Autogenous Tungsten Inert Gas Research Articles

Performance analysis of various fluxes in different variants of the TIG welding process on the quality of welding

The tungsten inert gas (TIG) welding process is widely used in various industries for its ability to produce high-quality welds at a low cost. However, TIG welding struggles with welding thick stainless steel in a single pass, reducing production efficiency. To address this, new TIG variants such as activated TIG (A-TIG), flux bound TIG (FB-TIG), and flux zone TIG (FZ-TIG) have been developed to enhance penetration in austenitic stainless steel. This study investigates the effects of TiO2 and Fe2O3 flux on 304 stainless steels welded using A-TIG, FB-TIG, and FZ-TIG processes. Results show a slight increase in the depth-to-width (d/w) ratio for A-TIG and FB-TIG, while FZ-TIG achieved a 59% higher d/w ratio compared to autogenous TIG welding. The increased penetration is attributed to the reversal Marangoni convection and arc constriction. Microstructural analysis reveals a higher delta ferrite content in A-TIG and FZ-TIG welds due to increased heat input. Additionally, FZ-TIG welds exhibited an 11.5% higher microhardness compared to autogenous TIG welds. FZ-TIG welding enhances penetration and mechanical properties effectively.

Dissimilar autogenous TIG joint of Alloy 617 and AISI 304H steel for AUSC application

To reduce costs and improve high-temperature performance in Advanced Ultra Super Critical (AUSC) boilers, it is necessary to weld austenitic steel to Inconel alloy. In this study, the autogenous tungsten inert gas (TIG) welding process was used to join Alloy 617 and an austenitic AISI 304H steel plate of thickness 5 mm. Microstructural analysis showed that the microstructure formation was uneven along the weldments, with columnar and cellular dendrites near the interface while the central area of the weld exhibited a combination of columnar, cellular, and equiaxed dendrites. The use of energy dispersive spectroscopy and electron probe micro-analysis unveiled the presence of an unmixed layer at the interface between the weld and AISI 304H steel. Furthermore, a notable variation in the concentration of alloying elements such as Fe, Cr, Ni, Co, and Mo was observed. Within the weld metal, inter-dendritic areas showed the presence of precipitates rich in Cr, Ti, and Mo. Meanwhile, the heat-affected zone (HAZ) of Alloy 617 exhibited the presence of phases like Cr and Mo-rich M23C6 as well as Mo-rich M6C. Hardness tests showed non-uniform hardness along the weldments, with a hardness of 199 ± 6 HV in the weld metal and 225 ± 4 HV in Alloy 617 HAZ, and 207 ± 7 HV in AISI 304H HAZ. The Mo and Cr segregation in the inter-dendritic spaces led to a decline in the tensile properties of the welded parts and resulted in failure from the region of the weld metal.

EVALUATION OF THE MECHANICAL PROPERTIES AND MICROSTRUCTURE OF A-TIG AND TIG WELDMENTS OF INCONEL 617

This work is based on a comparative study of the weldments fabricated by Activated Flux Tungsten Inert Gas (A-TIG) welding and autogenous Tungsten Inert Gas (TIG) welding of 10 mm thick Inconel 617 plates. Flux powders used for A-TIG welding were Titanium dioxide (TiO2) and Silicon dioxide (SiO2). Macrostructure and microstructure analyses and characterization of mechanical properties of both A-TIG and TIG weldments were investigated. The microstructure of Inconel 617 was made up of several secondary phases and fine austenitic grains. Mechanical testing carried out in this study included Bend Test, Tensile Test, Vicker’s Micro-Hardness Test and Charpy Impact Test at room temperature (RT) and a sub-zero temperature (SZT) of −50[Formula: see text]C. The Bend test was found satisfactory for both A-TIG and TIG weldments. TIG weldments’ tensile strength and microhardness were determined to be 782 MPa and 265.44 HV, respectively. However, it was determined that the base metal had a tensile strength of 756 MPa and that the tensile strength and microhardness of the A-TIG weldment were 707 MPa and 252.73 HV, respectively. The TIG weldment was proved to have the highest tensile strength and microhardness due to the availability of strengthening elements like Molybdenum (Mo) and Chromium (Cr), as carbides in the fusion zone. Impact toughness of the A-TIG weldment was higher than that of the TIG weldment both at room and sub-zero temperatures due to the application of TiO2 as flux and the high heat input during A-TIG welding. The ductile mode of fracture was observed in all weldments.

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.

Numerical Prediction for the Effects of Welding Interpass Temperature on the Thermal History and Microstructure of Duplex Stainless Steels

Numerical simulation was used to predict the thermal behavior and the resulting microstructure at the heat-affected zone (HAZ) of a 170 mm diameter and 3.5 mm thickness super duplex stainless steel (SDSS) UNS S32750 tube. In order to evaluate the thermal response from the model, a usual welding situation involving interpass temperature (IT) and its influence on the HAZ microstructure was exploited. Thus, two superimposed autogenous welding passes were simulated, the first clockwise with the tube in the room temperature and the second, counterclockwise, with the tube at the temperature of 250oC. Even subjected to successive thermal cycles and high interpass temperature, the proportion and morphology of the phases at the HAZ and Fusion Zone (FZ) did not present significant differences when comparing the two welding passes. Meanwhile, nitrogen losses should be avoided during welding in order to obtain a balanced microstructure in DSS welds, contributing to guarantee satisfactory toughness in addition to resistance to pitting corrosion. The predictions from the simulation were validated by using experimental results obtained from the autogenous TIG (Tungsten Inert Gas) process.

Fabrication of Aluminum 5083/SiC Surface Composite on Tungsten Inert Gas Weld Joint by Novel Direct Friction Stir Processing Technique

For the creation of surface reinforcement particles in the metal matrix, friction stir processing is frequently utilized. Formation of aluminum/SiC surface composite on Tungsten Inert Gas (TIG) butt weld of Al5083 by a novel technique of direct friction stir processing (DFSP) using a hollow tool is successfully demonstrated in this present work. Deposition of SiC in the stir zone of DFSP was confirmed by X-Ray diffraction (XRD) method. Micro analysis of weld joint was achieved using metallographic microscope and scanning electron microscope (SEM). Microstructure of stir zone of DFSP shows finely distributed SiC reinforcement particles in aluminum matrix. Absence of detrimental intermetallics was confirmed by energy dispersive spectroscopy (EDS) analysis. Tensile strength of DFSPed specimen was found to be 227.3 MPa which is 19.5% lower than UTS of autogenous TIG weld specimen. Microhardness of SZ of DFSP was found to be increased from TIG weld microhardness of 86 Hv to 107 Hv due to presence of SiC particles.

Gas Tungsten arc welding of Ti-6Al-4V sheet for pressure vessels used in aerospace application: A detailed characterization of weldment

Titanium-Ti alloys are the most demanded material in manufacturing industries worldwide. Ti-6Al-4V alloys are the most commonly used material in the aerospace, chemical, and nuclear industries (pressure vessels) due to their excellent corrosion resistance and mechanical properties. In this present study, an autogenous Tungsten inert gas (TIG) welding process was successfully employed to fabricate the butt joint of the Ti-6Al-4V sheet of 1.6 mm thick. The mechanical properties and microstructural characterization of the welded joint were examined. Due to intense heat (TIG arc), a complex microstructure variation has occurred in the welded joint. The microscopic images of the welded joint indicated the existence of α and β phases. Electron backscatter diffraction (EBSD) analysis shows that the high angle grain boundary proportion to the Heat affected zone (HAZ) and Fusion zone (FZ) increases with the volume of applied heat input. The average hardness values for Parent metal (PM), HAZ, and FZ is 315.5 HV0.5, 352.5 HV0.5, and 395.52 HV0.5, respectively. Tensile strength of the welded joint reached 928.9 MPa and fracture location is noticed in the PM. Bend test results confirmed that it has better ductility under a bend of 90°. A good corroboration was noted in between mechanical behavior and microstructure appearance in the welded joint. In addition to that finite element analysis was performed using ABAQUS software to predict tensile strength (Smooth and V-notch tensile specimens). Their results are validated with experimental outcomes. Scanning electron microscopy (SEM) images reveals that fractured tensile samples were failed in ductile mode.

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 study on corrosion behaviour of various modes of ATIG welded plain carbon steel

The purpose of this study is to look at the corrosion behaviour of various current modes of Autogenous Tungsten Inert Gas (ATIG) welded powder metallurgy plain carbon steel (Fe-0.5% C). The impacts of different current modes (DC, AC, Mixed, and Pulsed) on ATIG corrosion welded joints are looked at. To get the highest density, the rectangular sintered plain carbon steel strips were subjected to a cold upset. The parent and welded specimens were subjected to aqueous immersion and electrochemical corrosion tests. The corrosion test findings were compared to the microhardness, corroded surface morphology, microstructure, and SEM of the corroded area. It is observed from the test results that as the parent metal contains pores could lead to a high corrosion rate and the ATIG welded specimens exhibit less corrosion rate due to pore free region at the weldment. The DC mode of the welded specimen is observed to exhibit a lesser corrosion rate compared to the other modes of welded specimens due to higher heat generation.

Brief study on δ-ferrite characterization: A review

The superior thermo-physical properties and long-term creep strength of P91 and P92 steels make it the attractive material in power plant units for high-temperature operating components. The Weldability of such steel is a serious issue and it depends on the welding process and heat treatment employed before and after welding. With respect to varying temperature regimes of heat treatment procedure, the nature of strengthening and mechanical properties of P91 and P92 steel vary. The present work describes the effect of autogenous tungsten inert gas (TIG) process on soft δ-ferrite formation in weld fusion zone of P91/P92 welded joint. The effect of heat treatment on morphology of the ferrite patches was also studied. The formation of the soft δ-ferrite patches was attributed to the presence of ferrite stabilizer like W and Mo in base steel and heat input.

Impact of the Welding Parameters on the Width of the Welding beat in TIG Carbon Steel Welding

Tungsten Inert Gas (TIG) welding is otherwise known as the Gas Tungsten Arc soldering (GTAW) process which when significant levels of weld quality or high precision welding are required, is known to represent an advanced arc welding process. However the impact of the welding factors on this form of welding is important for its welding produced in single-pass welding. In this investigation, the autogenous Tungsten Inert Gas (TIG) welding was performed on a carbon mild steel plate with four parametric welding variables. High and low values of material thickness, welding current, welding speed and filler rod diameter have been measured in order to have an impact on an observable parametric response i.e. welding distance. Geometry of the weld bead has been investigated. An expert statistical software design expert has created a mathematical model, The experimental design is central composite design (CCD) and the sold width is the response measured by the Surface Response Methodology (RSM). It has been shown that the maintenance of a suitable parametric welding factor for a carbon steel plate gives substantial values of welding width.

Influence of the Interpass Welding Temperature on Microstructure and Corrosion Resistance of Superduplex Stainless Steel SAF 2507

The planning and execution of the adequate welding procedure for the superduplex stainless steel (SAF 2507 SDSS) in multiple passes is a complex technological task since thermal cycling may cause the precipitation of harmful phases, such as the sigma (σ) and chi (χ) phases. For this reason, technical standards limit the maximum interpass temperature (T.I.) in an extremely conservative manner at 100 °C. In order to investigate a possibly wider temperature range for this procedure, SAF 2507-SDSS tubes were subjected to autogenous Tungsten Inert Gas (TIG) welding with interpass temperatures ranging from 150°C to 400°C. The different welding zones were characterized by microscopy, Vickers microhardness, and polarization corrosion tests. The results indicated that in the Fusion Zone (FZ), columnar grains of ferrite were formed surrounded by allotriomorphic austenite (AA), besides intragranular austenite (AI) and Widmanstatten austenite (AW). The heat-affected zone (HAZ) had a lower ferrite content and was composed of equiaxed grains of ferrite, also surrounded by AA, besides AI and AW. Hardnesses varied between HV272 and HV293, regardless of the region or the interpass temperature used. Furthermore, the corrosion resistance has not been significantly affected by the interpass temperatures between 150 °C and 400°C.

Corrosion study on AA-TIG welding of duplex stainless steel

Abstract Duplex Stainless steel composition has high amounts of Cr, Ni, Mo and Fe content. Due to the high chromium content passive layer of chromium precipitate is formed on the surface of the material which resists the corrosion in the metal. Duplex Stainless steel (DSS) has good weldability and formability. Based on previous Investigations found through various literatures there is no detailed investigation was carried out on the corrosion behaviour of Automated Autogenous Tungsten Inert Gas (AA-TIG) Welding on Duplex stainless steel. To study the corrosion behaviour of Duplex Stainless Steel, This investigation was carried out in Sodium chloride (NaCl) solution environment. The main objective is to study the corrosion behaviour of the welded material by using PARSTAT 2273. To study the electrochemical impedance technique was chosen to test the AA-TIG welded DSS 2205.

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.

The Effect of Welding Parameter on Mechanical Properties and Macrostructure of AA1100 Using Autogenous Tig Welding

In this paper, an autogenous tungsten inert gas (TIG) welding was performed to understand the characteristic effect of butt joint weld on AA1100 under various parameters. The effect of TIG current and welding speed was selected to study the mechanical properties, porosity, and macrostructure of the weld metal (WM). Based on experimental results, the top bead width (TBW) will increase directly proportional to the increased of welding current. Furthermore, welding current and welding speed affected the strength drop in the heat-affected zone (HAZ). More heat added will result in a deeper drop in strength. Mechanical properties result showed that the tensile strength reduced by 40 – 45% and the hardness reduction in the WM and HAZ area from the base metal (BM) was 17.3% and 27.7%, respectively. Subsequently, X-Ray radiography images showed that there was no large porosity occur in all welding current. The macrostructure showed that the weld bead typically has the concavity shape or U-shaped geometry from a cross-sectional view.

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

Optimization of the microstructure and mechanical properties of the high nitrogen stainless steel weld by adding nitrides to the molten pool

The nitrides were added to the molten pool to optimize the microstructure and mechanical properties of high nitrogen stainless steel weld. The nitrides of the alloy element that promote the nitrogen dissolution were selected. The alloy element and nitrogen element were thereby simultaneously added to the weld. MnN was selected from TiN, VN, CrN and MnN because the nitrogen content of the autogenous tungsten inert gas weld that brushed the MnN powder was the highest and manganese is an austenite forming element. And then MnN was filled into the gas metal arc welding molten pool as the way of bypass MnN-cored wire. The proportion of ferrite of the weld reduced by 51.4 %, the tensile strength of the joint increased by 7.4 % and the impact toughness of the weld increased by 28.1 %. The action mechanism of MnN during the welding was discussed. MnN was decomposed under the high temperature of the arc and the nitrogen and manganese entered the molten pool respectively. Nitrogen escape occurred along with the mass transfer process.

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 aluminide coatings on penetration and microstructure of TIG welded 9Cr-1Mo steel for fusion blanket applications

Aluminide coatings with a top alumina layer on 9Cr steels are considered candidates for fusion blanket applications. One of the critical issues associated with such coating is the fabrication sequence. It is therefore important to investigate the effect of aluminide coating on weld properties of 9Cr steels. This work is a preliminary investigation of the weldability of aluminide coated 9Cr-1Mo steels using bead-on-plate welding experiments. Alumina coated GRADE 91 steel samples by hot dip aluminizing followed by normalizing and plasma tempering were generated. Bead-on-plate welding studies were conducted at different heat inputs by varying the weld speed (100,125,150 mm/min) and using a constant current of 200 A by autogenous tungsten inert gas (TIG) welding process. The effect of coating on the weld microstructure was investigated using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive x-rays (SEM-EDX) and microhardness tests. It was observed that the presence of alumina (Al2O3) on the top of coated samples resulted in improved depth of penetration (DOP) due to arc constriction. The presence of Al rich inclusions (AlN) in the weld bead were also observed. The marginal increase in Al concentration of the weld bead appears to reduce the grain size of weld metal for coated sample and microhardness was enhanced compared to the uncoated 9Cr-1Mo steels.

Delta (δ) Ferrite Formation in the Welds of Aluminized 9Cr-1Mo Steels

Delta (δ) ferrite phase has several detrimental effects on mechanical properties such as toughness, creep, impact and ductility. It is necessary to examine δ-ferrite content in the weld zone of aluminized coated steels. This manuscript presents the investigation of δ-ferrite formation in the weld of aluminized P91 steels. The welds were prepared with different heat inputs by varying the weld speed at constant current by autogenous Tungsten Inert Gas (TIG) welding process. The concentration of Al in the weld zone may favor δ-ferrite formation during the welding as Al is a ferrite former. Hence, the weld zone prepared at maximum heat inputs was compared for both coated and bare P91 samples. Microstructures were examined and correlated with the temperatures and cooling curve measured during welding. The various empirical formulae such as Schneider, Schaeffler, Newhouse, and Kaltenhauser were used to predict the δ-ferrite formation based on the chemical composition of weld metal obtained with the help of spark emission spectroscopy. Among these, Kaltenhauser’s equation is more accurate for aluminized coated P91 steels. X-ray diffraction, optical microscopy, scanning electron microscopy, and microhardness measurement were done to analyze and predict the shape and morphology of δ-ferrite for coated steel and bare P91 steels. The investigation indicates that higher heat input (~ 2.12 kJ/mm) for coated steel and Al concentration (~ 0.19%) in the weld zone caused the formation of δ-ferrites in various shapes such as polygonal and isolate islands and it has an average volume fraction of ~ 5.09%. The average microhardness values were ~ 396–410 Hv for martensitic laths, while it was ~ 192–198 Hv for delta ferrite which is 52% lower.