Pulsed Current Gas Tungsten Arc Research Articles

Experimental investigation on solidification cracking & intergranular corrosion of AISI 321 & AISI 316 L dissimilar weld on pulsed current gas tungsten arc welding (PCGTAW)

Dissimilar metal combinations are frequently employed in the power generation and nuclear industries. Where stainless steel piping systems are connected to pressure vessels made of low-alloy steel, the subsystems of liquid rocket engines also have different, dissimilar material combinations. Dissimilar welding plays a vital role in ensuring the integrity, performance, and reliability of components and structures operating in cryogenic environments, in this study, plates of AISI 316L and AISI 321, each 5 mm thick, were successfully joined using the pulsed current gas tungsten arc welding (PCGTAW) technique with optimized process parameters. These weld joints are mostly present in rocket engines subjected to a cryogenic environment. Due to the low temperature environment, the metallurgical properties of these joints change, which affects their mechanical properties. As it is a structural part, PCGTAW welding is most common method for joining this kind of material.In this work, Microstructural analysis of the weldment revealed a combination of vermicular, lacy, and acicular ferrite morphologies in the fusion zone at the root, mid, and crown locations.Furthermore, no solidification cracking was detected in the weldments based on the optical micrograph and SEM results. Intergranular corrosion (IGC) testing indicated the absence of a ditch structure, suggesting that the heat-affected zone (HAZ) on both sides of the weld joint was not being susceptible to sensitization. However, the HAZ of the AISI 316L side exhibited coarser grains compared to AISI 321. Analysis of tensile properties revealed a significant influence of the testing environment on the tensile strength of the dissimilar welded joints. At room temperature, the average ultimate tensile strength (UTS) was measured as 621 MPa. Remarkably, at cryogenic conditions, the average tensile properties significantly increased to 1319 MPa.Microhardness analysis showed the highest hardness associated with the AISI 321 side. The fusion zone exhibited a large deviation in the hardness profile (205 ± 10 HV), with the highest average hardness observed in the middle part of the weld. However, the hot cracking behavior of the weld was investigated by using a suutula diagram at various locations of the weld. The investigation revealed that the Creq/Nieq ratio exceeded the critical threshold value, effectively diminishing the propensity for hot cracking in the fusion zone. Overall, these findings underscore the effectiveness of the PCGTAW technique in joining dissimilar materials, as well as the importance of microstructural and mechanical property evaluations, especially under extreme operating conditions such as cryogenic temperatures.Paraphrase.

Characterization of the spin arc welding technique for dissimilar materials Hastelloy C-2000 and C-276

Hastelloy C-2000 and C-276 are primarily employed in the petrochemical and pharmaceutical industries. Finding an effective way to combine these alloys is still a complex task in industry. The main focus of this study is to investigate the potential efficacy of the spin arc welding process on Hastelloy C-2000 and C-276. The welding process was carried out under various conditions, such as weld current, spinning speed, and spin diameter. ERNiCrMo-4, with a diameter of 1.2 mm, was employed as a filler. Optical microscopy, XRD and FESEM were used for microstructural examination. The mechanical properties of the welded samples were critically analyzed. The results of the ultimate tensile strength (UTS), hardness value (HV), and impact tests of spin arc welding were compared with those of the multipass pulsed current gas tungsten arc welding process (MPCGTAW). In spin arc welding, Hastelloy C-2000 and C-276 exhibited higher UTS, HV, and toughness compared to MPCGTAW because there was no secondary TCP phase formation in the weld centre and hot cracking in spin arc weldments. Additionally, compared to MPCGTAW, the elongation with spin arc welding was noted to be lower. Moreover, microstructural analysis revealed no evidence of grain segregation, which may have contributed to the improved UTS and HV of the materials during spin arc welding. Thus, spin arc welding proves to be superior for dissimilar Hastelloy joints of C-2000 and C-276.

An innovative pulsed current arc welding technology for armor steel: Processes, microstructure, and mechanical properties

This study presents a novel pulsed current arc welding technology, specifically pulsed current gas tungsten arc welding (PC-GTAW), single and double pulse gas metal arc welding (SP/DP-GMAW), and dual process welding (D-process). This study aims to investigate the effectiveness of these welding techniques for armor steel weldments. This research focused on investigating the welding processes, resulting microstructures, and mechanical properties of welded joints. Based on the macrography analysis, it was determined that the weldments exhibit no signs of porosity, inclusions, or inadequate penetration. This finding substantiates the optimum settings for the weldment production process. The weldment optical microstructure, fusion, and heat-affected zone were examined in the weld interface. The microstructural properties of the FZ include δ-ferrite, austenite, bainite, and acicular martensite. The HAZ has a bainite-untempered martensite microstructure. The chemical composition and variations across the weldment (base, weld and HAZ) were identified. The grain borders contained greater quantities of Cr, Ni, Mn, Si, and Mo than those of the grain cores. EBSD revealed average weld zone grain sizes of 17.7 µm, 32.6 µm, 30.8 µm, and 24.6 µm for PC-GTAW, SP-GMAW, DP-GMAW, and D-Process, respectively.Furthermore, the hardness measurements showed a progressive transition across different regions. Additionally, the D-Process-fabricated material exhibited a maximum ultimate tensile strength of 872 MPa and an elongation of 4%. The mechanical properties exhibited by this new process variant exceed those of other weldments, indicating its potential for fabricating armor steel. The impact toughness demonstrated superior performance in all the weldments. Within this context, the new use of pulsed current advanced welding methods has shown the ability to generate welded parts of exceptional quality.

A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding

A Comparative Study on High-Temperature Oxidation Behavior, Microstructure Characterization, and Texture of UNS R30155 Superalloy Weldment Joint Using Pulsed Current and Constant Current Gas Tungsten Arc Welding

Evaluate Effect of Pulsed Current Gas Tungsten Arc Welding Process Parameter on Intergranular Corrosion of SS304L Weld

Austenitic stainless steel (ASS) is the most common type of stainless steel which offers excellent weldability and mechanical properties. ASS is being used for various applications i.e. automotive, oil and gas and chemical industries in which the welding process plays a prominent role. Welding process selection is the main factor that emphasizes mechanical and corrosion resistance properties in various aggressive environments. There are various corrosion occurs in ASS but intergranular corrosion (IGC) forms during welding at elevated temperatures. IGC mainly occurs at grain boundaries of structure and resulting chromium depletion due to precipitation of chromium carbide at the grain boundary. In present work pulsed current gas tungsten arc welding (PCGTAW) process was used to investigate intergranular corrosion by oxalic acid test as per ASTM A262 Practice A. Experiments performed based on Taguchi L9 using design of experiments and corrosion rates are evaluated at base metal, heat affected zone and weld zone. This work is aimed to optimize process parameters followed by regression analysis to IGC susceptibility in the weldment. In this investigation, it has been found from ANOVA and main effects plots that peak current and base current are the most significant parameters in the PCGTAW process. The results of the corrosion test revealed that heat affected zone is more susceptible to IGC. At the end, it has been observed that the optimum value of peak current, base current and frequency based on regression analysis are 100 A, 50 A and 6 Hz respectively.

Microstructural and Mechanical Characterization of Welded Joints between Stainless Steel and Hastelloy Made Using Pulsed Current Gas Tungsten Arc Welding

Microstructural and Mechanical Characterization of Welded Joints between Stainless Steel and Hastelloy Made Using Pulsed Current Gas Tungsten Arc Welding

Mechanical behavior of austenitic stainless-steel welds with variable content of [formula omitted]-ferrite in the heat-affected zone

δ-ferrite solidified in the fusion zone (FZ) mitigates the microfissuring susceptibility in multi-pass welded joints performed on austenitic stainless steel (ASS). The herein investigation studied welded joints between two 304L grade ASS with different chemical compositions, which varied δ-ferrite content in the heat-affected zone (HAZ). The pulsed-current gas tungsten arc welding (GTAW-P) process was used along with filler metals ER 308L and ER309L. Additionally, an autogenous joint was made with stainless steel (SS) of high δ-ferrite content (10%). A thermo-mechanical finite element (FE) model was applied to estimate the thermal history, residual stress (RS) and distortion distributions on SS joints. Then, numerical results were correlated with the fracture analysis. The tensile test corroborated the increment in ductility due to δ-ferrite content increasing in the HAZ. The enhancement of mechanical strength observed in the autogenous welded joint was associated with the pinning effect produced by δ-ferrite stringers formed in the HAZ, which inhibited grain growth. Despite the high joint efficiency of SS 304L weldments, the FZ was fractured due to the microfissuring and precipitated particles. The FZ rupture starts in the FZ-HAZ interface of the first weld bead related to the ductility loss with the heat input. Microfissures found in the FZ of all weldments were related to the tensile stress concentration caused by the uneven distortion distribution and the ductility increment (up to 39%) provided by the high δ-ferrite content. Some chromium carbides in the FZ acted as stress raisers.

Hot corrosion and air oxidation behavior of pulsed current gas tungsten arc welded and CO2 laser beam welded SMO 254 at 800 °C

This research aims to investigate the hot corrosion behaviour of SMO 254 steel samples after PCGTA and CO2 laser beam welding, as well as air oxidation. A salt mixture simulated the waste incinerator environment involving 40 wt. % Na2SO4 + 40 wt. % K2SO4 + 10 wt. % NaCl + 10 wt. % KCl are employed. The hot corrosion tests were carried out for 103.33 h at 800 °C, with a thermogravimetric investigation availed to calculate the impact of corrosion. The weight gain rate for PCGTAW molten salt corroded specimens is greater (33.45 mg/cm2) than the weight gain rate for CO2 Laser molten salt corroded specimens, which is 67.55% higher. The weight of the hot corroded sample rises in the molten salt surroundings due to the creation of compounds including CrS, FeMo2S4, Na2S, Fe2O3, K2S3, Cl4CrNa2. CO2 LBW air oxidation has the lowest rate of corrosion due to the synthesis of beneficial oxides, such as NiCr2O4, NiO, and Cr2O3. Optical microscopy and SEM/EDS were employed on both surface and cross-sectional surfaces to get microstructure at the interface of the fusion region, parent metal, and fusion region using point mapping, line mapping, and X-ray mapping techniques. The corrosion products produced during corrosion were studied using XRD.

Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe

Orbital pipe welding is carried out in this study by Pulse Current Gas Tungsten Arc Welding (PC-GTAW) without metal filler (autogenous) of AISI 304L stainless steel pipe. The dimensions of the specimen are 114 mm outside diameter and the thickness of 3 mm. This study investigates the effect of pulse current parameters, weld position, and pulse width on the characteristics of weld geometry, mechanical properties, and microstructure. The welding method used in this study is the continuous current and pulse current. The mean current of each parameter is the same at 100 ± 0.5 Amperes, but in the pulse current, there are variations in peak current, base current, peak current time, and the base current time. The welding speed used is constant at 1.4 mm/s. The result of weld geometry on the outside of pipe has shown that the flat (0°) position is concave and the overhead (180°) position is convex due to the influence of gravity. The microstructure indicates that the fine cellular dendritic structures appear at PC-GTAW. The PC-GTAW can produce good mechanical properties such as the tensile strength and the micro-hardness. The tensile strength of the specimen is reduced 14.23 % from the base metal at parameter 65-B and the flat position.

Influence of hot corrosion on pulsed current gas tungsten arc weldment of aerospace-grade 80A alloy exposed to high temperature aggressive environment

• The performance of alloy 80A weldment in a high-temperature aggressive environment was studied. • The effect of hot corrosion on different welding techniques (GTAW and PCGTAW) and filler wires (ERNiCrMo-3 and ERNiCr-3) were studied. • Influence of PCGTAW technique in protecting the surface of the welded substrate from an aggressive environment.IV) The mechanism of the formation of corrosive and protective oxides and its effect on the corrosion behaviour of welded substrates were studied. One of the significant issues that shorten the life of components used in high-temperature applications is hot corrosion. The current study compares the performance of welded aerospace-grade 80A fabricated through continuous and pulsed gas tungsten arc welding techniques. Weld coupons are produced using two different filler wires (ERNiCrMo-3 (Mo-3) and ERNiCr-3 (Cr-3)). Welded substrates are subjected to 50 cycles of air oxidation and Na 2 SO 4 + 60%V 2 O 5 molten salt environmental conditions at 900 °C. Corrosion products were analysed through scanning electron microscope/energy dispersive spectroscopy and X-ray diffraction analyses. Thermogravimetric analysis revealed that all welded substrates trailed the parabolic rate of law kinetics. In the molten salt (MS) environment, gas tungsten arc welded (GTAW) Mo-3 substrate showed more weight gain. In contrast, a minor weight gain was observed in the pulsed current gas tungsten arc welded (PCGTAW) Cr-3 substrate. It indicates that accelerated corrosion kinetics was observed in the molten salt environmental condition that showed more weight gain than air oxidation. amongst the weldments, pulsed current gas tungsten witnessed superior corrosion-resistant behaviour. This phenomenon is observed due to grain refinement suppression of heat-affected zones and secondary phases in the weld fusion zone. In addition, the appearance of protective oxides such as Cr 2 O 3 , NbO and NiCr 2 O 4 helps arrest the oxidation at the surface and sub-surface layer by providing good resistance against hot corrosion to the welded substrate. Thus, utilizing the PCGTAW technique during the fabrication/refurbishing process helps promote the material's corrosion resistance against a hot corrosion environment.

Effect of Nb-free consumables on the microstructure and structural integrity of pressure vessel grades of dissimilar austenitic stainless steel welded joints

The research article demonstrates the role of fillers in the evolution of the microstructure and mechanical integrity of dissimilar joints of stabilized austenitic stainless steels. Pulsed direct current (PDC) gas tungsten arc welding (GTAW) technique was adopted to obtain the joints of dissimilar grades of stabilized austenitic stainless steels such as AISI 321 and AISI 347. The joints of these dissimilar grades of stainless steels were achieved using a ferritic-austenitic stainless-steel filler ER2553 and Ni-rich austenitic fillers ERNiCrMo-4, ERNiCrMo-10. Delta ferrite was observed in heat-affected areas (HAZ) on both sides of stainless steels, regardless of joints. Precipitation of Mo–Nb, Mo–W rich phases was noticed in the fusion zones (FZ) while adopting Ni-based austenitic fillers. During the tensile load, the fractures occurred on the base metal side of the AISI 321 for the Ni-based fillers and on the FZ while using the ER2553 fillers. The joint efficiencies achieved by these dissimilar joints were 103.2%, 128.11% and 116.16% for ER2553, ERNiCrMo-4 and ERNiCrMo-10 fillers respectively. The joints established with the ERNiCrMo-4 filler improved the notch's impact resistance in ambient temperature and below zero conditions compared to other weld seams.

Improvements on hot corrosion behaviour of HVOF coated CO2 laser beam and pulsed gas tungsten arc weldments in 2.5% sulphur gas plus molten salt in industrial waste incinerator environment

This research article discusses in detail how the‌ ‌rate‌ ‌of‌ ‌corrosion‌ ‌increases‌ for the Alloy 254 in the ‌molten‌ ‌salt‌ ‌mixture‌ ‌of‌ ‌10‌ ‌wt%‌ ‌NaCl‌ ‌+ 40‌ ‌wt%‌ ‌K‌2‌SO‌4‌ + 40‌ ‌wt%‌ ‌Na‌2‌SO‌4‌ ‌+‌ ‌10‌ ‌wt%‌ ‌KCl‌ ‌and‌ ‌corrosive‌ ‌gas‌ combination of ‌ ‌2.5‌%‌ ‌SO‌2‌ ‌+‌ ‌3‌%‌ ‌O‌2‌ ‌+‌ ‌25‌%‌ ‌CO‌2‌ ‌+‌ ‌69.5‌%‌ ‌N‌2 in simulated municipal‌ ‌solid‌ ‌waste‌ ‌‌incinerator environment at 700 °C and 800 °C.‌ ‌In addition, the article shows rate of ‌thermal corrosion abridged due to the addition‌ ‌of‌ ‌80‌ ‌Ni-‌ ‌20‌ ‌Cr‌ ‌-‌High-velocity oxygen fuel ‌coating‌ ‌on‌ ‌the‌ ‌SMO‌ ‌254‌ ‌specimen. Thermogravimetric analysis is adapted to analyze the corrosion rate. A‌ ‌higher‌ ‌hardness‌ ‌was‌ ‌obtained‌ ‌for‌ ‌the‌ ‌High-velocity oxygen fuel coated‌ ‌specimen‌ ‌than‌ ‌that‌ ‌of‌ ‌base‌ ‌metal.‌ ‌Surface‌ ‌roughness‌ ‌was‌ ‌measured‌ ‌on‌ ‌the‌ ‌thermal‌ ‌barrier‌ ‌coated‌ ‌surface.‌ As a result of the impact of molten salt and corrosive gas, hot corrosion by-products such as ‌sulphides, chlorides‌ ‌and‌ ‌Na‌ are produced, which are observed to increase the severity of corrosion rate. ‌‌ The study provides a detailed analysis of the metallurgical changes along the cross-section on the hot corroded samples by optical and Scanning electron microstructural image analysis. X-ray diffraction analysis was used to know about the corrosion products formed during corrosion. Formation‌ of the major protective oxide phases such as NiCr2O4, Cr2O3, NiO and CrMnO4 provide better corrosion resistance to the substrate in the coated samples. The diffusion of the corrosive elements along the cross-section of the weld interface, weld zone, and base metal zone was analyzed in detail using Electron dispersive spectroscopy‌ ‌data in the point scan, line scan, and x-ray mapping techniques. Thermal spray coatings were found to be effective to prevent the hot corrosion, however, a higher weight gain (17.75 mg cm−2) was observed on the pulse current gas tungsten arc weldment sample in the simulated environment compared to a weight gain (2.66 mg cm−2) base metal specimen at 700 °C. Spallation of coated surface occurred at 800 °C, and it could be concluded that the coating has found to be effective in preventing the hot corrosion and safe to operate at a temperature of 700 °C for Alloy 254 in this aggressive simulated environment.

Effect of constant current and pulsed current gas tungsten arc welding process on microstructure and mechanical properties of superalloy 59 joints

This research paper investigates the microstructure, microsegregation and mechanical behaviour of Ni-based superalloy 59 which is an important candidate in the pollution control application. The weld joints were produced with continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) by applying both autogenous mode and filler wire ERNiCrMo-13. Weld flaws and weld aspect ratio of weld joints were identified using a macro analysis. An optical microscope (OM) and scanning electron microscope (SEM) were used to examine the microstructure of the welded joints. PCGTA weldments exposed refined grain structure, reduced heat-affected zone and narrow weld bead compared to CCGTAW. Microsegregation of the alloying elements at the weld center (WC) and weld interface (WI) was examined using Energy Dispersive x-ray spectroscopy (EDS). The findings of the metallurgical characterisation proved that the PCGTA weldments offer minimal microsegregation at the interdendritic region in comparison to CCGTA weldments. X-Ray Diffraction (XRD) examination reveals that there is a 16.7% enhancement in grain refinement in the autogenous mode and a 17.4% improvement in the filler wire ERNiCrMo-13 when switching from CCGTA to PCGTA welding. Tensile, Charpy impact and microhardness tests were used to assess the strength, toughness and hardness of the weld joints. Weld joints fabricated by PCGTAW offers higher tensile strength (∼1.4 to 1.6%), higher toughness (∼4.4 to 5.4%), and higher hardness (∼4.8 to 7.7%) than CCGTAW weld joints.

Hot corrosion behaviour of constant and pulsed current welded Hastelloy X in Na2SO4, V2O5, and NaCl salt mixture at 900 °C

The high-temperature corrosion behavior of constant current gas tungsten arc (GTA) and pulsed current gas tungsten arc (PCGTA) welded Hastelloy X with different filler wires (C263 and ERNiCr-3) are studied for 50 cycles at 900 °C. Molten salt I (MS I) (75% Na2SO4 + 25% V2O5) and molten salt II (MS II) (75% Na2SO4 + 20% V2O5 + 5% NaCl) were coated on the welded specimens. MS II coated substrate shows the highest weight gain than MS I with a parabolic constant for GTA ERNiCr-3 as 21.440 × 10–6 mg2/(cm4.s). Whereas PCGTA C263 welded sample with MS I, revealed parabolic constant (lowest) of 0.008 × 10–6 mg2/ (cm4.s). Based on the results, an increasing pattern of hot corrosion resistance of substrates is arranged as GTA ERNiCr-3 < GTA C263 < PCGTA C263 < PCGTA ERNiCr-3. PCGTA shows more refined grains, higher grain boundary volume, better corrosion resistance, and more protective phases like Cr2O3, NiO, NiCr2O4, CoCr2O4, Al2O3, NiFe2O4, NbO than GTA weldment. But phases such as Fe2O3, MoO3, and Cr2S3 (non-protective phases) decrease corrosion resistance due to acid fluxing of alloying elements that promote the oxide scale exfoliation, spallation, chipping, and cracking. This study observed that PCGTA with C263 filler in MS I and MS II environment provides good corrosion resistance at high temperatures.

Influence of Different Frequency Pulse on Weld Bead Phase Ratio in Gas Tungsten Arc Welding by Ferritic Stainless Steel AISI‐409L

The objective of the present experimental work is to obtain an appropriate welding parameter on pulsed current gas tungsten arc welding (GTAW) ferritic stainless steel AISI 409L with a thickness of 4.5 mm. Frequency affected penetration, and the ratio of bead width to penetration (aspect ratio) is the main objective of the research. A Taguchi L9 orthogonal array with three level four factors was chosen to execute the bead on plate welding. It leads to optimize the input process parameters on main effect plot via analysis of variance, and it has imposed to determine their contribution level of each parameter with respect to responses. Taguchi optimized conditions for butts weld with the pulsed TIG and its surface morphology, and mechanical characteristics of AISI 409L weld was investigated. A full penetration with an optimal aspect ratio was accomplished using high‐frequency pulsing, according to the findings. The mechanical properties were characterized using Vickers microhardness and tensile tests on the base material and weld metals. Microstructural study revealed that these variables have a greater impact on the bead profile. Pulsed TIG showed maximum UTS of 445 MPa and a minimum of 385 MPa, with an average of three samples of 415 MPa. The weld metal in all of the zones had influenced superior tensile strength (UTS) as compared to base metal, according to the findings. The obtained strain percentage for both butt and TIG welds, however, was smaller than that of the parent metal. The formation of martensitic was attributed for the higher tensile strength with minimized ductility of the pulsed TIG welds. Furthermore, results on the hardness are in concurrence with the tensile experiments, as the zone for fusion has a higher hardness than the base metal. Corrosion behavior of the parent metal and welded specimen was analyzed using a potentio‐dynamic polarization technique. The electrochemical behavior of base material and weld samples confirmed that the overall corrosion resistance is better in parent material than the other zones.

Hot corrosion performance of bare and pulsed current welded Fe-based A-286 alloy in chlorine and sulphur environment

This present research work focuses on the hot corrosion performance of the base metal, weldment, and weld metal of A-286 alloy in sodium sulphate (Na2SO4)–5% sodium chloride (NaCl)–7.5% sodium metavanadate (NaVO3) (3SM) atmosphere at 700 °C. A pulsed current gas tungsten arc welding process is employed to make a similar joining of A-286 alloy using the filler material ERNiCrMo-3. The corrosion kinetics of the specimens has been determined using the thermo-gravimetric technique. The phase compositions of the reaction products are studied by X-ray diffraction, and the surface morphology of the scales is explored by scanning electron microscope analysis. The corroded samples are subjected to a cross-sectional study to ensure the corrosion attack and scales thickness using a SEM with elemental mapping technique. The result indicates that weldment showed better corrosion resistance than bare metal. A thick oxide scale could be found in the bare metal specimen than the weld metal. In the case of base metal, the formation of non-adherent and porous iron (III) oxide (Fe2O3) leads to rapid corrosion. The weight gain of weldment is about 1.96 and 1.13 times less than bare alloy and weld metal.

Improvement of hot corrosion resistance of dissimilar weldments by current pulsing in a simulated power plant environment

Hot corrosion studies are of utmost importance for welded components in the power plant industry as well as for industries which deal with exposure to the high-temperature corrosive environment. The failure of welded components at high temperatures has often led to the reduced service life of a component and catastrophic disasters. This has been a significant engineering challenge in the design of welded components. It is generally seen that the failure of the welded sections mostly occurs because of the deposition of molten salt over the weldments which accelerate the hot corrosion reactions. In this present research work, two dissimilar base materials, AISI 4340 and AISI 304L have been welded with two different welding processes namely continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) while making use of ERNiCr-3 as filler material. A comparative study of the dissimilar welded plates was carried out by simulating a molten salt environment at 600°C involving hot corrosion behavior. By analyzing the microstructure and thermo-gravimetric data, it is concluded that the pulsed current gas tungsten arc welding process has superior corrosion resistance properties while using ERNiCr-3 as the filler material as compared to the continuous current gas tungsten arc welding process.

Effects of pulsing current and filler materials on the mechanical and metallurgical properties of DSS 2205 weldments

The control of balance in austenite to ferrite ratio of duplex stainless steel (2205) during welding is critical due to not choosing the optimum heat input and cooling rate and welding processes, which leads to the development of embrittlement of intermetallic precipitates in the weldment. Further, the imbalance of austenite to ferrite ratio primes the stress corrosion cracking (ferrite < 25 %), low impact toughness and corrosion resistance (ferrite > 75 %). The pulse current gas tungsten arc (PCGTA) welding has utilized to weld the DSS 2205 using ERNiCrMo-3 and ERNiCrMo-4 fillers for better control of austenite to ferrite ratio. The tensile strength of Mo-3 weldment is 4.06 % higher than Mo-4. Besides, the Mo-3 weldment also provided the enhanced impact toughness and microhardness compared to Mo-4. The macrographs show similar weld bead width. The microstructure of both fillers Mo-3 & Mo-4 confirmed columnar structure at the weld interface and the finer equiaxed structure at weld center. The scanning electron microscope along with energy dispersive spectroscopy assured the absence of Cr2N, Chi and sigma phases. The PCGTA of DSS 2205 with Mo-3 is giving the improved properties with respect to Mo-4.

Development of arc welding technique to preclude microsegregation in the dissimilar joint of Alloy C-2000 and C-276

Hastelloy C-2000 and C-276 are widely used in Flue Gas Desulphurization (FGD) system and Chemical Processing Industries (CPI). Current work is focused on weld microstructure, and mechanical properties (structure-property relationship) of the dissimilar combination of alloy C-2000 and C-276. Multi-pass Pulsed Current Gas Tungsten Arc (PCGTA) welding was adopted for joining the dissimilar alloys using the filler ERNiCrMo-17. Microstructural characteristics of the weld joint were assessed by Optical and Scanning Electron Microscope (SEM). Weld interface microstructure examination revealed the presence of grain coarsening near the Heat Affecting Zone (HAZ) of the alloy C-276 side. SEM analysis shows the absence of secondary Topologically Closed Packed (TCP) phases in the Inter-Dendritic (ID) regions of the dissimilar weld. Micro-segregation of alloying elements in the weldment was assessed by Energy-Dispersive X-ray Spectroscopy (EDS). X-Ray Diffraction (XRD) analysis had been carried out to identify the phase constitution and average grain size. Strength, toughness, and hardness of the dissimilar weld were evaluated with the support of the tensile test, Charpy impact test, and Vicker’s hardness test. Tensile study showed that all the tensile fracture occurred at the base metal side of alloy C-276. The average toughness of the dissimilar alloy joint was noted about 84 J. Hardness test results indicated that fusion zone (FZ) hardness value was 6.19% and 2.27% superior to the candidates’ material (C-276 and C-2000) employed in this study. The refined grain structure and absence of microsegregation resulted in the highest hardness in the dissimilar weld FZ. Results revealed the substantiated use of PCGTA welding for the effective joining of dissimilar alloys of C-2000 and C-276 through the evaluation of metallurgical and mechanical characteristics.

Prospects of pulsed current arc welding on aerospace grade Hastelloy X

The conventional constant current arc welding of Hastelloy X (Ni-Cr-Fe-Mo) leads to the solidification and liquation cracks in the weldment. The higher heat supplied in constant current weldment develops the secondary carbide precipitates. It promotes the development of hot cracks in the weldment. In this study, joining of Hastelloy X plates was carried out by constant current gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) with C263 filler wire. The result discovered that no hot cracks were formed in the weldment. In constant current mode, Cr-rich and Mo-rich Cr23C6 (M23C6), Fe2MoC, Fe3Mo3C (M6C), and Cr2Ti precipitates were observed. Whereas, in pulsed current mode, Ni3(Al, Ti), Ni3Ti, Co3Ti, Cr2Ti precipitates are found due to the segregation of Co, Al, and Ti. No Cr-rich and Mo-rich carbide phases identified in pulsed current weldment due to rapid cooling rate and higher thermal gradient observed during solidification. The tensile results revealed that 8.23% increase in the ultimate tensile strength and a 29.62% increase in elongation of pulsed current mode welding compared to constant current welding. Further, the microhardness and impact toughness of PCGTAW is 3.32% and 5.45% higher than GTAW, respectively. In pulsed current welding, better mechanical properties were identified compared to constant current welding. The nonappearance of Cr and Mo-rich phases and refined microstructure in the weldment are the main reason for better strength.