Activated Tungsten Inert Gas Research Articles

Zone-wise investigation of creep behaviour 9Cr–1Mo steel weld joints

ABSTRACTDistinct regions such as weld metal, heat-affected zone (HAZ) and base metal of P9 steel weld joints fabricated by various welding processes were investigated using impression creep testing. Smaller prior austenitic grain size, lower density of precipitates and dislocations resulted in faster recovery and higher creep rate of HAZ in comparison to the weld and base metal. Compared to base metal, shielded metal arc weld (SMAW) and activated tungsten inert gas (A-TIG) weld of the P9 steel weld joints exhibited better resistance to creep and displayed higher activation energy due to their coarser prior austenite grain size. A-TIG HAZ exhibited superior creep properties compared to the SMAW and TIG HAZ due to the presence of higher number density of precipitates.

Effect of oxide fluxes on activated TIG welding of AISI 316L austenitic stainless steel

In this work, activated TIG (A-TIG) welding on 8 mm thick plates of AISI 316L stainless steel was carried out. The effect of various single component fluxes and a multi-component flux on weld bead geometries was analysed. The multi-component flux mixture resulted in though thickness penetration in a single pass. Metallography of different zones was observed and weld zone was found to exhibit austenitic-ferritic microstructure. Delta ferrite content was measured with Ferritoscope and increase in delta ferrite content was observed in A-TIG weld zones as compared to base metal. From microhardness measurements, weld zone was found to be harder than the base metal due to increase in delta ferrite fraction.

Effect of Activated Flux on TIG Welding of 304 Austenitic Stainless Steel

Abstract Autogenous bead on plate (BOP) welding was performed on 3 mm thick AISI 304 stainless steel plate by flux activated TIG (A-TIG) welding and conventional TIG (C-TIG) welding process. TiO2, Al2O3 and CaF2 were employed as flux material, and their effect on the weld geometry, microstructure and micro-hardness value were analysed and compared with the C-TIG welding method. The experimental results showed that weld penetration depth enhanced approximately 75% for using TiO2 and 10 % for Al2O3 as compared to C-TIG welding; whereas, for using CaF2 the weld penetration depth reduced marginally. Although the width of the A-TIG welded samples were higher than the C-TIG welded sample, it was evident that the weld aspect ratio improved significantly for using TiO2 as flux material. The microstructural analysis showed that spacing between the skeleton ferrite and the size of lathy ferrite structure is more for using TiO2 as activated flux.

Investigation on un-peened and laser shock peened dissimilar weldments of Inconel 600 and AISI 316L fabricated using activated-TIG welding technique

The joining of Inconel 600 and AISI 316L plates using compound flux of 50% SiO2 + 50% TiO2 by activated tungsten inert gas (ATIG) welding process has been addressed in this article. The various mechanical and metallurgical studies were performed on the un-peened ATIG (UP-ATIG) dissimilar weldment. The results portrayed that the tensile failure of UP-ATIG weldment had occurred at the weld zone because of the presence of coarse grains and intermetallic phases. Laser shock peening (LSP) carried out on the UP-ATIG dissimilar weldment divulged that the laser peened ATIG (LP-ATIG) weldment possesses higher tensile strength (630.33 ± 28.02 MPa) than the UP-ATIG weldment (573.11 ± 41.11 MPa) due to the presence of compressive residual (CR) stresses induced by LSP. The residual stress measurements revealed that the UP-ATIG weldment possesses tensile residual (TR) stresses and the LP-ATIG weldment encompasses CR stresses in the weld zone. Potentiodynamic polarization test results show that the corrosion resistance of the LP-ATIG weldment is slightly higher (Icorr = 0.19 ± 0.02 mA/cm2) than the UP-ATIG weldment (Icorr = 0.21 ± 0.05 mA/cm2).

Studies on the weldability, mechanical properties and microstructural characterization of activated flux TIG welding of AISI 321 austenitic stainless steel

The presence of titanium in AISI 321 austenitic stainless steel, mitigates the corrosion when deployed in specific applications such as boiler shells, aircraft exhaust manifolds and process equipment. Using Commercial flux purchased from Edison Welding Institute (EWI), studies were conducted to note the effect of Activated Tungsten Inert gas (A-TIG) welding on the surface morphology of type 321 austenitic stainless steel welds and compared with conventional TIG welding. A thin flux layer was applied to the surface of the 6 mm thick plate, followed by a conventional TIG welding process. The bead on trial results shows that compared with the TIG welding process, the flux causes the weld depth to increase, weld bead width to decrease and weld area to increase. This incredible depth of penetration (DOP) has been accomplished by the mechanisms of reversal of Marangoni flow and Arc constriction. From various experimental trials, arc length of 3 mm, welding current of 220 Amps and welding speed of 120 mm min−1 were found to be optimal and subsequently used as input parameters to produce a good quality A-TIG welded butt joint. The welded joint is subjected to transverse and longitudinal tensile and bend tests, charpy impact toughness tests, microhardness, optical microscope, x-ray diffraction analysis, ferrite number measurement and Scanned electron fractography. The welded joint exhibited improved tensile strength, bend and charpy impact toughness and hardness. The weld metal microstructure was observed to be austenite, delta-ferrite and TiC intermetallic compounds (Titanium carbides). The XRD pattern indicates that austenite and ferrite phases are present in both base and weld metal. The results of Fischer Feritscope FMP30 (ferrite measurement) show that the content of delta-ferrite in the weld metal (5.9 FN) is much higher than the parent metal (1.2 FN) and shows excellent mechanical properties in the A-TIG welded joint. Scanned electron fractography indicates that the failure of weld metal and base metal occurs in the ductile mode of fracture.

Effect of Single Oxide Fluxes on Morphology and Mechanical Properties of ATIG on 316 L Austenitic Stainless Steel Welds

Tungsten inert gas (TIG) is a wide common process used in fabrication due to its low cost equipment, high quality and accuracy welds but has low productivity related to the low penetration depth in single pass. A new perspective, the Activated Tungsten Inert Gas (ATIG), in which the same equipment as TIG is used, except that a thin layer of activated flux is deposited on a workpiece surface. In this work, eight kinds of oxides were tested on 316L austenitic stainless steel. Three levels of welding current were used to study the effect of different activating fluxes on weld bead geometry and mechanical properties. X-ray Photoelectron Spectroscopy (XPS) was used for the first and the second level energy for different ATIG welds to analyze the relationship between the weld shape and oxygen content in welds. The experimental results showed that the weld profile is related to the thermodynamic stability of selected oxides and in relation to the energy provided. ATIG with TiO2, SiO2, MnO2 oxides presented the deepest welds followed by Cr2O3, Fe2O3, and ZnO. Finally ZrO2, CaO oxides had no effect on the weld depth. The ATIG welded joint showed better tensile strength than TIG. The ATIG hardness measurements carried out showed also better if not the same as TIG weld except for the Silicon oxide weld. Results of the impact test showed that, except for the titanium dioxide TiO2 which has a good benefit, the weldment using the other oxide fluxes exhibits worse withstanding to sudden shock than TIG welding.

Thermo-Mechanical Analysis of Activated Tungsten Inert Gas Welding (A-TIG) of Type 316LN Stainless Steel Thin Plates

Abstract In the present study, thermo-mechanical behavior of 316LN stainless steel thin plates during activated tungsten inert gas (A-TIG) welding was investigated using SYSWELD®. A-TIG welding was carried out with more reduced heat input for fabricating 3-mm-thick 316LN stainless steel plates than that of the conventional TIG welding process. Induced transient temperature during welding was measured using a K-type thermocouple. A pulse-echo ultrasonic test was carried out using a 2-MHz probe employing critically refracted longitudinal waves for measuring residual stresses across the weld joint. A digital height gauge was used to quantify the distortion caused during welding. There was a good agreement between the predicted and measured thermal cycles, residual stresses, and distortion. The concentrated heat intensity of A-TIG welding induced higher surface temperature in the weld center, produced a narrow weld bead, and exhibited a sharp temperature gradient at the weld/base metal interface. Peak residual stress and distortion of the A-TIG weld joint were found to be less than that of the TIG weld joint.

Development and Deployment of Welding Technologies for the Indian Sodium-Cooled Fast Reactor and Advanced Ultra Super Critical Thermal Power Programmes

Robust manufacturing technology for Sodium-cooled Fast Reactor (SFR) components necessitates development of various research-backed innovative welding technologies. Prior to the start of construction of the 500 MWe Prototype Fast Breeder Reactor, extensive technology development was planned and implemented for development of welding consumables, procedures and technologies for fabrication of components with stringent specifications. With close interaction amongst design, materials and non-destructive evaluation engineers, materials and welding consumable manufactures, and the fabrication industries, it has been possible to overcome the challenges and establish robust manufacturing technologies for fabrication of all the structural components. Extensive welding is involved in the fabrication of reactor vessels, steam generators, fuel sub-assemblies etc. Further, Activated Tungsten Inert Gas (A-TIG) welding process, along with activated flux developed in-house, has been successfully implemented on various SFR-related components. Also, a computational-intelligence based welding system for online monitoring and control during welding has been developed for obtaining near defect-free welded components. Plasma Transferred Arc Welding process has been deployed for deposition of the chosen nickel-base alloy for hardfacing of SFR components, which require improvement in resistance to high temperature wear, especially galling, of mating surfaces in liquid sodium. To reduce carbon footprint substantially, India has initiated a national mission programme of design, development and establishment of 800 MWe Advanced Ultra Supercritical (AUSC) power plant having steam parameters of 710°C / 720°C / 310 bar. Materials and fabrication technologies play decisive roles in the success of such mission project. For this purpose, two important India-specific high-temperature tube materials, 304HCu austenitic stainless steel (304HCu SS) and modified Alloy 617M, as also large cylindrical forgings of Alloy 617M of up to 800 mm diameter for turbine rotors have been indigenously developed. Development of welding consumables and welding procedure has also been established for TIG welding of the tubes, including the 304HCu SS/Alloy 617M dissimilar joint. Based on the tensile and creep tests properties, welding consumables for the tubes and their dissimilar joint have been finalized. Technology for dissimilar metal welding between Alloy 617M and 10Cr-steel forgings for turbine rotors has also been developed. Using narrow-gap TIG welding process, the dissimilar metal weld between 200 mm Alloy 617M and 10Cr-steel have been produced by directly welding the two forgings using Alloy 617 filler wire. The weld exhibited no lack-of-penetration defects and passed dye-penetrant, radiographic and ultrasonic examinations. Similarly procedure for NG welding of superheater headers has also been demonstrated. The details of the Indian efforts towards development and deployment of welding technologies for application to the fabrication to components for the Indian programmes for SFR-based nuclear power and AUSC thermal power plant are presented and discussed.

Investigation on the Effect of Activating Flux on Tungsten Inert Gas Welding of Austenitic Stainless Steel Using AC Polarity

Tungsten Inert Gas (TIG) welding is a popular joining process due to its inherent capability in producing superior quality welding in a wide range of materials. However, lower productivity of it paves the way for introduction of a number of variants of TIG welding, including Flux Bounded TIG (FB-TIG) welding and Activated TIG (A-TIG) welding. In this paper, variations of weld morphology and characteristics with heat input in AC A-TIG welding of both bead-on-plate and butt joining of 6mm thick 316L stainless steel plates using TiO 2 , Cr 2 O 3 and Fe 2 O 3 as activating flux and a stainless steel filler material are investigated. Results are also compared with that obtained in conventional TIG welding. Variations of various weld characteristics viz. depth of penetration, width of weld bead, reinforcement, Reinforcement Form Factor (RFF), and Penetration Shape Factor (PSF) against change in heat input are analyzed and compared. It is observed that TiO2 and Fe 2 O 3 fluxes effectively enhance the penetration due to increase in fluidity and wettability of molten metal and, at the same time, reduce the width of weld bead; whereas, Cr 2 O 3 flux gives inferior results as it reduces penetration instead of increasing it as compared to conventional TIG welding.

High Temperature Fatigue Crack Growth Rate Studies in Stainless Steel 316L(N) Welds Processed by A-TIG and MP-TIG Welding.

Welded stainless steel components used in power plants and chemical industries are subjected to mechanical load cycles at elevated temperatures which result in early fatigue failures. The presence of weld makes the component to be liable to failure in view of residual stresses at the weld region or in the neighboring heat affected zone apart from weld defects. Austenitic stainless steels are often welded using Tungsten Inert Gas (TIG) process. In case of single pass welding, there is a reduced weld penetration which results in a low depth-to-width ratio of weld bead). If the number of passes is increased (Multi-Pass TIG welding), it results in weld distortion and subsequent residual stress generation. The activated flux TIG welding, a variant of TIG welding developed by E.O. Paton Institute, is found to reduce the limitation of conventional TIG welding, resulting in a higher depth of penetration using a single pass, reduced weld distortion and higher welding speeds. This paper presents the fatigue crack growth rate characteristics at 823 K temperature in type 316LN stainless steel plates joined by conventional multi-pass TIG (MP-TIG) and Activated TIG (A-TIG) welding process. Fatigue tests were conducted to characterize the crack growth rates of base metal, HAZ and Weld Metal for A-TIG and MP-TIG configurations. Micro structural evaluation of 316LN base metal suggests a primary austenite phase, whereas, A-TIG weld joints show an equiaxed grain distribution along the weld center and complete penetration during welding (Fig. 1). MP-TIG microstructure shows a highly inhomogeneous microstructure, with grain orientation changing along the interface of each pass. This results in tortuous crack growth in case of MP-TIG welded specimens. Scanning electron microscopy studies have helped to better understand the fatigue crack propagation modes during high temperature testing.

Optimization of Activated Tungsten Inert Gas Welding of 304L Austenitic Stainless Steel

The objective of the present investigation is to find the optimal set of process parameters to achieve higher depth of penetration (DOP) in A-TIG welding of stainless steel (SS) alloy 304L. Input parameters selected for experiments were current, welding speed and arc gap and design of experiments was carried out using central composite design of response surface methodology. Autogenous bead on plate welds in the presence of mono-component flux were made on SS 304L plates of thickness 6 mm to generate data and to study the influence of input variables on DOP. ANOVA was carried out to determine the significance of the process parameters and it was found that welding current is the most significant input variable influencing DOP. A linear regression equation was developed to predict DOP for a given set of input process parameters. Then, desirability approach of RSM is used for numerical optimization to obtain maximum depth of penetration.

Assessment of Stress Corrosion Cracking Resistance of Activated Tungsten Inert Gas-Welded Duplex Stainless Steel Joints

The stress corrosion cracking behavior of duplex stainless steel (DSS) weld joint largely depends on the ferrite-austenite phase microstructure balance. This phase balance is decided by the welding process used, heat input, welding conditions and the weld metal chemistry. In this investigation, the influence of activated tungsten inert gas (ATIG) and tungsten inert gas (TIG) welding processes on the stress corrosion cracking (SCC) resistance of DSS joints was evaluated and compared. Boiling magnesium chloride (45 wt.%) environment maintained at 155 °C was used. The microstructure and ferrite content of different weld zones are correlated with the outcome of sustained load, SCC test. Irrespective of the welding processes used, SCC resistance of weld joints was inferior to that of the base metal. However, ATIG weld joint exhibited superior resistance to SCC than the TIG weld joint. The crack initiation and final failure were in the weld metal for the ATIG weld joint; they were in the heat-affected zone for the TIG weld joint.

Effect of Activating Flux on Penetration in ATIG Welding of 316 Stainless Steel

Tungsten inert gas welding is popular in some industries due to the possibility of obtaining good weld bead surface and high-quality joint without any weld defect. However, compared to many welding processes, shallow penetration of TIG welding hinders its applicability to weld thick components in one pass, thus the productivity is relatively low. An increased depth of penetration can be achieved by Activated TIG (ATIG) welding leading to overall reduction in number of welding passes, and thus increasing productivity. In the present work, attempts were made to find out the optimum flux mixture of SiO and TiO from various ratio of mixtures by carrying out 2 2 bead-on-plate welding on AISI 316 Stainless Steel specimens. From the obtained experimental data, suitable flux ratio was tried to find out giving the highest depth of penetration.

Effect of Activating Flux on Penetration in ATIG Welding of 316 Stainless Steel

Tungsten inert gas welding is popular in some industries due to the possibility of obtaining good weld bead surface and high-quality joint without any weld defect. However, compared to many welding processes, shallow penetration of TIG welding hinders its applicability to weld thick components in one pass, thus the productivity is relatively low. An increased depth of penetration can be achieved by Activated TIG (ATIG) welding leading to overall reduction in number of welding passes, and thus increasing productivity. In the present work, attempts were made to find out the optimum flux mixture of SiO and TiO from various ratio of mixtures by carrying out 2 2 bead-on-plate welding on AISI 316 Stainless Steel specimens. From the obtained experimental data, suitable flux ratio was tried to find out giving the highest depth of penetration.

Effects of graphene nanoplates on microstructures and mechanical properties of NSA-TIG welded AZ31 magnesium alloy joints

The effects of graphene nanoplates (GNPs) on the microstructures and mechanical properties of nanoparticles strengthening activating tungsten inert gas arc welding (NSA-TIG) welded AZ31 magnesium alloy joints were investigated. It was found that compared with those of activating TIG (A-TIG), and obvious refinement of α-Mg grains was achieved and the finest α-Mg grains of fusion zone of NSA-TIG joints were obtained in the welded joints with TiO2+GNPs flux coating. In addition, the penetrations of joints coated by TiO2+GNPs flux were similar to those coated by the TiO2+SiCp flux. However, the welded joints with TiO2+GNPs flux coating showed better mechanical properties (i.e., ultimate tensile strength and microhardness) than those with TiO2+SiCp flux coating. Moreover, the generation of necking only occurred in the welded joints with TiO2+GNPs flux.

Effects of heat treatment on the activated flux TIG-welded AZ31 magnesium alloy joints

The effects of heat treatment on the microstructures and mechanical properties of tungsten inert gas-welded AZ31 magnesium alloy joints with Cr2O3 flux coating were investigated by microstructural observations, microhardness, and tensile tests. The results showed that the activating flux of Cr2O3 improved the weld penetration and the depth/width ratio of the tungsten inert gas-welded AZ31 magnesium alloy joints markedly. Heat treatment (1) eliminated the coarsened network-like β-Mg17(Al, Zn)12 particles which formed in activating tungsten inert gas and (2) resulted in more uniform grain size distribution of partially melted zone. Apart from that, either the microhardness of the seams, the ultimate tensile strength, or the elongation of the welded joints was improved by aging treatment, while too high aging temperature would give rise to a sharply decreased ultimate tensile strength.

Uniform design and optimization of active agent and technology research for A-TIG welding of 2219 aluminum alloy

A uniform design method was used to obtain the active flux formula for direct current electrode negative polarity activated tungsten inert gas (DCEN A-TIG) welding of 2219 aluminum alloy. According to the test results of the tensile strength of welded joint, a mathematical model was established to determine the best component of each component in the active agent and the correctness of the regression equation was verified. Compared with conventional TIG welding without active agent, DCEN A-TIG welding can effectively avoid the presentation of macroscopic and microscopic weld porosity, increasing penetration and strength of the welded joint. The three surfaces in the DCEN A-TIG weld zone presented different morphologies. The upper surface of the weld zone was composed of strong directional dendrites, whereas the cross section and longitudinal section of the weld zone were mainly composed of equiaxed dendrites. Cellular crystals were also observed on the bottom of the longitudinal section. The base metal of the joint was the hardest, and the hardness in the heat-affected zone was higher than that of the weld zone. The weakest area in the welded joint was near the fusion zone. Compared with conventional TIG welding, DCEN A-TIG welding can provide advantages.

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.

Optimization of Welding Parameters, Influence of Activating Flux and Investigation on the Mechanical and Metallurgical Properties of Activated TIG Weldments of AISI 316 L Stainless Steel

This research investigation articulates the joining of AISI 316 L austenitic stainless steel plates of thickness 5 mm by activated tungsten inert gas (A-TIG) welding. Prior to the welding, the optimization of process parameters and the selection of suitable flux have been carried out to join the plates in a single pass welding. The experimental results show that the complete weld penetration can be achieved by using activating flux. The microscopic study divulges the presence of delta ferrite, sigma phase and various forms of austenite in the weld zone. Fischer Feritscope result indicates that the delta ferrite content in the weld is higher (7.8 FN) than the base metal (1.3 FN) which results in superior mechanical properties of the weld. Field Emission-Scanning Electron Microscope (FE-SEM) fractography reveals that the failure of weldments occurs in ductile mode. 180° bend test study reveals the good ductility of the joint.