Gas Tungsten Arc Welding Technique Research Articles

A Comparison Study of High-Temperature Low-Cycle Fatigue Behaviour and Deformation Mechanisms Between Incoloy 800H and Its Weldments

The high-temperature low-cycle fatigue (LCF) behaviour of Incoloy 800H and its weldments with Haynes 230 and Inconel 82 filler metals, which were fabricated with the gas tungsten arc welding (GTAW) technique, was investigated and compared at 760 °C. The results revealed that the Incoloy 800H weldments showed lower fatigue lifetimes compared to the base metal. However, the weldments with the Haynes 230 filler metal demonstrated an improved fatigue life at the low strain amplitude compared to both Incoloy 800H and the weldment with the Inconel 82 filler metal. The Incoloy 800H base metal showed pronounced initial cyclic hardening with hardening factors increasing with strain amplitudes. In contrast, the weldments with Haynes 230 and Inconel 82 filler metals displayed short initial cyclic hardening and saturation stages, followed by long continuous cyclic softening. The fractography and microstructure after LCF the tests were characterized with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Transgranular fracture with multiple crack initiations was the predominant failure mode on the fracture surfaces of both Incoloy 800 base metal and the weldments. TEM examination revealed that planar dislocation slips at the low strain amplitude evolved to wavy slips, eventually forming a cell structure at high strain amplitudes in the Incoloy 800H material as the strain amplitudes increased. However, the weld metal exhibited a planar slip mode deformation mechanism regardless of cyclic strain amplitude in the weldment specimens. The differing cyclic hardening and softening behaviours between Incoloy 800H and its weldments are attributed to the higher strength of the weldment specimens compared to the base metal. In the Incoloy 800H base material specimens, the reverse strains during LCF created wavy dislocation structures, which could not fully recover due to the non-reversible nature of the microstructure. As a result, cells or subgrains formed within the microstructure once created. In contrast, the higher strength of the weld metal in the weldment specimens significantly suppressed the formation of wavy dislocation structures, and deformation primarily manifested as planar arrays of dislocations.

Experimental investigation on solidification cracking & intergranular corrosion of AISI 321 & AISI 316 L dissimilar weld on pulsed current gas tungsten arc welding (PCGTAW)

Dissimilar metal combinations are frequently employed in the power generation and nuclear industries. Where stainless steel piping systems are connected to pressure vessels made of low-alloy steel, the subsystems of liquid rocket engines also have different, dissimilar material combinations. Dissimilar welding plays a vital role in ensuring the integrity, performance, and reliability of components and structures operating in cryogenic environments, in this study, plates of AISI 316L and AISI 321, each 5 mm thick, were successfully joined using the pulsed current gas tungsten arc welding (PCGTAW) technique with optimized process parameters. These weld joints are mostly present in rocket engines subjected to a cryogenic environment. Due to the low temperature environment, the metallurgical properties of these joints change, which affects their mechanical properties. As it is a structural part, PCGTAW welding is most common method for joining this kind of material.In this work, Microstructural analysis of the weldment revealed a combination of vermicular, lacy, and acicular ferrite morphologies in the fusion zone at the root, mid, and crown locations.Furthermore, no solidification cracking was detected in the weldments based on the optical micrograph and SEM results. Intergranular corrosion (IGC) testing indicated the absence of a ditch structure, suggesting that the heat-affected zone (HAZ) on both sides of the weld joint was not being susceptible to sensitization. However, the HAZ of the AISI 316L side exhibited coarser grains compared to AISI 321. Analysis of tensile properties revealed a significant influence of the testing environment on the tensile strength of the dissimilar welded joints. At room temperature, the average ultimate tensile strength (UTS) was measured as 621 MPa. Remarkably, at cryogenic conditions, the average tensile properties significantly increased to 1319 MPa.Microhardness analysis showed the highest hardness associated with the AISI 321 side. The fusion zone exhibited a large deviation in the hardness profile (205 ± 10 HV), with the highest average hardness observed in the middle part of the weld. However, the hot cracking behavior of the weld was investigated by using a suutula diagram at various locations of the weld. The investigation revealed that the Creq/Nieq ratio exceeded the critical threshold value, effectively diminishing the propensity for hot cracking in the fusion zone. Overall, these findings underscore the effectiveness of the PCGTAW technique in joining dissimilar materials, as well as the importance of microstructural and mechanical property evaluations, especially under extreme operating conditions such as cryogenic temperatures.Paraphrase.

Creep Performance Study of Inconel 740H Weldment Based on Microstructural Deformation Mechanisms

Abstract The creep behavior of Inconel 740H weldment at the temperature of 760 °C is investigated experimentally and analytically using the deformation-mechanism-based true stress (DMTS) model. The Inconel 740H weldment specimens are prepared with the gas tungsten arc welding technique. Creep testing is performed on the Inconel 740H weldment specimens under a range of stress levels from 190 MPa to 447 MPa at the temperature of 760 °C. The DMTS model is employed to analyze the creep curves and creep rates. The model parameters for Inconel 740H weldment are determined from the analyses of the creep testing data in combination with that from the previous studies of similar materials based on the same creep mechanisms that involve grain boundary sliding and intragranular dislocation climb-plus-glide with dislocation multiplication. The creep life predictions of the DMTS model for Inconel 740H weldment agree very well with creep rupture test data within a temperature range of 700–800 °C. The fractured surfaces and longitudinal sections of creep-tested Inconel 740H weldment specimens are examined using scanning electron microscopy, which corroborates the DMTS model inference that the creep failure of Inconel 740H weldment is in a mode of predominantly intergranular fracture. The present study suggests that grain boundary sliding is the most significant controlling factor for the creep failure of Inconel 740H weldment.

Thermal analysis of AISI 1020 low carbon steel plate agglutinated by gas tungsten arc welding technique: a computational study of weld dilution using finite element method

An important goal in a number of optimization studies is a high-quality weld joint. Thermal analysis of AISI 1020 low carbon steel plate agglutinated by gas tungsten arc welding technique was carried out using S 2021 version. With SOLIDWORKS Premium, the simulation was run. The simulation was performed using the Thermal Simulation programme with 20 weld runs. With the findings of the initial study serving as a sensor, a design study was conducted. A total of 15 runs were completed, and the weld dilution and thermal conductivity responses were available. A range of welding temperatures including 3397 to 3688 °C were experimentally applied in the joining process of AISI 1020 low carbon steel plate of 10 mm thickness, and a strain gauge indicator was used to measure the thermal stresses induced in the steel plate. However, minimum and maximum weld dilution values of 73.1 and 46.8% were obtained with FEM at an input of arc heat of 66.4 and 37.2 J/mm, while the minimum and maximum weld dilution values of 71.55 and 45.5% were computed using experimental approach at the same heat input. On the other hand, maximum and minimum weld dilution of 71.55 and 44.5% were computed from experimental process at minimum and maximum welding current of 199.77 and 250.23 A, while 73.1 and 46.8% were obtained for the maximum and minimum weld dilution through FEM procedure at the same welding input variables. Hence, gas tungsten arc welding input parameters should be properly selected and controlled during welding operation, in order to minimize thermal effects and welding flaws such as high dilution rate.

High-Temperature Creep and Microstructure Evolution of Alloy 800H Weldments with Inconel 625 and Haynes 230 Filler Materials

Alloy 800H stands as one of the few code-qualified materials for fabricating in-core and out-of-core components operating in high-temperature reactors. Welding is a common practice for assembling these components; however, the selection of a suitable filler material is essential for enhancing the high-temperature creep resistance of Alloy 800H weldments in high-temperature applications. In this study, Inconel 625 and Haynes 230 filler materials were used to weld Alloy 800H plates by employing the gas tungsten arc welding technique. The high-temperature tensile and creep rupture properties, microstructural stability, and evolution of the weldments after high-temperature exposure were investigated and compared with those of Alloy 800H. The results show that both weldments exhibit enhanced tensile and creep behavior at 760 °C. The creep rupture times of the weldments with Inconel 625 filler and Haynes 230 filler materials were about two and three time longer, respectively, than those of Alloy 800H base metal when tested at 80 MPa and 760 °C. Carbides (MC and M23C6) were commonly observed in the microstructures of both the weld and base metals in the two weldments after high-temperature creep tests. However, the Inconel 625 filler weldment displayed detrimental δ and Laves phases in the fusion zone, and these precipitates could be potential sites for initiating cracks following prolonged high-temperature exposure. This study shows that the weldment with Haynes 230 filler material exhibit better phase stability and creep rupture properties than the one with Inconel 625, suggesting its potential for use as a candidate filler material for Alloy 800H for further investigation. This finding also emphasizes the critical consideration of microstructural evolutions and phase stability in evaluating high-temperature materials and their weldments in high-temperature reactor applications.

Multi-Weld Quality Optimization of Gas Tungsten Arc Welding for Aluminium 6061 using the Grey Relation Analysis-Based Taguchi Method

The optimization of parameters is crucial in the joining process, particularly in welding, to attain connections with exceptional mechanical properties. In the present study, the welding of aluminium 6061 was conducted with a TIG, an acronym for tungsten inert gas, is formally referred to as gas tungsten arc welding (GTAW) technique, employing a suitable ER 4043 electrode and argon shielding gas. The investigation of optimal welding parameters, specifically current, voltage, and flow rate, is conducted utilizing statistical methodologies such as the hybrid Grey-based Taguchi process. The desired attributes for high-quality welds were established as having high tensile strength, hardness, and a low rate of corrosion. Given the presence of three responses and one objective, the hybrid Grey-based Taguchi method is employed. The statistical approaches have converged on optimal parameters of 120 A, 20 V, and 15 L/min. The present analysis reveals that the ideal welded junction exhibited the following characteristics: a tensile strength of 190.169 MPa, a hardness value of 77HV, and a corrosion rate of 0.29 mm. The current parameter was found to have the highest contribution, accounting for 65.66% of the overall performance of the weldments. Confirmatory testing was conducted in order to confirm the optimization strategy, and the findings indicated that the Grey-based Taguchi technique is a straightforward yet effective approach for optimizing welded connections across several performance criteria.

Editorial—Special Issue on Functional Surfaces: Manufacturing, Measuring, and Performance

Abstract Surface treatments are intimately linked to mitigating or avoiding failures due to fatigue, corrosion, and wear. In addition, the advent of new challenges in the industry—mainly associated with an enhanced sustainability of industrial processes—makes surface engineering a critical scientific field. Controlling the superficial and subsuperficial aspects of integrity is crucial in keeping mechanical components at the allowed level of energy consumption. Hence, designing functional surfaces means examining more than just the operating surface processes to get an overview of the whole chain of inputs/outputs. It has been an absolute pleasure to be guest editors for ASTM International’s Materials Performance and Characterization Special Issue on Functional Surfaces: Manufacturing, Measuring, and Performance. The call for papers was based on the investigations presented at Symposium T of XX B-MRS Meeting in Iguassu Falls, Brazil, from September 25–29, 2022. In the symposium, four invited lectures, 12 oral presentations, and 11 posters were presented to the conference attendees. From this total, seven manuscripts were revised for the Special Issue. The other two papers are from the same meeting after we called through other symposia on surface processing. The papers herein cover relevant topics on surface engineering. The first two focus on plasma technology applied to structural steel to increase its tribological and corrosion behaviors and to a polymer for a microfluidic application. Furthermore, we can find an investigation into diamond-like carbon coatings applied to the automotive industry. Additive manufacturing is another presented technology, and the effect of laser on additive manufacturing was investigated in a fourth manuscript. Another case is the plasma transferred arc, which investigated the incorporation of intermetallic for exposure at high temperatures. Next, we have a pair of two papers using double-pack cementation, incorporating the effect of metallic elements or boron into their performances. Following that is one paper about the high-velocity oxygen fuel process using metallic alloys, and the final paper is about developing the gas tungsten arc welding technique through flux-core-double-wire, enhancing the wear performance through hard carbides. We sincerely thank the authors and reviewers for their hard work and dedication. We wholeheartedly thank the ASTM staff for dealing with the issues of publishing an outstanding journal. We hope that all papers contribute to the state-of-art of the surface engineering field. Professor Giuseppe Pintaude Universidade Tecnológica Federal do Paraná, Curitiba, Brazil Professor Ana Sofia C. M. d’Oliveira Universidade Federal do Paraná, Curitiba, Brazil Professor André P. Tschiptschin Universidade de São Paulo, São Paulo, Brazil Dr. Filipe Fernandes Instituto Superior de Engenharia do Porto (ISEP), Porto, Portugal

Study the Effect of Fluxes on Weld Penetration during Activated TIG Welding of SS304

Stainless steel is widely employed in a variety of industries, including aerospace, chemical processing, and transportation. It can be recycled indefinitely with no loss of property. The Gas Tungsten Arc Welding (GTAW) or Tungsten Inert Gas (TIG) technique is widely used for connecting thin pieces of stainless-steel. However, it is ineffective for combining heavy parts in a single pass. Activated TIG (A-TIG) dramatically enhances weld penetration up to 1.5- 4 times in a single pass. A-TIG is the centre of investigation among researchers because of its deep penetrating capacity. This article discusses the effects of particular flux powders, such as NaF and Fe2O3, on surface appearance and geometric shape. Weld of satisfactory appearance is produced using NaF powder as a flux in TIG welding, whereas, Fe2O3 powder results in a substantial increase in both the joint-penetration and weld-aspect ratio.

Influence of AZ61 Filler Composition on Grain Refinement of Mg-Al-Zn Alloy GTA Welds

The enhancement of mechanical properties in welds is heavily reliant on grain refinement. This study aims to investigate the impact of the addition of AZ61 filler and the impact of the absence of filler on the macrostructure and microstructure, as well as the mechanical properties, of Mg-Al-Zn alloy (AZ31) gas tungsten arc (GTA) welds. The AZ61 filler was employed to introduce a higher concentration of aluminum into the molten pool of AZ31 using the alternating-current GTA welding technique. It has been shown that the welds prepared with AZ61 filler had high strength and low ductility [yield strength (YS): 121 MPa, ultimate tensile strength (UTS): 226 MPa, and percent elongation (%El): 5] when compared with other welds made without filler (YS: 105 MPa, UTS: 164 MPa, and %El: 8), and the presence of the refined equiaxed grains and a significant volume fraction of second-phase Mg17Al12- β particles in the fusion zone (FZ) may explain this phenomenon. The results revealed that the average grain size of the weld decreased from 104 to 56 μm as the Al content in the weld metal increased from 2.7 wt% (without filler) to 4.5 wt% (with AZ61 filler). This grain refinement that was observed with the AZ61 filler may be attributed to the high growth restriction factor value caused by increased constitutional supercooling ahead of the solid-liquid interface.

Effect of solutionizing and double ageing treatments on the microstructural characteristics and tensile properties of Inconel 718 welds

Inconel 718 joints were fabricated using the pulsating direct current gas tungsten arc welding (PDCGTAW) and laser-arc hybrid welding (LAHW) techniques using Ni-Cr-Mo-rich filler. A cyclic post-weld heat treatment (PWHT) comprising 980 °C/20 min/air cooling; followed by two-stage ageing 720 °C/8 h/furnace cooling and 620 °C/8 h/air cooling was performed on both joints. The liquation cracking was noticed on the heat-affected zone (HAZ) of the LAHW joints. Microstructural characteristics were assessed on the joints in both as-welded (ASW) and PWHT conditions. Regardless of the joints, the coarse Mo-rich segregates were noticed in the fusion zone (FZ) in the ASW conditions. On the contrary, the partial dissolution of MC, precipitation of δ-Ni3Nb needles and the coarsening of strengthening precipitates were observed on LAHW and PDCGTAW joints after subjecting to cyclic PWHT respectively. Tensile studies corroborated that there is a considerable enhancement in the tensile and 0.2% offset yield strengths of LAHW joints after being exposed to PWHT, despite the formation of HAZ liquation cracking.

Metallurgical investigation of leakage observed in welded interface of Pilot pressure distributor of liquid stage for aerospace application

Pilot Pressure Distributor (PPD) system is used in liquid fuel stage of launch vehicles for the pressurized flow of liquid propellant. The PPD system is fabricated out of AISI304L austenitic stainless steel. The system consisted of adaptor and plumbing lines is welded together using Gas Tungsten arc welding technique. The distributor system is subjected to hydro test at 120 bar pressure and then post- harnessing command line leak check is carried out after the hydro test. During the leak test at 60 bar with snoop solution, a frothing leak is observed at PPD distributor weld joint. A pressure drop of 6 bar was also observed over a duration of 10 min. The leaked PPD distributor was dismantled from the assembly and subjected to detailed metallurgical investigation to identify the root cause of leakage. The metallographic analysis revealed leakage in PPD distributor attributed to the lack of fusion in the weld joint.

Microstructural Evolution and Mechanical Performance of Two Joints of Medium-Mn Stainless Steel with Low- and High-Alloyed Steels

In this work, 2 mm thick medium-Mn austenitic stainless steel (MMn-SS) plates were joined with austenitic NiCr stainless steel (NiCr-SS) and low-carbon steel (LCS) using the gas tungsten arc welding technique. A precise adjustment of the welding process parameters was conducted to achieve high-quality dissimilar joints of MMn-SS with NiCr-SS and LCS. The microstructural evolution was studied using laser scanning confocal and electron microscopes. Secondary electron imaging and electron backscatter diffraction (EBSD) techniques were intensively employed to analyze the fine features of the weld structures. The mechanical properties of the joints were evaluated by uniaxial tensile tests and micro-indentation hardness (HIT). The microstructure of the fusion zone (FZ) in the MMn-SS joints exhibited an austenitic matrix with a small fraction of δ-ferrite, ~6%. The tensile strength (TS) of the MMn-SS/NiCr-SS joint is significantly higher than that of the MMn-SS/LCS joint. For instance, the TSs of MMn-SS joints with NiCr-SS and LCS are 610 and 340 MPa, respectively. The tensile properties of MMn-SS/LCS joints are similar to those of BM LCS, since the deformation behavior and shape of the tensile flow curve for that joint are comparable with the flow curve of LCS. The HIT measurements show that the MMn-SS/NiCr-SS joint is significantly stronger than the MMn-SS/LCS joint since the HIT values are 2.18 and 1.85 GPa, respectively.

The Effect of Welding Process on Mechanical Properties and Pitting Corrosion Resistance of Aisi 316l Austenitic Stainless Steel Welds

The effect of welding process on mechanical properties and pitting corrosion resistance of AISI 316L austenitic stainless steel welds has been investigated using gas tungsten arc welding technique. The influence of the gas tungsten arc welding process on the toughness via the Charpy test, the hardness using Brinell hardness test, the tensile strength with the aid of a Universal tensile test machine and the pitting corrosion resistance by weight loss method were carried out on austenitic stainless steel 316L respectively. The welding process being a relatively high temperature process resulted in phase transformation in the weld and transition zone. Thereby culminating in observable differences in mechanical properties and pitting corrosion resistance between the parent material, transition zone and the weld. Higher concentration of austenite phase accounted for better mechanical properties in the transition zone and weldment. The weldment and HAZ being areas with lesser amount of Chromium and Molybdenum are the most probable for the initiation of corrosion pits and hence lesser pitting corrosion resistance compared to the parent material.

Development of Multipass Gas Tungsten Arc Welding Technique for Aerospace Grade 18% Ni-Co-Mo Based Maraging Steel to Improve the Metallurgical and Mechanical Properties by Reducing Austenite Pools

Abstract The maraging steel is an impeccable choice for aerospace applications due to its high strength and excellent toughness. Welding is importantly involved in fabricating various structures out of maraging steel. Gas tungsten arc welding (GTAW) is the most commonly adopted technique for joining maraging steel. However, the major concern regarding the welding of maraging steel is the formation of the reverted austenite phase in the fusion zone and the heat affected zone. This reverted austenite deteriorates the mechanical property performance of welded joints. The present study focuses on GTAW of 12 mm thick MDN 250 maraging steel. An attempt was made to suppress the reverted austenite by employing suitable post-weld heat treatments. Three different types of post-weld heat treatments were adopted, i.e, (i) direct aging (W-DA), (ii) solutionizing + aging (W-SA), and (iii) homogenizing + solutionizing + aging (W-HSA). The micrograph and XRD analysis of the fusion zone with W-DA and W-SA conditions reveal the presence of reverted austenite. The SEM/EDAX examination of the fusion zone of as-welded, W-DA, and W-SA conditions revealed micro-segregation of Ni, Mo, and Ti elements from the matrix to the grain boundaries. On the other hand, the W-HSA condition was free from micro-segregation and austenite reversion. Electron backscatter diffraction (EBSD) analysis was used to estimate the percentage of reverted austenite in the fusion zone. The tensile test shows the highest strength of 1721 MPa (UTS) in W-HSA conditions. Similarly, the microhardness of the W-HSA conditions depicts a higher hardness with an even distribution in the microhardness values across the weldment. Hence, considering both metallurgical and mechanical examination of the weldment, the W-HSA heat treatments give superior properties in the case of GTA welded MDN 250 grade maraging steel.

Influence of hot corrosion on pulsed current gas tungsten arc weldment of aerospace-grade 80A alloy exposed to high temperature aggressive environment

• The performance of alloy 80A weldment in a high-temperature aggressive environment was studied. • The effect of hot corrosion on different welding techniques (GTAW and PCGTAW) and filler wires (ERNiCrMo-3 and ERNiCr-3) were studied. • Influence of PCGTAW technique in protecting the surface of the welded substrate from an aggressive environment.IV) The mechanism of the formation of corrosive and protective oxides and its effect on the corrosion behaviour of welded substrates were studied. One of the significant issues that shorten the life of components used in high-temperature applications is hot corrosion. The current study compares the performance of welded aerospace-grade 80A fabricated through continuous and pulsed gas tungsten arc welding techniques. Weld coupons are produced using two different filler wires (ERNiCrMo-3 (Mo-3) and ERNiCr-3 (Cr-3)). Welded substrates are subjected to 50 cycles of air oxidation and Na 2 SO 4 + 60%V 2 O 5 molten salt environmental conditions at 900 °C. Corrosion products were analysed through scanning electron microscope/energy dispersive spectroscopy and X-ray diffraction analyses. Thermogravimetric analysis revealed that all welded substrates trailed the parabolic rate of law kinetics. In the molten salt (MS) environment, gas tungsten arc welded (GTAW) Mo-3 substrate showed more weight gain. In contrast, a minor weight gain was observed in the pulsed current gas tungsten arc welded (PCGTAW) Cr-3 substrate. It indicates that accelerated corrosion kinetics was observed in the molten salt environmental condition that showed more weight gain than air oxidation. amongst the weldments, pulsed current gas tungsten witnessed superior corrosion-resistant behaviour. This phenomenon is observed due to grain refinement suppression of heat-affected zones and secondary phases in the weld fusion zone. In addition, the appearance of protective oxides such as Cr 2 O 3 , NbO and NiCr 2 O 4 helps arrest the oxidation at the surface and sub-surface layer by providing good resistance against hot corrosion to the welded substrate. Thus, utilizing the PCGTAW technique during the fabrication/refurbishing process helps promote the material's corrosion resistance against a hot corrosion environment.

Effect of Nb-free consumables on the microstructure and structural integrity of pressure vessel grades of dissimilar austenitic stainless steel welded joints

The research article demonstrates the role of fillers in the evolution of the microstructure and mechanical integrity of dissimilar joints of stabilized austenitic stainless steels. Pulsed direct current (PDC) gas tungsten arc welding (GTAW) technique was adopted to obtain the joints of dissimilar grades of stabilized austenitic stainless steels such as AISI 321 and AISI 347. The joints of these dissimilar grades of stainless steels were achieved using a ferritic-austenitic stainless-steel filler ER2553 and Ni-rich austenitic fillers ERNiCrMo-4, ERNiCrMo-10. Delta ferrite was observed in heat-affected areas (HAZ) on both sides of stainless steels, regardless of joints. Precipitation of Mo–Nb, Mo–W rich phases was noticed in the fusion zones (FZ) while adopting Ni-based austenitic fillers. During the tensile load, the fractures occurred on the base metal side of the AISI 321 for the Ni-based fillers and on the FZ while using the ER2553 fillers. The joint efficiencies achieved by these dissimilar joints were 103.2%, 128.11% and 116.16% for ER2553, ERNiCrMo-4 and ERNiCrMo-10 fillers respectively. The joints established with the ERNiCrMo-4 filler improved the notch's impact resistance in ambient temperature and below zero conditions compared to other weld seams.

Comparing the effect of continuous and pulsed current in the GTAW process of AISI 316L stainless steel welded joint: microstructural evolution, phase equilibrium, mechanical properties and fracture mode

In this paper, the effect of continuous and pulsed current in the gas tungsten arc welding (GTAW) on the various properties of an AISI 316L stainless steel joints was investigated. 316L austenitic stainless steel sheets with a thickness of 10 mm were used together with ER309L filler. The sheets were welded together by the GTAW technique in two modes of continuous and pulsed currents. Microstructural characterization and phase equilibria were done using optical microscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with electron backscatter diffraction (EBSD) detector, techniques. Charpy impact, uniaxial tensile, and microhardness tests were used to investigate the effect of the type of the welding current on mechanical properties of the joints. The fracture surfaces were evaluated by FE-SEM after tensile and Charpy impact tests. Results showed that the weld metal (WM) microstructure is austenitic-ferritic (AF). It was also consisted of columnar and coaxial structures, in a way that varying the welding current from continuous to the pulsed mode changed the morphology of the grains from elongated columnar to a fine coaxial morphology. In addition, such a change in the welding current reduced the size of the grains in the WM, and the width of the unmixed zone (UMZ) as well. XRD analysis showed that the predominant phase and the preferred crystal plane of the WM are austenite, and (111), respectively. Both joints were broken from the base metal (BM) during the tensile test. Also, the above change of the welding current mode increased hardness and fracture toughness of the WM. Finally, fractography of the joints indicated that both joints experienced a completely ductile fracture.

Study on the Mechanical Performance of Dissimilar Butt Joints between Low Ni Medium-Mn and Ni-Cr Austenitic Stainless Steels Processed by Gas Tungsten Arc Welding

In the present work, dissimilar butt joints between a low-Ni, medium-Mn austenitic stainless steel, M-Mn SS, and a Ni-Cr austenitic stainless steel, Ni-Cr SS, were processed by utilizing the gas tungsten arc welding (GTAW) technique at different heat inputs. A filler metal of ER308 was employed in the welding process. The filler yields 480 MPa, which is equivalent to the yield strength of M-Mn SS. The microstructural analysis and mechanical performance (i.e., tensile strength and hardness properties) of the concerned joints were studied by using an optical microscope and uniaxial tensile tests, respectively. The results revealed that a duplex structure from austenite matrix and delta ferrite is promoted in the fusion zone (FZ) of the dissimilar joints processed with low and high energy inputs (0.486 kJ/mm and 0.558 kJ/mm). The FZ of the specimens welded at high heat input exhibited the lowest hardness value (151.2 HV) in comparison to heat affected zone (HAZ) (166.3 HV). Moreover, the joints exhibited a low tensile strength of 610 MPa. The achieved strength is significantly lower than the strengths of the base metals (BMs) M-Mn SS and Ni-Cr SS. This is mainly attributed to the inhomogeneous dendritic structure of the FZ with Cr-carbides precipitation.

Influence of Filler Wire and Welding Process to Mitigate the Microsegregation of Alloy C-2000 Using Continuous and Pulsed Current Gas Tungsten Arc Welding Techniques

Influence of Filler Wire and Welding Process to Mitigate the Microsegregation of Alloy C-2000 Using Continuous and Pulsed Current Gas Tungsten Arc Welding Techniques

Influence of heat input on microstructure, hardness and pitting corrosion of weld metal in duplex stainless steel welded by keyhole-TIG

The efficient and accurate welding technologies, including several high-energy density beam welding technologies, are generally used to weld mid-thick duplex stainless steel (DSS). However, there are still some unresolved welding problems, i.e. blowhole, excessive content of ferrite, and coarse columnar grain. Therefore, in the present paper, the keyhole gas tungsten arc (K-TIG) welding technique, a novel process, was used. The microstructural characterization, hardness and pitting corrosion of weld metal (WM) with different heat inputs were investigated in detail. The results show that weld defects in the welded joint could be effectively avoided by appropriate welding parameters. As the heat input is enhanced, Widmanstätten austenite (WA) content increases, while fine-grained intergranular austenite (IGA) content decreases. The hardness of austenite in WM is associated with solution nitrogen and dislocation proliferation caused by deformation. Besides, the PREN of ferrite in the same WM is lower than austenite. The variation of Epit in each WM could be neglected owing to the similar chemical composition. However, the corrosion rate of WM gradually increases with the enhancement of heat input. Meanwhile, the initiation and propagation of pits could be significantly affected by the precipitate Cr2N, PREN as well as Σ3 coincident site lattice (CSL) boundaries. Furthermore, fine-grained IGA could be beneficial to improve the stability and continuity of the passive film.