original research article · research article resistance spot welding of aisi-316l ss and 2205 dss...

Original Research Article

Resistance spot welding of AISI-316L SS and2205 DSS for predicting parametric influences onweld strength – Experimental and FEM approach

K. Vignesh a,*, A. Elaya Perumal b, P. Velmurugan c

aDepartment of Mechanical Engineering, PSNA College of Engineering & Technology, Dindigul 624622, Tamil Nadu,IndiabDepartment of Mechanical Engineering, College of Engineering Guindy, Anna University, Chennai 600025,Tamil Nadu, IndiacDepartment of Automobile Engineering, RVS School of Engineering & Technology, Dindigul 624005, Tamil Nadu,India

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 9 ( 2 0 1 9 ) 1 0 2 9 – 1 0 4 2

a r t i c l e i n f o

Article history:

Received 25 January 2019

Received in revised form

8 April 2019

Accepted 11 May 2019

Available online 31 May 2019

Keywords:

RSW

AISI-316L

Duplex stainless steel 2205

Interfacial failure

Simulation

a b s t r a c t

The present study reports the effects of RSW process parameters like heating cycle, welding

current and electrode tip diameter on the tensile shear strength and nugget size of dissimilar

metal welding of 2205 duplex stainless steel (DSS) and AISI-316L stainless steel sheets.

Tensile shear tests were conducted to access the tensile shear strength and associated

physical variations of the nugget formed. Finite element (FE) simulation of the tensile–shear

test was performed using ABAQUS explicit FE software. The finite element results were

compared with experimental results through the aid of graphical representation by com-

paring the obtained stress–strain values for validation. The resistance spot welds are

subjected to Vickers microhardness test and identified that hardness of HAZ is less for

AISI-316L and high in DSS-2205 as compared to respective base metal, moreover heteroge-

neous hardness values obtained in the weld metal zone (WMZ) exhibits higher hardness in

ASS-316L and low hardness in DSS-2205 side as compared with base metal. Furthermore,

SEM fractography indicates that the failure of tensile shear spot welded specimen occurs in

the ductile mode of fracture.

© 2019 Politechnika Wroclawska. Published by Elsevier B.V. All rights reserved.

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1. Introduction

Resistance spot welding (RSW) process consumes low heatinput, due to the flow of electrical current through the parts to

* Corresponding author.E-mail address: [email protected] (K. Vignesh).

https://doi.org/10.1016/j.acme.2019.05.0021644-9665/© 2019 Politechnika Wroclawska. Published by Elsevier B.V

be welded while the heat is generated by the resistance offeredat the contact interfaces [1]. RSW provides high joining qualityand high productivity welds owing to which it is widely used inassembling thin metal sheets [2]. Many manufacturingindustries make use of RSW due to its repeatability, cost-

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effective equipment, and simple operational processes [3].Many varieties of vehicle parts are now manufactured usingstainless steel [4]. Consequently, significant interest is shownby automobile industries by preferring RSW technique forjoining stainless steel [5]. Joining of dissimilar materials isgaining interest in a wide range of industrial applications.Further, automotive industries are focusing on the imple-mentation of light weight materials in their applications byjoining dissimilar material combinations. The benefits injoining of dissimilar materials are a combination of lowspecific weight, the good corrosion resistance of one materialand good mechanical properties of other material. The majoradvantage of RSW derives from its applicability to joindissimilar materials [6]. AISI-316L grade of stainless steel(SS) is one among the most widely used austenitic stainlesssteels which has a microstructure of ferrite and austenitephases. Hence, this grade of SS is utilized in variousprocessing industries owing to its decorative appearance,excellent weldability and superior corrosion resistance [7].Duplex stainless steel (DSS) consists of dual phase austenite(d) and ferrite (a) microstructure and exhibits the perfectcombination of mechanical and corrosion resistance proper-ties [8]. During spot welding, a notable change has beennoticed in mechanical and metallurgical properties of spotwelds and associated heat affected zone. Hence, it isnecessary to carry out investigations of these changes forthe joint strength in high load-bearing applications and safety[9]. Joints made from spot welding are favoured extensively inapplications involving high load bearing conditions. Further,the mechanical strength has a dominant impact on thereliability of the welded structures. Hence, it is necessary toknow the deformation pattern during elastic-plastic condi-tions of spot welded joints at various loading conditions [10]and to understand time-dependent deformation [11]. Plasticdeformation in the welded structure is dependent on manyparameters such as the property of material, interactionbetween the geometry of joint and conduct of bond. Also, byvarying different base materials accurate predictions can beobtained by varying significant design parameters like sheetthickness, nugget size to understand the structural propertyand choice of perfect welding parameters [12]. The modes ofspot welded failure (i.e., the propagation of crack in the weldnugget during axial loading) are a qualitative indication ofweld enactment. Normally, spot weld joints fail at thesemodes [13]:

1. Pullout failure (PF) mode (removal of partial or completenugget from one sheet)

2. Interfacial failure (IF) mode (crack propagation throughnugget)

N. Akkas studied the influence of welding time on tensileshear strength in spot welding of SPA-H steel sheets. Thesamples were subjected to mechanical loading for measuringthe tensile–shear strength of the joints [14]. Hasanbasogluet al. observed the influence of the process parameters on theheat input namely tensile shear load bearing capacity,microhardness and peak current of dissimilar welds betweenDIN EN 10130-99 (7114 grade) interstitial free steel and AISI-316L austenitic stainless steel [15]. Hayat carried RSW test on

a dissimilar material combination of Al and Mg at differentvalues of weld current. Spot welds were exposed to thetensile shear tests for determining the failure mode and itsstrength [16]. Jagadeesha made an attempt to investigate theweld quality of spot welds for AISI-316 Laustenitic stainlesssteel sheets. They studied the influence of significant inputprocess parameters such as welding current and heatingtime on failure modes, weld nugget diameter and ultimatetensile shear strength [17]. Alizadeh-Sh et al. analysed thefailed samples after tensile-shear test of resistance spotwelded AISI-316L and lean duplex steel. Observations werethat the failure occurred in DSS base metal. Further, workhardening capability of DSS was lower compared to ASS [18].Vignesh et al. studied and determined the optimal processparameters set for attaining high tensile shear strengthwelds and larger nugget size for dissimilar spot welding of2 mm thick 2205 DSS and AISI-316L [19]. To accurately predictthe mechanical deformation of spot welds, FE analysis wasdeployed in modelling the RSW process. Also, some of theresearch work has been focused to validate the simulationresults with actual experiments, which includes Kong et al.studied the strength of spot welds of low carbon steel andobtained stress–strain curves. A fracture model was devel-oped using FEA technique to predict deformation of spotwelded joint beyond the onset of initial yield undermechanical loading [20].

In current industrial scenario, resistance spot welding is aninevitable practical requirement for welding dissimilar mate-rials like austenitic/duplex stainless steels, etc. Dissimilarresistance spot welding is more complex than similar weldingdue to its different physical and mechanical properties of thesheets; hence many studies were performed on the subject.However, to the best of our knowledge, no investigation wasdone on the predicting parametric influences of weld strengthof AISI-316L and DSS-2205 using experimental and FEMapproach. The research here explores the implications ofvarious process parameters namely the tip diameter of theelectrode, heating cycle and welding current on the nugget sizeand tensile shear strength of dissimilar metal spot weld. Finiteelement model is deployed to examine the behaviour ofspecimen computationally under static tensile–shear loadingand eventually fine-tune the model to predict the stress–strainvalues to match the experimental approach and establish itsfeasibility for real-time applications. The cross-sectioned RSWjoints were exposed to Vickers microhardness test diagonallyalong the radius of nugget. Further, the fractured specimenswere analysed using SEM–EDS to study the mode of fractureand elemental analysis.

2. Characterization and testing methods

2.1. Materials

DSS-2205 and AISI-316L with a thickness of 2 mm are selectedfor the study considering the wide application of thisparticular material and the desired dimensions. The chemicalcompositions of DSS-2205 and AISI-316L are presented inTables 1 and 2, respectively. Fig. 1 shows the tensile shear testsample prepared as per AWS D8.9M standard.

Table 1 – DSS-2205 chemical composition (Wt. – %).

UNS number Ni Cr N Mo Mn Si S Cu C Nb P Fe

Composition 5.74 22.37 0.17 3.2 1.52 0.4 0.02 0.17 0.02 0.05 0.02 Balanced

Table 2 – AISI-316L nominal composition (Wt. – %).

UNS number Mn Ni Mo Cr Co P Cu W Si S V C Ti

Composition 1.323 10.326 2.102 16.542 0.005 0.029 0.346 0.003 0.379 0.005 0.036 0.025 0.009

Fig. 1 – Tensile shear test sample (all dimensions are in mm).

Fig. 2 – Resistance spot welds of dissimilar materials – 9 trials.

Table 3 – Tensile properties of DSS-2205 and AISI-316L.

Grade Tensile stress (MPa) Tensile strain (%)

DSS-2205 501 1.18AISI-316L 465 0.33

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 9 ( 2 0 1 9 ) 1 0 2 9 – 1 0 4 2 1031

2.2. Welding process and parameters

A 50 kVA resistance spot welding machine is used for carryingout the spot welds of DSS-2205 and AISI-316L grade stainlesssteel. The operating parameters like heating cycles, weldingcurrent and electrode tip diameter are considered for welding.

Totally, 2 sets of 9 experimental welding trials were conductedon samples (Fig. 2) by varying the operating parameters. Oneset of welds is utilized for macroscopic examination andanother is employed to carry out the tensile–shear test.Experimental design matrix of each trials and subsequentnugget generated during each trials is measured in terms oflength, height and nugget area which is presented in Table 4.

2.3. Tensile shear test

Resistance spot welded samples are subjected to uni-axialtensile shear test using Tinius Olsen make 50 kN UTM with1 mm/min rate of loading to determine ultimate stress andplastic strain of the material as reported in Table 3. During the

Table 4 – Experimental design matrix.

Trialnumber

Weldingcurrent (kA)

Electrode tipdiameter (mm)

Heatingcycles

Nugget size Nugget area(mm2)

Length/diameter(mm)

Height (mm)

1 7 8 7 4.9214 2.8414 13.98362 8 8 7 5.2583 2.7715 14.57333 7 8 8 5.0311 2.7616 13.89384 8 6 8 5.9053 2.5781 15.22445 9 8 9 5.6070 2.6059 14.61126 8 7 9 5.6287 2.3029 12.96237 9 8 8 5.5375 2.5516 14.12948 7 8 9 4.8313 2.8185 13.61709 8 7 8 4.5640 2.3794 11.0595

Fig. 3 – Sheet accommodating a partial nugget.


test, once the peak load reaches, the tensile shear strength, i.e.,ultimate stress of the weld nugget is calculated from theobtained load–displacement curve. Yield stress, plastic strainand ultimate tensile shear strength of each trials aredetermined. Experiments are conducted for nine trials basedon the measured nugget size and nugget area.

3. Finite element (FE) analysis

FE simulation of the tensile shear test is performed usinga commercially available finite element code ABAQUS-6.14. Components such as sheet, nugget are modelledas deformable bodies. Two sheets having dimensions100 mm � 25 mm � 2 mm respectively are modelled withoverlapping length of 25 mm to create a lap joint. Spacerhaving a dimension of 50 mm is attached at the end of bothsheets to provide support and align the nugget with loadingline during a tensile test. The nugget is presumed to becircular (refer Fig. 3) and is modelled according to thedimensions obtained during each experimental trials. As-

sembly of parts is carried out by slicing the nugget into twohalves, each half of nugget is accommodated in both sheetsrespectively and at the centre of overlapping length bymerging of common nodes as shown in Fig. 3 and completeassembly is presented in Fig. 4. Material properties of sheetand nugget are assigned from performed experimental tensiletest values. Supplementing material properties assigned tothe parts are listed in Table 5. As the nugget is made of acomposition of two homogeneous mixtures of dissimilarmetals assigning material property during FE simulationbecomes difficult. Hence, each sheet with attached nuggethalf is assumed as identical material.

A suitable model for fracture initiation is necessary to usein addition with the stress model for characterizing thematerial failure, which takes into account the effects ofpressure, temperature, strain rate and equivalent stress. Inthis study, Johnson–Cook material model [21] was employedfor ductile damage in AISI-316L [22] and DSS-2205 [23] givenmathematically in Eqs. (1) and (2). The Johnson–Cook damageparameters assigned are presented in Tables 6 and 7respectively.

Fig. 4 – Complete assembly of the tensile shear test sample.

Table 5 – General material property assigned for AISI-316L and DSS-2205 sheets.

Material Youngs modulus (GPa) Poissons ratio Density (kg/m3)

AISI-316 L 193 0.3 7800DSS-2205 200 0.3 7860

Table 7 – Johnson–Cook damage parameters assigned forDSS-2205.

D1 D2 D3 D4 D5 Reference strain rate _e0 (s�1)

0.69 0 0 0.0546 0 1

Table 6 – Johnson–Cook damage parameters assigned forAISI-316L.

D1 D2 D3 D4 D5 Reference strain rate _e0 (s�1)

0.05 3.44 2.12 0.002 0 1


The failure is expected when parameter D = 1.

D ¼XDe

ef(1)

ef ¼ ½D1 þ D2 exp D3s��½1 þ D4 ln _e��½1 þ D5T�� (2)

where ef ¼equivalent strain to fracture;_e� ¼dimensionless strain rate; T* = homologous temperature;D1, D2, D3, D4 and D5 are material dependent constants; s* is

Table 8 – Parameters used for meshing in FE analysis.

Part Shape of element Meshing technique Elements generated

Sheet Hexagonal Sweep 10,128

Nugget Hexagonal Sweep 110,480

the ratio of the average of the three normal stresses to the vonMises equivalent stress assumed s* ≤ 1.5.

The Johnson–Cook damage model is not available for DSS-2205 in open literature, AISI 304 steel values are used, assimilar material properties are observed between the twomaterials.

Mesh convergence study is performed for tensile shearstrength test model to attain good balance of computationtime with minimal error in prediction of weld strength. Thepredicted results showed good validation with experimentalresults, when tensile test model is meshed with 10,128 and110,480 elements for sheet and nugget respectively. The seedsize in fine and course mesh region of sheet is 5 mm and15 mm respectively. Similarly, the seed size in meshed regionof nugget is 0.1 mm. The mesh parameters employed inpresent study are shown in Table 8. The mesh density in sheetis concentrated near the nugget area as shearing is observed inthe lap joint region. Course mesh is applied at the end of theplates as results are not expected in that region andconsequently reduce the simulation time. General contactwith penalty friction coefficient of 0.25 is assigned forspecifying interaction between the nugget and sheet surfaces.

Boundary conditions adopted in the model are presented inFig. 5. One end of plate (AISI-316L) region is applied ENCASTRE(U1 = U2 = U3 = UR1 = UR2 = UR3 = 0) boundary conditionrestricting movement in all directions and the second plate

Element type

C3D8R (an 8 node linear brick, reduced integration with hourglasscontrol)C3D8R (an 8 node linear brick, reduced integration with hourglasscontrol)

Fig. 5 – Boundary conditions incorporated in the model.

Fig. 6 – Macrographs of resistance spot welds for Trial Nos. (a) 5 and (b) 6.


(DSS-2205) is allowed to move in the X direction and the load isassigned in the same direction. The FE simulation wasperformed till there is separation of nugget and results areextracted.

4. Results and discussions

For accurately predicting the tensile shear failure produced bythe tensile shear test in resistance spot welds, Finite ElementModelling is adopted due to its flexibility in modelling and itscapability in obtaining full field numerical solutions. Finally,the simulated results are compared with the experimentaloutcomes to examine the reasonableness of the developed FEmodel.

4.1. Macrograph test

Fig. 6 shows the macrograph of the spot welds for differentinput process parameters. It is inferred from the results thatthe length/diameter and height of the nugget has a directrelationship with the heat input during spot welding and itusually decreases with the decrease in heat input. The effect ofheat input clearly brings out the difference in the nugget area.From the macrographs, it is evident that the fusion boundaryof the weld nugget is distinct with a very narrow heat affectedzone (HAZ) on both sides of AISI-316L and DSS-2205. Further,macro examination reveals that the weld nugget is free fromdiscontinuity and defects and shows adequate penetrationwith AISI-316L and DSS-2205 sheets.

Also, the height of the nugget is observed to be almost thesame in the DSS-2205 side and AISI-316L side (Fig. 6(a)

1.3887 mm (DSS) and 1.2171 mm (SS) and (b) 1.1985 mm(DSS) and 1.1043 mm (SS)). However, there is a slight variationin the nugget area, i.e., the nugget area is observed to be muchhigher in the DSS-2205 side as compared to AISI-316L side. Thisis attributed to the fact that the thermal conductivity of AISI-316L (16.3 W/mK) is lower than the DSS-2205 (19 W/mK).

AWS has formulated an empirical relation, Eq. (3) forcalculating a minimum weld nugget diameter of a given sheetthickness for joining similar materials [13]. This formulationhas been made to meet the various industrial standards:

d ¼ 4ffiffit

p(3)

where d = diameter of nugget and t = thickness of sheet.

Based on the relation, a minimum weld nugget diameter fora 2 mm thick sheet is calculated and observed to be around5.6 mm. From the macroscopic examination of the weldnugget, it is revealed that the nugget diameters obtained inthe present research study, i.e., for joining dissimilar materials(DSS + AISI-316L) are very close to the recommended value.Hence the developed welds are readily used for industrialapplications.

4.2. Experimental tensile shear test analysis

The stress–strain and ultimate tensile strength values of weldspecimen obtained from the uni-axial tensile test is given inTable 9. Trial 5 has shown the highest tensile load of 16,400 Nalong with the ultimate stress of 660.32 N/mm2 and plasticstrain of 0.0737%. The graphical representation of the stress–strain curve for all the trials is presented in Fig. 7.

Table 9 – Tensile shear strength of resistance spot welds.

Trial number Ultimate stress (N/mm2) Plastic strain (%) Ultimate load (N)

1 538.31 0.0417 10,3002 585.99 0.0512 12,8003 580.10 0.0438 11,6004 493.66 0.0530 13,6005 660.32 0.0737 16,4006 583.32 0.0551 14,6007 577.92 0.0711 14,0008 650.76 0.0423 12,0009 802.15 0.0486 13,200

Fig. 7 – Experimentally obtained stress–strain curves for all the trials.


It is noticed from the tensile shear test, the load carryingcapacity of the developed spot welds is observed to be morethan 10 kN. The results show that with increasing weldingcurrent from 7 kA to 9 kA, the tensile–shear force increasedand the failure occurs through weld nugget. This behaviour isattributed to an increase in the diameter of weld nugget. Aswelding current increases, the nugget diameter enlarges, andconsequently, the spot weld will fail in higher tensile–shearforce. Though, high amount of energy is required for completerupture in welded sheets. Here, the welds are failed underinterfacial failure mode. This may occur due to the fact that theenergy absorption capability of these welds is less and there isa small necking in the weld nugget. In this mode of failure,stresses are distributed along weld circumference and at theinterface region. Hence, a crack is propagating through theweld nugget due to dominant shear stresses resulting in

interfacial failure. Generally, it is reported that an interfacialfailure in resistance spot welds is indicative of poor weldintegrity. But the statement is true only for low strength steels(tensile strength < 300 MPa) and joining of similar sheetmetals. Here, the investigation is carried out on spot weldsof dissimilar sheet metals with a minimum tensile strength of450 MPa.

4.3. Finite element tensile shear test analysis

Tensile–shear test simulation is performed using ABAQUSexplicit software to evaluate the tensile shear strength of thesample. Initially, a single trial will be considered for numericalanalysis. Based on the trial analysis and results, the study willbe continued for remaining trials. Hence, Trial-5 has beenselected as a personal choice among the remaining trials for

Fig. 8 – Shearing of nugget from one sheet.

Fig. 9 – Separation of plates after the nugget is broken.

Fig. 10 – Final separation of nugget.


Fig. 11 – Numerically obtained graphical representation of stress–strain curve.

Fig. 12 – Graphical representation of stress–strain curve comparison between experimental and numerical analysis.


numerical analysis. When the load is applied both the platesundergo small deflection. Generally, as tensile load goes onincreasing the loading plate undergoes more displacementcompared to the stationary plate. As, the peak load is reachedthe lap joint starts to deform and finally break due to a

combination of tensile and shear forces as shown in Fig. 8. Thebreak-up of nugget was observed to be separation mode offailure for Trial-5 with welding current of 9 kA, heating time of9 cycles and electrode tip diameter of 8 mm, respectively. Theultimate tensile shear strength was taken as maximum weld

Fig. 13 – Comparison between experimental and finite element analysis of the tensile shear test.

Fig. 14 – Experimental microhardness measurement of spot welded specimen (a) various zones in the weld nugget.


strength, after the weld joints have broken. The weld nuggetgets sheared off from the weld specimen and finally, the platesget separated as shown in Fig. 8. The separation of two sheetsafter the nugget gets sheared in both the experimental andsimulation results is shown in Fig. 9. Good agreement in termsof nugget breakage and spot weld region after the separation of

two plates is observed and found to be exact in both the cases.Fig. 9(a) depicts the bottom side of the plate with a clearindication of nugget sheared region, whereas Fig. 9(b) depictsthe top side of the plate with the impression of heat affectedzone of the spot weld. When the induced stress level in theweld zone reaches a maximum stress of 659.95 MPa, the

Fig. 15 – SEM fractograph of the tensile shear spot weldedspecimen (a) DSS-2205 at 500T and (b) AISI-316L at 1000T.


nugget finally gets separated from the weld joint and is shownin Fig. 10. From experimental analysis considering Trial-5, itwas seen that ultimate tensile stress was 660.32 MPa. Hence, agood correlation is noticed between the experimental and FEanalysis with an error percentage of 0.1. Fig. 11 depicts thegraphical representation of stress with respect to strain for FEsimulation. It can be observed that maximum tensile stresswas observed to be 659.95 MPa with respect to the strain of0.07%. Grain size variations due to thermal implications alsoform a key component in improving the weldability andstrength of the joints. The process of nucleation is restrictedoccasionally which is reflected in the mechanical behaviour ofthe system. In specific, an appropriate characteristic of nuggetcombined with the depth of indentation, nugget diameter, andhomogeneous weld quality is advantageous to the mechanicalproperties.

Graphical representation depicting the comparison ofstress–strain curves for experimental and FEA simulation ofthe tensile–shear test is shown in Fig. 12. It can be observedthat experimental and simulation curves are synchronous intheir approach from initial to a final point of fracture. Hence,from the comparison, it was observed that a close conferenceis observed between them in terms of the stress–strain curve.Further, remaining trials of numerical analysis was undertak-en and good validation was observed. Fig. 13 shows the visualcomparison of the shear tensile test between experimental asshown in Fig. 13(a) and simulation as shown in Fig. 13(b), goodmatch can be observed in terms of separation of sheetsaccompanied with a bend at the free ends of the plates. Tensileshear strength improved with a small decline with an increasein welding time, electrode force and welding current. Thecoarse ferrite adjacent to the fracture surface appears toexperience larger plastic deformation in the direction ofapplied load.

4.4. Microhardness test analysis

The resistance spot weld sample was subjected to Vickersmicrohardness test to determine the hardness values. TheVickers microhardness number (VHN) was measured through-out the weld area at a load of 500 gf and a residence time of 15 sat an equal pitch of 0.5 mm using the Matsuzawa MMT-Xseries.

Fig. 14 shows the profile of longitudinal hardness in theweld metal. AISI-316L HAZ exhibited softening in comparisonto the base metal (BM). Generally, AISI-316L softens in the HAZdue to the growth of the grain in the annealed material orrecrystallization and growth of the grain in the cold workedmaterial. The originally tested AISI-316L was in the millannealing condition, it can be assumed that the grain growthphenomenon induces the softening of the heat affected zone(HAZ). The microstructure at the weld nugget (FZ) consists ofequiaxed grains at the centre of the nugget (zone A) andcolumnar grains at the AISI-316L nugget edge (zone B) andDSS-2205 nugget edge (zone C) as highlighted in the hardnessplot (refer to inset Fig. 14(a)). The heat produced during thewelding is mostly used for the formation of nugget and fastercooling allows to form equiaxed grains in the centre. Theequiaxed to columnar transition takes place as columnargrains is mostly observed in the nugget edge at the both sides.

In general, for ASS the equiaxed grains give higher hardnessand for columnar grains lower hardness. Further, themechanical properties of the DSS-2205 are dependent on thed/g ratio. The higher d/g ratio, results in greater hardnessbecause of slight increase in hardness of ferrite phase incomparison to the austenitic phase. From Fig. 14, it is noticedthat the hardness in HAZ of DSS-2205 is greater as that of DSS-2205 BM. This contradiction can be clarified by the rise in thecarbon % at the HAZ because of the dissolution of TiC particles,which leads to an increase in the hardness at HAZ by themechanism of the solid solution strengthening. Based on thenugget macro structure, greater hardness of the AISI-316LWMZ can be credited to its equiaxed grain structure with moreboundaries between phases and lower hardness of the DSS-2205 WMZ is due to its columnar grain morphology [18].

4.5. Fractography examination

The main reason for the interfacial failure is attributed tocreation of shear stress at the interface. As the intensity ofthe shear stress goes beyond the shear strength of the nugget,failure of nugget occurs at the interface. Further, fractogra-phy test was conducted to validate the above point by

Fig. 16 – Elemental mapping of DSS-2205 spot welded fractured surface.


preparing the shear tensile tested sample by ultrasonicallycleaning and examining the surface of fracturedspecimen under a scanning electron microscope (SEM).Fig. 13 represents the surface of fracture in spot weldspecimen that failed in the IF mode during a tensile sheartest along with dimples. The elongated dimples show thatthe failure mechanism is shear mode. Also, during theinterfacial failure in the open mode of the tensile shear testexperience (i.e., I mode of fracture mechanics) in which thetendency to fail in a brittle manner is high, the presence of

dimples on the fracture surface indicates the ductile naturefail. This is due to the fact that AISI-316L and DSS-2205 aresoft materials which exhibit large plastic deformationbefore the final fracture. In addition, as it can be seen, thedimples are almost equiaxed, which indicates that thefracture occurred under normal tensile stress. This showsthat main reason for the IF mode in the present case is theshear stress to the traction. A typical quasi-cleavage fractureis also conveyed by the presence of Torn bands as observed inFig. 15(a) and (b) [24–26].

Fig. 17 – Elemental mapping of AISI-316L spot welded fractured surface.


4.6. Elemental mapping analysis of spot welded fracturedsurface weldments

Fig. 15(a) and (b) shows the scanning electron microscope(SEM) image of a spot weld that failed in the IF mode during atensile shear test and the corresponding elemental distribu-tion mapping. The elemental distribution in the fracturedsurface zone (refer Figs. 16 and 17) reveals that the dimples andtorn bands are rich in Fe, Ni, Cr and comparatively low in Mo

elements. The elemental analysis also, confirms the mode ofinterfacial failure indicating ductile type failure.

5. Conclusions

Two metallic sheets, i.e., AISI-316L and DSS-2205, each of2 mm thickness were welded in a lap joint configuration usingresistance spot welding process. Further, the specimens were


subjected to a uni-axial tensile test to determine the tensileshear strength of weld and evaluate its effects by changingprocess parameters. Based on the present investigations, thefollowing conclusions can be drawn:

� Tensile–shear load carrying capability of spot weldedspecimens increased with the increase in welding current,as a result of enlargement in weld nugget size.

� Trial-5 is having parameters of 8 mm electrode tip diameter,9 kA welding current and 9 cycles heating time showedmaximum tensile shear strength by sustaining a load of16,400 N before failure.

� The maximum weld strength of spot weld is taken as thestress obtained at the point of failure, and it is observed to be660.32 MPa during experimentation and 659.95 MPa for FEsimulation. Hence, a good correlation is noticed between theexperimental and FE analysis with an error percentage of 0.1.

� Heterogeneous hardness values obtained in the weld metalzone (WMZ) exhibit higher hardness in AISI-316L and lowhardness than BM in the DSS-2205 side.

� The fractographic study indicates the presence of dimplesand torn bands on surface of fracture in spot weldedspecimen conforming the ductile type failure.

Acknowledgements

This research did not receive any specific grant from fundingagencies in the public, commercial, or not-for-profit sectors.

r e f e r e n c e s

[1] N.T. Williams, J.D. Parker, Review of resistance spot weldingof steel sheets. Part 1 Modelling and control of weld nuggetformation, Int. Mater. Rev. 49 (2) (2004) 45–75.

[2] S. Chen, T. Sun, X. Jiang, J. Qi, R. Zeng, Online monitoring andevaluation of the weld quality of resistance spot weldedtitanium alloy, J. Manuf. Process. 23 (2016) 183–191.

[3] M. Vural, A. Akkus, On the resistance spot weldability ofgalvanized interstitial free steel sheets with austenitic stainlesssteel sheets, J. Mater. Process. Technol. 153–154 (2004) 1–6.

[4] A. Saha Podder, A. Bhanja, Applications of stainless steel inautomobile industry, Adv. Mater. Res. 794 (2013) 731–740.

[5] V. Zohoori-Shoar, A. Eslami, F. Karimzadeh, M. Abbasi-Baharanchi, Resistance spot welding of ultrafine grained/nanostructured Al 6061 alloy produced by cryorolling processand evaluation of weldment properties, J. Manuf. Process. 26(2017) 84–93.

[6] C.H. Muralimohan, S. Haribabu, Y.H. Reddy, V. Muthupandi,K. Sivaprasad, Evaluation of microstructures and mechanicalproperties of dissimilar materials by friction welding,Procedia Mater. Sci. 5 (2014) 1107–1113.

[7] D. Kianersi, A. Mostafaei, A.A. Amadeh, Resistance spot weldingjoints of AISI 316L austenitic stainless steel sheets: phasetransformations, mechanical properties and microstructurecharacterizations, Mater. Des. 61 (2014) 251–263.

[8] J. Verma, R.V. Taiwade, Effect of welding processes andconditions on the microstructure, mechanical properties andcorrosion resistance of duplex stainless steel weldments—areview, J. Manuf. Process. 25 (2017) 134–152.

[9] D. Özyürek, An effect of weld current and weld atmosphereon the resistance spot weldability of 304L austenitic stainlesssteel, Mater. Des. 29 (3) (2008) 597–603.

[10] S.M. Darwish, Weldbonding strengthens and balances thestresses in spot-welded dissimilar thickness joints, J. Mater.Process. Technol. 134 (3) (2003) 352–362.

[11] M. Palmonella, M.I. Friswell, J.E. Mottershead, A.W. Lees,Finite element models of spot welds in structural dynamics:review and updating, Comput. Struct. 83 (8) (2005) 648–661.

[12] Y.J. Chao, Ultimate strength and failure mechanism ofresistance spot weld subjected to tensile, shear, orcombined tensile/shear loads, J. Eng. Mater. Technol. 125 (2)(2003) 125–132.

[13] M. Pouranvari, S.P.H. Marashi, Critical review of automotivesteels spot welding: process, structure and properties, Sci.Technol. Weld. Join. 18 (5) (2013) 361–403.

[14] N. Akkas, Welding time effect on tensile–shear loading inresistance spot welding of SPA-H weathering steel sheetsused in railway vehicles, Acta Phys. Pol. A 131 (2017) 52–54.

[15] A. Hasanbasoglu, R. Kaçar, Resistance spot weldability ofdissimilar materials (AISI 316L–DIN EN 10130-99 steels),Mater. Des. 28 (6) (2007) 1794–1800.

[16] F. Hayat, The effects of the welding current on heat input,nugget geometry, and the mechanical and fracturalproperties of resistance spot welding on Mg/Al dissimilarmaterials, Mater. Des. 32 (4) (2011) 2476–2484.

[17] T. Jagadeesha, Experimental studies in weld nugget strengthof resistance spot-welded 316L austenitic stainless steelsheet, Int. J. Adv. Manuf. Technol. 93 (1) (2017) 505–513.

[18] M. Alizadeh-Sh, S.P.H. Marashi, Resistance spot welding ofdissimilar austenitic/duplex stainless steels: microstructuralevolution and failure mode analysis, J. Manuf. Process. 28(2017) 186–196.

[19] K. Vignesh, A. Elaya Perumal, P. Velmurugan, Optimization ofresistance spot welding process parameters andmicrostructural examination for dissimilar welding of AISI316L austenitic stainless steel and 2205 duplex stainlesssteel, Int. J. Adv. Manuf. Technol. 93 (1) (2017) 455–465.

[20] X. Kong, Q. Yang, B. Li, G. Rothwell, R. English, X.J. Ren,Numerical study of strengths of spot-welded joints of steel,Mater. Des. 29 (8) (2008) 1554–1561.

[21] K.N. Wang, Eu-Gene, Calibration Of The Johnson–CookFailure Parameters As The Chip Separation Criterion In TheModelling Of The Orthogonal Metal Cutting Process, 2016.

[22] N. Sawarkar, G. Boob, Finite element based simulation oforthogonal cutting process to determine residual stressinduced, International Conference on Quality Up-gradationin Engineering, Science and Technology, IJCA J. (2014) 33–38.

[23] P. Krasauskas, S. Kilikevicius, R. C?esnavicius, D. Pacenga,Experimental analysis and numerical simulation of thestainless AISI 304 steel friction drilling process, Mechanika20 (6) (2014) 590–595.

[24] M. Pouranvari, Marashi Pirooz, Failure mode transition inAISI 304 resistance spot welds, Weld. J. 91 (11) (2012) 303–309.

[25] M. Pouranvari, H.R. Asgari, S.M. Mosavizadch, P.H. Marashi,M. Goodarzi, Effect of weld nugget size on overload failuremode of resistance spot welds, Sci. Technol. Weld. Join. 12 (3)(2007) 217–225.

[26] X. Yuan, C. Li, J. Chen, X. Li, X. Liang, X. Pan, Resistance spotwelding of dissimilar DP600 and DC54D steels, J. Mater.Process. Technol. 239 (2017) 31–41.

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original research article · research article resistance spot welding of aisi-316l ss and 2205 dss...

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