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This paper deals with the influence of micro-pulsed direct current on microstructure and mechanical properties of gas tungsten arc welding (GTAW) weldments of Ti-6Al-4V (Ti-64). Bead-on-plate GTA welds were made on the samples in the un-pulsed and micro-pulsed (125 Hz and 250 Hz) conditions. Post-weld heat treatment (PWHT) was performed on a few coupons at 700 °C for 3 h in an inert atmosphere, followed by furnace cooling. In the microstructure, the fusion zone (FZ), base metal (BM), and heat-affected zone (HAZ) can be easily distinguished. The top surface of the FZ has large columnar grains because of lower heat loss to the surrounding atmosphere, and the bottom region of the FZ has comparatively smaller equiaxed grains. The micro-pulsed samples' FZ grain size was lower than that of those made without pulsing. This shows that high-frequency current has substantially refined prior β grains. The microstructure of the FZ is characterized by an acicular morphology composed of α, martensitic α′, and retained β phases. The FZ's hardness was higher than the BM due to the presence of martensitic α′. Additionally, the hardness in the HAZ was elevated due to the formation of finer martensitic α′. Micro-pulsed DC welding led to improved mechanical properties, including higher hardness, ultimate tensile strength (UTS), and ductility compared to un-pulsed welding. This enhancement is attributed to the grain refinement achieved with micro-pulsed DC. After PWHT, the prior β grain size remained relatively unchanged compared to the as-welded condition. However, the hardness in the FZ decreased due to the decomposition of α′ into α and β phases. The ductility of all samples improved as a result of the widening of the diffusional α phase. [ABSTRACT FROM AUTHOR]

This study analyzes the effects of Post Weld Heat Treatment (PWHT) on the mechanical properties and microstructure of Inconel 617 weldments produced by the Activated Tungsten Inert Gas (A-TIG) welding and Tungsten Inert Gas (TIG) welding. The TIG weld joints considered for this study were in an as-welded condition and underwent two different conditions of heat treatment including 1050∘C for 3 and 5 h, respectively. The A-TIG weld joints studied were the as-welded type and the weldment was heat-treated at 1050∘C for 3 h. The microstructure and the characterization of mechanical properties were performed for all weldments and a comparative assessment was made. Tensile strength and the hardness of the heat-treated samples were considerably higher than that of the as-welded samples. Impact toughness was slightly reduced after PWHT. Improvement in tensile strength could be attributed to the precipitation of the carbides and segregation of Chromium (Cr) and molybdenum (Mo). [ABSTRACT FROM AUTHOR]

The bridge structure of bridge crane is a typical welded structure, and fatigue cracks often appear in the weld area of the main beam during daily service. In order to ensure the service safety of the crane, a multi-level sub model of the dangerous crack region was established based on the multi-scale finite element analysis method. The thermal structural coupling welding finite element model was established on the secondary sub model, and the whole welding process was simulated and analyzed. The influence of post weld heat treatment on residual stress was simulated. Combined with the multiaxial critical interface method, a fatigue analysis method using the strain amplitude as the multiaxial damage parameter was constructed, and the fatigue performance of the dangerous crack region was evaluated. The results show that the proposed method transforms the overall fatigue problem of the structure into the fatigue problem of the local welding position, which not only increases the calculation efficiency, but also considers more influencing factors of the fatigue details, and provides a certain reference for the fatigue life assessment and life extension of the crane weld. [ABSTRACT FROM AUTHOR]

In this study, the effect of heat treatment on the mechanical and microstructural properties of welded joints after friction stir welding of age-hardenable Al-Zn-Mg-Si-Cu wrought aluminum alloy plates was investigated. For this purpose, some of the samples welded using FSW technique with a rotational speed of 1250 rpm and a traverse speed of 40 mm·min-1 were subjected to annealing and some to artificial aging heat treatment at different temperatures and times. In FSWed artificial aged samples where AlFeSi precipitate formations were detected, hardness and strength increase were realized with grain-boundary strengthening and Orowan hardening mechanisms. The lowest ultimate tensile strength was 156.3 N·mm-2 in the annealed sample, while the highest ultimate tensile strength was 210.8 N·mm-2 in the sample artificially aged at 190 °C for 2 hours. Fractographic examination revealed that ductile fracture occurred in all specimens. [ABSTRACT FROM AUTHOR]

Tungsten Inert Gas (TIG) is a welding technique that stands out due to its high precision, controlled heat input, and equipment's cost-effectiveness. TIG welding is utilized to join various grades of steel. Presently, numerous research studies are actively seeking to improve the quality of welded joints, focusing on aspects such as strength, ductility, formability, appearance, and corrosion resistance. These improvements are achieved through the modification of welding methods and/or welding parameters. In this investigation, welding current and gas flow rate were selected as input parameters. Additionally, PWHT at 700 °C for 1.5h was applied to relieve the residual stresses occurring during the welding operation. The objective of this investigation is to examine how the welding current, gas flow rate, and post-weld heat treatment (PWHT) affect the bending properties of welded joints. The bending test was conducted to assess both the bending resistance and bending strain of the joints. The bending resistance increases to attend a maximal value of 790 N and the bending strain decreases to 7.1%, with the welding current and the gas flow rate due to the high heat input and cooling rate. The applied PWHT decreases the bending resistance by 11% and increases the bending strain by 18%, due to the decrease of the joint's hardness. [ABSTRACT FROM AUTHOR]

The effects of the post weld heat treatment (PWHT) on the microstructure and hardness of the underwater wet welding (UWW) SS400 steel have been evaluated. The UWW was performed using Shielded Metal Arc Welding (SMAW) in water depth of 5.0 m, while PWHT was carried out on underwater welded specimen with temperature of 660 oC for 75 minutes. The result showed that the PWHT caused increasing the grain size of the microstructure and decreasing in hardness.

Investigation explores the weldability of Niobium stabilized TP347H austenitic stainless steel tubes through the application of optimized welding parameters using Auto TIG welding. This research investigates the influence of post weld heat treatment conditions on microhardness, microstructures, sensitization due to Cr23C6 precipitation, presence of Niobium carbides and formation of twin boundaries in the weldment. Extended post weld heat treatment duration resulted in notable decline in microhardness from 280 to 180 VHN within initial 5-h of soaking. Nevertheless, further prolongation of soaking time (10–15 h) exhibited subsequent rise in microhardness levels to 200 VHN in base, weld and heat affected zone. Increase in hardness is attributed to the emergence of annealing twins in base metal and the precipitation of Niobium carbides within weld and heat affected zone, confirmed by advanced analytical scanning electron microscope. Energy dispersive spectrum line mapping reveals presence of Cr23C6 precipitation following 1-h soak at 720 °C. Subsequent prolongation of soaking time (5-h) demonstrates desensitization in the base metal. Additionally, cooling rate of 300 °C/hr during post weld heat treatment reduces required time for microstructure homogenization, resulting in increased hardness compared to 100 °C/hr rate in the weldment. However, beyond a 5-h soaking time, the cooling rate has a negligible impact on microhardness. Ultimate Tensile Stress of 674.82 and 665.28 N/mm2 for TP347H was achieved against the minimum requirement of 515 N/mm2 as per American Society of Mechanical Engineers Section IX standard. [ABSTRACT FROM AUTHOR]

The main objective of this investigation is to study the effect of post weld heat treatments (PWHTs) on tensile properties, hardness, and microstructure of pulsed CMT–MIG (cold metal transfer arc–metal inert gas) welded AA20214-T6 aluminum alloy joints. The welded joints were subjected to PWHT of artificial aging (AA), solution annealing treatment (ST) and ST + aging (STA). The tensile properties and microhardness of joints were evaluated. The microstructure of joints was studied using optical microscope (OM) and transmission electron microscope (TEM). The fractured surface of tensile specimens was analyzed using scanning electron microscope (SEM). Results showed that the tensile properties and hardness of as welded and PWHT joints are inferior compared to base metal (BM). This mainly refers to the microstructural heterogeneity in different regions of joints and softening of heat affected zone (HAZ) induced by the weld thermal cycle. The PWHTs of AA and ST did not show significant effect on tensile strength and hardness of AW joints. However, the slight reduction in elongation was observed in AA and ST joints. The STA joints showed higher joint efficiency of 71.6%, than other joints by compromising on the elongation. This refers to the greater precipitation of hardening precipitates in STA joints compared to AA and ST joints. It exhibited the higher tensile and yield strength of 326 MPa and 266 MPa and the lowest elongation of 3.8%. The STA joints showed 28.35%, 38.28% and 57.77% reduction in tensile strength, yield strength and elongation compared to BM respectively. All the tensile specimens of joints failed in HAZ owing to the lower hardness. This refers to dissolution of precipitates in HAZ. However, the HAZ softening is less severe in STA joints than AW, AA, and ST joints.

The high entropy alloys (HEAs) are relatively a new class of materials that have attracted significant attention of engineering sector in recent years due to their extensive mechanical properties, high strength to weight ratio, thermal stability and resistance to corrosion and oxidation. HEAs are characterized by their unique composition that is typically composed of five or more elements in equal or somewhat substantial proportions. This leads to the evolution of highly complex microstructure that makes it challenging to weld. To fulfil the key requirements of the design and manufacturing, these HEAs must be capable of being welded in a satisfactory manner. The joining of similar and dissimilar combinations of HEAs and other engineering materials system have been proved to be feasible which further expands their structural applications in aerospace, nuclear and defence sector. Additionally, the fillers of HEAs disclosed greater potential in suppressing the evolution of detrimental intermetallics and enhancing the mechanical properties of joints. So, in this study, a comprehensive review on the current state of research in fusion welding of HEAs particularly AlxCoCrFeNi and CoCrFeMnNi is provided to address the weldability of HEAs under the diversity of composition, initial working condition, welding processes, operating parameters, configuration of joint and operating conditions. The latest challenges, progress and future perspectives in fusion welding of HEAs are reviewed critically with a particular focus on microstructure and mechanical properties of joints. The effect of fusion welding processes such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), electron beam welding (EBW) and laser beam welding (LBW) on microstructural characteristics, mechanical properties and corrosion behaviour of HEAs joints is reviewed and discussed. The effect of post weld heat treatment and HEAs fillers on the mechanical properties and microstructural evolution of welded joints is also discussed. Further, an insight into the potential application of HEAs in advanced engineering applications is provided. The current review article aims to provide an overview of challenges, opportunities, current state of research and main directions in fusion welding of AlxCoCrFeNi and CoCrFeMnNi HEAs and to highlight their potential as high-performance material in a range of applications.

This paper deals with the influence of micro-pulsed direct current on microstructure and mechanical properties of gas tungsten arc welding (GTAW) weldments of Ti-6Al-4V (Ti-64). Bead-on-plate GTA welds were made on the samples in the un-pulsed and micro-pulsed (125 Hz and 250 Hz) conditions. Post-weld heat treatment (PWHT) was performed on a few coupons at 700 °C for 3 h in an inert atmosphere, followed by furnace cooling. In the microstructure, the fusion zone (FZ), base metal (BM), and heat-affected zone (HAZ) can be easily distinguished. The top surface of the FZ has large columnar grains because of lower heat loss to the surrounding atmosphere, and the bottom region of the FZ has comparatively smaller equiaxed grains. The micro-pulsed samples’ FZ grain size was lower than that of those made without pulsing. This shows that high-frequency current has substantially refined prior β grains. The microstructure of the FZ is characterized by an acicular morphology composed of α, martensitic α′, and retained β phases. The FZ’s hardness was higher than the BM due to the presence of martensitic α′. Additionally, the hardness in the HAZ was elevated due to the formation of finer martensitic α′. Micro-pulsed DC welding led to improved mechanical properties, including higher hardness, ultimate tensile strength (UTS), and ductility compared to un-pulsed welding. This enhancement is attributed to the grain refinement achieved with micro-pulsed DC. After PWHT, the prior β grain size remained relatively unchanged compared to the as-welded condition. However, the hardness in the FZ decreased due to the decomposition of α′ into α and β phases. The ductility of all samples improved as a result of the widening of the diffusional α phase.

The main objective of this investigation is to study the effect of post weld heat treatments (PWHTs) on tensile properties, hardness, and microstructure of pulsed CMTeMIG (cold metal transfer arcemetal inert gas) welded AA20214-T6 aluminum alloy joints. The welded joints were subjected to PWHT of artificial aging (AA), solution annealing treatment (ST) and ST þ aging (STA). The tensile properties and microhardness of joints were evaluated. The microstructure of joints was studied using optical microscope (OM) and transmission electron microscope (TEM). The fractured surface of tensile specimens was analyzed using scanning electron microscope (SEM). Results showed that the tensile properties and hardness of as welded and PWHT joints are inferior compared to base metal (BM). This mainly refers to the microstructural heterogeneity in different regions of joints and softening of heat affected zone (HAZ) induced by the weld thermal cycle. The PWHTs of AA and ST did not show significant effect on tensile strength and hardness of AW joints. However, the slight reduction in elongation was observed in AA and ST joints. The STA joints showed higher joint efficiency of 71.6%, than other joints by compromising on the elongation. This refers to the greater precipitation of hardening precipitates in STA joints compared to AA and ST joints. It exhibited the higher tensile and yield strength of 326 MPa and 266 MPa and the lowest elongation of 3.8%. The STA joints showed 28.35%, 38.28% and 57.77% reduction in tensile strength, yield strength and elongation compared to BM respectively. All the tensile specimens of joints failed in HAZ owing to the lower hardness. This refers to dissolution of precipitates in HAZ. However, the HAZ softening is less severe in STA joints than AW, AA, and ST joints. [ABSTRACT FROM AUTHOR]

The high entropy alloys (HEAs) are relatively a new class of materials that have attracted significant attention of engineering sector in recent years due to their extensive mechanical properties, high strength to weight ratio, thermal stability and resistance to corrosion and oxidation. HEAs are characterized by their unique composition that is typically composed of five or more elements in equal or somewhat substantial proportions. This leads to the evolution of highly complex microstructure that makes it challenging to weld. To fulfil the key requirements of the design and manufacturing, these HEAs must be capable of being welded in a satisfactory manner. The joining of similar and dissimilar combinations of HEAs and other engineering materials system have been proved to be feasible which further expands their structural applications in aerospace, nuclear and defence sector. Additionally, the fillers of HEAs disclosed greater potential in suppressing the evolution of detrimental intermetallics and enhancing the mechanical properties of joints. So, in this study, a comprehensive review on the current state of research in fusion welding of HEAs particularly AlxCoCrFeNi and CoCrFeMnNi is provided to address the weldability of HEAs under the diversity of composition, initial working condition, welding processes, operating parameters, configuration of joint and operating conditions. The latest challenges, progress and future perspectives in fusion welding of HEAs are reviewed critically with a particular focus on microstructure and mechanical properties of joints. The effect of fusion welding processes such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), electron beam welding (EBW) and laser beam welding (LBW) on microstructural characteristics, mechanical properties and corrosion behaviour of HEAs joints is reviewed and discussed. The effect of post weld heat treatment and HEAs fillers on the mechanical properties and microstructural evolution of welded joints is also discussed. Further, an insight into the potential application of HEAs in advanced engineering applications is provided. The current review article aims to provide an overview of challenges, opportunities, current state of research and main directions in fusion welding of AlxCoCrFeNi and CoCrFeMnNi HEAs and to highlight their potential as high-performance material in a range of applications. [ABSTRACT FROM AUTHOR]

The stability of microstructure and mechanical properties of 9Cr heat resistant steel under high temperature and long term service conditions has been a hot issue of great interest. In the present study, the relationships between microstructure and mechanical properties evolutions of 9Cr heat resistant deposited metals with different Si contents (0.25 wt.% and 1.07 wt.%) at 550 °C aging for different times were investigated systematically. The results indicate that the degradation of mechanical properties during aging is mainly attributed to the coarsening of precipitates, transformation of precipitate types, decreasing of dislocation density and coarsening of martensite laths, and these factors are related to the Si content in the deposited metals and the aging time. It is worth mentioned that the sub-grain boundaries pinned by M23C6 forming after post weld heat treatment (750 °C/2.5 h) stabilize the tensile strength during aging. The recrystallization occurring after post weld heat treatment and high temperature aging is beneficial for the impact toughness but not for the strength. During aging process, the precipitate transformation follows the following sequence: M23C6→M6X→Laves phase. Moreover, the increase of Si content promotes the nucleation and coarsening of M6X, and then deteriorates the mechanical properties of the deposited metals.

Duplex stainless steels (DSSs), are used commonly under severe working conditions, subject to high stresses associated with corrosion. A typical DSS is composed of the combination involving two types of microstructures, ferritic and austenitic, which characterizes it as a material with corrosion resistance in aggressive media, due to its ability to passivate. The use of DSS has been increasingly exploited in the oil industry, and its use has occurred in numerous areas, standing out in the production of flexible pipelines, which in most applications, is associated with a welding process. They require special care when welded by the tungsten inert gas (TIG) welding process. Temperature variations in this process, along with heat treatment, promote the formation of precipitates in the matrix and change the phase balance. This significantly influences the mechanical and corrosion properties of DSSs. The objective of this work is to study the influence of two different parameters of solubilization heat treatment after welding on the microstructure and corrosion resistance of a DSSs welded joints. After the autogenous TIG welding process, the welds were subjected to thermal solubilization treatments for 10 and 25 s at 1050 °C. The conditions subjected to the solubilization heat treatment were compared with the as TIG welded control condition. The microstructure was analyzed by confocal microscopy and the corrosion resistance was evaluated by the ''A'' method of the ASTM G48 standard.

The influence of parameters involved in the pulsed electric arc, used as an energy source in the tungsten inert gas (TIG)-mediated welding of Duplex UNS S31803 stainless steel, to attend the manufacture of flexible pipes for the extraction of oil and gas is presented. A fundamental part in the manufacturing process of flexible pipelines is the welding of these strips so that corresponding TIG welds will be subjected to the same process and work conditions. Therefore, it is necessary to maintain the same properties in the welded regions. Covering the effects of each parameter of the pulsed electric arc such as peak and base current as welds, cyclic ratio, and pulsation frequency is a desirable endeavor. The final objective is the mitigation of problems that have a great impact on production, such as weld breakage during the conformation of the strip in the process and test failures. With this, tensile, bending, and ferrite percentage tests were performed on 12 samples that qualified as satisfactory in the visual aspect. A minimum tensile strength of 734.57 MPa and a maximum of 775.77 MPa were obtained where all values found are above the tensile strength limit of the base material of 620 MPa. With the completion of the study, it is possible to understand not only the response of the process to each parameter but also the tendency when changing them. Moreover, it is possible to explore the possibility of guiding the changes to achieve results about the visual aspect and the mechanical properties of the welded material. [ABSTRACT FROM AUTHOR]

In this paper, the Arrhenius-type constitutive equation based on strain compensation was developed, and the constants of the constitutive equation were determined by linear fitting to construct the material models of Ti62A alloy. Meanwhile, the creep parameters of Ti62A alloy at high temperature were corrected by existing experiments, and the Norton creep model during post weld heat treatment (PWHT) was established. The sequential coupling finite element method was used to calculate the residual stress distribution in the welding and PWHT processes of Ti62A alloy plates. The effects of PWHT parameters on the residual stress relief of welded joints were revealed, such as creep, heating rate, and heat treatment temperature. The results reveal that the creep has an important influence on residual stress relief during PWHT. Compared with longitudinal residual stress, the effects of heating rate and heat treatment temperature on transverse residual stress are more significant. A lower heating rate or higher heat treatment temperature will be beneficial for releasing residual stress. The results of this paper will contribute to a better understanding of PWHT mechanisms and provide a good theoretical guidance for optimizing process parameters.

Distribution of weld-induced residual stress plays a significant effect on the service life of a welded component. The accumulation of high residual stress accelerates the crack propagation even if the crack is of microscopic level, reducing the service life of the welded component. Prior understanding of residual stress distribution can aid in the design of a component with an adequate factor of safety and reduce the probability of failure. In the present study, two separate circumferential butt welded pipes were fabricated using Alloy 617 and then subjected to post weld heat treatment) at 720°C and 980°C. The deep hole drilling method was used to measure the distribution of residual stress. The fabrication of the welded joint was done using the hot-wire TIG welding process. High welding speeds are possible with hot-wire tungsten inert gas (TIG) welding because it uses less heat than conventional TIG welding. Using hot-wire TIG welding, the welded joint's mechanical properties, such as hardness, are improved in addition to its metallurgical properties. The computational approach is provided to analyze temperature and residual stress fields in multi-pass TIG welds with different passes. Based on ABAQUS FEA software, a coupled thermomechanical computational approach was developed to analyze the residual stress distribution on the welded joint. A 3D finite element model for Alloy 617 tube was created to estimate the welding stress field in two separate multi-pass welded joints. Mixed hardening model (kinematic and isotropic) was used during the numerical analysis. The effectiveness of the computational approach was verified with experimental measurements. The magnitude of hoop and axial residual stresses were observed to be maximum at a depth of 6 mm from the upper surface. The stress gradient in the welded zone and heat-affected zone is dramatically reduced by 70–80% of the as-welded condition during the post weld heat treatment at 980°C. [ABSTRACT FROM AUTHOR]

In-service patch welding is frequently used to repair corroded or damaged steel structures. However, the repair welding may adversely affect the long-term mechanical integrity of the structure. Fatigue treatment techniques could reduce such drawbacks. However, the effectiveness of treatment techniques in the case of in-service fillet welded steel patch repairs has not received due attention. This paper deals with the fatigue behavior of fillet welded patch repairs made on normalized A516 GR.70 carbon steel plates. The test specimens received different thermal treatments, including post-weld heat treatment (PWHT), TIG-dressing (TD), and temper bead (TB) welding. The pros and cons of these treatments were evaluated through quasi-static tensile tests, high-cycle constant amplitude fatigue testing, microstructural assessments, and hardness measurements. The TD treatment provided the most significant fatigue improvement, owing to beneficial changes it made to the geometry, microstructure and hardness of the weld toe area. The fatigue life and the fatigue-prone locations in the PWHT and TB specimens did not significantly vary from those in the untreated welded specimens. However, there was a reduction of the ultimate tensile strength in the PWHT specimens. The microstructure of the heat-affected zone plus the hardness of the weld toe areas significantly contributed to the fatigue performance. The fatigue lives of the fillet welded patch repairs were also interrelated to the geometrical changes caused in the weld toe by the treatment method.

In this investigation, the effect of post weld heat treatment (PWHT) conditions on weld metal (WM) microstructure and hardness of ASTM B670 alloy joints are studied for gas turbine engine applications. This high temperature alloy was joined using high frequency compressed arc TIG (HFCA-TIG) welding process. The precipitation hardening was performed on ASTM-B670 alloy joints directly after welding (DPH); after solutionizing the welds at 980 °C (980ST+PH) and at 1065 °C (1065ST+PH). The WM of ASTM-B670 alloy showed better response to PWHT in minimizing the Laves phases and enhancing the WM hardness of joints. The DPH, 980ST+PH and 1065ST+PH joints showed 55.63%, 58.80% and 64.08% enhancement in hardness of WM compared to as welded (AW) joints owing to the precipitation of hardening phases after PWHT. The 1065ST+PH joints revealed higher hardness of WM than DPH and 980ST+PH joints It is attributed to the complete dissolution of Laves phases in WM causing more Nb available for precipitation hardening of WM. Nevertheless, the PM hardness of 1065ST+PH joints are lower than 980ST+PH joints owing to the severe grain growth. The HFCA-TIG welds showed volume fraction of Laves phase up to 5.10% in WM which is 80.38% and 36.25% lower than constant current TIG (CC-TIG) and pulsed current TIG (PC-TIG) welds. It is attributed to magnetic compression and high frequency pulsation of arc which minimizes input of heat in welding and offers greater refinement of WM.

Post weld heat treatment, or PWHT, is often used to improve the mechanical properties of materials that have been welded. Several publications have investigated the effects of the PWHT process using experimental designs. However, the modeling and optimization using the integration of machine learning (ML) and metaheuristics have yet to be reported, which are fundamental steps toward intelligent manufacturing applications. This research proposes a novel approach using ML techniques and metaheuristics to optimize PWHT process parameters. The goal is to determine the optimal PWHT parameters for both single and multiple objective perspectives. In this research, support vector regression (SVR), K-nearest neighbors (KNN), decision tree (DT), and random forest (RF) were ML techniques employed to obtain a relationship model between PWHT parameters and mechanical properties: ultimate tensile strength (UTS) and elongation percentage (EL). The results show that the SVR demonstrated superior performance among ML techniques for both UTS and EL models. Then, SVR is used with metaheuristics such as differential evolution (DE), particle swarm optimization (PSO), and genetic algorithms (GA). SVR-PSO shows the fastest convergence among other combinations. The final solutions of single-objective and Pareto solutions were also suggested in this research. [ABSTRACT FROM AUTHOR]

The Gas Tungsten Arc Welding (GTAW) between P22 (2.25Cr-1Mo) and P91 (9Cr-1Mo) steels are quite common in heavy vehicle structures like; railway locomotives and war (or combat) vehicles. After welding, high hardness values of the Heat-Affected Zones (HAZs) of these dissimilar weld joints are possibly obtained. The uneven hardness in HAZ comes from the austenite transformation to Martensite, because of highly uncontrolled cooling rates. The considerable difference in hardness among various zones leads to prior cracking and is bound to failure during high-temperature operations. Therefore, there is a dire need to establish an appropriate Post Weld Heat Treatment (PWHT) to temper the dissimilar weld joints for required durability. The study investigates the microstructure and mechanical properties of various erupted zones of steel, before and after the application of PWHT. Before and after PWHT, weld zone and HAZ in P22 and P91 are mechanically tested and metallurgically examined. Further PWHT is tried to be optimised strategically and statistically, for the least variation in hardness among different zones. So that any failure due to thermal stresses or strains, during normal running conditions can be avoided. [ABSTRACT FROM AUTHOR]

Residual stress affects the service safety of pipelines, but there are few efficient methods to reduce the residual stress, especially for long-distance pipelines with large diameters. In this paper, a Secondary Post Weld Heat Treatment (S-PWHT) stress reduction method with low temperature and two narrow heating bands is proposed, and this method fully considers the failure of the corrosion resistance layer caused by high temperature. The temperature distribution and stress distribution under different S-PWHT parameters are compared to obtain the optimal S-PWHT parameters using finite element numerical simulation. The thermocouples are conducted to verify the temperature, and the coercivity experiment is used to verify the stress distribution. Results show that two heating bands width of 80 mm and a peak temperature of 120 °C are the optimal S-PWHT parameters with the stress reduced by 61 %. Besides, the levels of stress reduction on the inner surface and the HAZ are higher than those on the outer surface and the base metal, respectively. The high-stress zone is transferred from the inner surface to the outer surface, and from the HAZ to the base metal. Furthermore, the stress reduction mechanism of S-PWHT has been revealed through constraint theory. Temperature change is the initial force, and the constraint is the driving force for stress reduction. [Display omitted] • Established a stress reduction process for the girth welds of the narrow width of the heating bands and the low peak temperature. • This process homogenizes and reduces the stress. The high-stress zone transfers from the HAZ to the base metal. • Constraint theory becomes the supporting theory for this process. [ABSTRACT FROM AUTHOR]

Nowadays there is an increasing demand to develop light weight defense vehicles, fighter aircrafts and warships in order to enhance their mobility and fuel economy. It can be achieved by using the light weight structures made up of Aluminum and Magnesium plates which will reduce the weight, increase the payload carrying capacity and efficiency of the vehicles. In the present work, experimental ballistic performance of Magnesium (AZ31B) Base Metal (BM), friction-stir-welded (FSW) and post-weld-heat treated (PWHT) target plates have been determined by using the 7.62 mm Armor Piercing Projectiles (APP). Prior to ballistic testing, Magnesium joints were prepared by the FSW process for various tool rotational and welding speeds. Defect-free welds with better tensile and impact properties, were obtained with tool rotational speed of 1200 rpm and the welding speed of 50 mm/min. PWHT was carried out with the annealing temperature at 250 °C for about 1 hour. Microhardness and microstructure of the FSW and PWHT joints were investigated. Highest hardness (67 HV) was obtained for fine grain structure and precipitated particles were observed for PWHT targets. Depth of Penetration of PWHT target plates was approximately 17.55% and 16.31% lower than the BM and FSW target plates respectively. Scanning Electron Microscopic observation of projectile penetrated channel showed the formation of Adiabatic Shear Bands (ASBs). Due to a larger number of ASB lines, ballistic impacted FSW surface showed more number of macro cracks compared to PWHT surface. The PWHT joints showed the absence of fragmentation failure, lesser cracks and ASB lines which increased the ballistic performance. [ABSTRACT FROM AUTHOR]

Underclad cracking in nuclear pressure vessels was of significant concern in the 1970s and 1980s before mitigating adjustments were made both to steel compositions and manufacturing practice. Unfortunately, the cracking mechanisms are still not well understood, and this can undermine confidence when changes to cladding operations are under consideration. In this work, Charpy-sized test coupons of 18MND5 steel were subject to a range of thermal cycles that can be experienced by the substrate immediately adjacent to the interface with the overlay. The Charpy test results are considered in combination with analysis of the samples through field emission gun (FEG) scanning electron microscopy (SEM) and wavelength dispersive X-ray spectroscopy (WDXS). The findings suggest that the heat affected zone subject to the coarse grained plus intercritical thermal cycle, before post weld heat treatment, has a peculiar and potentially brittle microstructure. However, in a steel with no obvious macrosegregation, no clear evidence of intergranular cracking in the early stages of the post weld heat treatment could be found. The second part of the work focuses on the effects of segregation regions in large forgings, more specifically ghost lines, on the tendency for underclad cracking. Ghost line regions that subsequently form a coarse grained heat affected zone (CGHAZ), and are then heated to just under the A 1 temperature, seem to be the most prone to intergranular cracking. Cracking susceptibility appears to be associated with elevated concentrations of alloying and impurity elements at grain boundaries. • The underclad cracking mechanism in 18MND5 seems different from that in Cr-Mo steels. • Solidification segregation, temper embrittlement appear to cause underclad cracking. • Intergranular fracture risk was highest where prior austenite grain size was highest. • The intercritical heat affected zone had intermediate tendency for fracture. • Deposition strategies should aim at maximum refinement of prior austenite grains. [ABSTRACT FROM AUTHOR]

In this study, the effect post weld heat treatment (PWHT) on microstructural evolution and mechanical properties of weld metal of HT700P alloy with Inconel 617 filler metal was investigated. After welding, columnar grain, dendritic microstructure and segregation of Mo, Co and Ti elements related to the equilibrium distribution coefficient were observed in the weld metal. The PWHT was conducted in both direct-aging treatment with different time and solution treatment with different cooling methods. The results showed that direct-aging treatment had a limit impact on homogenization of weld metal, while microstructural homogenization and elemental segregation were significantly improved after solution treatment and massive M 6 C and M 23 C 6 carbides precipitated at the grain boundaries and interdendritic region of weld metal. It was found that the elongation at 700 °C of welded joints after solution treatment was relatively increased, which was related to the decrease of residual stress and the precipitation of Mo-rich carbides at the grain boundaries. The fracture occurred in the weld metal presented interdendritic fracture characteristics, and the fracture mechanism for stress relaxation cracking was the strong grain interior induced by the precipitation of γ′ phase, leading to the stress concentration and nucleation of cavities at grain boundaries. After solution treatment, the creep lifetime of furnace cooling was much greater than that of water quenching. The superior creep properties of furnace-cooled joint could be attributed to the lower residual stress and the migration of carbon element in the fusion line, which inhibited the nucleation and aggregation of cavities in the partially melted zone. • Effect of PWHT on microstructure and properties of welded joints of a Fe-Ni-based alloy is studied. • The segregation of Mo, Co, Ti in the weld metal and fusion line is analyze. • The mechanism for stress relaxation cracking is illustrated after different PWHT. • Residual stress and carbon migration in fusion line dramatically affect creep life of joints. [ABSTRACT FROM AUTHOR]

• HF-ERW welding resulted in the formation of tensile residual stress, resulting in failure of the tube during flattening operation. • Thermo-mechanically heat-affected zone were found to have (1 1 0)[0 0 1],(1 1 0)[1 1 ¯ 0], (0 0 1)[1 1 ¯ 0], (0 0 1)[ 11 ¯ 0] texture. • Post weld heat treatment was found to be effective in alleviating tensile residual stress and preventing tube failure. High-frequency electric resistance welding is used for manufacturing hydro formable tubes. Tube forming and welding results in the formation of residual stress. The hole drilling technique was used to evaluate the residual stress of the welded tube. Tensile residual stress of varying magnitude was observed at different locations on the tube. The weld, heat affected zone was observed to have the highest residual stress as a result of phase transformation, forming and gradually reduced towards the parent material. The generated tensile residual stress led to failure of the tube during mechanical evaluation. Additionally, electron backscattered diffraction studies (EBSD) of the fusion line and the thermo-mechanically heat-affected zone were found to have goss and cube texture. These detrimental textures can lead to easy crack propagation in the presence of defects along the fusion line. A post-weld heat treatment (PWHT) was carried out to alleviate the tensile residual stress and alter the weld microstructure. PWHT helped transform the bainite in the weld to ferrite and pearlite. The inter-critical annealing significantly reduced the tensile residual stress along the circumferential direction resulting in improved formability. [ABSTRACT FROM AUTHOR]

To improve the mechanical properties in supermartensitic stainless steel weld deposits, suitable post weld heat treatments (PWHT) are required, since these properties are controlled by the resulting microstructure. Some aspects of localized corrosion resistance could also be enhanced by the PWHT. In this sense, the austenite transformation or stability is a key issue. The aim of this work is to “in-situ” analyze the evolution of austenite during the thermal cycle associated to a post weld inter-critical heat treatment in a supermartensitic stainless steel weld deposit, by means of a thermomechanical simulator integrated on a synchrotron X-ray diffraction line. An all-weld metal coupon was welded with a semi-automatic process. Dilatometry measurements were performed at different heating rates (1, 10 and 100 K/s) in the thermomechanical simulator, to determine the critical transformation temperatures (Ac1 and Ac3) of the all-weld metal. To study the phase transformation during the applied thermal cycle (heating to 938 K at 1 K/s, maintenance during 15 min and cooling to room temperature at 2 K/s), in-situ synchrotron X-ray diffraction measurements were carried out in the facilities of National Laboratory Synchrotron Light (Campinas, Brasil). The microstructural evolution was discussed in terms of volumetric phase fractions, micro-deformation and crystallite size. The techniques used allow to detect the critical transformation temperatures, phase transformations and their kinetics, monitoring particularly the austenite evolution during the post weld heat treatment cycle. At the inter-critical temperature 71% of austenite was formed, after the 8.5 min from the 15 min of permanence. Finally, at room temperature 29% of stable reverted austenite was obtained. Both martensite and austenite there did not show significant variations during the thermal cycle both for microstrain and crystallite size.

Inconel alloys are one of the materials of choice for high temperature applications whether it is aerospace, nuclear or gas turbine. This is due to their excellent mechanical and non-corrosion properties even under harsh environments at elevated temperatures. Joining Inconel alloys through conventional fusion welding techniques have posed many different problems and hence, solid state joining processes could well be an alternative welding method for these alloys, wherever the design permits. Friction welding being a solid state welding process, is well established for its capability of producing high quality welds and joining dissimilar metals. In this paper, Inconel alloys are introduced initially, and then friction welding in general has been discussed. Thereafter, the published works on the friction welding of Inconel alloys are reviewed with an emphasis on microstructural and mechanical properties of similar and dissimilar Inconel weld joints. [ABSTRACT FROM AUTHOR]

Abstract Supermartensitic steels represent a new sub-class of martensitic stainless steels with higher toughness and corrosion resistance than conventional grades. These properties were improved by the drastic reduction of carbon content, and the addition of nickel and molybdenum. These chemical composition changes also increased the weldability of these steels, since the soft and ductile martensite formed is not susceptible to cold cracking during welding. However, post weld heat treatment may be necessary for uses in sour, aggressive and embrittlement environments. This work investigates the mechanical properties of a weld produced by gas tungsten arc welding (GTAW) of a pipe of 12%Cr supermartensitic stainless steel with 625 nickel alloy as filler metal. The response of the weld metal to post weld heat treatments at 650oC was also evaluated.

The formation mechanism of the reversed austenite and the interaction between austenite inversion and plastic deformation in the G520 martensitic stainless steel welds was studied by adjusting the tempering holding time during post-weld heat treatment. The results show that the weld microstructure has consisted mainly of tempered lath martensite, reversed austenite, and grain boundary precipitation carbides. The volume fraction of the reversed austenite has a great influence on the mechanical properties of the weld. The nucleation position and size of reversed austenite formed at the tempered martensite laths sub-block boundaries or austenite grain boundary are strictly restricted by the orientation of crystal attributing to the parallel orientation relationship between {110} M and {111}A. The reversed austenite with low dislocation density is mostly flakiness particle morphology, which greatly refines the tempered martensite laths. The transformation of martensite into reversed austenite is a diffused phase transformation, and the increase in reversed austenite is consistent with the increase in Mn content and Mo content reduction in the weld. For weld with Mn 0.87 wt.% and Mo 1.16 wt.%, the volume fraction of reversed austenite is 14.53%, and the welds exhibit excellent mechanical performance. [ABSTRACT FROM AUTHOR]

Aluminium alloys of 6xxx series are widely used in the fabrication of light weight structures especially, where high strength to weight ratio and excellent weld-ability characteristics are desirable. Gas metal arc welding (GMAW) is the most predominantly used welding process in many industries due to the ease of automation. In this investigation, an attempt has been made to identify the best variant of GMAW process to overcome the problems like alloy segregation, precipitate dissolution and heat affected zone (HAZ) softening. Thin sheets of AA6061-T6 alloy were welded by cold metal transfer (CMT) and Pulsed CMT (PCMT). Among the two joints, the joint made by PCMT technique exhibited superior tensile properties due to the mechanical stirring action in the weld pool caused by forward and rearward movement of the wire along with the controllable diffusion rate at the interface caused by shorter solidification time. However, softening still exists in the welded joints. Further to increase the joint efficiency and to minimize HAZ softening, the joints were subjected to post weld heat treatment (PWHT). Approximately 10% improvement in the tensile properties had been observed in the PWHT joints due to the nucleation of strengthening precipitates in the weld metal and HAZ.

The paper analyses the possibility of post weld heat treatment (PWHT) quality assessment with the help of magnetoacoustic emission (MAE) signal measurements. Two welded superheater tubes, made of high chromium VM12 steel, were analysed—as welded and heat treated one. The analysed sample in the as welded state exhibited significantly higher hardness, accompanied by a big difference in the MAE signal intensity (of order of about 50%). In order to explain that, the influence of tempering on the MAE signal intensity is demonstrated for the very similar X20CrMoV12.1 steel. It is shown that the observed increase of the MAE intensity as a function of annealing time is directly correlated with the change in hardness. The as described dependence allows to propose a method based on the MAE signal measurements as a new tool for the PWHT assessment. [ABSTRACT FROM AUTHOR]

In recent years, the usage of dual phase (DP) steels, transformation induced plasticity (TRIP) steels and boron steels in some auto body parts has become a necessity because of their strength and lightweight. Resistance spot welding (RSW) being a process were steel is heated and cooled in a very short period of time, the resulting weld nugget is generally fully martensitic, especially in the case of DP, TRIP and boron steels but that also holds for plain carbon steels as AISI 1010 grade which is extensively used in auto body inner parts. Martensite in is turn must be avoided as much as possible when welding steel because it is the principal source of brittleness. Thus, this work aims in finding a mean to reduce martensite fraction and increase phase diversity in weld nugget. The prediction of phase transformation during RSW has been done. Simulations have been performed for 2 mm AISI 1010 sheets and results show that the application of post weld heat treatment leads to the reduction of martensite fraction, and formation of ferrite and bainite in the nugget. Welding experiments have been done in parallel and experimental weld nugget geometry is in good agreement with simulation results. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effect of post-weld heat treatment (PWHT) on the microstructure, microhardness, and sulfide stress corrosion cracking (SSCC) of IN625 weld overlay on AISI 4130. In this paper, cladding was conducted by TIG (tungsten inert gas arc welding) technique, then PWHT was carried out at 650, 750, and 850°C temperatures with the constant time of 1 h. Also, the SSCC test was performed for 720 h. According to the results, columnar dendrites with MC carbide in g solid solution matrix comprise the microstructure. Furthermore, there was not any crack in the Weld Overlay (WO), tempered martensite, bainite in the base metal (BM), coarse tempered martensite, and ferrite in the heat-affected zone (HAZ). The results demonstrate that as the temperature of PWHT rises, the hardness of BM and HAZ reduces while hardness in the WO increases; it can be seen that at 750°C γ'' phase rapidly emerged and changed to stable δ at 850°C by the shearing mechanism. Furthermore, the results of the magnetic test showed stress crack in samples that heat-treated at 850°C. SEM images reveal that stress cracks in BM continued along grain boundaries and reached the WO. [ABSTRACT FROM AUTHOR]

9CrMoCoB heat-resistant steel was transient liquid phase (TLP) bonded by using a Ni–Cr–B amorphous filler metal. Results indicated that the TLP-bonded joint was composed of three feature regions, and the precipitates in the diffusion affected zone (DAZ) were M _23 (C,B) _6 -type carboborides and M _3 B _2 -type borides with different morphologies and locations. Fine granular Fe _2 Mo-type Laves phases and MX-type carbides that existed in the original base metal were found in the grain. The carboborides and borides in the DAZ that grew with the increase in bonding time and temperature were reduced or completely dissolved after post weld heat treatment (PWHT). The joints without PWHT showed high strength and low elongation due to the high hardness and high hardenability of the matrix. The initiation of cracks occurred on borides in the athermal solidification zone and carboborides in the Ni-DAZ and passed through in the bonded seam, resulting in the reduction in the tensile strength of the bonded joints. The hardness of the joints was obviously reduced, and their toughness was obviously improved after PWHT. The highest tensile strength reached to 744 MPa when the TLP joints were bonded at 1150 °C for 30 min, which was comparable with the original base metal.