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The tungsten inert gas welded P91 steel welded joints were subjected to the two different type of heat treatments including the postweld direct tempering (PWDT) and re-austenitizing based tempering (PWNT) treatment. The microstructure of weld fusion and heat affected zone (HAZ) were characterized in different heat treatment conditions using optical microscope and scanning electron microscope. For as-welded joint, a great heterogeneity was observed in microstructure and mechanical properties across the weldments. The Charpy toughness of the as-welded joint was measured much lower than the minimum recommended value of 47J and it was measured 8±5J. The PWHTs have found a beneficial effect in decreasing the microstructure heterogeneity across the welded joint and improving the mechanical properties. The PWDT resulted in a drastic improvement in the Charpy impact toughness of the welded joint and it was measured 59±5J which was higher than the minimum required value of 47J but still inferior than the base metal. The δ ferrite still remained in overlap zone of the weld fusion zone. The PWNT treatment resulted in homogeneous microstructure and hardness variation across the welded joint in transverse direction and Charpy impact toughness (149±6J) exceeded than that achieved in base metal.

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.

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.

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.

Thermal excursions during post-weld heat treatment (PWHT) and on-site fabrication frequently compromise the integrity of Grade 92 steel. While hardness fluctuations are documented, the correlation between initial properties and long-term creep stability remains controversial. This study aims to evaluate the relationship between thermal history and subsequent creep performance. Heat treatments of T92 steel across a wide temperature range (760–1000 °C) were performed, followed by creep tests at 600 °C/130 MPa and microstructural characterization. Results reveal a non-monotonic evolution of hardness and strength, reaching a minimum at 850 °C due to martensitic lath recovery into ferrite, but nearly doubling the as-received (AR) values above 900 °C due to fresh martensite formation. Creep life drops to a minimum at 850 °C and recovers to the AR level at 950 °C. A significant “decoupling” occurs at 1000 °C, where the sample possesses the highest hardness but only exhibits one-fourth the life of the 950 °C sample. Superior performance stems from the retained M23C6 and its dynamic precipitation, which pins dislocations to form micro-lath structures. Conversely, 1000 °C facilitates full carbide dissolution, accelerating dislocation recovery. These findings emphasize precise PWHT control and demonstrate that a 950 °C rejuvenation treatment can restore over-tempered or damaged components.

Dual-phase (DP) steels have gained considerable attention in the automotive sector because of the remarkable strength and formability combination, owing to the complex thermomechanical treatment employed during the production of steel. Weld fabrication, which is inevitable during the production of automotive components, often results in microstructure that adversely affects the mechanical properties. A post-weld heat treatment (PWHT) can be employed to improve the formability in addition to stress relieving. The present work investigates the microstructure and mechanical properties of similar and dissimilar gas metal arc-welded (GMAW) and post-weld heat-treated (300, 400 and 500 °C) joints of DP590 and DP780 steels. The weldments in the as-welded condition have shown a considerable reduction in the tensile elongation (%El) (up to 60-65%) and formability (up to 50-60%) due to the microstructural modifications in various zones. Subsequent PWHT at 500 °C resulted in a significant (25%) increase in the formability of the weldments. However, the formability of the weldments after the PWHT is still lower than that of the corresponding base metals due to the existence of microstructural inhomogeneity across the weldment.

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.

Local mechanical properties (LMPs) of welded joints are strongly affected by the experienced thermal cycle, controlling the global behavior of the joint. In this work, LMP of GTAW-pulsed welded joints of maraging C250 steel was studied by small punch tests (SPTs) throughout the welded joint, both in as welded (AW) and post-weld heat-treated (PWHT) conditions. LMPs were estimated by SPT from the weld metal up to the base metal, obtaining the yield and tensile strength and elongation to fracture for each zone. The results were compared with microhardness profiles, and microstructural analysis was also done to correlate it with the peak temperatures reached in each zone of the welded joint. For AW conditions, the weld metal and austenitized heat-affected zone show the lowest strength values and the highest ductility. Then, a transition to the highest local strength at the zone reached at the position that experienced A c1 temperature. Finally, a decrease in strength values up to reach the base metal take place in the subcritical heat-affected zone. The local strength estimated by SPT was considerably improved after PWHT, reaching the base material strength in aged condition except in the weld metal zone, mainly associated with the presence of reverted austenite. This zone controls the mechanical properties of the welded joints. In the PWHT condition, the welded joint achieved an efficiency of 95%. SPT has shown its capacity for the estimation of LMP of welded joints of ultrahigh strength maraging steels, providing additional information of the local mechanical behavior.

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.