Post-weld Heat Research Articles

Effect of impurity elements on the creep rupture strength of Gr. 91 steel welded joints at 650 °C

The upper limits for Sb, As, and Sn in Gr. 91 steel are set by the recent standardized Gr. 91 Type 2 specification. To clarify how the three impurities impact the microstructures and creep rupture strength of Gr. 91 welded joints, two types of steel with varying impurity concentrations were prepared. The first contained high impurity concentrations (Steel 1), while the other had low impurity concentrations (Steel 2). The results of the creep tests on the welded joints showed that Steel 1 had lower creep rupture strength compared to Steel 2, indicating premature failure caused by the impurities. Comparing the microstructures in the as-welded joints, it was observed that Steel 1 had more M23C6 particles in the fine-grained heat affected zone (FGHAZ) than Steel 2. This finding indicates that M23C6 dissolution during the welding process was hindered in Steel 1. It is believed that M23C6 dissolution was reduced due to the segregation of impurities at the grain boundaries or the interface between the matrix and M23C6 particles. Consequently, the microstructure in FGHAZ of Steel 1 showed lower creep resistance because the pinning force by M23C6 was decreased due to the reduction of re-precipitation on the grain boundaries during post weld heat treatment. The degradation in the creep rupture strength due to the impurities was attributed to the earlier progression of recovery process in FGHAZ during creep, leading to premature creep void formation.

Enhancing microstructure and mechanical properties of dissimilar TIG welded duplex 2205 and Ni-based inconel 718 superalloy through post weld heat treatment

In demanding applications, maintaining structural integrity in dissimilar welded joints like those between duplex stainless steel and Ni-based superalloys requires achieving the best possible mechanical properties. This work examines the impact of post-weld heat treatment (PWHT) on the mechanical characteristics of joints made via double-sided tungsten inert gas (TIG) welding. The dissimilar welded joint was investigated by exposing it to the PWHT for 12 h at 650 °C. Reducing the negative impact of heat generated by welding on the mechanical characteristics and microstructure of the fusion zone was the main goal. To study for changes in the microstructure before and after PWHT, optical microscopy and scanning electron microscopy methods were used for microstructural analysis. To determine the effect of PWHT on the welded joints, mechanical properties such as tensile strength, toughness, and ductility were also assessed. The mechanical properties showed significantly enhanced characteristics and refined grain structures in the fusion zone.

Microstructure and corrosion behavior of A390-10 wt% SiC composite-AA2024-T6 aluminum alloy dissimilar joint: Effect of post-weld heat treatment

The weldability of aluminum matrix composites to other materials, such as aluminum alloys, is an essential point in expanding the use of these materials. This study investigated the effect of rotational speed and post-weld heat treatment on the microstructure, mechanical properties, and corrosion behavior of A390-10 wt% SiC composite/AA2024-T6 aluminum alloy dissimilar joint. Friction stir welding is performed using a square frustum pyramid pin tool with a rotational speed of 400–1200 rpm and a traverse speed of 40 mm/min. Results found that a surface groove formed on the weld crown at a rotational speed lower than 800 rpm due to insufficient material flow. Also, the tunnel defect formed on the advancing side at a rotational speed higher than 1000 rpm due to the turbulent flow of material. By increasing rotational speed from 800 to 1200 rpm, the average grain size of the advancing and retreating sides increased by 41.1 and 46.3 %, respectively. Compared to AA2024-T6 and A390-10 wt% SiC composite base metals, the average hardness of the stir zone of the joint fabricated by the rotational speed of 800 rpm increased by 8.4 and 38.2 %, respectively. By increasing the rotation speed from 800 to 1000 rpm, the yield strength and ultimate tensile strength decreased by 6.8 and 6.5 %, respectively. By decreasing rotational speed from 1000 to 800 rpm, the elongation and corrosion resistance decreased by 5.4 % and 34.7 %, respectively. After post-weld heat treatment, the hardness, yield strength, ultimate tensile strength, and corrosion resistance increase 15.9, 12.7, 7.8, and 28.9 %, respectively.

Improvement of sulfide stress corrosion cracking resistance of the Inconel 625/X80 weld overlay by post-weld heat treatment

Improvement of sulfide stress corrosion cracking resistance of the Inconel 625/X80 weld overlay by post-weld heat treatment

Enhancing tensile properties of MIG welded AA6061 joints: Effect of pulse mode and post-weld heat treatment

Metal-Inert Gas (MIG) welding is one of the most important welding technologies commonly used in the manufacturing industry due to its high degree of automation and welding adaptability. However, softening is prone to occur in fusion zone (FZ) and heat affected zone (HAZ) of AA6061 MIG welded joint, which limits its application. In this work, AA6061 was welded by MIG welding with different pulse modes, and the post-welding heat treatment was carried out. The results show that the dual pulse MIG (DP-MIG) and PWHT can significantly improve the mechanical properties of AA6061 butt joint, and its ultimate tensile strength (UTS) is 331.3 MPa, even more than 90% of the base material (BM). In this paper, the microstructure of welded joints under different pulse conditions before and after PWHT was compared, and the relationship between the welding process, microstructure, and mechanical properties was established Furthermore, the influence mechanisms of pulse mode and PWHT on the mechanical properties of welded joints were explained in detail.

The relationship between austenite stabiliser element and post-weld heat treatment on the corrosion behaviour of the welded duplex stainless steel made by gas tungsten arc welding

The corrosion behaviour and the influence of nickel and post-weld heat treatment (PWHT) on the susceptibility to corrosion in welded duplex stainless steels were investigated. After PWHT, the amount of nickel for the weld region increases resulting in the generation of austenite and consequently, helping to obtain a favourable ferrite-to-austenite ratio. Comparing the experimental outcomes, it is noticed that the pits initiate and propagate in HAZ indicating this area is more susceptible to corrosion resistance compared to the fusion zone. The pitting resistance equivalent number alone is not sufficient reason to study the complex corrosion phenomenon, and the influence of other parameters namely microstructural evolution on the breakdown of passivity by pitting and the existence of intermetallic phases should be determined together.

Effect of post-weld heat treatment on mechanical and microstructural properties of high strength steel weld metal

The usage of high strength steel (HSS) is steadily increasing, primarily driven by the pursuit of weight reduction, leading to a subsequent decrease in greenhouse gas emissions. This paper investigates the impact of various post-weld heat treatment (PWHT) temperatures of 525 °C, 550 °C and 575 °C with a holding time of 2 h on both the microstructure and mechanical properties of weld metal produced using a HSS metal cored wire. The investigation reveals that PWHT does not significantly alter strength but has a more pronounced influence on toughness. The as-welded condition exhibited the highest toughness. Among the samples subjected to the PWHT, the one treated at 575 °C showed the highest impact energy, reaching 69 J at −60 °C. This outcome is attributed to the increased presence of acicular ferrite in the microstructure, surpassing that of samples subjected to PWHT at different temperatures.

Residual stress relief strategy in thick steel weldments via local induction heat treatment: Simulation and neutron diffraction experiment

This study investigated the effect of local induction post-weld heat treatment (PWHT) on residual stress relief in thick submerged arc welded steel plates. A combination of numerical and neutron diffraction methods was used to examine the effect of various PWHT parameters, such as annealing temperature and holding time, on the relief of residual stress in welded plates with various thicknesses. A sequentially coupled thermal–mechanical finite element model was used to calculate the residual stress distribution in welded AH36 steel plates before and after PWHT. The model was validated by comparing its predictions with the experimental measurements, and the results showed good agreement. The residual stress of the thick welded plates was effectively reduced via PWHT with local induction. The primary mechanism for this stress release was identified as stress relaxation caused by creep strain. Furthermore, a process map was established considering the PWHT conditions and plate geometry. This map provides a means of determining the optimal PWHT conditions to achieve desired stress reduction levels.

EVALUATION OF WELDED JOINT (SMAW) AFTER POST WELD HEAT TREATMENT (PWHT)

Joining of two materials having similar physical, chemical, and thermal properties and to make the joint tough and stiff, special attention and investigation are required. In this research, the welding joint between two mild steel (MS) of IS 2062 grade E, was accomplished by using shielded metal arc welding (SMAW). To investigate the effect of electrode in the welding joint, MS electrode was exercised. For post-weld heat treatment (PWHT), temperature of 700 °C were investigated over the welded specimen. To explore the optimum welding process and PWHT process for this joint, both tensile and bending tests were carried out. Destructive tests have suggested that PWHT at 700 °C is better for the SMAW process with MS electrode. As the smallest hardness values were observed in the heat-affected zone (HAZ) which makes the sample susceptible to failure. The hardness values have decreased after PWHT which justified the achievement of higher ductility after heat treatment.

Effect of Ni content on microstructure and mechanical properties evolutions of 9Cr high Si heat resistant steel deposited metals

This work presents the effect of Ni content on the morphology of microstructure and changes of mechanical properties of high Si 9Cr heat resistant steel deposited metals with different states: as-welded, as-post weld heat treated (750 °C/2.5 h) and as-aged (550 °C/3000 h). With the increase of Ni content, the martensitic laths are refined improving the overall mechanical properties. δ ferrite deteriorates the impact toughness. During aging process, Ni facilitates the formation of M6X. Therefore the overall mechanical properties of deposited metal decreases as the Ni content increases after long-term aging owing to the formation of chain-like precipitates consisted mainly of M6X. The process of post weld heat treatment improves the negative effect of small-sized δ ferrite on impact toughness.

Microstructure evolution and corrosion behavior of TIG welded joint of a new Mg[sbnd]Gd[sbnd]Nd[sbnd]Zn[sbnd]Zr alloy during post-weld heat treatment

The corrosion behavior of the tungsten inert gas (TIG) welded Mg3Nd3Gd0.2Zn0.5Zr alloy with different post-weld heat treatments was systematically investigated. The results show that the corrosion resistance of the sand-cast base material (BM) was inferior to that of the fusion zone (FZ), which was attributed to the larger grain size and exacerbated galvanic corrosion caused by coarser Mg3(Nd, Gd) eutectic phases and numerous β precipitates. It is found that post-weld solid-solution (T4) treatment could significantly enhance the corrosion resistance of the joint due to the dissolution of the cathodic second phases and the denser protective film abundant in RE oxides generated in corrosive solution. The precipitation of nanosized phases and ZnZr clusters would slightly increase the susceptibility to localized corrosion of the peak-aged (T6) joint. As the main corrosion products, MgO and Mg(OH)2 are distributed throughout the whole corrosion film, while RE oxides and RE hydroxides are mainly distributed in the inner layer, which can be explained by inward oxidation and replacement reactions between RE elements and MgO/Mg(OH)2. Based on the composition and structure of the corrosion product film, a physical model has been proposed for depicting the microstructure evolution associated with the corresponding corrosion behavior of the joints. This work could promote the applications of welded MgRE alloy joint in some corrosion environments.

Influence of post-welding heat treatment on microstructure and peculiarity of 10Cr9Mo1VNb boiler steel welded by hot wire TIG

Hot wire tungsten noble gas (HW-TIG) soldering tests are conducted on 10Cr9Mo1VNb boiler steel with multi-layer and multi-pass, and the soldered joints are subjected to post-weld heat treatment (PWHT) at different temperatures and times from 740°C to 790°C and 1 hour to 4 hours. The influence of PWHT on the microstructure and peculiarity of the joints are analyzed by using hardness, metallography, room temperature tensile testing, Charpy impact testing, SEM, and other experimental methods. The results show that the PWHT can transform the martensite formed in the welding process into tempered martensite, which can significantly improve the uniformity of the microstructure and peculiarity of each area of the joint. When subjected to heat treatment at 740°C, both strength and ductility improve with the increase of heat treatment time, while the plasticity gets a slight decrease. However, when subjected to heat treatment at 790°C, strength, plasticity, and ductility decrease with the increase of time, mainly due to the carbide coarsening such as M23C6 in the joint.

Effect of heat treatment on microstructures and properties of vacuum laser welding Ti–6Al–4V titanium alloy

Vacuum laser welding of titanium alloys is currently being explored for use in UAVs and military-related fields, but the impact of post-weld heat treatment has been seldom studied. In this paper, the Ti–6Al–4V titanium alloy was welded by vacuum laser welding(VLW)with IPG 50 kW fiber laser, and analyze the microstructure and properties of the welds in as-welded state and post-welding heat treatment (850 °C/2h/FC(FC:furnace cooling)and 980 °C/10min/FC+720 °C/2h/FC).The results show that the microstructure of the as-welded weld is composed of primary columnar crystal (primary β phase) and grain boundary martensite (α′), and the microstructure of primary columnar crystal is composed of α'+ (α'+β). The proportion of high-angle grain boundary(HAGB) is 92.3%. The tensile strength is 1009 MPa, and the elongation is 9.3%. The average impact toughness at room temperature is 13J. The weld microstructure at 850 °C/2h/FC is composed of the acicular α phase and the α+β between the acicular α phases, the primary columnar crystals basically disappear, and the acicular α phases criss-cross weave into the net basket structure.The proportion of HAGB is 97.4%.The tensile strength is 988.3 MPa,and the elongation is 14.8%. The average impact toughness is 17J. The microstructure of the weld at 980 °C/10min/FC+720 °C/2h/FC is composed of the coarser acicular α phase and the (α+β) between the coarser acicular α phases. The proportion of HAGB is about 83.2%. The tensile strength is 586 MPa, and the elongation is 1.6%. The average impact toughness is 1.4J.

A Study on the Microstructure and Mechanical Properties of Electron Beam Welds of SA508 Gr.3 Cl.1 steel with Different Heat Treatment conditions for Small Modular Reactor

Electron beam welding was conducted on SA508 Gr.3 Cl.1 steel, which is being considered as a material used in the pressure vessel steel of small modular reactors. The characteristics of the welds were analyzed under various heat treatment conditions. The heat treatment conditions were categorized as as-welded, post weld heat treatment(PWHT), quality heat treatment(QHT), and their features were examined and compared through cross-sectional structure and composition analyses, as well as mechanical property tests. The electron beam welded joints displayed no defects, including pores or cracks. weld metal of the as-welded specimen revealed a needle-type martensite with high hardness, whereas the base metal was characterized by tempered bainite. The weld cross-section bead of the QHT specimen exhibited no significant difference in microstructure compared to the base metal. Tensile testing revealed that both the as-welded and PWHT specimens fractured at the base metal, whereas the QHT specimen fractured at the weld metal. The PWHT specimens showed enhanced impact values in the welds compared to the as-welded specimens. In the QHT specimens, both the base metal and the weld metal demonstrated similarly favorable impact values, approximately 200 Joules. It is evident that post-welding heat treatment improves the toughness value, and quality heat treatment can result in the weld metal being similar to the base metal.

The effect of weld heat input on the microstructure and mechanical properties of wire arc additively manufactured 15-5PH stainless steel

Precipitation hardening (PH) stainless steels, such as 15-5PH, have a high strength combined with excellent corrosion resistance. These properties make them valuable in critical industries such as defence, construction, aerospace, energy and maritime. Recent advancements in additive manufacturing (AM) technology enable the rapid and cost-effective production of components. In the case of 15-5PH components manufactured using wire arc additive manufacturing (WAAM), the as-deposited mechanical properties are not suitable at present for industrial applications. This paper explores the mechanical properties of this process and alloy combination without post weld heat treatment with the aim of eventual adoption in this condition by industry. The impact of weld heat input on the microstructure and mechanical properties of stainless steel 15-5PH produced using WAAM was investigated. The microstructure was examined using hardness testing in addition to optical and electron microscopy. Furthermore, mechanical properties were measured with tensile and impact testing. Investigations were conducted on material produced using weld heat inputs of 0.223 kJ/mm and 0.565 kJ/mm. These results indicate that reducing the weld heat input leads to a minor decrease in strength but an 80% increase in impact toughness. This reduction in weld heat input is correlated with a 50% reduction in volume fraction of δ-ferrite while also noting a 55% increase in carbide precipitates. In addition, the fracture surfaces were predominantly cleavage or quasi-cleavage in morphology.

Effect of post-weld heat treatment methods on microstructure and fatigue behavior of Al-Mg-Si alloy oscillating laser welding

To address the softening issue in aluminum alloy weld joints, post-weld heat treatment(PWHT) techniques were employed to enhance the mechanical properties of Al-Mg-Si alloy weld joints joined by oscillating laser welding(OLW). A systematic investigation was conducted on the impact of two different PWHT methods, artificial aging(AA) and solution treatment followed by aging(STA), on the static mechanical properties, fatigue performance, and microstructure of the weld joints. The results indicated that both AA and STA could improve the tensile strength and fracture strain of the welded joints. Compared to AA, STA did not show a significant improvement in increasing tensile strength and elongation at break. Notably, AA significantly increases the fatigue life of the joints, while STA also contributes to enhanced fatigue life, albeit to a lesser degree. At the lowest stress level, the fatigue life of both STA and as-welded(AW) joints exceeded 106 cycles, with the STA joints exhibiting approximately 57.9% higher fatigue life than the AW joints. Microstructural analysis of the AW joints revealed the presence of dislocations and a few large-sized precipitate phases, primarily Mg2Si and AlFeSi phases. After AA, nano-scale second phases, mainly the AlFeSi phase, appeared in the weld joints, accompanied by a reduction in dislocation density. Following STA, there was a significant increase in the density and size of precipitate phases, with the coarse AlFeSi phase becoming more prominent and large-sized grain boundary precipitates appearing. The AA treatment, due to grain refinement and second phase precipitation, enhanced the hardness, tensile strength, and fatigue strength of the joints. As the STA joints exhibited more β-AlFeSi precipitates and grain boundary precipitates, the second phase strengthening effect was reduced. Although the mechanical properties of STA joints were better than those of AW joints, they were inferior to those of AA joints.

Influence of Post-weld Heat Treatment on Microstructure and Corrosion Behavior of Dissimilar Friction Welded Joint of IN713LC Superalloy and AISI 4140 Steel

Influence of Post-weld Heat Treatment on Microstructure and Corrosion Behavior of Dissimilar Friction Welded Joint of IN713LC Superalloy and AISI 4140 Steel

Stress Relaxation Cracking in 347H Stainless Steel Arc Welds: Susceptibility Evaluation of Heat-Affected Zone

Stress relaxation cracking (SRC) is considered one of the major failure mechanisms for 347H stainless steel welds at elevated service temperatures or during post weld heat treatment (PWHT), especially within the heat-affected zone (HAZ). This work focuses on the characterization of SRC susceptibility within 347H physically simulated arc welded HAZ at elevated temperatures. A four-step SRC thermomechanical test in combination with finite element modeling (FEM) of the welding and testing processes is developed to establish a susceptibility map for HAZ. The test first runs a thermal cycle with three different peak temperatures (1335, 1275, and 1150 °C) to duplicate representative HAZ subzone microstructures, followed by time-to-failure examination under a variety of pre-stress (260–600 MPa) and pre-strain conditions (0.03–0.19) as a function of reheat temperatures between 750 and 1050 °C. With the aid of FEM, SRC susceptibility maps are generated to identify the threshold stress, plastic strain, and creep strain as a function of test temperature. It was found out that HAZ subzone with a lower peak temperature (1150 °C) appears to be slightly less susceptible to SRC than the other two subzones that experienced higher peak temperatures. Generally, time-to-fracture reduces with increasing initially applied stress and strain for all test temperatures. The pre-stress thresholds decrease from about 500 to 330 MPa as the testing temperature increases from 800 to 1050 °C, while the corresponding initial plastic strain thresholds reduces from 0.15 to 0.06. The SRC susceptibility was also evaluated through the Larson–Miller Parameter (LMP) analysis as a function of plastic strain, initial stress and starting stress upon reaching the testing temperature, respectively. The 1050 °C test with a high pre-applied strain (0.1) exhibits an extremely short time to failure (t = 3 s) that lies outside the general trend in LMP analysis. Additionally, it was identified that a plastic strain above 0.07 is identified to significantly reduce the bulk creep strain tolerance to fracture and therefore increases SRC susceptibility. Hardness measurement and fractography analysis indicated that the strain aging of niobium carbonitrides and other potential phases in conjunction with intergranular precipitates contributes to an increase in microhardness and increased intergranular cracking susceptibility.

Identifying multiple synergistic factors on the susceptibility to stress relaxation cracking in variously heat-treated weldments

The 347H austenitic stainless steel has been widely used for pressure vessels and pipeline (PVP) applications due to its excellent creep and corrosion resistance, which fit ideally to the harsh conditions in petrochemical industries, fossil fuel or nuclear power plants, and modern energy storages. However, a failure mode has been commonly observed with cracks emerging at the heat affected zone (HAZ) of weldments during post-weld heat treatment (PWHT) or under intermediate to high temperature service conditions. This phenomenon is termed as Stress Relaxation Cracking (SRC) since the purpose of PWHT is to relieve the welding-induced residual stress fields, or as Stress Age Cracking (SAC) if failure happens during service. A leading literature explanation of this failure suggests that the residual stress relaxation and the precipitation dissolution and/or re-precipitation occur in the same temperature range, which can lead to locally high strains and thus to crack at the grain boundaries. Since in situ spatial measurements of residual stress fields, microstructural evolution, and failure processes are nearly infeasible, this work recourses to a micromechanical finite element framework that models the high temperature failure as the nucleation and growth of grain boundary cavities, whereas various parameters such as thermomechanical loading history and its evolution, the competition of grain-interior dislocation creep and grain-boundary diffusion in failure lifetime, and microstructural heterogeneities (such as the precipitate free zone near grain boundaries) can be quantitatively incorporated. It can be concluded from these microstructure-explicit simulations that an accurate knowledge of residual stress evolution and a carefully calibrated set of material constitutive parameters are the essential prerequisites for lifetime predictions. The understanding of individual governing factors also leads to a mechanistic interpretation of the observed SRC susceptibility C-curves. These results suggest that the criticality of residual stress evolution, but not the precipitation-induced local strains, be the leading factor for SRC.

Role of residual stress in the failure of HF-ERW welded tubes

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.