Manual Gas Tungsten Arc Welding Research Articles

Effects of Autogenous Gas Tungsten Arc Welding (GTAW) on Corrosion Resistance of Stainless Steel 316L

The autogenous manual gas tungsten arc welding (GTAW) process was used for cladding austenitic stainless steel 316L using a single pass with various contact tip-to-work distances (CTWDs). Immersion and electrochemical tests were used to evaluate the corrosion resistance of the welded specimens, and a microstructural analysis was conducted to investigate the chemical composition of the molten pool and the heat-affected zone of welding. The key findings of this study indicate that the corrosion resistance improved under a CTWD of 5 mm due to the optimal distribution of ferrite and a refined microstructure. Additionally, the highest hardness was observed in specimens with a CTWD of 3 mm, attributed to the increased ferrite content in the weld metal. As the CTWD increased, the ferrite fraction decreased, and the hardness also diminished. However, in the CTWD 7 mm case, the higher heat input influenced the microstructure and molten pool shape significantly through the Marangoni effect, resulting in a lower corrosion resistance. These results suggest that optimizing the CTWD can enhance the corrosion resistance of welded 316L stainless steel.

Effect of alloy 625 buffer layer on corrosion resistance of nickel base hardfacing

Nickel base hardfacing alloys serve to mitigate corrosion losses at elevated temperatures. Efficacy of Nickel base hardfacing alloys can be compromised when applied onto Fe base substrates due to iron dilution in hardfacing. The degree of Fe dilution can be reduced by using advanced deposition methods and optimized deposition parameters. Gas Tungsten Arc Welding (GTAW) method is commonly employed for its cost-effectiveness and versatility, but it tends to induce higher Fe dilution due to increased heat input. This study aims to reduce the degree of Fe dilution and enhance corrosion resistance by introducing a nickel base buffer layer (alloy 625) between the nickel base hardfacing alloy and AISI 316L stainless steel substrate. For comparative purposes, Ni base hardfacing alloy was deposited on the substrate without any buffer layer. Hardfacing depositions were prepared using manual GTAW process. Process parameters namely, deposition current, voltage, travelling speed, pre-heating temperature, and cooling method were kept constant. Samples underwent aging at 1123 K for 4 h, followed by microstructural examination via optical and scanning electron microscopes. Iron (Fe) dilution quantification was performed using energy dispersive spectroscopy (EDS). The EDS analysis showed that the use of buffer layer between the hardfaced deposit and the substrate decreased the degree of Fe dilution in the hardfaced deposit. X-Ray diffraction (XRD) analysis was performed to identify various phases formed in the hardfaced deposit. Potentiodynamic polarization test was performed to assess the corrosion resistance of hardfaced deposit in 3.5 wt% NaCl solution. Results show significant improvement in corrosion resistance of hardfacings deposited sample with buffer layer as compared to those without buffer layer. Aging treatment further enhanced corrosion resistance. The corrosion resistance data is correlated with the microstructure and phases formed in various samples.

Possibilities of Repairing Functional Surfaces of Molds for Injecting Al Alloys Using Manual GTAW Cladding

The paper presents the results of research that is focused on the renovation of molds for high-pressure aluminum casting. An analysis of the worn molds was carried out after they were removed from the operator. The extent and mechanism of the wear were determined. GTAW (Gas tungsten arc welding) technology was chosen for the renovation of the shaped parts of the molds. The renovation layers were realized with four types of additional materials Cronitex RC 44, UTP A 73 G 3, UTP A 673 and Dievar® TIG. The quality of the coatings was assessed by destructive as well as non-destructive tests. The mixing of the build-up layers with the base material was determined on the basis of structural analyses. The hardness of the cladding was determined by a metallographic analysis of the cross crowns with the Vickers method. The resistance of the cladding was tested by a complete immersion in a melt of AlSi8Cu3 aluminum alloy which was maintained at a temperature of 680 ± 20 °C in a laboratory resistance furnace for 120 and 300 min. The tribological properties of the produced deposits were determined using the ball-on-disc dry method. Based on the experiments that were carried out, it is possible to recommend the additive material UTP A 73 G 3 for the restoration of the functional surfaces of molds for the injection of Al alloys as the patterns that were created by it have shown the best results in terms of their resistance to Al melt, which is the dominant degradation factor limiting the life of the molds.

Development of a simulation model of the manual gas tungsten arc welding process and visualization of the welder’s skill

Development of a simulation model of the manual gas tungsten arc welding process and visualization of the welder’s skill

Effects of W and Ce micro addition in filler metal on microstructure and creep strength of Cr35Ni45NbM alloy weld joint

The effect of the filler metal chemical composition on the performance of Cr35Ni45NbM alloy weld joint is studied in this paper. The Cr35Ni45NbM alloy weld joints with two type filler metals are produced through manual gas tungsten arc welding (GTAW) process. The number of carbide in weld metal is more than that of base metal, and the size of carbide is smaller. The carbide size in the fusion zone of the weld joint with addition Ce and W elements in filler metal is smaller than that without Ce and W elements. The micro addition of W and Ce in filler metal could improve the high temperature creep strength of weld joint, and has no evident effect on the tensile properties at room temperature. After high temperature creep test, the creep test specimens break at fusion zone, which indicates that the weak part of the weld joint is the fusion zone during service. In the creep process, the cracks first nucleate at the interface between carbide and γ matrix, and then propagate along the carbide, finally the weld joint fractures along the dendrite boundary.

A Comparison of Weldability, Structure, and Mechanical Properties of CM64 and Tribaloy T-800 Welds for Hard-Facing of Turbine Blades

Abstract In this study, the weldability, microstructure, and tensile properties of CM64 and Tribaloy T-800 (T800) cobalt-based hard-facing materials were studied. Successful CM64 hard-facing could be achieved at ambient temperature using manual gas tungsten arc welding (GTAW-MA). It was shown that T800 welded at ambient temperature was prone to cold cracking due to a combination of low ductility with high welding stresses that limited the accommodation of residual stresses by plastic deformation within the weld beads. Sound T800 welds of various geometries and sizes were produced on cobalt- and nickel-based X-40 and Haynes 230 superalloys, respectively, using GTAW-MA when preheating above 900 °C was used. Microstructural analyses on the sound CM64 and T800 welds were performed using optical and electron microscopy and X-ray diffraction. The distribution of elements and phases in each alloy was evaluated and revealed the epitaxial dendritic structure with the Cr–W–Si-based phase in the interdendritic region in CM64 welds compared with petal-like and equiaxed hard Mo–Co–Si-based dendrites and fine particles in T800. Tensile testing from room temperature up to 1093 °C was performed on both alloys. T800 welds possessed lower ultimate tensile strengths and elongations in this temperature range when compared with the CM64 alloy. Recommendations for hard-facing of turbine engine components were provided.

Argon localizing by concentration method for GTAW welding process of high chromium alloy steel pipes

The present invention relates to a novel argon purging device in butt joint welding for high chromium alloy steel pipes or more predominantly relates to a device which can be used for focusing of argon at root area of welding and also an approach for purging out the atmospheric air through the inert gas argon at butt welding of high thickness pipes of high pressure steam generators. The butt joint root welding of high chromium alloy steel pipes carried out by manual Gas Tungsten Arc Welding (GTAW) requires shielding from atmospheric oxygen. Otherwise, Chromium reacts with oxygen and forms Chromium Oxide (CrO2) which is termed as oxidation. In the conventional method of purging, the argon gas is fed into both ends of the pipe using two argon cylinders. The ends are closed with metallic end covers which have many inherent limitations like ineffective purging at the butt joint, more wastage of the inert gas argon, incomplete fusion, lack of penetration, root oxidation and formation of weak brittle structures etc. Present invention is to provide a device for argon supply in butt welding of high chromium alloy steel pipe which ensure substantially better shielding and thereby avoiding the root oxidation. The developed argon purging device has resulted in elimination of root oxidation in high chrome high alloy steel pipe butt joint welding, improved weld quality as well as reduced process time. Argon gas savings up to 87.5%, as only one fourth of an argon cylinder is used in place of 2 argon cylinders for purging one butt joint and the overall cycle time is reduced by 40%.

Advanced microstructural characterisation of cast ATI 718Plus\xae\u2014effect of homogenisation heat treatments on secondary phases and repair welding behaviour

The influence of base metal conditions on the weld cracking behaviour of cast ATI 718Plus® is investigated by comparing 4 h and 24 h dwell time pseudo-hip homogenisation heat treatments at 1120, 1160 and 1190 °C with the as-cast microstructure. Scanning electron microscopy (SEM), X-ray diffraction (XRD) on electrolytically extracted powder and transmission electron microscopy (TEM) were used to identify Nb-rich secondary phases in interdendritic areas as the C14 Laves phase and Nb(Ti) MC-type carbides. All homogenisation heat treatments but the 1120 °C 4-h condition dissolve the Laves phase. A repair welding operation was simulated by linear groove multi-pass manual gas tungsten arc welding (GTAW). The Laves phase containing microstructures resulted in lower total crack length for heat affected zone cracking. Constitutional liquation of Nb(Ti) MC-type carbides is observed as a liquation mechanism in Laves-free microstructure, while thick liquid film formation due to the Laves eutectic melting could reduce the formation of weld cracks in microstructures containing the Laves phase.

Open-Closed-Loop Iterative Learning Control With a Self-Adjustive Factor of the Gas Tungsten Arc Welding (GTAW) Process

Human welder's experiences and skills are critical for producing quality welds in manual gas tungsten arc welding (GTAW) process. For batch welding of the same workpiece, and the welding experience accumulated in same welding track, the welding process has a very high-degree reduplication. In this article, an open-closed-loop iterative learning control algorithm is constructed and implemented as an intelligent controller in automated GTAW process to reach the desired trajectory well. During the welding process, there will encounter external interference, such as random changes in voltage, resulting in pool surface fluctuations. Therefore, we introduce a self-adjustive factor based on ILC algorithm. The self-adjustive factor can adjust the input of the controller according to the error and error rate of change of the system, so that the system body has self-adaptation to improve the ability of anti-interference of the system. The simulation shows that a new proposed ILC control is an effective method for weld penetration in GTAW.

On the Dissimilar Metal Welding of 1.4742 Ferritic to 310S Austenitic Stainless Steels Utilizing Different Filler Metals

In this work, the microstructural, mechanical, and physical properties of dissimilar welding between the 1.4742 ferritic and 310S austenitic stainless steels have been investigated. The welding was performed by the manual gas tungsten arc welding process utilizing ER310, ERNiCr-3, and ER446 filler metals. The weld metal microstructure of the ER310 and ERNiCr-3 filler metals was fully austenitic. The ER446 weld metal exhibited a ferritic-austenitic dual-phase microstructure. Carbide precipitates enriched with Cr, Fe, and or Nb were detected in all of the three weld metals. The unmixed zone was observed on both sides of the ERNiCr-3 weld metal, while for the ER310 and ER446 weld metals it was formed solely on one side. The ER446 weld metal displayed the maximum hardness values, 221.9 ± 5 HV, with relatively large fluctuations. The highest and lowest impact energy was achieved in the ERNiCr-3 weld metal, 40 ± 3 J, and ER446 weld metal, 25 ± 3 J, respectively. The ERNiCr-3 weld metal had a linear coefficient of thermal expansion (CTE) value about the mean value of the linear CTE of the two base metals. At last, for the dissimilar welding of these two base metals, it was concluded that the ERNiCr-3 filler metal is a better selection.

Fatigue life enhancement of TIG-welded 304L stainless steels by shot peening

Shot peening is a cold working process that leads to changes of residual stress in the surface layer and the microstructure. In this paper, we studied the effect of the stress ratio and shot peening on the fatigue life of AISI 304L austenitic stainless steel welded using a fully manual gas tungsten arc welding process (GTAW). The specimens are prepared by welding flat plates with thickness of 1 mm using GTAW process and the 308 stainless steel as the filler metal. Results indicate that the fatigue life of the as-welded material under tension–compression loading (stress ratio R = − 1) is longer compared to fatigue life under tension–tension loading (stress ratio R = 0). Furthermore, the microhardness and fatigue life are found to be improved after shot peening post-welding treatment for durations ranging from 5 to 7 min. The improvement in tensile stress and microhardness of treated material is as good as the results reported using the more advanced and costly techniques. Also, the findings suggest that influence of duration of shot peening is more significant on the fatigue life than on the microhardness.

Weldability of wrought Haynes\xae 282\xae repair welded using manual gas tungsten arc welding

The ability of the precipitation hardening superalloy Haynes® 282® to be repaired by multi-pass gas tungsten arc welding is investigated in this study. The repair welding has been carried out on forged discs having four pre weld heat treatments, resulting in different grain sizes and precipitate structures of the base material. Another set of discs has additionally been put through a post weld heat treatment. The tendency to form cracks in the heat-affected zone and the fusion zone has been investigated metallographically. No cracks in the base metal heat-affected zone were found, whereas solidification cracks were present in the weld fusion zone of all tested conditions. While high heat input during welding increased cracking by a factor of 1.5, none of the heat treatments had a measurable influence on the cracking behaviour. Voids with solid state crack-like appearance turned out to be aluminium-rich oxides being present from the deposition of previous weld deposit layers.

Experimental investigation of local tensile and fracture resistance behaviour of dissimilar metal weld joint: SA508 Gr.3 Cl.1 and SA312 Type 304LN

AbstractThe aim of the paper is to evaluate the local tensile and fracture toughness properties of the dissimilar metal weld joints between SA508Gr.3 Cl.1 and SA312 Type 304LN pipe. Weld joints have been prepared by manual gas tungsten arc welding (GTAW) process with conventional V‐groove and automatic hot wire gas tungsten arc welding with narrow gap using different filler wires/electrode such as Inconel 82/Inconel 182 and ER309L/ER308L. The tensile and fracture toughness test specimens have been machined from different regions of dissimilar metal weld such as heat affected zones, fusion lines, buttering layer, weld metal and both base metals. Tensile and fracture toughness tests have been carried out as per the ASTM standard E8 and E1820 respectively. Tensile and fracture toughness results of all the regions of dissimilar metal weld joints have been discussed in this paper. Metallurgical and fracture surface examinations have also been reported to substantiate the tensile and fracture toughness results. Need for the local properties for integrity assessment of the dissimilar metal weld joints has also been brought out.

A mobile sensing system for real-time 3D weld pool surface measurement in manual GTAW

An innovative mobile sensing system has been developed to non-intrusively monitor the manual pipe gas tungsten arc welding (GTAW) process. The system consists of a projective torch held by a welder, and a sensory helmet on the welder’s head. The three-dimensional (3D) weld pool surface is effectively measured in real-time as the welder performs the weld despite the movements of the torch and the helmet. In this study, the sensing system is first analyzed by numerical simulations in which the adjustment boundaries of the torch and helmet, i.e. their translation and orientation ranges, for effective sensing have been determined. Then, the sensing system is further evaluated using a simulation platform in which the movements of the helmet/welder’s head is mimicked by a tripod head with 6 degree-of-freedom (DOF), and a convex spherical mirror with a comparable size of a typical weld pool in a GTAW process is applied as a weld pool substitute. The effectiveness of the proposed system is validated by successfully capturing laser reflections from the mirror without great constraints on the welder’s movements of the torch and the helmet. Based on the analysis of the spatial relations among the torch, the helmet and the weld pool, an innovative real-time algorithm is proposed to reconstruct the 3D weld pool surface. The effectiveness and robustness of the algorithm have been verified by accurately reconstructing the convex spherical mirror surface despite the movements of the torch and the helmet in the simulation platform.

Interval model control of human welder’s movement in machine-assisted manual GTAW torch operation

Torch maneuver skills possessed by a skilled welder typically require a long time to develop. A machine-assisted feedback control system that can stabilize the welder movement would thus be of interest in the manufacturing industry. In this paper, an interval model-based feedback control system is designed to assist the welder to adjust the torch movement for tracking desired speed in manual gas tungsten arc welding (GTAW) process. To this end, an innovative helmet-based manual welding platform is utilized. In this system, vibrators are installed on the helmet to generate vibration sounds to instruct the welder to speed up or slow down the torch movement. The torch movement is monitored by a leap motion sensor. The torch speed is used as the feedback for the control algorithm to determine how to change the vibrations. To design the control algorithm, dynamic experiments are conducted to correlate the arm movement (torch speed) to the vibration control signal. Linear models are first identified and the corresponding linear parameter intervals are obtained. Interval model control algorithm is then implemented. Simulation results reveal that the proposed interval model control algorithm outperforms traditional Proportion Integration Differentiation (PID) controller. Experiments further verified that the welder’s speed is controlled with acceptable accuracy.

Wear and tribocorrosion behaviour of 304L stainless steel welds

The influence of the microstructures of the base metal and weld metals on the wear and tribocorrosion properties of 304L stainless steel (SS) welds prepared by Manual Gas Tungsten Arc Welding (M-GTAW) and Activated Flux Gas Tungsten Arc Welding (A-GTAW) processes are reported. Increase in sliding speed increased both friction forces as well as wear rate. Higher hardness in M-GTAW weld metal resulted in increased wear resistance than A-GTAW weld metal and base metal. The inferior wear resistance of the base metal was due to the strain hardening behaviour under sliding condition. The polarization curves showed increase in passive current density under sliding condition. The applied potential was found to influence the tribocorrosion resistance of the material. Under tribocorrosion condition, the total material loss was higher in base metal followed by A-GTAW weld metal and M-GTAW weld metal. Characterization of worn surface by SEM indicated a mixed wear mechanism of abrasive and adhesive wear. The worn surface appeared relatively smoother in nitric acid medium than in dry condition. The influence of microstructure affecting the hardness, wear and tribocorrosion resistance of the base metal and weld metals of 304L SS is discussed.

EFFECT OF FILLER METALS ON THE MECHANICAL PROPERTIES OF DISSIMILAR WELDING OF STAINLESS STEEL 316L AND CARBON STEEL A516 GR 70

This paper describes an investigation on the effect of using three different filler metals to weld two dissimilar metals namely, stainless steel 316L and low alloy carbon steel A516 gr 70. Manual Gas Tungsten Arc welding (GTAW) with three filler metals including ER 80S-Ni1, ER309L, ER NiCrMo-3 were selected to weld the two metals. Radiography and penetrant tests were performed on the welded metals to ensure the surface and internal soundness of the welds based on the tensile tests results, all the specimens failed at the carbon steel A516 gr 70 base metals with fully ductile fracture mode (cup and cone). Welded samples using Inconel 615 filler metal has the highest strength of 512 MPa while other samples show almost similar strength of 481 and 487 MPa. The tensile strength of all the welded samples is found to be in between the tensile strength of the base metals. Micro-hardness test showed that ER80S-Ni1weld has the highest hardness, meanwhile hardness profile of ER309L presented a sharp drop in the stainless steel side and ER NiCrMo-3 weld metal illustrated hardness above the two base metals with fewer variations across the weld metal.

Machine assisted manual torch operation: system design, response modeling, and speed control

Skills possessed by human welders typically require a long time to develop. Especially, maintaining the torch to travel in desired speed is challenging. In this paper, a feedback control system is designed to assist the welder to adjust the torch movement for the desired speed in manual gas tungsten arc welding process. To this end, an innovative helmet based manual welding platform is proposed and developed. In this system, vibrators are installed on the helmet to generate vibration sounds to instruct the welder to speed or slow down the torch movement. The torch movement is monitored by a leap motion sensor. The torch speed is used as the feedback for the control algorithm to determine how to change the vibrations. To design the control algorithm, dynamic experiments are conducted to correlate the arm movement (torch speed) to the vibration control signal. Linear model is firstly identified using standard least squares method, and the model is analyzed. A nonlinear adaptive neuro-fuzzy inference system (ANFIS) model is then proposed to improve the model accuracy. The resultant nonlinear ANFIS model can estimate the welder’s response on the welding speed. Based on the response model, a PID control algorithm has been designed and implemented to control the welder arm movement for desired torch speed. Experiments verified the effectiveness of the system for the desired speed with acceptable accuracy.

Dynamic Neuro-Fuzzy-Based Human Intelligence Modeling and Control in GTAW

Human welder's experiences and skills are critical for producing quality welds in manual gas tungsten arc welding (GTAW) process. In this paper, a neuro-fuzzy-based human intelligence model is constructed and implemented as an intelligent controller in automated GTAW process to maintain a consistent desired full penetration. An innovative vision system is utilized to real-time measure the specular 3D weld pool surface under strong arc light interference. Experiments are designed to produce random changes in the welding speed and voltage resulting in fluctuations in the weld pool surface. Adaptive neuro-fuzzy inference system (ANFIS) is proposed to correlate the human welder's response to the 3D weld pool surface as characterized by its width, length and convexity. Closed-loop control experiments are conducted to verify the robustness of the proposed controller. It is found that the human intelligence model can adjust the current to robustly control the process to a desired penetration state despite different initial conditions and various disturbances. A foundation is thus established to explore the mechanism and transformation of human welder's intelligence into robotic welding systems.

Solidification structure in Ti–5Ta–1·8Nb weld

Solidification structure of a weld in a manual gas tungsten arc welding of 3 mm thick Ti–5Ta–1·8Nb plates has been examined using optical/scanning electron microscopy, EDX spectroscopy and electron backscattered diffraction techniques. The weld exhibited columnar grains of prior β, with a substructure of martensitic α′. The backscattered electron image revealed the solidification mode to be cellular–dendritic, and the EDX analysis confirmed the partitioning of Ta atoms between the dendrites. The crystal orientation of the product α′ obtained by electron backscattered diffraction and the Burgers orientation relationship (for β→α′ transformation) were used to predict the orientation of parent β grains in the weld zone, and the long dendritic arms were found to be aligned parallel to β<100>. Analytical solution based on Rosenthal equation was used to calculate the temperature cycle of the welding process. The solidification mode predicted from calculated G/R ratio (where G is solidification gradient and R is rate of solidification) and Kurz–Fischer map matched with the observed cellular–dendritic solidification structure.