Materials Sciences and Applications, 2010, 1, 135-140
doi:10.4236/msa.2010.13022 Published Online August 2010 (
Copyright © 2010 SciRes. MSA
Effects of Fillerwire Composition along with
Different Pre- and Post-Heat Treatment on
Mechanical Properties of AISI 4130 Welded
by the GTAW Process
Ali Emamian1, Ardalan Emamian2, Amir Hossein Kowkabi3
1Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Canada; 2Department of Mechanical
Engineering, IAU, Esfahan, Iran; 3Department of Material Science and Engineering, Sharif University of Technology, Tehran, Iran.
Received May 8th, 2010; revised May 31st, 2010; accepted June 8th, 2010.
This research intends to find out the optimal mechanical properties of AISI 4130 steel welded by the GTAW process. Six
test plates were joined by two types of filler wire with similar chemical composition to the base metal, and with lower
carbon content and slightly higher alloy elements content compared to the first one. Test plates then exerted three dif-
ferent pre-heat and post-heat treatments on both groups. The three types of heat treatments were alternatively without
pre-heat and post-heat, with pre-heat only, and finally with pre-heat and post-heat. Tensile, side bends and impact tests
(for weld zone and HAZ) have been conducted. Results show that using low-carbon filler wire along with pre- and
post-heat resulted in outstanding mechanical properties.
Keywords: HAZ (Heat Affected Zone), Filler Wire, Pre- and Post-heat Treatments, GTAW Process
1. Introduction
The unending search for novel mechanical properties has
led to significant development in material with high str-
ength. The 4130 grade of chrom-moly is in the HSLA
group of steel. Although 4130 is not lighter than general
steels, its higher specific strength ratio enables the engi-
neers to reduce the weight of designs by using thinner
thicknesses. Having ductility and specific strength at the
same time increases the applications of 4130 in the aero-
space, machinery, and motor sports industries.
The sensitivity of high-strength and ultra-high-strength
steel to the welding, increases the need to investigate the
weld ability and mechanical properties of these types of
steel. In the welding process the heat affected zone is he-
ated above its critical temperature (A3 or Acm). On the
other hand, the cooling rate of steel affects its microstr-
ucture and constructs different phases. According to the
chemical composition of AISI4130 (Table 1), due to its
hardness and CCT diagram, it is probable to have ferritic-
perlitic, ferritic-bainaitic or martensitic structure. Con-
sequently, different microstructures result in different
mechanical properties.
During the welding process, mechanical properties of
weld joints can drop dramatically [1,2]. Bevis and Fulcer
et al. provide information about welding of 4130 tubes
with thicknesses less than 1/8 inches. Todd et al. studied
tube welding and technical issues of 4130 [3,4]. Earolino
et al. studied the effect of carbon content and alloy ele-
ments on maximizing the hardness of liquid boundaries
[5]. They observed an increase in the hardness of weld
metal and the liquid boundary. Changing the chemical
composition by filler wire and dilution does not affect the
HAZ in constant welding parameters. Therefore, the
afore-mentioned studies do not provide sufficient infor-
mation about HAZ properties.
Kyte et al. and Hooijmians et al. have investigated hy-
drogen cracking and hydrogen removal during GTAW
welding. They developed a model which shows the relat-
ion between hydrogen content and welding parameters
[6,7]. Still et al. investigated the necessary conditions for
cold cracking and the forming of bainite or martensite
In the past decade, a considerable portion of the litera-
ture has focused on technical aspects or advanced tech-
nology devices such as laser or electron beam welding to
Effects of Fillerwire Composition Along with Different Pre- and Post-Heat Treatment
onMechanical Properties of AISI 4130 Welded by the GTAW Process
study fatigue, crack growth or residual stress on 4130 [9].
Fatigue is a complex phenomenon compared to tensile,
impact or bending properties. Without complete unders-
tanding of a material’s behavior in tensile, impact or ben-
ding tests, dynamic test results are difficult to interpret.
Also using lasers or other advanced devices is not always
an option in many cases due to their exorbitant cost.
Ravi et al. have studied the effect of post weld heat tr-
eatment on estimated fracture toughness. They assert that
PWHT does not affect the impact toughness of weld met-
al [10].
Marcelino et al. have studied the crack growth rate in
weld metal, HAZ and base metal in repaired welded joi-
nts. They discovered that the fastest fatigue crack growth
was in weld metal [11]. Bultel et al. have investigated the
effect of temperature on fatigue life considering the ph-
ase transformation of ferritic-perlitic and bainitic in 4130
steel [12].
In the welding of 4130 steel, two important factors sh-
ould be taken into the account: the chemical composition
of the weld metal and heat-affected zone mechanical pro-
perties. Throughout the literature, no detailed or satisfac-
tory explanation was found regarding controlling weld
and HAZ mechanical properties. This lack of data is due
in part the majority of published papers being technical
reports. Most of the published papers related to this res-
earch field can be found in 1980-1997, where HSLA pro-
perties generally, either in weld metal or in HAZ, are
investigated [13-16]. However, there remains a profound
lack of knowledge about the relationship between heat
treatment/weld composition and the mechanical proper-
ties of AISI 4130 welded parts.
The purpose of this research is to define the optimal
condition for welding of 4130 steel with the GTAW pro-
cess by considering the chemistry of weld metal affected
by filler wire and heat treatment simultaneously.
2. Experimental Method
AISI 4130 plates sized at 400 × 200 × 10 mm were sele-
cted to weld perpendicular to the rolling direction.
To protect the weld pool and focus the weld spot in
order to lessen the heat affected zone area, the GTAW
process is selected.
Next, a single Vee-Joint is made by the milling mach-
ine at an angle of 30˚. The number of plates provided is
twelve, which results in six test plates after being welded
two by two. Three of the six test plates are welded by the
filler wire B, whose analysis is like the base metal as pr-
esented in Table 3. The remaining test plates are welded
by a very low carbon filler wire L (Table 4).
In both cases, the test plates are first welded without
pre-/post-heat treatments (prefix 1). Next, the test plates
are welded with pre-heat treatments (prefix 2). Finally,
the test plates are welded with both pre- and post-heat
treatments (prefix 3). In the case studies clarified above,
all conditions and welding parameters such as amperage,
voltage, argon gas flow (for protection) and welding sp-
eed are controlled to be constant. The pre-heat treatment
is done by a torch at about 200˚C. At this stage, the tem-
perature is controlled by a thermometer. The inter-pass
temperature in all samples is determined to be about
In the post-heating treatment, the samples are placed in
a furnace with temperature of about 200˚C, which slowly
rises to 600˚C. The samples remain at this temperature
inside the furnace for about an hour. They are then taken
out of the furnace to cool to room temperature. Afterw-
ards, a non-destructive testing process (ultrasonic and
radiography) is applied to the samples in order to ensure
that the weldments are sound and crack free. The test
specimens are cut from the test plates according to AWS
D1.1 and ASME SEC 9 standards. The test plates include
two tensile, four side bending and six impact test speci-
mens, of which three belong to the weld metal and three
to the HAZ. The temperature of the impact tests is de-
creased to –50˚C by alcohol and dry ice.
3. Results and Discussion
Table 1 shows the coding system of samples. Micro
hardness test results are illustrated in Table 5. Each res-
ult is an average of at least five measurements at the
same level of weld or heat affected zone. Only the pre
and post-heated samples show uniform hardness results
in the weld metal and HAZ.
Table 1. Coding system
Tensile test Hardness test Bending test Impact test
A can be L (stands for low carbon, high alloy filler metal) or B (stands for filler metal with same chemical composition as base metal)
B can be 1 (stands for without pre-/post-heat treatment), 2 (stands for pre-heat
be treatment) or 3 (stands for pre- and post-heat treatment samples)
D is sample number
C can W (stands for weld metal) or H (heat affected zone)
Copyright © 2010 SciRes. MSA
Effects of Fillerwire Composition Along with Different Pre- and Post-Heat Treatment
onMechanical Properties of AISI 4130 Welded by the GTAW Process
Table 6 shows that the ultimate tensile strength in both
types of filler wires decreases when applying both pre-
heat treatments and pre- and post-heat treatments. Pre-
heat resulted in lower cooling rate and retard the forma-
tion of brittle and hard phases in weld and HAZ. More-
over, post weld heat treatment decreases the strength by
tempering of formed brittle phases which are constructed
during the welding process. Generally higher amounts of
tensile testing can be observed in samples which are
welded by filler metal with higher carbon content (B pre-
fix compared to L). Samples were broken out of the weld
and close to the fusion line; hence, a higher amount of
carbon in the filler wire B is the main reason for elevated
tensile results.
Table 2. Chemical analysis of AISI4130 steel
%C %Si %S %P %Mn %Ni %Cr
0.25 0.23 0.003 0.010 0.49 0.088 0.91
%Mo %Cu %Ti %Sn %V %Al
0.19 0.11 0.003 0.008 0.007 0.019
Table 3. Chemical analysis of high carbon filler wire (similar to base metal ) type B
%C %Cr %Mo
0.3 0.8 0.24
Table 4. Chemical analysis of low carbon filler wire type L
%C %Cr %Mo
0.04 1.1 0.58
Table 5. Hardness test results (HVN)
Sample No. HAZ Weld Metal Base Metal
B11 267 325 241
B21 260 338 245
B31 222 227 211
L11 270 274 259
L21 265 267 272
L31 220 271 248
Table 6. Tensile test results
Sample No. % Elongation Ultimate Tensile Strength (N/MM2)
As rolled 4130 23 766
As rolled 4130 17 773
B11 - 800
B12 - 793
B21 - 760
B22 - 753
B31 - 664
B32 - 653
L11 - 746
L12 - 762
L21 - 693
L22 - 687
L31 - 615
L32 - 660
Copyright © 2010 SciRes. MSA
Effects of Fillerwire Composition Along with Different Pre- and Post-Heat Treatment
onMechanical Properties of AISI 4130 Welded by the GTAW Process
Table 7 depicts impact test results at –50˚C for weld
metal and heat affected zones (HAZs) which are the ave-
rage of three samples values. According to the results,
there is no considerable difference in weld metal impact
test values in the samples. However, heat affected zone
impact test results have been dramatically changed. Opt-
imal toughness results belong to pre- and post-heated sa-
mples. This is because of the tempering of brittle phases
which formed during cooling.
Table 8 illustrates side bend results. Samples without
pre/post heat treatment (group 1) and with pre-heat but
without post-heat (group 2) fractured when bent more
than 34˚. However, in both types of filler wires, pre- and
post-heated samples could be bent to 180˚ without being
fractured or cracked. It is worth knowing that failure in
weld only can be observed in sample with higher amount
of carbon content in filler wire (group B1).
Unlike carbon steels, HSLA steels such as 4130 can be
hardened even at a slow cooling rate. Figure 1 shows a
CCT diagram of 4130 steel. As alloy elements retard the
diffusion, the CCT diagram shifts to the right of the chart.
Therefore, depending on cooling rate values, ferrite, re-
mained austenite or martensite can be formed during the
cooling. At very slow cooling rates, 2.2˚C/Sec, ferrite
Table 7. Impact test results in (–50˚C)
Sample No. Impact Energy (J) Sample No. Impact Energy (J)
BW11 21 LW11 15
BW12 18 LW12 17
BW13 19 LW13 14
BH11 6 LH11 6
BH12 5 LH12 4
BH13 5 LH13 5
BW21 12 LW21 16
BW22 15 LW22 21
BW23 20 LW23 26
BH21 7 LH21 8
BH22 9 LH22 8
BH23 10 LH23 7
BW31 15 LW31 30
BW32 17 LW32 25
BW33 21 LW33 20
BH31 133 LH31 130
BH32 125 LH32 110
BH33 84 LH33 125
Table 8. Side bend test results
Sample No. Bend Test Result Sample No. Bend Test Result
B11 Fracture in HAZ & weld L11 Fracture in HAZ
B12 Fracture in HAZ & weld L12 Fractured in HAZ
B13 Fracture in HAZ & weld L13 Fractured in HAZ
B14 Failure in HAZ L14 Fractured in HAZ
B21 Failure in HAZ L21 Micro crack in HAZ
B22 Failure in HAZ L22 Micro crack in HAZ
B23 Failure in HAZ L23 Micro crack in HAZ
B24 Failure in HAZ L24 Bend to 34°
B31 Bend to 180º L31 Bend to 180º
B32 Bend to 180º L32 Bend to 180º
B33 Bend to 180º L33 Bend to 180º
B34 Bend to 180º L34 Bend to 180º
Copyright © 2010 SciRes. MSA
Effects of Fillerwire Composition Along with Different Pre- and Post-Heat Treatment
onMechanical Properties of AISI 4130 Welded by the GTAW Process
Figure 1. CCT diagram for 4130 steel [17]
and remained austenite can be formed. However, the re-
mained austenite can still find a chance to transform to
the upper or lower bainite, depending on the cooling rate
at that specific point.
A small and focused weld spot in the GTAW process
develops a considerable thermal gradient, which increa-
ses the cooling rate by conduction resulting from the heat
sink of test plates. Subsequently, depending on the dista-
nce from the weld spot, diverse cooling rates result. Hen-
ce, a variety of non-equilibrium and brittle phases should
be expected in heat affected zones.
With post-heat treatment, brittle phases such as bainite
or martensite can be tempered. Hardness results in Table 5
illustrate a 10-12% drop in hardness values for samples
which are post-heated (B31 and L31). Moreover, hard-
ness results show that pre-heating by itself does not cause
a considerable change in hardness. The higher hardness
of weld metal in group B compared to group L is due to
the higher amount of carbon contents in group B.
Carbon content increases the hardness and encourages
the brittle phases during the cooling. Therefore, using
high carbon filler wire increases the probability of crack
formation in weld metal (side bend test results Table 8).
Since dilution occurs during welding, alloy elements
such as carbon enter the melt pool from the base metal.
Thus, weld chemical composition has a higher carbon co-
ntent compared to the filler wire, which should be taken
into account.
4. Conclusions
From this article, the following conclusions can be dra-
wn: High carbon filler wire, type B (similar to the base
me- tal composition), caused more failures in weld metal
and fusion boundaries in bend test results.
Low carbon filler wire shows better results in terms of
decreasing the risk of crack formation.
Tempered martensite in HAZ resulting from post-weld
heat treatment shows valuable results in 4130 steels.
Pre- and post-heat treatments play a crucial role in co-
ntrolling cooling rates and tempering the formed brittle
phases in HAZ, respectively. Post-heat treatment incre-
ases the HAZ impact toughness up to 20 times.
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onMechanical Properties of AISI 4130 Welded by the GTAW Process
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