Autogenous Tungsten Inert Gas Welding Research Articles

Effect of solubilization heat treatment on microstructure and corrosion resistance of joints welded with the autogenous TIG process duplex stainless steel

Duplex stainless steels (DSSs), are used commonly under severe working conditions, subject to high stresses associated with corrosion. A typical DSS is composed of the combination involving two types of microstructures, ferritic and austenitic, which characterizes it as a material with corrosion resistance in aggressive media, due to its ability to passivate. The use of DSS has been increasingly exploited in the oil industry, and its use has occurred in numerous areas, standing out in the production of flexible pipelines, which in most applications, is associated with a welding process. They require special care when welded by the tungsten inert gas (TIG) welding process. Temperature variations in this process, along with heat treatment, promote the formation of precipitates in the matrix and change the phase balance. This significantly influences the mechanical and corrosion properties of DSSs. The objective of this work is to study the influence of two different parameters of solubilization heat treatment after welding on the microstructure and corrosion resistance of a DSSs welded joints. After the autogenous TIG welding process, the welds were subjected to thermal solubilization treatments for 10 and 25 s at 1050 °C. The conditions subjected to the solubilization heat treatment were compared with the as TIG welded control condition. The microstructure was analyzed by confocal microscopy and the corrosion resistance was evaluated by the "A" method of the ASTM G48 standard.

Sensitivity analysis and multi-objective optimization of tungsten inert gas (TIG) welding based on numerical simulation

In welding processes, many factors contribute in achieving a required quality of the welds. Those factors are numerous and they may interact with each other, affecting response parameters such as welding penetration and the heat-affected zone (HAZ) size. Some factors are more important while the influence of others is negligible. To find an optimum factor combination in order to maximize penetration and minimize the HAZ is not an easy task. This contribution is aimed to evaluate the influence of welding energy (E) versus the influence of current (I) and welding speed (Vw) on the penetration and HAZ volume in the autogenous tungsten inert gas welding process. For this purpose, two numerical models are proposed. The first considers an in-house finite volume numerical model, and the second is based on response surface method. A sensitivity analysis of the proposed numerical model using two strategies is also performed. In addition, to determine the best-operating conditions, a multi-objective optimization problem is proposed and solved. The presented numerical models were found to provide good concordance in terms of coefficient of determination and p-value, indicating its significance. Each model (with one or more independent variables) represents detailed information about the physical process and can be used for optimization. The sensitivity analysis demonstrates that the current affects penetration and HAZ volume much stronger than the welding speed does. Physically, this is due to the fact that the current has linear (arc coupling) and non-linear (Joule effect and pressure gradient) influence, and the welding speed contributes linearly, modulating the heat conduction. Finally, it was demonstrated a compromise between the penetration and the HAZ volume by addressing multi-objective optimization. In this context, point C (I = 250 A; Vw = 24.8 cm/min) of the Pareto curve is the optimal option for operation since it provides a lower relative HAZ volume while keeping the same penetration and higher productivity (welding speed).

A New Perception of Activated Flux Tungsten Inert Gas (A-TIG) Welding Techniques for Various Materials

Tungsten inert gas welding (TIG) is more stable and allows for more precise control than most other arc welding processes. TIG welding is desired in the aerospace sector when thin parts have been welded with accuracy. However, when welding thick sections, autogenous TIG welding is not commonly recommended due to the limited depth of penetration required. It is in effective for joining the thick parts in a particular pass. Welding with activated flux tungsten inert gas (A-TIG) enhances weld penetration by four times in a single pass. This process will improve penetration depth, depth/width ratio and also, minimize angular distortion and residual stresses. A-TIG is the topic of investigation among researchers due to its deep penetration capacity. Properties of A-TIG welding in diverse materials was investigated in this study which also discusses the mechanisms, varied forces like lorentz force, buoyancy force, shear stress prompted by plasma jet, shear stress prompted by surface tension gradient, reverse marangoni force and aerodynamic drag force induced in the weld pool. The impact of activated fluxes on various materials of A-TIG weld was also investigated in this study. Recent advancements in TIG welding methods were also explored. According to the findings, A-TIG welding improves weld penetration significantly, but there is a lot of slug on the weld surface. This constraint can be addressed by using new versions of the A-TIG welding progression, such as flux bounded and the flux zone.

Autogenous Tungsten Inert Gas Welding of 430 Ferritic Stainless Steel: The Effect of Inter-pass Temperature on Microstructure Evolution and Mechanical Properties

Effect of inter-pass temperature on the microstructure evolution and mechanical properties of AISI 430 ferritic stainless steel welded by autogenous tungsten inert gas (TIG) technique was investigated. The relationship between the structure and the property of the weldments with inter-pass temperature and without inter-pass temperature is elaborated in this study. Microstructure studies depicted the presence of martensite in the weld metal and some parts of the heat affected zone (HAZ). Increasing inter-pass temperature resulted in higher amount of martensite both in the weld metal and in the HAZ. In addition, high inter-pass temperatures resulted in large HAZ width and grain growth which in turn led to poor tensile strength and ductility of the weldments. An optimum inter-pass temperature of 150 °C provided the best mechanical properties. However, it was inferred that when it is not possible to have a precise control on inter-pass temperature during manufacturing AISI 430 joints, it is better to complete welding without applying inter-pass temperature in order to at least keep tensile strength and ductility of the weldments.

Comparative Study of Weld Characteristics of Friction Stir Welded Joints on Aluminium 7075 with Autogenous TIG

Abstract Aluminium 7075 being the workhorse of the Aluminum series has a wide range of applications in industries like aerospace, automotive, transport, etc. due to its high strength to density ratio, light weight and good corrosion resistance. It has been observed that it is difficult to weld the 7075 alloy using Tungsten inert gas (TIG) welding metal inert gas (MIG) welding or any other conventional method as it encounters solidification and recrystallization problems like cracking and porosity which hamper the weld strength. Hence, in this paper we have attempted to weld the 7075 alloy using friction stir welding, a solid state welding process that does not involve the melting of the sample and hence avoids problems related to solidification of the weld. The weld strength of the same is tested by applying tensile test, hardness test and microstructure analysis. The aforementioned tests are applied on the 7075 alloy welded by autogenous TIG welding and the weld strength of the two welding methods is compared

Physical and Theoretical Modeling of the Nitrogen Content of Duplex Stainless Steel Weld Metal: Shielding Gas Composition and Heat Input Effects

Duplex stainless steels (DSSs) are gaining more and more attention in corrosion-resistant applications and also in the transport and automotive industry. The outstanding mechanical and corrosion properties of DSSs highly depends on the austenite-to-ferrite phase balance (A/F). This phase ratio can shift in a large scale during welding. Thus, the heat input and the shielding gas composition should be optimized. Nitrogen addition to argon shielding is frequently used in DSS welding, because it is a potent austenite former. The dissolved nitrogen content in the heat-affected zone and the weld metal (WM) predetermines the A/F. To determine the effect of heat input and nitrogen content in shielding gas, two different heat inputs and six different gas compositions were used in autogenous tungsten inert gas welding. An improved theoretical model was established in order to simulate the WM dissolved nitrogen content, which calculates it with less error than the initial models. The correlation between nitrogen content and arc voltage was also determined. This improved model delivers the basics for shielding gas selection and the subsequent weld design for optimal A/F for industrial applications.

Effect of filler and autogenous TIG welding on microstructure, mechanical properties and corrosion resistance of nitronic 50 stainless steel

This paper addresses and compares the effect of filler (ERNiCrMo-4) and the performance of autogenous tungsten inert gas welding process of high concentration nitrogen-based austenitic stainless steel namely Nitronic 50. Weldability of Nitronic 50 in terms of microstructural analysis results, mechanical properties and corrosion behavior are investigated with the help of optical microscopy, scanning electron microscopy equipped with energy-dispersive spectrometer, x-ray diffraction and electrochemical assessment. The observed results indicated that the autogenous and filler weld showed different microstructures because of different chromium and nickel equivalent ratio. Filler (ERNiCrMo-4) based weld showed coarse columnar microstructure of austenite, whereas autogenous weld showed austenitic solidification mode having dendritic microstructure. X-ray diffraction results indicated the presence of carbide and nitride precipitates in both filler and autogenous welds. Higher mechanical properties were measured in the filler and autogenous weld compared to base metal. Higher hardness and tensile strength were obtained in the filler based weld. Pitting and intergranular corrosion resistance of filler based weld was poor compared to autogenous and base metal. Higher weight loss was measured in case of filler based weld.

Characterisation of dissimilar P91 and P92 steel welds joint

ABSTRACTIn the present study, dissimilar weld joint was prepared using the P91 and P92 steel plate of 8-mm thickness, using the multi-pass gas tungsten arc (GTA) welding with filler (weld 1) and autogenous tungsten inert gas welding (A-TIG) process (weld 2). Evolution of δ-ferrite patches was studied in weld zone and heat affected zone (HAZ) for both weld 1 and weld 2. Effect of varying post weld heat treatment (PWHT) duration was also studied on δ-ferrite patches and mechanical properties of the dissimilar weld joint. PWHT was carried out at 760°C. For weld 2, weld zone showed poor impact toughness and higher peak hardness as compared to weld 1. After the PWHT, a considerable reduction in hardness was obtained for both weld 1 and weld 2,while impact toughness of weld zone showed a continuous increment with PWHT duration. For weldments characterisation, optical microscope, scanning electron microscope (SEM) and microhardness tester were utilised.

Effect of current and speed on porosity in autogenous Tungsten Inert Gas (TIG) welding of aluminum alloys A1100 butt joint

Autogenous Tungsten Inert Gas (TIG) welding has been conducted on aluminum alloy A1100. The purpose of this research is to determine the proper current and speed of autogenous TIG welding with butt joint pattern. Variations on welding current are 150 A, 155 A, and 160 A with the variations on welding speed are 1 mm/seconds, 1.1 mm/seconds, 1.2 mm/seconds. The welded results were tested using non-destructive test (NDT) method using X-Ray radiography. After the test, it is found that the appropriate current for the best result without porosity can be achieved using the welding parameter of welding current of 160 A and the welding speed of 1.1 mm seconds.

Autogenous Tungsten Inert Gas and Gas Tungsten Arc With Filler Welding of Dissimilar P91 and P92 Steels

Creep strength ferritic/martensitic modified 9Cr-1Mo-V-Nb (P91) steel also designated as ASTM A335 and P92 steel are used for piping, cladding, ducts, wrappers, and the pressure vessel in Gen IV nuclear reactors. In the present investigation, a comparative study of the effect of autogenous tungsten inert gas welding (A-TIG) with double pass and multipass gas tungsten arc (GTA) welding with filler on microstructure evolution in the weld fusion zone and the mechanical properties of P91 and P92 steel welded joints was carried out. The microstructure evolution was studied in as-welded and postweld heat treatment (PWHT) condition. The study also focused on the evolution of δ-ferrite patches and their influence on the tensile properties of welded joints. PWHT was carried out at 760 °C with durations from 2 to 6 h. To study the effect of δ-ferrite evolution on mechanical properties, Charpy toughness, microhardness, and tensile tests were performed. The acceptable microstructure and mechanical properties were obtained after the 6 h of PWHT for A-TIG arc welding process while for GTA weld with filler wire, it was obtained after the 2 h of PWHT at 760 °C.

Experimental Investigations on Welding and Mechanical Characteristics of Sintered-Forged Plain Carbon Steel under Autogenous TIG Welding

Abstract The present research work embraces the experimental studies on mechanical and metallurgical properties of powder metallurgy (P/M) plain carbon steel (Fe-0.5 %C) welded autogenously with various modes of current, namely, alternate current, direct current, mixed mode current, and pulse current (PC) using autogenous Tungsten Inert Gas (TIG) welding. The sintered specimens of rectangular shape synthesized through the P/M route were densified by cold upsetting to obtain maximum density. A pair of specimens were welded, and the weld quality was checked by standard nondestructive testing methods. Various mechanical tests were conducted using standard size specimens as per the ASTM standards. It is found from the results of various mechanical tests that the welded joint made by PC TIG welding exhibits the greatest tensile and impact strengths among the other modes of welded joint. Scanning Electron Microscopy (SEM) fractography of the tensile fractured surfaces reveal the brittle mode of fracture irrespective of the mode of welding currents, which are being used for joining the specimens. Optical microscopy, Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) analyses have been carried out to investigate microstructural changes and phase transformation of chemical constituents at the welded region. The hardness at the fusion zone is found to be higher because of pore-free microstructure.

Comparative study of autogenous tungsten inert gas welding and tungsten arc welding with filler wire for dissimilar P91 and P92 steel weld joint

Creep strength enhanced ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel is also designated as ASTM A335 used for out-of-core and in-core (piping, cladding, ducts, wrappers, and pressure vessel) of Gen IV reactors. In present investigation, the dissimilar weld joint of P91 and P92 steel were made using the autogenous tungsten inert gas (TIG) welding with single pass, double side pass and multi-pass gas tungsten arc (GTA) welding with filler wire. Microstructure evolution in sub-zones and mechanical properties of dissimilar welded joints were studied in as-welded and post weld heat treatment (PWHT) condition. Formation of δ-ferrite patches in weld fusion zone and heat affected zones (HAZs) and their influence on the mechanical behaviour of the welded joints were also studied. Presence of higher content of ferrite stabilizer in P92 steel have resulted the formation of δ-ferrite patches in weld fusion zone as well as HAZs. The δ-ferrite was observed in autogenous TIG welds joints. The δ-ferrite patches were formed in as-welded condition and remained in the microstructure after the PWHT. The δ-ferrite patches leads to reduction in Charpy toughness of autogenous TIG welds joint and also lower down the average hardness of weld fusion zone. Peak hardness and poor impact toughness were observed for autogenous TIG welds joint as compared to GTA welds. For microstructure characterization, field-emission scanning electron microscope (FESEM) with energy dispersive spectroscopy (EDS) and optical microscope were utilized.

Dissimilar joining of CSEF steels using autogenous tungsten-inert gas welding and gas tungsten arc welding and their effect on δ-ferrite evolution and mechanical properties

Ferritic/martensitic 9Cr-1Mo-V-Nb steel also designated as ASTM A335 used in construction of several components of power plants operating in temperature range of 600–650°C. In present investigation, dissimilar weld joints of P91 and P92 steel were prepared using the autogenous tungsten inert gas welding (A-TIG) and multi-pass gas tungsten arc (GTA) welding process. A comparative was performed on evolution of δ-ferrite patches in weld fusion zone and heat affected zone (HAZ) of welded joints. The evolution of δ-ferrite patches was carried out in as-welded and post-weld heat treatment (PWHT) condition. PWHT was carried out at 760°C for 2h for both A-TIG and GTA welding process. For A-TIG weld joint higher yield strength, ultimate tensile strength (UTS) and peak hardness were measured due to higher heat input in single pass and higher carbon content in weld fusion zone. Higher heat input, fast cooling rate and higher weight percentage of ferrite stabilizer like vanadium (V) and niobium (Nb) in A-TIG weld joint were resulted in formation ferrite patches in weld fusion zone and heat affected zone. Higher weight percentage of V and Nb in A-TIG weld zone was resulted poor impact toughness of A-TIG weld fusion zone than GTA welds in as-welded condition. After the PWHT at 760°C–2h, Charpy toughness of A-TIG weld fusion zone (48J) just meet the minimum required value as required by the EN: 1557:1997 (47J).

An Approach to Maximize Weld Penetration During TIG Welding of P91 Steel Plates by Utilizing Image Processing and Taguchi Orthogonal Array

P-91 is modified 9Cr–1Mo steel. Fabricated structures and components of P-91 has a lot of application in power and chemical industry owing to its excellent properties like high temperature stress corrosion resistance, less susceptibility to thermal fatigue at high operating temperatures. The weld quality and surface finish of fabricated structure of P91 is very good when welded by Tungsten Inert Gas welding (TIG). However, the process has its limitation regarding weld penetration. The success of a welding process lies in fabricating with such a combination of parameters that gives maximum weld penetration and minimum weld width. To carry out an investigation on the effect of the autogenous TIG welding parameters on weld penetration and weld width, bead-on-plate welds were carried on P91 plates of thickness 6 mm in accordance to a Taguchi L9 design. Welding current, welding speed and gas flow rate were the three control variables in the investigation. After autogenous (TIG) welding, the dimension of the weld width, weld penetration and weld area were successfully measured by an image analysis technique developed for the study. The maximum error for the measured dimensions of the weld width, penetration and area with the developed image analysis technique was only 2 % compared to the measurements of Leica-Q-Win-V3 software installed in optical microscope. The measurements with the developed software, unlike the measurements under a microscope, required least human intervention. An Analysis of Variance (ANOVA) confirms the significance of the selected parameters. Thereafter, Taguchi’s method was successfully used to trade-off between maximum penetration and minimum weld width while keeping the weld area at a minimum.

Thermo-mechanical Analysis of TIG Welding of AISI 316LN Stainless Steel

In this research, thermoelastoplastic analysis using finite element modeling was carried out to study the thermomechanical behavior of 316LN stainless steel during autogenous tungsten inert gas welding. The efficiency of nondestructive testing was explored by validating the numerical simulations. Online temperature measurements were performed using infrared thermography. A detailed study of surface and bulk residual stress was performed using numerical modeling, and stress profiles were validated using X-ray diffraction and ultrasonic testing, respectively. Distortion analysis was validated using mechanical measurement. Nondestructive testing was efficiently used to validate the numerically predicted thermo-mechanical behavior of welded components.

Finite Element Modeling of TIG Welding of Aisi 304l Stainless Steel and Experimental Validation

In this research work, thermo-elasto-plastic analysis using finite element modeling (FEM) was carried out to study the thermo mechanical behavior of AISI 304L stainless steel plate of 3 mm thick during the autogenous tungsten inert gas welding. Sysweld software has been employed for simulating the temperature distribution, residual stresses and distortion. Physical and mechanical properties of 304 L stainless steel required for simulation were obtained from the literature. Bead-on-plate experiment was carried out at 140 A and 120 mm/min for obtaining weld bead dimensions which are required for heat source fitting in the simulation. Heat source parameters in the simulation were frozen when the bead profile obtained in the simulation matched with the actual bead profile. Then thermal cycles were simulated with the frozen heat source parameters. The thermal cycles and the peak temperatures predicted by the model were compared with that of the experimentally measured values. There was good agreement between the predicted and measured values. The experimentally validated thermal model was further used for simulating residual stresses and distortion. The calculated residual stress profile was validated using experimentally measured residual stress profiles using an Ultrasonic technique. There was good agreement between the predicted and measured residual stress profiles. The simulated distortion values were compared with measured distortion values using height gauge. There was good agreement between the simulated and measured distortion values. The Finite Element model developed for simulating the TIG welding of 304 L stainless steel predicted the thermal cycles, residual stresses and distortion with minimum error.

Intelligent Modeling Using Adaptive Neuro Fuzzy Inference System (ANFIS) for Predicting Weld Bead Shape Parameters During A-TIG Welding of Reduced Activation Ferritic-Martensitic (RAFM) Steel

Reduced-activated ferritic-martensitic steels are considered to be the prime candidate for structural material of the fusion power plant reactor design. Tungsten inert gas (TIG) welding is preferred for welding of those structural materials. However, the depth of penetration achievable during autogenous TIG welding is very limited and hence productivity is poor. Therefore, activated-flux tungsten inert gas (A-TIG) welding, a new variant of TIG welding process has been developed in-house to increase the depth of penetration in single pass welding. In structural materials produced by A-TIG welding process, weld bead width, depth of penetration and HAZ width decide the mechanical properties and in turn the performance of the weld joints during service. To obtain the desired weld bead geometry, HAZ width and make a reliable quality weld, it becomes important to develop predictive tools using soft computing techniques. In this work, adaptive neuro fuzzy inference system is used to develop independent models correlating the welding parameters like current, voltage and torch speed with bead shape parameters like weld bead width, depth of penetration, and HAZ width. During ANFIS modeling, various membership functions were used. Triangular membership function provided the minimum RMS error for prediction and hence, ANFIS model with triangular membership functions were chosen for predicting for weld bead shape parameters as a function of welding process parameters.

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.

Advances in Fusion Welding Technique of Austenitic Stainless Steels

Activated flux assisted tungsten inert gas (TIG) welding of austenitic 316L stainless steel was investigated. Autogenous TIG welding was used to produce a bead-on-plate weld. The FeO, FeS, and FeF2 were selected as the flux powders. The results showed that the FeS and FeO fluxes produced high aspect ratio welds, while the FeF2 flux produced a relatively low aspect ratio weld. The undercut defect was produced with use of the FeS flux. An experimental result suggested the constriction of arc column as a mechanism in improving activated TIG penetration. In addition, activated TIG process can increase the delta-ferrite content in austenitic stainless steel weld metal.

Study of the characteristics of duplex stainless steel activated tungsten inert gas welds

The purpose of this study is to investigate the effects of the specific fluxes used in the tungsten inert gas (TIG) process on surface appearance, weld morphology, angular distortion, mechanical properties, and microstructures when welding 6 mm thick duplex stainless steel. This study applies a novel variant of the autogenous TIG welding, using oxide powders (TiO 2, MnO 2, SiO 2, MoO 3, and Cr 2O 3), to grade 2205 stainless steel through a thin layer of the flux to produce a bead-on-plate joint. Experimental results indicate that using SiO 2, MoO 3, and Cr 2O 3 fluxes leads to a significant increase in the penetration capability of TIG welds. The activated TIG process can increase the joint penetration and the weld depth-to-width ratio, and tends to reduce the angular distortion of grade 2205 stainless steel weldment. The welded joint also exhibited greater mechanical strength. These results suggest that the plasma column and the anode root are a mechanism for determining the morphology of activated TIG welds.