Gas Tungsten Research Articles

Overview of in-bore pipe cutting and welding tools for the maintenance of CFETR and EU-DEMO

In the remote maintenance of fusion nuclear devices, one of the most challenging tasks is the cutting and the re-welding of large pipes that feed the breeding blanket. The narrow space around some of the pipes hinders the suitability of conventional orbital processes. For such pipes, both the cutting system and the welding one have to be compact enough to move along their interior, lock against the pipe inner wall and keep the position during the operation. The inner diameter and thickness of the pipes together with the other severe requirements related to the remote maintenance drive the choice of the processing technologies and the design of the tooling configuration. In this work, activities carried out by a joint team from EU-DEMO and CFETR on the in-bore cutting and welding operations are presented and discussed. For the in-bore cutting system a solution for the simultaneous parting and bevelling has been developed opting for a mechanical cutting with a pair of symmetrically distributed knives. A preliminary dimensioning of the motors has been made assuming the radial feed and the cutting speed of the knives. For the in-bore welding system, the TIG welding with filler wire has been considered as the most reliable and suitable technology within prescribed requirements and constraints. A multi-pass welding operation has been assumed. A conceptual design of both tools has been developed. The space constraint remains the most critical issue. Further verification and validation work is planned in close collaboration between European laboratories and the Comprehensive Research fAcility for Fusion Technology (CRAFT) at ASIPP in Hefei.

ANALYSIS OF THE MICROSTRUCTURE AND MECHANICALPROPERTIES OF DUPLEX STEEL JOINTS

The article presents a study, the aim of which was to analyze the microstructure and mechanical propertiesof welded joints of austenitic-ferritic duplex steel X2CrMnNiN21-5-1. This steel is characterized by goodresistance to various types of corrosion, good strength properties and good weldability. Due to all theseadvantages, it is used in many industry sectors, and the main joining techniques are welding technologies. Inthis study, two joining techniques were used, SMAW (Shielded Metal Arc Welding) and GTA (Gas TungstenArc). The obtained welded joints were subjected to: macroscopic and microscopic metallographic tests,mechanical tests (static bending test and microhardness measurements), diffraction tests, and wear resistancetests. The results showed that the microhardness of the welds is similar and does not depend on the weldingmethod used. In the microstructure of the analyzed joints there are two phases: austenite (γ) and ferrite (δ),with different morphologies depending on the welding conditions, which affect the phase transformations.Material wear within the weld is greater than in the base material.

Mechanical and micro-structural studies of pulsed and constant current TIG weldments of super duplex stainless steels and Austenitic stainless steels

Abstract In the present research work, the influence of heat input rates on microstructures, hot tensile properties, and weld surface hardness number of Super Duplex Stainless Steel 2507 super duplex steels and austenitic steels 316L plates were investigated. Pulsed current and constant current modes were used in Tungsten Inert Gas (TIG) welding to join the dissimilar metals using ER2205 as filler. Microstructural studies were revealed at different zones of pulsed and constant current TIG weldments using optical microscopy. The tensile test was conducted at two different temperature conditions (i.e., 27 and 350°C) to investigate the strength of dissimilar weldments. Hardness measurements were made on the weld surface along the transverse direction using Vicker’s hardness tester. The microstructures revealed the formation of inter-granular austenite at the fusion zone with grain boundaries with austenite structures. Due to the constant heat input, a significant microstructural development with high austenite fractions was observed in constant current (CC)-TIG weldment. In comparison to CC-TIG weldments (UTS at 27°C = 600 MPa UTS at 350°C = 456 MPa), higher tensile characteristics were noted in Pulsed Current (PC)-TIG weldments (UTS at 27°C = 695 MPa UTS at 350°C = 475 MPa). The UTS of PC-TIG weldment is improved by 15.8% when compared to CC-TIG weldment due to the controlled heat input rates. PC-TIG weldments exhibited improved hardness numbers in various zones with smaller HAZ widths than CC-TIG weldments.

Assessing the pros and cons of wire-arc additive manufacturing for material production

A promising new method for mass-producing metal components and structures for a range of industries, including shipbuilding, automotive, aviation, and other technical sectors, is wire arc additive manufacturing (WAAM). Additive manufacturing (AM) called 3D printing, it is a disruptive manufacturing technique that starts with digital design data and manufactures products layer by layer. WAAM has been utilized to create parts from a variety of materials, such as alloy wires based on aluminium (Al), titanium (Ti) and nickel. This review article focuses on the most important facets of the WAAM process, including the technology utilized, the drawbacks encountered, the steps taken during and after the process, the tools used to monitor the process, the gases involved, and the materials. The comparison of WAAM with other additive manufacturing technologies is also emphasized in the article. Moreover, it compares and analyses several WAAM techniques, including plasma arc welding (PAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) in terms of material deposition rate, the method GMAW have higher material deposition rate when compared to other approach. Material manufacturing using WAAM has great potential. The accuracy of the manufacturing and smoothness of WAAM-made parts can be enhanced in the future to better suit tight-tolerance uses.

Effects of Weld Heat Input on Mechanical Characteristics of Low Carbon Sheet Steels

This study focuses on examining the variation in mechanical characteristics of low-carbon sheet steels when they are subjected to heat input from Tungsten Inert Gas (TIG) welding. The weld heat input parameters, such as welding speed and current, were controlled through the TIG welding process. A finite element analysis was performed to evaluate the couple field thermomechanical effects of the weld heat line, using the Gauss heat flux approach for thermal heat variation across the weld heat-affected zone. The numerical study yielded results for weld heat-affected deflection, residual stress, and modal analysis through the finite element model. It was found that the ductility decreased and hardness increased in the fusion zone, as a function of weld current and speed. The residual stresses and their zone of influence, as determined by weld line parameters, were found to be key factors affecting deflection and natural frequencies in structural aspects of low carbon sheet steels.

Effect of welding current and speed on solidification cracking susceptibility in gas tungsten arc fillet welding of dissimilar aluminum alloys: Coupling a weld simulation and a cracking criterion

In order to study the effect of welding current and speed on the solidification cracking susceptibility of weld, gas tungsten arc welding of a fillet weld with a cold filler wire was simulated. Simulation was conducted for dissimilar welding of Al–Cu–Mg to Al–Mg–Si aluminum alloys with an Al–Mg filler metal at the welding current range of 145–175 A and welding speed of 18–24 cm/min. The outcomes of simulations, namely temperature gradient, velocity of isotherms, and weld chemical composition obtained for various welding currents and speeds, were used as inputs for a solidification cracking model. The results showed that the dimensions of the weld profile obtained from the simulation exhibited good agreement with experimental results. However, a discrepancy of 10–23% was observed between experimental and simulated results in relation to one dimension of the weld profile, i.e. the distance between the fillet weld corners. This discrepancy was addressed to identify the underlying reasons. According to the model proposed in this study for solidification cracking of aluminum alloys, both higher welding current and higher welding speed led to a higher susceptibility to solidification cracking. This result was justified by considering factors such as secondary arm spacing of dendrites, isotherm velocity, backfill time, and chemical composition and viscosity of the weld pool. Weldability tests were employed to validate the model's performance for predicting the solidification cracking susceptibility. Thus, the optimal welding parameters can be chosen in accordance with these results and production demands.

In Situ Analysis of Stress and Microstructure Evolution during Welding of High-Alloy Steels Using Energy-Dispersive X-Ray Diffraction

Constrained thermal expansion and contraction during welding cause a compression-tension cycle and plastic deformation in the heat-affected zone, leading to work hardening. The nature of this hardening effect—isotropic or kinematic—determines the final local yield stress and thus affects the residual stress state. Therefore, mechanical hardening must be modeled correctly in welding simulations for accurately predicting welding residual stresses. Previous studies, relying on comparisons with experimental ex situ results, led to different recommendations regarding the choice of the hardening model and thus require clarification. In this work, the stress evolution in the heat-affected zone of a tungsten inert gas weld is studied in situ using energy-dispersive x-ray diffraction and a novel method of stress analysis based on crystallite anisotropy. Additionally, microstructural information is gathered through line profile analysis. Results are shown for both austenitic and ferritic high-alloy steels and compared to ex-situ results including a validation of the new method of stress analysis. Finally, conclusions on the nature of work hardening are drawn.

Investigating the effect of different flux combinations, welding current and speed for optimizing D/W ratio in a novel Flux zone TIG welding of SS304

Investigating the effect of different flux combinations, welding current and speed for optimizing D/W ratio in a novel Flux zone TIG welding of SS304

Analysis of Welding Characteristics of Two Dissimilar Metal (FSS 409 and ASS 304) Using TIG Welding

Analysis of Welding Characteristics of Two Dissimilar Metal (FSS 409 and ASS 304) Using TIG Welding

Study on the effect of current pulsing during gas tungsten arc welding of Ti – 6Al – 4V alloy

Study on the effect of current pulsing during gas tungsten arc welding of Ti – 6Al – 4V alloy

Investigation of effect of post weld heat treatment on microhardness and microstructure of auto TIG welded stabilized SA213 TP347H weldments

Investigation explores the weldability of Niobium stabilized TP347H austenitic stainless steel tubes through the application of optimized welding parameters using Auto TIG welding. This research investigates the influence of post weld heat treatment conditions on microhardness, microstructures, sensitization due to Cr23C6 precipitation, presence of Niobium carbides and formation of twin boundaries in the weldment. Extended post weld heat treatment duration resulted in notable decline in microhardness from 280 to 180 VHN within initial 5-h of soaking. Nevertheless, further prolongation of soaking time (10–15 h) exhibited subsequent rise in microhardness levels to 200 VHN in base, weld and heat affected zone. Increase in hardness is attributed to the emergence of annealing twins in base metal and the precipitation of Niobium carbides within weld and heat affected zone, confirmed by advanced analytical scanning electron microscope. Energy dispersive spectrum line mapping reveals presence of Cr23C6 precipitation following 1-h soak at 720 °C. Subsequent prolongation of soaking time (5-h) demonstrates desensitization in the base metal. Additionally, cooling rate of 300 °C/hr during post weld heat treatment reduces required time for microstructure homogenization, resulting in increased hardness compared to 100 °C/hr rate in the weldment. However, beyond a 5-h soaking time, the cooling rate has a negligible impact on microhardness. Ultimate Tensile Stress of 674.82 and 665.28 N/mm2 for TP347H was achieved against the minimum requirement of 515 N/mm2 as per American Society of Mechanical Engineers Section IX standard.

Comparative Analysis of Microstructure Evolution and Mechanical Properties of Dissimilar Welded Joints of AA7075/AA6061 via Friction Stir Welding, Tungsten Inert Gas Welding, and Tungsten Inert Gas + Friction Stir Processing

Comparative Analysis of Microstructure Evolution and Mechanical Properties of Dissimilar Welded Joints of AA7075/AA6061 via Friction Stir Welding, Tungsten Inert Gas Welding, and Tungsten Inert Gas + Friction Stir Processing

Corrosion Resistance and Mechanical Properties of Cr-Rich 316 Stainless Steel Coatings Fabricated by the TIG Process Using Flux-Cored Wires.

Arc welded 316 stainless steel coatings with flux-cored wires are very promising for marine service environments due to their low cost, high efficiency, and satisfactory performance, while they suffers from Cr dilution during the preparation process. Herein, based on the consideration of increasing the Cr content and ensuring the same value of the Cr/Ni equivalence ratio (Creq/Nieq), 316-modified flux-cored wires, 316F (19Cr-12Ni-3Mo) and 316G (22Cr-14Ni-3Mo), were designed under the guidance of a Schaeffler diagram for the improvement of the electrochemical and mechanical properties of 316 stainless steel coatings. The designed flux-cored wires were welded into a three-layer cladding by the tungsten inert gas welding (TIG) process, and the microstructure, corrosion resistance, and mechanical properties of the claddings were investigated. The results showed that 316F and 316G consist of γ-Fe (austenite) and a small portion of δ-Fe (ferrite) as the Creq/Nieq is approximately 1.5. However, due to the higher value of the equivalent Cr content (ECC), 316G has an additional intermetallic phase (σ), which precipitates as a strengthening phase at grain boundaries, significantly increasing the tensile and yield strength of 316G but reducing its plasticity. In addition, the corrosion current density (icorr) and pitting potential (Eb) for 316G are 0.20447 μA·cm-2 and 0.634 V, respectively, while the values for 316F are 0.32117 μA·cm-2 and 0.603 V, respectively, indicating that 316G has better anti-corrosion performance.

Fabrication of tungsten inert gas-welded dissimilar aluminium joints using different friction stir processing tools through response surface method

ABSTRACT AA6061-T6 and AA7075-T6 materials find wide application in manufacturing industries due to their excellent engineering properties. Fusion welding generates solidification cracks, high residual stresses, and brittle intermetallic compounds that degrade joint qualities. To solve these difficulties, friction stir processing (FSP) is frequently employed, which improves joint properties through local microstructural refinement. In this study, the combined effect of FSP parameters, namely tool pin profile (TPF), tool rotation speed (TRS), and travel speed (TS), on tungsten inert gas (TIG) weld properties was investigated. Response surface methodology (RSM)-based mathematical models were developed to predict responses, namely ultimate tensile strength (UTS), impact toughness (IT), microhardness (MH), and residual stress (RS). The optimal FSP parameters were determined through the desirability function technique. Post-FSP increased the UTS, IT, and MH of TIG welds by 71.51%, 95.40%, and 72.46%, respectively, and decreased the RS by 58.46%. ANOVA findings exhibited that TPF was the most influential parameter, followed by TRS and TS. The dissimilar aluminium TIG+FSP joints showed an optimal UTS of 282.08 MPa, an IT of 17.32 J, a MH of 121.48 HV, and an RS of 22.09 MPa when using a TRS of 1108.49 rpm and a TS of 37.74 mm/min with a THF pin.

Structural integrity and corrosion behavior assessment of the dissimilar gas tungsten arc welded joint of sDSS 2507/ IN625 superalloy

This study investigates the effect of filler materials on the structural integrity of dissimilar welded joints (sDSS 2507/IN625) employed in marine subsea manifold applications. Multi-pass gas tungsten arc welding (GTAW) using ER2594 and ERNiCrMo-3 fillers investigates microstructure evolution, solidification mechanisms, mechanical characteristics, residual stresses, and corrosion behavior. Optical and scanning electron microscopy revealed an unmixed zone (peninsula/island-shaped) at the weld interface and weld zone (WZ) in both filler weldments. Segregation of Mo, Nb, and Ni was observed in the interdendritic region of ERNiCrMo-3 filler WZ, whereas the skeletal ferrite matrix of ER2594 filler WZ revealed the existence of the Laves phase (Fe2Nb form). Electron beam scattered diffraction (EBSD) investigation showed austenitic solidification for ERNiCrMo-3 and fully ferritic solidification for ER2594 with distinct dendrite formations. Inhomogeneity has been observed in microhardness maps, with ER2594 and ERNiCrMo-3 WZ averaging 310 ± 7 Hv0.5 and 270 ± 10 Hv0.5, respectively. ERNiCrMo-3 (165 ± 5 J and 180 ± 3 J) and ER2594 (100 ± 3 J and 110 ± 6 J) fillers exhibited distinct effects on toughness in the weld cap and root due to laves phase precipitation. Additionally, ER2594 (750 ± 6 MPa) and ERNiCrMo-3 (790 ± 7 MPa) fillers exhibited lower tensile strength than base metals. The structural integrity of WZ can be better understood by residual stress analysis, which showed compressive cap pass and tensile root pass residual stresses for both fillers. In a 3.5 wt% NaCl solution, both fillers exhibited outstanding corrosion resistance in marine conditions. These findings improve subsea manifold structure integrity and performance in corrosive marine environments.

Unveiling the microstructure evolution and mechanical properties in a gas tungsten arc-welded Fe–Mn–Si–Cr–Ni shape memory alloy

Fe–Mn–Si–Cr–Ni shape memory alloys (SMAs) are unique low-cost materials with shape memory properties that grant them the ability to be used in both functional and structural applications. Such SMAs are especially sought in the construction sector for the creation of new components and/or the reinforcement of damaged ones. In this study, a Fe–17Mn–5Si–10Cr–4Ni–1(V, C) wt% SMA was gas tungsten arc welded, with the objective to investigate the microstructure and mechanical performance changes occurring after welding. A comprehensive assessment of processing, microstructure and properties relationships was established combining microscopy (optical and electron), synchrotron X-ray diffraction, microhardness mapping and tensile testing including cycling assessment of the joint’s functional performance. It is shown that the present SMA has good weldability, with the joints reaching nearly 883 MPa at fracture strain of 23.6 ± 2.1%. Alongside this, several microstructure differences were encountered between the as-received and as-welded condition, including the formation of ferrite and Fe5Ni3Si2 P213 cubic precipitates amidst the fusion zone in the latter region.Graphical abstract

An Investigation about Microstructures, Mechanical Properties and Corrosion Behaviour of the TIG - MIG Hybrid Welded Dissimilar UNS 2205 and is 2062 Steels

The connecting of contrasting metals, namely double stainless steel to steel made of carbon, has taken place. performed using a hybrid welding system. A TIG and MIG welding joining based hybrid joining method was designed. The microstructures of the dissimilar metal joints were studied and the grains are coarser as contrast to the use of a single the welding process process by itself. With the addition of TIG welding to the process of MIG welding, the water-holding capacity of the metal in molten state pool is significantly improved. The nominal corrosion behaviour of the weldments was found better than the single arc welding system alone. The passivation behaviour of the joints was in the similar line to that of double stainless steel base metal. The pitting resistance of the joints in 1 M NaCl solution was inferior to the base metals.

Evaluation of microstructure, corrosion resistance performance, and mechanical properties of 316L austenitic stainless steel FCAW welded joints: a comparative study

ABSTRACT This research aims to not only examine the effect of different mixtures of Ar and CO2 on microstructural features and corrosion behavior of double-pass FCAW of 316L SS but also compare these characteristics with gas tungsten arc welding (GTAW) and self-shielded FCAW. Different shielding gas mixtures, namely 100%Ar, 100%CO2, 82%Ar+18%CO2 were used to make the specimens. All specimens represent biphasic microstructures containing austenite (Ɣ) and delta-ferrite (δ-ferrite). Based on the potentiodynamic (PD) test results, the anti-corrosion protection performance of the welded region was enhanced when using GTAW compared to self-shielded FCAW. Additionally, the impedance value of the GTAW joint was higher than that of the FCAW-welded specimens. The ductility of welded joints was ranked as GTAW > CO2 +Ar shielded FCAW > self-shielded FCAW > CO2 shielded FCAW. The ranking of transverse tensile strength was as follows: CO2 shielded FCAW> self-shielded FCAW > CO2+ Ar shielded FCAW> GTAW.

Effects of gas tungsten arc welding on the mechanical properties and microstructure of 316L stainless steel by powder bed fusion

Effects of gas tungsten arc welding on the mechanical properties and microstructure of 316L stainless steel by powder bed fusion

Microstructure and mechanical properties of ultra-light Mg[sbnd]8Li[sbnd]3Al[sbnd]2Zn[sbnd]0.5Y alloy manufactured by directed energy deposition-Arc

The ultra-light Mg8Li3Al2Zn0.5Y (LAZ832–0.5Y) thin wall parts with excellent performances were successfully fabricated by Gas Tungsten Arc Welding (GTAW) in this study. The microstructure of the top, middle and bottom regions of the thin wall fabricated under various conditions was examined and the mechanical properties of these thin walls were tested. The results showed that much finer microstructure was obtained by GTAW than that made by conventional casting method. In the as-deposited samples, the needle-like shaped α-Mg phase emerged at the top of the thin wall whereas the bar-shaped α-Mg phase showed up in the middle and bottom regions of the thin wall due to the complex thermal history. The Al2Y phase was dispersed throughout both α-Mg and β-Li while the AlLi phase was mainly located in the β-Li. The best combination of ultimate tensile strength (UTS), yield strength (YS) and elongation to fracture of the as-deposited thin wall were 218.9 MPa, 171.4 MPa and 20.9%, respectively, which was manufactured under the optimal condition of 120 A 1800 mm/min 220 mm/min. After solid solution treatment at 350 °C for 4 h, the UTS increased slightly by 13% but the YS increased significantly by 65% compared with the samples before solid solution. The solution of the AlLi phase was believed to be the main strengthening mechanism. It is interesting to note that the UTS and YS of the as-deposited sample was better than those of the as-cast sample while the opposite situation took place after solid solution treatment.