ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT
AZOJETE March 2020. Vol. 16(1):18-27

Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria.
Print ISSN: 1596-2490, Electronic ISSN: 2545-5818

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Corresponding author’s e-mail address: mbodude@unilag.edu.ng 18

ORIGINAL RESEARCH ARTICLE

MECHANICAL AND STRUCTURAL RESPONSES OF LOW CARBON STEEL TO COLD
ROLLING AND STRESS RELIEF ANNEAL TREATMENTS

M. A. Bodude1*, W.A. Ayoola1, and A. Oyetunji2
(1Department of Metallurgical and Materials Engineering, University of Lagos, Lagos, Nigeria

2Dept. of Metallurgical and Materials. Eng., Fed. Univ. of Technology Akure, Ondo State, Nigeria)
* Corresponding author’s email address: mbodude@unilag.edu.ng

1.0 Introduction
Plain Carbon Steels are widely used for many industrial applications and manufacturing on
account of their low cost and ease of fabrication. In general, plain carbon steels are classified
based on their carbon content, Steels with carbon content varying from 0.3% to 0.6% are
classified as medium carbon, while those with carbon content less than 0.25% are termed low
carbon. Those with high carbon content in the range 0.65-1.5% are classified as high carbon
steels.

Low carbon steel has attracted a lot of research around the globe due to its numerous industrial
applications. In industries, cold rolling is largely responsible for structural changes in
engineering materials which often result in improved mechanical properties due to gradual
extension of grains in the direction of the principal deformation stress with no recrystallization
occurring. A Low Carbon Steel subjected to intercritical annealing at 850oC exhibited a dual
phase microstructure consisting of ferrite martensite and presented excellent mechanical
properties in term of hardness, strength and elongation (Phoumiphon et al., 2016). To further
enhance the mechanical properties of engineering materials, heat treatment operation is carried
out on low carbon steels to obtain desirable mechanical properties like hardness; toughness;
ductility; strength. Low carbon steel is the most common form of steel as its price is relatively
low while it provides material properties that are acceptable for many applications. LCS has a

ARTICLE INFORMATION ABSTRACT
This study investigated the effect of deformation by cold rolling and
stress relief anneal on the mechanical and structural properties of low
carbon steel. The as-received steel samples were cold rolled at 20% – 40
% degrees of deformation using Buhler rolling machine in Metallurgical
and Materials engineering department University of Lagos, Nigeria.
Additionally, some of the cold rolled samples were annealed at a
temperature of 650° C and soaked for 1 hour in a muffle furnace. The
results revealed that the ultimate tensile strength (UTS), percent
elongation, hardness and impact strength of the cold rolled low carbon
steel improved significantly after stress relief anneal due to the
elimination of induced strain hardening caused by cold rolling. The
micrographs show that cold rolled + stress relief anneal caused
significant recrystallization of ferrite-austenite phase to refine
martensite with reduction of dislocations. Therefore, the low carbon
steel can be used effectively for structural purposes in machines and
equipment.

© 2020 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved.

Submitted 02 April, 2018
Revised 12 August, 2019
Accepted 17 August, 2018

Keywords:
Stress relief anneal
degree of deformation
residual stresses
ultimate tensile strength
recrystallization.

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low carbon content (up to 0.3%) and is therefore neither extremely brittle nor ductile. It
becomes malleable when heated, and so can be forged, rolled or machined into any shape.

Several studies have been conducted to examine the influence of cold rolling and heat
treatment on the mechanical properties of engineering materials. The effect of soaking time on
the mechanical properties of annealed cold drawn carbon steel has been conducted (Raji and
Oluwole, 2012). Similarly, Rintaro et al. (2003) investigated the effect of the rolling reduction on
the ultrafine grained structure and mechanical properties of plain low-carbon steel processed
from martensite starting structure (Ueji et al., 2004). In addition, the effect of severe plastic
deformation on the mechanical properties of chosen material was studied. It was found that the
microstructure was highly refined resulting in formation of nanosized grains that enhanced the
tensile and hardness of the material. Ayoola and Oyetunji (2014) studied the effect of
deformation and annealing processing on the texture and mechanical properties of aluminium
alloy AA1200. The study found that ultimate tensile strength and hardness depends on the
degree of deformation (Ayoola and Oyetunji,2014). Furthermore, the influence of cold rolling
and annealing on mechanical properties of steel QStE420 was investigated (Schindler et al.,
2009). It was observed that combination of size of previous cold deformation and parameters of
the following annealing, it was possible to influence mechanical properties of particular steel.
Phoumiphon et al. (2016) examined the effect of cold rolling and intercritical annealing on the
mechanical properties of plain low carbon steel. Many steel components failed in service due to
residual stresses from previous processing and fabrication techniques such as forging, extrusion
and rolling. Therefore, this study aimed to investigate the effect of cold rolled deformation and
stress relief anneal on the mechanical and structural properties of low carbon steel with a view
to solving failures caused by plastic deformations during materials processing.

2. Materials and Methods
2.1 Materials
The steel used in this study was procured from Finlab Scientific Store in Lagos Nigeria. The
nominal chemical composition of the steel shown in Table 1 indicated that the steel is a
commercial grade low carbon steel rod with a diameter of 16 mm.

Table 1: Chemical Composition of As-Procured Plain carbon Steel used (Finlab Scientific Store,
Lagos. Nigeria)

2.2 Samples preparation
The as-procured low carbon steel rod was cut into 250 mm long samples and cold rolled at
room temperature (28° C) in a Buhler two-high rolling machine 150 x 80A at Metallurgical and
Materials Engineering Foundry Unit, University of Lagos, Akoka, Lagos Nigeria. Table 2 shows
the deformation parameters used to produce samples in accordance with ASTM E8-8ST
standard (Adeosun et al., 2011). The rolling was done by feeding the sample in the rolling
machine, which is preset to allow for the required degree of deformation and number of passes.
The deformed samples were heat treated in a muffle furnace at a temperature of 650 °C soaked
for 1 hour and later cooled to room temperature in air.

Elements Fe C Si Mn P S Cr Ni
Weight (%) 98.940 0.225 0.170 0.540 0.017 0.008 0.074 0.026

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Bodude et al: Mechanical and Structural Responses of Low Carbon Steel to Cold Rolling and Stress Relief Anneal
Treatments. AZOJETE, 16(1):18-27. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: mbodude@unilag.edu.ng 20

Table 2: The Deformation parameters and their values (Adeosun et.al, 2011)
Deformation parameters Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Sample diameter (mm) 12.80 12.0 11.20 10.40 9.60
Degree of deformation (%) 20 25 30 35 40
Reduction in diameter (mm) 3.20 4.00 4.80 5.60 6.40
Number of passes 1 2 4 8 16

2.3 Mechanical Testing
2.3.1 Tensile Test
The tensile test was conducted on Instron Universal Testing Machine model (USA). The tensile
test pieces were prepared from the rolled and heat treated samples to ASTM E-8 standard
(Ayoola et al., 2012, Tewary et al., 2015). Figure 1 shows the standard dimensions of the
specimen used in this study. From the tensile tests carried out, tensile strength and percentage
elongations were determined.

Figure 1: Cylindrical Tensile Test Piece

2.3.2 Flexural Test
The flexural test was done using M500 tensometer (USA) with a load of 25KN on samples.
Specimens of 120 mm long by 50 mm wide were cut and loaded in three point flexural with a
recommended span of 100 mm and also with a test speed of 40 mm/min.

2.3.3 Hardness Test
To evaluate the hardness of the material the Rockwell hardness test was carried out according
to ASTM E-18 specification (Paul et al., 2007).

2.3.4 Impact Test
Impact test was carried out on the samples using the Avery- Denison Universal Impact –Testing
Machine. (USA) The energy absorbed by the machined sample was measured and recorded
when the machine pendulum was released from the maximum position corresponding to
charpy test, striking the test piece with a load of 300 J (Paul et al., 2007). The same procedures
were repeated on other samples

2.3.5 Microstructural Analysis
Microstructural examination of samples was conducted using a metallurgical optical microscope
in line with Gladkousky et al. (2016). The specimens for the optical microscopy were ground

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using a series of emery papers of grit sizes ranging from 500 – 1500 μm while fine polishing was
done afterwards. The specimens were etched with 2% Nital solution for 5 seconds before
observation in the optical microscope.

3. Results and Discussion
This study investigated the effect of deformation by cold rolling and stress relief anneal on the
mechanical and microstructural properties of low carbon steel. Table 3 indicates the Mechanical
properties of the control sample while Figure 2 shows the mechanical properties of the samples
that were cold rolled with and without stress relief anneal at various degree of deformation. The
Ultimate Tensile Strength of the cold rolled samples without stress relief anneal increased with
increasing degree of deformation and significantly higher than that of control and stress relief
anneal samples. Figure 2 also reveals that increase degree of deformation has no significant
effect on the UTS for the cold rolled + stress relieved samples. This implies that stress relief
anneal at 650° C for 1 hour is sufficiently high enough to eliminate the strain hardening and
induced residual stresses completely. This is because the recovery process, that is, stress relief
anneal significantly allowed redefined and rearranged of large numbers of dislocations within
grains resulted in reduce or complete elimination of residual stresses. The UTS of rolled + stress
relief anneal samples were approximately 2.5 higher than the cold rolled samples. This may be
linked to the stress relief anneal temperature of 650° C investigated. At higher annealing
temperatures, both recovery and recrystallization occur rapidly and resulted in grain growth
which reduces the UTS of the samples (Ueji et al., 2004).

Table 3: Mechanical properties of the As Received Low Carbon Steel.
UTS (MPa) Impact Energy (J) % Elongation Hardness
505.56 206 15.03 4.40

Figure 2: Variation of Ultimate Tensile Strength with Annealing and Degree of Deformation

Figure 3 shows the dependence of percent elongation on the degree of deformation. While the
percent elongation increased with the degree of deformation for the cold rolled samples the
rolled + stress relief anneal samples show some form of recovery. The percent elongation
dropped at all levels of deformation after stress relief of the samples. Figure 3 shows that 18%
and 75 % reduction in elongation were obtained at 20% and 40 % degree of deformation,
respectively. The elongation recovers when the samples are annealed at temperatures higher

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Bodude et al: Mechanical and Structural Responses of Low Carbon Steel to Cold Rolling and Stress Relief Anneal
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than 550° C (Ueji et al., 2004). A gradual increase in the elongation was noticed beyond 30 %
degree of deformation for the cold rolled + stress relief anneal. Elongation of materials is a
measure of its ductility. Stress relief anneal improved the ductility of the low carbon steel
investigated due to the elimination of residual stresses induced. Between 20 and 30 % degree of
deformation, percent elongation of cold rolled + stress relief anneal samples was observed to
be closer to the original ductile of the as-received sample of 15 %.

Figure 3: Variation of Elongation with Annealing and Degree of Deformation

Figure 4 shows the response of flexural strength to the degree of deformation. Flexural strength
decreases with increasing degree of deformation. The maximum flexural strength obtained for
the rolled sample and rolled + stress relief anneal sample are 1900 MPa and 840 MPa
respectively. Similarly, the least flexural strength obtained for the rolled sample and rolled +
stress relief anneal sample are 1260 MPa and 360 MPa respectively.

Figure 4: Variation of Flexural Strength with Annealing and Degree of Deformation

Figure 5 shows the effect of stress relieved annealing and degree of deformation on the sample
hardness. As expected, the hardness value of the samples is a function of the processes the

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material is undergone. The rolled samples without stress relief anneal exshibited higher
hardness compared to rolled + stress relief anneal samples. However, the slopes of the plots are
similar. It can also be seeen that the hardness increased with increasing degree of deformation
and dependent of stress relief anneal. Cold rolled samples without stress relief anneal
introduced commpressive residual stress, which is beneficial for parts that are subject to cyclical
loads because it helps to prevent the initiation and propagation of cracks. However, with the
annealed samples, compressive residual stress have been largely eliminated and tensile residual
stress seems to have been introduced, which translated to drasstical reduction in hardness. The
hardness of the stress relief anneal samples is higher than that of the control sample.

Figure 5: Variation of Hardness with Annealing and Degree of Deformation

The absorbed impact energy by the samples cold rolled with and without stress relief anneal is
shown in Figure 6. The trend of the two curves is similar. The linear regression lines fitted show
that the impact strength is not enhanced by increasing the degree of deformation irrespective
of treatment undergone. However, the influence of stress relief anneal can be seen. The impact
energy of 220 J and 135 J were recorded for stress relieved and cold rolled samples, respectively.

Figure 6: Variation of Impact Strength with Annealing and Degree of Deformation

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Bodude et al: Mechanical and Structural Responses of Low Carbon Steel to Cold Rolling and Stress Relief Anneal
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Figure 7 shows the micrograph of the as-received low carbon steel. Figures 8, 9, 10, 11 and 12
show the micrographs of the samples deformed at 20, 25, 30, 35 and 40 %, respectively.
Interestingly, the micrographs are predominantly ferrite-austenite and martensite phases. It is
noteworthy that large grains of the martensite phase of the as-received sample are regular in
shape and well visible within the matrix of ferrite-austenite phase, as shown in Figure 7. The
volume fraction of the martensite and ferrite-austenite phases are well distributed. Figures 8a,
9a, 10a, 11a and 12a are the micrographs of cold rolled samples while Figures 8b, 9b, 10b, 11b
and 12b are the micrographs of cold rolled + stress relief anneal samples at the same degree of
deformation, in that order. The micrographs of the cold rolled samples contain deformed grains
of smaller sizes which contain a very large number of dislocation than the cold rolled + stress
relief anneal samples. The presence of these dislocations are largely responsible for the
enhanced mechanical properties attained in the stress relieved samples. Expectedly, stress relief
anneal above 0.4*Tm (Tm, melting temperature of low carbon steel) caused recrysallisation of
low carbon steel, elimination of the residual stresses and most dislocations, which subsequently
reduce ultimate tensile strength with high ductility (Ueji et al., 2004). Application of stress relief
anneal to the cold rolled samples caused major coalesence of the smaller martensite grains to
larger grains of irregular shapes and increased the volume fraction due to recrystallisation.
Phoumiphon et al., 2016 reported that the ferrite-austenite dual phase region by referring to the
lever rule, the volume fraction of austenite increases depends on annealing temperature, then
will transform to martensite. Also, Gladkousky et al. (2016) revealed the possibility of the
formation of an ultrfine grained structure in a steel layer during rolling. The stress relief anneal
temperature is significantly high enough for recrytallisation of low carbon steel (Knupfer and
Moore, 2010; Phoumiphon et al., 2016). Figure 12b shows that sample cold rolled at 40 %
deformation and stress relief anneal exhibited highest presence of mentensite phase, which
transilated to the highest hardness and UTS. The higher hardness and UTS recorded for the
Figure 12a over Figure 12b was due to the large volume of dislocation present. The findings
from this work is in agreement with most of the earlier studies cited and the results further
revealed the adaptability and hence the effective utilisation of the low carbon steel for structural
applications when rolled and stress relieved optimally.

Figure 7: Micrograph of the control sample in as-received condition

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Figure 8: Micrograph of samples at 20% deformation (a) rolled and (b) rolled + stress-relief
anneal

Figure 9: Micrograph of samples at 25% deformation (a) rolled and (b) rolled + stress-relief
anneal

Figure 10: Micrograph of samples at 30% deformation (a) rolled and (b) rolled + stress-relief
anneal

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Bodude et al: Mechanical and Structural Responses of Low Carbon Steel to Cold Rolling and Stress Relief Anneal
Treatments. AZOJETE, 16(1):18-27. ISSN 1596-2490; e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: mbodude@unilag.edu.ng 26

Figure 11: Micrograph of samples at 35% deformation (a) rolled and (b) rolled + stress-relief
anneal

Figure 12: Micrograph of samples at 40% deformation (a) rolled and (b) rolled + stress-relief
anneal

4. Conclusion
The mechanical and microstructural characterizations of a low carbon steel subjected to cold
rolling and annealing heat treatment was carried out in this work. The outcome of the study
showed that the stress relief annealing heat treatment caused significant change in the grain
size, distribution and volume fractions of the phases present in the resulting microstructure. This
is therefore responsible for the significant increase in the ultimate tensile strength (UTS),
hardness, impact strength and percent elongation (ductility) of the low carbon steel. In addition,
the heat treatment reduces the compressive residual stresses of the rolling, hence an increase in
the degree of deformation has no significant effect on the UTS for the rolled + stress-relieved
samples due to complete elimination of the strain hardening and induced residual stresses.
Therefore, the outcome of the rolling and stress relief annealing in this work revealed the
adaptability and hence the effective utilisation of the low carbon steel for structural applications
when rolled and stress relieved.

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