. At lower speed the pin surface
332 K. V. Arun and K.V. Swetha Vol.10, No.4
experiences severe damage resulting in a high wear rate as shown in figure 6. The wear rate of
normal and 2500C material condition is increased compared to other treated conditions as the
sliding speed increases.
Figure 6 Shows Variations of Wear Rate of Spring Steel with Speed.
It can be noticed from Figure 6 that the wear rate increases with the increase in speed. If the
normal specimen is considered the wear is increasing continuously upto 800 rpm. If the 3500C
treated and 2500C treated specimens are considered wear will increase up to 500 rpm speed
beyond which it becomes stable up to 600 rpm due to the formation of the smeared layer and the
wear rate again increases continuously upto 800 rpm because the smeared layer gets peeled off
and again it becomes stable. In cryogenic treated specimen the wear is continuously increasing
upto 700 rpm after that it becomes stable because there is decrease in wear rates because of this
reason the material becomes good one for further application. At 700 rpm the wear is less for
3500C treated specimen and relatively the wear rate is more for cryogenically treated specimens
and at 900 rpm the wear is less for cryogenic specimen and relative wear is high for normal
From the above comparison the best one is to use the 3500C heat treated specimen because it can
sustain the load, distance, speed and gives less wear compared to other specimens. The heat
treated specimens are suitable to use because in heat treated specimens the crack gets healed on
tempering but in cryogenically conditioned specimens even though the hardness is high the
cracks go on widening. So for further usage the tempering should be done after cryogenic
treatment which again reduces the crack density and heals the crack. From above figures 5,6,7
the 3500C heat treated specimen will sustain more for varying load, speed and distance as
compare to other specimens because of high hardness due to tempering and the crack density so
less wear will takes place.
Vol.10, No.4 Wear Behavior of Spring Steels 333
3.5. Design of Experiments
In order to reduce the number of experiments and also to determine the interaction of the
individual parameters, the experimental design is made. In this L9 array is used. The experiments
were carried according to the standard L9 array. The results of the experimentations are shown in
the Table 5.
Table 5 Weight Loss of Wear Specimen
Trial no. Load(P) in
in m Material Weight loss
1 7 900 5000 3500C 0.1143
2 7 700 3000 2500C 0.0301
3 7 500 1000 270C 0.0227
4 5 900 3000 270C 0.0997
5 5 700 1000 3500C 0.0548
6 5 500 5000 2500C 0.0049
7 3 900 1000 2500C 0.0021
8 3 700 5000 270C 0.0148
9 3 500 3000 3500C 0.0034
During the initial periods of sliding the LVDT showed negative wear due to expansion (of pin,
holder assembly and disc) by frictional heat. During this period wear rate showed a non-linear
behavior with time followed by a steady linear positive wear. This was confirmed by allowing
the whole assembly to cool down after the experiment, simultaneously recording the contraction
using the LVDT. At high load (7kg) it was found that wear rate was more (0.1143) whereas at
low load (3kg) the wear rate was less (0.0034). The wear test results were subjected to the
analysis of variance. Analysis of influence of each control factor on the weight loss has been
performed with so called signal- to- noise(S/N) response table. The below table shows
experimental layout and results of dry sliding wear test of spring steel. The S/N ratio at each
level of control factors changes when settings of each control factor are changed from L1 to L3.
The control factor with a strongest influence is determined by difference in values. The higher
the difference, more influential is the control factor. In view of the fact that the theory claims
that applied load and hardness of materials are most important factors affecting the sliding
process. For EN-47 steel however load exerted greatest effect on sliding wear which is closely
334 K. V. Arun and K.V. Swetha Vol.10, No.4
followed by material conditions. The effect of sliding distance on the wear was less. The
strongest control factors are shown in the Table 6.
Table 6 Signal to Noise Ratio of Wear Specimens
Trial no. Load(P) in
in m Material
1 7 900 5000 3500C 18.839
2 7 700 3000 2500C 30.428
3 7 500 1000 270C 32.879
4 5 900 3000 270C 20.026
5 5 700 1000 3500C 25.224
6 5 500 5000 2500C 46.196
7 3 900 1000 2500C 53.555
8 3 700 5000 270C 36.594
9 3 500 3000 3500C 49.370
3.6 Analysis of Variance (ANOVA)
The ANOVA is used to investigate which design parameters significantly affect the quality
characteristics. It is accomplished by separating total variability of S/N ratio, which is measured
by sum of square deviation from total mean S/N ratio into contributions by each of the design
parameters and the errors.
Table 7 Percentage Contribution of Wear Specimens
Trial no. Parameters Sum of squares Degrees of
freedom ℅ contribution
1 P 632.106 2 49.205
2 N 289.832 2 22.56
3 D 27.101 2 2.109
4 M 335.63 2 26.126
Total 8 100
Table 7 indicates the percentage of each factor contribution on the total variation and thus
exhibiting the degree of influence on result. For EN-47 steel, the load factor (P≈49.205℅) had a
Vol.10, No.4 Wear Behavior of Spring Steels 335
significant influence on the weight loss of the steel. While the material conditions (P≈26.126℅),
speed (P≈22.561℅) and the sliding distance (P≈2.109℅) had a slight effect. The contribution of
applied load is greater which may be due to the sufficiently induced stress at contact area within
the experimental conditions. The linear regression equation for the wear loss of the spring steel is
shown in equation below:
W = -0.145+0.00125P+0.000154N+0.000005D+0.000005M.
The coefficients of applied load, sliding distance, sliding speed and material conditions are
positive, which indicates that wear increases with the increase in the wear parameters. It
indicates that load is the main factor on wear rate for spring steel. It is followed by material
conditions and sliding speed while the sliding distance was less effective than the other
Design of experiments approach by taguchi method enabled us to analyze successfully the wear
behavior of the spring steel on load, sliding distance, material conditions and sliding speed as test
variables. Effect of variables that is load, sliding speed and material conditions are more
pronounced on the wear of the spring steel than sliding distance. The pooled error associated was
zero. Wear rate of cryogenic material is decreased as the load and speed increases compared to
normal and treated conditions.
Based on experimental analysis carried out on the heat treated spring steel material, the
following conclusions have been drawn.
The heat treated spring steel material has maximum strength whereas the normal material
is found to be very poor in strength aspects.
Condition of materials influences on the wear rate. Tempered material is having high
wear rate as compared to cryogenic specimen.
The tempered specimens are best suitable to use because in tempered specimens the
crack gets healed but in cryogenically conditioned specimens even though the hardness
is high the cracks go on widening.
For further usage the tempering should be done after cryogenic treatment which again
reduces the crack density and heals the crack.
Wear rate of spring steel material increased with increasing load, speed and distance and
wear rate of material depends on the heat treated conditions of the material and the
applied load, speed and distance.
The strength influences more on hardness. Heat treated material have more hardness
compared to normal material.
336 K. V. Arun and K.V. Swetha Vol.10, No.4
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