Activated TIG Welding Process Research Articles

Study of Weldability for Aluminide Coated Steels through A-TIG Welding Process

Abstract To achieve higher efficiency in high-temperature environments, 9Cr-1Mo steels (also known as P91 steels) are promising candidates in power plants, petrochemical industries, heat exchangers, and nuclear applications. To enhance the performance against harsh environments, such as high-temperature oxidation and corrosion during operations, adding aluminum oxide (Al2O3)/iron aluminide (FeAl) coating through the aluminizing process has been found promising. Such coatings have been considered reliable for resistance to liquid-metal corrosion against flowing lead-lithium liquid breeders and against tritium permeation in blanket modules of fusion reactors. However, the welding process for aluminized coated steels is a challenge and is scarcely reported. The aluminum-rich coating at the top may alter the metallurgy of weld metal and subsequently the mechanical properties after welding. To investigate the same, preliminary bead-on-plate trials with a novel activated-tungsten inert gas welding process has been attempted for the first time. Bead-on-plate welding samples were prepared (with the same welding parameters) with five different fluxes, such as iron (III) oxide (Fe2O3), nickel (II) oxide (NiO), copper (II) oxide (CuO), cobalt tetroxide (Co3O4), and Al2O3, for aluminized coated 9Cr-1Mo steel. The resultant weld metal microstructure was evaluated using optical and electron microscopy, elemental analysis using energy-dispersive X-ray spectroscopy, phase analysis using X-ray diffraction, and Vickers hardness testing. It was observed that the presence of oxide-type fluxes results in arc constriction, which thereby affects the depth of penetration. The weld metal prepared with Fe2O3 flux demonstrates a superior depth-to-width ratio compared to other fluxes. An analysis for delta ferrite was also carried out and was observed to be present in Fe2O3 flux welds only. A detailed analysis of the weld metal under different activated fluxes is presented in the paper. The outcome of this work presents the feasibility of the welds of aluminized 9Cr steels as relevant for fusion reactor applications.

Develop a sustainable welding procedure for chromium manganese austenitic stainless steel using the ATIG process

Chromium manganese austenitic stainless steel is exhibiting an admirable amalgamation of higher strength and stress corrosion resistance. This economical steel is developed to fulfill the requirement of a variety of consumers for high temperature and structural applications. Hitherto, the limitation associate with the TIG welding process is a low depth of penetration which reduces productivity. Activated tungsten inert gas welding (ATIG) is the best suitable option to overcome this problem and satisfy the sustainable welding requirement. Welding procedure has been developed for chromium manganese austenitic stainless steel during ATIG welding using a box behken design (BBD) to improve penetration depth and productivity. The activated flux using SiO2 and TiO2 flux indicates improvement in penetration 5.3 mm and 5.1 mm as compared to TIG welding. The ATIG welded test coupon has strength and hardness of 495 MPa and 195 HV when using SiO2 flux, and 487 MPa and 190 HV when using TiO2 flux, compared to 435 MPa and 165 HV for the TIG welded test coupon. ATIG welds have higher strength and hardness because of their finer grain size when compared to TIG welded test coupons.

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.

Numerical modelling of fluid flow and weld penetration in activated TIG welding

This research work emphasis on understanding the weld pool development while carrying out Activated Tungsten Inert Gas (A-TIG) welding by employing Computational Fluid Dynamics (CFD). The influence of temperature coefficient of surface tension (∂γ/∂T) and the concentration of oxygen, the main surface active component on weld bead geometry is studied. A three-dimensional (3D) numerical model has been developed for A-TIG welding process with varying oxygen levels employing ANSYS Fluent for 316LN stainless steel. The general conservation equations consisting mass, energy and momentum were solved in order to acquire the temperature and velocity fields with oxygen levels varying from 50 to 300 ppm in weld pool. The impact of driving forces particularly buoyancy and Marangoni on the weld pool convection were examined. The simulation confirmed that the weld bead shape was influenced mainly by Marangoni convection consecutively dependent on the oxygen content in the weld metal in the course of A-TIG welding. The addition in oxygen content changes the surface tension temperature coefficient ∂γ/∂T from negative to positive gradient causing inward flow. It was found that minor oxygen content in the molten pool until 150 ppm exhibited outward flow and with higher oxygen content beyond 150 ppm exhibited an inward flow. The oxygen content in the weld bead without flux and with flux was found to be 69 and 336 ppm respectively for the type 316LN stainless steel plates welded by A-TIG welding. The simulated weld bead profile was validated by comparing with the experimentally obtained weld bead profile. There was excellent agreement between the two weld bead profiles.

Optimization of A-TIG Welding Process Parameters for P92 (9Cr-0.5Mo-1.8W-VNb) Steel by Using Response Surface Methodology

Abstract Response surface methodology (RSM) is a mathematical and statistical technique useful for the modeling and optimization of processes in which a response of significance is influenced by a number of process parameters called input variables. The major concern faced by fabrication engineers during activated tungsten inert gas (A-TIG) welding is the selection of the optimum combination of input variables for achieving the desired weld bead geometry. In this research work, the optimization of A-TIG welding process parameters for P92 (9Cr-0.5Mo-1.8W-VNb) steel have been carried out using RSM. The design matrix for conducting experiments was generated using the central composite design of RSM. The four input process variables, such as welding current, torch speed, arc gap, and electrode tip angles, are varied at five levels. A-TIG bead-on-plate welds were made on a 10 mm-thick P92 steel plate as per the combination of input parameters given by the design matrix. Weld bead geometry, such as the depth of penetration, bead width, and width of the heat-affected zone, were measured and recorded as responses. Second-order response surface models were developed for predicting the response for the set of given input process parameters. Moreover, the response optimization was carried out for obtaining the maximum depth of penetration, minimum bead width, and target heat-affected zone width using the desirability approach. The validation experiments were carried out on the determined optimized process parameters, and it was found that there was good agreement between the predicted weld bead dimensions and actual values obtained during the experiments.

Dissimilar metal welding of P91 steel-AISI 316L SS with Incoloy 800 and Inconel 600 interlayers by using activated TIG welding process and its effect on the microstructure and mechanical properties

This study investigates dissimilar metal weldments between P91 steel and AISI 316 L austenitic stainless steel fabricated by activated TIG welding (A-TIG) with and without the use of interlayers of Incoloy 800 and Inconel 600. Through thickness penetration in 8 mm thick plates was achieved in a single pass A-TIG welding using a pre-coated mixture of metallic oxides. Hot cracking was eliminated in A-TIG weld joints in contrast to conventional TIG weld joints without flux. Fully martensitic structure was observed in the weld metal developed without the use of interlayer. Microstructural modifications were achieved with the use of interlayers. The weldment with Incoloy 800 interlayer exhibited martensitic-austenitic structure whereas fully austenitic structure was observed with Inconel 600 interlayer. Interlayers improved impact toughness and ductility of the weld joints without significant loss of tensile strength. The effect of interlayers on carbon migration after aging treatment (620 °C/500 h) was evaluated with the help of thermodynamic simulations and it was observed that the use of interlayers reduced the severity of carbon migration.

Attaining optimized A-TIG welding parameters for carbon steels by advanced parameter-less optimization techniques: with experimental validation

Enhanced penetration potential of activated TIG (A-TIG) welding process over conventional TIG welding has made the former process preferred for welding in recent times. The quality and shape of the weld in A-TIG are not only influenced by the chemical composition of the flux, but also by the selection of welding parameters. As a variety of process parameters influence the results, a proper understanding of process performance and identification of favorable welding conditions (optimum setting of process parameters) are indeed necessary to improve quality. The present work highlights the application potential of multi-response optimization route by integrating response surface methodology with the JAYA optimization algorithm, particularly for optimizing the A-TIG welding process parameters for carbon steels. Systematic experiments were carried out considering welding current, arc gap and travel speed as input parameters, whereas the depth of penetration, depth-to-width ratio, heat input and total width of heat-affected zone were considered as output performance characteristics. An attempt has been made in the current study to recognize the precise setting of selected input process parameters for simultaneous optimization of the aforementioned performance characteristics. The result of JAYA algorithm has also been compared with the teaching–learning-based optimization technique. While fairly similar results were achieved, the implementation of JAYA algorithm was computationally efficient. Experimental validation of the single-objective as well as multi-objective optimization results indicates that the empirical models for the response parameters as well as the proposed optimization framework are accurate tools in A-TIG welding research.

Experimental Investigation of SS-304 by using Orbital Welding with A-TIG Process

Tungsten Inert Gas (TIG) welding is the mostly used fabrication technique used for joining stainless steel pipe in industry. By this process limited Depth of Penetration (DOP) can be achieved in a single pass. To overcome this problem, the current, speed and flow rate needs to be significantly changed and it will effect productivity. Therefore Activated TIG welding (A-TIG) is explored in the present study. The effect of hybrid mixture is evaluated in terms of DOP on AISI 304 by an automatic orbital welding setup. Hence a mathematical modelling is being done DOP by varying thickness, current, travel speed, and flow rate. A Leica microscope is used to capture the image of microstructure of weld bead. The result shows that a significant increase in DOP and width to penetration ratio by increasing the current for higher thickness after using of activated flux.

Evaluation of strength property variations across 9Cr-1Mo steel weld joints using automated ball indentation (ABI) technique

The variations of strength properties across 9Cr-1Mo steel weld joints fabricated by different arc welding processes such as shielded metal arc welding (SMAW), tungsten inert gas (TIG) and activated tungsten inert gas (A-TIG) have been evaluated employing automatic ball indentation (ABI) technique. ABI tests were conducted at 298K across various zones of the weld joints comprising of base metal, weld metal, heat affected zone (HAZ) and intercritical HAZ (ICHAZ) regions. The flow curves obtained from ABI tests were correlated with corresponding conventional tensile test results. In general, the tensile strength decreased systematically across the weld joint from weld metal to base metal. Inter critical HAZ exhibited the least strength implying that it is the weakest zone. The incomplete phase transformation in the ICHAZ during weld thermal cycle caused the softening. The A-TIG weld metal exhibited higher UTS and strain hardening values due to higher carbon in the martensite. The strain hardening exponent exhibited only slight variation across the various regions of the weld joints. A-TIG weld joint exhibited higher weld metal and HAZ strength, marginally higher UTS to YS ratio in the weld metal and HAZ compared to that of the other two processes. Hence, among the three welding processes chosen, A-TIG welding process is found to be superior in producing a 9Cr-1Mo steel weld joint with better strength properties.

Investigation on un-peened and laser shock peened weldment of Inconel 600 fabricated by ATIG welding process

The present investigation articulates the joining of Inconel 600 plates using activated tungsten inert gas (ATIG) welding process. Before joining of Inconel 600 plates, welding parameters have been optimized and suitable flux has been selected to produce complete weld penetration in a single pass welding. The various mechanical and metallurgical characterizations were performed on the un-peened ATIG (UP-ATIG) weldment. The experimental results attested that the tensile failure occurred in the weld zone and also the tensile strength is lower than the base metal (BM) because of coarser grain structures and tensile residual stresses in the weld zone. Laser shock peening (LSP) was carried out on the welded joint to enhance its properties. After LSP treatment, the significant improvement was observed in the laser peened ATIG (LP-ATIG) weldment and the fracture occurred at the parent metal side owing to the compressive residual stresses developed by LSP. Residual stress measurements indicated that the compressive residual stresses were higher at the surface and they decrease with increasing depth.

Effect of Multipass TIG and Activated TIG Welding Process on the Thermo-Mechanical Behavior of 316LN Stainless Steel Weld Joints

The primary objective of this work was to develop a finite element model to predict the thermo-mechanical behavior of an activated tungsten inert gas (ATIG)-welded joint. The ATIG-welded joint was fabricated using 10 mm thickness of 316LN stainless steel plates in a single pass. To distinguish the merits of ATIG welding process, it was compared with manual multipass tungsten inert gas (MPTIG)-welded joint. The ATIG-welded joint was fabricated with square butt edge configuration using an activating flux developed in-house. The MPTIG-welded joint was fabricated in thirteen passes with V-groove edge configuration. The finite element model was developed to predict the transient temperature, residual stress, and distortion of the welded joints. Also, microhardness, impact toughness, tensile strength, ferrite measurement, and microstructure were characterized. Since most of the recent publications of ATIG-welded joint was focused on the molten weld pool dynamics, this research work gives an insight on the thermo-mechanical behavior of ATIG-welded joint over MPTIG-welded joint.

Optimization of A-TIG welding process parameters for RAFM steel using response surface methodology

In the present work, the optimization of Activated TIG (A-TIG) welding process parameters to achieve the desired weld bead shape parameters such as depth of penetration, bead width, and heat-affected zone (HAZ) width have been carried out using response surface methodology (RSM). The main problem faced in fabrication of weld joints is the selection of optimum combination of input variables for achieving required quality of welds. This problem can be solved by development of mathematical model and execution of experiments by RSM. Central composite design of RSM has been used to generate the design matrix for generating data on the influence of A-TIG welding process parameters. The input variables considered were welding current, torch speed, electrode tip angle, and arc gap. The response variables considered were depth of penetration, bead width and HAZ width. A second-order response surface model is developed for predicting the response for the set of given input process parameters. Then, numerical and graphical optimization is performed using RSM to obtain the desired depth of penetration, bead width, and target HAZ width using desirability approach.

Effects of Activating Flux on Inconel 718 Alloy and AISI 304 Stainless Steel Dissimilar TIG Welds

The purpose of this work is to investigate the effects of activating flux on the penetration, depth-to-width ratio (DWR), angular distortion and hardness of Inconel 718 alloy and AISI 304 stainless steel (SS) dissimilar welds in the tungsten inert gas (TIG) welding process. In the activated TIG (A-TIG) process, the single component fluxes such as SiO2, NiO, MoO3 and MoS2 and the mixed component fluxes that using 50 % of each single component flux to create six new mixtures were used in the experiment. The experimental results showed that the A-TIG welds coated with 100% SiO2 flux was provided with best DWR of dissimilar welds. In addition, the experimental procedure of A-TIG welding process not only produced a significant increase in penetration and DWR of weld bead, but also improved the angular distortion and hardness of Inconel 718 alloy and AISI 304 SS dissimilar welds.

Optimisation of welding process for modified 9Cr-1Mo steel using genetic algorithm

Modified 9Cr-1Mo steel is used as the structural material for steam generator components of power plants. Activated tungsten inert gas (A-TIG) welding is increasingly used for fabricating these components. With the aim to achieve maximum depth of penetration (DOP) and minimum heat affected zone (HAZ) width, computational methodologies were adopted for optimisation of A-TIG welding process. Genetic algorithm (GA)-based model has been developed to determine the optimum process parameters. In this methodology, independent artificial neural network (ANN) models correlating DOP and HAZ width with process parameters (current, torch speed and arc voltage) respectively were developed. Then GA code was developed whose objective function was evaluated using the artificial neural network (ANN) models. The developed GA produced multiple outputs of the process parameters for the same target DOP and HAZ width. Thus, a methodology using GA has been developed for optimising the A-TIG process parameters for modified 9Cr-1Mo steel.

Effect of Activated Flux on the Microstructure, Mechanical Properties, and Residual Stresses of Modified 9Cr-1Mo Steel Weld Joints

A novel variant of tungsten inert gas (TIG) welding called activated-TIG (A-TIG) welding, which uses a thin layer of activated flux coating applied on the joint area prior to welding, is known to enhance the depth of penetration during autogenous TIG welding and overcomes the limitation associated with TIG welding of modified 9Cr-1Mo steels. Therefore, it is necessary to develop a specific activated flux for enhancing the depth of penetration during autogeneous TIG welding of modified 9Cr-1Mo steel. In the current work, activated flux composition is optimized to achieve 6 mm depth of penetration in single-pass TIG welding at minimum heat input possible. Then square butt weld joints are made for 6-mm-thick and 10-mm-thick plates using the optimized flux. The effect of flux on the microstructure, mechanical properties, and residual stresses of the A-TIG weld joint is studied by comparing it with that of the weld joints made by conventional multipass TIG welding process using matching filler wire. Welded microstructure in the A-TIG weld joint is coarser because of the higher peak temperature in A-TIG welding process compared with that of multipass TIG weld joint made by a conventional TIG welding process. Transverse strength properties of the modified 9Cr-1Mo steel weld produced by A-TIG welding exceeded the minimum specified strength values of the base materials. The average toughness values of A-TIG weld joints are lower compared with that of the base metal and multipass weld joints due to the presence of δ-ferrite and inclusions in the weld metal caused by the flux. Compressive residual stresses are observed in the fusion zone of A-TIG weld joint, whereas tensile residual stresses are observed in the multipass TIG weld joint.

Creep rupture strength of activated-TIG welded 316L(N) stainless steel

316L(N) stainless steel plates were joined using activated-tungsten inert gas (A-TIG) welding and conventional TIG welding process. Creep rupture behavior of 316L(N) base metal, and weld joints made by A-TIG and conventional TIG welding process were investigated at 923 K over a stress range of 160–280 MPa. Creep test results showed that the enhancement in creep rupture strength of weld joint fabricated by A-TIG welding process over conventional TIG welding process. Both the weld joints fractured in the weld metal. Microstructural observation showed lower δ-ferrite content, alignment of columnar grain with δ-ferrite along applied stress direction and less strength disparity between columnar and equiaxed grains of weld metal in A-TIG joint than in MP-TIG joint. These had been attributed to initiate less creep cavitation in weld metal of A-TIG joint leading to improvement in creep rupture strength.

Genetic algorithm for optimisation of A-TIG welding process for modified 9Cr–1Mo steel

It is essential to set up the activated tungsten inert gas (A-TIG) welding process parameters to produce the desired weld bead geometry and heat affected zone (HAZ) width in modified 9Cr–1Mo steel weld joints. Therefore, it becomes necessary to develop a tool for optimisation of A-TIG welding process. Genetic algorithm (GA) based model has been developed to determine the optimum process parameters. In this methodology, first independent ANN models correlating depth of penetration, weld bead width and HAZ width with current, voltage and torch speed respectively were developed. Then, GA code was developed in which the objective function was evaluated using the ANN models. There was good agreement between the target and actual values of bead geometry and HAZ width obtained using the GA optimised process parameters. Thus, a methodology using GA has been developed for optimising the A-TIG process parameters for modified 9Cr–1Mo steel.