Engineering, 2010, 2, 502-506
doi:10.4236/eng.2010.27066 Published Online July 2010 (
Copyright © 2010 SciRes. ENG
Effect of Welding on Microstructure and Mechanical
Properties of an Industrial Low Carbon Steel
Zakaria Boumerzoug1, Chemseddine Derfouf1, Thierry Baudin2
1Department of Mechanical Engineering, Biskra University, Biskra, Algeria
2Université Paris-Sud 11, ICMMO, Laboratoire de Physico-Chimie de lEtat Solide, Orsay, France
E-mail:,, Thierry.Baudi
Received February 5, 2010; revised April 12, 2010; accepted April 18, 2010
In this work, the effect of arc welding on microstructures and mechanical properties of industrial low carbon
steel (0.19 wt. % C) was studied. This steel is used for making gas storage cylinders. In order to realize the
objective, optical microscopy, EBSD, X-ray diffraction, and hardness tests were used. Different zones and
some phases are identified. New microstructural phenomenons are observed by using EBSD technique.
Keywords: Steel, Welding, HAZ, Ferrite
1. Introduction
Welding is a process of joining materials into one piece.
Generally, welding is the preferred joining method and
most common steels are weldable. The phase transfor-
mation and mechanical behavior after the welding of
many steels have been investigated. For example, Bay-
raktar et al. [1] have studied the grain growth mechanism
during the welding of interstitial free steels. Observations
in the welded joints indicate the presence of very large
grains near the fusion line and these are oriented along
the directions of the heat flow. Concerning the welding
of low carbon steels, it has been shown that the grain-
coarsened zone (GCZ) and heat affected zone (HAZ) are
very critical since embitterment is concentrated in these
areas [2].
It is also known that the final microstructures and me-
chanical properties of welded steel depend on some pa-
rameters like percentage of carbon and presence of oth-
ers elements such as sulfur or phosphorus. Low carbon
steels that have less than 0.25% carbon, display good
welding ability, because they can be generally welded
without special precautions using most of the available
processes. Concerning the previous studies related to the
welding of low carbon steel, there are limited publica-
tions [2-8]. For example, Gural et al. [2] have studied the
heat treatment in two phase regions and its effects on
microstructure and mechanical strength after welding of
the low carbon steel. On the other hand, Eroglu and Ak-
soy [3] investigated the effect of initial grain size on mi-
crostructure and toughness of intercritical heat-affected
zone of low carbon steel.
Concerning the present study, it has been chosen to
investigate the effect of welding on industrial low carbon
steel used for making of gas storage cylinders. Optical
microscopy, EBSD, X-ray diffraction, and hardness tests
have been used as characterization tools.
2. Experimental Procedure
The chemical composition of the base metal is given in
Table 1.
Steel electrodes were used to deposit the welds using
the shielded metal arc welding process. The chemical
composition of the weld metal is presented in Table 2.
Figure 1 illustrates a part of welded sheets of a gas
cylinder and the sample size used in this study. The sur-
face studied S is indicated in this figure.
For metallographic observation, the specimens were
etched with 2% nital for 20 s and consequently the mi-
crostructures of the base, weld and the heat affected zone
were defined. Specimens were prepared for Electron
Back Scattered Diffraction (EBSD) analysis using stan-
dard sample preparation method. A Zeiss 940SEM with a
tungsten filament was used. The SEM device is coupled
with automatic OIMTM (Orientation Imaging Microscopy)
software from the TSL Company. The hardness across
the weld was measured by microhardness tester using a 2
kg load. In addition, X-Ray Diffraction (XRD) was used
to determine the main phases in welded steel by using
Cu α radiation. K
Table 1. Chemical composition of the base metal (0.19 wt. % C).
C% Si% Mn% P% S% Al% Mn% Nb% Ti%
0.19 0.25 0.4 0.025 0.015 0.09 0.009 0.05 0.03
Table 2. Chemical composition of electrode, wt %.
C% Si% Mn% P% S% Al% Nn% Nb% Ti%
0.06-0.12 0.01 0.40-0.6 0.025 0.025 - - - -
Weld metal
Base metal
Figure 1. Part of welded sheets and sample used in the study. (S: Surface studied).
3. Results and Discussion
In the first part of this paper, the microstructure of base
metal of industrial low carbon steel (0.19 wt. % C) is
presented. In the second part, the effect of welding on the
microstructure evolution is illustrated.
3.1. Base Metal
Typical microstructure of sheet (base metal) is composed
of ferrite and small regions of pearlite (α-Fe + Fe3C) at
grain boundaries edges and corners (Figure 2(a)). Fig-
ure 2(b) shows an EBSD image of the base metal, which
is largely composed of equiaxed ferrite grains.
Figure 2(c) illustrates a histogram of grain size which
indicates that average grain size is 10 µm. On the other
hand, Figure 2(d) shows curve of misorientation distri-
bution (blue) which is near the istropic materials (red).
For low magnification (Figure 3), the bands of per-
lite-rich area (banding) were observed. This macroseg-
regation phenomenon, which is called banding, is due to
the presence of high percentage of Mn (0.4-0.5%) in
these zones. In more alloyed weld metals, elements such
as chromuim and molybdenum can be found to be seg-
regated in these areas [9].
3.2. After Welding
In order to clarify the effect of welding on sheets, the
microstructures of welded joints were analyzed using
optical microscopy and EBSD. The EBSD map of near-
est region to HAZ (Figure 4) shows the effect of direc-
tion heat flow on elongation of ferrite grains. Bayraktar
et al. [1], have observed in interstitial free steels that the
welded joints are characterized by the presence of very
large grains near the fusion line and these grains are ori-
ented along the directions of the large heat flow.
This strongly “oriented” structure is in some aspects
very similar to certain solidification microstructure, whose
morphology depends also on heat flow. On the other
hand, it has been found that solidification theory can be
applied to welding [10,11].
Concerning the heat-affected zone (HAZ), Figure 5 ill-
ustrates clearly the microstructures of this zone. It contains
Copyright © 2010 SciRes. ENG
50 μm
001 101
70 μm
(a) (b)
(c) (d)
Figure 2. Microstructures of industrial low carbon steel (0.19 wt. % C) in base metal by (a) optical and (b) EBSD
map–distribution of directions <hkl>//z superimposed to the Kikuchi pattern quality factor (c) Histogram of grain size and (d)
curves of misorientation distribution (blue: experimental results and red: isotropic distribution).
Widmanstatten ferrite, and some colonies of pearlite. It is
known that solid-state phase transformations, such as
grain growth, recrystallization, phase transitions, anneal-
ing, and tempering, all occur in the HAZ of steel welds.
The coarse grained region of the HAZ is adjacent to the
weld fusion zone and contains grains larger than those in
the base metal. It has been found that there are two phase
transformations that occur in the HAZ during cooling.
The first is the high temperature transformation of δ-Fe
to γ-Fe. The second transformation is the γ-Fe to α-Fe
transformation [12].
However, Figure 6 shows that the center of weld metal
is totally different from the other zones, because it is
characterized by pseudo-grains and a microstructural in-
homogenity which is a result of the fastest cooling rates.
It appears that this zone contains mainly ferrite and some
colonies of pearlite. The microstructure that evolved in
the weld is heterogeneous due to the temperature gradi-
ents and the chemical gradients that evolve during the
process [11].
In order to know the main phases in the welded joints
(Weld metal + HAZ), XRD diffraction was particularly
applied in this region (Figure 7). From three ferrite
peaks observed in this spectrum: the bcc (110), bcc (200)
Bands of
Figure 3. Microstructure of industrial low carbon steel
(0.19 wt. % C) in base metal.
Copyright © 2010 SciRes. ENG
70 μm
001 101
Figure 4. EBSD map (distribution of directions <hkl>//z
superimposed to the Kikuchi pattern quality factor) in
nearest region to HAZ after arc welding of an industrial
low carbon steel (0.19 wt. % C) (map taken in the base
metal but just near the welded metal “near the weld fusion
Coarse grained α ferrite
Figure 5. Microstructure of HAZ after welding of an in-
dustrial low carbon steel (0.19 wt. % C).
50 μm
Figure 6. Center of weld metal “in the weld fusion zone”.
Figure 7. XRD spectrum of welded low carbon steel in all
the welded zone (Weld metal + HAZ).
and bcc (111), we conclude a presence only of ferrite
phase observed by optical microscopy.
On the other hand, by using EBSD observation (Fig-
ure 8) a fusion line is determined. We can observe clearly
the microstructural difference between weld metal zone
and HAZ. This transition zone is characterized by bands
of coarse grains, where each band of grain has quite the
same orientation (Figure 9). In this coarse-grained zone,
it seems that the grains tend to grow along a certain pre-
ferred crystallographic directions.
large grains
70 μm
Figure 8. EBSD map (distribution of directions <hkl>//z
superimposed to the Kikuchi pattern quality factor) in
transition zone (4mm from the core of weld metal) after arc
welding of an industrial low carbon steel (0.19 wt. % C).
100 μm
Figure 9. Map of the same EBSD analysis of Figure 8 and
corresponding pole figure of the colored grains.
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distance ( mm )
25 mm
Figure 10. Microhardness measurments on surface S (indi-
cated in Figure 1) from the base metal across the weld
metal after welding of an industrial low carbon steel (0.19
wt. % C).
Concerning the effect of welding on different regions
of welded steel, it was reported that a hardness testing
is the usual approach in delineating the properties of
these various zones, but the information obtained is very
limited [13]. For other researchers, a simple rapid way to
obtain important information is by hardness testing [9].
Concerning the present material, the hardness distribu-
tion in different zones is shown in Figure 10. The hard-
ness values of 178-250 HV in Figure 10 are observed at
location within 1 mm from the base metal, through the
HAZ across the weld metal to the other base plate. These
hardness results are partially in good agreement with
literature. Indeed, Gul et al. [2], have found that maxi-
mum hardness values are measured in the area of weld
metal (WM). But in the present study, the maximum
hardness is both in weld metal and heat-affected zones.
The variation in properties across the weld can be attrib-
uted to several factors, mainly to residual stresses just
after welding. However, other factors can contribute to
this hardening like grain size, phase composition and
metallic inclusions.
4. Conclusions
This work represents a contribution to the study of the
effect of shielded metal arc welding on industrial low
carbon steel (0.19 wt. % C). The microstructures in dif-
ferent zones are determined from the base metal to the
weld metal. The microstructure of the center of weld
zone is completely different from the heat-affected zone.
he HAZ contains Widmanstatten ferrite, large grains of
ferrite and colonies of pearlite. We have observed that
bands of coarse grains grow along a certain preferred
crystallographic directions. Moreover, we have found
that maximum hardness values are situated in the area of
weld metal and HAZ which indicates its specificity.
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