Multi-pass Gas Tungsten Arc Research Articles

Autogenous Tungsten Inert Gas and Gas Tungsten Arc With Filler Welding of Dissimilar P91 and P92 Steels

Creep strength ferritic/martensitic modified 9Cr-1Mo-V-Nb (P91) steel also designated as ASTM A335 and P92 steel are used for piping, cladding, ducts, wrappers, and the pressure vessel in Gen IV nuclear reactors. In the present investigation, a comparative study of the effect of autogenous tungsten inert gas welding (A-TIG) with double pass and multipass gas tungsten arc (GTA) welding with filler on microstructure evolution in the weld fusion zone and the mechanical properties of P91 and P92 steel welded joints was carried out. The microstructure evolution was studied in as-welded and postweld heat treatment (PWHT) condition. The study also focused on the evolution of δ-ferrite patches and their influence on the tensile properties of welded joints. PWHT was carried out at 760 °C with durations from 2 to 6 h. To study the effect of δ-ferrite evolution on mechanical properties, Charpy toughness, microhardness, and tensile tests were performed. The acceptable microstructure and mechanical properties were obtained after the 6 h of PWHT for A-TIG arc welding process while for GTA weld with filler wire, it was obtained after the 2 h of PWHT at 760 °C.

A through-process, thermomechanical model for predicting welding-induced microstructure evolution and post-weld high-temperature fatigue response

This paper is concerned with the development of a modelling framework to predict the effects of welding and post-weld heat treatment on thermo-mechanical performance of welded material, as a step towards a design tool for industry. A dislocation mechanics, through-process finite element model, incorporating thermal, microstructural and mechanical effects is presented, for predicting thermo-mechanical fatigue of welds. The model is applied to multi-pass gas tungsten arc welding of 9Cr martensitic steel. The predicted high-temperature low-cycle fatigue performance of cross-weld samples is comparatively assessed for a range of different post-weld heat treatment durations. It is shown that longer post-weld heat-treatment (PWHT) durations increase the predicted number of cycles to failure and that Vickers hardness gradient across the heat-affected zone can be used as an indicator of fatigue life.

Effect of welding process and PWHT on δ-ferrite evolution in dissimilar P91 and P92 steel joint

Ferritic/martensitic 9Cr-1Mo-V-Nb (P91) and 9Cr-0.5Mo-1.8W-V-Nb (P92) steel are used for high temperature (600-650°C) operating components in nuclear and thermal power plants. The present research work deals with the dissimilar joining of P91 and P92 steel using autogenous tungsten inert gas (TIG) welding and multi-pass gas tungsten arc welding (GTAW) with filler. The evolution of δ-ferrite patches in weld fusion zone and heat affected zones (HAZs) were characterized in as-welded and post weld heat treatment (PWHT) condition. PWHT was carried out at 760 °C for 2 h and 6 h, for both autogenous-TIG and GTA weld joints. Charpy toughness and microhardness tests were performed for autogenous-TIG welding and GTA welding process under as-welded and PWHT condition.

A brief study on δ-ferrite evolution in dissimilar P91 and P92 steel weld joint and their effect on mechanical properties

Ferritic/martensitic 9Cr-1Mo-V-Nb steel also designated as ASTM A335 used in construction of several components of power plants operating in temperature range of 600–650°C. In present investigation, dissimilar weld joint of P91 and P92 steel were prepared using the autogenous tungsten inert gas (A-TIG) welding and multi-pass gas tungsten arc welding (GTAW) process. A comparative study was performed on evolution of δ-ferrite patches in weld fusion zone and heat affected zones (HAZs) of welded joints. The evolution of δ-ferrite patches was studied in as-welded and post-weld heat treatment (PWHT) condition. PWHT was carried out at 760°C for tempering time of 2h and 6h, for both A-TIG and GTA weld joints. It was observed that presence of higher content of ferrite stabilizer in P92 steel promote the formation of δ-ferrite patches in weld fusion zone as well as HAZs. To study the effect of welding process and PWHT, Charpy V impact energy and microhardness tests were performed. For microstructure characterization, field-emission scanning electron microscope (FESEM) and optical microscope were utilized.

Comparative study of autogenous tungsten inert gas welding and tungsten arc welding with filler wire for dissimilar P91 and P92 steel weld joint

Creep strength enhanced ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel is also designated as ASTM A335 used for out-of-core and in-core (piping, cladding, ducts, wrappers, and pressure vessel) of Gen IV reactors. In present investigation, the dissimilar weld joint of P91 and P92 steel were made using the autogenous tungsten inert gas (TIG) welding with single pass, double side pass and multi-pass gas tungsten arc (GTA) welding with filler wire. Microstructure evolution in sub-zones and mechanical properties of dissimilar welded joints were studied in as-welded and post weld heat treatment (PWHT) condition. Formation of δ-ferrite patches in weld fusion zone and heat affected zones (HAZs) and their influence on the mechanical behaviour of the welded joints were also studied. Presence of higher content of ferrite stabilizer in P92 steel have resulted the formation of δ-ferrite patches in weld fusion zone as well as HAZs. The δ-ferrite was observed in autogenous TIG welds joints. The δ-ferrite patches were formed in as-welded condition and remained in the microstructure after the PWHT. The δ-ferrite patches leads to reduction in Charpy toughness of autogenous TIG welds joint and also lower down the average hardness of weld fusion zone. Peak hardness and poor impact toughness were observed for autogenous TIG welds joint as compared to GTA welds. For microstructure characterization, field-emission scanning electron microscope (FESEM) with energy dispersive spectroscopy (EDS) and optical microscope were utilized.

Dissimilar joining of CSEF steels using autogenous tungsten-inert gas welding and gas tungsten arc welding and their effect on δ-ferrite evolution and mechanical properties

Ferritic/martensitic 9Cr-1Mo-V-Nb steel also designated as ASTM A335 used in construction of several components of power plants operating in temperature range of 600–650°C. In present investigation, dissimilar weld joints of P91 and P92 steel were prepared using the autogenous tungsten inert gas welding (A-TIG) and multi-pass gas tungsten arc (GTA) welding process. A comparative was performed on evolution of δ-ferrite patches in weld fusion zone and heat affected zone (HAZ) of welded joints. The evolution of δ-ferrite patches was carried out in as-welded and post-weld heat treatment (PWHT) condition. PWHT was carried out at 760°C for 2h for both A-TIG and GTA welding process. For A-TIG weld joint higher yield strength, ultimate tensile strength (UTS) and peak hardness were measured due to higher heat input in single pass and higher carbon content in weld fusion zone. Higher heat input, fast cooling rate and higher weight percentage of ferrite stabilizer like vanadium (V) and niobium (Nb) in A-TIG weld joint were resulted in formation ferrite patches in weld fusion zone and heat affected zone. Higher weight percentage of V and Nb in A-TIG weld zone was resulted poor impact toughness of A-TIG weld fusion zone than GTA welds in as-welded condition. After the PWHT at 760°C–2h, Charpy toughness of A-TIG weld fusion zone (48J) just meet the minimum required value as required by the EN: 1557:1997 (47J).

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.

Investigation on the multi-pass gas tungsten arc welded Bi-metallic combination between nickel-based superalloy and Ti-stabilized austenitic stainless steel

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Effect of fillers on the microstructure, mechanical properties, and hot corrosion behavior of Nb stabilized austenitic stainless steel welds

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Monte Carlo simulation and experimental measurements of grain growth in the heat affected zone of 304 stainless steel during multipass welding

Grain growth in the weld heat-affected zone (HAZ) of multipass welds in 304 stainless steel was studied experimentally and theoretically. A finite element heat flow model was developed and calibrated using experimental temperature data collected during multipass gas tungsten arc welding. Output from the heat flow model was used to provide temperature data as an input to a Monte Carlo (MC) HAZ grain growth model and simulation adapted to multipass welds. The grain growth, grain size, and distribution in the HAZ predicted by the MC model were consistent with metallographic measurements of grains in the HAZ. Grains near the fusion boundary grew two to three times the size of grains in the unaffected base material. The MC model was then used to investigate the influence of initial base material temperature and interpass temperature on HAZ grain growth. As initial temperature increased, the width of the fusion zone in the first pass increased and the width of and grain size in the HAZ near the first pass increased. As interpass temperature increased, the width of the fusion zone and the width of and grain size in the HAZ increases after the first pass increased.

Investigations on the microstructure and mechanical properties of multi-pass pulsed current gas tungsten arc weldments of Monel 400 and Hastelloy C276

This research article reported the weldability, microstructure and mechanical properties of the dissimilar combinations of nickel alloys such as Monel 400 and Hastelloy C276. Multi-pass pulsed current gas tungsten arc (PCGTA) welding was employed for joining these dissimilar metals using ERNiCrMo-3 filler. Interface microstructures showed the absence of unmixed zone at the HAZ of both the sides. It was evident from the studies that all the tensile failures occurred at Monel 400 side. The average impact toughness portrayed by these dissimilar weldments was found to be 41J. Bend test results showed that these dissimilar combinations offer augmented ductility. The outcomes of the study substantiated the use of current pulsing for the successful joints of Monel 400 and Hastelloy C276 by correlating the mechanical and metallurgical properties.

Impact toughness of welds deposited on H13 hot work tool steel

Abstract This paper presents the experimental results of the impact toughness and hardness of welds deposited on H13 hot work tool steel. To obtain the optimum combination of high hardness and high toughness, multipass gas tungsten arc welding was used to melt four different commercially available filler materials suitable for repair welding of HWTS. Special geometry of the welding sample is presented in this work. The focus is also on the technique of the preparation of the V-shaped notch in order to precisely evaluate the impact toughness. Two different preheating temperatures and two different post weld heat treatments were applied to the samples in order to obtain the effect of heat treatment on the impact toughness and hardness. Data show that weld deposited with filler material C on the base of the hot work tool steel and alloyed with vanadium exhibits high impact toughness in combination with high hardness in the as-welded condition and also after tempering.

Microstructure Development in Gas Tungsten arc Welded Al Alloy AA2219

Development of microstructure in the weld pool as well as in the partially molten zone is influenced by weld geometry and cooling of the weld metal besides heat input. Evolution of refined microstructure has definite advantage in AA2219 weldment to restrict the crack path. In the present paper, mechanisms of microstructure development in single pass and multipass gas tungsten arc welding of Al-alloy AA2219 alloy have been studied. Role of backing bar material and weld configuration in development of morphology and growth of microstructure have been discussed.

Microstructure and corrosion behavior of multipass gas tungsten arc welded 304L stainless steel

The purpose of this study was to discuss the effect of single pass and multipass (double and triple pass) gas tungsten arc welding (GTAW) on microstructure, hardness and corrosion behavior of 304L stainless steel. In this investigation, 308 stainless steel filler metal was used. Microstructures and hardness of the weldments were investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD) and Vickers microhardness (HV0.5). A ferritescope was also used in the non-destructive evaluation to observe the ferrite content on the weldments. Corrosion behavior of weldments in 1M H2SO4 solution at 25±1°C was investigated using potentiodynamic polarization and immersion tests. Results indicated that the microstructure of fusion zones exhibited dendritic structure contained lathy and skeletal δ-ferrite. The contents of δ-ferrite in the weld zone increased by increasing the number of passes. Therefore, as the number of passes increased, the hardness and corrosion resistance increased.

Tungsten heavy alloy as a filler metal for repair welding of dies for high pressure die casting

Abstract This paper presents the preliminary test of tungsten heavy alloy as a filler metal for repair welding of high pressure die casting dies. H13 grade hot work tool steel was used as a base material. Multipass gas tungsten arc welding was used to fill a single-V butt joint with tungsten heavy alloy in the form of a welding rod. The microstructure of the weld was examined using scanning electron microscopy and optical microscopy. It was found that tungsten grains are not dissolved completely during welding and areas of fine eutectic were formed during solidification of the weld. The hardness of the weld was measured in three courses across the weld and increased in the heat affected zone while the weld hardness was below 380 HV0.3. Charpy V-notched samples were prepared from the weld. The high content of tungsten grains distributed in the nickel–iron weld matrix resulted in low impact toughness of 5.1 J. Face bend testing of the weld was conducted in order to study weld ductility.

Elucidating the microstructure and wear behavior of tungsten carbide multi-pass cladding on AISI 1050 steel

In this work, tungsten carbide powder was clad on AISI 1050 medium carbon steel by multi-pass gas tungsten arc welding (GTAW) method. The microstructure and wear performance of the multi-pass clad layers were characterized by micro-analysis rigs and reciprocating tribometer. A local alloying process was used to synthesize a vein-like phase in the microstructure of multi-pass clad layers. The vein-like phase was identified by X-ray diffraction as Fe 3W 3C. Both the hardness and the wear performance of the multi-pass clad layers exceeded that of AISI 1050 medium carbon steel. However, under specific wear test conditions, wear loss was higher in the multi-pass clad layers than in the substrate. Further wear tests and micro-analyses were conducted to clarify the peculiar phenomenon. Experimental results suggest that some metastable phases are transformed in situ to a stable phase, which reduces the wear resistance of clad layer during the dry rubbing process.

Investigation into Microstructures of Maraging Steel 250 Weldments and Effect of Post-Weld Heat Treatments

This study was undertaken to gain a better understanding of microstructures obtained by multipass gas tungsten arc welding in maraging steel grade 250. Metallography and microhardness measurements were carried out on sheet and welded joints in as-welded and post-weld aged conditions. It was found that there was a significant amount of reverted austenite formed on cell boundaries of weld metal after aging at 758-823 K for 3-5 h, and was stable at room temperature. Aging at higher temperatures led to an increase in the continuous network of patchy austenite along the cell boundaries. The reason for the above, in our opinion, is the concentrational heterogeneity which characterizes the microstructure of maraging steel welds. No reverted austenite was observed in as-welded specimens. Solution annealing at 1093 K for 1 h did not completely eliminate the chemical heterogeneity associated with weld structures. However, homogenizing at 1373 K produced homogenous structure that on subsequent aging produces austenite-free lath martensitic structure.

Suitability of Maraging Steel Weld Cladding for Repair of Die-Casting Tooling

Abstract A comprehensive study of 18 % Ni maraging steel welds is done in order to determine the suitability of repair welding of aluminum die-casting dies and to prolong the in-service tool life. This study emphasizes the influence of welding parameters and post-welding precipitation annealing heat treatment on the welds' mechanical and metallurgical properties. A series of U-grooved specimens of 1.2344 tool steel is prepared. These grooves are filled with 1.6356 maraging steel as filler wire using multi-pass Gas Tungsten Arc welding. The metallurgical properties of the filler welds, in the as-welded condition and after precipitation annealing with a series of different parameters, are studied. The influence of preheat temperature, heat input during welding, and hot working of maraging steel welds is evaluated regarding mechanical and metallurgical properties. The response surface models for the prediction of mechanical properties (i. e. hardness, toughness, tensile strength, and yield stress after post-welding heat treatment) are developed. The results show that metallurgical and mechanical properties significantly depend on welding technology and post-welding heat treatment parameters. Gas Tungsten Arc welding with low heat input permits the omission of solution heat treatment after welding, while hot working of welds during welding increases the mechanical properties. Developed models for the prediction of mechanical properties enable selection of precipitation annealing parameters for a particular application based on desired mechanical properties.

Improvement of mechanical properties of gas tungsten arc and electron beam welded AA2219 (Al–6 wt-%Cu) alloy

Despite its excellent weldability characteristics, AA2219 suffers from poor fusion zone strength under the as welded condition. In the present work, it is attempted to increase the mechanical properties of the as welded fusion zone of this alloy by increasing the weld cooling rates and multipass welding. The cooling rate was increased with the use of high intense heat source, namely electron beam in a pulsed current mode. Multipass gas tungsten arc welding was carried out using direct current straight polarity. These techniques resulted in a significant improvement in fusion zone hardness and tensile properties, which is attributed to reduced copper segregation and natural aging as well as aging caused by heat of multipass welding.

Three-dimensional thermal simulation and experimental investigation of GTAW circumferentially butt-welded Incoloy 800 pipes

Abstract A three-dimensional finite element model was developed to simulate the multipass gas tungsten arc welding (GTAW) process of Incoloy 800 petrochemical pipes. The birth and death technique was used to consider mass addition from the ERNiCr3 filler metal into the weld pool. Movement of the GTAW torch was modelled in a discontinuous manner assuming a constant welding speed. The arc heat input was applied in the weld zone using different forms of surface, volumetric and combined heat flux distribution functions. In order to validate the thermal simulation model, temperature distribution within the heat-affected zone of the welds was precisely measured during the welding process by thermocouples. The simulation results showed that a fully volumetric arc heat input represents the best match to the thermocouple measurements for welding of the thin-walled pipes used in this work. It was also shown that increasing the heat input results in a wider weld pool root along with a higher maximum temperature of the heat-affected zone which is in agreement with the measurements. The present simulation model can be used as a proper tool to investigate the effect of different GTAW process parameters.