Pandey, Chandan

Friction stir welding (FSW) is a non-traditional welding procedure for joining identical and divergent substances that are comparatively hard to weld using fusion techniques. The FSW is more competent and eco-responsive when correlated with the traditional processes. The tensile characteristics of thermally susceptible alloys are minimized as a result of heat iterations. The roughening of the consolidated deposits in friction stir welding induces joint moderation. For non-heat-treatable alloys, intergranular and stress corrosion cracking are developed in grain boundaries during the FSW. Because of this, the overall performance and mechanical properties were reduced. Underwater friction stir welding (UWFSW) is preferred to prevail over the problems. UWFSW is appropriate for both heat-treatable and non-heat-treatable alloys that are receptive to thermal activity throughout the procedure. This research examines the effects of response surface methodology (RSM)-based grey relational methods on the optimization of UWFSW procedural characteristics such as the straight hexagonal tool profile (SH), tool rotational speed (TRS) of 1200 rpm, tool transverse velocity (TTV) of 20 mm/min, and water head (WH) of 10 mm in military-grade AA5083 alloy. The mechanical properties of the AA5083 UWFSW joint, such as its average ultimate tensile strength (UTS) and hardness, have been greatly improved. Grey Relation Analysis was used to determine welding specifics such as UTS and hardness. The ANOVA was used to assess the formulation's significance. The micro-structural behaviour and grain structure of different weld zones were investigated with the help of the scanning electron microscope (SEM). The image processing technique can be used to quantitatively assess the UWFSW process using the non-destructive testing (NDT) ultrasonic B-scan image and radiographic image. Confirmation tests at the optimal parameter level improved the performance of each response.

This study examines the influence of the ERNiCr-3 (Inconel 82) butter layer on the microstructure and mechanical feature of the dissimilar weld joint (DWJ) of ferritic grade P92 and austenitic grade AISI 304 L steel, manufactured using gas tungsten arc welding (GTAW) method with IN82 filler. The butter layer aims to prevent the formation of a hard martensitic layer adjacent to the fusion line by mitigating the carbon migration from the P92 steel to the welding pool. The optical microscope, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and electron probe microanalyzer (EPMA) were used to examine the microstructures of the buttered welded plate. The mechanical characteristics of the joints were assessed using the standard and sub-sized tensile and Charpy tests. The flat and round specimens underwent the tensile test to determine their relative tensile properties at room temperature and high temperature. The high-temperature tensile properties were assessed at 600 °C and 650 °C at 1 mm/min extension rates. Along the weldments, hardness profilometry was also performed. Microstructural analysis validated that the application of a buttering layer successfully eliminated the extensive martensitic layer on the P92 side. Nevertheless, in the vicinity of the interface between the buttering layer and P92, there was evidence of a narrow unmixed zone and macrosegregation. SEM/EDS and EPMA studies confirmed that the predominant phases identified in IN82 butter and weld metal are NbC and TiC. The butter layer, overall, improved elongation/ductility by 25 % without a noticeable reduction in tensile strength. During tensile testing, the specimen fractured from the IN82 butter layer, revealing the presence of dimples and voids on the fracture surface, along with the TiC/NbC phases, as confirmed by SEM analysis. Tensile specimens subjected to high-temperature testing exhibited failure at the base materials of AISI 304 L (tensile strength=404 MPa) and P92 (307 MPa), specifically at 550 °C and 650 °C, respectively, rather than at the buttering layer or weld metal. The results of the tensile tests met the minimum criteria specified for Ultra-Supercritical (USC) boilers. More importantly, the IN82 butter layer successfully serves as a protective barrier between the weld pool and the P92 HAZ. As a result, the dual hardness peaks on either side of the welding pool are eliminated. After adding the buttering layer, the peak hardness in the coarse-grained heat-affected zone (HAZ) of P92, which ranged from 450 to 500 HV in the unbuttered sample, dropped by 200 MPa. The relationships between microstructural characteristics and mechanical properties have been thoroughly examined and discussed.

Often known as the workhorse among titanium alloys, Ti-6Al-4 V has been useful in the aerospace and biomedical sectors. For further enhancement of the mechanical characteristics of Ti-6Al-4 V alloy, its sheets procured for the present study have been subjected to equal channel angular pressing (ECAP) using a die setup having a channel angle of 120° and corner angle of 10° at its forming temperature of 650 °C followed by appropriate annealing treatments. Microstructural analysis post the hot-ECAP process has demonstrated ultrafine grain (UFG) refinement because of this severe plastic deformation technique of ECAP. Phase analysis has further substantiated the reduction of β-phase in the alloy as a controlling factor in improving the mechanical properties. As a result, the room temperature hardness and tensile strength have improved by 10% and 15%, respectively, due to a drastic reduction in grain size from ~ 906 nm to ~ 359 nm, which is in line with the well-established Hall–Petch equation. Basic finite element modeling has been studied as concerned with the sustainability and feasibility of the die setup to withstand the heavy metal forming forces involved in the ECAP of Ti-6Al-4 V. This success in processing Ti-6Al-4 V by a single pass of an ECAP using channel angle of 120° and corner angle of 10° under a controlled equivalent strain further opens doors for incorporating additional steps and criteria to achieve even higher grain refinement and strength enhancements thereby catering to the needs for manufacturing the assault vehicles and bioimplants.

The present research focuses on investigating the changes in microstructure–mechanical integrity of the dissimilar joint between X-70 pipeline steel and super duplex stainless steel (sDSS 2507). Gas tungsten arc welding with ER 309L austenitic filler at 0.73 and 1.4 kJ/mm heat inputs was employed. The microstructure was characterized using a scanning electron microscope with energy-dispersive spectroscopy and an optical microscope. The weld joint’s mechanical characteristics and overall integrity were evaluated through microhardness, cross-weld tensile, and impact toughness tests. Oil and gas pipelines and hydrocarbon drilling risers use this type of dissimilar joint. The filler material ER309L solidifies into a ferrite–austenite microstructure with skeletal and lathy ferrites and interdendritic austenite. The study revealed that the weld zone and heat-affected zone (HAZ) microstructure displayed Type II boundaries and macro-segregation for lower heat input (LHI) and higher heat input (HHI) welding conditions. Additionally, three distinct types of HAZs were identified in the X-70 base metal, each associated with a different thermal peak temperature during welding: coarse grain, fine grain, and inter-critical. The hardness values ranged from 190 to 290 Hv0.5, with an average of 205 ± 6 Hv0.5 for LHI and 225 ± 4 Hv0.5 for HHI weldment. The tensile strength and elongation of the LHI samples were found to be 609.4 MPa and 25.3%, while the HHI samples were 601.7 MPa and 30.8%. The impact toughness was 195 ± 5 J and 185 ± 2 J for the cap and root sections of the LHI weldment, compared to 180 ± 4 J and 200 ± 3 J for the HHI weldment. As a result, the investigation sheds insight into the evolution of welding processes and microstructural evolution in the weld zone and HAZ, variations in mechanical characteristics, and changes in residual stresses for the sDSS 2507/X-70 DWJ.

High-entropy alloys (HEAs) consist of five or more major alloying elements, resulting in outstanding characteristics, namely, compressive strength, high temperature strength, and hardness. For a wide range of applications, specific properties such as, compressive strength and strain, tensile strength and strain, and hardness, or their combinations are necessary. However, it also noticeable that achieving a balance of properties (like strength and ductility) in HEAs is still a big hurdle for its wide application. Therefore, this chapter emphasizes on the influence of alloying elements on the properties of HEAs, which would enable researchers to design HEAs with the desired attributes for specific applications.

This research focuses on the effect of heat input of super duplex stainless steel (sDSS 2507) and nitronic steel (N50) dissimilar welded joints. Two heat input combinations selected as lower heat input (LHI) (0.62 kJ/mm) and higher heat input (HHI) (1.01 kJ/mm) were preferred during the operation of the gas tungsten arc welding process (GTAW) process using ER2594 filler. The macrosegregation like an island, peninsulas are observed in both weldments' HAZ and weld zone. The presence of secondary austenites (γ2) precipitation is observed in HAZ and root region of weldments. As heat input increases, the ferrite content of the weld zone in HHI decreases. Nevertheless, HHI had an advantageous effect on austenite nucleation in the HAZ. To ascertain the mechanical characteristics of the dissimilar metal welds (DMWs), tests such as the Vickers micro-hardness test, Charpy impact test, and tensile test were conducted. The mechanical evaluation reveals that the average hardness of LHI shows more hardness of 280 ± 4 Hv0.5 than HHI weldment of 270 ± 3 Hv0.5. Hence, weld zone, HAZ, and interface hardness do not indicate any significant change with the increment in heat input, which can be credited to the phase balance of ferrite/austenite. The tensile strength of LHI and HHI weldment is 895 ± 4 MPa and 900 ± 5 MPa, respectively, but LHI weldment displays better ductility. The Charpy impact test reveals that the impact toughness value decreases with increased heat input (i.e., 165 ± 5 J and 145 ± 3 J for LHI and HHI weldment, respectively) because of the secondary phase formation and increased grain size. However, the weld metal's Charpy impact toughness was more than the ASME standard value (> 41 J) and the EN 1599:1997 standard value (> 47 J). The microstructural observation and mechanical characterization suggest that lower heat input could be beneficial for weld’s structural integrity.

In this present study, a novel approach of measuring through-thickness residual stresses based on the general strain relaxation methodologies has been described. This new method is an amalgam of the conventional deep hole drilling technique and the contour method with a reduced degree of damage to the component made during measurements. The annular deformation of a reference hole made at the measurement location has been interpreted as the displacement boundary conditions in a two-dimensional finite element model. In this regard, a thick, partially plastic four-point bent bar specimen was used to validate the proposed method. Through-thickness axial residual stresses induced in the bar were measured using the proposed technique and were observed to be in a reasonably close match with the theoretical and DHD results.

The Cr–Mo steel containing 9% Cr is generally preferred in producing high-temperature operating components (lower than 620 °C) like steam pipes and headers due to their outstanding combination of elevated temperature mechanical properties and creep strength. The components with an operating temperature of more than 620 °C (superheater and reheaters tubes) are mainly produced using stainless steel or Ni-based superalloy. Hence due to economic aspects of boilers, joining of P92 steel with Ni-based superalloy is inevitable in advanced ultra-supercritical (AUSC) plants. Thus the development of joining technology without diminishing the high-temperature mechanical properties of the weldments becomes essential. The present work introduces the microstructure evolution in gas tungsten arc welded (GTAW) dissimilar joint of P92 steel and Inconel 617 alloy produced by using the P92 filler. The microstructure study along weldments was examined using an optical microscope (OM) and field emission scanning electron microscope (FESEM). The mechanical properties of welded joint and joint integrity were determined by using the microhardness measurement, cross-weld tensile tests, and impact toughness test. The effect of the post-weld heat treatment (PWHT) on mechanical properties and microstructure evolution was also performed. The residual stresses were also examined using the blind hole drilling methods, and the effect of PWHT on the nature and magnitude of the residual stresses were also conducted. The microstructure observation showed the martensitic lath structure in the weld metal, which resulted in poor impact toughness (36 ± 5 J) and high hardness (458 ± 25 HV) of weld metal in the as-welded condition. A considerable increase in impact toughness (90 ± 4 J) and a decrease in hardness (371 ± 11 HV) of weld metal were observed after the PWHT. A wide region of the unmixed zone at the interface of weld metal and Inconel 617 was formed due to the difference in chemical composition and structure. The unmixed zone formation led to the poor tensile properties of the welded joint, and failure was observed both in P92 BM and at the interface of weld metal and Inconel 617 interface. The tensile tested sample failed from the interface region and showed the presence of Ti(C, N) particles, while secondary phase M23C6 particles were obtained from the tensile sample fractured from P92 BM. The impact test results also showed the variation in impact toughness along the weldments. The P92 BM was found the strongest zone, while weld metal was noticed as the weakest zone in terms of impact toughness. The variation in residual stresses was also measured along with the thickness of the plate, and the peak magnitude of the residual stresses was measured in the capping pass, which was compressive in nature.

The present study investigates the tribological behavior and residual stresses of sDSS 2507/X-70 dissimilar weld joints, focusing on their structural integrity for marine applications. Gas tungsten arc welding was performed using ER2594 and ER309L filler metals at lower heat input (LHI-0.7 kJ/mm) and higher heat input (HHI-1.4 kJ/mm). Utilizing a slurry pot tester with varying silica sand concentrations (10 and 30 wt pct), weight loss, erosion wear, and wear mechanisms are analyzed in marine environment. The investigation provides a comprehensive understanding of erosive behaviors by analyzing surface and microstructure characteristics using scanning electron microscopy. All specimens experienced significant weight loss in response to increasing slurry concentrations. Weight loss increased by 17 pct for sDSS 2507 base metal (BM) and 36 pct for X-70 BM with increased slurry concentration. High slurry concentrations induce significant weight loss due to sand particle density, particle-to-surface contact, particle interactions, and fluid impacts. ER309L-LHI lost 55 pct more weight than ER2594-LHI in response to increased slurry concentration, while ER309L-HHI lost 56 pct more weight than ER2594-HHI. Compared to both BM, ER2594-LHI and ER309L-LHI exhibit superior resistance to slurry erosion. ER2594-LHI and ER309L-LHI erosion rates increased 1.14 and 1.32 times with slurry concentration. Material removal mechanisms included micro-cutting, crater formation, lip fragmentation, and ridge formation. Deep-hole drilling method has been used to estimate the residual stress in the weld zone. ER2594 weldment exhibited predominantly tensile residual stress distributed throughout its thickness. The weld surface experienced a longitudinal residual tensile stress of 241 MPa, with the lowest residual stress observed at the weld root. In the ER309L weldment, the maximum residual stress recorded was 175 MPa. The study recommends suitable welding parameters in terms of heat input and filler metals (ER2594 and ER309L) for improved slurry erosion resistance in sDSS 2507/X-70 welds, highlighting the significance of residual stress analysis to evaluate weld structural integrity under operational conditions.

Restrictive operating conditions (even exceeding 700 °C) of materials in advanced ultra super critical (AUSC) power plants and the need to minimize manufacturing and maintenance costs require the production of dissimilar metal welded joints (DMW). Significant differences in the physical and chemical properties of welded materials lead to phenomena that reduce the weldability of the metals used and force the search for solutions that limit unfavorable phenomena, e.g., the use of buttering layers. The study presents a comparison of two types of joints with Alloy 617 (UNS N06617) and ferritic P92 (UNS K92460) steel made using Inconel 82 (ENiCrFe-3) and Inconel 617 (ERNiCrCoMo-1) alloys buttering layer and the corresponding chemical composition of filler metals. All areas of the joints made with the gas tungsten arc welding process were subjected to structural investigations (optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) and mechanical tests (microhardness, room and high temperature tensile, and toughness testing). Despite the more complicated welding procedure, sound welded joints were obtained with favorable properties resulting, inter alia, from the reduced thickness of the martensite layer in HAZ of P92 steel and the limited diffusion of alloy components compared to welded joints without the buttering layer. This also resulted in a reduction of the maximum hardness (especially in the case of Inconel 82 buttering—by 15–30 HV0.5 in comparison with Inconel 617 buttering) and an increase in strength while limiting the decrease in plasticity (even 663 MPa tensile strength and 21% of elongation for Inconel 617 buttered joint). Moreover, improved high-temperature performance (approximately 70–100 MPa) of the welded joint following the application of the buttering layer was confirmed. The presented results allow for drawing general conclusions that both proposed welding procedures can be recommended for use in the working conditions occurring at AUSC.