FIELD OF THE INVENTION
The present invention relates to metal processing, more particularly, the
present subject matter is associated with optimization of parameters in multi-
pass MIG welding of steel plates of L&E grade having 8-12 mm thickness.
BACKGROUND OF THE INVENTION
When welding together steel plates to construct a welded structure, to
reduce the construction costs or improve the welding work efficiency, usually
the large heat input welding method is used, but in a welded joint formed by
the large heat input welding method, the weld heat affected zone
(hereinafter sometimes referred to as the "HAZ") falls in toughness. Further,
the HAZ increases in width and the fracture toughness value (indicator
relating to brittle fracture) also falls.
Lifting and excavating equipment should be reliable and strong as per
application requirements. The assembly of different functional parts of large
equipment often requires welding. Narrow-gap welding procedure is often
adopted for joining of thick plates as it provides several advantages such as
shortening of welding time, less consumption of consumables and reduction
of weld metal resulting in higher efficiency and better mechanical properties
of the weld zone.
However, lack of fusion and insufficient penetration remains the key
challenges in a narrow-gap welding. HAZ softening or lower toughness in
HAZ due to grain growth on the other hand remains a general issue in
GMAW process. Therefore, optimization of the welding parameters to attain

superior toughness is a challenge in thick plates because of (a)
microstructure variations in the weld joint under the influence of multiple
thermal cycles and (b) improper side wall fusion in the welds. Further the
mechanical properties at the fusion zone and heat affected zone (HAZ) are
significantly different from the base metal as they have different thermal
history. The toughness of the HAZ can be studied with help of fracture
toughness measurements on samples extracted from the HAZ.
OBJECT OF THE INVENTION
The prime objective of the present invention is to develop a method for
obtaining defect free weld with improved fracture toughness of HAZ (twice
that of weld and base metal) by tweaking the weld parameters which can be
easily adoptable in practice.
Another object of the present invention is to do away with any costly and
time-consuming post weld heat treatments for improving the mechanical
properties of the heat affected zone.
Still another object of the present invention is to leverage the benefits of
narrow gap welding to reduce heat input, number of consumables and
welding time of thick plates while resolving the issues of lack of side wall
fusion in the weld.
A further object of the invention is to engineer the microstructure of heat
affected zone to achieve fine grain size so as to obtain good toughness,

avoiding grain growth and HAZ softening which are typical issues in multi-
pass MIG welding of thick plates.
SUMMARY OF THE INVENTION
The present disclosure relates to a method for multi-pass MIG welding of a
plurality of steel plates by an MIG welding arrangement. The method
including arranging the plurality steel plates in a butt joint configuration;
clamping the plurality steel plates to a welding table with a rigid clamping
arrangement; operating the MIG welding arrangement in a synergic mode
for a root pass of the steel plate with voltage 25±1 V, current 240±5 A,
travel speed 300± 20 mm/min, wire feed rate 4 mm/sec, root gap 2 mm,
nose height 2 mm, gas flow rate 12 lit/min; operating the MIG welding
arrangement for a first pass with voltage 28.1±1 V, current 260±5A, travel
speed 219±20 mm/min, wire feed rate 5 mm/sec, root gap 2 mm, nose
height 2 mm, gas flow rate 12 lit/min; and operating the MIG welding
arrangement for a second pass with voltage 22.6±1 V, current 250±5 A,
travel speed 355±20 mm/min, wire feed rate 4 mm/sec, root gap 2 mm,
nose height 2 mm, gas flow rate 12 lit/min.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more apparent from
the ensuing description when read in conjunction with the accompanying
drawings of the exemplary embodiments and wherein:
Figure 1 shows - illustrates an MIG welding arrangement.

Figure 2 shows - the MIG welding arrangement of Fig. 1 provided with a
welding torch 202
Figure 3 shows - illustrates a schematic showing the single bevel
configuration associated with the steel plates
Figure 4 shows - illustrates a method for multi-pass MIG welding on the
steel plates
Figure 5 shows - Cross section of the weld showing the weld profiles
Figure 6 shows - Illustration of fine grain HAZ between fusion zone and
the base metal
Figure 7 shows - Illustration of area from where the specimen for fracture
toughness were machined
Figure 8 shows - Specimen geometry for J-R testing
Figure 9 shows - J-R curve for fusion zone (FZ)
Figure 10 shows - J-R curve for base metal (BM)
Figure 11 shows - J-R curve for heat affected zone (HAZ)
Figure 12 shows -J-R curve for HAZ, FZ and base metal – compared
simultaneously
The figure(s) depict embodiments of the present subject matter for the
purposes of illustration only. A person skilled in the art will easily recognize
from the following description that alternative embodiments of the structures
and methods illustrated herein may be employed without departing from the
principles of the disclosure described herein.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING
DRAWINGS
The present invention now will be described more specifically with reference
to the following specification.
It should be noted that the description and figures merely illustrate the
principles of the present subject matter. It should be appreciated by those
skilled in the art that conception and specific embodiment disclosed may be
readily utilized as a basis for modifying or designing other structures for
carrying out the same purposes of the present subject matter. It should also
be appreciated by those skilled in the art that by devising various
arrangements that, although not explicitly described or shown herein,
embody the principles of the present subject matter and are included within
its spirit and scope. Furthermore, all examples recited herein are principally
intended expressly to be for pedagogical purposes to aid the reader in
understanding the principles of the present subject matter and the concepts
contributed by the inventor(s) to furthering the art, and are to be construed
as being without limitation to such specifically recited examples and
conditions. The novel features which are believed to be characteristic of the
present subject matter, both as to its organization and method of operation,
together with further objects and advantages will be better understood from
the following description when considered in connection with the
accompanying figures.
These and other advantages of the present subject matter would be
described in greater detail with reference to the following figures. It should

be noted that the description merely illustrates the principles of the present
subject matter. It will thus be appreciated that those skilled in the art will be
able to devise various arrangements that, although not explicitly described
herein, embody the principles of the present subject matter and are included
within its scope.
Fig. 1 illustrates an MIG welding arrangement 100 configured for welding a
plurality of steel plates 102. In an embodiment, the plurality of steel plates
102 are 8-12mm thick and are welded in butt joint configuration. The steel
plates 102 have the composition range of 0.1 wt % or less of C, 1.5 wt % or
less of Mn, 0.005 to 0.05 wt % of Ti, 0.01 to 0.05 wt % of Nb, 0.005 to 0.05
wt % of Al with a semi-automatic MIG welding arrangement 100. In an
embodiment, as is evident from Fig. 1, the plurality of steel plates 102 are
cut into rectangular sections of 150 mm by 300 mm, and are provided with
Single bevel groove with a groove angle of 45º. The configuration as shown
in Fig. 1 ensures a straight heat affected zone (HAZ).
Fig. 2 illustrates the MIG welding arrangement 100 provided with a welding
torch 202 configured for welding of the steel plates 102. In an embodiment,
a 500 mm long welding torch 202 of MIG welding machine Fronius TPS-
3200 is used in the MIG welding arrangement 100. The welding filler wire
used in the MIG welding arrangement 100 is specified as per AWS SFA5.1
ER70S-6 of 0.8 mm diameter solid wire with a shielding gas mixture of argon
and carbon dioxide in a ratio of 82% and 18% respectively.
As shown in Figs. 1 and 2, the steel plates 102 are held tightly to a welding
table 104 with a rigid clamping arrangement 106 to avoid any misalignment

between the steel plates 102 due to thermal stress during welding process. A
copper backing with a slot arrangement is provided with the welding
arrangement 100 to avoid any burn through. Further, the welding torch 202
angle is controlled, as it is essential in narrow gap welding to achieve
appropriate fusion between the side walls of the steel plates 102.
Fig. 3 illustrates a schematic showing the single bevel configuration
associated with the steel plates 102. In an embodiment, the welding torch
202 angle is kept between 20º-25º (from vertical) with a stick out distance of
10-15 mm and a contact tip to work distance of 8 mm. The welding was
carried out in three steps. The heat input at the root pass was in the range
of 10-15 kJ/cm. The heat inputs at the 2nd and 3rd pass were in the range
of 20-25 kJ/cm and 8-12 kJ/cm respectively. The accumulated slag particles
were removed with a metallic brush between subsequent passes to ensure
proper fusion. As shown in Fig. 3, the nose height is 2 mm and root gap is
kept at 2mm with respect to the single bevel configuration associated with
the steel plates 102.
The welding of the steel plates 102 via the welding arrangement 100 is
carried out in three steps or passes. The heat input at the root / 1st pass is in
the range of 10-15 kJ/cm. The heat input at the 2nd and 3rd pass is in the
range of 20-25 kJ/cm and 8-12 kJ/cm respectively. The accumulated slag
particles are removed with a metallic wire brush between subsequent passes
to ensure proper fusion among the steel plates 102.
In an embodiment, Fig. 4 illustrates a method 400 for multi-pass MIG
welding on the steel plates 102 of 8-12mm thickness in the butt joint

configuration. At step 402, the method 400 includes arranging the steel
plates 102 in the butt joint configuration. In an embodiment, the steel plates
102 are arranged in half K joint design configuration with an included angle
of 45 deg. At step 404, the method 400 includes clamping the steel plates
102 to a welding table 104 with a rigid clamping arrangement 106. At step
406, the method 400 includes operating the MIG welding arrangement 100
in a synergic mode for a root pass of the steel plate with voltage 25+1V,
current 240+5A, travel speed 300+20 mm/min, wire feed rate 4 mm/sec,
root gap 2mm, nose height 2mm, gas flow rate 12 lit/min.
At step 408, the method 400 includes operating the MIG welding
arrangement 100 for a first pass with voltage 28.1+1V, current 260+5A,
travel speed 219+20 mm/min, wire feed rate 5 mm/sec, root gap 2mm, nose
height 2mm, gas flow rate 12 lit/min. At step 410, the method 400 includes
operating the MIG welding arrangement 100 for a second pass with voltage
22.6+1V, current 250+5A, travel speed 355+ 20 mm/min, wire feed rate 4
mm/sec, root gap 2mm, nose height 2mm, gas flow rate 12 lit/min.
The following Table 1 provides welding parameters associated with the
method 400 for welding of the steel plates 102.



The welded joint of the steel plates 102 based on the method 400 is
characterized by optical microscopy carried out on a metallographically
prepared cross-sectional plane as shown in Fig. 5. The resulting photo-
micrograph has been presented in the Fig. 6. Three different zones such as,
base metal (BM), heat affected zone (HAZ) and fusion zone (FZ) are clearly
visible in the Fig 6.
Further, the present subject matter provides fracture toughness assessment
associated with specimens prepared from the steel plates 102 based on the
method 400. The specimen includes a three-point single-edge bend, [SE(B)]
prepared according to ASTM –E1290 standard [refer Fig. 7] from the steel
plates 102 [refer Fig. 8].
An initial notch of length equal to 0.40w was machined by electro discharge
machining (EDM) where w stands for the width of the specimen.
Subsequently, fatigue pre-cracking was done to attain a length to width ratio
of a0/w≈ 0.5 where a0 stands for the initial crack length of the specimen.
Side grooves were cut into both the faces of the sample along the pre-crack
to introduce sufficient constraint to minimize plastic deformation.
Single specimen technique was adopted for obtaining the Load vs. Crack
Mouth Opening Displacement (CMOD). A clip gauge of 5 mm gauge length
and 12 mm travel length was used for measurement of crack mouth opening
displacement. The specimens were then loaded monotonically until fracture

with partial unloading at regular intervals during the test in a displacement
control mode with a cross head speed of 0.008 mm/min. Unloading
compliance method was used to monitor the crack growth during the
loading–unloading cycles. The fracture toughness parameter J is then
calculated at several intervals of loading unloading sequences of the load vs.
CMOD curve.
The J-value was determined combining the elastic and plastic contributions
of strain energy associated with a cracked body. This is obtained from the
load-CMOD curve under Mode-I deformation as follows,
J= Je + Jp
Where, the elastic component Je is obtained from
Je=KI2/E
Where KI is the Mode-I stress intensity factor and E is elastic modulus.
The plastic component Jp is given as
Jp=ηJAp/bB
Where, ηJ is non-dimensional parameter, Ap is the plastic area under load-
CMOD curve, b is the effective thickness and B is the width of the specimen.
A least squares curve is then fitted through the plot of J versus the change in
crack length to construct the J-R curve. The intersection of the regression
line with the offset line is considered as Jp – which is considered as fracture
toughness of the material.
The J-R curves constructed from load-CMOD data originated from fusion
zone (FZ), base metal (BM) and heat affected zone (HAZ) are shown in Fig.

9 – Fig. 11 respectively. Fig. 12 represents all three J-R curves in a
superimposed manner for easy comparison.
It is to be noted that the present invention is susceptible to modifications,
adaptations and changes by those skilled in the art. Such variant
embodiments employing the concepts and features of this invention are
intended to be within the scope of the present invention, which is further set
forth under the following claims.

WE CLAIM:
1. A method (400) for multi-pass MIG welding of a plurality of steel
plates (102) by an MIG welding arrangement (100), the method
(400) comprising:
arranging the plurality steel plates (102) in a butt joint
configuration;
clamping the plurality steel plates (102) to a welding table (104)
with a rigid clamping arrangement (106);
operating the MIG welding arrangement (100) in a synergic mode
for a root pass of the steel plate with voltage 25+1V, current
240+5A, travel speed 300+20 mm/min, wire feed rate 4 mm/sec,
root gap 2mm, nose height 2mm, gas flow rate 12 lit/min;
operating the MIG welding arrangement (100) in a first pass with
voltage 28.1+1 V, current 260+5 A, travel speed 219+20 mm/min,
wire feed rate 5 mm/sec, root gap 2 mm, nose height 2 mm, gas
flow rate 12 lit/min; and
operating the MIG welding arrangement (100) in a second pass
with voltage 22.6+1V, current 250+5A, travel speed 355+ 20
mm/min, wire feed rate 4 mm/sec, root gap 2mm, nose height
2mm, gas flow rate 12 lit/min.
2. The method (400) as claimed in claim 1, wherein the plurality steel
plates (102) are of Lifting and Excavation (L&E) grade.

3. The method (400) as claimed in claim 1 and 2, wherein the
plurality steel plates (102) are 8-12 mm thick.
4. The method (400) as claimed in claim 1, wherein the MIG welding
arrangement (100) includes Fronius TPS- 3200 welding machine.
5. The method (400) as claimed in claim 1, wherein the plurality of
steel plates (102) are arranged in half K joint design configuration
with an included angle of 45 deg.
6. The method (400) as claimed in claim 1, wherein toughness of
heat affected zone (HAZ) associated with the plurality of steel
plates (102) after welding is twice of that of base metal and fusion
zone.
7. The method (400) as claimed in claim 1, wherein the plurality of
steel plates (102) have composition range of 0.1 wt % or less of C,
1.5 wt % or less of Mn, 0.005 to 0.05 wt % of Ti, 0.01 to 0.05 wt
% of Nb, 0.005 to 0.05 wt % of Al.
8. The method (400) as claimed in claim 1, wherein operating the
welding arrangement (100) includes welding done by a welding
torch (202).

9. The method (400) as claimed in claim 8, wherein a torch angle of
the welding torch (202) with respect to the plurality of steel plates
(102) is 20º-25º.