Hot Wire Gas Tungsten Arc Welding Research Articles

Experimental and numerical study on the distribution of temperature field and residual stress in a multi-pass welded tube joint of Inconel 617 alloy

The purpose of this study is to compare the residual stress generation during hot wire gas tungsten arc welding (HW-GTAW) welding and conventional gas tungsten arc welding (GTAW) in a multi-pass pipe weld of a nickel-based superalloy. HW-GTAW yields better mechanical properties at low heat input than conventional GTAW, and decreases the accumulation of residual stress significantly. The distribution of residual stress developed in the through-thickness direction is determined experimentally using the Deep hole drilling method. As a result of the analysis, it was observed that the highest residual stress arises in Fusion Zone (FZ) and Heat Affected Zone (HAZ). In the case of conventional GTAW the hoop stress was observed to be tensile and distributed over 70% of the weld whereas only 20% of the weld is found to be under tensile hoop stress in the case of HW-GTAW along the weld center. The results show that shrinkage at the weld HAZ region affects the stresses produced at the cylinder's outer surface. The bending effect created during the welding process is primarily responsible for the distribution of residual stresses in the weld zone. A comprehensive numerical analysis has been carried out using ABAQUS software to predict the level of thermal and residual stresses in the weld zone, FZ, and HAZ in the case of both welding process. A 2D finite element models have been developed to simulate the welding process using the ABAQUS FE tool based on coupled thermal-mechanical analysis. A double ellipsoidal heat source model has been developed using a DFLUX subroutine file to simulate the welding process during the numerical analysis. The predicted residual stresses were validated with the experimentally obtained results.

Effect of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by narrow gap hot wire gas tungsten arc welding process

Hot wire Gas Tungsten Arc Welding (GTAW) process is selected for fabrication of thick section modified 9Cr 1Mo steel components of Steam Generators (SGs) for 500MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, India. During the welding procedure qualification for fabrication of SGs, the 30 mm and 62 mm thick modified 9Cr 1Mo steel welds were subjected to chemical analysis, visual examination, liquid penetrant examination, radiography examination, micro-hardness tests, longitudinal and transverse tensile tests (at ambient temperature and 525 °C), bend tests, drop weight tests and impact tests (at 0 °C and +18 °C). Literature reveals both positive and negative view on the welding of thick section steel components. Limited information is available in open literature on the effect of thickness on material properties of modified 9Cr 1Mo steel welds made by hot wire GTAW method. In view of the above, authors attempted to systematically investigate the influence of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by hot wire GTAW process. In this paper, the chemical compositions, hardness, tensile strength, bending strength and impact properties of 30 mm and 62 mm thick welds produced by narrow gap hot wire GTAW process are characterized and compared. It is found that the mechanical properties of 30 mm and 62 mm thick welds are comparable except the impact properties at 0 °C. The impact strength at 0 °C for 62 mm thick weld was found inferior in comparison with 30 mm thick weld.

Developments and Improvements Using Hot Wire Gas Tungsten Arc Welding – A Review

Gas tungsten arc welding (GTAW) is a high quality welding process widely used in most industries. However, the process is limited to higher welding speed and higher deposition rate. To overcome this limitation, the GTAW process is modified in such a way that filler metal is heated prior to entering into the weld pool. This heating is carried out by resistance heating. Hot wire GTAW (HW-GTAW) ensures the availability of arc energy to melt the base metal. This results in an increase in deposition rate and additionally, increases the welding speeds to a large extent. Welding is an important form of joining materials and is most significant for the application of structural components. This paper reviews the application of the hot wire technique during conventional GTA welding, thereby providing the benefits in terms of metallurgical control, energy efficiency and rate of deposition. This process has the potential to achieve high efficiency and welding faster with lower heat input. The HW-GTAW process is widely used in welding various novel materials and it is a promising alternative to the conventional GTAW process with lower heat input and narrower heat affected zones. This process not only eliminates the various defects in the weld joints but also increases productivity in industries.

Impact properties of modified 9Cr 1Mo steel welds: Comparison between cold wire and hot wire gas tungsten arc welding processes

Modified 9Cr 1Mo steel is used for the manufacture of Steam Generators (SG) for Prototype Fast Breeder Reactor at Kalpakkam, India. The hot wire Gas Tungsten Arc Welding (GTAW) process was selected for the manufacture of SGs wherever feasible in addition to the conventional cold wire GTAW process due to various advantages. Drop weight tests on modified 9Cr 1Mo steel welds produced by hot wire and cold wire GTAW processes were carried out in accordance with ASTM E208. It is found that the Nil Ductility Transition (NDT) behavior of the hot wire and cold wire GTA welds were similar during drop weight tests performed up to −10 °C. Subsequently, Charpy V notch impact tests were carried out at +18 °C and 0 °C in accordance with ASME Boiler and Pressure Vessel Code. The impact strength at 0 °C of welds produced by cold wire GTAW process was found to be superior compared to the welds of hot wire GTAW process. Subsequently, the analysis of impact strength was carried out using a two-sided students t-test. With a 95% confidence level, the results of the t-test revealed that there is a genuine difference in impact strength at 0 °C between the welds of hot wire and cold wire GTAW processes.

Microstructure and Fracture Performance of Wire Arc Additively Manufactured Inconel 625 Alloy by Hot-Wire GTAW

In this work, an Inconel 625 thin-wall structure was fabricated by the gas tungsten arc welding (GTAW) hot-wire arc additive manufacturing process. The microstructure and mechanical properties of the Inconel 625 samples, extracted from different orientations and locations of the thin-wall structure, were investigated and compared. The results showed that the additively manufactured Inconel 625 component, made by hot-wire GTAW, had good quality. Its microstructure consisted of dendrites, equiaxial crystals, and cellular crystals. The average hardness from the bottom to the top was similar, indicating that the thin wall had good consistency. The plasticity in the deposition direction was better than those in the other three regions, which was related to the dendritic structure in the sedimentary direction.

The Toughness of High-Strength Steel Weld Metals

Low-temperature phase transformation (LTPT) welding consumables are a new class of welding wires developed to mitigate hydrogen-induced cracking in the welding of high-strength steels without preheating or postweld heat treatment. LTPT weld metals have a high strength, but their toughness needs further investigation. LTPT weld metals predominately contain a martensite microstructure, which is necessary to achieve high strength; however, martensitic weld metals containing oxide inclusions have relatively poor toughness. Three welding processes — gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and hot wire GTAW — were investigated. Optical microscopy, scanning electron microscopes, and transmission electron microscopes were employed for characterization. The role of the shielding gas in the formation of oxide inclusions in LTPT weld metals was investigated. The formation of oxide inclusions in the weld metals was related to the CO2 in the shielding gas. When 100% Ar or a pure inert shielding gas mixture was used for all three welding processes, oxide inclusions were greatly reduced, and the weld metal toughness improved considerably, matching the base metal toughness. The mechanism by which inclusions promote fracture propagation in the weld metal was proposed.

Prediction of distortions and residual stresses in narrow gap weld joints prepared by hot wire GTAW and its validation with experiments

The present paper aims to predict distortions and residual stresses in thick plate weld joints of austenitic stainless steel material prepared by automatic hot wire gas tungsten arc welding (GTAW) process and narrow gap technique using finite element analysis (FEA). The prediction has been validated by carrying out experiments. The variables considered in welding of plate joints are narrow groove configuration, high deposition rate leading to lower heat input (hot wire GTAW), and stress relieving treatment. A suitable stress-relieving treatment has been proposed for relaxing residual stresses and preventing sensitization of the heat-affected zone (HAZ) of the ASS weld joint. Predicted and experimental results of temperature distribution, distortions, and residual stresses were found to be in good agreement. The applicability of prediction of residual stresses for higher weld thicknesses has also been verified. The nature of residual stresses across thickness has also been compared with that given in Structural Integrity Assessment Procedures for European Industry (SINTAP) and BS 7910 standards. Details of the above finding are discussed in this paper.

Microstructural characterization of the transition zone between a C–Mn steel pipe and a 70%Ni30%Cu alloy cladding welded by HW-GTAW

Offshore seawater systems are commonly manufactured using a monolithic copper–nickel alloy (90%Cu10%Ni). However, because of the high cost of this material, they have been replaced in some Brazilian oil and gas platforms by C–Mn steel pipes clad with a Ni–Cu alloy (70%Ni30%Cu, Monel 400®). Therefore, considering the complex transition zone (TZ) in dissimilar weldments and its influence on the performance of the clad component, the present work aims to characterize the TZ of an API 5L X65 steel pipe clad with a 70%Ni30%Cu alloy by hot-wire gas tungsten arc welding (HW-GTAW). The TZ was evaluated using optical microscopy, scanning electron microscopy, electron backscatter diffraction, Vickers microhardness measurements, and bending tests. It exhibited beach, peninsula, and island macrosegregation morphologies with martensite (high hardness) and type II grain boundaries as well as an abrupt chemical composition gradient and Zone M. Moreover, the cladding solidified epitaxially, even though the cladding and the substrate had different crystal lattices. A solidification grain boundary crack, observed in the pipe end, nucleated in the substrate and propagated through the beach macrosegregation and posteriorly along the cladding grain boundaries. Despite this crack, the API 5L X65 steel pipe clad with 70%Ni30%Cu was approved according to ISO 15614 Part 7 and is a potential candidate for seawater systems.

Assessment of Microstructure and Tensile Behavior of Hot Wire Gas Tungsten Arc Welded Pure Nickel Tubes

The interest in hot wire gas tungsten arc welding (HWGTAW) process is increasing in industrial sector in the current decade. Pure nickel (Ni 200) tubes having 4-mm-thickness and 44-mm-outer diameter were effectively joined by HWGTAW. The heating current of the filler wire was varied from 80 amps to 120 amps in steps of 10 amps. The joint microstructure was recorded using conventional optical microscope and advanced transmission electron microscope. Electron backscatter diffraction was applied to visualize the grain structure and orientation. The increase in heating current enlarged the fusion zone geometry and caused coarsening of grains. There were no cracks or pores present in the joints. Three kinds of microstructure zones were observed across the joints. Few dislocations were formed in the fusion zone which recorded the lowest hardness. All joints demonstrated excellent ductility. The joint fabricated using a heating current of 100 amps showed highest tensile strength.

Predicting the tensile strength and deducing the role of processing conditions of hot wire gas tungsten arc welded pure nickel tubes using an empirical relationship

There is a renewed interest to utilize the advantages of hot wire gas tungsten arc welding (HWGTAW) process in industrial area. This manuscript reports HWGTAW of pure nickel tubes of 4 mm thickness. Design of experiment (DoE) approach was adopted to bring down the number of the joints. Welding plan was executed according to 3 factors, 5 levels central composite design (CCD). Electrode current, wire feed rate and hot wire current were considered as process parameters and varied in 5 levels. DoE approach allowed to develop an empirical relationship which was used to predict the role of process parameters on the tensile strength of joints within the chosen range. The predicted trends were correlated to the observed macrostructure and microstructure. The joint strength varied due to changes in fusion zone grain size and macroscopic level defects such as lack of penetration, incomplete fusion and lack of coalescence.

Characterization of the interpass microstructure in low alloy steel/Alloy 625 HW-GTAW narrow groove welds

A dissimilar weld between a low alloy steel (LAS) butter weld joined to a F65 steel pipe using a narrow groove hot wire gas tungsten arc welding (HW-GTAW) procedure with Alloy 625 filler metal was investigated. The weld interpass microstructure is comprised of large swirls formed by a macrosegregation mechanism involving partial, non-uniform mixing of liquid base metal with the lower melting temperature weld pool, followed by fast solidification. This mechanism produces steep gradients in composition and solidification behavior. The resulting swirls are composed of alternating iron-rich peninsulas and partially mixed zones (PMXZ) that are surrounded by planar and cellular zones exhibiting multiple solidification directions. Large austenitic grains, encompassing planar, cellular, and dendritic morphologies, nucleate off peninsulas in direct contact with the weld pool. The highest hardness was found in nickel and chromium rich PMXZs that exhibited a lath martensite microstructure. In the event of exposure to hydrogen containing environments, the PMXZs could serve as nucleation sites for hydrogen assisted cracking.

Assessment of Impact Strength of Welds Produced by Cold Wire and Hot Wire Gas Tungsten Arc Welding (GTAW) Processes

Modified 9Cr 1Mo material is used as principal material of construction of Steam Generators (SG) for 500MWe Prototype Fast Breeder Nuclear Reactor (PFBR), at Kalpakkam, India. One of the major problems associated with welding of modified 9Cr 1Mo steel is poor impact strength of weld metal produced from the processes that involves the use of flux. Due to this reason, 100% Gas Tungsten Arc Welding (GTAW) process is chosen for fabrication of PFBR Steam Generators.The major limitation of conventional cold wire GTAW process is low deposition rate which makes it highly uneconomical especially for welding component with large section thickness. Therefore, hot wire GTAW process is selected for welding of PFBR Steam Generators wherever possible in addition to the conventional cold wire GTAW process. The impact properties of modified 9Cr 1Mo welds produced by hot wire GTAW process are compared with impact properties of cold wire GTAW welds. The impact strength of welds produced by hot wire GTAW process is found to be inferior compared to that of welds produced by cold wire GTAW process. Nevertheless, hot wire GTAW system has the benefit of high weld deposition rate with excellent profile of weld with reduced dilution and porosities

Hot-wire GTAW cladding: inconel 625 on 347 stainless steel

Gas tungsten arc (GTA) cladding has been widely applied in surface modification and repairing. In this study, low current gas tungsten arc welding (GTAW) cladding in the range of 60 to 100 A was performed with resistively heating hot-wire filler Inconel alloy (IN625) on the 347 stainless steel substrate. A 70 A or more primary current can be used to clad a continuous and uniform layer on the substrate by resistively heating the wire and varying the torch angle. Lower dilution and higher contact angle were observed for lower current clad. An analytical model has been used to understand the resistively heating hot-wire effect. The microstructure of the clad bead and the substrate was analyzed. A heat-affected zone (HAZ) cracking was observed in the higher range of primary current. An EDX analysis was performed to reveal iron (Fe) elemental dilution and elemental segregation.

Results of tensile, hardness and bend tests of modified 9Cr 1Mo steel welds: Comparison between cold wire and hot wire gas tungsten arc welding (GTAW) processes

Hot wire Gas Tungsten Arc Welding (GTAW) process is considered in addition to conventional cold wire GTAW process for the manufacture of Steam Generators (SG) for India's Prototype Fast Breeder Reactor (PFBR). During manufacture, it is an obligatory requirement to weld one test coupon for every 20 m of weld length on the actual SG for ascertaining the properties during fabrication. Weld pads thus prepared were used for characterization of hardness, bend and tensile properties of modified 9Cr 1Mo steel welds produced by hot wire and cold wire GTAW processes and the test results were compared. The results revealed that hardness, bend and tensile properties of modified 9Cr 1Mo steel welds of hot wire and cold wire GTAW processes are similar and no genuine difference exist between these two welding processes. Further, the advantage of high quality with excellent weld profile and high productivity has been realized using hot wire GTAW process.

Comparative study of microstructure and properties of low-alloy-steel/nickel-based-alloy interfaces in dissimilar metal weld joints prepared by different GTAW methods

Low-alloy-steel/buttering (or welding) metal interfaces in safe-end dissimilar metal weld joints (DMWJs) at nuclear power plants are weak parts. To optimize the quality of the safe-end DMWJs used for the construction of domestic nuclear power plants and to improve the welding productivity, a series of DMWJs in full-size have been manufactured by using different gas tungsten arc welding (GTAW) methods. The microstructure, chemical composition distribution and local properties across the SA508/52(M) interfaces in these DMWJs are studied. The high heat input and long high temperature duration during hot-wire GTAW process promote the carbon diffusion and grain boundary migration and hence the DMWJ by hot-wire GTAW has the largest amount of type I and type II boundaries and the widest carbon depleted zones and carbon enriched zones, which resulting in the worst performance among the DMWJs in simulated primary water. Type I and type II boundaries are high angle random grain boundaries (RGBs) and Cr-depleted zones are found along type II boundaries resulting in their high susceptibility to SCC. In addition, these boundaries are prone to be cracked during mechanical bending process.

Design of Special Purpose Machine for TIG Welding of Circumferential Seam of Motor Body

Gas Tungsten Arc Welding (GTAW) offers high quality weld deposit that becomes suitable for higher alloy contents with low rate of deposition. Hot wire GTAW is a further development of the GTAW process which is used in industries that need high quality welding with high productivity. It is essential to have an automated welding machine in pump industries to increase productivity and quality which can also make the work easier for a welder. GTAW welding with hot wire for circumferential seam welding of motor body is a major development for pump industries which is required for good quality welding and mass production of the pump motor body. So it has been planned and designed a Special Purpose Welding Machine for Circumferential Seam Welding of Motor Body which will be a major challenge for all pump industries with latest technologies at low cost with respect to the current market scenario and also the customer requirements by analyzing and implementing their needs.

Design of Special Purpose Machine for TIG Welding of Circumferential Seam of Motor Body

Gas Tungsten Arc Welding (GTAW) offers high quality weld deposit that becomes suitable for higher alloy contents with low rate of deposition. Hot wire GTAW is a further development of the GTAW process which is used in industries that need high quality welding with high productivity. It is essential to have an automated welding machine in pump industries to increase productivity and quality which can also make the work easier for a welder. GTAW welding with hot wire for circumferential seam welding of motor body is a major development for pump industries which is required for good quality welding and mass production of the pump motor body. So it has been planned and designed a Special Purpose Welding Machine for Circumferential Seam Welding of Motor Body which will be a major challenge for all pump industries with latest technologies at low cost with respect to the current market scenario and also the customer requirements by analyzing and implementing their needs.

On the effect of temperature coefficient of surface tension on shape and geometry of weld beads in hot wire gas tungsten arc welding process

S304HCu stainless steel is inevitable materials in super heater and reheater tubes in steam power boiler industries. The major challenge in welding of T92 steel and S304HCu stainless steel is the selection of the appropriate filler wire and establishing welding procedures especially in dissimilar welding such that the weld joints meet the service requirements at high temperatures. This present work is aimed to study the effect of welding current and wire feed rate on weld bead geometry produced with hot wire gas tungsten arc welding (HW-GTAW) process using different filler wires of 0.8mm diameter viz., ERNiCrFe-7A (IN 52M) and ERNiCrCoMo-1 (IN 617) on S304HCu stainless steel tubes. These weld bead depositions were made at hot wire current of 30A with two different welding currents viz., 130A and 110A at a constant wire feed rate and travel speed. From the results, it is established that temperature distribution and the presence of surface active elements are the causes for the formation of weld beads in different shapes.

Effect of vibration and hot-wire gas tungsten arc (GTA) on the geometric shape

Bead-on-plate experiments were carried out, and the weld-bead size and shape were compared and discussed. The welding droplet parameters were measured by a high-speed camera. A computation fluid dynamics (CFD) model utilizing VOF (volume of fluid) method, incorporating the experimental droplet parameters has been developed to understand the weld pool dynamics and subsequent weld pool geometry. From the experimental results, a narrower and deeper penetration was observed with hot-wire while wider and shallow penetration was observed with cold wire gas tungsten arc welding (GTAW). The developed model has been applied to predict and analyze the mechanism for narrower and deeper penetration. A modified relationship has been established for droplet detachment in hot wire GTAW.

A Study on Process Characteristics and Performance of Hot Wire Gas Tungsten Arc Welding Process for High Temperature Materials

Hot wire gas tungsten arc welding (HW-GTAW) process is the one where the filler wire is pre-heated close to its melting point before it is fed in to the arc. The effect of HW-GTAW parameters such as welding current, hot wire current and the wire feed rate during welding of super ASS 304H stainless steel tubes were evaluated in terms of heat input, voltage-current (V-I) characteristics and weld bead characteristics such as bead weight and geometry. The results obtained indicate that for a constant welding current, increasing the hot wire current and wire feed rate provides a stable V-I characteristics and higher bead weight. Further, increasing the hot wire current and wire feed rate also provides better or desired weld pool and hence the bead geometry was described in terms of width, penetration depth, area of fusion and toe angle. By utilising the above knowledge, the tube to tube butt welding of SS 304H material was carried out. It was observed that, the weld joint is qualified as per the quality requirement of ASME: Sec IX standard.