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ATIG Welding of 316L & 2205 Stainless Steel: Microstructure & Corrosion
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materials Article Mechanical, Microstructure, and Corrosion Characterization of Dissimilar Austenitic 316L and Duplex 2205 Stainless-Steel ATIG Welded Joints Kamel Touileb 1, *, Abdeljlil Chihaoui Hedhibi 1,2 , Rachid Djoudjou 1 , Abousoufiane Ouis 1 , Abdallah Bensalama 3 , Albaijan Ibrahim 1 , Hany S. Abdo 4,5 and Mohamed M. Z. Ahmed 1,6 1 2 3 4 5 Citation: Touileb, K.; Hedhibi, A.C.; Djoudjou, R.; Ouis, A.; Bensalama, A.; Ibrahim, A.; Abdo, H.S.; Ahmed, M.M.Z. Mechanical, Microstructure, and Corrosion Characterization of Dissimilar Austenitic 316L and Duplex 2205 Stainless-Steel ATIG Welded Joints. Materials 2022, 15, 2470. https://doi.org/10.3390/ ma15072470 Academic Editors: Dwayne D. Arola, Filippo Berto, Abílio M.P. De Jesus and José A.F.O. Correia Received: 1 March 2022 Accepted: 24 March 2022 Published: 27 March 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. 6 * Department of Mechanical Engineering, College of Engineering in Al-Kharj, Prince Sattam Bin Abdulaziz University, P.O. Box 655, Al-Kharj 16273, Saudi Arabia; a.hedhibi@psau.edu.sa (A.C.H.); r.djoudjou@psau.edu.sa (R.D.); a.ouis@psau.edu.sa (A.O.); i.albaijan@psau.edu.sa (A.I.); moh.ahmed@psau.edu.sa (M.M.Z.A.) Department of Mechanical Engineering, National Engineering School of Tunis (ENIT), El-Manar University, P.O. Box 37, Belvedere Tunis 1002, Tunisia Department of Electrical Engineering, College of Engineering in Al-Kharj, Prince Sattam Bin Abdulaziz University, P.O. Box 655, Al-Kharj 16273, Saudi Arabia; m.benslama@psau.edu.sa Center of Excellence for Research in Engineering Materials (CEREM), King Saud University, P.O. Box 800, Al-Riyadh 11421, Saudi Arabia; habdo@ksu.edu.sa Mechanical Design and Materials Department, Faculty of Energy Engineering, Aswan University, Aswan 81521, Egypt Department of Metallurgical and Materials Engineering, Faculty of Petroleum and Mining Engineering, Suez University, Suez 43512, Egypt Correspondence: k.touileb@psau.edu.sa Abstract: The present work analyzed the microstructure, mechanical, and corrosion properties of a dissimilar activated tungsten inert gas (ATIG) welded 2205 duplex stainless-steel (2205 DSS) plate and AISI 316L austenitic stainless steel (316L ASS) and compared them to conventional dissimilar welded tungsten inert gas (TIG). The mixing design method is a tool used to establish the optimal combined flux to achieve a full-penetrated weld bead in one single pass. A microstructure study was carried out by scanning electron microscopy (SEM). The ATIG and TIG fusion zones revealed a matrix ferrite structure with intragranular austenite, Widmanstätten needles, allotriomorphic austenite at the grain boundaries, and plate-like precipitates free of deleterious phases such as sigma and chi phases or second austinite owing to the moderate heat input provided of 0.8 kJ/mm. Ferrite volume proportion measurements were carried out utilizing the areas image processing software. The average ferrite volume proportion attained 54% in the ATIG weld zone; however, it decreased to 47% for the TIG weld zone. The results showed that the optimal flux composed by 91% Mn2 O3 and 9% Cr2 O3 allowed a full penetrated weld to be obtained in one single pass. However, a double side weld is required for conventional TIG processes. The values of the tensile (599 Mpa), hardness (235 HV), and impact test (267 J/cm2 ) measurements of ATIG welds were close to those of conventional TIG welds. The elaborated flux did not degrade the mechanical properties of the joint; on the contrary, it reinforced the strength property. The width of the ATIG heat-affected zone was narrower than that of TIG welding by 2.6 times, ensuring fewer joint distortions. The potentiodynamic polarization test results showed a better electrochemical behavior for ASS 316L than with the weldment and the parent metal of DSS 2205. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article Keywords: ATIG; mixing method design; weld aspect; microstructure; mechanical properties; corrosion resistance distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Materials 2022, 15, 2470. https://doi.org/10.3390/ma15072470 https://www.mdpi.com/journal/materials Materials 2022, 15, 2470 2 of 21 1. Introduction Nowadays, the industry has increasingly opted for high-performance materials and processes, which contribute to economic development. Dissimilar welding is a technical feat that meets the expectations of manufacturers. Dissimilar welding is beneficial on two aspects. First, it is beneficial from an economic point of view. Dissimilar welding allows the joining of expensive materials characterized by good corrosion resistance and good mechanical properties with another, cheaper material but of lower quality without altering the soundness of the joint, and it must meet the requirements of strength and safety of the structure being joined [1–3]. Secondly, a judicious choice of materials to be welded allows the targeted mechanical properties and corrosion resistance to be reached, needed for specific industry applications such as the nuclear industry, pipelines in desalination plants, and offshore oil and gas pipelines [4,5]. DSS grades are predominately used in marine fabrication industries such as the fabrication of ocean mining machinery, desalination plants, chemical tankers in ships, offshore concrete structures, pipelines, and oil and gas separators [6]. DSSs are usually selected where both high strength and corrosion resistance are required. DSS 2205 has been developed over the last two decades by metallurgists to obtain a stainless steel that is not only stronger than standard marine grade 316 but also offers much better corrosion resistance. The corrosion resistance of DSS 2205 is almost twice that of the ordinary 316. This is due to added levels of nickel, chromium, molybdenum, and nitrogen [7,8]. DSS 2205 is a combination of a ferritic phase with a BCC crystal structure and austenitic phase that crystallizes in FCC with a balance around 50%:50%. The ferrite structure assures high strength and withstands perfectly to stress corrosion cracking (SCC), while the austenite ensures good ductility and general corrosion resistance [9,10]. Austenitic stainless steels remain the most popular grades due to their unique combination of high weldability, high strengthening ability, high ductility, high toughness even at extra-low temperatures, and high corrosion resistance. The good weldability of austenitic stainless steel is affected by the hot cracking that occurs during the welding operation. This defect is ascribed to the presence of a susceptible chemical composition (low-melting-point constituents such as sulfur) and a high level of restraint or tensile stresses present in the weld [11]. The difficulties arising while welding dissimilar materials together are related to the fact that the larger the difference in melting point, the difference in linear expansion coefficient, and the thermal conductivity, the more difficult it is for the weld and the two base metals to meet the requirement of equal strength. To overcome these concerns, metal fillers are chosen related to materials to be joined [12,13], and when required, postweld heat treatment (PWHT) is used [14] to reduce the mechanical properties to the targeted values. In other cases, the preheat is carried out to avoid any drawbacks in the weld, as in the work conducted by Ghosh et al., to achieve satisfactory joining between AISI 304 austenitic stainless steel to AISI 420 martensitic stainless steel [15]. The joining of austenitic stainless steel and duplex stainless steel is widespread in marine applications due to their combination of better corrosion resistance and good mechanical properties. However, problems such as the hot cracking tendency, the formation of a secondary austenite (γ2 ) phase, particularly in multiple weld passes [16,17], or the appearance of detrimental intermetallic phases such as sigma (σ), chi (χ), and chromium nitride (Cr2 N) seriously affect the mechanical properties and corrosion resistance of the joint [11,18–22]. Tungsten Inert Gas (TIG) is the most widely used fusion welding process in industry due to its flexibility, on the one hand, and, on the other hand, a variety of materials can be welded using this technique. Unfortunately, this technique allows only 3 mm of depth to be reached in one single pass. In addition, TIG welding is very sensitive to microchemistry variations from cast to cast [23]. Activated Tungsten Inert Gas (ATIG) is an alternative method. The ATIG process was developed at the E.O. Paton Institute of Welding in Kiev in the 1960s. In ATIG welding, a thin layer of flux powder is deposited on edges to Materials 2022, 15, 2470 3 of 21 be joined. With this technique, 7 mm can be achieved in one single pass without filler metal or edge preparation. ATIG meets the requirements of manufacture in enhancing the productivity [24,25]. The improvement of penetration is related to the following mechanisms. The first mechanism is related to reverse Marangoni convection [26,27]. The second one is related to constriction of arc welding [28,29]. Many studies have investigated the dissimilar DSS 2205 and ASS 316L weld bead by testing different filler metals. For instance, Dhananjay et al. [30] tested different filler metals ER316L and ER309L. They showed in this study that the maximum average tensile strength of 548 MPa was obtained while ER316L filler metal was used compared to the value of 544 MPa when ER309L was tested. In another study, Verma et al. investigated the effects of different filler metals such as E2209, E309LMo, and E309L on dissimilar DSS 2205 and ASS 316L weld beads using multiple weld passes. The obtained tensile strength values were 554 MPa, 544 MPa, and 532 MPa for E2209, E309LMo, and E309L, respectively [31,32]. Limited works have been dedicated to establishing the effects of single flux powders on welds [33], and even fewer have been interested in the effect of combined powders on dissimilar DSS 2205 and ASS 316L weld beads. The novelty of this paper is in the use of the design of experiments mixing method tool to determine the best combination from the available oxide powders as an optimal flux in order to achieve a full penetrated dissimilar DSS 2205 and 316L ASS weld in a single pass without edge preparation, without altering mechanical properties and corrosion resistance of the joints, and without resorting to post-weld heat treatment (PWHT). 2. Materials and Methods 2.1. Material The materials used in this study were the austenitic stainless-steel grade 316L and the duplex stainless-steel grade 2205 in rectangular plates of 6 mm thickness and 200 mm length × 100 mm width. The chemical composition of both stainless steels is given in Table 1. Table 2 depicts the oxides used and their physical properties. Table 1. Chemical composition (wt.%) of 316L and duplex grade 2205 stainless steels. Elements C Mn Si P S Cr Ni Mo N Cu Co Fe 316L SS 0.026 1.47 0.42 0.034 0.0016 16.60 10.08 2.14 0.044 0.50 - Balance 2205 SS 0.016 1.35 0.47 0.025 0.001 22.42 5.71 3.15 0.17 0.21 0.14 Balance Table 2. Oxides used and their physical properties. Oxides SiO2 TiO2 Fe2 O3 Cr2 O3 ZrO2 Mn2 O3 V2 O5 Co2 O3 MgO Melting Temperature (◦ C) 1722 1830 1540 2435 2715 940 690 895 2600 902 941 826 1128 1080 971 1551 577 572 Dissociation energy ∆H◦ (kJ/mol) 2.2. Welding Procedure ATIG welding was used to weld austenitic SS 316L and duplex SS 2205 in dissimilar butt joints. Before welding, the plates were cleaned with acetone. To eliminate humidity of the powder, it was heated separately in a furnace at 100 ◦ C for 1 h. A thin layer of a mixed powder with methanol in the proportion of (1:1) made in a form of paste was applied using a brush on plain edges to be joined. The mean coating density of flux was about 4–5 mg/cm2 . The joints were executed with a square butt weld design without edge preparation. Both plates were clamped with zero gap distance, as shown in Figure 1. The welding parameters used are reported in Table 3. The heat input recommendation is 0.5 to 2.5 kJ/mm, so the welding parameters chosen provided an acceptable range of moderate heat input of 0.8 kJ/mm. Materials 2022, 2470 Materials 2022, 15, x FOR PEER REVIEW Materials 2022, 15,15, x FOR PEER REVIEW 44 of 22 4 of 2221 Figure 1.The The deposition of the mixed flux on the workpiece before ATIG welding. Figure 1.1.The deposition ofof the mixed flux onon the workpiece before ATIG welding. Figure deposition the mixed flux the workpiece before ATIG welding. Table 3.Welding Welding parameters used this study. Table 3.3.Welding parameters used ininin this study. Table parameters used this study. Parameters Parameters Parameters Welding voltage Welding voltage Welding voltage Arc efficiency Arc efficiency Arc efficiency Welding current Welding current Welding current Welding speed Welding speed Welding speed Arc Length Arc Length Arc Length Electrode angle Electrode tiptip angle Electrode tip angle Shielding gas workpiece Shielding gas on the workpiece Shielding gason onthe the workpiece Shielding backside Shielding gasgas onon the backside Shielding gas onthe the backside Welding mode Welding mode Welding mode Range Range Range Volts 1010 Volts 75% 10 Volts 75% 180180 A A75% 180 A mm/min 110110 mm/min 110 mm/min 2 mm 2 mm 2 mm 45°45° 45◦ Argon with a flow rate 12 L/min Argon with a flow rate of of 12 L/min Argon with a flow rate of 12 L/min Argon with a flow rate 5 L/min Argon with a flow rate of of 5rate L/min Argon with a flow of 5 L/min Negative direct current electrode Negative direct current electrode Negative direct current electrode After the ATIG welding, the samples were cut from the welded joints far from the After the ATIG welding, the samples were cut from the welded joints far from the After the ATIG welding, the samples were cut from the welded joints far from the welding starting point to be sure that the arc welding was stabilized, as shown in Figure welding starting point to be sure that the arc welding was stabilized, as shown in Figure 2. welding starting point to be sure that the arc welding was stabilized, as shown in Figure2.2. Figure Schematic drawing showing test specimens taken from the dissimilar ATIG welded DSS Figure 2.2.2. Schematic drawing showing test specimens taken from the dissimilar ATIG welded DSS Figure Schematic drawing showing test specimens taken from the dissimilar ATIG welded DSS 2205 and 316L stainless steels different types tests. 2205 and 316L stainless steels forfor thethe different types of of tests. 2205 and 316L stainless steels for the different types of tests. 2.3. Design of Experiments Methodology 2.3. Design ofof Experiments Methodology 2.3. Design Experiments Methodology Design of Experiments (DOE) considered one of the most essential statistical tools Design ofof Experiments (DOE) isisis considered one ofof the most essential statistical tools Design Experiments (DOE) considered one the most essential statistical tools for designing high-quality experimental systems a reduced cost. this study, mixfor designing high-quality experimental systems atat cost. In In this study, the mixing for designing high-quality experimental systems at aa reduced this study, thethe mixing method was used and Minitab 17 software was the most appropriate tool for this purmethod was used and Minitab 1717 software was thethe most appropriate tool for this purpose. ing method was used and Minitab software was most appropriate tool for this purIn the step, eight kinds ofkinds oxides (SiO TiO O23, ,Fe V2O ,3,CoO pose. In first step, eight oxides (SiO 2, 2TiO 2Cr , Fe 23O 3, ,ZrO Cr 3Mn , ZrO 23, ,Mn 23O pose. Infirst thethe first step, eight kinds of of oxides TiO 2O ,3Cr 2O23O ,5V 2V O25O , 35,, 2 , (SiO 22,, Fe 2O 2, ,ZrO 22,OMn 2O MgO) tested. Single oxides were deposited on bothon materials and welding operation CoO 3,were MgO) were tested. Single oxides were deposited on both materials and welding CoO 3, MgO) were tested. Single oxides were deposited both materials and welding was carried out. Among these eight oxides, three oxides candidates Cr and operation was carried out. Among theseeight eight oxides, three oxidescandidates candidates 23O operation was carried out. Among these oxides, three oxides Cr3Cr 2,O , 3, 2 O3 , Fe2 O Mn O that gave the best depth of penetration and high ratio were selected to be used O 3,3 and Mn 3 that gave best depth penetration and high ratio were selected FeFe 2O232 , and Mn 2O23O that gave thethe best depth of of penetration and high ratio were selected to to Materials 2022, 15, x FOR PEER REVIEW Materials 2022, 15, 2470 5 of 22 5 of 21 be used in the mixing design method. In the second step, based on the simplex lattice in the mixing design method. In the second step, based on the simplex lattice degree of degree of four designs, nineteen combinations from the selected oxides were prepared. four designs, nineteen combinations from the selected oxides were prepared. Finally, the Finally, the optimal combination obtained was 91% Mn2O3 and 9% Cr2O3. Finally, a conoptimal combination obtained was 91% Mn2 O3 and 9% Cr2 O3 . Finally, a conventional TIG ventional TIG welding line and another with the ATIG technique were carried out. welding line and another with the ATIG technique were carried out. 2.4. 2.4. Microstructure Microstructure Investigation Investigation The microstructural welds was was The microstructural evolution evolution of of the the fusion fusion zone zone of of both both TIG TIG and and ATIG ATIG welds investigated using a JEOL JSM-7600F scanning electronic microscope (SEM). Before invesinvestigated using a JEOL JSM-7600F scanning electronic microscope (SEM). Before investitigation, thesamples sampleswere werepolished polishedup upto to1200 1200grit gritfineness, fineness, followed followed by by aa cloth cloth polishing polishing gation, the to a 0.05 μm alumina surface finish. Then, samples were etched using Glyceregia solution to a 0.05 µm alumina surface finish. Then, samples were etched using Glyceregia solu(15cc HCl + 5cc HNO3 + 10cc glycerol). The areas image processing software from tion (15cc HCl + 5cc HNO3 + 10cc glycerol). The areas image processing softwareMicrofrom vision Instruments was used measure the ferrite volume proportions. Microvision Instruments was to used to measure the ferrite volume proportions. 2.5. Tensile Test Test The tensile tests were carried out using a computer computer control electrohydraulic electrohydraulic servo universal testing testingmachine machinemodel modelWAW-300E WAW-300E a cross head speed of 0.5 mm/min, a loadatat a cross head speed of 0.5 mm/min, a loading 1 . The tensile tests were conducted raterate of 0.5 andand a strain raterate of 1.6 × 10 ing of kN/s, 0.5 kN/s, a strain of 1.6 ×− 104 −4s−s−1 . for both dissimilar TIG, dissimilar dissimilar ATIG, ATIG,316L/316L 316L/316L butt joints, and and 2205 2205 DSS/2205 DSS/2205 DSS butt joints. For each sample category, three samples were prepared and tested. The tests were conducted according to the requirements requirements of of ASTM ASTM E8M-04, E8M-04, as as shown shown in in Figure Figure 3. 3. Figure 3.3. Tensile testtest specimen (a); dimensions of specimen according to ASTMtoE8M-04 (units Tensile specimen (a); dimensions of specimen according ASTM(b) E8M-04 in mm). (b) (units in mm). 2.6. Hardness Test Micro Vickers hardness tests were performed by a digital hardness tester model HVS-50 with with aa standard HVS-50 standard load load of of 100 100 gf gf and and dwell dwell time time of of 10 10 s. s. The The test test was was conducted conducted according to to ASTM The hardness hardness line line and and tracks are displayed according ASTM E-384-99. E-384-99. The tracks indentation indentation are displayed in in Figure 4. The measurements were performed on each sample with about 0.5 mm between Figure 4. The measurements were performed on each sample with about 0.5 mm between two indentations. indentations. The The hardness hardness line line measurements measurements were were far far from from the the top top surface surface by by 22 mm. mm. two Materials 2022, 15, x FOR PEER REVIEW 6 of 22 Materials FOR PEER REVIEW Materials2022, 2022,15, 15,x2470 6 6ofof22 21 Figure 4. Microhardness test specimens' indentation locations (a) for ATIG samples (b) after hot mounting. Figure testtest specimens' indentation locations (a) for samples (b) after hot Figure4.4.Microhardness Microhardness specimens’ indentation locations (a) ATIG for ATIG samples (b) after mounting. hot mounting. 2.7. Impact Test 2.7.Impact Impact Test tests, 3 samples for the dissimilar TIG welds and 3 samples for the dis2.7. Test For impact similar ATIG welds were prepared to the ASTM E23 standard with the dimenFor impact tests, 33samples for the dissimilar TIG welds andand 3 samples for the For impact samples foraccording the dissimilar TIG welds 3 samples fordissimilar the dissions shown in Figure 5. A Charpy “V” notch impact testing machine was used for ATIG welds were prepared according to the ASTM E23 standard with the dimensions similar ATIG welds were prepared according to the ASTM E23 standard with the impact dimentesting. shown in Figure 5. A Charpy “V” notch impactimpact testingtesting machine was used impact testing. sions shown in Figure 5. A Charpy “V” notch machine wasfor used for impact testing. Figure Figure5.5.Impact Impacttest testspecimen specimen(a); (a);dimensions dimensionsofofspecimen specimen(b) (b)(units (unitsininmm). mm). Figure 5. Impact test specimen (a); dimensions of specimen (b) (units in mm). 2.8.Corrosion CorrosionBehavior Behavior 2.8. Corrosion testswere werecarried carriedout outusing usinga apotentiodynamic potentiodynamicpolarization polarizationelectrochemelectrochem2.8. Corrosion Behavior Corrosion tests ical system to obtain the main corrosion parameters such as corrosion potential (Ecorr), ical system to obtain the main corrosion parameters such as corrosion potential (Ecorr), Corrosion tests were carried out using a potentiodynamic polarization electrochempitting potential (Ep), and corrosion current density (icorr) that can be used to evaluate pitting potential (Ep), the andmain corrosion current density (icorr) can be used to evaluate ical system to obtain corrosion parameters such asthat corrosion potential (Ecorr), the corrosion resistance. Electrochemical tests were performed using a potentiostat system the corrosion resistance. Electrochemical tests were performed using system pitting potential (Ep), and corrosion current density (icorr) that cana potentiostat be used to evaluate of AUTOLAB-PGSTAT302N. Before testing, the samples were cut to the dimensions of Before testing, samples were cut to the dimensions of 20of theAUTOLAB-PGSTAT302N. corrosion resistance. Electrochemical teststhe were performed using a potentiostat system 20 mm × 10 mm and grinded up to 1200 grit with SiC emery papers, taking into account mm × 10 mm and grinded up Before to 1200testing, grit with SiC emerywere papers, taking into accountofsix of the samples cut to the dimensions 20 sixAUTOLAB-PGSTAT302N. different regions of the welded joint: TIG weld metal, ATIG weld metal, TIGASS ASS316L 316L different regions of the welded joint: TIG weld metal, ATIG weld metal, TIG mm × 10 mm and grinded up to 1200 grit with SiC emery papers, taking into account six HAZ, ATIG ASS 316L HAZ, TIG DSS HAZ, and ATIG DSS HAZ, in addition to ASS 316L HAZ, ATIG ASS 316L HAZ, TIG joint: DSS HAZ, and ATIG DSS HAZ, in addition to ASS different of the welded TIG weld metal, ATIG weld metal, TIG ASS 316L 316L and DSSregions base metals. The data were collected after immersion in 3.5% NaCl solution for and DSS baseASS metals. The data were collected after immersion in in 3.5% NaCl solution for HAZ, ATIG 316L HAZ, TIG DSS HAZ, and ATIG DSS HAZ, addition to ASS 316L 1 h at room temperature. The tests were performed in the 3.5% NaCl solution at a scan rate 1and h at room temperature. The tests performed in the 3.5%inNaCl solution at a scan base metals. The werewere collected after immersion 3.5%chloride NaCl solution for of 1DSS mV/s. Platinum (Pt) data was used as the auxiliary electrode, silver (Ag/AgCl) rate of 1 mV/s. Platinum (Pt) was used as the auxiliary electrode, silver chloride (Ag/AgCl) 1was h atused room temperature. The tests were performed in the 3.5% NaCl solution at a scan as the reference electrode, and the sample was used as the working electrode. was as thePlatinum reference(Pt) electrode, and was used assilver the working rate used of 1 mV/s. was used as the the sample auxiliary electrode, chlorideelectrode. (Ag/AgCl) was used as the reference electrode, and the sample was used as the working electrode. Materials 2022, 15, 2470 7 of 21 3. Results and Discussions 3.1. Weld Bead Aspect 3.1.1. Selection of Candidate Oxides The joints were executed with the butt weld design without edge preparation. Both plates were clamped with zero gap distance. Single oxide flux was deposited on plates to be welded with a total width of 10 mm. TIG weld and nine ATIG welds were carried out. The results in Table 4 clearly display that the three oxides candidates for the next steps are Cr2 O3 , Fe2 O3 , and Mn2 O3 because they exhibit the highest penetrated weld beads and ratios (7.47 mm-1.66, 8.66 mm-1.68, and 7.02 mm-1.63), respectively. Table 4. Weld aspect of single oxides flux of dissimilar ATIG welds. Oxides SiO2 TiO2 Fe2 O3 Cr2 O3 ZrO2 Mn2 O3 V2 O5 Co2 O3 MgO Depth (mm) 6.59 5.36 7.47 8.66 4.33 7.02 7.02 7.01 4.16 Width(mm) 7.61 10.72 8.43 9.68 8.66 8.01 9.21 9.04 8.32 Ratio 1.60 0.50 1.66 1.68 0.5 1.63 1.61 1.57 0.50 3.1.2. Mixture Contour of Plot According to the mixture method, simplex lattice degree four is the most appropriate for our experiments. We prepared nineteen compositions with different proportions of oxides selected, which were Fe2 O3 , Cr2 O3 , and Mn2 O3 . Table 5 shows the chemical compositions of the nineteen combinations and the related results of depths and ratios. Table 5. Dimensions of depth (D) and R (ratio) of ATIG weld beads. Exp. Fe2 O3 % Cr2 O3 % Mn2 O3 % Depth (mm) R = (D + Wb)/Wf 1 75 25 0 8.78 1.83 2 75 0 25 8.84 1.65 3 50 25 25 8.68 1.64 4 50 0 50 8.27 1.64 5 50 50 0 7.95 1.83 6 25 75 0 7.48 1.7 7 25 50 25 7.3 1.66 8 25 25 50 7.15 1.54 9 0 75 25 8.74 1.84 10 0 50 50 7.75 1.66 11 0 25 75 8.5 1.65 12 25 0 75 7.91 1.61 13 33.33 33.33 33.33 8.79 1.7 14 66.667 16.667 16.667 7.89 1.61 15 16.667 66.667 16.667 7.69 1.7 16 16.667 16.667 66.667 7.83 1.66 17 100 0 0 8.41 1.74 18 0 100 0 7.97 1.82 19 0 0 100 8.27 1.82 The compositions of the flux were the input data, and both the depth (D) and the ratio (R) were the output response. To visualize the relationships between the components in a Materials 2022, 15, 2470 8 of 21 three-component mixture, the triangular coordinate systems were used. Figure 6 shows the Materials 2022, 15, x FOR PEER REVIEW 8 of is 21 contour plots for depth, and the ratio that generated based on the experimental results Materials 2022, 15, x FOR PEER REVIEW 8 of 21 shown in Figure 7. Figure 6. Mixture contour plot for the depth D of penetration. Figure Figure6. 6.Mixture Mixturecontour contourplot plotfor forthe thedepth depthD Dof ofpenetration. penetration. Figure 7. Mixture contour plot for ratio R. Figure7. 7.Mixture Mixturecontour contourplot plotfor forratio ratioR. R. Figure From the mixture contour plot depth D, regions be From contour plot for for depth D, three mainmain regions can becan observed, where Fromthe themixture mixture contour plot for depth D, three three main regions can be observed, observed, where the maximum depth can be attained. The first region is close to manganese the maximum depth can be attained. The first region is close to manganese oxide, the where the maximum depth can be attained. The first region is close to manganese oxide, oxide, the second region is close to chromium oxide, and the third one is far from the base of second region is close to chromium oxide, and the third one is far from the base of the the second region is close to chromium oxide, and the third one is far from the base of the the triangle, as can be seen in Figure triangle, triangle,as ascan canbe beseen seenin inFigure Figure6.6. 6. The mixture contour for flux ratio three main regions the The plotplot for flux three main regions the where maximum Themixture mixturecontour contour plot for ratio flux shows ratio shows shows three mainwhere regions where the maximum depth can be achieved. The first region is close to manganese oxide, the second depth can be achieved. first region is close to manganese oxide, the oxide, secondthe region is maximum depth can beThe achieved. The first region is close to manganese second region is close to chromium oxide, and the third one is close to the triangle rib (Cr 2O3– close to chromium oxide, and the third one is close to the triangle rib (Cr O –Fe O ) from 2 3 2 3 region is close to chromium oxide, and the third one is close to the triangle rib (Cr2O3– Fe 3) from the base the triangle, as the base of the in Figure 7. in Fe22O O 3) from thetriangle, base of of as theshown triangle, as shown shown in Figure Figure 7. 7. The optimizer module available in Minitab 17 to the The optimizer module available in Minitab 17 waws waws used toused find the optimal The optimizer module available in Minitabsoftware 17 software software waws used to find find the optimal composition. Figure 8 shows the optimization plot that indicates how composition. Figure 8 shows the optimization plot that indicates how the variables of optimal composition. Figure 8 shows the optimization plot that indicates how the the variables of Fe 2 O 3 , Cr 2 O 3 , and Mn 2 O 3 affect the predicted responses in terms of both Fe and Mn2 O responses in terms of both penetration depth 2 O3 , Cr2 O 3 3affect variables of3 ,Fe 2O3, Cr 2O , and the Mnpredicted 2O3 affect the predicted responses in terms of both penetration depth D and flux ratio R. It should be at the D and flux ratio R. It should be noted that the numbers atthat the the top of the columns show penetration depth D and flux ratio R. It should be noted noted that the numbers numbers at the the top top of ofthe the columns show the current variable settings and the high and low variables settings in columns show the current variable settings and the high and low variables settings in the the data. data. Two Two points points for for each each cell cell represent represent the the two two levels levels of of the the categorial categorial variable. variable. If If the the level level for for each each variable variable is is equal equal to to 1, 1, it it indicates indicates aa high high level, level, and and if if it it is is equal equal to to 0, 0, it it indicates indicates aa Materials 2022, 15, 2470 9 of 21 Materials 2022, 15, x FOR PEER REVIEW 9 offor 22 current variable settings and the high and low variables settings in the data. Two points each cell represent the two levels of the categorial variable. If the level for each variable is equal to 1, it indicates a high level, and if it is equal to 0, it indicates a low level. The level between the high levels represents the best mixing flux composition, which is 91% level between theand highlow and low levels represents the best mixing flux composition, which Mn O + 9% Cr O + 0% Fe O . 2 3 Mn2O3 + 29%3 Cr2O3 + 0% 2 3Fe2O3. is 91% Figure 8. 8. Optimization Optimization plot plot for for depth depth D D and and ratio ratio R. R. Figure Figure Figure 88 shows shows the the predicted predicted response response “y” and the individual desirability score “d” for for both both the the depth depth and and ratio ratio for for the the current current variable variable settings, settings, as as can can be be seen seen from from the the first first column. corresponding column. Hence, Hence, the the predicted predictedresponse responsefor forthe thedepth depthisisyy== 8.75 mm and the corresponding desirability desirability is is 0.99. 0.99. The The predicted predicted response response for for the the ratio ratio is is yy== 1.76 1.76 and and the the corresponding corresponding desirability is 0.97. Thus, the overall composite desirability becomes 0.98. This indicates that desirability is 0.97. Thus, the overall composite desirability becomes 0.98. This indicates the variables achieve favorable results for all responses, and it means that both responses that the variables achieve favorable results for all responses, and it means that both reare within acceptable limits. limits. sponses are within acceptable 3.1.3. 3.1.3. Validation Validation Test Test The third step the validation weld line. Accordingly, the combination flux was The third stepisisabout about the validation weld line. Accordingly, the combination flux prepared. ATIG dissimilar welding was executed using the optimal composition with the was prepared. ATIG dissimilar welding was executed using the optimal composition with same conventional parameters of the TIG weld. The transverse cross-sections of the weld the same conventional parameters of the TIG weld. The transverse cross-sections of the beads were investigated using an optical microscope CAROLINA (CAROLINA, Burlington, weld beads were investigated using an optical microscope CAROLINA (CAROLINA, NC, USA). Based on that investigation, the obtained penetration depth (D) is 8.93 mm and Burlington, NC, USA). Based on that investigation, the obtained penetration depth (D) is the bead face width (W) is 8.87 mm for ATIG welding, which lead to an aspect ratio D/W of 8.93 mm and the bead face width (W) is 8.87 mm for ATIG welding, which lead to an 1.94. It can be noted that the depth is increased by about 2.4 times and the ratio is enhanced aspect ratio D/W of 1.94. It can be noted that the depth is increased by about 2.4 times and by about 5.7 times compared to the conventional TIG welding. Better yet, the measured the ratio is enhanced by about 5.7 times compared to the conventional TIG welding. Better depth and ratio are higher than the predicted values of 8.75 mm and 1.75, respectively. The yet, the measured depth and ratio are higher than the predicted values of 8.75 mm and depth bead profile data of the conventional TIG weldments and of ATIG with the optimal 1.75, respectively. The depth bead profile data of the conventional TIG weldments and of flux are listed in Table 6. Figure 9 presents macrographs for the cross-section of the TIG ATIG with the optimal flux are listed in Table 6. Figure 9 presents macrographs for the welded bead and those of the ATIG with the optimal flux. It is clearly observed that the cross-section of the TIG welded bead and those of the ATIG with the optimal flux. It is bead has a full penetration after ATIG welding. clearly observed that the bead has a full penetration after ATIG welding. Table 6. Dissimilar weldment bead profiles data of TIG (conventional) and ATIG (optimal flux). TIG ATIG D W D/W D Wf Wb D/W 3.74 10.89 0.34 8.93 8.87 8.31 1.94 Figure 9. Transverse optical macrographs of the dissimilar welded beads using TIG (a) and ATIG (b). aspect ratio D/W of 1.94. It can be noted that the depth is increased by about 2.4 times and the ratio is enhanced by about 5.7 times compared to the conventional TIG welding. Better yet, the measured depth and ratio are higher than the predicted values of 8.75 mm and 1.75, respectively. The depth bead profile data of the conventional TIG weldments and of ATIG with the optimal flux are listed in Table 6. Figure 9 presents macrographs for the 10 It of is 21 cross-section of the TIG welded bead and those of the ATIG with the optimal flux. clearly observed that the bead has a full penetration after ATIG welding. Materials 2022, 15, 2470 Materials 2022, 15, x FOR PEER REVIEW 10 of 22 Table 6. Dissimilar weldment bead profiles data of TIG (conventional) and ATIG (optimal flux). TIG ATIG D W D/W D Wf Wb D/W 3.74 10.89 0.34 8.93 8.87 8.31 1.94 Figure 9. Transverse Transverseoptical opticalmacrographs macrographsofofthe thedissimilar dissimilar welded beads using ATIG Figure 9. welded beads using TIGTIG (a) (a) andand ATIG (b). (b). 3.2. 3.2.Microstructure MicrostructureAssessment Assessment Based on a WRC-1992 ratio equals 2.63. Based on a WRC-1992diagram diagrambefore beforewelding, welding,the theDSS DSSCreq/Nieq Creq/Nieq ratio equals 2.63. DSS inin ferrite mode. TheThe DSSDSS microstructure consists of both (α) and DSSsolidifies solidifies ferrite mode. microstructure consists of ferrite both ferrite (α)ausand tenite (γ) phases in almost equal proportion. However, thethe ASS austenite (γ) phases in almost equal proportion. However, ASS316L 316LCreq/Nieq Creq/Nieqratio ratio equaling equaling1.56 1.56solidifying solidifyingininaustenite-ferrite austenite-ferritemode modeleads leadstotothe theformation formationofofaustenite austenite(γ) (γ) with the formation of strip δ ferrite. with the formation of strip δ ferrite. The in Figure Figure10a 10afor forthe theATIG ATIG weld and Figure Theweld weldbead beadmicrostructure microstructure shown shown in weld and Figure 10b 10b weld indicates existence of delta ferrite (δ) and austenite (γ) phases. forfor thethe TIGTIG weld indicates the the existence of delta ferrite (δ) and austenite (γ) phases. First, First, the solidification of molten metal results in the formation of ferrite matrix immedithe solidification of molten metal results in the formation of ferrite matrix immediately ately solidification, and then the nucleation of austenite starts aupon a further afterafter solidification, and then the nucleation of austenite phasesphases starts upon further cooling cooling cycle. In the weldthree region, three austenite different phases’ austenite phases’ morphologies are cycle. In the weld region, different morphologies are found. They found. They are a thin grain boundary austenite, an elongated Widmanstätten austenite are a thin grain boundary austenite, an elongated Widmanstätten austenite structure, and structure, and an intragranular austenite phase. Transverse profile ferriteproportions volume proporan intragranular austenite phase. Transverse profile ferrite volume of the tions of the 2205/316L stainless-steel welded joint are depicted Table 7 andin 2205/316L stainless-steel dissimilardissimilar welded joint are depicted in Table 7inand shown Figurein11. They11. reveal evolution of ferriteofvolume proportions seen from the HAZ shown Figure Theyan reveal an evolution ferrite volume proportions seen from theof the 316L toASS the 2205 The average ferriteferrite volume proportion in theinATIG HAZ of theASS 316L to theDSS 2205HAZ. DSS HAZ. The average volume proportion the weldweld zone zone reaches 57%, 57%, greater than that theofTIG zone zone of 47%. ATIG reaches greater thanof that theweld TIG weld of 47%. 5, 5, xx FOR FOR PEER PEER REVIEW REVIEW 11 22 11 of of (b)22 (a) Figure Figure10. 10.TIG TIGweld weldzone zone(a)(a)and andATIG ATIGweld weldzone zone(b) (b)(500×). (500×). Table proportions % weld and for ATIG and TIG weldments. Table 7. 7. Ferrite Ferrite volume volumeTable proportions % in in weld zone zone and HAZ HAZ forweld ATIG andand TIGHAZ weldments. 7. Ferrite volume proportions % in zone for ATIG and TIG weldments. Weld Weld Weld ATIG ATIGATIG Ferrite Ferrite Volume Volume Proportion Proportion % % Ferrite Volume Proportion % Ferrite Volume in DifFerrite Volume in Dif- Average Average HAZ 316L HAZ 2205 ferent LocaFerrite Volume Locations Average ferent Loca- in Different HAZ 316L HAZ 2205 in HAZ 316L in WZ WZ tions<break/>in WZ Side Side in WZ tions<break/>in WZ Side in WZ Side Side 11 33 2 44 1 22 3 4 52 52 53 5253 54 54 5355 55 54 54 54 6.9 55 6.9 63 54 63 (a) HAZ 2205 Side 6.9 63 (b) Figure 11. Ferrite proportion measurements of dissimilar TIG (a) and ATIG (b) welds (500×). TIG TIG TIG 41 41 4144 44 48 48 4453 53 47 48 47 53 88 47 69 69 The The ATIG ATIG weld weld with with optimal optimal flux flux increases increases the the arc arc voltage, voltage, and and the the amount amount of of heat heat input per unit length in a weld is also increased. The energy density of the source leads input per unit length in a weld is also increased. The energy density of the source leads to to high high heat heat input. input. However, However, the the arc arc weld weld of of TIG TIG welding welding without without flux flux has has aa lower lower energy energy density and, therefore, in this case, a lower heat input in comparison with ATIG. TIG 8 69 Materials 2022, 15, x FOR PEER REVIEW 11 of 22 Table 7. Ferrite volume proportions % in weld zone and HAZ for ATIG and TIG weldments. Materials 2022, 15, 2470 (a) (b) 11 of 21 Ferrite Volume Proportion % Figure 10. TIG weld zone (a) and ATIGFerrite weld zone (b) Volume(500×). in DifAverage Weld ferent LocaHAZ 316L HAZ 2205 in WZ tions<break/>in WZ Side Side 1 2 3 4 ATIG TIG (a) 52 53 54 55 54 41 44 48 53 47 (b) 6.9 63 8 69 Figure 11.11. Ferrite proportion measurements ofofdissimilar Figure Ferrite proportion measurements dissimilarTIG TIG(a)(a)and andATIG ATIG(b) (b)welds welds(500×). (500×). The ATIG weld with optimal flux increases thethe arcarc voltage, and thethe amount of of heat The ATIG weld with optimal flux increases voltage, and amount heat input per unit length in a weld is also increased. The energy density of the source leads to to input per unit length in a weld is also increased. The energy density of the source leads high heat input. However, the arc weld of TIG welding without flux has a lower energy high heat input. However, the arc weld of TIG welding without flux has a lower energy density and, therefore, in in this case, a lower heat input in in comparison with ATIG. TIG density and, therefore, this case, a lower heat input comparison with ATIG. TIG welding associated with low heat input is characterized by a relatively rapid cooling rate welding associated with low heat input is characterized by a relatively rapid cooling rate in in comparison to that of the ATIG weld [34].[34]. In theInATIG weld weld zone, zone, a slowacooling rate comparison to that of the ATIG weld the ATIG slow cooling allows for more of ferrite different types oftypes austenite (GBA (ferrite rate allows fortransformation more transformation ofto ferrite to different of austenite (GBA grain (ferrite boundaries), Widmanstätten, IGA (Intragranular grain austenite)). However, the TIGthe grain boundaries), Widmanstätten, IGA (Intragranular grain austenite)). However, weld specimen executed using double passes receives more heat transferred to the joint TIG weld specimen executed using double passes receives more heat transferred to the and, consequently, more formation of austenite is expected, as wellas aswell higher ferrite ferrite voljoint and, consequently, more formation of austenite is expected, as higher ume proportions that influence the mechanical properties and reinforce the strength and volume proportions that influence the mechanical properties and reinforce the strength hardness properties [35]. [35]. and hardness properties For thethe TIG weld, thethe HAZ width of of about 300–500 μm is is observed onon thethe duplex For TIG weld, HAZ width about 300–500 µm observed duplex steel side, asas shown in in Figure 12a. The HAZ microstructure consists of of lamellar austenite steel side, shown Figure 12a. The HAZ microstructure consists lamellar austenite precipitates located mainly onon thethe equiaxial high ferrite grain boundaries and, in in a minor precipitates located mainly equiaxial high ferrite grain boundaries and, a minor amount, inside thethe ferrite grains with thethe presence of of small proportions of of Widmanstätten amount, inside ferrite grains with presence small proportions Widmanstätten side plates ferrite grain boundary. The ferrite volume proportion 69% that side plates offoff thethe ferrite grain boundary. The ferrite volume proportion is is upup 69% in in that zone, which significantly higher comparison parent material 2205 DSS. The zone, which is is significantly higher in in comparison to to thethe parent material of of 2205 DSS. The wide HAZ about 120–160 µm is observed 316L ASS side, shown in Figure 12b. wide HAZ of of about 120–160 μm is observed onon thethe 316L ASS side, as as shown in Figure 12b. The microstructure consists strips ferrite precipitates that surround austenite grains. The microstructure consists of of strips of of ferrite precipitates that surround austenite grains. 316L ASS HAZ side, ferrite volume proportion is up listed in Table InIn thethe 316L ASS HAZ side, thethe ferrite volume proportion is up to to 8%,8%, as as listed in Table 7. 7. The width the DSS HAZ side higher than that 316LHAZ HAZbyby2.5–3.1 2.5–3.1times. times.This This The width ofof the DSS HAZ side is is higher than that ofof316L result good concordance with that obtained the study Topolskaetetal.al.[36]. [36]. result is is inin good concordance with that obtained inin the study ofof Topolska (a) (b) Figure 12.12. TIG HAZ DSS side (a)(a) and 316L side (b)(b) (×100). Figure TIG HAZ DSS side and 316L side (×100). In the ATIG weld, the HAZ of about 120–200 µm is observed on the duplex steel side, as shown in Figure 13a. Moreover, the microstructure consists of continuous networks of austenite at the ferrite grain boundaries (GBA) and also the austenite phase formed as Widmanstätten (WA), in addition to intragranular austenite within the ferrite grains (IGA). Materials 2022, 15, 2470 Widmanstätten (WA), in addition to intragranular austenite within the ferrite grains (IGA). The ferrite volume proportions in this zone reaches 63%, which is significantly higher compared to the parent material of 2205 DSS. The wide zone of about 60–80 μm is observed on the HAZ 316L side, as shown in Figure 13b. The ATIG HAZ DSS side is wider than that of the TIG HAZ 316L side by 2 to 12 of 21 2.5 times. The microstructure consists of δ ferrite precipitates in a matrix of austenite grains. The ferrite volume proportions in this zone decrease to 6.9%. We notice that the TIG HAZ is wider than that of ATIG HAZ for both sides, respectively. This effect can be ascribed to thevolume fact that the heat provided to the ATIG weld bead isismore concentrated The ferrite proportions in this zone reaches 63%, which significantly higher owing to constriction of the ATIG arc weld than that of the TIG weld [37]. compared to the parent material of 2205 DSS. (a) (b) Figure 13.13. ATIG HAZ DSS side (a)(a) and 316L side (b)(b) (×100). Figure ATIG HAZ DSS side and 316L side (×100). about 60–80 µm is observed on the HAZ OnThe the wide otherzone hand,ofthe HAZ of the DSS side for both ATIG and316L TIG side, weldsasisshown wider in Figure ATIG HAZ DSS is wider than conductivity that of the TIG 316Lcompared side by 2 to than that 13b. of theThe 316L side, owing toside a higher thermal of HAZ 2205 DSS The microstructure consists of δ ferrite in a matrix of austenite grains. to 2.5 thattimes. of 316L. This result is in good agreement withprecipitates the results obtained by Taheri et al. [35]. The ferrite volume proportions in this zone decrease to 6.9%. We notice that the TIG HAZ wider than that of ATIG HAZ for both sides, respectively. This effect can be ascribed 3.3.isSEM/EDS Analysis to Referring the fact that the heat provided to the ATIG weld bead more concentrated owing to to Figure 14a, we notice an increase in the Cr is element at the fusion border the ATIG weld than that of theclearly TIG weld [37]. the presence of more of constriction the 316L sideofin the TIG arc weld. This observation indicates On the other hand, the HAZ of the DSS side for both ATIG and TIG welds is wider δ ferrite phase in this region compared to the ATIG weld shown in Figure 14b. than that of the 316L side, owing to a higher thermal conductivity of 2205 DSS compared to that of 316L. This result is in good agreement with the results obtained by Taheri et al. [35]. 3.3. SEM/EDS Analysis Materials 2022, 15, x FOR PEER REVIEW Referring to Figure 14a, we notice an increase in the Cr element at the fusion border of 13 of 22 the 316L side in the TIG weld. This observation clearly indicates the presence of more δ ferrite phase in this region compared to the ATIG weld shown in Figure 14b. (a) (b) Figure 14. SEM-EDS micrographs and data for TIG for (a) and (b) ATIG ASS 316L side fusion Figure 14. SEM-EDS micrographs andobtained data obtained TIGATIG (a) and (b) ASS 316L side border. fusion border. We also remark, in the latter region, the presence of the Mo element close to that of 316L parent metal that suggests that the ATIG weld could withstand aggressive environments. Cr, Ni, Mn, and Mo element contents labeled in Figure 15b of the ATIG DSS 2205 side (b) Figure 14. SEM-EDS micrographs and data obtained for TIG (a) and ATIG (b) ASS 316L side fusion border. Materials 2022, 15, 2470 13 of 21 We also remark, in the latter region, the presence of the Mo element close to that of 316L parent metal that suggests that the ATIG weld could withstand aggressive environments.We also remark, in the latter region, the presence of the Mo element close to that of 316L parent metal that suggests that the ATIG weld could withstand aggressive environments. Cr, Ni,Ni, Mn, and MoMo element contents labeled in Figure 15b of15b theof ATIG DSS 2205 Cr, Mn, and element contents labeled in Figure the ATIG DSSside 2205 fusion borderborder are close the parent to moreto ferrite formation. Howside fusion aretoclose to the metal, parentleading metal, leading morephase ferrite phase formation. ever, in Figure 15a, we an increase in the austenite phase, promoting elements However, in Figure 15a,remark we remark an increase in the austenite phase, promoting elements such asas NiNi and the ofof more phase compared toto such andMn, Mn,which whichindicates indicates theformation formation moreaustenite austenite phase compared ATIG DSS 2205. ATIG DSS 2205. (a) (b) Figure 15.15. SEM-EDS micrographs and data obtained for TIG and(a) ATIG DSS (b) 2205 side2205 fusion Figure SEM-EDS micrographs and data obtained for(a)TIG and(b) ATIG DSS side border. fusion border. 3.4. Tensile Test The average value of the ultimate tensile strength (UTS) of the ATIG dissimilar weld is 599 MPa, which is close to that of conventional TIG welding (594 MPa), as shown in Table 8. Table 8. Measurements of tensile strength and standard deviation of TIG welds and ATIG welds with optimal flux. Sample Number of Tests UTS Max. (MPa) UTS Min. (MPa) UTS Average (MPa) Standard Deviations σ 316L SS BM 3 615 594 600 4 2205 DSS BM 3 820 796 815 11.5 TIG 2205 DSS/2205 DSS 3 800 791 795 4.73 TIG 316L SS/316L SS 3 598 594 596 2.08 TIG 2205 DSS/316L SS 3 597 591 594 1.00 ATIG 2205 DSS/316L SS 3 601 597 599 2.08 We notice that the fractures for ATIG and TIG dissimilar welds are localized at the base metal, precisely at the ASS 316L base metal and outside the weld zone, as shown in Figure 16. This may be ascribed to differences in the chemical composition that promote the dual-phase nature and a stronger solid solution strengthening mechanism as mentioned in TIG316L 316LSS/316L SS/316LSS SS TIG TIG2205 2205DSS/316L DSS/316LSS SS TIG ATIG2205 2205DSS/316L DSS/316LSS SS ATIG Materials 2022, 15, 2470 33 33 33 598 598 597 597 601 601 594 594 591 591 597 597 596 596 594 594 599 599 2.08 2.08 1.00 1.00 2.08 2.08 Wenotice noticethat thatthe thefractures fracturesfor forATIG ATIGand andTIG TIGdissimilar dissimilarwelds weldsare arelocalized localizedatatthe the We 14 of 21 basemetal, metal,precisely preciselyatatthe theASS ASS316L 316Lbase basemetal metaland andoutside outsidethe theweld weldzone, zone,as asshown showninin base Figure16. 16.This Thismay maybe beascribed ascribedtotodifferences differencesininthe thechemical chemicalcomposition compositionthat thatpromote promote Figure thedual-phase dual-phasenature natureand andaastronger strongersolid solidsolution solutionstrengthening strengtheningmechanism mechanismas asmenmenthe some works [38,39]; hence, a reduction in ductility of these zones must be expected. tioned in some works [38,39]; hence, a reduction in ductility of these zones must be extioned in some works [38,39]; hence, a reduction in ductility of these zones must be The exDSS BM has a strength superior by 205 MPa of that of 316L BM. Indeed, the duplex material pected.The TheDSS DSSBM BMhas hasaastrength strengthsuperior superiorby by205 205MPa MPaofofthat thatofof316L 316LBM. BM.Indeed, Indeed,the the pected. contains the ferrite phase,the which allows a material with greater UTS. duplexmaterial material contains the ferrite phase, whichallows allows material withgreater greaterUTS. UTS. duplex contains ferrite phase, which aamaterial with Figure16. 16.Specimens Specimensof ofthe thetensile tensiletesting testingafter afterthe thetest. test. Figure Figure 16. Specimens of the tensile testing after the test. Thefracture fracturefaces facesininboth bothcases casesshow showsimilar similar ductile elongated large dimples, attestThe fracture ductile elongated large dimples, attesting The both cases show similar ductile elongated large dimples, attestingthe thereduction reduction ductility 316Laustenitic austenitic stainless steel withcleavage cleavage facets,as as the reduction in ductility of 316L stainless steel with cleavage facets, asfacets, shown in ing ininductility ofofaustenitic 316L stainless steel with shown in Figure 17. Figure 17. shown in Figure 17. (a) (a) (b) (b) Figure17. 17.Fracture Fracturesurface surfaceof ofTIG TIG(a) (a)and andATIG ATIG(b) (b)dissimilar dissimilar316L316L-2205 2205DSS DSS break zone Figure (b) dissimilar 316L2205 DSS atat break zone Figure 17. Fracture surface of TIG at break zone (×1000). (×1000). (×1000). The obtained strength does not denote the strength of the weld joint. The weld joint strength is higher than the value obtained in TIG and ATIG welds. The TIG specimen fractured at 594 MPa is about 96% of the 316L base metal strength. In addition, the ATIG specimen breaks at 599 MPA, which is about 97% of the 316L base metal strength. The test shall be accepted because it meets the requirements. The values of the standard deviations (σ) are less than 5 MPa, which attests the accuracy and reliability of the obtained results. Figure 18 displays the tensile test curves of the welds, which are similar TIG 316L (#1), similar DSS 2205 (#2), dissimilar ATIG (#3), and dissimilar TIG (#4). The used flux does not negatively affect the tensile property of the weld. 3.5. Hardness Test Variations in the Vickers micro hardness as a function of the distance from the DSS 2205 to the 316L SS in the sample are shown in Figure 19 for both ATIG and TIG welds. The hardness at the weld zone of the ATIG weld (average 235 HV) shows little variation compared to that of the TIG weld (237 HV), which is more constant. The average hardness value in the ATIG fusion region (235 HV) is roughly equal to that of the TIG fusion zone (237 HV) weld. The highest value of hardness (242 HV) is located at the TIG weld zone at the nearest point of DSS/WZ. The standard deviations are less than 4 HV, which indicates good hardness homogeneities in the joints, as shown in Table 9. Materials 2022, 15, 2470 fractured at 594 MPa is about 96% of the 316L base metal strength. In addition, the ATIG not negatively affect the tensile property of the weld. specimen breaks at 599 MPA, which is about 97% of the 316L base metal strength. The test shall be accepted because it meets the requirements. The values of the standard deviations (σ) are less than 5 MPa, which attests the accuracy and reliability of the obtained results. Figure 18 displays the tensile test curves of the welds, which are similar TIG 316L (#1), 15 of 21 similar DSS 2205 (#2), dissimilar ATIG (#3), and dissimilar TIG (#4). The used flux does not negatively affect the tensile property of the weld. Figure 18. Stress vs. strain curves of the different weldments. 3.5. Hardness Test Variations in the Vickers micro hardness as a function of the distance from the DSS 2205 to the 316L SS in the sample are shown in Figure 19 for both ATIG and TIG welds. The hardness atvs. the weld zoneofofthe thedifferent ATIG weld (average 235 HV) shows little variation Figure18. 18. Stressvs. strain curves curvesof weldments. Figure strain the different comparedStress to that of the TIG weld (237 HV), weldments. which is more constant. 3.5. Hardness Test Variations in the Vickers micro hardness as a function of the distance from the DSS 2205 to the 316L SS in the sample are shown in Figure 19 for both ATIG and TIG welds. The hardness at the weld zone of the ATIG weld (average 235 HV) shows little variation compared to that of the TIG weld (237 HV), which is more constant. Figure19. 19.Micro Microhardness hardness profiles across the centerline of dissimilar and dissimilar TIG Figure profiles across the centerline of dissimilar ATIG ATIG and dissimilar TIG welds. welds. Table 9. Measurements of hardness and standard deviation of TIG and ATIG (optimal flux) at FZ. The average hardness value in the ATIG fusion region (235 HV) is roughly equal to that of the TIG fusion (237 HV) highest value HV of hardness Standard (242 HV) is Zone zone of HV weld. The HV Sample Testszone at theMax. Min. Average Deviations σ located at the TIG weld nearest point of DSS/WZ. The standard deviations are Figure 19. 4Micro hardness profiles good acrosshardness the centerline of dissimilarinATIG and dissimilar TIG less than HV, which indicates homogeneities the joints, as shown in TIG FZ 242 232 237 2.96 welds. Table 9. ATIG FZ 240 229 235 3.62 The average hardness value in the ATIG fusion region (235 HV) is roughly equal to that The of the TIG collected fusion zone (237 10 HV) The highest value of hardness (242HAZ HV)ofis results in Table areweld. related to the micro hardness tests at the located at the TIG weld zonehardness at the nearest of DSS/WZ. The standard deviations are the weldments. The average valuepoint is found to be greater at the HAZ of the DSS less than 4 HV, which indicates good hardness homogeneities in the joints, as shown in 2205 side (257.5–257 HV) compared to that of the 316L side (222–210 HV) for dissimilar TIG Table 9. and dissimilar ATIG welds. On the other hand, the standard deviations are less than 4 HV, which attests the small disparities in the obtained hardness values between the maximum and the minimum values. 3.6. Impact Test The impact tests were carried out only in the fusion zones of ATIG and TIG welds. The obtained experimental results are displayed in Figure 20. The average energy absorbed in the fusion zone in the case of the ATIG 2205 DSS/316L SS dissimilar weld (267 J/cm2 ) is slightly lower than that of the dissimilar TIG weld (275 J/cm2 ). The dissimilar ATIG and dissimilar TIG welds have almost the same ability to withstand shocks. The standard deviations are less than 8 J/cm2 . Figure 21 shows the broken TIG and ATIG dissimilar weld specimens after the impact test. 2205 side (257.5–257 HV) compared to that of the 316L side (222–210 HV) for dissimilar TIG and dissimilar ATIG welds. On the other hand, the standard deviations are less than 4 HV, which attests the small disparities in the obtained hardness values between the maximum and the minimum values. Materials 2022, 15, 2470 16 of 21 Table 10. Measurements of hardness and standard deviation of TIG and ATIG with the optimal flux at HAZ. StandTable 10. Measurements of hardness and standard deviation of TIG HV<break/>A and ATIG with the optimal flux HV<break/ HV<break/ Sample Zone of Tests ard<break/>Deat HAZ. >Max. >Min. verage viations σ HAZ FZ/Duplex 2205SS 258 257 257.5 0.71 Zone of HV HV HV Standard TIG Sample HAZ 225 222 3.61 TestsFZ/316L SS Max. Min.218 Average Deviations σ HAZHAZ FZ/Duplex 2205SS 258 255 257 2.12 ATIG HAZ FZ/316L SS 258 210 210 1.53 FZ/Duplex 257 209 257.5 0.71 2205SS TIG 3.6. Impact Test HAZ 225 218 222 3.61 FZ/316L The impact tests wereSScarried out only in the fusion zones of ATIG and TIG welds. The obtained experimental results are displayed in Figure 20. The average energy abHAZ FZ/Duplex 255 DSS/316L SS 257dissimilar weld 2.12 (267 sorbed in the fusion zone in the case258 of the ATIG 2205 2205SS 2 2 J/cm )ATIG is slightly lower than that of the dissimilar TIG weld (275 J/cm ). The dissimilar ATIG and dissimilarHAZ TIG welds have almost the same ability to withstand shocks. The 210 209 210 1.53 FZ/316L SS than 8 J/cm2. Figure 21 shows the broken TIG and ATIG disstandard deviations are less similar weld specimens after the impact test. Materials 2022, 15, x FOR PEER REVIEW 17 of 22 Figure energy absorbed of of TIG andand ATIG (optimal flux) at fusion zone for for Figure20. 20.Measurements Measurementsofof energy absorbed TIG ATIG (optimal flux) at fusion zone dissimilar dissimilar2205 2205DSS/316L DSS/316LSS SSweld. weld. (a) (b) Figure ofof TIG (a)(a) and ATIG Figure21. 21.Specimens Specimens TIG and ATIG(b) (b)after afterthe theimpact impacttesting. testing. TheSEM SEMfractography fractographyrepresented representedininFigure Figure22a 22abelongs belongstotothe theTIG TIGweld. weld.It Itindicates indicates The multipleand andfine finedimples dimpleswith withductile ductiledimple dimpletearing tearingresulting resultingfrom fromthe thecoalescence coalescenceofof multiple microvoids, voids,which whichconfirms confirmsthe theductile ductilefracture fracturemode modeduring duringthe theimpact impacttest. test.Figure Figure22b 22b micro showsthe theformation formationofofa anetwork networkofofmultiple multiplehomogenous homogenousdimples dimpleswithout withoutvoids, voids,which which shows characterizesthe theductile ductile fracture fracture for absorbed energy of the ATIG weld characterizes for the theATIG ATIGweld. weld.The The absorbed energy of the ATIG is close to that of the TIG weld, which ensures that the elaborated flux does not adversely weld is close to that of the TIG weld, which ensures that the elaborated flux does not adaffect the resistance of the ATIG suddensudden loads. loads. versely affect the resistance of the weld ATIGduring weld during Materials 2022, 15, 2470 The SEM fractography represented in Figure 22a belongs to the TIG weld. It indicates multiple and fine dimples with ductile dimple tearing resulting from the coalescence of micro voids, which confirms the ductile fracture mode during the impact test. Figure 22b shows the formation of a network of multiple homogenous dimples without voids, which characterizes the ductile fracture for the ATIG weld. The absorbed energy of the ATIG 17 of 21 weld is close to that of the TIG weld, which ensures that the elaborated flux does not adversely affect the resistance of the ATIG weld during sudden loads. (a) (b) Figure 22. SEM fractography of dissimilar TIGTIG (a) and ATIG (b) weldments in the FZ (×500). Figure 22. SEM fractography of dissimilar (a) and ATIG (b) weldments in the FZ (×500). Corrosion Behavior 3.7.3.7. Corrosion Behavior potentiodynamic polarization curves of the metals, heat-affected zones, TheThe potentiodynamic polarization curves of the basebase metals, heat-affected zones, andand weld metals in the 3.5% NaCl solution at room temperature are illustrated in Figures weld metals in the 3.5% NaCl solution at room temperature are illustrated in Figures 23 23 24. The corrosion current (Icorr), the corrosion potentials the pitting andand 24. The corrosion current (Icorr), the corrosion potentials (Ecorr),(Ecorr), and theand pitting popotentials the different samples are summarized in11. Table 11. be It can seen tentials (Epit) (Epit) of the of different samples are summarized in Table It can seenbe that thethat the weld metals display a passive behavior similar to those of the ASS 316L and DSS 2205 weld metals display a passive behavior similar to those of the ASS 316L and DSS 2205 base metals. However, the anodic behavior of the weld metal in TIG and ATIG are notably base metals. However, the anodic behavior of the weld metal in TIG and ATIG are notably different from the ASS 316L and DSS base metals, both in terms of the corrosion potential different from the ASS 316L and DSS base metals, both in terms of the corrosion potential (Ecorr) and current density, which can be attributed to the difference in the chemical com(Ecorr) and current density, which can be attributed to the difference in the chemical comMaterials 2022, 15, x FOR PEERposition REVIEW and microstructure. The parent metal of ASS 316L exhibits a minimum 18corrosion of 22 position and microstructure. The parent metal of ASS 316L exhibits a minimum corrosion rate when compared to DSS 2205, TIG, and ATIG weldment. ASS-BM exhibits a corrosion rate when compared to DSS 2205, TIG, and ATIG weldment. ASS-BM exhibits a corrosion potential of −927 mV versus SCE, which is more notable than the potentials observed potential of −927 mV versus SCE, which is more notable than the potentials observed for deformation from the microstructural changes for DSS-BM, as resulting well as weld metals TIG and ATIG (−and 974 the mV,residual −1050,stresses and −gener1032 mV), DSS-BM, as by well as weld metals TIG and ATIG (−974 mV, −1050, and −1032 mV), respecated the welding thermal cycle [40]. respectively. On the other hand, Table 11 shows the values of icorr for both the TIG weld tively. On the other hand, shows valuesATIG of icorr for both as the TIGasweld zone Furthermore, it Table isATIG also 11 noted thatthe TIG weld andHAZ zone (54.5 µA/cm2 ) and weld zone (54.1and µA/cm2 ), andmetals, those for well TIG andTIG ATIG 2) and ATIG weld zone (54.1 μA/cm2), and those for TIG and ATIG HAZ in (54.5 μA/cm ATIG HAZ in DSS region, have values of pitting potentials higher than those of the base 2 and in both ASS and DSS regions are higher than those of the base metals (24.4 µA/cm 2 and metals (−455 mVSCE) and DSS (−434 mVSCE), means that regions have both ASS and ASS DSS regions are higher than those of thewhich base metals (24.4these μA/cm 29.8 2 29.8 µA/cm for ASS and DSS, respectively). This indicates that protection of the passive 2better performance with respect to localized corrosion. μA/cm for ASS and DSS,regions respectively). This that indicates protection of the passive film film formed in these is less than of thethat base metals. This can be explained On the other hand, it than is again observed that TIG and ATIG HAZbeinexplained ASS regions disformed in these regions is less that of the base metals. This can by the by the deformation from the microstructural changesthat and theregions residual play low values ofresulting Epit in the solution of 3.5% NaCl, indicating these of stresses the generated theare welding thermal cycle [40]. pitting corrosion. weldedby joint more susceptible to localized Figure 23. Curve of potentiodynamic forelectrolyte electrolyte 3.5% NaCl solution obtained Figure 23. Curve of potentiodynamicpolarization polarization for 3.5% NaCl solution obtained underunder the areas of TIG ATIG weld metaland andbase base metals. metals. the areas of TIG andand ATIG weld metal Materials2022, 2022,15, 15,2470 x FOR PEER REVIEW Materials 19 of 21 22 18 of Figure Figure24. 24.Curve Curveof ofpotentiodynamic potentiodynamicpolarization polarizationfor forelectrolyte electrolyte3.5% 3.5%NaCl NaClsolution solutionobtained obtainedunder under the theareas areasofofHAZ HAZofofthe theAISI AISI316L 316Lalloy alloyand andHAZ HAZofofthe theAISI AISI2205 2205alloy alloyfor forboth bothTIG TIGand andATIG, ATIG,and and againfor forthe theweld weldmetal metal(kept (keptasasreference). reference). again Table 11. Electrochemical data of ASS, DSS base metals, TIG, and ATIG weld metals obtained from potentiodynamic polarization studies in 3.5 M NaCl solution. Sample No. βc mV·dec−1 ECorr mV βa mV·dec−1 jCorr µA·cm−2 Epit mV SCE DSS 314 −974 204 29.8 −434 ASS 288 −927 204 24.4 −455 WZ (TIG) 332 −1050 134 54.5 −383 WZ (ATIG) 331 −1032 170 54.1 −394 HAZ DSS (TIG) 337 −1012 149 31.3 −432 HAZ ASS (TIG) 236 −1021 124 37.9 −462 HAZ DSS (ATIG) 246 −1035 124 40.3 −323 HAZ ASS (ATIG) 422 −1005 187 38.7 −479 Furthermore, it is also noted that TIG and ATIG weld metals, as well as TIG and ATIG HAZ in DSS region, have values of pitting potentials higher than those of the base metals ASS (−455 mVSCE) and DSS (−434 mVSCE), which means that these regions have better performance with respect to localized corrosion. Materials 2022, 15, 2470 19 of 21 On the other hand, it is again observed that TIG and ATIG HAZ in ASS regions display low values of Epit in the solution of 3.5% NaCl, indicating that these regions of the welded joint are more susceptible to localized pitting corrosion. 4. Conclusions In this work, a comparison between dissimilar ATIG and dissimilar TIG welds of DSS grade 2205 steel and ASS grade 316L was carried out. Having investigated the mechanical properties, microstructure, and corrosion behavior of the welds, the following main conclusions can be drawn: − − − − − − − The mixing method design is a key tool to elaborate the flux composed by 91% Mn2 O3 and 9% Cr2 O3 . The ATIG weld carried out with the optimal flux achieves a full penetration weld without edge preparation or the use of a filler metal. The depth in the ATIG weld is greater than that of conventional TIG by 2.4 times. The volume proportion of ferrite, based on areas image analysis, shows that the average ferrite volume proportion in the ATIG weld zone reaches 57%, greater than that of the TIG weld zone (47%). Moreover, the welds are free of deleterious phases such as sigma phases owing to the moderate heat provided to the weld pool of 0.8 kJ/mm. In the ATIG weld, the 2205 DSS HAZ width is 200 µm, while in the 316L ASS one, HAZ is about 80 µm. In the same way, in the TIG weld, the 2205 DSS HAZ is very wide, attaining 500 µm, while in the 316L ASS one, the HAZ width is 160 µm. The HAZ of 2205 DSS sides contains more ferrite phase, while the 316L sides are mainly composed by the austenite phase with sparse bands of δ ferrite. The tensile strength value of the ATIG weld metal reaches 599 MPa, which is closer to that of the TIG weld (594 MPa). The hardness measurements at the weld zones shows close results for both TIG and ATIG, with average values of 237 HV and 235, respectively. The average energy absorbed during the toughness impact test reaches 267 J/cm2 for the ATIG weld compared to 275 J/cm2 for the TIG weld. The elaborated optimal flux has no negative effect on the mechanical properties of the welds. The weld metals display passive behavior similar to those of ASS 316L and DSS base metal. The parent metal of ASS 316L was subjected to a minimum corrosion rate when compared to DSS 2205, TIG, and ATIG weldment. Moreover, TIG and ATIG HAZ in ASS regions display low values of Epit, indicating that these regions of the welded joint are very susceptible to localized pitting corrosion. Author Contributions: Conceptualization, K.T. and A.C.H.; methodology, K.T. and R.D.; software, K.T., A.B. and A.C.H.; validation, K.T., R.D., A.O. and A.C.H.; formal analysis, K.T. and M.M.Z.A.; investigation, K.T., R.D., A.O., H.S.A. and A.C.H.; resources, A.I.; data curation, K.T.; writing—original draft preparation, K.T.; writing—review and editing, K.T., R.D., A.O. and M.M.Z.A.; visualization, K.T. and M.M.Z.A.; supervision, K.T. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. 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