Gas Tungsten Arc Welding Process Research Articles

Using Hybrid Artificial Neural Network and Particle Swarm Optimization Algorithm for Modeling and Optimization of Welding Process

This study addresses a hybrid procedure used for modeling and optimization of gas tungsten arc (GTA) welding process of AL5052 alloy. There are different process input parameters among which welding current ([Formula: see text], frequency ([Formula: see text], welding speed ([Formula: see text], and gap ([Formula: see text] are the most important ones considered in GTA welding process. Furthermore, heat affected zone (HAZ) is considered as the most important quality measure of the process. To gather the required data for the modeling and optimization purpose, design of experiments (DOE) approach has been used. Image processing technique is used to take accurate measurements of HAZ values. In order to determine the relationship between process input variables and output measures, artificial neural networks (ANNs) have been used. Then, the trained ANNs have been used to find the optimal value of the outputs using particle swarm optimization (PSO) algorithm. Experiments have been done to verify the optimal levels of the input parameters. Verification results demonstrate that the proposed ANN-PSO procedure is quite efficient in modeling and optimization (with about 4% error) of GTA welding process.

Experimental Analysis of T23–T91 Dissimilar Steel Joining in Supercritical Boiler by a Cost‐Effective Fusion Welding Route

The critical aspect of joining T23 steel to T91 steel in a supercritical boiler is studied by a low‐cost gas tungsten arc welding (GTAW) process using an iron‐based filler wire (ER90S‐G). The hardness variation across the weldment does not reflect any drastic fall in hardness, thereby indicating an absence of “soft zone.” A significant joint strength (UTS = 318 MPa) together with a modest ductility (%Elongation = 6) is established by carrying out tensile test at boiler operation temperature (571 °C) and thereafter carrying out advanced characterization keeping all different regions of the weldment intact. During high‐temperature tensile deformation, Cr23C6 particles are found to be pushed along with grain boundary sliding and finally are clustered around the cavity formed thereby. The presence of Cr23C6 particles surrounding cavity promotes a cleavage mode of failure so as to negate a high ductility to be achieved. Yet, a modest ductility is still retained by virtue of soft α‐ferrite matrix promoting a concomitant dimple mode of failure. Furthermore, these Cr23C6 particles are also found to be responsible for an accumulation of dislocation loops around them, thereby providing quite significant high‐temperature strength with 88% joint efficiency.

Analysis of Current on Mechanical Properties and Microstructure of A53 Gr B Material with Gas Tungsten Arc Welding Process

The welding use correct process parameters will produce joint with optimum in mechanical properties. The current is a very important process parameter in welding. Gas Tungsten Arc Welding process carbon steel A53 Gr B uses current variations can be an option to get the best quality joints. The purpose of this research is to get optimum mechanical properties and microstructure by varying the current. The experimental method uses GTAW process by varying current in welding A 53 Gr B using a single V butt joint and a 5G welding position, the Argon protective gas flow rate of 15 liters per minute with filler rod ER 70 S-6. This process also uses 11-13 Volt voltage with DCEN polarity and current 70, 90, and 110A. Based on ASME Section IX, the test results show that the specimen with a current of 90A gives optimum results with a tensile strength of 480 MPa and a hardness value of 190 HV, whereas specimens with welding current of 70A bring incomplete penetration defects in the weld area. The use of welding current 90A in this research provides welding results with better mechanical properties and microstructure compared to the use of currents of 70 and 110A

Effect of Heat Input on Dilution, Hardness, and Microstructure in DMW Stainless Steel and Carbon Steel

The success of Dissimilar Metal Welding (DMW) occurred in optimal Heat-input (HI) parameters. The quality of welding joints was affected by dilution, hardness value, and intermetallic microstructure. DMW quality research was carried out on stainless steel SA SS312-TP304 and SA 53GrB carbon steel using the GTAW (Gas Tungsten Arc Welding) process with Heat-input of 1866.6 to 2362.2 J/mm. Visual observation on weld joints was not found weld defects. The optimal dilution area in the Schaeffler Diagram was obtained 35.35% austenitic area and without ferrite content. The lowest hardness value on carbon steel was 145 HV. The highest hardness value of 197 HV occurred in filler-metal dilution on carbon steel, so the difference in the value of hardness was high. The hardness value on stainless steel was 184 HV and in filler-metal stainless steel dilution was 172– 90 HV, so the difference in hardness value was low. Microstructure filler-metal dilution on stainless steel was austenite-dendritic, filler-metal dilution on carbon steel was fine-grained dendritic, and on allweld metal coarse-grained dendritic metal. HAZ stainless steel austenite microstructure and ferrite-pearlite carbon steel with an indication of a ferrite net. Observation of dilution, hardness value, and microstructure in DMW did not have a significant effect. This welded joint could be used as a reference in the DMW fabrication process for stainless steel and carbon steel pipe connections.

Study on effect of grain refinement of P92 steel base plate on mechanical and microstructural features of the welded joint

The work described the effect of the grain refinement in virgin P92 steel plate on the microstructural and mechanical behavior of the P92 welded joint. The as-received P92 steel plate was subjected to varying heat-treatment, i.e., conventional heat treatment (CNT) and double normalized heat treatment (DNT) to refine the grain structure. The DNT is mainly done for the grain refinement in the as-received P92 steel plate. The autogenous gas tungsten arc welding (GTAW) process was utilized to prepare the P92 steel welds joint. Four set of the welds joint were prepared, two by using the CNT plate, termed as AW1 and two by using the DNT plate, termed as AW2. The welded plate has been subjected to heat treatment at 760 °C for 3 h (T1, T2) for both the conditions to stabilize the microstructure of weldments, i.e., tempering of the fresh martensite. The grain growth, particle size, and particle distribution in P92 weldments have been studied. For mechanical characterization, tensile tests, hardness tests and Charpy toughness tests (CTT) have been carried out. Soft δ ferrite formation was observed in weld fusion zone (WFZ) and coarse-grained heat-affected zone (CGHAZ) for AW and T condition and formation is attributed to high heat input and presence of the ferrite stabilizer like W and Mo. Heterogeny in microstructure and mechanical properties was measured across the weldments for AW condition and get minimized as a result of the PWHT. The average hardness for WFZ was measured 363 and 358 HV for AW1 and AW2 conditions, respectively. The difference in the hardness of WFZ can be neglect. The peak hardness of CGHAZ was measured at 358 and 397 HV for AW1 and AW2, respectively and it is attributed to the solid solution strengthening mechanism. The variation in hardness along the welded joint was reduced to a minimum level as a result of the heat treatment. The AW 2 welds joint showed maximum tensile strength of 943 MPa and get reduced drastically after the heat-treatment (T2) (700 MPa) but still showed a higher value as compared to T1 (602 MPa). A significant improvement in tensile strength without any loss in ductility was obtained for the welds joint prepared using the DNT plate as compared to CNT plate.

Influence of the groove shape on welding residual stresses in P92/SUS304 dissimilar metal butt-welded joints

Two dissimilar metal butt-welded joints between P92 steel and SUS304 stainless steel were fabricated with different groove shape, namely single V-groove and X-groove, by gas tungsten arc welding process. Based on Sysweld software, three-dimensional thermal-metallurgical-mechanical coupled finite element analyses were performed to investigate the welding-induced residual stresses in P92/SUS304 dissimilar metal butt-welded joints. Meanwhile, the hole-drilling strain gauge method was used to measure the distributions of residual stresses on the top and bottom surfaces of the two butt-welded joints. The results obtained indicate that the predicted welding residual stresses achieve good levels of agreement with the measurements. In the numerical model, the solid-state phase transformation in P92 steel, the strain hardening and annealing effect in SUS304 stainless steel, and the discrepancy in thermal expansion coefficients between dissimilar metals were carefully considered. The simulated results show that these three factors have significant influence on the formation of longitudinal residual stresses in P92/SUS304 butt-welded joints. In addition, the distribution of welding residual stresses in the butt-welded joint with X-groove was compared with that in the joint with single V-groove. The results suggest that the butt-welded joint with X-groove may be superior to that with single V-groove in reducing the region of high tensile residual stress.

Improvement of hot corrosion resistance of dissimilar weldments by current pulsing in a simulated power plant environment

Hot corrosion studies are of utmost importance for welded components in the power plant industry as well as for industries which deal with exposure to the high-temperature corrosive environment. The failure of welded components at high temperatures has often led to the reduced service life of a component and catastrophic disasters. This has been a significant engineering challenge in the design of welded components. It is generally seen that the failure of the welded sections mostly occurs because of the deposition of molten salt over the weldments which accelerate the hot corrosion reactions. In this present research work, two dissimilar base materials, AISI 4340 and AISI 304L have been welded with two different welding processes namely continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) while making use of ERNiCr-3 as filler material. A comparative study of the dissimilar welded plates was carried out by simulating a molten salt environment at 600°C involving hot corrosion behavior. By analyzing the microstructure and thermo-gravimetric data, it is concluded that the pulsed current gas tungsten arc welding process has superior corrosion resistance properties while using ERNiCr-3 as the filler material as compared to the continuous current gas tungsten arc welding process.

Role of the Ni-based filler (IN625) and heat-treatment on the mechanical performance of the GTA welded dissimilar joint of P91 and SS304H steel

The objective of the current investigation to carry out a detailed research study on the relationship of microstructure and mechanical properties of the dissimilar Gas Tungsten Arc Weld (GTAW) joint of heat-resistant ferritic/martensitic P91 and austenitic SS304H steel, prepared using the Ni-grade ERNiCrMo-3 filler. The metallographic characterization of the weldments (P91 HAZ, weld metal, SS304H HAZ) was performed by availing the optical microscope and scanning electron microscope equipped with energy dispersive spectroscopy for precipitate size, their distribution in matrix, morphology and chemical composition. Mechanical properties of the weldments were also evaluated and for that, tensile testing, microhardness testing and Charpy testing were conducted. The metallographic and mechanical characterization of the weldments were also performed after the post-weld heat treatment (PWHT) at 775 °C for 60 min and compared with the as-welded condition. The results indicated that a complete heterogeneous microstructure formation across the weldments which led to variation in the mechanical behaviour of the weldments. The tensile strength and Charpy impact toughness (CIT) of the weld metal were measured 631 MPa and 79 J, respectively, in the as-welded condition. The coarse-grained HAZ region of P91 side showed the peak hardness of 412 HV (as-welded), which was higher than the hardness of the weld metal (303 HV). After the PWHT, an improvement in tensile properties was observed and tensile strength and % elongation was measured 666 MPa and 16.14 %, respectively. After the detailed study, it was concluded that the GTAW process with ERNiCrMo-3 filler offered a better combination of the microstructure and mechanical properties in as-welded condition for the dissimilar welded joint of P91 and SS304H.

Investigations on microstructural characteristics and mechanical properties of 316 L stainless steel welded joints using nickel coated filler material by gas tungsten arc welding

The main objective of this present study is to weld the 316 L stainless steel (SS) joints by gas tungsten arc welding (GTAW) process using nickel coated filler materials. The existing modified filler metals with flux coatings used in GTAW are generally accompanied with more complications. Therefore it is essential to suppress complications and enhance the welding strength which significantly depends on filler metals properties. In this work, the filler materials used in GTAW are coated with nickel in several grades for welding process. The results of these filler metals are compared with the Plain-316 filler metal. Ni-304 filler metal shows better uniformed weldment and heat affected zone (HAZ) with less planer slip micorstrucutre on its surface. The tensile test results reveal that Ni-316, Ni-304 & Ni-308 filler metals produces fracture on the parent metal. Among the various filler metals used, Ni-304 filler metal shows the highest impact toughness of 69.10 J and it is 71% higher toughness than Plain-316 filler. Average hardness of Ni-308 filler metal is 2.78% higher than the Plain-316 filler metal. Scanning electron microscope (SEM) images of weldments and HAZ were analysed to investigate the effect of nickel on the microstructure changes.

Gas-Tungsten Arc Welding of Dissimilar Aluminum Alloys With Nano-Treated Filler

AbstractArc welding of dissimilar aluminum alloys is in high demand in industry but often challenging in practice. Dissonant material properties between the base metals often lead to solidification cracking in the weld metal upon cooling. Here, we report a nano-treatment approach that infuses TiC nanoparticles into filler material mimicking commercial ER5183 to successfully join dissimilar systems of AA2024 + AA5083 and AA2024 + AA7075 with the gas-tungsten arc welding process. Welded specimens were free of hot cracking, and microstructural studies revealed globular, refined grains smaller than 20 µm in the weld metals of both systems. Mechanical properties of both systems were examined with microhardness and tensile testing, and they showed sound behavior in their as-welded conditions. Nano-treatment therefore presents a new way to reliably weld dissimilar systems that are traditionally considered unweldable.

GTAW Welded Inconel 625 Alloy Fuel Cladding for the Canadian SCWR: Microstructure and Mechanical Property Characterization

Abstract Inconel 625 is considered one of the candidate materials for reactor fuel cladding in the Canadian supercritical water reactor (SCWR) design. Gas tungsten arc welding (GTAW) is being evaluated as a joining technique for SCWR fuel cladding since this method is widely used to join components in the power and nuclear industry. During the GTAW process, the welding thermal cycle produces different types of microstructures in both the heat-affected zone (HAZ) and fusion zone (FZ) that affect the material's mechanical properties. A series of welding experiments at various weld conditions were performed using an automatic GTAW orbital process on Inconel 625 alloy tubing. Simple analytical heat conduction and grain growth models were developed to predict weld temperature profiles and metallurgical transformations. Weld characterization included mechanical tests, optical microscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) elemental analysis, and microhardness measurements. Weld microstructural characterization revealed that a characteristic dendritic structure was formed in the FZ, while the HAZ exhibited larger equiaxed grains than those found in the base material (BM). SEM-EDS analysis showed no distinct alloying element segregation in both the HAZ and FZ. Welds produced with heat inputs of about 3.00 J/mm3 presented similar mechanical properties as those observed in the BM. In these welds, grain growth was homogenously minimized in the FZ. It is concluded that the effective welding heat input control can optimize the weld microstructure and the weld mechanical properties in Inconel 625 tubing used as Canadian SCWR reactor fuel cladding.

Investigations on quality characteristics in gas tungsten arc welding process using artificial neural network integrated with genetic algorithm

Gas tungsten arc welding (GTAW) technology is widely used in industry and has advantages, including high precision, excellent welding quality, and low equipment cost. However, the inclusion of a large number of process parameters hinders its application on a wider scale. Therefore, there is a need to implement the prediction and optimization models that effectively enhance the process performance of the GTAW process in different applications. In this study, a five-factor five-level central composite design (CCD) matrix was used to conduct GTAW experiments. AISI 1020 steel blank was used as a substrate; UTP AF Ledurit 60 and UTP AF Ledurit 68 were used as the materials of two tubular wires. Further, an artificial neural network (ANN) was used to simulate the GTAW process and then combined with a genetic algorithm (GA) to determine welding parameters that can provide an optimal weld. In welding experiments, five different welding current levels, welding speed, distance to the nozzle, angle of movement, and frequency of the wire feed pulses were used. Using GA, optimal welding parameters were determined: welding current = 222 A, welding speed = 25 cm/min, nozzle deflection distance = 8 mm, travel angle = 25°, wire feed pulse frequency = 8 Hz. The determination coefficient (R2) and RMSE value of all response parameters are satisfactory, and the R2 of all the data remained higher than 0.65.

Effect of Heat Input in Dissimilar Welding on SS304H and T22 to Hardness Distribution and Delta Ferrite Content with GTAW Process

In this paper, a study was carried out on the effect of various heat input on the hardness distribution and delta ferrite content in dissimilar welding on T22 and SS304H tube boilers in power plants using Gas Tungsten Arc Welding (GTAW). The heat input used in this study is 2.9 KJ/mm, 3.1 KJ/mm and 3.6 KJ/mm. Controlling the heat input parameter is one method to reduce problems in dissimilar welding. The general problem occurs in dissimilar welding is the failure on the weldment to occur due to differences in chemical composition, mechanical properties and thermal coefficients of the two materials where it makes degradation in the microstructure in the fusion zone and creating residual stress than susceptibility to fatigue in material or cracks. All variation of heat input in this study is safe to operate in the welding process and low tendency to hot cracking. Using the lowest variation of heat input 2.9 KJ/mm has the highest value of hardness distribution and lowest FN value.

Investigating the effect of arc offsetting in AISI 304 stainless steel and copper welding using gas tungsten arc welding

The present study investigates the effect of welding arc offsetting on weldments of AISI 304 stainless steel and oxygen-free copper (C10200) sheets, 1.00 mm thick. A dissimilar weld joint is fabricated using the gas tungsten arc welding process. Due to the large differences in material properties, there is uneven partitioning of the heat at the joint interface in dissimilar welding. Consequently, the welding arc was offset toward the copper side. The weldments are prepared using different offsetting distances for the welding arc. The finite element (FE) formulation is developed to study the thermal behavior due to welding arc offsetting in the dissimilar weldment. In this study, the offsetting distance is considered within the range of 0.0–3.0 mm. The Time–Temperature trends and the resulting temperature contours over the domain obtained using FE analysis are compared vis-a-vis experimental observation to find the optimum values of the offset for the welding arc for this combination. The analysis revealed that AISI 304 Stainless Steel is prone to melting at lower values of the offset as compared to copper which reflects the opposite trend in higher values of offset.

Effect of autogenous GTAW on the reciprocating sliding wear behavior of a carbon martensitic steel

Martensitic steels have been successfully employed in resource-based industries where components must endure aggressive conditions. In industrial practice, many parts of these components are joined by welding techniques. The aim of this work was to understand the influence of welding on the wear resistance of quenched and tempered carbon martensitic steel subjected to dry linear reciprocating sliding micro-wear tests. Weld-joints were produced using autogenous Gas Tungsten Arc Welding process (GTAW). Micro-wear tests were performed at base metal (BM), weld metal (WM), coarse grained heat affected zone (CG-HAZ) and lowest hardness region of heat affected zone (LHR-HAZ). LHR-HAZ was softened during welding process so plastic deformation was facilitated, and consequently adhesion, material displacement and micro-ploughing. WM and CG-HAZ presented a similar martensitic structure, which explain the similarities found on wear behavior. These regions presented the lowest worn volume average values (w). It was interesting to note that despite its highest microhardness value, the highest w was observed for BM. For some BM samples, debris had a key role promoting material loss by micro-cutting which causes great extent of material removal compared to other micro-wear mechanisms as micro-ploughing and adhesion. Due to debris action BM also presented a great dispersion in w results. The results suggest that material loss of welded joint and BM was strongly controlled by micro-wear mechanisms.

The Weld Microstructure and Mechanical Properties of the Alloy 52 and Its Variants with Applied Electromagnetic Stirring during Welding

This study investigated the impact of electromagnetic stirring (EMS) on nickel-base alloy welds prepared with the gas tungsten arc welding process. Alloy 52 and its variants, Alloy 52M and Alloy 52MSS, were carefully evaluated with their weld microstructure and mechanical properties. The results showed that the welds exhibited a typical microstructure of dendrites, and that the dendrites could be refined by electromagnetic stirring. Meanwhile, with an application of EMS, the precipitates became smaller and more evenly distributed in the inter-dendritic areas. Ti(N,C)s, Nb/(Nb,Si)Cs, and large-scale Laves phase with (Nb,Mo,Ti)Cs were the precipitates present in the Alloy 52, Alloy 52M, and Alloy 52MSS welds, respectively. With the refined microstructure, both Alloy 52 and Alloy 52M welds were observed to have an increase in their tensile strength, with a decrease in their elongations. Comparatively, for the Alloy 52MSS weld, the tensile strength was enhanced along with a slight increase in elongation. Deep and dense dimples were a dominant feature of low-Nb-additions welds, and dendrite-like features were found prevalent among the Alloy 52MSS welds. With EMS, the dimples of Alloy 52 welds and the dendrite-like features of Alloy 52MSS welds became finer, while the dimples of Alloy 52M welds grew coarser.

Effect of Carbon Content on the Creep Rupture Properties and Microstructure of 316H Weld Metals

Two types of 316 butt welds with carbon contents of 0.016% and 0.062% have been produced using the gas tungsten arc welding process. The δ-ferrite content decreased from 7.2 to 2.8% in volume as the carbon content increased. The creep-rupture strength and creep ductility of the two types of weld metals have been measured at 550 ℃ over the stress range of 290–316 MPa and at 600 ℃ over 230–265 MPa. The microstructure change and precipitation behavior of the weld metals were observed and related to the creep rupture properties. The creep rupture strength of the C2 (0.062% C) weld metal was higher than that of the C1 (0.016% C) weld metal at both 550 ℃ and 600 ℃. At 550 ℃, as the decrease in the applied stress, the difference of the creep-rupture life between the two weld metals diminished due to the higher depletion rate of carbon by precipitation of M23C6 in the C2 weld metal, while at 600 ℃, the difference enlarged due to the massive precipitation of σ phase and extensive crack formation and propagation along σ/austenite boundaries in the C1 weld metal. For both the C1 and C2 weld metal, the decrease in ductility was adverse with the transformation percentage and related to products of the δ-ferrite transformation.

Effect of Welding Heat Input and Post-weld Thermal Aging on the Sensitization and Pitting Corrosion Behavior of AISI 304L Stainless Steel Butt Welds

Heat input for gas tungsten arc welding process was varied at three different levels to fabricate three AISI 304L stainless steel welds to examine the influence of variable arc energy input on their sensitization and pitting performance. Welds were subjected to post-weld thermal aging treatments comprising of low-temperature sensitization of 500 °C for 1, 5, and 11 days and classical sensitization of 650 °C for 1, 12, and 24 h. Different morphologies of ferrite present in the fusion zone and the degree of the coarsening of grains in the heat-affected zone (HAZ) of the weldments under different aging conditions influenced their tendencies for carbide formation, which consequentially affected their sensitization and pitting corrosion behavior significantly. Lower heat input welds having lathy morphology of δ-ferrite in the fusion zone along with less coarsened HAZ exhibited a lesser degree of carbide precipitation. They hence showed a lower degree of sensitization (DOS), which accounted for higher pitting potential (Epitt). However higher heat input welds having vermicular morphology of δ-ferrite in the fusion zone and relatively higher grain coarsened HAZ promoted a higher degree of carbide precipitation, and thus accounted for the higher value of DOS and lower pitting potential (Epitt).

Effect of Fillers and Autogenous Welding on Dissimilar Welded 316L Austenitic and 430 Ferritic Stainless Steels

This experimental study examines the effects of dissimilar welding of 316L austenitic and 430 ferritic stainless steels, welded with gas tungsten arc welding process with (ER316L and ER309L) and without fillers (autogenous). Microstructural examination was performed by optical and scanning electron microscopy. ER316L and ER309L fillers welds illustrated equiaxed and columnar grains; ER309L weld showed higher Creq/Nieq ratio than that of ER316L weld, produced vermicular ferrite, while autogenous weld shows lathy ferrite and martensite. Chromium carbide precipitate was also observed in autogenous weld. The mechanical properties were measured and higher hardness was obtained in autogenous weld compared to ER316L and ER309L filler weld. Higher tensile and impact strength was measured in ER316L filler weld as compared to ER309L filler and autogenous weld. The corrosion resistance of the joints was carried out by double loop electrochemical potentiokinetic reactivation and potentiodynamic polarization test to assess the sensitization and pitting resistance, respectively. Higher degree of sensitization and pitting were observed in autogenous weld as compared to ER316L and ER309L filler weld due to precipitation formation, but the pitting corrosion was found to be lower for ER309L filler weld as compared to ER316L filler and autogenous weld due to the effect of mode of solidification.

Assessment of Microstructure and Tensile Behavior of Hot Wire Gas Tungsten Arc Welded Pure Nickel Tubes

The interest in hot wire gas tungsten arc welding (HWGTAW) process is increasing in industrial sector in the current decade. Pure nickel (Ni 200) tubes having 4-mm-thickness and 44-mm-outer diameter were effectively joined by HWGTAW. The heating current of the filler wire was varied from 80 amps to 120 amps in steps of 10 amps. The joint microstructure was recorded using conventional optical microscope and advanced transmission electron microscope. Electron backscatter diffraction was applied to visualize the grain structure and orientation. The increase in heating current enlarged the fusion zone geometry and caused coarsening of grains. There were no cracks or pores present in the joints. Three kinds of microstructure zones were observed across the joints. Few dislocations were formed in the fusion zone which recorded the lowest hardness. All joints demonstrated excellent ductility. The joint fabricated using a heating current of 100 amps showed highest tensile strength.