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ELK ASIA PACIFIC JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING
ISSN Online: 2394-0425; Volume 1 Issue 2 (2016)
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THE EFFECT OF WELDING ON MECHANICAL AND MICROSTRUCTURAL
PROPERTIES OF MATERIALS- A CRITICAL REVIEW
Md. Anis Raza
Post Graduate Scholar, Production
Technology and Management,
Birsa Institute of Technology, Sindri,
Dhanbad, Jharkhand
Sudhir Kumar Kashyap
Sr. Principal Scientist, CSIR- Central
Institute of Mining & Fuel Research,
Dhanbad, Jharkhand,
& Professor, Academy of Scientific &
Innovative Research
(AcSIR – CIMFR)
Rakesh
Assistant Professor,
Deptt. Of Production Engg, Birsa
Institute of Technology, Sindri,
Dhanbad, Jharkhand,
ABSTRACT
Keywords: steel casting production, tensile strength, HAZ, plasma weldin
Welding is extensively used in the finishing stage of steel casting production and in fabricating components for
joining. The ease of welding as well as the effects of welding on mechanical properties is thus very pertinent
considerations in the production of engineering components. The purpose of this review is therefore to summarize
and evaluate the published literature with respect to weld ability and the effects of welding processes on mechanical
properties. In this paper a critical review has been presented on the effect of different welding processes like friction
stir welding, arc welding, laser welding, plasma welding on mechanical properties such as tensile strength,
toughness, hardness and microstructural properties of different grade of steels. The different steels which were taken
for studies are stainless steel, low carbon steel, high strength low alloy steel, aluminum alloy etc. After critical
review of related papers it was concluded that there were microstructural change as more pearlite and ferrite were
present in weld zone and HAZ compared to base metal that resulted in increased hardness and loss of tensile
strength. The welding parameters like welding speed, heat input and welding conditions have also resulted on the
affect the weld joint properties and weld joint strength. The mechanical properties of weld joints have also been
affected by filler material composition and type of welding used. Finally, out of all the welding processes friction
welding and laser welding led to superior quality compared to other fusion welding.
ELK ASIA PACIFIC JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING
ISSN Online: 2394-0425; Volume 1 Issue 2 (2016)
INTRODUCTION
Welding is a permanent joining process in
which two or more parts are coalesced at their
contacting surface by suitable application of
heat and/or pressure [1]. In modern time
welding is widely used in various industries
like power generation, oil and gas, marine
transportation, petrochemical industry etc. It
has advantages over other joining process due
to design flexibility, cost saving, overall
weight reduction and structural performance.
Welded joints have high corrosion resistance
compared to bolted and riveted joints and thus
different variety of joints can be made by
welding. Due to such advantage it is widely
used in boiler, pressure vessels, off structure,
naval vessel and mining machinery of
underground and open cast mines [2].
Welding is considered as an extension of hot
forging which Egyptian and other eastern
Mediterranean used for making weapon and
tools. Modern welding technology was
established in 1800s by an English scientist
Sir Humhrey Davy. In 1801 Sir Davy
observed that electric arc could be struck
between two carbon electrodes. In mid 1800s
Nikolai Benardos, a Russian working on a
laboratory in France was granted a series of
patent for carbon arc- welding process. In
1892 an American, Charles Coffin developed
arc welding using filler and electrode. The
resistance welding such as spot welding and
seam welding were developed by E.
Thompson in between 1885 and 1900 [1].
LITERATURE REVIEW
Welding has eminent effect on mechanical
property of materials due to heat produced
during welding. Some of the properties which
affect the material due to welding are:
1. Tensile property :
Tensile strength is the maximum stress that a
material can sustain in tension. In other words
we can say the amount of applied load per
cross sectional area that a material can
withstand before failure. Mathematically it is
calculated as the ratio of maximum tensile
load to the original cross section area.
As per a research done on AA6061 aluminum
alloy using GMAW (Gas Metal Arc
Welding) it was observed that in GMAW
joints elongation (in length) and reduction in
cross section area were 8.4 % and 5.8 % while
of parent material were 18% and 12.24%. It
suggests that there is reduction of around 53%
in ductility due to GMA welding. The same
material when welded using FSW the
reduction were 14.2 % and 9.56 % [3].
Another test was carried to study effect of Gas
Tungsten Arch Welding (GTAW) on AA6061
T6 alloy by machining the alloy to ASTM E8-
ELK ASIA PACIFIC JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING
ISSN Online: 2394-0425; Volume 1 Issue 2 (2016)
04 standards and welding was done using
AlMg5 as filler alloy wire for welding and
following result was obtained [4].
(Refer table 1)
(Refer figure 1)
From Table 1 and figure 1 we can conclude
that toughness has decreased due to welding
and the tensile strength of the specimen has
reduced about 54% [4].
Tensile test was carried on torr (torsteg) steel
joined by Shielded Metal Arc Welding
(SMAW) and the transverse tensile strength
observed was 524 MPa while that of parent
material was 523 MPa. It is higher than the
minimum specified tensile strength. Similarly
transverse strength for Cu-TMT bar was found
to be 600 MPa which was above the MSTS
(minimum specified tensile strength) [5].
A study was done on rolled plate of ferric
stainless to see the effect of CCGTAW
(continuous current gas tungsten arc welding),
PCGTAW (pulsed current gas tungsten arc
welding) plasma arc welding (PAW), GTAW,
SMAW, GMAW and concluded that the joints
made by the PAW (tensile strength 990 MPa)
were higher by 40 % compared to CCGTAW
(600MPa) and by 35 % to PCGTAW (650).
But there is reduction in strength by 41 % in
case of SMAW and 44 % in GTAW. The
tensile strength of base metal was 524 MPa.
The elongation study of each specimen
showed that PAM joints exhibit higher
ductility than other two types, but less than the
parent material. The elongation in base metal,
PAW joints, CCGTAW joint and PCGTAW
joint was 12 %, 7.5 %, 4.5 % and 6.2 %
respectively, which means there is reduction in
ductility by 62 % and 48 % in CCGTA and
PCGTAW respectively. In SMAW and
GMAW the reduction in ductility were 30 %
and 39 % respectively [6] [7].
The weld joint tensile test was carried on
stainless steel to see the effect of GTAW and
SMAW and found that GTA welds exhibits
greater strength and ductility due to equi-axed
fusion zone grain morphology and protective
nature of the shielding gas. By the addition of
oxygen in the shielding gas in GTAW and
addition of Ar+O2 backing in SMAW reduced
the ductility and strength. The addition of
copper resulted in increase of strength but
reduction in ductility. It has also been
observed that initially with increase in
austenite, strength decreases and with further
increase in austenite content results as increase
in strength [8].
The effect of different welding process on
naval grade High Strength Low Alloy steel
(HSLA) was studied and found that weld
metal was comparatively stronger than the
base metal. The yield strength of all type of
welding joints on HSLA steel was higher than
the base metal and this was associated with
precipitate hardening. The increase in strength
in case of FSW (Friction Stir Welding) was
8% more than the base metal due to fine grains
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of acicular, upper banite and small martensite
region. The comparison between various weld
joints tensile strength can be done from figure
2 [9]. The effect of filler material was
observed using E309L and 18Cr-8Ni-6Mn
(18-8-6) as filler and found that tensile
strength of both weld joints were 1230 MPa
and 1260 MPa respectively which are quite
low compared to base metal (1720 MPa). The
failure has ductile mode. The joint efficiency
was around 72% compared to base metal when
calculated on UTS (Ultimate Tensile Strength)
basis [10].
(Refer figure 2)
Another study made on HSLA HY-80 steel
showed that during tensile test all the
specimens failed at the base metal which
means HAZ (Heat Affected Zone) and weld
metal has higher strength than the base metal.
The yield stress and strain of welded specimen
were 639 MPa and 6.8% respectively and of
the base metal was 577 MPa and 20.7 % [11].
From the study of FSW (friction stir welding)
on ferric stainless steel we can conclude that
ultimate tensile strength of base metal and
welded joint was almost comparable (536MPa
and 574 MPa respectively) when failure occur
in base metal. A notched tensile strength test
was done to know the tensile strength of
friction stir welded joint and was found to be
1030 MPa which is 57% higher than the base
metal [12]. The Friction welded joints showed
ductile mode of fracture and shear failure of
material occurred at the fractured surface [13].
In study of GTA and Laser beam welding on
duplex stainless steel showed that the failure
occurred in the HAZ and they showed ductile
mode of fracture. The UTS of both joints were
less than the base metal by 1 % and was
associated with ferrite – austenite ratio that
resulted due to high cooling rate. The laser
beam welding produces better mechanical
property due to finer grain size [14]. The weld
joint made using low hydrogen ferritic steel
consumables have high tensile strength due to
ferrite presence in the weld metal [15]. A
comparative study was made on stainless steel
joints made by TIG, Laser and Laser –Tig
hybrid welding and it was observed that TIG
welded joint showed a cup-cone shaped
fracture while Laser and Laser-TIG hybrid
showed shear fracture. The tensile strength for
TIG Laser and Laser-TIG hybrid were 560,
733 and 683 MPa respectively [16].
2. Hardness
The ability of materials to resists penetration,
abrasion, scratching or cutting is known as
hardness. It is the property by which material
resists permanent deformation. Various
hardness tests are available such as Rockwell
Hardness Test, Vickers Hardness Test, Brinell
Hardness Test, Knoop Hardness Test,
Scleroscope Test and Durometer Test. In
Rockwell Hardness test a cone shape indenter
ELK ASIA PACIFIC JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING
ISSN Online: 2394-0425; Volume 1 Issue 2 (2016)
or a small ball is pressed into the specimen.
Similarly Vickers Hardness test and Knoop
Hardness test use Pyramid shaped indenter.
The difference between Vickers and Knoop is
that the later use indenter having length to
width ratio about 7:1. Knoop Hardness Test is
generally done to measure micro hardness
which means measuring small thin specimens
or hard material which might fracture when
heavy load is applied.
Using Vickers Micro hardness testing machine
the hardness value of parent material (AA6061
aluminum alloy) was 105 VHN while of
GMAW and FSW (Friction Stir Welding)
joints was found to be 58 VHN and 85 VHN.
This suggests that the hardness across the
welded section has decreased in the GMAW
specimen and increased in FSW [3].
The effect of hardness with distance has been
checked using Rockwell hardness as per
ASTM E18-05 standards on AA6061 T6 alloy
and the result obtained can be seen in table 2
and figure 3. Hardness is expressed as HRF
which means Rockwell test is carried out at
load of 60 Kgf [4].
(Refer table 2)
(Refer figure 3)
A hardness examination was carried on torr
steel using 10 kg load and found that hardness
vary along the different zones of the specimen
from 146 HV to 236 HV (figure 4). Similarly
for Cu-TMT bar it varied from 256 VHN to
422 VHN (figure 5). The hardness values at
some location in HAZ were found to be
significantly higher in one or two locations.
This shows that weld joints in both of these
show sufficient internal soundness [5].
(Refer figure 4)
(Refer figure 5)
From the hardness examination by Zakaria on
industrial low carbon steel (0.19 wt. % C) it
can be said that maximum hardness was in the
weld metal as well as in the heat affected
zone, which was result of residual stresses just
after welding and grain size etc [17]. The
micro-hardness of different zone can be easily
seen in figure 6.
(Refer figure 6)
Another microscopic observation was done on
HAZ of a weld joint made of 30CrMo5-2 plate
(base metal) using austentic stainless steel
EN160018 8 Mn B22 as filler material and the
result obtained showed that, although filler
material has very low hardness yet when we
move away from the fusion boundary the
hardness value of HAZ increases slightly [18].
The study of friction stir weldment of X80
(0.13 C, 1.52 Mn, 0.26 Si, 0.17 Mo, 0.034 Cr,
0.026 Ni, 0.0002Nb, 0.003 Ti, 0.062 V, 0.041
Al, 0.032 Cu, 0.0003 B) concluded that there
was little softening of HAZ and the overall
hardness of weld area was more compared to
base metal and the hardest zone was TMAZ
ELK ASIA PACIFIC JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING
ISSN Online: 2394-0425; Volume 1 Issue 2 (2016)
(Thermo Mechanical Affected Zone) at the
advancing side. The softening of HAZ was
due to lower peak temperature attained in the
FSW HAZ and the hardness in TMAZ is due
to formation of acicular phases such as LM
and LB. In L80 (steel (0.32 C, 1.20 Mn, 0.35
Si, 0.65 Mo, 1.30 Cr, 0.20 Ni, 0.04 Nb, 0.04
Ti, 0.05 V, 0.04 Al, 0.20 Cu, and 0.0025 B)
hardness of TMAZ was higher compared to
HAZ (figure 7). A comparison was made
between hardness of fusion welding and FSW
on X 80 steel as shown in figure 8 and
concluded that in fusion welding hardest zone
was HAZ while in FSW it was TMAZ [19].
On ferric stainless steel the hardness varied
from 320 HV to 382 HV which is higher
compared to base metal (170 HV) as shown in
figure 9 [12]. The relation of hardness and
post welded banitic structure was studied for
FSW and concluded that hardness increases
almost linearly with decreasing banite-lath and
packet sizes. The maximum hardness was
found in the region of upper banitic structure
and the lowest hardness was in the HAZ. In
the stir zone due to frictional heat and plastic
flow; granular banite and recrystallized eqi-
axed polygonal ferritic structure were formed
in HAZ. In the hard zone classical lath- like
upper banitic structure was formed [20].
In ferric stainless steel the hardness value of
plastic zone (PZ) is higher than partially
deformed zone (PDZ) due to formation of
finer grain size in PZ [13].
(Refer figure 7)
(Refer figure 8)
(Refer figure 9)
A research was done on low carbon steel plate
(SAE 1020 steel) to see the effect of coarse
initial grain size and heat input on
microstructure using heat input for welding as
0.5, 1 and 2 kJ/mm and concluded that lower
heat input (0.5 KJ/mm) resulted in maximum
hardness due to formation of martensite.
While observing effect on Initial Coarse Grain
(ICG) size it was seen that the maximum
hardness was obtained for ICG specimen with
heat inputs of 0.5 and 1 kJ/mm and this was
associated with high carbon, martensite and
banite. As the heat input increased to 2 kJ/mm
there was decrease in the hardness of weld
metal and HAZ due to ductile phases, pearlite
and ferrite formation. For the same heat input
the coarse grain has very little effect in
hardness of weld metal (figure10). The
hardness value from the fusion line of base
metal was decreasing almost linearly, while of
coarse grained one was fluctuating due to
existence of martensite and polygonal ferrite
[21]. The effect of ICG on hardness of inter-
critical HAZ can be observed by figure 11.
The maximum hardness value was associated
with heat input of 0.5 kJ /mm due to the
formation of coarse grain; similarly the
maximum hardness loss was seen with heat
input of 2 kJ/mm due to formation of
polygonal ferrite and fine grain pearlite in
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specimen 1 &2, and fine grain pearlite in
specimen 3. While the hardness of specimens
with heat input 1 kJ/mm was between the
above results [22]. The increase in heat input
is inversely proportional to hardness as
experiment showed when heat input increased
from 5 to 8 kJ/cm and hardness decreased to
148 BHN from 160 BHN [23].
(Refer figure 10)
(Refer figure 11)
In the study of hardness of CCGTAW,
PCGTAW, SMAW, GMAW and PAW
welded ferric stainless steel specimen it was
observed that regardless of the welding
process hardness value of weld region is
greater than HAZ as shown in figure 12 [6]
[7].
(Refer figure 12)
The hardness study of different weld joints of
HSLA steel showed that there was
transformation of banite ferrite with carbide
and acicular ferrite at the weld joint that
resulted into high hardness. The hardness in
case of FSW is higher compared with HAZ
and base metal of parent material due to
plastic deformation, continuous dynamic
recrystallization and fast cooling rate. Due to
micro-segregation of alloying agent the
hardness increased where prior-austenite grain
size was smaller compared to fusion line. [9]
The effect of filler materials E309L and 18-8-
6 showed that the maximum hardness was in
the HAZ and the hardness decreased in from
HAZ to base metal (as shown in figure no13)
and the increased hardness of weld zone may
be associated with the martensite formation
[10]. In HSLA HY-80 steel the weld zone has
higher hardness value (275 HV) than the
parent metal (235 HV), and the maximum
hardness was achieved by SMAW and lowest
by GMAW when comparison was made
between SMAW, GMAW, and Shielded Arc
welding [11]. Another study was done to see
the effect of Nb (Niobium) microalloyed
HSLA steel and found that the parent steel
was harder than the Nb alloyed steel [24].
(Refer figure 13)
The study of hardness on laser beam and GTA
welded joints on Duplex stainless steel
revealed that there is no significance
difference in hardness of WM, HAZ and base
metal in-spite of variation of ferrite and
austenite ratio [14].The welds having acicular
ferrite structure have higher hardness [15].
The examination of microhardenss in
Titanium Aluminide varied with change in
welding speed and heat input. The fusion zone
was wider at low speed and high heat input
(analyzed from figure 14) [25].
(Refer figure 14)
In the study of ferrite morphology of stainless
steel weldment it was concluded that ferrite
distribution in the austentic matrix affects the
stress rupture behavior particularly at elevated
temperature. And the ferritic distribution
mainly depends upon heat input [26].
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3. Microstructure
The structural features such as grain and
phase structure which are subjected to
microscopic observation are called
microstructure. Microstructure is very
useful in study and characterization of
materials. Various microscopic techniques
are Optical microscopy, Electron
Microscopy, Scanning Electron
Microscopy etc.
In AA6061 aluminum alloy the base metal
contains coarse and elongated grain with
uniformly distributed very fine
precipitates, on the other hand in GMAW
the fusion zone have dendritic structure. In
FSW the weld region of FSW contains
very fine equiaxed grains. The dendritic
structure was due to fast heating of base
metal and fast cooling of molten metal
(molten by welding heat) and the fine
equiaxed grain formed in FSW may be due
to dynamic recrystallisation occurred
during welding [3].The microstructure of
AA 6061 T6 alloy was studied using
scanning electron microscopy (SEM) and
found that grain growth took place at HAZ
[4].
In Low alloy steel 16Mo3 the
metallographic observation was made by
an optical microscope Olympus PMG3 for
MMA and MAG joints and following
structure were obtained for different region
as shown in figure15 [27].
(Refer figure 15)
The optical microstructure examination of torr
steel show that the weld metal has refined
polygonal pearlite structure and the HAZ has a
transition to coarse ferrite structure with large
volume of pearlite. Similarly in case of Cu-
TMT bar the weld metal has ferrite –pearlite
structure and the HAZ has Widmanstatten
ferrite structure with some percentage of
banite [5].
From the microscopic examination (figure 16
and 17) of industrial low carbon steel (0.19 wt.
% C) shows that the microstructure of weld
zone and HAZ are different. HAZ contains
widmanstatten ferrite and some colonies of
pearlite, while that of base metal has eqiaxed
ferrite grains [17]. During cooling of the HAZ
first transformation occur as δ-Fe to γ-Fe and
second transformation occur as γ-Fe to α-Fe
transformation [28].
(Refer figure 16)
(Refer figure 17)
Another microscopic observation was done on
HAZ of a weld joint made of 30CrMo5-2 plate
(base metal) using austentic stainless steel
EN160018 8Mn B22 as filler material and the
result obtained showed that there was
tempered martensite in the HAZ as well as
base metal [18].
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A research was done on FSW weldments of
X-80 and concluded that the grain size of
HAZ region and the base metal was almost
same around 5 microns. Grain size increases
up to 30 micron as we advance towards
TMAZ. While in Fusion Welding coarse grain
are present. This shows that the conventional
coarse grain structure has moved to the
advancing side of TMAZ in FSW that were at
fusion line in Fusion Welding. The base metal
of X-80 steel contains ferrite, granular banite
and martensite while HAZ contains ferrite,
granular banite, and lath martensite. TMAZ
contain large fraction of granular banite,
degenerated upper banite and lath martensite.
Similar experiment was carried out for L-80
and observed that coarsening of carbide and
hard martensite were formed at the HAZ and
in TMAZ higher coarse grain of lath
martensite was formed while the base metal
contain mainly tempered carbides [19]. In
ferric stainless steel joined by FSW, due to
rapid cooling and high strain due to plastic
deformation the microstructure changed to
ferrite and martensite [12].
A research was done on low carbon steel to
see the effect of coarse initial grain size on
microstructure and as a result of increase in
heat input the microstructure in weld metal
changed from martensite and banite to grain
boundary ferrite, Widmanstatten ferrite,
acicular ferrite and pearlite. And HAZ
containing martensite, banite, pearlite and
polygonal ferrite changed to pearlite and
polygonal ferrite (as shown in figure 18). The
amount of pearlite has been formed with
decrease in martensite and banite also the
microstructure in the GCHAZ has refined
[21]. The study on intercritical HAZ showed
that the microstructure in fine grained
specimen transformed from grain boundary
ferrite and pearlite to polygonal ferrite, and in
coarse grain it changed from martensite to
ferrite and fine grain pearlite. The ferrite
changed to polygonal in original and coarse
grain specimen and pearlite grains tended to
refine [22]. The microstrucute of the HAZ in
low carbon steel depends on the chemical
composition, the peak welding temperature
and the welding voltage. The amount of
pearlite is inversely proportional to heat input
[23]. The welded region in high strength steel
contains acicular ferrite and pro eutectic ferrite
on boundary at low heat input while at higher
heat input the ferrite side is the main phase
[29].
(Refer figure 18)
In weldability study of Titanium Aluminide it
was found that the microstructural
characteristics of weldment were function of
welding speed, heat input and cooling rate. At
low welding speed (low cooling rate or high
heat input) fine acicular were formed and at
high welding speed (high cooling rate or low
heat input) β and ordered β were formed. The
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microstructure in HAZ gradually varies from
fusion line to far HAZ [25].
The microstructure of GCHAZ in HSLA steel
showed that with decrease in heat input the
fraction of baintite increase and ferrite
decrease by volume. At 30 kJ/cm only fine
lathe bainite and at 60kJ/cm only granular
banite was formed [24]. In comparative study
between TIG, laser and TIG –laser hybrid
welding showed that only in TIGW transition
zone and HAZ were present [16].
4. Toughness
The ability of materials to absorb
energybefore fracture is called toughness. The
area under stress strain curve gives toughness.
Izod and Charpy test are most common
method to find toughness of material.
V notch Charpy impact test on HAZ was
carried for low alloy 16Mo3 and found that
MMA and MAG welded specimen has value
136 J and 89 J while that of base metal have
31 J, which means toughness has increased
after welding [27].
The charpy test carried on torr steel and Cu-
TMT bar suggest that SMAW joints on these
materials posses sufficient toughness at room
temperature and 00 C, but as the temperature
drops down below 00 C the steels are
susceptible to brittle fracture. CIT (Charpy
Impact Test) of torr steel for Parent Metal
show drop down from 117 J at 260C to 7.8 J at
00C, it shows high ductile -brittle transition in
the temperature range of 250 C. [5].
In friction stir welding of ferric steel the
toughness decreased in weld centre line (28 J)
and HAZ (30 J) compared to base metal (34 J)
[12].
The research was carried out in low carbon
steel SAE 1020 steel and SAE 1020 steel with
coarse initial grain size (CIG steel) for finding
toughness at different heat input showed that
maximum toughness at weld metal for both
steel were achieved with 1 kJ/mm due to
presence of tougher acicular ferrite. On the
other hand due to martensite formation at heat
input of 0.5 kJ/mm, minimum toughness was
obtained and there was small decrement in
weld metal at 2 kJ/mm due to coarsened phase
(figure 19 and 20). In the same way for HAZ it
was seen that maximum toughness of base
material was observed at 1 kJ/mm and for CIG
steel at 2 kJ/mm. The maximum toughness is
associated with ductile phase’s ferrite and
pearlite. The minimum toughness was
observed with heat input 0.5 kJ/mm. In CIG
steel compared to base metal the loss of
toughness is more due to high carbon
martensite formation [21]. The toughness of
steel can be controlled by varying welding
parameters. Toughness varied from 92.3 to
40.8 kJ as welding condition varied from
130A/20V to 180 A/30V as in figure 19 [23]
[30].
(Refer figure 19)
(Refer figure 20)
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(Refer figure 21)
The toughness of PAW joints were 20 J
comparable to base metal (22 J) while of
PCGTAW and CCGTAW were less than base
metal and PAW joints. There was decrease in
SMAW by 18% and in GMAW by 27% [6]
[7].
Due to presence of martensite –austenite and
ferrite lath in banitic mixture in the GMA
weld zone of HSLA steel the toughness has
enhanced. But in FSW joints the presence of
martensite lowers the toughness [9]. The
charpy V notch test showed that toughness of
HAZ region matched with base material when
309L and 18-8-6 filler materials were used,
however toughness of joint made E309L filler
material was greater by factor of 3/2 [10].
The presence of nickel and austenite phase in
the weld metal leads to more toughness [15].
Due to auto tempering low carbon martensite
has higher toughness than upper banite [31].
The toughness of HSLA depend on
temperature and it increases almost linearly
with the heat increase in temperature as the
experiment showed variation from 55 J to 125
J when temperature changed from -50C to 00C
[32].
CONCLUSION
From the above study following conclusions
were drawn:
For ferrous as well as non ferrous
material there is decrease in tensile
strength when fusion welding (except
PAW) is employed.
FSW increases the tensile strength to
some extent.
Higher the ferrite content higher is the
Tensile strength.
The decrease in tensile strength
depends on the electrode material,
filler material, welding speed, heat
input.
The parent material and the welding
process decide whether failure will
occur in base material or weld zone.
Almost all experiment showed ductile
mode of failure.
In all the research the hardness of the
weld zone was greater, followed by
HAZ and base metal due to martensite
and banite formation.
Hardness increases with decrease in
heat input, also the hardness depend on
the composition of filler material.
The weld zone is wider for low speed
welding.
Martensite and banite is mainly present
in weld area and HAZ. The
microstructure transformation depends
on heat input. The amount of peralite is
inversely proportional to heat input.
The toughness of material is associated
with pearlite and ductile ferrite phases.
The filler material constituents also
decide the toughness of the welded
ELK ASIA PACIFIC JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING
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joints.
ACKNOWLEDGEMENT
Authors are thankful to Director, CSIR-
CIMFR, Dhanbad for his kind permission to
do the experimentation with reference to our
post-graduation research work and
publication thereof.
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LIST OF TABLES
Table 1: Tensile property for welded and un-welded specimen of AA6061 T6 [4].
Table 2: Hardness value for welded specimen[4].
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LIST OF FIGURES
Figure 1: Stress – Strain relationship for welded and un-welded specimen of AA6061 T6alloy [4].
Figure 2: Load vs. displacement curves of Parent Metal and welded joints [9].
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Figure 3: Hardness profile for welded area and away from the weld [4].
Fig 4: Hardness profile of torr steel [5]. Fig 5: Hardness profile of Cu TMT steel
[5].
Figure 6: Hardness measurement on surface across the weld metal of industrial low carbon steel [17].
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Figure 9: Hardness profile of friction stir welded 409M ferritic stainless steel [12].
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Figure10: Hardness measurement result with heat input a) 0.5, b) 1 c) 2 kJ/mm [21].
Specimen 1 SAE 1020 steel (base metal)
Specimen 2 SAE 1020 steel with coarse initial grain size
Figure11: Relationship between hardness value of intercritical HAZ and heat input [22].
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Figure 12: Hardness value across weld in ferric stainless steel due to different welding process [6][7].
Figure 13: Hardness profile of HSLA using a) 309L filler b) 18-8-6 filler [10].
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Figure 14: Microhardness variation of Titanium aluminide Electron Beam weldments made at three
welding speeds and heat inputs [25].
Figure 15: Microstructure of different zone for a) MMA joints b) MAG joints [27].
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Figure 16: Microstructure of HAZ after welding of an industrial low carbon steel [17].
Figure 17: Center of weld metal “in the weld fusion zone”[17].
Figure 18: The formation of microstructure in GCHAZ in SAE 1020 steel with coarse initial grain
size for a heat input 0.5 kJ/mm [21].
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Figure 19: Variation of temperature with current and voltage [23].
Figure 20: Relationship of weld metal toughness vs heat input (B, base metal) [21].
Figure: 21Relationship between toughness of HAZ and heat input (B,base metals) [21].
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