The hot corrosion behaviours of 5-mm-thick plates of dissimilar AISI 904L and Inconel 625 weldments produced by continuous current gas tungsten arc welding process using Ni-Cr-Mo-enriched filler wires (ERNiCrMo-4 and ERNiCrCoMo-1) were investigated. Optical microscopy was used to examine the microstructure of these weldments. The corrosion performance of the weldments and base metals was determined in the mixture of K2SO4 + 60% NaCl molten salt (MS) and air oxidation conditions at 700 degrees C for 50 cycles. The thermogravimetric plots derived the corrosion kinetics of the weldments. The microstructure and the elemental analysis of the scales formed on the corroded samples were evaluated by scanning electron microscopy and energy-dispersive spectroscopy. The phases developed on the oxide layers during the corrosion were analysed using X-ray diffraction. The fusion zones of ERNiCrCoMo-1 weldment and AISI 904L base metal were vulnerable to degradation in the MS environment, causing severe cracks and spallation compared to ERNiCrCoMo-1 weldment.

Alloy 625 joining was employed by pulsing current gas tungsten arc (PCGTA) welding method using ERNiCrMo-4 filler wire. The cyclic high-temperature performance of the weldments was investigated at 700 degrees C in molten salt (MS) K2SO4-60 %NaCl and air environment. The weldments' corrosion kinetics were accessed by the weight change method. A thin scale with no significant failure was found on the surface of the oxidized weldment. The oxide scale cracking and spallation occurred on the weldment in MS condition due to the deposited salts. The damage mechanism of the scales developed on the weldments is discussed in MS condition.

This research investigates the hot corrosion behavior of Inconel 625 similar joints welded using pulsed current gas tungsten arc welding (PCGTAW). Specific emphasis has been given to the microstructural changes at the fusion zone and weld interface while employing two different Ni-Mo-rich fillers (ERNiCrCoMo-1 and ERNiCrMo-4). The microstructure of the weldments was evaluated using scanning electron microscopy (SEM) and optical microscopy (OM) techniques. The weld joints employed with ERNiCrMo-4 filler showed slightly higher strength than that of ERNiCrCoMo-1, and the fractures were found on the base metal regions. The performance of the alloy 625 bi-metallic joints has been ascertained by exposing both cyclic molten salt K2SO4 + 60% NaCl and an air oxidation environment at 700 °C. A thermogravimetric plot was employed to determine the weldment kinetics of corrosion. SEM/EDS systematically examined the oxide scales formed on the weldments, and x-ray diffraction (XRD) was used to identify the phases of the corrosion products. The test results revealed that the corroded samples in the salt condition experienced severe corrosion attacks as compared to air conditions by sulfidation and chlorination. Based on the specific outcomes of this study, ERNiCrMo-4 filler is recommended for joining these similar combinations of welds and it imparts better corrosion resistance at elevated temperatures in simulated boiler environments.

Inconel 718 joints were fabricated using the pulsating direct current gas tungsten arc welding (PDCGTAW) and laser-arc hybrid welding (LAHW) techniques using Ni-Cr-Mo-rich filler. A cyclic post-weld heat treatment (PWHT) comprising 980 degrees C/20 min/air cooling; followed by two-stage ageing 720 degrees C/8 h/furnace cooling and 620 degrees C/8 h/air cooling was performed on both joints. The liquation cracking was noticed on the heat-affected zone (HAZ) of the LAHW joints. Microstructural characteristics were assessed on the joints in both as-welded (ASW) and PWHT conditions. Regardless of the joints, the coarse Mo-rich segregates were noticed in the fusion zone (FZ) in the ASW conditions. On the contrary, the partial dissolution of MC, precipitation of 8-Ni3Nb needles and the coarsening of strengthening precipitates were observed on LAHW and PDCGTAW joints after subjecting to cyclic PWHT respectively. Tensile studies corroborated that there is a considerable enhancement in the tensile and 0.2% offset yield strengths of LAHW joints after being exposed to PWHT, despite the formation of HAZ liquation cracking. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Pulsed direct current (PDC) gas tungsten arc welding (GTAW) of 12 mm thick plates of naval, marine-grade high strength low alloy steel (HSLA) using ER80S–Ni3 filler metal was investigated. The microstructural characteristics were examined by both optical microscopy and field-emission scanning electron microscopy (FE-SEM) techniques. The fusion zone is comprised of mixed microstructures of acicular ferrite (AF), polygonal ferrite (PF), grain boundary ferrite (GBF), and bainite ferrite (BF) laths in the various welding passes. The yield and tensile strengths of the PDCGTA weld joints were found to be superior to that of the base metal. A joint efficiency of 122% was observed for the weld seams while conducting the notch tensile studies (NTS). The impact toughness of the weld joints was higher than that of the base metal. The tensile and impact properties in the room temperature (RT) conditions were superior due to the formation of acicular ferrite (AF) and bainite ferrite (BF) laths in the weld seam microstructure. A higher toughness value of 173 J and ductile fracture mode was observed when the joints were impact loaded at −40 °C. On the other hand, the brittle cleavage fracture was observed for the joints subjected to impact loading at −196 °C. The impact toughness data indicated that the joints experienced a transition from a ductile to a brittle mode of fracture on lowering the temperature.

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.

The enhanced SA 335 P91 steels are specially designed to be used in the super-heaters in thermal power plants which are commonly operated at an elevated temperature. The present study involves an analysis of microstructure and the tensile property of the used P91 tubular steel of such heat exchanger in as-received conditions. The joints were fabricated by gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) by employing ErNiCrMo-3 and E9018 B9 fillers. The microstructure showed the presence of flakes of martensite, formation of Nb-rich phases with an unmixed zone in the interface of the weld followed by the columnar and equiaxed dendrites in the centre of the weld zone, while employing the ERNiCrMo-3 filler in GTAW. Whereas in SMA welding, no such unmixed zone was observed while employing E9018 B9 filler except the precipitation of carbides. The metallurgical and mechanical characterization of welded joints was performed by optical microscope, scanning electron microscopy with energy dispersive spectroscopy (EDS), hardness, toughness and tensile tests. From the SEM/EDS analysis in the fusion zone of joints inferred the uniform distribution of the element with Nb phases and oxide formation in the pre used P91 steel for both the weldments irrespective of the fillers employed. Alongside the hardness of the SMA weld zone showed a higher hardness by the precipitation of M23C6 and martensitic structure compared to the GTAW weld zone which is found to be lower owing to the presence of elements such as Mo, Nb, Al and C. In both the joints, the tensile failure occurred away from the fusion zone in the parent metal and SMAW joints imparted better strength than GTAW joints. The GTAW joints showed better toughness by ensuring the ductile mode of failure in fractography studies.

The 3-mm-thick plate joints of the UNS S32750 were successfully established using cold transfer welding (CMT) technology with Inox 2509 MoW B as filler. Metallography studies indicated that the austeno-ferrite phase equilibrium in the HAZ and weld seam was greatly affected compared to the base metal. The occurrence of various forms of austenite, i.e., grain boundary austenite, Widmanstätten austenite, and intergranular austenite, was observed in the CMT weld seam. While there was a slight increase in hardness, tensile failures occurred in CMT welds during tensile failure tests. The absence of secondary austenite and deleterious intermetallic phases in the CMT weld has improved the joint strength and moderate ductility. A ductile–brittle transition is observed in both the base metal and the CMT-welded joints when subjected to an impact load at sub-zero temperatures.

The precipitation effects on the mechanical behavior of electron beam welded joints of Inconel 625 in the as-welded [AW] and post-weld heat treatment [PWHT] conditions have been investigated in this research study. A PWHT comprising of direct aging [DA] treatment at 700 degrees C for 100 h in vacuum at a pressure of 10(-5) mbar was performed on the weld joints. The microstructure of the base alloy opined the precipitation of MC system carbides and gamma" strengthening phase after subjecting to DA. Also, Nb-Mo rich precipitates and the Laves phase was noticed in the inter-dendritic arms of the fusion zone (FZ) of welded joints in the AW conditions. DA treatment has a notable effect on the weld mechanical characteristics of Inconel 625 joints. The precipitation of gamma" strengthening phase is reasoned for the significant rise in the yield strength [YS] and tensile strength [TS] of the base alloy and EBW joints.

The oil and gas industries have been extensively utilizing 25Cr super duplex stainless steels because of their excellent mechanical properties and corrosion resistance. Wire arc additive manufacturing technology was employed to fabricate thin wall using ER2594 filler wire. The microstructural examination exposed the presence of ferrite, intragranular austenite, Widmanstätten austenite, grain-boundary austenite and secondary austenite. It was found that the austenite-ferrite fraction varied across the wall due to the complex cyclic thermal history during deposition. Detrimental phases such as sigma-σ or lambda-λ were not observed due to lower heat input and suitable inter-pass temperature. Micro-hardness measurements showed the gradual variation of hardness along the built direction (281–310HV0.2). Tensile specimens exposed anisotropy, and the tensile properties were better than the wrought counterparts and meet the minimum requirements as mentioned in ASTM A240/A240M-20a and ANSI/NACE MR0175/ISO 15156-1:2015.

In the current scenario, welding between two different metals is broadly utilized in various industrial applications owing to their cost-effective potentials. During welding, the elemental variation across the weld interface is inevitable due to the difference in their melting ranges of micro-constituent. In this research work, the microstructural growth and the effect of precipitation due to elemental variation across the fusion boundary is analysed. PCGTA welding were employed to join alloys AISI904L and Inconel 625 using ERNiCrCoMo-1 and ERNiCrMo-4 (enriched Ni-Cr-Mo) fillers. The optical microscopy and SEM images were employed to disseminate the microstructure characters of these joints. Micro-segregation and un-mixed zone are noticed in the HAZ of both the weldments. Multi-directional competitive grain growth containing fine equi-axed grains in the weld centreline along with cellular and columnar dendrites in the weld zone are observed for both the weldments. Migrated and solidification grain boundaries are distinctly observed in the ERNiCrCoMo-1 fusion zone. The research outcomes form the present work based on the elemental variation across the fusion interfaces (micron level) recommended the ERNiCrMo-4 filler to join these candidate alloys.

Precipitation strengthened Ni based alloy, Incoloy 925 is widely used in the H2S-containing hot sour environments because of its excellent properties. Metallurgical properties, which is known to affect the performace of this alloy greatly depends on the welding technique adopted, ageing condition, formation of inter-metallic phases and hardness. Hence, in this research work, the joints of Incoloy 925 are accomplished in a single pass with the use of nano-SiO2 activtated flux tungsten inert gas (A-TIG) welding process. Further, the A-TIG welded joints were subjected to direct ageing for 4 h and 8 h at 732 degrees C and air-cooled. Recrystallized grains were observed in the fusion region in the as-welded (AW) condition. The grain boundaries of the weld seams were precipitated with M7C3 carbides, discrete amounts of eta (Eta) and a (Sigma) phases after subjecting to DA. The tensile strength of the weld seams was increased to similar to 41 % and 31 % after having exposed to DA for 4 and 8 h respectively. The failures due to tension occurred in the fusion zone of Incoloy 925 irrespective of the DA conditions. The formation of ri phase and high angle grain boundaries (HAGBs) resulted in a lower percentage of elongation and impact toughness when aged for 8 h.

The fillers ER80S-Ni3 and ER2553 were deployed to obtain 10 mm thick joints of super-duplex stainless steel (SDSS) and high strength low alloy (HSLA) steel using pulsed direct current (PDC) welding approach. Laths of martensite/bainite with retained austenite were observed in the weld seam microstructure of ER80S-Ni3 joints; whereas austeno-ferrite microstructure was seen in ER2553 joints. Considerable changes in the ferrite percentage was noticed in the fusion region of ER2553 joints. Repeated thermal cycles resulted in austenite reformation and thus a lower ferrite percentage was ascertained in the root pass of ER2553 joints. The tensile ruptures were occurred on the base metal region of HSLA for both the cases. Notch tensile studies demonstrated that the weld seams employing ER80SNi-3 filler imparted better strength and failure occurred in the base metal of HSLA. A decrease of 19 % and 76 % in the impact toughness was observed for ER2553 and ER80S-Ni3 joints when operated in room temperature (RT). The impact toughness of the weld seams was drastically deteriorated while operating at -196 degrees C, reasoned to the ductile to brittle transition.

This study investigates the microbial-influenced corrosion of UNS S32750 super-duplex stainless-steel joints fabricated using different welding methods. Herein, the samples were introduced into a medium inoculated with Macrococcus equipercicus isolated from a marine environment. Confocal laser scanning microscopy and atomic force microscopy were used to characterise the topography and formation of pits in the corroded samples, respectively. Potentiodynamic polarisation studies were conducted on both the base alloy and weld seams exposed for 30 and 60 days in the experimental system inoculated with M. equipercicus and un-inoculated system. Results indicate that the thickness of the biofilm formed due to this bacterium increased and became heterogeneous with an increase in the exposure time, thereby resulting in micro-pits. Bacterial colonisation was observed in all the coupons after exposure to the inoculated medium. Although micro-pits were observed in all the coupons, the base metal and flux-cored arc weld seams showed highest sensitivity to bacterial attack. (C) 2020 Elsevier B.V. All rights reserved.

Incoloy 925 joints of 5 mm thick were accomplished by adopting high energy density, electron beam welding (EBW) process. Although the weld seam microstructure was completely austenitic and free from solidification cracking, the heat-affected zone (HAZ) of EBW joints experienced liquation cracking. The mechanical behaviour of the EB weld seams in the as-welded and direct aged (DA) at 732 degrees C for 4 h and air-cooled conditions were compared. Electron backscattered X-ray diffraction (EBSD) analysis revealed the formation of strengthening precipitate gamma' in the matrix and the precipitation of sigma (sigma) phase, M7C3, M23C6 and Ti-rich carbides formed along the crystallite boundaries in the DA condition. The tensile property outcomes opined that the joint efficiency of the weld seams in the DA condition (99.32 %) was found to be better than the ones in the as-welded condition (71.32 %). Also, the yield strength has been considerably improved in the EB weld seams subjected to DA conditions. The carbide precipitation along the grain boundaries is discontinuous and also not effective in pinning the dislocations under impact loads.

A wall component of super-duplex stainless steel was developed using cold metal transfer (CMT)-based wire + arc additive manufacturing (WAAM) technique with an ER2594 wire. The microstructure of the as-deposited wall was explored using optical microscopy and electron backscattered x-ray diffraction (EBSD) analysis. Ferrite count analysis indicated that the austenite-ferrite phase balance was altered along the as-deposited wall body. The average ferrite count near the as-deposited wall was 24.5%, compared with 32.3% in the root region. Widmanstätten and grain boundary austenite were formed near the wall boundary, and intragranular austenite was observed in the different layers. Secondary austenite in the transition layer was also observed. EBSD analysis revealed the sigma (σ) phase and austeno-ferritic phases across the WAAM wall. The tensile and yield strengths of the samples of the as-developed WAAM wall were almost identical regardless of orientations/tropism.

This work articulated the multi-pass, gas tungsten arc welding by adopting pulsating current for joining nitrogen-enhanced, low-carbon austenitic stainless steel, AISI 316L(N). An austeno-ferrite stainless steel (ER2594) and an over-alloyed (ERNiCrMo-3) fillers were employed to join 6-mm-thick plates of AISI 316L(N). Acicular and lathy ferrite in the weld zone of ER2594 and the occurrence of secondary phases in the fusion zone of over-alloyed filler were observed. The notch tensile strength data attested that the joint strength was greater for the welds employing an over-alloyed filler. This study also affirms that the welds obtained with ER2594 filler resulted in better impact toughness (144 J) compared with ERNiCrMo-3 filler and base metal. Also the notch impact toughness of ER2594 weldment is increased to 60% in comparison with that of candidate metal. Corrosion studies were also performed by exposing the coupons in a eutectic salt mixture comprising of 40%K2SO4-60%NaCl for 50 cycles at 650 °C. It is observed that the weld zone employing over-alloyed filler experienced better high-temperature corrosion resistance compared to the base metal. The specific results of this investigation will be of greater demand to the nuclear and marine applications utilizing these joints.

The joints of Incoloy 925 obtained from gas tungsten arc welding (GTAW) with pulsating current utilizing ERNiCrMo-3 and ERNiCrMo-10 were investigated under as-welded and direct aged conditions. The microstructure showed the microsegregation of Nb-Mo-, Ti-rich phases in the weld zone of ERNiCrMo-3 in the as-welded condition. Post-weld heat treatment (PWHT) involving direct aging was carried out on the weldments at 732 °C for 4 h followed by air cooling. On direct aging, the tensile strength of the base metal increases by 40% when compared to the as-received ones. The failures were experienced in the parent metal of Incoloy 925 upon tension testing in as-welded conditions. Although the tensile strength was improved considerably, the failures occurred at the fusion zones, for both the fillers in the direct aged conditions. The joint efficiencies of Incoloy 925 welds employing ERNiCrMo-3 and ERNiCrMo-10 were reported as 95 and 86%, respectively. The impact toughness of the weldments in both the as-welded and PWHT conditions was considerably greater compared to that of the candidate metal.

The effect of over-alloyed Ni-rich fillers on the weld mechanical properties of AISI 904L and Inconel 625 dissimilar joints achieved by pulsating current approach in gas tungsten arc welding (GTAW) is analysed in the present investigation. Micro-segregation and the migrated grain boundaries are noticed on the jointed zones of ERNiCrMo-4 and ERNiCrCoMo-1 respectively. The columnar dendrites near to the fusion line and the fine equiaxed dendritic structures at the centreline are witnessed in the weld regions of both the joints. Tension failures have occurred in the AISI 904L base metal. The notch tension test inferred that the weld strength is higher than the weak parent metal (AISI 904L). The impact toughness was considerably declined sharply compared to the parent metals. The notch tension and impact tests recommend the use of ERNiCrMo-4 filler for joining these dissimilar metals. The research findings based on the relationship between structure-property drawn from this investigation can be employed in the industries requiring the use of the novel joints.