Pandey, Chandan

The present work investigates the high-temperature tensile and creep properties of the dissimilar metal weld joints of 304L austenitic stainless steel (SS) and P92 creep strength-enhanced ferritic-martensitic (CSEF/M) steel under different testing condition. Thermanit MTS 616 filler rod (P92 filler) and the multi-pass tungsten inert gas (TIG) welding process were used to create the dissimilar weld connection. The ultimate tensile strength (UTS) was evaluated in the temperature range of 450–850 °C. Creep testing was conducted at a temperature of 650 °C while applying stress levels of 130 MPa, 150 MPa, 180 MPa, and 200 MPa. The shortest creep life (2.53 h) was recorded for the specimen tested at 650 °C and subjected to 200 MPa, whereas the longest creep life (~ 242 h) was observed for the specimen tested at 650 °C with a stress of 130 MPa. The linear regression model was developed using an applied stress (σ) v/s rupture time (tR) plot at 650 °C. The applied stress and rupture time followed the logarithmic equation: log(tR) = 22.57566 + (-9.55294) log (σ). The detailed microstructural characterization and micro-hardness distribution across the fractured specimens was carried out. The findings demonstrated that the service life span of this weld joint at high temperature and stress conditions is influenced by the undesired microstructural changes at elevated temperature, such as coarsening of the precipitates, development of the Laves phase, softening of the matrix, and strain-ageing phenomenon.

For this study, the researchers aimed to dissimilar weld the Nickel-based superalloy Inconel 718 (IN 718) with austenitic stainless steel 304L (ASS 304L) using the gas tungsten arc welding (GTAW) technique and Nickel-based filler IN 82 (ERNiCr-3). In order to examine the weld microstructures, we utilized optical microscopy (OM) and field emission scanning electron microscopy (FESEM) with energy-dispersive spectroscopy (EDS) to identify any segregation present in various weld zones. Through optical and FESEM analyses, it was revealed that the base metals (BM) exhibit an austenitic character. The IN 718 BM matrix contains dispersed γ′ and γ″ strengthening precipitates within the Nickel matrix. On the other hand, the ASS 304L BM displayed a unique austenitic microstructure characterized by twins features. The weld metal exhibited solidification grain boundaries (SGBs), migrated grain boundaries (MGBs), and distinct dendritic microstructures that had an impact on the properties of the weld. Through extensive analysis and mapping of the IN 82 weld zone, it was discovered that interdendritic regions contain carbides of Nb, Cr, and Ti. In addition, there were Unmixed zone (UZ) areas between the IN 82 filler and the base materials on both sides of the weld zone, appearing as islands and beaches. The texture of the different weld zones was evaluated using electron backscattered diffraction (EBSD) analysis. Additionally, the presence of a notable level of strain within the weld metal grains was observed through Kernel average misorientation (KAM) micrographs. Fractures were observed in the IN 82 weld zone, indicating that it is the weakest area in the IN 718/ASS 304L dissimilar weld at room temperature, according to the outputs of the tensile tests. The micro-hardness profile showed substantial hardness values in the weld zone, which can be attributed to the appearance of a diverse microstructure and additional precipitates. At room temperature, the recorded average tensile strength of the dissimilar weld joint was 626 MPa. In addition, experiments were carried out at high temperatures of 550 °C, 600 °C, and 650 °C to measure the tensile strength. In the high-temperature tensile tests, it was observed that the IN 82 weld zone exhibited higher tensile strength compared to the ASS 304L BM. Interestingly, the high temperatures tensile specimens failed in the 304L BM. The Charpy impact toughness test was performed with notches at ASS 304L HAZ, IN 718 HAZ, and the weld center. Using the deep hole drilling (DHD) technique, we were able to quantify residual stress and identify the location of the highest tensile residual stress, which was found to be 3 mm from the weld surface. (Figure presented.)

This study investigates the corrosion behavior of dissimilar gas tungsten arc (GTA) welded joints between super duplex stainless steel (sDSS 2507) and pipeline steel (X-70) using electrochemical and immersion corrosion tests. The GTA welds were fabricated using ER2594 and ER309L filler metals. The study examined the electrochemical characteristics and continuous corrosion behavior of samples extracted from various zones of the weldments in a 3.5 wt.% NaCl solution, employing electrochemical impedance spectroscopy, potentiodynamic polarization methods, and an immersion corrosion test. EIS and immersion investigations revealed pitting corrosion in the X-70 base metal/X-70 heat-affected zone, indicating inferior overall corrosion resistance due to galvanic coupling. The corrosion byproducts identified in complete immersion comprised α-FeOOH, γ-FeOOH, Fe3O4, and Fe2O3, whereas γ-FeOOH and Fe3O4 were predominant in dry/wet cyclic conditions. Corrosion escalated with dry/wet cycle conditions while maintaining a lower level in complete immersion. The corrosion mechanism involves three wet surface stages in dry/wet cycles and typical oxygen absorption during complete immersion. Proposed corrosion models highlight the influence of Cl−, O2, and rust layers.

The investigation carried out in the current study illustrates the dissimilar gas tungsten arc welding (GTAW) between Inconel 718 (IN 718) and austenitic stainless steel (ASS 304L) utilizing three different filler materials. This study utilizes Ni-based fillers (ERNiCrCoMo-1 (IN 617) and ERNiFeCr-2 (IN 718)), and austenitic filler ASS 304L and characterizes the relationship among microstructural and mechanical characteristics using identical weld parameters. The obtained dissimilar weld joint using Ni-based filler materials depicts no weld solidification cracking, whereas austenitic filler causes the weld solidification cracks. The microstructural characterizations were examined using optical and FESEM revealing the occurrence of columnar, cellular, and equiaxed dendritic structures in all three weld metals. FESEM/EDS analysis illustrates the occurrence of Mo and Cr-rich phases (M23C6 and Mo6C) in ERNiCrCoMo-1 weld metal, NbC, Mo/Ti–rich, and laves phases in ERNiFeCr- 2 weld metal and Cr- rich carbides in ASS 304L weld metals. EBSD assessment shows the improved texture of the weld metals through IPF and PF maps. The Vickers microhardness demonstrates the highest hardness value (271 HV5) for the ERNiFeCr- 2 weld metal due to the existence of the brittle intermetallic phases, and minimum in the case of ASS 304L weld metals (156 HV5). The ambient temperature tensile test exhibits the maximum (649 MPa) and minimum (404 MPa) UTS corresponding to ERNiCrCoMo-1 and ASS 304L weld metals respectively. The tensile specimens for all the weld metals experience fracture from the weld metals. The Charpy toughness values of the weld metals show lower values (ERNiCrCoMo-1 (70 J), ERNiFeCr-2 (56 J) and ASS 304L (32 J)) than the BMs (IN 718 (135 J) and ASS 304L (228 J). Residual stress analysis was conducted employing the deep hole drilling (DHD) technique, indicating that the highest residual stress occurs 2 mm below the top weld face, classified as tensile stress for all three used filler materials.

This study delves into the microstructure and mechanical properties of a dissimilar metal weld (DMW) joining Incoloy 800HT and P91 steel. The P91 was buttered with Inconel 82 (ERNiCr-3) filler layers, and the final DMW weld was fabricated using Inconel 617 (ERNiCrCoMo-1) filler. Weld interface regions were characterized using electron backscatter diffraction (EBSD) and scanning electron microscopy. EBSD uncovered unique microstructural characteristics across the DMW. Extensive investigation was conducted on the heat-affected zone (HAZ) of Incoloy 800HT, revealing a consistently stable austenitic microstructure characterized by random grain orientations. Nevertheless, the weld fusion zone (WFZ) exhibits an intricate microstructure characterized by dendrites that extend into packets. The WFZ and the buttering layer interaction exhibited a predominantly face-centered cubic (FCC) structure. Recrystallization was indicated in this region. During tensile testing, the DMW specimens experienced failures at different locations and exhibited varying mechanical properties. A standard specimen made of Incoloy 800HT base metal experienced failure during welding. The DMW exhibited a maximum ultimate tensile strength (UTS) of 671 MPa and a yield strength (YS) of 234 MPa. The buttering process helped avoid the post-weld heat treatment to a certain extent. A maximum of 98 ± 5 J Charpy impact toughness was observed in the WFZ of the DMW failing in a complete ductile mode.

Dissimilar metal welded (DMW) joint plays a crucial role in constructing and maintaining ultra-supercritical (USC) nuclear power plants while presenting noteworthy environmental implications. This research examines different welding techniques utilized in DMWJ, specifically emphasizing materials such as P91. The study investigates the mechanical properties of these materials, the impact of alloying elements, the notable difficulties encountered with industrial materials, and the concept of buttering. The USC nuclear power plants necessitate welding procedures appropriate for the fusion of diverse metal alloys. Frequently employed methodologies encompass shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and flux-cored arc welding (FCAW). Every individual process possesses distinct advantages and limitations, and the choice of process is contingent upon various factors, including joint configuration, material properties, and the desired weld quality. The steel alloy known as P91, which possesses high strength and resistance to creep, is extensively employed in advanced ultra-supercritical (AUSC) power plants. P91 demonstrates exceptional mechanical characteristics, encompassing elevated-temperature strength, commendable thermal conductivity, and notable resistance against corrosion and oxidation. The presence of alloying elements, namely chromium, molybdenum, and vanadium, in P91, is responsible for its improved characteristics and appropriateness for utilization in (AUSC) power plant applications. Nevertheless, the utilization of industrial materials in DMW joint is accompanied by many noteworthy concerns, such as the propensity for stress corrosion cracking (SCC), hydrogen embrittlement, and creep deformation under high temperatures. The challenges mentioned above require meticulous material selection, process optimization, and rigorous quality control measures to guarantee the dependability and sustained effectiveness of DMW joint. To tackle these concerns, a commonly utilized approach referred to as buttering is frequently employed. When forming DMW joint in nuclear facilities, it is customary to place a buttering coating on ferritic steel. This facilitates the connection between pressure vessel components of ferritic steel and pipes of austenitic stainless steel. The primary difficulty in DMW joint manufacturing is in mitigating the significant disparity in material characteristics resulting from carbon migration and metallurgical alterations along the fusion interface between ferritic steel and austenitic stainless steel. The process of buttering entails the application of a compatible filler material onto the base metal before the deposition of the desired weld metal. The intermediate layer serves as a mediator, enhancing the metallurgical compatibility, diminishing the probability of fracture, and enhancing the overall integrity of the joint. Buttering is still a new research area with a wide scenario of scope in terms of development, which could revolutionize developing high-temperature. These long-term sustainable joints could serve under critical conditions like AUSC power plants and reduce CO2 emissions by increasing the overall efficiencies of the systems.

The dissimilar welded joint (DWJ) comprising P92 steel and Inconel 617 (IN617) is frequently utilized in advanced ultra-supercritical (AUSC) boilers. In present work the creep rupture behaviour, rupture mechanism and microstructure evolution of DWJ of P92 steel and IN617 with Ni-based ERNiCrCoMo-1 filler, were examined at 650 °C under the stress range of 120–200 MPa. The results of the creep test indicated that the location of creep rupture varied across different testing conditions, encompassing areas such as P92 base metal and the fine-grained heat-affected zone (FGHAZ). The creep tested specimens within the stress range of 180–200 MPa exhibited failure originating from P92 base metal, predominantly influenced by plastic deformation. The failure manifested in a transgranular mode, driven by the formation, growth, and eventually coalescence of microvoids. The creep tested specimens within the stress range of 120–150 MPa displayed the characteristic ofType IV failure, primarily attributed to matrix softening and the absence of adequate precipitates to pin the PAGBs. Microstructural characterization unveiled the presence of microvoids along the PAGBs, facilitating microvoid nucleation primarily owing to the existence of the coarse brittle carbide phase. The growth of these microvoids over a period of time during tertiary stage of creep which lead to their coalescence and the formation of microcracks, ultimately resulting in premature intergranular failure. The specimen creep exposed at 650 °C under the lower stress of 120 MPa exhibited higher creep rupture life for 432 h. The SEM/EDS study of the crept sample of 120 MPa is also confirmed the presence of intermetallic laves phases in regions near the fracture tip and in the heat-affected zones (HAZs). Although the creep tested specimens at 150 MPa and 120 MPa exhibited failure in the FGHAZ and their elemental SEM/EDS analysis confirmed the presence of an oxide layer and notch formation near the interface of P92 base metal and ErNiCrCoMo-1 filler weld. The FESEM study revealed the growth of the oxide layer in the notch region, and it also showed the presence of multiple cracks and microvoids in the oxide layer. The formation and propagation of the oxide notch mainly led to the interfacial failure. The crept specimens subjected to 180 MPa and 200 MPa did not exhibit any cracks or microvoids in HAZs. However, specimens that failed under applied stresses of 120 MPa and 150 MPa revealed the presence of a high density of microvoids in the FGHAZ, inter-critical heat-affected zone (ICHAZ), and in the region of the coarse-grained heat-affected zone (CGHAZ) adjacent to the interface attached with an oxide layer.

AA5083 is an alloy of military-grade aluminum used to make lightweight combat vehicles. Combining this material with traditional welding methods results in the formation of grain agglomerations, alloy separation, porosity, and pores. To overcome these shortcomings, Friction stir welding was utilized. In this work, the problems arising from friction stir welding are reduced by performing the process underwater. A relative study was also conducted to determine the impact of various tool pin profiles. particularly straight hexagonal, straight cylindrical, straight threaded, and tapered cylindrical. Friction stir welding and Underwater friction stir welding were used for welding Aluminium alloy AA5083 alloys of 150 x100 × 6 mm, constant tool rotational speed of 1200 rpm, tool transverse speed of 40 mm/min, and tool tilt angle of 0°. This study revealed that the straight hexagonal pin produced joint in an underwater cooling medium had a greater tensile strength (UTS) of 295 MPa and a joint efficiency of 78 %.

This study investigates and establishes the effect of welding process parameters on the tribological performance of the fabricated weld using the gas tungsten arc welding (GTAW) process. Both ER 2594 and ER 70S-2 were used as filler metals to fabricate a dissimilar GTA weld between sDSS 2507 and N50 steels. sDSS 2507/N50 DWJs have substantial importance to the subsea oil-gas drilling industries, especially in tubing and coupler assembly. The thermodynamic study predicts microstructure evolution during weld fusion zone cooling. Dry-sliding tribology behaviors were investigated using a pin-on-disc dry-sliding wear tester with a constant load of 30 N, sliding speeds from 1.111 to 6.666 m/s, and distances from 500 to 3000 m. Scanning electron microscopy examined the worn surface’s wear mechanism and progression. ER70S2-LHI specimen had the lowest volume loss (12.83 mm3), and the N50 BM exhibited the greatest (112.65 mm3). Due to its martensitic structure, ER70S2-LHI has the lowest wear rate (4.28 × 10–3 mm3/m), while N50BM demonstrates the highest wear rate (37.5 × 10–3 mm3/m). For both LHI and HHI weld conditions, ER70S2 filler welds outperform ER2594 filler welds by 85 and 60%, respectively, in volume loss and by 81 and 48%, respectively, in wear rate. N50 BM had poorest wear progression and the ER70S2-LHI weld zone the most. Sliding wear on pins from base metal and filler weld zones exhibits mixed-mode abrasive, adhesive, and fatigue wear, producing material removal as spalling and flaking.

This study examines the welded joint between P91 steel and Incoloy 800HT using the activated tungsten inert gas (A-TIG) welding process. The focus is on analyzing the microstructure and evaluating the mechanical properties of joints made with different compositions of activating flux. Owing to the reversal of the Marangoni effect in which the conventional direction of molten metal flow in the weld pool is reversed due to the application of oxide-based fluxes, a complete depth of penetration of 8 mm was successfully achieved. Conducting mechanical tests, such as microhardness, tensile, and Charpy impact toughness tests, elucidates the behavior of the welded specimens under different loading conditions. The findings highlight the effects of grain size, dislocations, and the evolution of fine-sized precipitates in the high-temperature matrix. This study highlights the importance of choosing suitable flux compositions to achieve consistent penetration and dilution in the base metals. Insights into different failure modes and the influence of temperature on the tensile strength were evaluated. Beneficial mechanical properties of the joints (meeting the criteria of ISO and ASTM standards) were found: ultimate tensile strength of 585 ± 5 MPa, elongation 38 ± 2%, impact toughness of 96 ± 5 J, and maximum microhardness of 345 ± 5 HV.