S: RAJU GOVINDARAJ, S. KARUPPAN: MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED ...
127–134
MECHANICAL AND METALLURGICAL PROPERTIES OF
FRICTION-STIR-WELDED AISI 304 STAINLESS STEEL
MEHANSKE IN METALUR[KE LASTNOSTI TORNO VRTILNEGA
VARJENJA NERJAVNEGA JEKLA AISI 304
Sundar raju Govindaraj
*
, Sivakumar Karuppan
Department of Mechanical Engineering, Bannari Amman Institute of Technology, Erode, Tamil Nadu, India
Prejem rokopisa – received: 2022-11-03; sprejem za objavo – accepted for publication: 2023-01-23
doi:10.17222/mit.2022.678
Friction stir welding of AISI 304 stainless-steel sheets was successfully carried out with a tungsten-alloy (W+La2O3) tool and
the effect of the tool rotational speed on the microstructure and mechanical properties of the joints were evaluated. 3-mm-thick
plates were friction-stir welded at various rotational speeds of 600–1000 min
–1
and a constant welding speed of 40 mm/min with
a constant axial load of 15 kN. Defect-free joints were produced at 800 min
–1
and 900 min
–1
, indicating a proper plastic flow of
the material and ensuring adequate heat generation during welding. Tensile, Charpy impact, compression and microhardness
tests were performed to evaluate the joint mechanical properties. The microstructural behavior of the welded and base-metal
samples was examined with optical microscopy and scanning electron microscopy. According to the mechanical results, the
welded material has a higher yield strength than the base metal due to the grain refinement and work hardening effect in the stir
zone. FSW welds have a higher hardness than the base metal due to the high density of dislocations and continuous dynamic
recrystallization. The joints also exhibit acceptable impact toughness. Finally, the EDS analysis confirms that there is no sec-
ondary-phase formation in the weld zone of the fabricated material.
Keywords: tensile strength, tool rotational speed, welding speed, axial load
V ~lanku je opisano uspe{no torno vrtilno varjenje oziroma varjenje s trenjem in me{anjem (FSW; angl.: Friction stir welding)
plo~evin iz nerjavnega jekla AISI 304. Varjenje so izvajali z orodjem iz volframa (W+La2O3) in so pri tem analizirali vpliv
hitrosti vrtenja orodja na mikrostrukturo in mehanske lastnosti varjenih spojev. Jeklene plo~evine debeline 3 mm so varili s
postopkom FSW pri razli~nih hitrostih vrtenja orodja (od 600 do 1000) min
–1
in pri konstantni hitrosti varjenja 40 mm/min s
konstantno osno obremenitvijo 15 kN. Na ta na~in so uspeli izdelati zvarne spoje brez napak pri hitrostih 800 in 900 min
–1
s
primernim plasti~nim tokom materiala in ustrezno tvorbo toplote zaradi trenja med varjenjem. Ovrednotili so mehansko
kakovost izdelanih zvarnih spojev z nateznimi preizkusi, dolo~itvijo Charpyjeve udarne `ilavosti, tla~ne trdnosti in meritvami
mikrotrdote. Mikrostrukturo osnovnih plo~evin in zvarnih spojev so analizirali s pomo~jo svetlobnega in vrsti~nega
elektronskega mikroskopa. Na osnovi rezultatov mehanskih preiskusov so ugotavili, da imajo zvarni spoji v toplotno vplivaemn
obmo~ju vi{jo mejo plasti~nosti kot osnovni material zaradi udrobljenja kristalnih zrn in u~inka deformacijskega utrjevanja v
obmo~ju me{anja. S postopkom FSW izdelani zvarni spoji imajo vi{jo trdoto kot osnovni material zaradi ve~je gostote
dislokacij in kontinuirne dinami~ne rekristalizacije. Zvarni spoji imajo prav tako sprejemljivo udarno `ilavost. Poleg tega so
analize EDS potrdile, da ni pri{lo do tvorbe ne`elenih sekundarnih faz v obmo~jih varjenja izbranega materiala.
Klju~ne besede: natezna trdnost, hitrost vrtenja orodja, hitrost varjenja, osna obremenitev
1 INTRODUCTION
Friction stir welding (FSW) is a solid-state joining
technology developed in 1991 by the Welding Institute.
1
FSW is a hot working technique in which the workpiece
is deformed severely by the rotating pin and shoulder.
2
The heat required to soften the material is generated by
friction and plastic deformation.
3
Stainless steel fittings
made of AISI 304 (UNS S30400/S30403) are reliable in
a range of boating applications.
4
They are resistant to a
wide range of climatic conditions and used for coastal
handrails, hot-water pipes, and deck components for
boats and ships.
5
Friction stir welding has been utilized
on long straight welds used in the manufacture of
pre-fabricated panels. In case of high melting tempera-
ture materials (HMT), FSW is considered more difficult
to perform due to the tool wear and excessive frictional
heat. It causes severe damage to the tool.
6
In particular,
austenitic stainless steel endures high deformation at
high temperatures.
The use of tools for the FSW of stainless steel alloys
is problematic as it is difficult to retain the tool strength
at high temperatures. The weld durability and quality are
directly impacted by the tool selected. For this reason,
the polycrystalline cubic boron nitride material was em-
ployed as it meets the requirements for the tool high-
temperature stability and strength. However, the tool ma-
terial cost was excessively high, creating a barrier to
welding high-temperature materials.
7
Miyazawa et al.
8
used an iridium-based alloy tool for FSW. This alloy has
a high melting point, good mechanical qualities, and it is
resistant to oxidation at high temperatures. But, the main
drawback is the lack of availability of the material to be
commercialized.
Materiali in tehnologije / Materials and technology 57 (2023) 2, 127–134 127
UDK 539.412:621.791 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 57(2)127(2023)
*Corresponding author's e-mail:
sunmetly@gmail.com (Sundar raju Govindaraj)

Lakshminarayan et al.
9
investigated the FSW of AISI
304 using a surface-coated tool. According to the results,
the atmospheric plasma sprayed (APS) coatings exhib-
ited inadequate shear and bond strength, causing prema-
ture failure during the plunging stage. Raghunathan et
al.
10
investigated the deterioration of different tool mate-
rials in FSW, finding that among tungsten alloy tools the
one with 99 % of W and1%ofLa
2
O
3
maintains good
properties at high temperatures with negligible tool de-
bris and base-material degradation. These authors fo-
cused on the tool material and geometry required for
AISI 304 welding. The FSW process is controlled by
welding-process parameters such as the tool material,
tool shape, welding speed, rotational speed and axial
forces. Abbasi et al.
11
found that rising the tool traverse
speed enhances the weld nugget size and reduces incom-
plete root penetration. Ahmed et al.
12
showed that an in-
creased FSW speed results in a higher grain-size reduc-
tion and improved hardness values. Guo et al.
13
maintained that thin sheets are always prone to a heat in-
put, and that the pin wear is pretty high when the weld-
ing speed is too slow. Plaine et al.
14
maintained that the
FSW process generates fine grains with good mechanical
properties with a low heat input. Mishra et al.
15
stated
that the material flow during friction stir welding is quite
complex as it depends on the tool geometry, process pa-
rameters and material to be welded.
The tool rotational speed has a direct effect on the
thermal history, frictional heat stirring, oxide layer
breaking, and mixing of the materials of FSW joints.
Jabbari et al.
16
found that increasing the rotation speed
results in an increase in the grain size in the nugget zone.
Ko et al.
17
found that the tensile strength and hardness of
the stir zone increased as the tool rotational speed in-
creased. Li et al.
18
found that when the rotational speed
increases, the hardness of the heat-affected zone de-
creases gradually, and the hardness of the stir zone in-
creases. For this reason, this study will focus on the ef-
fect of the tool rotation speed on the mechanical and
microstructural properties of AISI 304 steel using a
W-La
2
O
3
alloy tool.
2 EXPERIMENTAL PART
The base material for this experiment was a
cold-rolled and annealed AISI 304 stainless-steel sheet
with a thickness of 3 mm. A spectrum analysis was per-
formed in three locations to determine the alloy compo-
sition, with the average values reported in Table 1.
A semi-automatic friction stir welding machine with
a spindle speed of 2000 min
–1
and a Z axial force of
15 kN, and a Rexroth controller with a liquid-cooled tool
holder machine were employed in this operation. The
W-alloy tool utilized with this technique was a cylindri-
cal tool with a shoulder diameter of 25 mm, a probe di-
ameter of 12 mm and a conical-pin length of 2.9 mm.
The FSW joints were tested at various tool rotational
speeds of (600, 700, 800, 900 and 1000) min
–1
, with a
constant welding speed of 40 mm/min and a 15 kN axial
load. ASTM E8M-04 was used to prepare tensile speci-
mens. Experiments were performed in a computer-con-
trolled UTM machine (M-30 model). Charpy impact
specimens were made according to ASTM E23-06. To
examine the impact toughness of the samples
(AIT-300-EN type), an impact test machine with a 300 J
capacity was used. The specimens were produced fol-
lowing the ASTM E190-03 specifications and tested in a
compression testing machine with a load capacity of
400 kN (model number: TUE-CN-400). Microhardness
tests were carried out on the base metal, weld metal and
TMAZ, using a Vickers microhardness testing machine
(model number: Qness Q10A+) with an applied load of
500 gf and a dwell time of 10 s.
3 RESULTS AND DISCUSSIONS
FSW joints were prepared at various tool rotational
speeds of 600 min
–1
to 1000 min
–1
with intervals of
100 min
–1
. Surface and volumetric defect-free weld
joints were achieved at tool rotational speeds of
S: RAJU GOVINDARAJ, S. KARUPPAN: MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED ...
128 Materiali in tehnologije / Materials and technology 57 (2023) 2, 127–134
Table 1: Chemical composition of the base metal (w/%)
Material/ elements C Cr Ni Mn Si Mo S P Cu Co V Fe
AISI 304 0.06 18.4 8.09 0.84 0.23 0.22 0.001 0.042 0.294 0.186 0.062 Rem
Figure 1: FSW joints at various tool rotational speeds

800 min
–1
and 900 min
–1
(Figures 1c and 1d). The joint
made at a tool rotational speed of 600 min
–1
exhibits
poor consolidation of the weld nugget defect due to a
low temperature and low material flow in the stir zone.
The weld produced at 700 min
–1
exhibits a lack of bond-
ing defect because of a low frictional force, which cre-
ated an insufficient heat input. The welds in the stir zone
consist of smooth onion rings at 800 min
–1
and
900 min
–1
, indicating a proper plastic flow of the mate-
rial and adequate heat generation during welding.
Finally, at a tool rotational speed of 1000 min
–1
, exces-
sive flash generation and tunnel flaws are observed. This
is due to the excess heat input and high tool shoulder
pressure. As a result of the above, a low rotational speed
and high rotational speed are not advisable. The opti-
mum tool rotational speed should be used to attain
flaw-free welds. Thus, the tool rotational speeds of
800 min
–1
and 900 min
–1
resulting in sound weld joints
were selected for further investigations.
3.1 Tensile test
Stress-strain curves and transverse tensile character-
istics of the base metal (BM) and FSW joints are shown
in Figure 2. The yield strength (YS) and ultimate tensile
strength (UTS) of the base metal are 343 MPa and
674 MPa, respectively. The joint yield strength at the
tool rotational speeds of 800 min
–1
and 900 min
–1
are
greater than that of the base metal in both cases. The av-
erage of three specimen yield strengths (YS) was mea-
sured at 351 MPa and 362 MPa. The grain refinement
and work hardening effect in the weld zone were the key
reasons for the increased yield strength. The average of
the ultimate tensile strength was measured at 575 MPa
and 647 MPa when the tool rotational speeds were
800 min
–1
and 900 min
–1
. At the 800 min
–1
and 900 min
–1
tool rotational speeds, the joint efficiency was estimated
to be 85 % and 96 % with regard to the base metal. The
base metal melted more when the coefficient of friction
between the tool and the parent material decreased. This
caused a stirring action, lowering the joint tensile
strength.
The tensile-test results indicated that the tool rota-
tional rates of 800 min
–1
and 900 min
–1
provide enough
heat input and a defect-free weld joint. The location of
fracture was seen in the stir zone and the TMAZ of the
advancing side at the 800 min
–1
tool rotational speed.
The advancing-side gradient of velocity was high when
compared to the retreating side. A fracture was found in
the stir zone, adjacent to the TMAZ on the advancing
side, with a tool rotational speed of 800 min
–1
. When
compared to the retreating side, the advancing side had a
higher velocity gradient. Under the influence of the pin,
the stir zone exhibits significant plastic deformation, pro-
ducing small grains through dynamic recovery and
recrystallization and leading to an increased hardness
and tensile strength as shown by Li et al.
19,20
According
to the fine-grain strengthening theory, small grains in the
stir zone increase the weld strength.
3.2 Impact test
The impact toughness of the base metal and FSW
joints is shown in Figure 3. The test results show that the
base-metal impact toughness is 64 J at room tempera-
ture. The welded-metal impact-toughness values ob-
tained at the tool rotational speeds of 800 min
–1
and
900 min
–1
are 44 J and 48 J. Comparing the base metal
and welded metal, we find that the toughness value
slump rapidly at both tool rotational speeds. This is due
to the tool wear during the FSW process. A similar result
was described by G. Sundar raju et al.
21
The addition of
tungsten particles to the tool-wear debris reduces the
ductility and toughness of the particles in the pin-af-
fected zone. Lakshminarayan et al.
22
report that the pres-
ence of tool debris at the bottom of the stir zone may be
the reason for the reduction in ductility and toughness of
a friction-stir-welded joint compared to the base metal.
S: RAJU GOVINDARAJ, S. KARUPPAN: MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED ...
Materiali in tehnologije / Materials and technology 57 (2023) 2, 127–134 129
Figure 3: Impact toughness properties of BM and FSW joints Figure 2: Transverse tensile properties of BM and FSW joints

3.3 Bend test
The three-point guided bend test result helps to deter-
mine the ductility of the weld on both the surface and
root side (bottom side). This test was performed in the
transverse direction on the FSW joints. The compressive
strength of the base metal and FSW joints is shown in
Figure 4. The base-metal compressive-strength value is
58.6 N/mm
2
. It is estimated that at the tool rotational
speeds of 800 min
–1
and 900 min
–1
the face-side weld-
metal compressive-strength values are 46.4 N/mm
2
and
53.9 N/mm
2
while the root-side weld-metal compres-
sive-strength values are 44.5 N/mm
2
and 52.9 N/mm
2
.
The results of the face bend and root bend tests indicate
that the 800 min
–1
joint has a lower compressive strength
than the base metal. However, the FSW joints show satis-
factory ductility in both bend tests.
3.4 Microhardness test
The microhardness of the butt joints obtained at 800
and 900 min
–1
was tested in the transverse direction, at
the center, and the values are shown in Figure 5. The av-
erage base-metal hardness is 223±5H V .A l lt h ed e -
fect-free weld joints show a substantial increase in the
hardness when compared to the base metal. With the tool
rotational speed of 800 min
–1
, the hardness of the stir
zone varies from 224 HV to a peak hardness of 243 HV
in the centerline, and the average hardness is 235±5HV .
Similarly, with the tool rotational speed of 900 min
–1
,a
high hardness of 294 HV is observed in the stir zone, and
the average hardness is estimated to be 278±5H V ,
which is greater than the base-metal and TMAZ hardness
values. The hardness in the TMAZ is higher than that of
the base metal and lower than that of the stir zone. In the
TMAZ, high dislocation and subgrain boundaries tend to
improve the hardness as reported by Guo et al.
23
The
hardness profile increases from the TMAZ to the center
of the stir zone on both the advancing and retreating
sides. FSW welds have higher hardness than the base
metal due to the high density of dislocations and contin-
uous dynamic recrystallization, resulting in fine grains in
the stir zone.
3.5 Weld macrostructure
In Figure 6, the tool rotational speed of 800 min
–1
was observed to create a sound metal deposition, layer
by layer, on the advancing side (AS). This is because the
material flows from the advancing side to the retreating
side (RS), requiring more energy to flow from one side
to the other. Similarly, a defect-free weld joint was
formed at the tool rotational speed of 900 min
–1
, with
U-shaped shear bands in the stir zone and near the
thermo-mechanically affected zone (TMAZ). The
U-shaped shear band at the stir zone (SZ) was observed
by Shashikumar et al.,
24
indicating an adequate heat gen-
eration due to a consistent material flow and enhanced
material coalescence.
3.6 Weld microstructure
The base material has an austenite grain structure
( -Fe) with a low density of dislocations. Annealed twin
boundaries are also observed in some grains. The aver-
age grain size of the BM is about 8 μm. The parent-metal
and welded-metal microstructures are shown in Fig-
ure 7. There are three distinct zones in the microstruc-
tures: the base metal (BM), thermomechanically affected
zone (TMAZ) and stir zone (SZ). The grain structure in
the stir zone is generally equiaxed, and the stir zone has
a higher dislocation density than the base metal. The av-
erage grain size in the SZ is 7.0 μm, which is slightly
smaller than that of the BM. The microstructures from
Figures 7a and 7b show the BM and SZ of the shoulder
and pin-influenced region. Small equiaxed grains are ob-
served throughout the SZ. This zone is refined compared
S: RAJU GOVINDARAJ, S. KARUPPAN: MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED ...
130 Materiali in tehnologije / Materials and technology 56 (2022) 6, 127–134
Figure 6: Macrostructures of FSW joints at 800 min
–1
and 900 min
–1 Figure 4: Compressive strength properties of BM and FSW joints
Figure 5: Transverse microhardness surveys of FSWs at 800 min
–1
and 900 min
–1

S: RAJU GOVINDARAJ, S. KARUPPAN: MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED ...
Materiali in tehnologije / Materials and technology 57 (2023) 2, 127–134 131
Figure 8: Fractographs and EDS of the tensile tests: a), b) base metal, c), d) weld metal
Figure 7: Optical micrographs of FSW joints

with the base metal, exhibiting an equiaxed recrys-
tallized grain structure. Further, no annealed twin grains
found in the SZ are completely reoriented by the stirring
action of the tool. The combined effect of thermal and
mechanical loads forms the TMAZ. Figures 7c and 7d
display the TMAZs of the advancing and retreating
sides. Because of the material flow process, the advanc-
ing side of the figure shows a most severe displacement.
Furthermore, the tool advancing side causes more plastic
deformation than the retreating side due to the shear
force. Figures 7e and 7f depict the microstructures of the
SZ and TMAZ interface regions of the advancing and re-
treating sides. The TMAZ at the bottom of the pin-influ-
enced region is smaller than the TMAZ-AS&RS of the
shoulder-influenced region and pin-influenced region
due to a higher cooling rate. Furthermore, similar micro-
structure properties were observed in a 304 ASS fric-
tion-stir weld by Park et al.
25
The microstructure at the
bottom of the advancing side of the stir zone is relatively
more sensitive to etching than the other regions; it con-
sists of austenite and ferrite phases. A microstructural
study exposes the quality of weld joints since the micro-
structures of weld joints have a significant impact on
their mechanical characteristics, as shown by Yan et al.
26
3.7 Fracture surface analysis – a tensile test
The fracture surfaces of the base-metal and weld-
metal tensile specimens are shown in Figure 8. The dis-
played fractograph in 8a invariably consists of dimples
with a large void volume fraction. Small or large dimples
and microvoids can be seen in the images, indicating that
the tensile specimens failed in a ductile manner under
the action of a uniaxial tensile load. The fracture surface
of the tensile specimen of the welded metal is shown in
Figure 8c. The fractograph shows a great amount of
small or large dimples and microvoids. Comparing the
base-metal and welded-metal fractographs, finer dimples
are found in the FSW joint. In addition, parabolically
shaped fine microvoids are present in the welded fracture
surface.
Figures 8b and 8d depict the tensile-test SEM-EDS
analysis of the base metal and weld metal, used to ana-
lyze the energy spectrum to determine the specific ele-
ments. In the FSW process, light etching features occur
between the tool and base material. These characteristics
are the result of high-pressure mechanical stirring and
the transfer of the tool material to the base material. In
the shown EDS photograph no substantial W-tool debris
is observed, so inclusion occurs in the weld joints.
3.8 Fracture surface analysis – an impact test
The fracture surfaces of the base-metal and weld-
metal impact specimens are shown in Figure 9. Fig-
ure 9a shows a typical SEM fractograph of the im-
pact-test image of the base metal. The fractograph dis-
plays a fibrous appearance and substantial deformation
before the fracture, indicating ductile fracture qualities.
Further, the void coalescence results in the development
of a shear lip, and the microvoids are responsible for a
higher self-energy fracture. Figure 9b depicts the
SEM-EDS analysis of the base metal. According to its
result, in the base metal, Ni and Mn are predominantly
present, following the Cr content, which acts as the aus-
tenite stabilizer.
S: RAJU GOVINDARAJ, S. KARUPPAN: MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED ...
132 Materiali in tehnologije / Materials and technology 57 (2023) 2, 127–134
Figure 9: Fractographs and EDS of the impact tests: a), b) base metal, c), d) weld metal

Figure 9c shows a typical SEM fractograph of the
impact-test image of the FSW joint. On the fractograph,
the microvoids and non-uniform dimples are signs of a
ductile fracture with a high energy mode. Moreover,
shear cleavage and minor broken grains inside the dim-
ples are also found. In comparison to the base metal, the
grain size and void size increased significantly, being the
origin of the poor toughness of the material. Figure 9d
depicts the SEM-EDS analysis of the weld metal. The re-
sult explains the composition of the weld metal in the
fracture area. It is noticed that the least amount of tung-
sten inclusion is present in the weld metal, resulting in
the reduced toughness of the weld metal. In addition,
sufficient levels of toughness and tensile strength are at-
tained at the welding speed of 900 min
–1
.
4 CONCLUSION
Friction stir welding of AISI 304 austenitic stainless
steel was effectively accomplished at an axial load of
15 kN, constant welding speed of 40 mm/min and tool
rotation speeds of 800 min
–1
and 900 min
–1
.
It was observed that increasing and decreasing the
tool rotational speed influenced the quality of the weld-
ing.
FSW produced sound welds with no cracks or cavi-
ties at tool rotational speeds of 800 min
–1
and 900 min
–1
.
Welding process parameters directly influenced me-
chanical properties, including a maximum tensile
strength of 647 MPa and compressive strength of
53.9 N/mm
2
, obtained at the welding speed of 900 min
–1
.
The microhardness of the base metal was 221±5HV .
At the tool rotation speed of 900 min
–1
, the stir zone
microhardness reached a maximum of 233±5HV .
The base-metal impact toughness was 64 J at room
temperature. The welded-metal impact toughness values
were 44 J and 48 J, obtained at the tool rotational speeds
of 800 min
–1
and 900 min
–1
.
SEM results showed the size and dimple distribution
for the welded tensile specimen, indicating characteris-
tics of a ductile fracture.
It was determined that the problem of excessive grain
growth and sigma-phase formation associated with fu-
sion welding can be overcome with FSW.
5 REFERENCES
1
W. M. Thomas, Friction stir butt welding, International Patent No.
PCT/GB92/02203, England 1991
2
F. Zhi-hing, H. Di-qiu, W. Hong, Friction stir welding of aluminum
alloys, J. Wuhan Univ. Technol. – Mat. Science Edition, 19 (2004),
61–64, doi:10.1007/BF02838366
3
S. Benavides, Y. Li, L. Murr, D. Brown, J. McClure, Low-tempera-
ture friction-stir welding of 2024 aluminum, Scripta Materialia, 41
(1999) 8, doi:10.1016/S1359-6462(99)00226-2
4
https://www.assda.asn.au/43-applications/marine/170-corrosion-re-
sistance-in-marine-environments, 10.10.1996
5
B. C. Gerwick Jr, Construction of marine and offshore structures, 3rd
edition, CRC Press, United States of America 2007, 8493–3052
6
D. G. Mohan, C. Wu, A Review on Friction Stir Welding of Steels,
Chinese Journal of Mechanical Engineering, 34 (2021) 1, 1–29,
doi:10.1186/s10033-021-00655-3
7
Y. N. Zhang, X. Cao, S. Larose, P. Wanjara, Reviews of tools for fric-
tion stir welding and processing, Canadian Metallurgical Quarterly,
51 (2012) 3, 250–261, doi:10.1179/1879139512Y.0000000015
8
T. Miyazawa, Y. Iwamoto, T. Maruko, H. Fujji, Friction stir welding
of 304 stainless steel using Ir based alloy tool, Science and Technol-
ogy of Welding and Joining, 17 (2012) 3, 207–212, doi:10.1179/
1362171811Y.0000000096
9
A. K. Lakshminarayanan, C. S. Ramachandran, V. Balasubramanian,
Feasibility of surface-coated friction stir welding tools to join AISI
304 grade austenitic stainless steel, Defense Technology, 10 (2014)
4, 360–370, doi:10.1016/j.dt.2014.07.003
10
S. R. Nathan, V. Balasubramanian, S. Malarvizhi, A. G. Rao, An in-
vestigation on metallurgical characteristics of tungsten based tool
materials used in friction stir welding of naval grade high strength
low alloy steels, International Journal of Refractory Metals and Hard
Materials, 56 (2016), 18–26, doi:10.1016/j.ijrmhm. 2015.12.005
11
M. A. Gharacheh, A. H. Kokabi, G. H. Daneshi, B. Shalchi, R.
Sarrafi, The influence of the ratio of "rotational speed/traverse
speed" ( /v) on mechanical properties of AZ31 friction stir welds,
International Journal of Machine Tools and Manufacture, 46 (2006)
15, 1983–1987, doi:10.1016/j.ijmachtools.2006.01.007
12
M. M. Z. Ahmed, B. P. Wynne, J. P. Martin, Effect of friction stir
welding speed on mechanical properties and microstructure of nickel
based super alloy Inconel 718, Science and Technology of Welding
and Joining, 18 (2013) 8, 680–687, doi:10.1179/1362171813Y.
0000000156
13
G. Guo, Y. Shen, Frictions stir welding of dissimilar stainless steels:
evaluation of flow pattern, microstructure and mechanical properties,
Materials Research Express, 6 (2019) 5, 056510, doi:10.1088/2053-
1591/ab015b
14
A. H. Plaine, N. G. D Alcântara, Prediction of FSW defect-free joints
of AISI 304 austenitic stainless steel through axial force profile un-
derstanding, Materials Research, 17 (2014), 1324–1327,
doi:10.1590/ 1516-1439.292714
15
R. S. Mishra, Z. Y. Ma, Frictions stir welding and processing, Mate-
rials Science and Engineering: R: Reports, 50 (2005) 1–2, 1–78,
doi:10.1016/j.mser.2005.07.001
16
M. Jabbari, C. C. Tutum, Optimum rotation speed for the friction stir
welding of pure copper, International Scholarly Research Notices,
(2013), doi:10.1155/2013/978031
17
Y. J. Ko, K. J. Lee, K. H. Baik, Effect of tool rotational speed on me-
chanical properties and microstructure of friction stir welding joints
within Ti–6Al–4V alloy sheets, Advances in Mechanical Engi-
neering, 9 (2017) 8, 1687814017709702, doi:10.1155/2013/978031
18
Y. Li, D. Sun, W. Gong, Effect of tool rotational speed on the
microstructure and mechanical properties of bobbin tool friction stir
welded 6082-T6 aluminum alloy, Metals, 9 (2019) 8, 894,
doi:10.3390/met9080894
19
J. Li, X. Liu, G. Li, P. Han, W. Liang, Characterization of the
microstructure, mechanical properties, and corrosion resistance of a
friction-stir-welded joint of hyper duplex stainless steel, Metals 7
(2017) 4, 138, doi:10.3390/met7040138
20
H. B. Li, Z. H. Jiang, H. Feng, S. C. Zhang, L. Li, P. D. Han, J. Z. Li,
Microstructure, mechanical and corrosion properties of friction stir
welded high nitrogen nickel-free austenitic stainless steel, Materials
& Design, 84 (2015), 291–299, doi:10.1016/j.matdes.2015.06.103
21
G. Sundar raju, K. Sivakumar, S. R. Nathan, Influence of tool rota-
tional speed on the mechanical and micro structural properties of
AISI 316 Austenitic stainless steel friction stir welded joints, Mate-
rials Research Express, 6 (2020) 12, 1265d7, doi:10.1088/2053-
1591/ab6248
22
A. K. Lakshminarayanan, V. Balasubramanian, M. Salahuddin,
Microstructure, tensile and impact toughness properties of friction
S: RAJU GOVINDARAJ, S. KARUPPAN: MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED ...
Materiali in tehnologije / Materials and technology 57 (2023) 2, 127–134 133

stir welded mild steel, Journal of Iron and Steel Research Interna-
tional, 17 (2010) 10, 68–74, doi:10.1016/S1006-706X(10)60186-0
23
R. Guo, Y. Huang, W. Zhang, W. Guan, Microstructures and mechan-
ical properties of thin 304 stainless steel sheets by friction stir weld-
ing, Journal of Adhesion Science and Technology, 32 (2018) 12,
1313–1323, doi:10.1080/01694243.2017.1409064
24
S. S. Kumar, N. Murugan, K. K. Ramachandran, Identifying the opti-
mal FSW process parameters for maximizing the tensile strength of
friction stir welded AISI 316L butt joints, Measurement, 137 (2019),
257–271, doi:10.1016/j.measurement.2019.01.023
25
S. H. C Park, Y. S. Sato, H. Kokawa, K. Okamoto, S. Hirano, M.
Inagaki, Microstructural characterization of stir zone containing re-
sidual ferrite in friction stir welded 304 austenitic stainless steel, Sci-
ence and Technology of Welding and Joining, 10 (2005) 5, 550–556,
doi:10.1179/174329305X46691
26
J. Yan, M. Gao, X. Zeng, Study on microstructure and mechanical
properties of 304 SS joints by TIG, laser and laser-TIG hybrid weld-
ing, Optics and Lasers in Engineering, 48 (2010) 4, 512–517,
doi:10.1016/j.optlaseng.2009.08.009
134 Materiali in tehnologije / Materials and technology 57 (2023) 2, 127–134
S: RAJU GOVINDARAJ, S. KARUPPAN: MECHANICAL AND METALLURGICAL PROPERTIES OF FRICTION-STIR-WELDED ...