1. 1
Development of Activated Flux for Tungsten Inert Gas Welding
of 304L(N) Austenitic Stainless Steel
V. Ramasubbu, S.K. Albert, A.K. Bhaduri and S.K. Ray
Materials Technology Division, Indira Gandhi Centre for Atomic Research,
Kalpakkam – 603102
e-mail:vrsubbu@igcar.ernet.in
Abstract
Tungsten inert gas (TIG) welds of the 300 series of austenitic stainless steels have
relatively poor weld bead penetration characteristics, thereby limiting the thickness of
plates/tubes that can be autogenously welded. However, use of activated fluxes can
significantly increase the depth of penetration during autogenous TIG welding. Hence, an
experimental programme was initiated to develop activated TIG (A-TIG) welding process that
uses an activated flux to improve weld penetration. Many trials were carried out by varying
flux composition and welding parameters and based on the results from these trials an
optimised A-TIG flux formulation was developed. Defect free full penetration welds could be
prepared from 8 mm thick AISI 304LN plates with this flux applied on the top surface of the
square butt joints and without any filler addition using TIG process in a single pass. Properties
of the weld joints prepared by A-TIG process were subsequently compared with those of the
weld joints prepared using conventional TIG process. For this weld joints were prepared from
10 mm thick plate. Since it was not possible to achieve full penetration from a single pass
using A-TIG process, welding was completed in two passes, one from each side of the joint.
For conventional joint, a weld groove was machined out and ER308L filler wire was used as
consumable. Tensile tests, impact tests, microstructural examination, delta ferrite
measurements, inclusion measurement and corrosion tests etc. were carried on both the weld
joints. All the results showed that the properties of weld joints prepared using A-TIG is
comparable to those prepared using conventional TIG process. Thus, the results show that the
A-TIG process is a good technique that could be used to weld thin section stainless
components that can lead to substantial saving with respect to machining cost, cost of welding
consumables and time.
1. 0 Introduction
AISI 300 series austenitic stainless steels particularly 304 & 316 are used as major
components like structural materials of nuclear industry because of their excellent oxidation
and corrosion resistance properties under severe corrosive environments. However one of the
problems associated with welding of this class of steels is the poor weld penetration. This is
due to very low levels of surface-active elements like sulphur and oxygen in these steels. This
led to extensive research on the effect of surface-active elements on weld penetration during
TIG welding which resulted in the development of activated flux that could be used along
with TIG welding process, which can significantly improve the weld penetration.
Use of activated flux during TIG (A-TIG) welding has many advantages, especially in
tube welding. With this flux applied at the joint surface, it is possible to improve the weld
penetration substantially. Hence, maximum thickness that could be welded without filler
addition is considerably higher in this process than in the conventional TIG process (~3mm).
In the absence of filler addition, there is no need for edge preparation resulting substantial
savings both with respect to time and money. Use of A-TIG can also facilitate repair welding
especially to remove fine cracks detected during inspection.
High depth of penetration is achieved during A-TIG process due to constriction of the
welding arc [3]. In the A-TIG process, it is proposed that arc constriction is produced by the
effect of the vapourised molecules capturing the electrons in the outer regions of the arc,
which results in a constricted plasma similar to the effect produced by the nozzle in the

2. 2
conventional plasma arc system. In the central regions of the arc, the temperature is higher
than the dissociation temperature of the molecules and the gas and flux atoms are ionised to
generate electrons and positive ions. In the cooler peripheral regions of the arc column,
however, the vapourised material still exists as molecules and dissociated atoms, which are
large enough for the electrons to become attached to form negatively charged particles.
Consequently, the numbers of electrons in the peripheral region of the arc, which are the main
charge carriers, are reduced. This forces the arc to constrict to a new equilibrium state with a
higher current density in the plasma and at the anode. It is considered that the reactions
occurring primarily in the cooler, peripheral regions of the arc, lead to a reduction in the
diameter of the plasma column and hence, the area of the anode root. The degree of
constriction determined by the effectiveness of the flux vapour to combine with the electrons,
for example, the depth of penetration varying with the change in composition of flux.
A new activated flux has been developed recently at our Centre for welding of
austenitic stainless steels. Weld joints made with application of this flux has been studied for
various properties. Results from this study are presented and discussed in the present paper.
2. 0 Experimental Procedure for Development of Activated Flux
More than eighty-flux formulation with varying chemistry and physical characteristics
was tried to arrive at the optimal combination, which is to be patented. The material used for
welding trials to optimize the flux composition was AISI stainless steel 304LN plate of size
125 x 30 x 8 mm3
and chemical composition given in Table 1. These plates were cleaned
thoroughly just before welding using wire brush, running water and finally with acetone to
remove any rust, grease and oil that may contaminate the surface. Then, a thin coating of the
flux was applied on the surface and an autogenous bead-on-plate was made using GTA torch.
The welding current and voltage employed were 175 A and 16 V respectively and the arc gap
was maintained at 2 mm. Welds were made at different welding speeds varying from 75 to
200 mm/min (heat input from 2 to 0.75kJ/mm). Figure 1 shows the welding set up employed
and the application of the flux using a brush on the plate surface just before welding.
Table 1: Chemical analysis (in wt.-%) of as-received AISI 304LN SS plate used
304LN SS C Cr Ni Mn Si S P V Cu Co Nb N (ppm)
8 mm thick 0.012 19.0 10 1.24 0.66 0.018 0.042 0.04 <0.05 0.05 <0.07 450
10 mm thick 0.015 18.2 9.6 0.85 0.50 0.006 0.038 0.09 0.16 0.173 <0.07 440
Using the flux composition optimized from the examination of the bead-on-plate
welds, actual weld joints were prepared for evaluation of various properties and their
comparison with those of the weld joint produced by conventional TIG process. For this,
plates of dimensions 200 x 75 x 10 mm3
were employed. Square butt welds (without edge
preparation or use of filler wires) were prepared using A-TIG process with the newly
developed flux applied on the surface of the plates at the joining location. Full penetration
weld could be obtained in two passes, one each from the two sides as shown in Fig. 2. The
chemical composition of the 10 mm plate is also given in Table 1 along with that of the 8mm
thick plate employed for bead-on-plate weld study. The welding parameters employed are
given in Table 2. In order to confirm that the composition of the weld metal was not altered
by flux addition, autogenous bead-on-plate weld was made with and without flux addition on
this plate and the chemical analysis of the fused metal was carried out using direct reading
optical emission spectrometer. Microstructures, inclusion content, hardness and delta ferrite
content of the fused weld metals produced by A-TIG and conventional TIG were also
compared. Optical microscopy was employed for microstructure and inclusion in the weld
metal. Delta ferrite content in the weld metal was measured using Ferritescope MP3C.
Hardness of the weld metal was measured using Shimadzu HMV 2000 microhardness tester

3. 3
at a load of 200g. Corrosion tests were also carried out as per ASTM G48-92 to compare the
susceptibility of the weld metal produced by two processes to pitting corrosion.
Fig. 1: Photograph showing experimental setup Fig. 2: Macrostructure of the butt weld
and flux being applied on the surface joint at 150A/125mm/min
Though, full penetration weld joints could be made using A-TIG process by welding
from both sides of the plates, it is not possible to make a weld joint form 10 mm thick plates
using conventional TIG welding processes employing the same welding parameters used for
A-TIG process. Hence, in order to compare the mechanical properties of the weld joints and
prepared by A-TIG and conventional TIG, it was required to make weld pads using
conventional TIG welding process in which a V-groove was machined out and ER 308L filler
was used as the welding consumable. The welding parameters employed for the preparation
of this joint is also given in Table 2. Both the weld pads (A-TIG and conventional TIG) were
subjected to radiography and were found to be defect free.
Specimens for tensile test (transverse) and sub-size impact test were extracted from
these weld joints. Tensile and impact tests were carried out as per the relevant ASTM
standards, E8M-95a and E23-94b respectively.
3.0 Results and Discussion
Depth of penetration of the TIG weld could be considerably increased with the use of
activated flux. With optimized flux composition, it was possible to achieve full penetration of
the 8 mm thick plate. Figure 3 compares the depth of penetration achieved in A-TIG process
and the conventional TIG process. In addition to increase in the depth of penetration, there
was a considerable decrease in the width of the weld bead; this means aspect ratio (defined as
the ratio of the depth of penetration to width) of the bead is very high. Appearance of the
weld bead was slightly greyish, and few spots with glassy slag were present on the surface.
However, with the help of wire brush these could be removed and original bright colour of the
stainless steel could be restored.
Fig. 3: Weld bead penetration: (a) A-TIG. (b) Conventional TIG.
Both the depth of penetration and aspect ratio of the weld beads produced by A-TIG
were found to be influenced significantly by welding speed. Figures 4 and 5 compares the
a b

4. 4
variation of depth of penetration and aspect ratio respectively with welding speed for A-TIG
and conventional TIG processes.
60 80 100 120 140 160 180 200
1
2
3
4
5
6
7
8
Depthofpenetration,mm
Weld travel speed, mm/min.
With flux
No flux
60 80 100 120 140 160 180 200
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Aspectratio
Weld Travel Speed, mm/min.
With flux
Without flux
Fig. 4: Variation of depth of penetration Fig. 5: Variation of aspect ratio with travel
with travel speed speed
Table 2: Parameters used for studying the strength properties.
Parameters A-TIG Conventional TIG
Joint type Square butt Single V groove
Number of passes 2 4
Welding Semi automatic Manual
Welding position Flat (1G) Flat (1G)
Current 150 A
Root pass 125 A
Subsequent pass 100–110A
Travel speed 125 mm/min 100 mm/min
Filler metal & Size Autogenous ER308L, dia. 2 mm (root)
Shielding Gas Argon Argon
Gas flow rate 10 litre/min 10 litre/min
Back purging 6 litre/min. 6 litre/min.
Electrode type & size 2% thoriated; dia. 3 mm 2% thoriated; dia. 3 mm
Arc gap 2mm Not measured
Polarity Straight (DCEN) Straight (DCEN)
By reducing welding speed, the depth of penetration and aspect ratio could be
increased considerably in A-TIG process. The depth of penetration achieved by the addition
of flux at travel speed of 200mm/min is nearly the same as that achieved without the addition
of flux at a travel speed of 75mm/min. This shows that a substantial increase in welding speed
can be obtained by addition of flux there by causing an increase in rate of production. Based
on these results, the optimized welding parameters chosen for making the actual weld joints
using activated flux for evaluation of the mechanical properties were: welding speed of
125 mm/min., welding current of 150 A, voltage of 16 V and arc gap of 2 mm.
3.1 Comparison of the Properties of A-TIG and Conventional TIG Weldments
Chemical composition of the fused weld metals produced by autogenous bead-on-
plate welding with A-TIG and conventional TIG processes are shown in Table 3.
Compositions of both the fused weld metals are almost the same. Further, they differ from the
composition of the original base metal (shown in Table 1) only marginally. This shows that
the use of activated flux does not affect the composition of the weld metal.

5. 5
Table 3. Chemical analyses of weld samples by A-TIG and without flux addition.
304LN SS C Cr Ni Mn Si S P V Cu Co Nb N (ppm)
A-TIG 0.017 17.8 9.5 0.96 0.47 0.005 0.029 0.075 0.156 0.173 <0.07 456
No Flux 0.015 17.7 9.6 0.9 0.49 0.004 0.028 0.076 0.154 0.173 <0.07 450
Figure 6 compares the inclusion content in the weld metal produced by A-TIG and
that produced by conventional TIG process. Inclusion contents in both the weld metals are
comparable indicating that use of activated flux does not adversely affect the inclusion
content in the weld metal.
Fig. 6: Inclusion content in: (a) A-TIG; and (b) Conventional TIG weld metals
Microstructures of the weld metals produced by both the processes shown in Fig. 7
also show that they do not differ significantly with the process used. Results obtained from
the delta ferrite measurement were also similar. For both the weld metals, the delta ferrite
content varied in the range 4-6 FN. Figure 8 compares the microstructures of the weld metals
produced by the two processes after etching with Murakami reagent to reveal the
microstructure. The morphology of the delta ferrite also did not vary with the process.
Fig 7: Microstructure of: (a) A-TIG; and (b) Conventional TIG weld metals.
Fig. 8: Photomicrograph showing delta-ferrite present in: (a) A-TIG;
and (b) Conventional TIG weld metals
Hardness variation across the fusion boundary for two welding processes is shown in
Fig. 9. It is clear from the results that hardness of the weld metal is also not affected by the
welding processes employed.
a b
ba
ba
20µm 20µm
200µm
200µm
50µm 50µm

6. 6
Results from the corrosion tests also
indicated that the difference in the corrosion
behaviour of both the weld metals are only
marginal. Weight loss obtained for specimens
from both the weld metals after corrosion test is
shown in Table 4 and Fig. 10 compares the
surfaces of the corrosion coupons after the
corrosion test. The specimens for corrosion test
contained both weld metal and the base metal
and a comparison of Figs. 10(a) and 10(b) shows
that for the weld metal corrosion was less in the
A-TIG weld metal than the conventional weld
metal even though weight loss was more for the
former than the latter (Table 4).
Table 4: Average value of corrosion results.
Specimen type Weight before gm Weight after gm Weight loss gm
A-TIG 111.127 100.843 10.284
Conventional metal weld 111.038 102.379 08.659
Fig. 10: Photomacrograph showing the corrosion-tested surface of specimens of: (a) A-TIG,
and (b) Conventional TIG welds
Mechanical properties of the weldments also did not vary much between A-TIG and
conventional TIG processes. During tension test, both the weld joints fractured close to the
weld interface (Fig. 11) with no significant difference in the yield strength and UTS. Results
from the tension tests are given in Table 5. Ductility was slightly better for the A-TIG joint
than the conventional joint. Results from impact tests (conducted on sub-size Charpy V-notch
specimens) on the weld metal indicated that impact energy is also distinctly higher (84 J) for
the A-TIG weld metal than for conventional TIG (64 J).
Table 5: Average value of the tensile test results.
Type of weld Yield Strength,
MPa
UTS,
MPa
%
Elongation
% Reduction
in area
A-TIG 311 630 56.24 57.92
Conventional TIG 305 591 42.78 48.5
The above results clearly show that the properties of the weld were not adversely
affected in any way by the use of activated flux. Further, there is a significant improvement
with respect to increase in depth of penetration and aspect ratio; stainless steel plates of tubes
ba
Weld metal
Weld metal
-4 -3 -2 -1 0 1 2 3 4 5
160
165
170
175
180
185
190
195
200
205
Fusionline
Base metal Weld metal
HardnessVHN,Kg/mm
2
Distance from fusion line, mm
With flux
Without flux
Fig. 9: Microhardness profile
across the fusion line for
A-TIG and conventional
TIG welds
10mm 10mm

7. 7
Weld metal
Fig. 11: Fracture location of
the tensile specimen
prepared from A-
TIG weldment
of thickness up to 8 mm can be joined by A-TIG processes
without edge preparation and filler metal addition. Hence, A-
TIG process can be safely employed in thin section welding
where substantial benefits could be derived both with respect
to reduction in cost and time by avoiding edge preparation
and use of welding consumable. Another important finding
from the present study is the effect of welding speed on the
penetration depth and aspect ratio of the A-TIG joint (Figs. 4
and 5). Unlike in the conventional TIG, depth of penetration
varies significantly with reduction in welding speed in the A-
TIG process allowing the option of using welding speed as
variable to achieve the desired depth of penetration.
4.0 Conclusions
The following are the major conclusions from the present study.
1. An activated flux that can be used for weld austenitic stainless steel without edge
preparation and filler metal addition for thickness up to 8 mm has been developed.
2. The properties of the weld metal and weld joints produced by the A-TIG process is
comparable to those of the weld metal and joint produced by conventional TIG processes.
3. Effect of welding speed on both the depth of penetration and aspect ratio is higher on A-
TIG process than the conventional TIG process. Hence, welding speed could be varied to
obtain the desirable depth of penetration in this process.
4. By using this process, considerable savings could be achieved both with respect to time
and cost especially for welding thin sections.
Acknowledgements
The authors thank Dr. T.P.S. Gill and Shri N.V.L. Narasimha Rao who were initially
associated with this work. The assistance received from Shri. V. Srinivasan, Materials
Chemistry Division, IGCAR for weld metal chemical analysis is also gratefully
acknowledged.
References
1. R.H. Tupkary, “Introduction to modern Steel making” Khanna Publishers, Delhi, 1995.
2. B. Pollard, “Effect of minor elements on the welding characteristics of stainless steel” W.
J; 202s-213s, 1988.
3. W. Lucas and D. Howse, "Activating flux-increasing the performance and productivity of
the TIG and Plasma processes" Welding and Metal Fabrication, pp11-17, January' 1996.
4. J. A. Lambert, "Cast to cast variability in SS Mechanized GTA welds", Welding Journal
70(5); 41-52, 1991.
5. C.R. Hieple, J.R. Roper, R.T. Stanger and R.I. Aden, "Surface active element effects on
the shape of GTA, Laser and electron beam welds" Welding Journal, pp 72s-77s. March
1983.
6. C.R. Heiple and J.R. Roper "Mechanism for minor element effect on GTA fusion
geometry" Welding Journal, pp 97s-102s, April 1982.
7. F.B.Pickering "Physical metallurgy of SS development" International metal review,
Dec'96.
8. P.C.J. Andweson and R. Wiktorowicz "Improving productivity with A-TIG welding"
Welding and Metal Fabrication, pp 108-110, March 1996.

8. 8
9. S. Chakravarty, V. Ramasubbu and T.P.S. Gill, “Development of activated flux for
GTAW process” National Welding Seminar, pp 145-151, 11-13th
, December 1997.
10. G.S. Mills, “Fundamental mechanism of penetration in GTA welding” Welding Journal
pp21s-24s, 1979.
11. ASTM E23-94b "Standard Test Methods for Notched bar Impact testing of metallic
materials".
12. ASTM E8M-95a "Standard Test method for Tension Tests of Metallic materials
(Metric)".
13. ASTM G46-94 "Standard guide for examination and evaluation of pitting corrosion,"
14. ASTM G48-92 "Standard Test Methods for Pitting and Crevice corrosion resistance of
stainless steels and related alloys by use Ferric Chloride solution".
15. A WS A4.2-91 "Standard procedures for calibrating Magnetic Instruments to Measure the
Delta-ferrite content of Austenitic stainless steel weld metal" - AWS, Miami, 1991.
16. AWS Welding Hand book, 8th edition, volume 4, American Welding Society, Miami,
Florida.
17. H.R. Castner, "What you should know about ASS" Welding journal, April-93.
18. J.C. Metacalfe and M.B.C. Quig1ey "Arc and pool instability in GTA Welding" Welding
Jounal, pp 133s-139s, May 1977.
19. K.J.lrvine et al.; J. Iron Steel Institute, 207,1017, 1969.
20. R. Kiessling, "Stainless steels-Material in competition" Metals Tech. 11(5), pp169-180,
1984.
21. T. Zacharia, S.A. David, J.M. Vitek and T. Debroy "Weld pool development during GTA
and Laser beam welding of type 304 SS Part I: Theoretical analysis" Welding Journal, pp
499s-509s, December 1989.
22. T.Zacharia, S.A.David, JoM.Vitek and T.Debroy "Weld pool development during GTA
and Laser beam welding of type 304 SS Part II: Experimental correlation" Welding
Journal, pp 510s-519s, December 1989.