Activated Tungsten Inert Gas Research Articles

Optimization of Activated Tungsten Inert Gas Welding Process Parameters Using Heat Transfer Search Algorithm: With Experimental Validation Using Case Studies

The Activated Tungsten Inert Gas welding (A-TIG) technique is characterized by its capability to impart enhanced penetration in single pass welding. Weld bead shape achieved by A-TIG welding has a major part in deciding the final quality of the weld. Various machining variables influence the weld bead shape and hence an optimum combination of machining variables is of utmost importance. The current study has reported the optimization of machining variables of A-TIG welding technique by integrating Response Surface Methodology (RSM) with an innovative Heat Transfer Search (HTS) optimization algorithm, particularly for attaining full penetration in 6 mm thick carbon steels. Welding current, length of the arc and torch travel speed were selected as input process parameters, whereas penetration depth, depth-to-width ratio, heat input and width of the heat-affected zone were considered as output variables for the investigations. Using the experimental data, statistical models were generated for the response characteristics. Four different case studies, simulating the real-time fabrication problem, were considered and the optimization was carried out using HTS. Validation tests were also carried out for these case studies and 3D surface plots were generated to confirm the effectiveness of the HTS algorithm. It was found that the HTS algorithm effectively optimized the process parameters and negligible errors were observed when predicted and experimental values compared. HTS algorithm is a parameter-less optimization technique and hence it is easy to implement with higher effectiveness.

Comparisons of Different Oxide Fluxes in Activated Gas Tungsten Arc Welding of Duplex Stainless Steels for Improved Depth of Penetration and Pitting Corrosion Resistance

ABSTRACT The present work analyses the effect of five types of oxide fluxes – SiO2, TiO2, CrO3, MnO2 and MoO3 – on the depth of penetration and pitting corrosion behaviour of UNS S32205 duplex stainless steel produced with the activated tungsten inert gas welding (A-TIG) process. Five bead-on-plate (BoP) weld samples prepared autogenously with constant weld parameters. Depth of penetration (DP), depth-to-width (D/W) ratio and weld bead width (BW) were measured and compared with reference to the weld thermal cycle. The test results of ferrite measurement and micro-hardness were compared with normal – without flux added TIG-welded sample. Macro analysis of all samples indicates that SiO2 and TiO2 flux offer enhanced penetration depth and D/W ratio, in contrast, to use of other fluxes. Possibly, under the effect of either reversed Marangoni or arc constriction or both, however, all TIG BoP weld samples exhibited poor pitting corrosion resistance. Enhanced heat input due to flux and thus resultant unbalanced ferrite austenite proportion affected pitting corrosion resistance. ASTM A 923 microstructures did not show any presence of nitride formation. Results of energy-dispersive X-ray spectroscopy and scanning electron microscopy analysis of corrosion pits showed no abnormality with the chemistry of standard 2205 DSS.

Microstructure and mechanical properties of 9Cr-0.5Mo-1.8W–VNb (P92) steel weld joints processed by fusion welding

Abstract Grade P92 steel is used for making steam generator components of thermal and nuclear power plants at temperatures up to 923 K. Microstructures, mechanical properties and the service life of the welded components are influenced by the welding process employed. In the present investigation, the effect of Tungsten Inert Gas (TIG) and Activated TIG (A-TIG) welding processes on the microstructure and mechanical properties of P92 steel weld joints are studied. Optical microscope, SEM and TEM were used for characterizing the microstructures. Application of the activated flux on the joint area during A-TIG welding significantly increases the depth of penetration. Due to high current density peak temperature is higher in the weld pool and steep temperature gradient is observed across the joint interface. Therefore, the microstructure is relatively coarse in the A-TIG weld metal. TEM investigations have confirmed that the precipitates present at the grain and lath boundaries are carbides of the form M23C6 and the precipitates seen within the matrix of the lath are niobium and vanadium rich carbides and nitrides of type MX. The tensile strength of the A-TIG weld joint both at room temperature and at 923 K is higher than that of the TIG weld joint. In comparison to the base metal and TIG weld joint, a decrease in the Charpy impact toughness is observed in the A-TIG weld joint due to the formation of δ-ferrite along the fusion interface. However, in contrast to the TIG weld metal, tensile residual stresses at the A-TIG weld are very low.

Productivity improvement in butt joining of thick stainless steel plates through the usage of activated TIG welding

Activated tungsten inert gas (A-TIG) welding is one variant of conventional TIG welding where a thin layer of suitable activating flux is deposited on the parent components prior to constituting the arc in order to harness enhanced penetration. Despite several benefits, industries are still reluctant in overwhelmingly using this new variant. This article attempts to highlight the productivity benefits in employing A-TIG welding either together with or superseding TIG welding during butt joining of 10-mm-thick AISI-316L austenitic stainless steel components. Initially, three single-component fluxes (Cr2O3, Fe2O3, and SiO2) are tested in forehand welding technique under varying currents but with straight polarity. Filler rod having similar metallurgical composition is also delivered during homogeneous welding. The extent of capability of each of the three fluxes is analysed by comparing the weld bead geometrical parameters (penetration, puddle width, and reinforcement) with the same obtained in conventional TIG welding under similar set of parameters. While Fe2O3 and SiO2 fluxes are found capable in enhancing penetration and reducing puddle width and heat affected zone, Cr2O3 flux failed to exhibit better performance. The article further demonstrates the time saving that can be obtained by adopting flux-assisted TIG for joining 10-mm-thick plates. When joining from both the faces is allowed, about 70% less time is desired if a combination of A-TIG and TIG is employed rather than using only TIG welding. If joining from only one face is allowed, then also usage of flux can reduce welding time by 33%.

Optimization of Welding Process Parameters for Activated Tungsten Inert Welding of Inconel 625 Using the Technique for Order Preference by Similarity to Ideal Solution Methodology

This investigation aims to recognize the advanced input parameters for Inconel 625 by activated tungsten inert gas (A-TIG) welding. Bead on trial experiments was conducted with desirable input parameters such as welding current, torch travel speed, and arc gap according to the Taguchi L25 orthogonal array. The aspect ratio of weld geometry and Brinell hardness (HB) were considered the output parameters. Technique for order preference by similarity to ideal solution (TOPSIS) is a multi-criteria decision-making approach to select an optimum combination of input responses. A step-by-step approach to the application of TOPSIS was followed in this study. Exploratory preliminaries revealed that welding current (300 Amps), torch travel speed (75 mm/min), and arc gap (1 mm) initiated optimum input parameters with optimum conditions of hardness (262 HB) and an aspect ratio of 0.421. Optimized weld zone microstructure and scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) analysis were undertaken for a complete report on the migration of Nb atoms towards the weld zone. From the attained outcomes, it was inferred that a faster cooling rate in A-TIG welding leads to the suppression of the laves phase which could be due to an activated flux combination.

Effect of hydrogen additions to shielding gas on activated TIG austenitic stainless steel weld

In tungsten inert gas (TIG) welding, less penetration depth is achieved in a single pass which adversely affects productivity, Activated TIG (A-TIG) welding techniques achieve better performances and higher penetration depths compared to conventional TIG welding. Pure argon does not have the potential to provide adequate penetration in austenitic stainless steel. Argon–hydrogen shielding gas mixture provides high heat flux, thereby influencing the arc voltage and penetration. In the present study, hydrogen is added to base shielding gas argon to study the effect on weld geometry during TIG and A-TIG of 310S stainless steel. The result shows a higher weld depth to width ratio and a significant reduction in the angular distortion. Also, higher tensile strength is obtained in A-TIG weld metal with 1% hydrogen addition, due to more efficient cooling of the weldment. However, increasing the hydrogen concentration in shielding gas resulted in defect formations in the weldment due to the interaction between activated flux and the hydrogen.

Implementation of TOPSIS optimisation technique in comparative analysis of conventional TIG and activated TIG welding of stainless steel 304L

The activated tungsten inert gas (TIG) welding mainly focuses on increasing depth of penetration, reducing width of weld, increase speed of welding and improve weld quality. The objective of this experimental work is to find optimal set of process parameters that achieve higher tensile strength, hardness and depth of penetration. The process parameters selected for experimental work were welding current, gas flow rate and root gap. The design of experiment was carried out using central composite design of response surface methodology. Silicon dioxide activated flux powder was used along with acetone for activated TIG welding process. For experimentation, austenitic stainless steel grade of 304L was used as parent material also the filler material was having same composition. The ANOVA was carried out determine significance of different process parameters on response factors. Further comparative analysis was presented with help of graphs. The TOPSIS optimisation approach was used to optimise the factors.

Optimization of Oxide-Based Activating Flux Combination Formula in Activated Tungsten Inert Gas Welding using a Hybrid Method Including Artificial Neural Networks and Particle Swarm Optimization

Optimization of Oxide-Based Activating Flux Combination Formula in Activated Tungsten Inert Gas Welding using a Hybrid Method Including Artificial Neural Networks and Particle Swarm Optimization

A systematic review about welding of super austenitic stainless steel

Super austenitic stainless steel is a superior grade of stainless steel with numerous meritorious properties including resistance to corrosion, pitting, crevice, and acid attack. These advantages are attributed to the presence of various alloying elements at higher concentrations. Due to the same, this special alloy is employed for a wide range of applications that too in challenging environments including nuclear power plants, aerospace, and chemical processing industries. To uphold the properties of super austenitic stainless steel, employing proper welding techniques is equally important. This investigation reviews various welding techniques including gas metal arc welding, shielded metal arc welding, friction welding, laser welding, tungsten inert gas welding, activated tungsten inert gas welding, and hybrid laser welding used for joining different grades of super austenitic stainless steel.

Augmentation of weld penetration by flux assisted TIG welding and its distinct variants for oxygen free copper

A comparative study to investigate the influences of single component fluxes on the depth-to-width ratio (DWR) of oxygen free copper was carried out with novel variants of tungsten inert gas (TIG) welding namely Activated TIG (A-TIG), Flux Bounded TIG (FB-TIG) and Flux Zoned TIG (FB-TIG) processes. The experiments to identify the fluxes delivering the higher DWRs in A-TIG welding among thirteen distinct fluxes were followed by the trials with FB-TIG and FZ-TIG employing those identified DWR fluxes. The fluxes which outperformed with all the techniques were MoO3 & MgO. Reversed Marangoni and arc constriction mechanisms were perceived to be opt for such an increase in DWR. Metallurgical characterization of the weldment indicated distinct grain morphologies and certain defects as well in the weld zones. The FZ-TIG welding is postulated to surpass all the techniques in terms of bringing about the upmost weld penetration.

Optimization of A-TIG Welding Process Using Simulated Annealing Algorithm

Flux-assisted tungsten inert gas welding process, also known as activated tungsten inert gas (A-TIG) welding, is extensively used in order to improve the performance of the conventional TIG welding process. In this study, the orthogonal array Taguchi (OA-Taguchi) method, regression modeling, analysis of variance (ANOVA) and simulated annealing (SA) algorithm have been used to model and optimize the process responses in A-TIG welding process. Welding current (I), welding speed (S) and welding gap (G) have been considered as process input variables for fabricating AISI316L austenitic stainless steel specimens. Depth of penetration (DOP) and weld bead width (WBW) have been taken into account as the process responses. In this study, SiO2, nano-particle has been considered as an activating flux. To gather required data for modeling, statistical analysis and optimization purposes, OA-Taguchi based on the design of experiments (DOE) has been employed. Then the process responses have been measured and their corresponding signal-to-noise (S/N) ratio values have been calculated. Different regression equations have been applied to model the responses. Based on the ANOVA results, the most fitted models have been selected as an authentic representative of the process responses. Furthermore, the welding current has been determined as the most important variable affecting DOP and WBW with 68% and 88% contributions, respectively. Next, the SA algorithm has been used to optimize the developed models in such a way that WBW is minimized and DOP is maximized. Finally, experimental performance evaluation tests have been carried out, based on which it can be concluded that the proposed procedure is quite efficient (with less than 4% error) in modeling and optimization of the A-TIG welding process.

Electrochemical studies and corrosion resistance of activated Tungsten inert gas AISI SS316L weldments

Welding is the most convenient fabrication process with tremendous development in past few decades. The noteworthy technique is Activated flux TIG welding method (also known as A-TIG welding) that was well-equipped a little while back, which enhances productivity and quality of weld joints by better depth of penetration. In this research work, the electrochemical studies are performed to investigate the corrosion resistance of excellent depth of penetration A-TIG welded 316L stainless steel (SS316L) sample at room temperature. At dilute aqueous ambience, Potentiodynamic studies reveal that the SS316L welding joints have an apathetic attitude with certain range. Electrochemical Impedance calculations illustrate the breakdown occurs due to corrosion in alkaline circumstances.

Numerical simulation of the influence of oxygen content on the weld pool depth during activated TIG welding

The required amount of surface-active element dissolved in the weld pool remarkably influences the depth of penetration during activated tungsten inert gas (A-TIG) welding process. This is mainly attributed to the changes in the surface tension coefficient sign by oxygen content, which in turn controls the reversal of fluid flow and the nature of heat transfer. It emphasizes that there is a strong correlation between the surface-active element oxygen content and the development of the weld pool. This research intends to find out the critical oxygen content required in the weld pool to cause complete reversal of Marangoni flow and its influence on the weld bead dimensions by numerical simulation during A-TIG welding. Three-dimensional evolution of thermal and velocity fields in the weld pool is simulated using ANSYS Fluent for 200 A and 300 A welding currents respectively by altering the dissolved oxygen levels in a 0.01 m thick 316 LN stainless steel (SS) plate. The simulated weld bead profile for varying dissolved oxygen levels is validated for 300 A current by carrying out A-TIG welding experiments in a 0.01-m–thick plate with different fluxes in order to achieve the diverse amounts of oxygen content in the weld pool. The simulated and experimentally obtained weld bead dimensions exhibited good agreement for various dissolved oxygen contents in the weld. The complete reversal of fluid flow has been found to occur in the weld pool when the dissolved oxygen in the weld pool is 335 ppm at 300 A and 200 ppm at 200 A current.

Computation of residual stresses, distortion, and thermogravimetric analysis of Inconel 625 weld joints

In the current investigation, Inconel 625 weld joints were fabricated by Activated tungsten inert gas (A-TIG) and Tungsten inert gas (TIG) welding techniques. The joint configurations employed square butt and V groove edge preparations. Residual stresses measurement was carried out by X-ray diffraction using the Proto iXRD measurement system. Distortion in weld joints was estimated by measuring the vertical displacement on the grids marked on the weld joints before and after welding by using an electronic height gauge. Weldment revealed distinctive microstructure, peak tensile residual stress, and angular distortion. A-TIG weld joint exhibited lower residual stresses and distortion compared to the TIG weld joint. Thermogravimetric analysis (TGA) has inferred that the fusion zone of A-TIG and TIG weldments revealed better hot corrosion resistance at high temperatures.

Effect of Polarity and Oxide Fluxes on Weld-bead Geometry in Activated Tungsten Inert Gas (A-TIG) Welding

Effect of Polarity and Oxide Fluxes on Weld-bead Geometry in Activated Tungsten Inert Gas (A-TIG) Welding

Study on Joint Structure and Fatigue Properties of Magnesium Alloy Active TIG Welding and TIG Welding

Magnesium alloys have many advantages, such as light weight, anti-seismic, anti-electromagnetic interference, high damping, high negative electricity and easy recycling. They are widely used in automobiles, motorcycles, and aerospace and are known as green engineering materials in the 21st century. Because of the special physical and chemical properties of magnesium alloys, the weldability of magnesium alloys is poor, which seriously hinders the use of magnesium alloy structural parts. Therefore, this paper analyses the welding problems of magnesium alloys, and discusses the fatigue properties of magnesium alloys.

Microstructure and mechanical properties of A-TIG welded AISI 316L SS-Alloy 800 dissimilar metal joint

The present work discusses the microstructure and mechanical properties of dissimilar metal weld joint between AISI 316L SS-Alloy 800 developed by activated TIG (A-TIG) welding. The evolution of fusion zone microstructure and solidification temperature range were investigated through equilibrium calculation and Scheil-Gulliver equation. Electron probe micro-analysis revealed the micro-segregation of Ti and Si in the inter-dendritic arms of the fusion zone. The presence of secondary phases (Ti(C,N) and FeSi2) in the fusion zone was confirmed with X-ray diffraction technique and transmission electron microscopy of electrochemically extracted precipitates. The A-TIG weld joint showed a decent combination of tensile strength and impact toughness. Tensile testing with digital image correlation revealed a transfer of strain localization from Alloy 800 side heat affected zone to the fusion zone due to lower hardening capacity of the fusion zone. During tensile loading, the formation of micro-cracks along the solidification grain boundaries reduces the peak tensile strength of the fusion zone.

Process enhancement using hydrogen-induced shielding: H2-induced A-TIG welding process

ABSTRACT Deeper penetration in a gas tungsten arc welding process is the essential requirement for the fabrication of duplex stainless steel pipes. Activated fluxes and associated activated tungsten inert gas’ (A-TIG) welding process has proved itself as the better option for improved dilution and the deeper penetration. Use of hydrogen in shielding environment of A-TIG process for different ranges of activated fluxes needs to assess for deeper penetration and associated weld properties. Present investigation addresses the issue of deeper penetration using different activated fluxes in A-TIG process along with mixing of 2.5% H2 in the argon gas shielding. An effect of H2-induced shielding during CrO3, MoS2, TiO2, and SiO2 fluxes in A-TIG process has been investigated with weld pool morphology, depth of penetration, weld chemistry, scanning electron microscopy, optical microscopy, energy dispersive spectroscopy, and X-ray diffraction analysis. The extra heat produced due to activated fluxes in H2-induced shielding have been quantify in the study. The decomposed oxygen in the weld pool reacts with hydrogen in shielding and enhances the arc density. The growths of ferrite and austenite grains as well as the dendrite arm spacing have been significantly affected due to the presence of H2 in the shielding. Oxide-based fluxes with H2-induced shielding could promote the arc constriction behavior and Peclet number with enhanced heat density.

Investigations on mechanical properties and microstructural examination of activated TIG-welded nuclear grade stainless steel

Nuclear grade austenitic stainless steel 321 contains titanium for severe corrosive conditions and is used for process equipment, aircraft exhaust manifolds and boiler shells. Taguchi-based grey relational analysis technique has been considered to optimize the input parameters for welding SS321 material using activated tungsten inert gas welding process. The optimized input parameters were identified from the multiple output responses, i.e. arc length of 3 mm, welding current of 220 Amps and welding speed of 120 mm/min (A1B3C1). The analysis of the variance table was performed to calculate the importance of the input parameters in the weldment quality. Also, the influence of the heat input on the depth of penetration and bead width at different arc lengths has been studied. The mechanical integrity is evaluated in terms of tensile strength for base metal (BM) (621 MPa) and weld metal (WM) (624 MPa) specimens by conducting the uniaxial tensile test. The 180° bend test with WM sample revealed the ductility level and was free from fissures and cracks. Charpy impact test results depicted the toughness values of BM (123.17 J) and WM (113.46 J) samples. Microstructural investigations at the SS321 WM highlighted the existence of columnar and equiaxed dendrites in the fusion zone. Moreover, the formation of titanium carbide reduces the chances of weld decay. Ferrite number measurement shows that the amount of delta ferrite is higher in WM (5.9) than in BM (1.2). The existence of dimples and voids in the fractographic analysis of the failed specimens (tensile and impact) confirms the ductile type of failure.

Effects of ATIG Welding on Weld Shape, Mechanical Properties, and Corrosion Resistance of 430 Ferritic Stainless Steel Alloy

Flux activated tungsten inert gas (ATIG) welding is a variant of tungsten inert gas (TIG) welding process with high production efficiency, high quality, low energy consumption, and low cost. The study of activating flux mechanism by increasing weld penetration has direct significance in developing flux and welding process. This study has been conducted on 430 ferritic stainless steel alloy. Design of experiment is used to get the best formulation of flux. Based on Minitab17 software, nineteen compositions of flux were prepared using the mixing method. Fluxes are combinations of three oxides (MoO3-TiO2-SiO2). Using the optimizer module available in Minitab 17 software, the best formulation was obtained to achieve the best weld depth. Hence, the obtained depth is twice greater than that achieved by conventional TIG welding. Moreover, mechanical properties and corrosion resistance have been investigated for TIG and ATIG welds respectively in tensile, impact, and hardness tests, and in potentiodynamic polarization measurement test.