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The effects of the post-weld treatment on the impact performance, microstructure, and carbide precipitation behavior of pressure vessel steel were evaluated under simulated post-weld conditions. The continuous cooling transformation and isothermal transformation curves of undercooled austenite for the steel were constructed based on the expansion curve, serving as a guide for the potential heat treatment of the steel plates. A more detailed study was conducted on the simulated post-weld process with an insulation temperature of 690 ℃ and an insulation time of 24 h, based on the delivery status of the steel plate. The microstructure was characterized using transmission electron microscopy, field emission scanning electron microscopy combined with electron backscatter diffraction, and electron probe microanalysis. The Charpy V-notch impact test was used to assess the impact performance of the steel plates. The results showed that refining the microstructure to 50% bainite and 50% ferrite, along with a high proportion of large-angle grain boundaries and large-angle misorientation grains at half the thickness of the steel plate, contributed to enhanced low-temperature impact toughness in its delivered state. Additionally, the steel predominantly consists of chromium-containing carbides. In the as-delivered state, the carbide size was measured at 110 nm. However, after post-weld heat treatment (PWHT), the carbide size significantly increased to 360 nm, reflecting a 227% growth. This coarsening is observed along the grain boundaries and through intragranular aggregation. Additionally, there was a change in carbide type from Cr7C3 in the as-delivered state to Cr23C6 following the heat treatment. This transformation was accompanied by a significant reduction in impact toughness, as evidenced by the impact energy dropping from 116 J to an unacceptable 43 J.

High Strength Low Alloy (HSLA) steels are the materials of choice in pipeline construction with the API X70 grade as the steel for the majority of pipeline networks constructed during the late 20th and early this century. This paper reports on the influence of Post-Weld Heat Treatment (PWHT) on the reduction of residual stresses, resulting changes in the microstructure, and mechanical properties of a multi-pass, X70 HSLA steel, weld joints made by a combined Modified Short Arc Welding (MSAW) and Flux Cored Arc Welding (FCAW) processes. Neutron diffraction results highlighted high magnitude of tensile residual stresses, in excess of yield strength of both parent and weld metal, in the as-welded specimen (~650 MPa), which were decreased substantially as a result of applying PWHT (~144 MPa). Detailed microstructural studies are reported to confirm the phase transformation during PWHT and its interrelationship with mechanical properties. Transmission Electron Microscopy (TEM) analysis showed polygonization and formation of sub-grains in the PWHT specimen which justifies the reduction of residual stress in the heat-treated weld joints. Furthermore, microstructural changes due to PWHT justify the improvement in ductility (increase in the elongations) with a slight reduction in yield and tensile strength for the PWHT weld joint.

Residual stresses arising from welding can adversely affect the mechanical properties of welded structures. Stress relief techniques involving thermal or mechanical methods are commonly employed to mitigate these stresses and improve the performance of welded structures. This study involved subjecting welded plates of ASTM A131 EH36 marine steel to thermal and vibrational stress relief methods, followed by conducting mechanical tests to evaluate the impact of stress relief on tensile, bending, microhardness, and toughness properties. Thermal treatment is a consolidated and already standardized method. On the other hand, vibrational treatment for stress relief is a method that lacks studies and standards, but it may become an excellent alternative to traditional thermal treatment. The aim is to compare the results obtained from each method, both with and without stress relief, including vibration welding conditioning. The study concluded that both stress relief techniques reduced stress intensity and altered mechanical properties, with thermal treatment being the most significant.

Dissimilar joints between Ti-6Al-4V (Ti-64) and Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242) were manufactured using linear friction welding. The weld quality, in terms of the microstructure and mechanical properties, was investigated after stress relief annealing (SRA) at 750 °C for 2 h and compared with the as-welded (AWed) results. The central weld zone (CWZ) microstructure in the AWed condition consisted of recrystallized prior-β grains with α’ martensite, which transformed into an acicular α+β structure after SRA. The hardness in the AWed condition was highest in the CWZ and decreased sharply through the thermomechanically affected zones (TMAZ) to the parent materials (PMs). After SRA, the hardness of the CWZ decreased, mainly due to tempering of the α’ martensite microstructure. Static tensile testing of the dissimilar welds in both the AWed and stress relief annealed (SRAed) conditions resulted in ductile fracture occurring exclusively in the Ti-6Al-4V side of the joint. The promising results on joining of Ti-64 to Ti-6242 provide valuable insight for tailoring performance of next-generation aero-engine products.

Over the past years, the alloy development has led to the development of new steels such as P91 (X10CrMoVNb9-1), P911 (X11CrMoWVNb9-1-1), and P92 (9Cr–0.5Mo–1.8W–V–Nb). The topic of the present research work was selected to concentrate on the dissimilar welding of P911 and P92 steels by using manual metal arc welding (MMAW) to work on the weldability with pre and post weld heat treatments. The welding procedure for components of 9–12% Cr steels was related to three main aspects: the materials, the process used for welding and the type of components used to weld these steels. MMAW process was applied to produce the dissimilar joint of the P911 and P92 steel by using E-911 electrode. Normalizing and tempering (N&T) and post-weld heat treatment (PWHT) were applied to the welded plates of thickness 12 mm and they were tested using tensile test, hardness test, Charpy toughness test, and microstructural investigations. During the room temperature tensile tests, serrations were also observed. PWHT of weldments resulted in a negligible increase in ultimate tensile strength and yield strength while a significant change was measured after N&T. The N&T condition resulted in minimum hardness gradient and maximum homogenization of microstructure across the dissimilar weldments. The room temperature Charpy toughness value was also found to be maximum for N&T treatment.

The study investigates the influence of post-weld heat treatment (PWHT) on the microstructure and hardness of hardfacing layers applied to hot forging tools. The research focuses on three tool steels (55NiCrMoV7, X37CrMoV5-1, and a modified X38CrMoV5-3) and uses robotized gas metal arc welding (GMAW) with DO015 filler material. It examines the structural and mechanical differences in the hardfaced layers before and after heat treatment involving quenching and tempering. The findings reveal that PWHT significantly improves microstructural homogeneity and hardness distribution, especially in the heat-affected zone (HAZ), mitigating the risk of crack initiation and tool failure. The study shows that untempered as-welded layers exhibit microstructural inhomogeneity and extreme hardness gradients, which negatively impact tool durability. PWHT leads to tempered martensite formation, grain refinement, and a more stable hardness profile across the joint. These improvements are critical for extending the service life of forging tools. The results underscore the importance of customizing PWHT parameters according to the specific material and application to optimize tool performance.

This technical paper presents a detailed discussion on formation and dissolution mechanism of δ -ferrite in weld fusion zone owing to induction based preheating and subsequent post-weld heat treatment (PWHT). The P91 butt joints were produced by induction assisted gas metal arc welding process (IGMAW). After welding, weldments were subjected to PWHT at 760 °C for 2 h duration in an automatic furnace. The x-ray diffraction (XRD), transmission electron microscopy (TEM) and optical microscopy were utilized to analyse the morphological features of δ -ferrite. In as-welded and induction preheated conditions, presence of δ -ferrite morphology was identified in the weld fusion zone while dissolution of δ -ferrite was confirmed after combination of induction preheating and PWHT (PPWHT). Moreover, experimental results also revealed that application of induction-based preheating with subsequent PWHT significantly affected the formation of fine precipitates and carbide particles in the weld zone. Apart from above analysis, the effect of PPWHT on mechanical properties of the welded joints was also investigated to knowing the mechanical responses of welded joints subjected to PPWHT. Hardness profiles of weldments were acquired by measuring the microhardness using Vickers hardness tester. On the other hand, toughness and tensile properties at room temperature were investigated using universal testing machine and Charpy impact tester. It was perceived that the implementation of PPWHT resulted in a uniform microhardness profile, increased ductility, and improved Charpy toughness of weldment. Thus, induction pre-heating combination with PWHT is shown to be superior methodology within present experimental domain. Based on the obtained results, induction assisted GMAW with subsequent PWHT may be recommended for joining of P91 steel to enhance the weldability by reducing delta ferrite formation as well as improving overall mechanical properties of welded joint.

In the present work, the effect of post weld heat treatment (PWHT) on the microstructure and micro-texture evolution in 316L austenitic stainless steel (ASS)/2205 duplex stainless steel dissimilar weldments were studied. Weldments were subjected to PWHT at 950 and 1100 °C for 1 h followed by water quenching. PWHT changed the γ (austenite)/ δ (ferrite) ratio, average grain size, and grains boundaries (GBs) fraction in the different zones of the weldments. Grain boundary austenite ( γ GB ), Widmanstatten austenite ( γ WS ), and intragranular austenite ( γ IG ) were observed in the heat affected zone (HAZ) on 2205 side and weld zone (WZ). The HAZ on 2205 side showed significant changes in microstructure after PWHT, whereas HAZ on 316L side did not show any significant changes. PWHT at 950 °C showed lower fraction (35%) of δ-phase, whereas PWHT at 1100 °C had a higher δ-phase fraction (53%) in the HAZ on 2205 side. Kurdjumov–Sachs (KS) orientation relationships (ORs) were observed between γ and δ phases in the as-welded and PHWT specimens. Higher fraction of γ / δ grains in HAZ on 2205 side followed the KS ORs for 1100 °C PWHT than as-welded specimen. γ in the as-welded condition (in 2205 BM) showed strong Brass and S components and weak Copper and Cube components. Texture evolution of δ phase in 2205 BM was the dominant Rotated Cube and weak ND//  fiber. PWHT causes change in the texture intensity for both γ and δ phase. A decrease in the microhardness values was observed for the PWHT specimens due to the coarsening of the microstructure.

Direct energy deposition with arc and wire (DED-AW) is a versatile, low-cost, and energy-efficient technology for additive manufacturing of medium- and large-sized metallic components. In this study, the effects of arc energy and shielding gas in cold metal transfer (CMT) welding of walls and blocks on cooling time, mechanical properties, and macro- and microstructure have been studied using precipitation-hardenable Ni-based superalloy Haynes® 282®. The arc energy and consequently the cooling rate were varied by changing the wire feed rate and the travel speed. As expected, increasing the arc energy leads to higher cooling times for the walls. Due to the 2D thermal conduction, the thin walls cool down much slower than multi-layer welded blocks, but this reduces the strength values only very slightly. While the walls have no sensitivity to the occurrence of unacceptable seam irregularities, the multi-layer blocks show isolated seam defects, such as hot cracks or lack of fusion. Despite shielding gas variation, the as-welded blocks show acceptable strength properties at room temperatures (RT) and impact values at RT and −196 °C. However, the use of an N-containing shielding gas results in lower elongation and notched bar impact energy. Precipitation-hardened specimens tested at 871 °C exhibit a similar strength level to transverse tensile specimens of gas metal arc welding (GMAW) welded joints on 12.7 mm thick plates with fracture in the weld metal.

In the present study, the influence of nickel (Ni) and silicon (Si) additions to the Ti-15 V-3Al-3Cr-3Sn (Ti-15-3) fillers on microstructure and mechanical properties of Ti-15-3 gas tungsten arc (GTA) weldments was investigated. Controlled amounts of Ni and Si as grain refiners were introduced into the molten pool of Ti-15-3 alloy by pre-placing the cast inserts (Ti-15-3- x wt.% Ni ( x  = 0.15, 0.30, 0.5) and Ti-15-3- x wt.% Si ( x  = 0.15, 0.30, 0.50)) by GTA welding (GTAW). Microstructural examination of welds with Ni and Si additions revealed refined grains in the fusion zone (FZ) characterized by nonlinear grain boundaries. The grain refinement that is mainly caused by Ni and Si additions develops constitutional supercooling (CS) ahead of the solid–liquid (S/L) interface in the FZ. It has been shown that welds prepared with Ti-15-3-0.5 Ni filler (yield strength (YS) of 688 ± 6 MPa, ultimate tensile strength (UTS) of 721 ± 5 MPa, and % elongation (%El) of 9 ± 0.5%) and Ti-15-3-0.5 Si filler (YS = 693 ± 6 MPa, UTS = 725 ± 5 MPa, %El = 8 ± 0.5%) exhibited higher strength compared to autogenous weld (YS = 575 ± 4 MPa, UTS = 597 ± 4 MPa, %El = 11 ± 0.5%). The increased strength observed in welds made using Ti-15-3-0.5Ni filler and Ti-15-3-0.5Si filler can be attributed to the narrower width of columnar β grains and the presence of equiaxed grains in the FZ. Post-weld heat treatment (PWHT) for all the weldments resulted in improved tensile strength and hardness of the weldments, which was attributed to the fine and uniform precipitation of the α phase in FZ.