Post-weld Heat Treatment Conditions Research Articles

Dissimilar joining of the martensitic grade P91 and Incoloy 800HT alloy for AUSC boiler application: Microstructure, mechanical properties and residual stresses

The presented study intends to analyze the microstructure and corresponding mechanical characteristics of P91 and Incoloy 800HT dissimilar welded joint (DWJ). The thermo-physical property differences between P91 and Incoloy 800HT arise due to their complex alloying composition, making their weldability difficult. Incoloy 800HT is difficult to weld due to its high susceptibility to solidification cracking. The recommended nickel-based filler metals for welding Incoloy 800HT were employed to weld P91 and Incoloy 800HT using conventional gas tungsten arc welding (GTAW). The welded joint morphology and characteristics were analyzed in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The PWHT was performed to observe changes in microstructural inhomogeneity and residual stress relaxation in weld after the heat treatment. An electron probe microanalyzer (EPMA) was utilized to observe the distribution and segregation of elements in different weld regions. The deep hole drill technique was employed to find the distribution of bi-axial residual stresses in the weld fusion zone (WFZ) and heat-affected zone (HAZ) of base metals in both AW and PWHT conditions. The two nickel-based fillers, ERNiCr-3 and ERNiCrMo-3, were employed, and their weld characteristics were compared. The mechanical strength of ERNiCr-3 filler-based DWJ was found superior to ERNiCrMo-3 filler-based DWJ. The standard AW and PWHT ERNiCr-3 filler-based DWJ tensile specimen failed from Incoloy 800HT base metal with an ultimate tensile strength (UTS) of 570 ± 4 MPa and 650 ± 4 MPa, respectively. The ERNiCrMo-3 filler-based DWJ obtained the highest UTS of 679 MPa after PWHT in a subsize specimen. The microhardness for ERNiCrMo-3 WFZ was found to be higher than ERNiCr-3 WFZ microhardness, and PWHT successfully tempered the P91 HAZ. Further, the impact toughness for the ERNiCr-3 WFZ in AW condition was 86 ± 3 J and PWHT did not provide any significant improvements, while ERNiCrMo-3 WFZ had an impact toughness of 47 ± 10 J in AW state and 41 ± 10 J in PWHT state. Thus, a successful weld characteristic study of defect-free P91 and Incoloy 800HT DWJ was completed, and ERNiCr-3 filler was concluded to be an optimum choice of filler to make the DWJ between P91 and Incoloy 800HT.

Microstructure anomaly upon high temperature exposure and its influence on the mechanical properties of a modified 9Cr-1Mo steel weld

The present work evaluates the microstructure stability of modified 9Cr-1Mo steel welds when subjected to high temperature exposure (HTE) at 775 °C for different times (5, 100, 500, and 1000 h). Prior to HTE, a post weld heat treatment (PWHT) at 760 °C for 2 h was performed. Upon HTE, the individual weld zones viz., weld metal (WM), coarse-grain heat affected zone (CGHAZ) and fine-grain heat affected zone (FGHAZ) demonstrate distinct microstructural variations in terms of precipitate size, grain size and substructure (lath/block/packet boundaries) fractions. The least- and the highest-microstructure stability are respectively seen in FGHAZ and WM after HTE. A detailed investigation involving electron backscattered diffraction (EBSD) and high-resolution transmission electron microscopy (HR-TEM) confirm that a pronounced recovery of the substructure in FGHAZ happens due to enhanced diffusion along the higher fraction of prior-austenite grain boundaries (PAGBs), leading to M23C6 precipitate coarsening and substantial grain growth. The microstructure degradation upon HTE for 1000 h had eventually resulted in deterioration of mechanical properties, where the hardness reduced the most for FGHAZ (~34%), while the least for WM (~7%). Similarly, after HTE, the tensile strength and toughness had deteriorated by ~67% and ~57%, respectively, from the PWHT condition. Fractography further confirms the pronounced degradation after HTE as they result in failure from FGHAZ.

Microstructure anomaly during welding and its influence on the mechanical properties of dissimilar weldments of P92 martensitic steel and AISI 304L austenitic stainless steel

In this investigation, microstructural characteristics, mechanical properties, and residual stress magnitude of dissimilar weld joints (DWJs) between creep strength enhanced ferritic-martensitic (CSEF) P92 steel and austenitic stainless steel (ASS) 304L has been investigated. The Thermanit MTS 616 (P92 filler) filler metal was employed to prepare P92/304L SS DWJs. The groove geometry also plays a crucial role in DWJs, so the conventional V-groove and narrow shape groove geometry was adopted for P92/304L SS DWJs. The microstructure characterization was performed using optical microscope (OM), scanning electron microscope (SEM), and filed emission SEM (FESEM). The microstructural examination showed the formation of the δ-ferrite grains and unmixed zone (UZ) at the weld interface. The martensitic microstructure produced after welding is brittle due to quenched martensite and the dissolution of precipitates. Thus, the post-weld heat treatment (PWHT) known as tempering was carried out at 760 °C for the period of 2 h to get tempered martensitic microstructure. The ultimate tensile strength (UTS) of the as-weld (AW) and PWHT tensile specimen of the P92/304L SS DWJs was 660 MPa and 643 MPa, respectively for V-groove geometry specimens and 640 MPa and 609 MPa, respectively for narrow groove geometry specimens. The tensile fracture was experienced at 304L base metal, and the UTS value of DWJs was very close to the UTS of the 304L SS. The average microhardness value of the martensitic weld metal (352HV0.5) and coarse-grain heat-affected zone (CGHAZ, 366HV0.5), fine grain HAZ (FGHAZ, 320HV0.5) in the AW state was beyond the maximum permissible hardness value of 265HV0.5, as per the A335/A335M − 15a standard. The hardness value beyond 265HV0.5 indicates the undesirable brittle martensitic microstructure. After PWHT, the micro-hardness value of the CGHAZ (235HV0.5), FGHAZ (215HV0.5), and inter-critical HAZ (ICHAZ, 201HV0.5) was below the maximum allowable value of 265HV0.5 for P92 material because of the tempering of the quenched martensite. However, the Charpy test result concluded that the problem associated with the martensitic P92 filler is to obtain an acceptable value of the impact toughness of weld metal in AW state. The Charpy impact toughness of weld metal for P92/304L SS DWJs in AW condition was 10 J (V-groove geometry) and 37 J (narrow groove geometry), while for PWHT condition, it was 188 J (V-groove geometry) and 150 J (narrow groove geometry). The impact toughness of the P92 filler weld was below the minimum requirement of 47 J (EN ISO 3580:2017) in AW state. However, the impact toughness of the welds made by using P92 filler metal met the minimum requirement of 47 J (EN ISO 3580:2017) after PWHT due to the tempering of the martensite. The residual stress analysis using deep hole drilling (DHD) technique revealed the existence of the compressive residual stresses in the weld metal and P92 HAZ in as-weld and PWHT condition. The compressive stress was dominant because of the martensitic phase transformation.

Effect of tempering heat treatment on the microstructure and impact toughness of a Ni–Cr–Mo–V steel weld metal

Microstructure evolution and impact toughness of Ni–Cr–Mo–V weld metal in as-welded (AW) and different post-weld heat treatment (PWHT) conditions were investigated using Transmission Electron Microscopy (TEM), Transmission Kikuchi Diffraction (TKD), and Charpy impact test. The enrichment of Mn and Ni in inter-dendritic (ID) regions caused by welding solidification segregation lowered the Ac1 temperature, making partial untempered martensite transform into reversed austenite during PWHT at 580 °C, which was confirmed directly by Laser Scanning Confocal Microscope (LSCM). The transformation kinetics and element distribution during austenite reversion were revealed by DICTRA simulation, suggesting the enrichment of C, Mn and Ni in reversed austenite. The microstructure at room temperature of ID regions depended on the tempering cooling rates. When weld metal was cooled by water after tempering, the microstructure in ID regions consisted of finer fresh martensite and over tempered martensite, which was a major contributor to the higher impact toughness. While weld metal was cooled at a rate of 5 °C/h, the reversed austenite in ID regions transformed into fresh ferrite and cementite, which was difficult to resist crack propagation, and resultantly the impact toughness was deteriorated. The impact absorbed energy of weld metal increased with the increase of tempering cooling rates, which was attributed to the microstructure change in ID regions from ferrite to martensite. The inherited substructures of martensite in ID regions had a hindering effect on crack propagation, and resultantly more energy was consumed.

Effects of different post-weld heat treatment conditions on mechanical properties and microstructure of welded joints

Post-weld heat treatment is a standard method to improve the performance of welded joints. Different heat treatment processes have different influences on the performance of welded joints. Therefore, it is of great significance to explore the impact of the heat treatment process on welded joints’ performance. This work applied three different heat treatment processes to the welded joints with three different properties. Then hardness test, impact test, tensile test, metallographic analysis and other means were used to evaluate the performance of welded joints after heat treatment. The following conclusions were drawn through the experiments: The change of phase compositions of the welded joints caused by the post-weld heat treatment was considered as the main reason for changes in mechanical properties of the welded joint. The difference in mechanical properties after different welding process and post-weld heat treatment combination was obtained, which has a guiding significance for practical production.

Influence of precipitate evolution on the impact fracture behavior in Nb-containing 16Cr–25Ni superaustenitic stainless steel weld metal

In this work, the precipitate evolution and its influence on the impact fracture behavior of Nb-containing 16Cr–25Ni superaustenitic stainless steel weld metal were systematically studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Results show completely transgranular ductile fracture mode of as-welded condition, of which the M6C carbides and Nb(C, N) carbonitrides contributed to the crack initiation, but the interface between M6C carbide and matrix was more prone to crack under impact load. In contrast, due to the semi-continuous distributed M23C6 carbides on the grain boundary, an intergranular/transgranular mixed mode was observed in the post-weld heat treatment (PWHT) sample. Additionally, the crack sources in grain interior were not limited to primary precipitation phases, whereas secondary M2(C, N) carbonitrides and M23C6 carbides also acted as preferential sites for crack initiation. The massive M2(C, N)/matrix and M23C6/matrix interfaces led to easier crack propagation path simultaneously. Moreover, the deformation mechanism were governed by dislocation slip and twinning in the impact fracture of as-welded sample, but the mechanical twins disappeared in the fractured sample at PWHT condition, which was attributed to the local stress concentration in the matrix could not exceed the critical twinning stress. Therefore, the combination of secondary precipitates induced embrittlement and weakened plastic deformation capacity of matrix, leading to the impact toughness declined from 91.0 ± 3.6 J to 34.3 ± 4.6 J after PWHT.

Study on microstructure and mechanical behavior relationship for laser-welded dissimilar joint of P92 martensitic and 304L austenitic steel

A dissimilar laser beam welded joint of ferritic/martensitic P92 steel, and 304L austenitic stainless steel (ASS) has been examined in as-weld and post-weld heat treatment (PWHT) at 760 °C for 120 min for microstructure feature and mechanical aspects. The microstructure of the weld metal, interface, and heat-affected zone (HAZ) was characterized in detail, and it was observed that a great level of inhomogeneity exists in a dissimilar joint. In addition, the effect of the inhomogeneity in microstructure on mechanical properties, microhardness, and impact strength of the welded joint was discussed. The welded joint's mechanical properties met the USC boiler requirement for both as-weld and PWHT situations. The welded joint showed a decent combination of tensile strength and impact strength for both as-weld and PWHT conditions. The tensile results showed the failure from the 304L SS base metal, which ensured the acceptable strength of the weld metal for the laser welded joints. The part of the welded joint with relatively poor impact strength was the weld metal. Though, the Charpy impact toughness of the weld metal (89 J) was measured higher than the ASME standard value (>41 J) and EN 1599:1997 standard value (>47 J) in the as-weld situation. The impact strength of the weld fusion zone was 138 J in PWHT condition.

Study on microstructure characterization of fracture frontier of post welds heat treatment and type IV cracking of P92 steel welded joint

In the research work presented in this study microstructure evolution at fracture frontier of crept P92 weld, creep rupture life and effect of creep exposure time on microstructure evolution in fine-grained heat affected zone were performed. Microstructure evolution and creep rupture behavior of metal arc welded joint of P92 steel plate in the as-welded have been studied. The different states of post weld heat treatment (PWHT). (i). post welded heat treatment at 760 o C for the 2h (ii). re-austenitizing at 1040 o C for 60 min and air cooled and tempering at 760 o C for 2h. In PWHT condition, most common type IV cracking was observed creep exposure 620 o C / 150 MPa. The martensitic matrix fracture is also observed in PWNT 1 condition. A move away from the fracture frontier, the cavities still remain in the microstructure while the martensitic matrix fracture is difficult to observe. The line mapping also confirmed the increase in weight percentage of Cr and Mo in M 23 C 6 . The elemental mapping of PWHT 2 condition is also carried out in FGHAZ which confirm the formation of Mo and Cr-rich M 23 C 6 precipitates.

Numerical investigation of laser beam-welded AA2198 joints under different artificial ageing conditions

The present study aims to investigate the effect of weld geometry and geometrical shape imperfections on the mechanical behavior of welded joints under different post-weld heat treatment conditions. Finite element analyses were performed using the local mechanical properties of laser beam welded AA2198 joints obtained from micro-flat tensile test specimens. The finite element results show that, for the as-welded condition show that the maximum strain was observed in the lower region of the fusion zone, independently the geometrical imperfections. By applying post weld heat treatment, the maximum strain concentration can now be noticed in the upper region of the fusion zone for all the ageing times due to the lower local elongation at fracture values.

Effect of filler metal combination and post weld heat treatment on pitting corrosion and impact toughness of GTA welded AISI 410 SS joints

The Experimental work was done to investigate the role of pitting corrosion resistance as well as impact toughness behavior of gas tungsten arc welded martensitic stainless steel (AISI 410SS) joints. In this study 6 mm thick cold rolled AISI 410 stainless steel plates were utilized as a base plate. The welding was accomplished by using three different filler materials (Inconel 625, AISI 316 SS, and AISI 410 SS). The effect of post weld heat treatment (PWHT) and different filler materials on the pitting corrosion resistance, impact strength, and metallurgical performance of the GTA welded plates was investigated. The analysis for pitting and impact was studied in two circumstances first in as-received situation and second in PWHT situation.The outcomes formulated from research work indicates that the filler material composition induces the significant variation in the impact toughness along with pitting corrosion resistance of the experimental specimens. The minimum mass loss (1.3818 mg) of Inconel 625 filler welded joint indicates that the maximum resistance of the tested samples against the pitting corrosion. Furthermore, the PWHT helps to enhance the pitting resistance. The maximum impact toughness (average CVN 121.5 J) shown by (WJ-2P) in PWHT condition. The experimental study indicates that the Inconel 625 filler material helps to improve the pitting resistance and impact toughness of the welded specimens in as-received along with PWHT condition.

High temperature creep behavior of a low alloy Mn-Mo-Ni reactor pressure vessel steel

Creep behavior of a low alloy Mn-Mo-Ni reactor pressure vessel steel received in post weld heat treatment condition has been studied in the temperature range of 600–900 °C. The steel exhibited three stage creep behavior. The steady or secondary creep rates for different stress conditions for a particular temperature were determined using stress change tests. Temperature change tests were conducted to determine the steady state creep rates at different temperatures at a particular stress. The creep rates obtained from different tests were analyzed using the Norton's and Bird-Mukherjee-Dorn creep equations to determine the stress exponent (n) and the creep activation energy (Q). The values of n and Q obtained signify dislocation climb as the underlying creep mechanism in steel. Electron back scatter diffraction (EBSD) study indicated formation of fine subgrain structure in the crept sample.

Study on Microstructural Characterization, Mechanical Properties and Residual Stress of GTAW Dissimilar Joints of P91 and P22 Steels.

This article deals with the dissimilar joining of two different grade Cr-Mo steel (2.25Cr-1Mo: P22 and modified 9Cr-1Mo: P91) for power plant application. The dissimilar butt-welded joint was produced for conventional V groove design by using the gas tungsten arc welding (GTAW) process with the application of an ERNiCrMo-3 Ni-based super alloy filler. A microstructure characterization was performed to measure the inhomogeneity in the microstructure and element diffusion across the interface in a welded joint. The experiments were also performed to evaluate the mechanical properties of the dissimilar welded joint in as-welded (AW) and post-weld heat treatment (PWHT) conditions. An acceptable level of the mechanical properties was obtained for the AW joint. After PWHT, a significant level of the element diffusion across the interface of the weld metal and P22 steel was observed, resulting in heterogeneity in microstructure near the interface, which was also supported by the hardness variation. Inhomogeneity in mechanical properties (impact strength and hardness) was measured across the weldments for the AW joint and was reduced after the PWHT. The tensile test results indicate an acceptable level of tensile properties for the welded joint in both AW and PWHT conditions and failure was noticed in the weak region of the P22 steel instead of the weld metal.

Investigation of the microstructure and mechanical properties of the laser welded joint of P22 and P91 steel

The present manuscript investigates the microstructural aspects and mechanical properties of laser beam welded ASTM A335 Grade P91 and P22 steel joint for power plant applications. Detailed microstructure characterization of the weld metal (WM) and heat-affected zone (HAZ) were carried out in as-welded and post-weld heat treatment (PWHT) conditions. A variation in microstructure was observed along the welded joint. This resulted in inhomogeneity in mechanical properties. The PWHT resulted in the formation of the stabilized microstructure in weldments and reduced heterogeneity in mechanical properties along the weldments. Tensile strength of weld joint in as-welded (AW) and PWHT condition was found slightly higher (617 MPa and 628 MPa, respectively) than the tensile strength of P22 steel (610 MPa). The fracture location for both AW and PWHT was observed in the P22 base region, which indicates that welded joint is stronger than the base material. Maximum tensile strength of the WZ was found 864 MPa in the as-welded condition. The hardness of WM, P91 CGHAZ and P22 CGHAZ were found 376 HV, 420 HV and 302 HV, respectively. After the PWHT, the hardness of the WM, P91 CGHAZ, P91 ICHAZ, P22 CGHAZ and P22 ICHAZ were measured 237 HV, 264 HV, 212 HV, 208 HV and 190 HV, respectively. The reduction in hardness is attributed to the tempering reaction, which results in the formation of the tempered martensite in WM and HAZ of P91 and tempered bainite in P22 HAZ. The impact toughness of the weld metal in as-welded condition was measured 85 J, which was lower than P22 and P91 steel. PWHT resulted in a drastic increase in impact toughness of WM and it was 145 J. The impact toughness of the P22 and P91 HAZ was measured 146 J and 92 J, respectively, for AW and 168 J and 140 J, respectively, after PWHT. The optimum microstructure and mechanical properties of the dissimilar welded joint were obtained after the PWHT.

Study on Microstructure and Mechanical Properties of Laser Welded Dissimilar Joint of P91 Steel and INCOLOY 800HT Nickel Alloy.

This investigation attempts to explore the weld characteristics of a laser welded dissimilar joint of ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel and Incoloy 800HT austenitic nickel alloy. This dissimilar joint is essential in power generating nuclear and thermal plants operating at 600–650 °C. In such critical operating conditions, it is essential for a dissimilar joint to preserve its characteristics and be free from any kind of defect. The difference between the physical properties of P91 and Incoloy 800HT makes their weldability challenging. Thus, the need for detailed characterization of this dissimilar weld arises. The present work intends to explore the usage of an unconventional welding process (i.e., laser beam welding) and its effect on the joint’s characteristics. The single-pass laser welding technique was employed to obtain maximum penetration through the keyhole mode. The welded joint morphology and mechanical properties were studied in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The macro-optical examination shows the complete penetrations with no inclusion and porosities in the weld. The microstructural study was done in order to observe the precipitation and segregation of elements in dendritic and interface regions. Solidification cracks were observed in the weld fusion zone, confirming the susceptibility of Incoloy 800HT to such cracks due to a mismatch between the melting point and thermal conductivity of the base metals. Failure from base metal was observed in tensile test results of standard AW specimen with a yield stress of 265 MPa, and after PWHT, the value increased to 297 MPa. The peak hardness of 391 HV was observed in the P91 coarse grain heat-affected zone (CGHAZ), and PWHT confirmed the reduction in hardness. The impact toughness results that were obtained were inadequate, as the maximum value of impact toughness was obtained for AW P91 heat-affected zone (HAZ) 108 J and the minimum for PWHT Incoloy 800HT HAZ 45 J. Thus, difficulty in obtaining a dissimilar joint with Incoloy 800HT using the laser beam welding technique was observed due to its susceptibility to solidification cracking.

Study on evaluation of through-thickness residual stresses and microstructure-mechanical property relation for dissimilar welded joint of modified 9Cr–1Mo and SS304H steel

Gas Tungsten Arc Welded dissimilar joint of modified 9Cr–1Mo (P91) and SS304H steel plate is prepared using Ni-based ERNiCrCoMo-1 super alloy filler and are post-weld heat treated (PWHT) at 760 °C for 2 h. In particular, joints are investigated for metallurgical and mechanical properties in different heat-affected zones. Furthermore, an attempt has been made to understand the following: (i) Is there any effect of mixing of Ni-based superalloy filler material on the joint? (ii) How does the PWHT process change the metallurgical and mechanical properties of joints and different sections? (iii) Does the PWHT process beneficial as compared to as-welded (AW) joint? Experimental results indicate that improper mixing of filler materials led to the formation of an unmixed zone near the weld metal and HAZ interface. The hardness, residual stress, and impact energy results confirmed the variation in mechanical properties along the weldments. The tensile strength varied from 539 MPa in as-joint to 516 MPa in PWHT, and impact energy varies from 165 J in as-joint to 40 J in PWHT condition. The maximum hardness of 375 H V is observed in P91 CGHAZ. The maximum longitudinal residual stress is estimated as 200 MPa at the top surface of the welded plate, i.e., about 2 mm depth, while the maximum magnitude of the transverse residual stresses is observed as 109 MPa at the same depth of 2 mm. In P91 HAZ, the longitudinal and transverse residual stress magnitudes are found to be in a range of 0 to ˗70 MPa. The SS304H HAZ shows the maximum value of longitudinal and transverse residual stress level at a depth of 3 mm, and it was 144 MPa and 92 MPa, respectively. The PWHT showed a drastic reduction in residual stress value in a different zone of the weldments.

Effect of Post-Weld Heat Treatment Conditions on Mechanical Properties, Microstructures and Nonductile Fracture Behavior of SA508 Gr.1a Thick Weldments

This study analyzes the effects of post-weld heat treatment (PWHT) on the mechanical properties and microstructures of SA-508 Gr.1a welds and proposes a new PWHT exemption criterion based on nonductile fracture evaluation considering welding residual stress. The welding coupons were prepared with submerged-arc welding, gas-tungsten arc welding, and shielded-metal arc welding, using ferritic steel, SA-508 Gr.1a. The microstructure of the heat-affected zone (HAZ) was analyzed using optical microscopy, electron-back-scatter diffraction and Vickers hardness testing. The mechanical properties of the welds were evaluated by uniaxial tensile test, transverse side bend test, Charpy V-notch impact test and side bend test. Bainite and ferrite structures formed mainly in the HAZ, and the grain size became coarser with proximity to the surface and fusion line. The mechanical properties did not depend strongly on PWHT, weldment thickness or welding techniques, and they satisfied the welding procedure qualification test specified in the ASME Boiler & Pressure Vessel code. Welding residual stresses were considered in assessing structural integrity using nonductile fracture evaluation. A margin of safety against nonductile fracture with residual stress was calculated for Korean Standard Nuclear Power Plant steam-generator welds, using its design parameters and operating conditions, and this safety margin is suggested as an acceptance criterion for residual stress for exemption from PWHT.Graphic abstract

Experimental investigation on microstructure, mechanical properties, and residual stresses of dissimilar welded joint of martensitic P92 and AISI 304L austenitic stainless steel

In this study, microstructural characteristics and mechanical properties of martensitic steel P92 and AISI 304L austenitic stainless steel (ASS) dissimilar metal weld (DMW) have been examined. The welding was performed using the multipass gas tungsten arc welding (GTAW) process. The ERNiCrMo-3 (Inconel 625) filler metal was used due to its excellent compatibility with the P92 and AISI 304L ASS metals. The microstructure characterization performed with an optical microscope and scanning electron microscope revealed the presence of an unmixed zone in the form of beach, peninsula, and island at the base metal and weld fusion zone interface. Secondary phases enriched with Nb and Mo, and migrated grain boundaries (MGBs) were also observed at the weld fusion zone. The microstructural characterization at the P92 side revealed the presence of a soft ferrite zone and delta ferrite at the weld and P92 interface. The different peak temperature experienced by the P92 metal during the welding process results into the formation of three distinct zones with diverse mechanical and microstructural properties namely coarse grain heat affected zone (CGHAZ), fine grain heat affected zone (FGHAZ), and inter-critical heat affected zone (ICHAZ). The post weld heat treatment (PWHT) at 760 °C for 2 h followed by air cooling was performed to homogenize this heterogeneous microstructure formed toward the P92 side. It was observed that this PWHT does not have any significant effect on weld fusion zone and 304L SS heat affected zone (HAZ) microstructure. But, PWHT modifies the microstructure of P92 side HAZ. The tensile test, Vickers micro-hardness test, and charpy impact test were carried out to determine the mechanical properties of the DMW. The tensile strength was found as 587.709 MPa in the as-welded condition and 594.515 MPa in PWHT condition. The tensile test results indicated that specimens were failed from 304L stainless steel (SS) base metal (BM) in as-welded and PWHT condition. The charpy impact toughness test results showed that the toughness of the weld joint was very low in as-welded and PWHT condition (47J) compared to the P92 (190J) and SS 304L (285J) BM. From the microhardness examination, it was observed that the ICHAZ was the weakest zone among all the other regions due to its lower micro-hardness value compared to the other regions. After welding process, residual stresses were measured in as-welded and after PWHT condition at the center of the weld and at the HAZ of P92 and SS 304L (through the thickness of the plate) using experimental-based deep hole-drilling (DHD) strain-gauge method. The results showed that both circumferential (hoop stress) and axial (longitudinal stress) welding residual stresses were decreased after PWHT.

Influence of Post Weld Heat Treatment on the Grain Size, and Mechanical Properties of the Alloy-800H Rotary Friction Weld Joints.

This study evaluated the microstructure, grain size, and mechanical properties of the alloy 800H rotary friction welds in as-welded and post-weld heat-treated conditions. The standards for the alloy 800H not only specify the composition and mechanical properties but also the minimum grain sizes. This is because these alloys are mostly used in creep resisting applications. The dynamic recrystallization of the highly strained and plasticized material during friction welding resulted in the fine grain structure (20 ± 2 µm) in the weld zone. However, a small increase in grain size was observed in the heat-affected zone of the weldment with a slight decrease in hardness compared to the base metal. Post-weld solution heat treatment (PWHT) of the friction weld joints increased the grain size (42 ± 4 µm) in the weld zone. Both as-welded and post-weld solution heat-treated friction weld joints failed in the heat-affected zone during the room temperature tensile testing and showed a lower yield strength and ultimate tensile strength than the base metal. A fracture analysis of the failed tensile samples revealed ductile fracture features. However, in high-temperature tensile testing, post-weld solution heat-treated joints exhibited superior elongation and strength compared to the as-welded joints due to the increase in the grain size of the weld metal. It was demonstrated in this study that the minimum grain size requirement of the alloy 800H friction weld joints could be successfully met by PWHT with improved strength and elongation, especially at high temperatures.

Effect of filler wire and post weld heat treatment on the mechanical properties of laser beam-welded AA2198

The mechanical behavior of autogenously and non-autogenously laser beam-welded joints of Al-Cu-Li alloy AA2198 and the effect of post weld heat treatment are examined in this contribution. The deformation texture of the base material does not present any significant change in the macrotexture with applying different artificial ageing times. Autogenously and non-autogenously laser beam-welded joints present a decrease in yield stress and ultimate strength in the as-welded condition, approximately 45% and 36–38%, respectively, when compared with AA2198-Τ3 base material. The addition of the AA4047 filler wire increases the Si and Cu content in the grain interior and in the grain boundaries of the fusion zone of the welded joint. Micro-hardness measurements for autogenously laser-welded joints showed a decrease in hardness by 27% for the fusion zone and 42% for the heat-affected zone, when compared with the non-autogenously laser beam-welded joints. Α quality index was exploited to evaluate the tensile mechanical performance of the welded joints. It is observed that the non-autogenously welded joints always show a higher ‘quality’ than the respective autogenously welded joints and the highest quality index in terms of mechanical performance is achieved for the as-welded and the peak-aged conditions, respectively. Regardless of the post weld heat treatment condition, both autogenously and non-autogenously laser-welded specimens fractured in between the equiaxed and fusion zone during tensile loading.

Dissimilar Welding of Nickel Based Superalloy with Stainless Steel: Influence of Post Weld Heat Treatment

ABSTRACT Dissimilar welding potentially has great importance for many industries. Joining of two different alloys is very challenging. In this paper, an attempt was made to produce a reliable joint between Nickel-based superalloy with stainless steel using the gas tungsten arc welding process with nickel-based filler wire. Post-weld heat treatment was executed at 700°C for 2 h. A critical comparison was made between the post-weld heat-treated samples and as-welded samples. The tensile test indicates that the strength of the joint is higher than the weaker base metal (Stainless Steel). The macrostructure and microstructure show proper fusion and bonding among the parent metals and filler wire. There is a formation of the partially melted zone at fusion boundary and secondary phase (Niobium-rich phase) at a region adjacent to the fusion boundary on heat-affected zone of Inconel side. It was also observed that the post-weld heat-treated samples have a significant reduction in the secondary phase. Vickers’ microhardness value indicates that the secondary phase has a higher value of hardness both in as-weld condition and post-weld heat treatment condition. Thus, Nickel-based filler wire is a compatible filler wire for the dissimilar joint.