Activated Gas Tungsten Arc Welding Research Articles

Comparative studies on weldability and mechanical characteristics of semi- killed steel using different arc welding technique

The main objective of this study is to examine the weldability and mechanical properties of semi-killed steel of E250BR grade which is mostly used in gear box casing. Three different arc welding methods i) GMAW (Gas Metal Arc Welding) ii) GTAW (Gas Tungsten Arc Welding), and iii) A-GTAW (Activated Gas Tungsten Arc Welding) were employed in this study, and the respective weld joints mechanical properties were evaluated and compared with each other. Visual inspection of the specimens shows that the GTAW and A-GTAW processes offer excellent weld bead geometry. Visual and radiographic inspections showed no crack or discontinuity is in the weld joints. The weldment produced by A-TIG welding has the highest aspect ratio, which is due to the reverse Marangoni convection effect. The tensile and hardness test outcomes exhibited that the mechanical properties of the parent metal were not affected by the welding processes, but impact test results showed a lack of energy absorption by the specimen from the A-GTAW process. A-GTAW welding had the highest Ultimate Tensile strength, which was 2.5 percent to 5 percent higher than the other processes employed in this study. Weldments fabricated using GTAW welding have the highest impact toughness, which is 43.5 percent and 51.85 percent more than the other two processes. Vickers hardness test reveals that joints made with the GTAW process are better than the other counter parts.

Modeling and optimization of A-GTAW process using Box–Behnken design and hybrid BPNN-PSO approach

Gas tungsten arc welding (GTAW) is the most extensively used process capable of fabricating a wide range of alloys based on its distinctive merits has been introduced. However, some demerits have been reported among which shallow penetration is the most crucial ones. In order to deal with the poor penetration of the process, different procedures have been proposed among which activated gas tungsten arc welding (A-GTAW) is the most extensively used one. In this study effect of percentage of activating fluxes (TiO2 and SiO2) combination (F) and the most important process variables (welding current (C), welding speed (S)) on the most important process measures (weld bead width (WBW), depth of penetration (DOP), and consequently aspect ratio (ASR)) in welding of AISI316L austenite stainless steel parts have been investigated. Box-behnken design (BBD) has been used to design the experimental matrix required for date gathering, modeling, and statistical analysis purposes. A neural network with a back propagation algorithm (BPNN) in artificial neural network (ANN) modeling approach has been employed to relate the process input variables and output characteristics. The proper BPNN architecture (number of hidden layers and neurons/nodes in each hidden layer) has been determined using particle swarm optimization (PSO) algorithm. Moreover, process optimization in such a way that maximum DOP, minimum WBW, and desired ASR achieved has been carried out using PSO algorithm. Next, the performance of PSO algorithm has been checked using simulated annealing (SA) algorithm. Finally, to evaluate the performance of the proposed method a set of confirmation experimental test has been conducted. Results of experimental tests revealed that the proposed method is quite efficient in modeling and optimization (with less than 4% error) of A-GTAW process.

Comparisons of Different Oxide Fluxes in Activated Gas Tungsten Arc Welding of Duplex Stainless Steels for Improved Depth of Penetration and Pitting Corrosion Resistance

ABSTRACT The present work analyses the effect of five types of oxide fluxes – SiO2, TiO2, CrO3, MnO2 and MoO3 – on the depth of penetration and pitting corrosion behaviour of UNS S32205 duplex stainless steel produced with the activated tungsten inert gas welding (A-TIG) process. Five bead-on-plate (BoP) weld samples prepared autogenously with constant weld parameters. Depth of penetration (DP), depth-to-width (D/W) ratio and weld bead width (BW) were measured and compared with reference to the weld thermal cycle. The test results of ferrite measurement and micro-hardness were compared with normal – without flux added TIG-welded sample. Macro analysis of all samples indicates that SiO2 and TiO2 flux offer enhanced penetration depth and D/W ratio, in contrast, to use of other fluxes. Possibly, under the effect of either reversed Marangoni or arc constriction or both, however, all TIG BoP weld samples exhibited poor pitting corrosion resistance. Enhanced heat input due to flux and thus resultant unbalanced ferrite austenite proportion affected pitting corrosion resistance. ASTM A 923 microstructures did not show any presence of nitride formation. Results of energy-dispersive X-ray spectroscopy and scanning electron microscopy analysis of corrosion pits showed no abnormality with the chemistry of standard 2205 DSS.

Microstructure and Mechanical Properties Relationship of Friction Stir- and A-GTA-Welded 9Cr-1Mo to 2.25Cr-1Mo Steel

Dissimilar weldment of 9Cr-1Mo (P9) to 2.25Cr-1Mo (P22) steel processed with fusion welding process must be subjected to post-weld heat treatment (PWHT) prior to operation due to the presence of martensitic microstructure in the weld. However, due to the gradient of carbon activity, PWHT results in the diffusion of carbon from low Cr to high Cr side, which results in a soft zone and hard zone formation in the weld. This would degrade the mechanical properties of the weld joint. In order to tackle this, the present study employed friction stir welding (FSW) process at two different rotational speeds via 200 and 500 rpm. The microstructure and mechanical properties of the FSW specimens were compared with that of activated-gas tungsten arc (A-GTA) weldments. Regardless of the tool speed, the FSW and A-GTA processed specimens indicated martensitic microstructure in the weldment, and hence, PWHT was carried out. The PWHT treated FSW specimen revealed soft and hard zone evolution throughout the weld matrix, whereas in A-GTA welds, no severe diffusional phenomenon was observed across the weld. The A-GTA weld joint exhibited better strength properties than that of the weld joint made by FSW process, and therefore, A-GTA welding can be suitable techniques for welding of P9–P22 steel.

Effect of friction stir and activated-GTA welding processes on the 9Cr–1Mo steel to 316LN stainless steel dissimilar weld joints

ABSTRACTThe consequence of friction stir welding (FSW) and activated-gas tungsten arc welding (A-GTAW) processes on the evolution of microstructure and mechanical properties of 9Cr–1Mo (P9) steel to 316LN stainless steel dissimilar weld joint is investigated. The FSW specimen shows considerably higher tensile strength (∼652 MPa) compared to A-GTAW specimen (∼595 MPa) as well as its base metal of P9 (∼642 MPa) and 316LN (∼608 MPa) owing to the formation of tempered martensite and refined austenite in P9 and 316LN weld portion, respectively. The cross-weld tensile test revealed that the specimens failed in the base metal of 316LN SS for both FSW and A-GTAW process with ductile mode fracture. This study proves that FSW could be an alternate joining technique.

Effect of Welding Process on Microstructure, Mechanical and Pitting Corrosion Behaviour of 2205 Duplex Stainless Steel Welds

An attempt has been made to weld 2205 Duplex stainless steel of 6mm thick plate using conventional gas tungsten arc welding (GTAW) and activated gas tungsten arc welding (A- GTAW) process using silica powder as activated flux. Present work is aimed at studying the effect of welding process on depth of penetration, width of weld zone of 2205 duplex stainless steel. It also aims to observe the microstructural changes and its effect on mechanical properties and pitting corrosion resistance of 2205 duplex stainless steel welds. Metallography is done to observe the microstructural changes of the welds using image analyzer attached to the optical microscopy. Hardness studies, tensile and ductility bend tests were evaluated for mechanical properties. Potentio-dynamic polarization studies were carried out using a basic GillAC electro-chemical system in 3.5% NaCl solution to observe the pitting corrosion behaviour. Results of the present investigation established that increased depth of penetration and reduction of weld width in a single pass by activated GTAW with the application of SiO2 flux was observed when compared with conventional GTAW process. It may be attributed to the arc constriction effect. Microstructure of the weld zones for both the welds is observed to be having combination of austenite and delta ferrite. Grain boundary austenite (GBA) with Widmanstatten-type austenite (WA) of plate-like feature was nucleated from the grain boundaries in the weld zone of A-GTAW process. Mechanical properties are relatively low in activated GTAW process and are attributed to changes in microstructural morphology of austenite. Improved pitting corrosion resistance was observed for the welds made with A-GTAW process.

Numerical simulation and experimental validation of arc welding of DMR-249A steel

Abstract The thermo-mechanical attributes of DMR-249A steel weld joints manufactured by shielded metal arc welding (SMAW) and activated gas tungsten arc welding (A-GTAW) processes were studied using Finite Element Model (FEM) simulation. The thermal gradients and residual stresses were analyzed with SYSWELD software using double ellipsoidal heat source distribution model. The numerically estimated temperature distribution was validated with online temperature measurements using thermocouples. The predicted residual stresses profile across the weld joints was compared with the values experimentally measured using non-destructive techniques. The measured and predicted thermal cycles and residual stress profile was observed to be comparable. The residual stress developed in double sided A-GTAW joint were marginally higher in comparison to five pass SMAW joint due to phase transformation associated with high heat input per weld pass for A-GTAW process. The present investigations suggest the applicability of numerical modeling as an effective approach for predicting the thermo-mechanical properties influenced by welding techniques for DMR-249A steel weld joints. The tensile, impact and micro-hardness tests were carried to compare the welds. Considering benefits of high productivity and savings of labor and cost associated with A-GTAW compared to SMAW process, the minor variation in residual stress build up of A-GTAW joint can be neglected to develop A-GTAW as qualified alternative welding technique for DMR-249A steel.