Gas Tungsten Arc Welding Technique Research Articles

Double-sided GTAW of nuclear grade steel: Mechanical and microstructure perspectives

This article investigates the microstructural evolution and mechanical integrity of austenitic stainless steel SS321, a titanium stabilized nuclear grade mainly preferred for severe corrosive environments. The double-sided gas tungsten arc welding (DS-GTAW) technique was utilized to fabricate the butt joint having a plate thickness of 6 mm. A heat input of 1.4058 kJ/mm was used to obtain the maximum depth of penetration (DoP) of 3.3 mm with welding speed 120 mm/min and current 220A. Optical microscopy reveals the microstructure of weldment and base metal (SS321). The DS-GTA weldments were subjected to tensile, bend, impact and microhardness tests and the results are evaluated. The fusion zone consists of columnar, equiaxed dendrites, and intermetallic compounds of Titanium carbide (TiC). From EBSD examination the higher fraction of Low Angle Grain Boundaries is corroborated to the increase in tensile strength and reduction in impact toughness of the weldment. The ferrite measurement reveals the increase in ferrite content in the weldment (6.1 FN) and this attributed to the presence of retained δ-ferrite in comparison to SS321 (1.2 FN). X-Ray Diffraction (XRD) pattern reveals austenite and ferrite peaks are present in the SS321 and weldment. Ductile mode of fracture (using SEM-Scanning electron microscope) was observed in the uni-axial tensile and impact test of weldment specimens.

Weldability of AA6063 alloys by using Keyhole Gas Tungsten Arc Welding Technique

Weldability of AA6063 alloys by using Keyhole Gas Tungsten Arc Welding Technique

Effect of Heat Input on the Microstructural, Mechanical, and Corrosion Properties of Dissimilar Weldment of Conventional Austenitic Stainless Steel and Low-Nickel Stainless Steel

In the present investigation, an attempt has been made to investigate the replacement compatibility of conventional austenitic stainless steel (316L) with low-Ni austenitic stainless steel (201) by employing their dissimilar welding using gas tungsten arc welding technique with varying heat input. The effects of heat input on the microstructural, mechanical, and corrosion properties were studied. The result depicts the balanced austenite/ferrite content in the fusion zone for both the heat inputs. The low heat input process, which results in a faster cooling rate, demonstrates higher tensile strength and microhardness. Similarly, the pitting corrosion resistance of the fusion zone demonstrates better properties on the low heat input process attributed to the lesser dendritic length and lesser interdendritic arm spacing.

Weldability and weld strength of dissimilar joint between UNS S32750 and Monel 400 developed by PCGTAW process

Dissimilar weldments of Monel 400 and UNS S32750 are widely used in pressure vessels and marine industries where the weldments are exposed hot corrosion and can withstand this effect as they offer excellent corrosion resistance and improve the service life. This research paper aims at investigation on the weldability and welding strength of dissimilar welded joints of UNS S32750 and Monel 400 developed by pulsed current gas tungsten arc welding technique. ERNiCrMo-4, ERNiCrMo-3 and ER309L fillers were used to join the base metals. Mechanical properties were demonstrated by using tensile test, impact toughness test and microhardness. The ultimate strength of ERNiCrMo-4 weldment was increased by 16.2% and 20.2% when compared to ERNiCrMo-3 and ER309L weldments, respectively. The fracture has occurred under direct tension test in all the cases at the base metal of Monel 400. The superior impact toughness value (169 J) was observed in ERNiCrMo-4 filler weldment than the ERNiCrMo-3 (144 J) and ER309L (76 J) filler weldments. The average hardness number of ERNiCrMo-4 filler weldment (318 HV0.1) was higher than those of ERNiCrMo-3 (306 HV0.1) and ER309L (286 HV0.1) filler weldments.

Development of Stellite 1 hardfacing procedure for crack-free SS 304 stainless steel orifice plate

This paper studies establishing an effective deposition technique of cobalt-based Stellite1 on austenitic stainless steel (SS 304) orifice plate component, used in offshore application. Stellite1 hardfacing was done using gas tungsten arc welding (GTAW) and flux-cored arc welding (FCAW) techniques, which resulted in intergranular and longitudinal cracks. In finite element analysis (FEA), a three-dimensional solid model was generated and simulated for spot heat welding using ANSYS software. After simulation for heat distribution with and without weld bordering, crack-free hardfacing of Stellite1 was carried out and validated experimentally using FCAW technique. A control on substrate preheating, thermal insulation, job clamping and cooling time reduced the intersecting cracks. Metallurgical analysis using Optical microscopy, SEM, EDS and XRD along with hardness measurements was done to investigate the mechanisms causing failure. Crack area measurements were done in gradient edge detection technique using MATLAB software and quantified.

Arc Characteristics and Weld Bead Microstructure of Ti-6Al-4V Titanium Alloy in Ultra-high Frequency Pulse Gas Tungsten Arc Welding (UHFP-GTAW) Process

To resolve the problem of grain coarsening occurring in the fusion zone and the heat-affected zone during conventional gas tungsten arc welding(C-GTAW) welded titanium alloy, which severely restricts the improvement of weld mechanical properties, welding experiments on Ti-6Al-4V titanium alloy by adopting ultra-high frequency pulse gas tungsten arc welding (UHFP-GTAW) technique were carried out to study arc characteristics and weld bead microstructure. Combined with image processing technique, arc shapes during welding process were observed by high-speed camera. Meanwhile the average arc pressure under various welding parameters were obtained by adopting pressure measuring equipment with high-precision. In addition, the metallographic samples of the weld cross section were prepared for observing weld bead geometry and microstructure of the fusion zone. The experimental results show that, compared with C-GTAW, UHFP-GTAW process provides larger arc energy density and higher proportion of arc core region to the whole arc area. Moreover, UHFP-GTAW process has the obviously effect on grain refinement, which can decrease the grain size of the fusion zone. The results also revealed that a significant increase of arc pressure while increasing pulse frequency of UHFP-GTAW, which could improve the depth-to-width ratio of weld beads.

Hot fissuring mitigation in arc welding of Nickelvac 23 superalloy

Nickelvac 23 is prone to hot fissuring due to elemental segregation in arc welding. The goal of the present research is to assess the possibility of mitigating the elemental segregation using arc welding processes with nickel-based filler wire. In this work, Nickelvac 23 weldments are made by gas tungsten arc welding techniques (Continuous and pulsed current modes) with ERNiCrMo-10 filler wire. The result of the macro evaluation depicts that defect-free welding with the proper fluid flow was accomplished in both weldments. The microscopical examination reveals the cellular and columnar structures in the weldment with CCGTAW and equiaxed structure in weldment with PCGTAW. Weldment with CCGTAW is detected with Mo segregation which forms the Mo23C6 phases in the interdendritic region. Segregation of Si is noticed in all the weldments. Suppression of elemental segregation is noticed with PCGTAW while using ERNiCrMo-10 filler wire. XRD analysis shows the formation of interstitial compounds like MC, M12C, M23C6 at the weldments. Tensile strength, hardness and toughness values are slightly improved in the PCGTAW as compared to CCGTAW due to the formation of interstitial compounds. Electron Backscatter Diffraction (EBSD) analysis confirmed the HAZ failure is due to the coarse grain structure. EBSD results also showed 36 % lesser grain sizes for the PCGTAW than the respective CCGTAW.

The comparison of gas tungsten arc welding and flux cored arc welding effects on dual phase steel

This work aims to investigate the effects of two welding techniques (gas tungsten arc welding (GTAW) with filler metal ER70S-3 and flux cored arc welding (FCAW) with filler metal E71T1C) on the microstructure and mechanical properties (including softening due to the conversion of martensite into tempered martensite) of DP steels with different martensite volume fractions ranging from 9 to 20%. Microstructure features and the constituents of base metals and heat affected zones of all weldments were examined and analyzed using an optical microscope and a scanning electron microscope integrated with energy-dispersive x-ray spectroscopy. Hardness, tensile, and v-notch impact toughness measurements were also carried out. Visual and radiographic inspection showed that both the FCAW and GTAW techniques produced sound weldments. However, DP steel weldments exhibited softening effects, which led to a decrease in joint efficiency. This decrease were related to transformation of the original martensite into tempered martensite. The results also revealed that the DP steel joints efficiencies are ranged from 85.9 to 87.7% using the FCAW process and ranged from 83.3 to 86% using the GTAW process. The impact toughness of the samples welded by FCAW is higher than the impact toughness of those welded by GTAW due to a higher percentage of acicular ferrite. This information should be valuable in the automotive and other industries, where DP steels are valued for their combination of high strength and ductility, which leads to weight savings and thus to reduced fuel consumption.

Influence of pulsed current arc welding to preclude the topological phases in the aerospace grade Alloy X

Alloy X is prone to liquation and solidification cracks in the weldments, because of the development of topologically close-packed precipitates such as σ, P, M6C, and M23C6 carbides during arc welding methods. The present work examines the possibility of alleviating the segregation of Cr and Mo content to eliminate the development of topologically close-packed phases using a conventional arc welding technique. The welding of Alloy X has been achieved with ERNiCrMo-2 filler material by gas tungsten arc welding and pulsed current gas tungsten arc welding technique. The optical microscope shows the refined microstructure in pulsed current gas tungsten arc with respect to gas tungsten arc welding. The Mo-rich segregation was identified in gas tungsten arc weldment, and the same was absent in pulsed current gas tungsten arc. These segregations of Mo-rich content encourage the development of M3C and M6C secondary precipitates in gas tungsten arc welding. Pulsed current gas tungsten arc welding shows the existence of NiCrCoMo precipitate. The present work confirmed the absence of P, σ, and M23C6 in both the weldments of Alloy X. The ultimate tensile strength, microhardness, and impact strength of pulsed current gas tungsten arc welding are increased by 3.39, 9.17, and 21.62%, respectively, with gas tungsten arc welding. The observed Mo-rich M3C and M6C secondary phases in the gas tungsten arc welding affect the tensile strength of the weldments.

The Effect of Welding Heat Input on the Structure–Property Relationship of a New Grade Super Duplex Stainless Steel

Herein, microstructural and mechanical characteristics and corrosion resistance of the UNS S32906 super duplex stainless steel (SDSS) welds are investigated. The gas tungsten arc welding technique is used with direct current electrode negative polarity. Welding is conducted in 1.19, 1.46, and 1.87 kJ mm−1 to evaluate the effect of heat input. The results show that the amount of ferrite phase decreases from 59.4% to 49.4% as the heat input increases. Moreover, only ferrite and austenite phases are observed in the microstructure without any other detrimental phases. Hardness test results show that the hardness of the weld metal rises up in comparison with that of the base metal. Furthermore, the more the heat input, the less the weldment hardness. The impact test shows that the toughness of the samples increases with heat input. Polarization tests show that base metal has a better corrosion behavior irrespective of the heat input of the weldments. With an increase in the heat input, the corrosion behavior is improved. It can be said that whether in terms of microstructure or mechanical properties or corrosion resistance, the specimens that are welded with the highest heat input show the best properties.

Studies on the effect of filler wires on micro level segregation of alloying elements in the alloy 617 weld fusion zone

Highly corrosion resistance nickel based superalloy 617 (UNS N06617) usually opts for high-temperature applications. This alloy is a constituent of alloying elements such as Cr, Co, and Mo, it also acts as solid solution strengtheners. The elements Mo and Cr segregation are prone to cracking tendency in this alloy. The current work investigates the mechanical and metallurgical behavior of the weldments produced by four different filler metals. The weldments were made by using Continuous current Gas Tungsten Arc Welding (CGTAW) technique with ERNiCrCoMo-1, ERNiCrMo-10, ERNiCrMo-4, and ERNiCrMo-14 filler metals. The existence of columnar and cellular structures in the weld zone was observed through microstructural inspection. Scanning Electron Microscope (SEM) confirmed the secondary phase existence in the subgrain boundaries region (SGBR) of all the weldments. Through Electron Dispersive Spectroscopy (EDS) examination Cr-rich phases were observed in ERNiCrCoMo-1 filler metal and Mo- rich phases in other filler metals (ERNiCrMo-10, ERNiCrMo-4, and ERNiCrMo-14). Weldment produced by ERNiCrCoMo-1 filler metal shows marginally higher tensile strength compared to the other weld joints. Ductile mode of failure was observed through SEM fractography for all the weldments. Results of bend test didn’t show any crack in the surface regions.

Improving Centerline Solidification Crack Resistivity of AA 2024 Using Tandem Side-by-Side GTAW Technique

Abstract In this study, four gas tungsten arc welding (GTAW) techniques were employed by varying the travel speed and arc motion to analyze centerline solidification crack resistivity, namely slow (3.6 mm/s), fast (8.4 mm/s), weaving (4.2 mm/s), and tandem side-by-side with alternating working electrodes (3.6 mm/s). Welding high-strength materials like aluminum alloy 2024 (AA 2024) using fusion welding processes may cause centerline solidification cracking due to the wide range of solidification temperatures. AA 2024 was used because of its high susceptibility to centerline solidification cracking; it is mainly used in aerospace industries. This alloy is considered a nonweldable material when fusion welding processes are applied. A GTAW process was used because it has better control over the welding parameters and produces high quality welds. Overall, the tandem technique resulted in thinner axial grain structure surrounded by some equiaxed grains in the weld zone. Moreover, the resistance of centerline solidification cracking was improved by using the tandem technique because of the resulting disordered grain orientation, which reduces crack energy by deflecting the crack path and preventing crack propagation through thickness. In addition, a reduction in the average grain size of 40–60 % was achieved by implementing the tandem technique because of its fast cooling rate. The tandem technique also showed better improvement in microhardness in the weld zone compared to the other three techniques.

Effect of Laser Shock Peening on Commercially Pure Titanium-1 Weldment Fabricated by Gas Tungsten Arc Welding Technique

This research work investigates the effect of laser shock peening (LSP) on commercially pure titanium grade 1 (CP Ti-1) weldment. The welding was done using gas tungsten arc welding (GTAW) with ERTi-2 filler wire. LSP was carried out on the cap surface of the weldment. The optical microstructure showed the Widmanstatten-type martensitic structure in the fusion zone (as-welded). The LSP fusion zone showed a refined microstructure compared to that of as-welded condition. Scanning electron microscope (SEM) of LSP weldment showed the indentation on the surface of the weld. This was a result of the surface ablation that occurred during LSP. X-ray diffraction analysis showed the absence of transformation of phases in the weldment. A reduction of 14.8% of crystalline size was observed in LSP weldment. A higher compressive residual stress was observed in LSP weldment than the as-welded condition. Tensile test showed the occurrence of failure in the base metal region in the case of LSP weldment, as against the failure in the case of as-welded condition in the fusion zone.

Investigations on the microstructure, mechanical properties and corrosion resistance of SUS 304 austenitic stainless steel welded joints by pulsed current gas tungsten arc welding

In the present research work, the joining of 3 mm thick sheets of SUS 304 stainless steel (SS) was addressed by pulsed current gas tungsten arc (PCGTA) welding techniques with ER308L filler wire, which came to a connection between the microstructure of the welds and the resultant mechanical and corrosion behavior. The main focus of the study involved the investigation on the effect of filler wire on welding quality of butt joints obtained. Trial experiments were carried out to find whether or not the proper filler wire was added could exert a great influence on the depth of penetration. The studies turned out that a full and sound penetration could be achieved with filler. Microstructure observations divulged the formation of different zones across the weldments, austenite/δ-ferrite at the weld zones (WZ), austenitic coarsening and growth at the heat affected zones (HAZ). Mechanical testing showed that better tensile properties and microhardness accrued in the filler weldments (FW) due to the presence of δ-ferrite and secondary phases which need further investigation, whose average tensile strength and maximum microhardness were 569 MPa and 392 HV respectively. For no filler weldments (NFW), its mechanical performances were distinctly inferior to FW. According to the electrochemical test results, base metal (BM) displayed the best corrosion resistance because it was far from such sources of pitting corrosion. Based on both passivation potential and breakdown potential, the ranking for corrosion resistance was: BM > FW > NFW. Practice proved that the results of the current study would also help in obtaining high-quality butt joints of SUS 304 SS sheets based on traditional PCGTA welding with ER308L filler wire.

Microstructure and mechanical behavior of an annealed automatic gas tungsten arc weld joint of TA16 and TC4 titanium alloys

The joining of TA16 (Ti-2Al-2.5Zr, wt%) and TC4 (Ti-6Al-4V, wt%) titanium alloys was carried out using an automatic gas tungsten arc welding technique. The microstructures of different zones in the annealed weld joints were investigated, and the mechanical properties of the annealed weld joints were assessed using microhardness, uniaxial tensile and fracture toughness tests. An asymmetrical hardness profile across the annealed weld joint was obtained in the dissimilar titanium alloys weld joint with a higher hardness value in the heat-affected zone of TC4 side. The fracture location of welded tensile specimens was always at the heat-affected zone of TA16 side. Test results showed that the fracture toughness of the heat-affected zone of TA16 side was the highest, that of TC4 base material was the lowest, and the fracture toughness of other zones were as follows: TA16 base material > fusion zone > heat-affected zone of TC4 side. Scanning electron microscope examinations were performed on the fracture surface in order to identify the relevant fracture mechanisms of different zones in the annealed weld joint.

Experimental Investigation of Dissimilar Metal Weld of SA335 P11 and SA312 TP304 Formed by Gas Tungsten Arc Welding (GTAW)

Dissimilar metal welds are widely used in process industries for applications such as pressure vessels, reactors, reheaters and heat exchangers. This helps in getting tailor-made properties in components required some heterogeneous working conditions. Joining of dissimilar metals has drawn great interest due to the challenges posed by variation in material composition and characteristics of joining metals. The present study empirically investigates the gas tungsten arc welding (GTAW) parameters to probe their effect on the mechanical and metallurgical behaviour of welded joints of SA335 P11 and SA312 TP304 alloys. Tensile test, hardness measurement and microstructure investigations were performed to check weld strength. The welded joint showed higher strengths than base metals due to carbide formation in weld zone. The strength of joint remains unchanged after heat treatment, whereas increase in hardness was observed due to grain boundary carbide precipitation. The present investigation determines that GTAW technique would be successfully used to join these particular dissimilar alloys.

Development of gas tungsten arc welding using current pulsing technique to preclude chromium carbide precipitation in aerospace-grade alloy 80A

Weldments were produced using gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) techniques with ERNiCr-3 filler wire. Macro examination revealed that the resultant weldments were free from defects. A refined microstructure was observed in the weldment fabricated through PCGTAW. Scanning electron microscopy (SEM) analysis revealed secondary phases in the grain boundaries. Energy-dispersive X-ray spectroscopy (EDS) analysis revealed that microsegregation of Cr carbide precipitates was completely eradicated through PCGTAW. The microsegregation of Nb precipitates was observed in the GTA and PCGTA weldments. X-ray diffraction (XRD) analysis revealed the existence of M23C6 Cr-rich carbide and Ni8Nb phases in the GTA weldments. By contrast, in the PCGTA weldments, the Ni8Nb phase was observed. The Cr2Ti phase was observed in both the GTA and the PCGTA weldments. Tensile tests showed that the strength and ductility of the PCGTA weldments were slightly higher than those of the GTA weldments.

Microstructural and local electrochemical characterisation of Gr. 91 steel-welded joints as function of post-weld heat treatments

Welded gr. 91 steel is widely used for structural components in the energy production field, where it suffers from selective corrosion near welded joints. In this work, Gr. 91 plates were welded using a gas tungsten arc welding technique and subjected to two different post-welding heat treatments (tempering or normalising plus tempering).Localised corrosion measurements performed with a microcell, coupled with microstructural characterisations, showed that corrosion was very active in the heat-affected zone (HAZ) in the as-welded condition and was worsened by the tempering treatment. In contrast, after a normalising treatment, the electrochemical behaviour of the welded joint was uniform.

Ageing Effects on Room-Temperature Tensile Properties and Fracture Behavior of Quenched and Tempered T92/TP316H Dissimilar Welded Joints with Ni-Based Weld Metal

The present work is focused on the investigation of isothermal ageing effects on room-temperature tensile properties and the failure of quenched and tempered martensitic/austenitic weldments between T92 and TP316H heat-resistant steels. The dissimilar weldments were produced by gas tungsten arc welding technique using a Ni-based Thermanit Nicro 82 filler metal. The welded joints were subjected to unconventional post-welding heat treatment consisting of the welds solutionizing (1060 °C/30 min), followed by their water quenching and final stabilization tempering (760 °C/60 min). The treatment was completed by spontaneous air cooling within a tempering furnace. The welds in their initial quenched and tempered condition were subsequently aged at 620 °C for up to 2500 h. Apart from room-temperature tensile tests performed for all the welds material states, additional cross-weld hardness measurements were carried out on longitudinal sections of broken tensile specimens. The applied thermal exposure resulted in recognizable deterioration of plastic properties, whereas their effects on strength properties were rather small. The welds tensile straining and fracture evolution exhibited competitive behavior between the austenitic TP316H region and Ni-based weld metal. The observed failure locations showed significant hardness peaks due to intensive, necking-related strain hardening effects occurred during the tensile tests.

Development of welding technique to suppress the microsegregation in the aerospace grade alloy 80A by conventional current pulsing technique

Alloy 80 A is prone to hot cracking during conventional arc welding process. Microsegregation of alloying element Cr lead to the formation of M23C6 carbide phase during solidification of fusion zone, and it contributes to hot cracking. The current study employs different welding techniques and filler wires to minimize the microsegregation. The weldments were fabricated by Gas Tungsten Arc Welding (GTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) techniques using filler wires 263 and ERNiCrMo-3. Scanning electron microscope (SEM) reveals the existence of secondary phase in the interdendritic region for all the weldments. Energy dispersive X-ray spectroscopy (EDS) analysis reports that PCGTAW eliminates microsegregation of Cr precipitate and suppress Nb and Mo precipitates better when compared to GTAW. X-ray Diffraction (XRD) analysis indicate the presence of M23C6 Cr and Mo-rich carbide phase in GTA weldment of 263 filler wire. Whereas in PCGTAW, NiCrCoMo phase is observed. In both GTAW and PCGTAW of ERNiCrMo-3, the intermetallic phases Ni8Nb and Cr2Ti are observed. The tensile test was conducted to assess the strength and ductility of the weldments. The results of the PCGTAW weldments have improved compared to their respective GTAW weldments.