Effect of Welding Parameter of welded joint of stainless steel 304 by TIG

welding
Manabendra Saha
Department of Mechanical Engg,
ABES Engineering College Ghaziabad-201009(UP)
Email: manabendra.saha@abes.ac.in

Abstract
Due to excellent welding joint quality, TIG welding process is extensively used for joining stainless steel. In
this paper an experiment was conducted with the help of some major input parameters. The values of the
parameters were selected on the basis of material characteristics and equipment available in the industry for
experimentation.

DOE (Design of experiments) was used for conducting the experiments. Optimum welding
parameter were determine for improving strength. UTS (Ultimate tensile strength) have been carried out to
evaluate the best process parameter for given stainless steel. A microstructural study was also conducted for
better understanding. Welding of stainless steel SS304 by using optimized parameters resulted in improvement
in joint tensile strength 7.36 %.

KEY WORDS: TIG welding, Optimization Technique, Stainless Steel.

INTRODUCTION
Manufacturing process have been developed in a wide range, in ordered to produce engineering components
of very simple to complex geometrics of different physical, chemical, mechanical and dimensional properties.
Welding is a process of joining metallic or other components with or without application of heat, with or
without pressure, with or without filler materiel in which -coalescence of the joining material occurs.
Stainless steel is a complex group of irons based alloys with at least 10.5% Chromium and maximum of 1.5%
carbon, usually along with Nickel. Chromium makes stainless steel corrosion resistance. Nickel is the main
element varied with in the alloys of this class while carbon is kept to low level.
There are a number of statistical techniques available for engineering and scientific studies. Taguchi method
have become increasingly popular in recent year. Taguchi analysis begins with the question of how to define
quality. This method involves reducing the variation in a process through robust design of experiments. Design
of experiment is a power full statistical techniques for improving product design and solving production
problems. The objective of the method is to produce high quality product at low cast to the manufacturer. It is
designed to investigate how different affect the mean and variance of a process performance characteristic. It
involves using orthogonal arrays to organized the parameters affecting the process and the levels at which they
should be varied instead of having to test all possible combination like the factorial design, the Taguchi method
tests pairs of combination. In the present work, some aspects of TIG of AISI 304 austenitic stainless steel have

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been studied. To identity the effect of some selected input parameters (welding current, gas flow rate and arc
gap) on the quality of butt welded joint

Many researchers have investigated the effect of input parameters on mechanical properties of TIG welded
Stainless steel. R. Kumar [1] investigated the welding behaviour of 304 stainless steel sheet metal in term of
joint strength and Microstructure. S. G. Nayee et al. [2] investigated the “effect of activating of activating
fluxes on mechanical and metallurgical Properties of dissimilar activated flux tungsten inert gas welds”. Effect
of current, welding speed, joint gap and electrode diameter on weld bead dimensions on 6 mm thick dissimilar
weld between carbon steel to stainless steel, was studied under activated flux-tungsten inert gas welding
process. J. Van Den Bosch [3] investigated to join and assess the development of gas tungsten arc welding
(GTAW) on dissimilar materials like austenitic stainless steel and low carbon steel.I. A. Ibrahim et al. [4]
discuss about the mechanical properties of austenitic stainless steel for the process of TIG welding. As with
other welding processes such as GTAW shielding gases are necessary and used to protect the welding area
from atmospheric gases such as nitrogen and oxygen.S. C. Juang et al. [5] proposed to study influence
parameters affecting to mechanical property of austenitic stainless-steel grade 304 (AISI 304) with Gas Metal
Arc Welding (GMAW). J. Yan et al. [6] performed TIG welding of structural steel plates of different thickness
with welding current in the range of 55-95 A, and welding speed of 15-45 mm/sec.Predict the weldment
microstructure zone, weld bead.D. Li et al. [7] proposed a double shielded TIG method to improve weld
penetration and compared with the traditional TIG welding method under different welding parameters i.e.
welding speed (90-300) mm/min, current (100-200) A and thickness of work piece 10 mm. N. Arivazhagan
[8] investigated the effect of activated TIG process on weld morphology, angular distortion, delta ferrite
content and hardness of 316 L stainless steel by using different fluxes like TiO2, MnO2, MnO3, SiO2 and
AlO3.M. Gurram et al. [9] investigated the influence of heat input on microstructure and corrosion resistance
of duplex steel welds in pulse generated GTAW process. The corrosion resistance was carried with 3.5% of
Nacl solution by potentiostatic polarization test at room temperature. Y. Morishima et al. [10] investigated
the fatigue behaviour of weld joints treated by the TIG dressing and ultrasonic peening under variable
amplitude load. From this investigation, they concluded that the effect of both TIG dressing and ultrasonic
peening were to be less under variable amplitude than under constant loading.

2.2 CONCLUDING REMARK

Research works have been done in the field of austenitic stainless steel. Several aspects in this context have
been investigated. Literature survey, as given above indicates that the research is still going on. Literature
survey suggests that there is a need of further extensive research in the area of TIG welding of austenitic
Stainless steel for improvement of UTS as well as microstructure. More extensive research may lead to develop
a sound knowledge base which will help in understanding of various aspects relating to austenitic stainless-
steel welding.

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3. PROBLEM FORMULATION

The S.K. Steel fabrication Pvt. Ltd, Sahibabad. is engaged in fabricating Hoardings of advertisement. The
company uses 304 stainless steel for making structures for hoardings of advertisements. The size of the
hoarding frame ranges from 3′ x 9′ to 10′ x 15′. The Company uses tubular structure of square or circular cross
section for fabricating the hoarding frames.
TIG welding is used in the fabrication. It has been observed that after a period of around 6 to 12 months, the
hoarding frame structures develop cracks at corners. As the cracks progress the whole structure breaks down
and causes economic as well as business loss to the company. The company has to fabricate and erect another
hoarding for the client as early as possible. This is a major concern to the company and therefore the company
wants the problem to be investigated and solved.

3. METHODOLOGY
By taking various reviews under consideration. There is certain methodology which is being adopted by us to
formulate steps hoping for the optimum result.
The following steps were followed for completing the task.
a. Study of the existing fabrication
b. Giving the shape of the specimen
c.Design of experiments
d.Joining process
e.Conducting UTS process
f. Microstructural study
g.Analysis of result.
h.Validation.
To perform the experiments firstly the two same size of the materials (SS304) is to be joined by TIG welding.
9 specimens were prepared for conducting the experiments as orthogonal array was developed on the basis of
design of experiments (DOE). The chemical composition is shown in the table 1.
Table 1 Composition of SS304
Type C Mg Ph Cr Ni S Si

304 0.08 2.00 0.045 18-20 10-12 0.03 0.75

The main aim of this paper to investigate the behaviour of strength of welded joint by varying the parameters
like current, gas flow and electrode diameter.
Taguchi design of the experiment under DOE is a optimization technique which is used for reducing the no of
conducting experiments. In this experiment, the three factors were selected with their levels are shown in the
table no 2. Depending on different process parameters, the joint was prepared. Nine specimen with unique

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dimension was ready for tensile test. specimens are fabricated as per standard (ASTM) and a test specimen is
shown in fig 1.

Figure 1 Specimen with ASTM standard

Table 2 Levels and Parameters

Symbol Welding parameter Level 1 Level 2 Level 3

A Current (ampere) 90 150 180
B Gas flow rate(Litre/min) 10 12 14
C Filler rod diameter (mm) 1.8 2.4 3.2

In the present experimental work, an L9 Orthogonal Array with 3 rows and 3 column was used. This array
can handle three level process parameters. Nine experiments were conducted to study the process
parameters using the L9 OA.OA and the corresponding values of process parameters are listed in Table
3.

Table 3 Response Table

Gas flow Filler rod UTS

Current Load S/N
Ex. No. rate diameter value
(A) (N) ratio
(mm3/min) (mm)
1 90 10 3.2 38750 431.71
91.76543414
2 90 12 2.4 40396 444.40
92.22384122
3 90 14 1.8 36250 425.17
91.18616022
4 150 10 2.4 37850 442.30
91.56131768
5 150 12 1.8 37580 422.81
91.49913552
6 150 14 3.2 39650 431.91
91.96486383
7 180 10 1.8 38150 406.50
91.62989085
8 180 12 3.2 38250 428.23
91.65262879

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 9 180 12 2.4 30850 382.10
89.78510337

Regardless of the category of quality characteristic a greater S/N ratio corresponds to better quality
characteristics. Therefore, the optimal value of process parameter was those for which greatest S/N ratio
are obtained. The S/N response ratio for ultimate tensile strength. The figure 2 shows main effects plot
for S/N ratio.

Main Effects Plot for SN ratios

Data Means
current gas flow rate
91.8

91.6

91.4
Mean of SN ratios

91.2

91.0
90 150 180 10 12 14
elec. dia.
91.8

91.6

91.4

91.2

91.0
1.8 2.4 3.2

Signal-to-noise: Larger is better

Figure 2 Main Effects Plot for S/N Ratios

From S/N ratio, Noise factors are those uncontrollable factors which affect the process result (Output),
whereas final response is known as the signal. The variation of the index is known as S/N ratio. Variations
are usually three types i, e “lower is better”, “higher is better’’ and “Normal is better”. In the Present study
depending upon the criteria Ultimate tensile strength (UTS), Ultimate tensile strength (UTS) consider as
“higher is better’’. In order to evaluate the influence of each selected factor on the response, S/N ratios for
each control factor was calculated.

Table 4 Response Value

Symbol Parameter Level 1 Level 2 Level 3
A Current 91.73 91.68 91.02
B Gas flow rate 91.65 91.79 90.98
C Filler rod diameter 91.44 91.19 91.79
RANK 1 2 3

The optimum solution for the combination is A1B2C3.

Means Current = 90 A Gas flow rate = 12 Litter/min
Filler rod diameter = 3.2 mm.

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 Figure 3 Cut Piece of Weld Joint

4. MICROSCOPIC ANALYSIS
For microstructure analysis, all HAZ and weldment area microstructures exhibit almost the same behaviour
(Figure). The grain looked coarser. This occurred due to when weld cooling rates are moderate, or when
the Cr is low but still within Ferrite Austenite (FA) range, skeletal ferrite morphology appeared. The figure
5.2 show as the cut piece of welded joint specimen for micro structure testing.

The figure 4 shows the microstructure of parent metal.

Figure 4 microstructure of parent metal.

5. ANOVA Analysis
Analysis of variance (ANOVA) was used to investigate the effects of various design parameters on microwave
curing characteristics. The analysis was carried out at 95% confidence level. ANOVA result for Ultimate
tensile strength (UTS) is given in table 5, shows that gas flow arte has the most significant effect with 94%,
while Current and filler rod diameter having least effect.
Table 5 ANOVA Table
Welding Mean of
Symbol DOF Sum of Square Fisher Ratio P Value
Parameter Square
A Current 2 1105.75 802.87 3.37 .028
B Gas flow 2 491.31 195.65 1.07 .943
Filler rod
C 2 4.73 1.364 0.01 .365
Diameter
Error ------------- 18 3304.43 183.57
Total ------------- 26 4906.22 1183.45

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6 CONCLUSIONS

The present work was aimed at minimizing the defect in weld joint in Stainless Steel SS304 for improving
strength and durability of hoarding structures. Following conclusion were drawn from experiment and analysis
of result.

i. Welding parameters Current (A), Gas flow rate (B) and electrode diameter (C) are major parameters which
affects the quality of weld joint. For each parameter, three levels were taken for experiments.
ii. The optimum parameters combinations for Ultimate tensile strength (UTS) differed only in terms of current
for optimum Ultimate tensile strength (UTS) a higher value of current 90 Ampere (A) was found to be suitable.
Therefore, the optimum combination for UTS (A1B2C3) i.e. Current 90 A, Gas flow rate 12 m/min, Filler rod
diameter 3.2 mm was selected.
iii. The tensile strength from 444.40 N/mm2 to 449.40 N/mm2
iv. The quality of weld joint was also checked for internal structure using microscopic testing. The result shows
carbon grains play a major role for optimum weld strength.

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