Post-weld Heat Treatment Samples Research Articles

Effect of post-weld heat-treatment and solid-state thermomechanical treatment on the properties of the AA6082 MIG welded joints

Post-weld heat treatment (PWHT) and solid-state thermomechanical treatment (TMT) via friction stir processing (FSP) have been shown to enhance the mechanical properties of aluminum alloys. The current work investigates the effects of PWHT and TMT on the microstructure and mechanical performance of AA6082-T6 welded butt joints welded using the MIG process. The 5 mm thick AA 6082-T6 plates were joined in butt configuration using MIG welding with ER 5356 filler wire, 120 A current, 0.3 mm/s weld speed, and argon shielding gas at 15 L/min flow rate. PWHT was performed on the MIG welds per the T6 temper procedure. TMT was implemented via FSP using a pinless tool rotating at 800 rpm and traversing speed at 200 mm/min with a 3° tilt angle. Microstructural analysis, hardness mapping, tensile testing, and fracture surface evaluation were utilized to characterize the as-welded, PWHT, and TMT samples. The results demonstrate that both PWHT and TMT significantly refine and homogenize the microstructures of the welded joints. However, the TMT samples displayed superior hardness and tensile strength compared to the as-welded and PWHT conditions. The TMT-processed welds achieved approximately 99% joint efficiency versus only 69% and 85% for the as-welded and PWHT samples. In summary, PWHT and especially TMT via FSP are effective at enhancing the mechanical properties of MIG welded AA6082-T6.

Effects of thermal ageing time and temperature during heat-treatment on the mechanical properties of fiber laser welded Nb-1%Zr-0.1%C alloy in continuous wave mode

The effects of thermal ageing time and temperature used during heat-treatment were studied on tensile strength, elongation, and microhardness of the laser welded Nb-1%Zr-0.1%C alloy in continuous wave mode. Post-weld heat treatment (PWHT) was carried out by varying the temperature and time in the ranges of (850–1050) °C (that is, about the recrystallisation temperature) and (0.5–4) h (as the weld samples were prepared in the form of sheets), respectively. The grain sizes of fusion zone (FZ), and FZ heat treated at 850 °C for 4 h and that at 950 °C for 2 h were found to be equal to 52.85 μm, 84.89 μm and 116.43 μm, respectively. The segregation of zirconium, carbon and oxygen increased grain boundary energy and induced brittleness to the grain boundary, resulting in loss of ductility. The micro-hardness and Young's modulus values were observed to increase in the FZ compared to that of the base metal (BM), but their decreasing trends were noticed during the heat-treatment due to the grains' softening. For the PWHT samples, the plasticity was found to decrease to about 57% of that of BM. This was attributed to the precipitation of carbides, grain growth, and dislocation pinning during the ageing process. During the heat-treatment of the welded samples, both Yield Strength (YS) and Ultimate Tensile Strength (UTS) were found to decrease to 77% and 86%, respectively, of that of the BM.

Effect of PWHT on metallurgical and mechanical characterization of dissimilar welded joint of P91 and P92 steels

P91 and P92 steels are widely used in nuclear and thermal power plant’s high-temperature (650–700 °C) operating components. The welding procedure, base plate composition, filler material composition, and post-weld heat treatment (PWHT) significantly affect the metallurgical characterization of weldments at room temperature. This work focuses on joining P91 and P92 steel by the TIG welding with filler ER90S-B9. The study analyzes the materialization of coarse-grained HAZ (CGHAZ), inter-critical HAZ (ICHAZ), and fine grained HAZ (FGHAZ) under welded and PWHT. PWHT was conducted at 840 °C for 2, 4 and 6h. An optical microscopic (OM) scanning electron microscope (SEM) was employed to characterize the welded and PWHT samples. It was perceived that the tensile strength of PWHT increased as the heat treatment times increased from 2 to 6 h, while the hardness value decreased accordingly. The maximum tensile strength (594.71 MPa) was observed in PWHT_6 h, while the minimum tensile strength (537.52 MPa) was perceived in the as-welded sample. The PWHT_6h reveals the minimum hardness values (271.12 HV) at the fusion zone among all the conditions. The WFZ consisted of an untampered lath martensitic grain structure, demonstrating an average hardness value of 314.15 HV in the PWHT_2h condition. The hardness value in CGHAZ samples for as-welded, PWHT_2h, PWHT_4h, and PWHT_6h was observed at 456.85, 436.81, 368.63, and 327.41 HV, respectively.

Influence of Microstructure and Mechanical Properties of Dissimilar Rotary Friction Welded Inconel to Stainless Steel Joints.

The present study aims to evaluate the microstructure, grain size, and mechanical properties of the dissimilar AISI 316L/Inconel 718 (IN 718) rotary friction welded joints under both the as-welded and post-weld heat treatment (PWHT) conditions. Because of reduced flow strength at elevated temperatures, the AISI 316L and IN 718 dissimilar weldments exhibited more flash formation on the AISI 316L side. At higher rotating speeds during friction welding, an intermixing zone was created at the weld joint interface due to the material softening and squeezing. The dissimilar welds exhibited distinctive regions, including the fully deformed zone (FDZ), heat-affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and the base metal (BM), located on either side of the weld interface. The dissimilar friction welds, AISI 316L/IN 718 ST and AISI 316L/IN 718 STA, exhibited yield strength (YS) of 634 ± 9 MPa and 602 ± 3 MPa, ultimate tensile strength (UTS) of 728 ± 7 MPa and 697± 2 MPa, and % elongation (% El) of 14 ± 1.5 and 17 ± 0.9, respectively. Among the welded samples, PWHT samples exhibited high strength (YS = 730 ± 2 MPa, UTS = 828 ± 5 MPa, % El = 9 ± 1.2), and this may be attributed to the formation of precipitates. Dissimilar PWHT friction weld samples resulted in the highest hardness among all the conditions in the FDZ due to the formation of precipitates. On the AISI 316L side, prolonged exposure to high temperatures during PWHT resulted in grain growth and decreased hardness. During the tensile test at ambient temperature, both the as-welded and PWHT friction weld joints failed in the HAZ regions of the AISI 316L side.

Friction Stir Welding Parameters: Impact of Abnormal Grain Growth during Post-Weld Heat Treatment on Mechanical Properties of Al–Mg–Si Welded Joints

Friction stir welding (FSW) is an alternative method to join aluminum (Al) alloys in a solid-state condition. However, the coarsening or dissolution of precipitation hardening phases in the welding zone causes strength reduction or softening behavior in the welded area of age-hardened Al alloys. Therefore, this research aimed to improve the mechanical properties of an FSW Al–Mg–Si alloy via post-weld heat treatment (PWHT) and the possibility of controlling the abnormal grain growth (AGG) using different welding parameters. FSW was performed with different rotational and travel speeds, and T6 heat treatment was carried out on the FSW samples as the PWHT. The results showed a decrease in the strength of the FSW samples compared with that of the base material (BM) due to the dissolution of precipitation hardening particles in the heat-affected zone. However, the emergence of AGG in the microstructure after the T6-PWHT was identified as the potential event in the microstructure of the PWHT samples. It is found that the AGG of the microstructure in similar joints of Al6061(T6) was governed by the welding parameters. The results proved that PWHT was able to increase the tensile properties of the welded samples to values comparable to that of Al6061(T6)-BM. The increased mechanical properties of the FSW joints were attributed to a proper PWHT that resulted in a homogeneous distribution of the precipitation hardening phases in the welding zones.

Distinctiveness of Welding Joints Design Based on Mechanical and Corrosion Environmental Influence on Low Carbon Steel

Experimental investigations were carried out to study the effect of weld joint designs and post weld heat treatment (PWHT) on mechanical and corrosion properties of low carbon steel. Butt, bevel and half-lap joints were produced with a voltage of 20 V and current of 110 A with the use of 3.2 mm diameter electrode E6013. Full annealing was carried out on part of the welded samples in order to consider the possibility of post weld heat treatment for better performance. The mechanical properties (tensile, hardness, and impact toughness) were studied for both the as welded (AW) and PWHT samples as well as the corrosion performance in a natural sea water environment containing 3.5 wt.% NaCl using potentiodynamic polarization method. The microstructure of the AW and PWHT samples of the welded joints with the most promising mechanical and corrosion properties were then characterized by means of an optical microscopy. The results obtained reveals that the bevel joint followed by half lap joint and the butt joint of the as weld samples gave the best combination of the mechanical properties considered. On the other hand, the corrosion properties of the butt joint were superior to that of the bevel and half lap joint, respectively in the PWHT condition as compared to the AW samples. This implies that PWHT improves the corrosion resistance of the welded steel joints.

Probing True Microstructure-Hardening Relationship in Simulated Heat Affected Zone of P91B Steels

The inducement of this paper was the revelation of true microstructure-hardening relationship in heat affected zones (HAZs) of P91B steels. This work reports erroneous metallographic practices in revealing true microstructure and establishes prior austenite grain (PAG) hardening and softening phenomenon. Different HAZs were simulated having distinguished microstructural features. True microstructure of simulated and post-weld heat treatment (PWHT) samples were revealed completely and discussed with respect to microhardness indicating the degree of hardening. It was revealed that true microstructure features of sub-HAZs were governed by peak temperature, hold time at peak temperature, PAG size, and microhardness. The simulated samples showed different microstructural features on using different reagents/etchants. Rate of revealing microstructural features and degree of keying force influencing PAG size were observed to be dependent on peak temperature and hold time at peak temperature. However, true-microstructural features of furnace simulated and PWHT samples were independent of reagents’ composition. Degree of hardening varied due to the difference in solid solution strengthening and formation of second phases at a given peak temperature and hold time at peak temperature. In simulated samples, PAG softening was observed for coarse-grained HAZ (CGHAZ) after PWHT, while in furnace simulated samples, softening occurred in inter-critical HAZ (furnace simulated ICHAZ). Interpass temperature with second pass led to the formation of mixed PAGs and PAG hardening. This hardening was retained in inter-critically reheated CGHAZ after PWHT, whereas it was absent in super-critically reheated CGHAZ.

Linear friction welding of AD730™ Ni-base superalloy: Process-microstructure-property interactions

Linear friction welding (LFW) is a near net shape solid state joining technology for aerospace applications. In this study LFW of a recently introduced Ni-based superalloy, AD730™, with superior properties for use in the hot section of gas turbines was studied. In order to minimize the number of experiments for achieving sound welds, an analytical method was developed that allowed to determine the optimum process parameters with a limited number of experiments. The predictions of the method were validated by LFW experiments, and sound samples without defects were produced. Microstructure evolution of the as-welded samples from the weld center to the base metal was investigated using laser confocal and field emission scanning electron microscopy (SEM) including electron back scatter diffraction (EBSD), energy dispersive spectrometer (EDS) and backscattered imaging (BSE). Post-weld heat treatment (PWHT), consisting of a γ′ sub-solvus solutionizing followed by aging, was conducted on LFWed blocks. Then, microstructure evolution and mechanical testing were conducted on PWHTed samples and compared with the as welded blocks. The obtained results were correlated with microhardness as well as tensile testing at room temperature and 650 °C, and interpreted in terms of fundamental metallurgical processes. Macroscopic examination of the PWHTed joints revealed that the samples failed out of the weld zone, further demonstrating the appropriate selection of LFW processing parameters using the proposed analytical method. PWHTed samples exhibited better room and high temperature tensile properties compared to those of the as-welded samples. Microscopic examination of the fracture zones of the samples showed that the higher levels of reprecipitation of γ′ particles in the thermomechanically-affected zone (TMAZ) of the PWHT samples were associated to their higher tensile properties compared to the as welded ones.

Performance Evaluation of the Effects of Post Weld Heat Treatment on the Microstructure, Mechanical and Corrosion Potentials of Low Carbon Steel

The effect of Post Weld Heat Treatment (PWHT) on the microstructure, mechanical and corrosion properties of low carbon steel have been investigated. The welding process was conducted on butt joint using Manual Metal Arc Welding (MMAW) techniques at a welding voltage of 23 V and welding current of 110 A with the use of E6013 and 3.2 mm diameter as filler material. Heat treatment through full annealing was carried out on the welded low carbon steel. The mechanical properties (hardness, impact toughness and tensile properties) of the AW and PWHT samples were determined. The microstructure of the AW and PWHT samples was characterized by means of an optical microscopy. Corrosion behavior of the sample was studied in3.5 wt.% NaCl environment using potentiodynamic polarization method. The results showed that the AW samples has good combination of mechanical and corrosion properties. The microstructure revealed fine grains of pearlite randomly dispersed in the ferrite for the AW base metal (BM) sample while agglomerated and fine particle of epsilon carbide or cementite randomly dispersed on the ferritic phase of the heat affected zone (HAZ) and weld metal (WM), of the AW, respectively. The PWHT samples shows that the annealing process allow diffusion and growth of the fine grains into partial coarse grains of ferrite and pearlite which did not encourage improvement of the properties. Therefore, it was concluded that the welding parameters put in place during welding of the low carbon steel are optimum for quality weld.

Effect of post weld heat treatment and TiAlSiN coating on the tensile strength of autogenous plasma arc welding of duplex/ super austenitic stainless steels

The present study shows the effect of post weld heat treatment (PWHT) and TiAlSiN coating on tensile, bending strength, hardness and corrosion of Duplex Stainless Steel (DSS) and Super Austenite Stainless Steel (SASS) joined materials in plasma arc welding. Direct aging PWHT process was conducted for 32 h at 918 °C on DSS - SASS materials. The hardness value reduced at the heat affected zone of PWHT samples due to the formation of pentagonal and hexagonal precipitates. TiAlSiN coating was applied in dissimilar material at 450 °C by Physical Vapor Deposition (PVD) process with pressure 3.0 × 10−3 Pa. In case of TiAlSiN coated sample, the tensile failures occurred at the SASS where as in case of DSS - SASS, PWHT the tensile failure occurred at the fusion zone. This investigation also showed the exhaustive mechanical property relationships of Autogeneous Plasma Arc (A-PA) weldments conducted on the fusion zone based on the process of DSS - SASS, PWHT and TiAlSiN coating by employing scanning electron microscopy, X-ray diffractometry and transmission electron microscopy techniques. Potentio dynamic polarization studies were carried out on both dissimilar and coated samples in 3.5% NaCl solution environment and the results showed that the corrosion resistance of coated samples was improved. When compared with DSS - SASS and PWHT samples, the absence of CrN in TiAlSiN coated materials resulted in high tensile strength and an increase in elongation at fracture surface compared to the coated samples.

A comparison of the effect of different heat treatment processes on laser-welded NiTinol sheets

In this work, an attempt is made to compare the weld properties obtained through three different post-weld heat treatment (PWHT) methods, viz. water quenching, normalizing and laser processing. Butt joint was made between two NiTinol sheets of thickness 1 mm using ytterbium: yttrium aluminum garnet (Yb: YAG) laser welding process. Phase transformation temperatures, microhardness, tensile strength and corrosion resistance of the weld were compared with PWHT samples, and it was observed that PWHT resulted in significant variation in the phase transformation temperatures, microhardness, tensile strength and corrosion resistance. Concerning phase transformation temperatures, laser processing relatively resulted in minor deviation than the water-quenched and normalized samples. Concerning corrosion resistance and tensile strength, water-quenched samples had better properties than the normalized and laser-processed samples.

Microstructure and mechanical properties of friction stir welded oxide dispersion strengthened AA6063 aluminum matrix composites enhanced by post-weld heat treatment

Oxide dispersion strengthened (ODS) AA6063 aluminum matrix composites (AMCs) sheets fabricated by a new method were successfully joined by friction stir welding (FSW) technique, and post-weld heat treatment (PWHT) was also performed to enhance the mechanical properties of the joints. Grain-size and maximum texture intensity obviously change in different weld zones. In the base metal (BM), the particles compose of complicated Al oxide (containing Al, O, Mg and Si) and AlFeSi intermetallics, and needle-shaped β″ precipitates were also observed. While, in the stir zone (SZ), the oxide particles mainly consist of MgAl2O4 instead of complicated Al oxide in BM, and β″ precipitates disappears. After PWHT, both MgAl2O4 and complicated Al oxide exist in SZ, and β″ were detected again. In the FSW joints, the microhardness values in SZ are far lower than those in BM. After PWHT, the microhardness values in SZ obviously increase, which was attributed to the contribution of β'' precipitates, Al oxides particles and AlFeSi intermetallics. The yield strength, ultimate tensile strength and elongation to fracture of PWHT samples are 291 MPa, 314 MPa and 5.0%, respectively, and joint efficiency for ultimate tensile strength is up to 92%, although a zigzag line was observed in SZ.

Effect of Post Weld Heat Treatment on Al 5052-SS 316 Explosive Cladding with Copper Interlayer

This study focuses on effect of post weld heat treatment (PWHT) on interfacial and mechanical properties of Al 5052-SS 316 explosive clad with copper interlayer at varied loading ratios and inclination angles. The use of interlayer is proposed for the control of additional kinetic energy dissipation and to alleviate the formation of intermetallic compounds at the interface. The Al-Steel clads are subjected to PWHT at varied temperatures (300°C-450°C) for 30 minutes and the results are presented. The microstructural characterization of as-clad and PWHT samples is observed by an optical microscope and Scanning Electron Microscope (SEM). Maximum hardness is obtained at the interface of the as-clad and PWHT samples. Increase in PWHT temperature enhances the tensile strength of the composite, whereas, the tensile strength decreases at 300°C due to the diffusion of Al and Cu elements and the formation of detrimental intermetallic compounds.

Structure–property relationships of PCGTA welds of Inconel X750 in as-welded and post-weld heat treated conditions—A comparative study

This article addresses the weldability, microstructure and mechanical properties of the multi-pass pulsed current gas tungsten arc welding (PCGTAW) of Inconel X750. PCGTA welding was accomplished using two fillers, namely ERNiCrCoMo-1 and ERNiCrMo-3. Interfacial and weld microstructures were characterized using optical and scanning electron microscopy techniques. Migrated grain boundaries (MGBs) were dominating at the fusion zone of both the weldments. Post-weld heat treatment (PWHT) was carried out on the weldments at 705°C for 22h and air cooled to assess the microstructural changes and its impact on the mechanical properties. Tensile studies corroborated that all the tensile failures occurred at the fusion zone for both the as-welded and the PWHT samples. Fascinatingly, the weldments after subjected to PWHT resulted in improved tensile strength and the joint efficiency of ERNiCrCoMo-1 and ERNiCrMo-3 weldments improved to 82.2% and 72.5%. However, ERNiCrMo-3 weldments exhibited better impact toughness than ERNiCrCoMo-1 weldments. The structure–property relationships of the weldments are also discussed in the present investigation.

The Effect of Microstructure and Mechanical Properties of Aluminium Aa6061 before and after Heat Treatment Using TIG

This work studies the effect of a post-weld heat treatment (PWHT) on the mechanical and microstructure properties of an AA6061 sample welded using Tungsten Inert Gas (TIG) method. TIG method is comparatively flexible and has good economy. The welded samples were divided into as-welded and PWHTs samples. The PWHTs samples were solution heat treatment, water quenching and artificial aging. Both welded samples were cut according to the ASTM E8M-04 standard to obtain the tensile strength and the elongation of the joints. The failure pattern of the tensile tested specimens was analysed using scanning electron microscopy (SEM). A Vickers microhardness testing machine was used to measure the hardness across the joints. From the results, the PWHTs were able to enhance the mechanical properties and microstructure characteristics of the AA6061 joints welded by the TIG method.

Effect of post-weld heat treatment and electrolytic plasma processing on tungsten inert gas welded AISI 4140 alloy steel

Post-weld heat treatment (PWHT) is commonly adopted on welded joints and structures to relieve post-weld residual stresses; and restore the mechanical properties and structural integrity. An electrolytic plasma process (EPP) has been developed to improve corrosion behavior and wear resistance of structural materials; and can be employed in other applications and surface modifications aspects. In this study the effects of PWHT and EPP on the residual stresses, micro-hardness, microstructures, and uniaxial tensile properties are explored on tungsten inert gas (TIG) welded AISI-4140 alloys steel with SAE-4130 chromium–molybdenum alloy welding filler rod. For rational comparison all of the welded samples are checked with nondestructive Phased Array Ultrasonic Testing (PAUT) and to ensure defect-free samples before testing. Residual stresses are assessed with ultrasonic testing at different distances from weld center line. PWHT resulted in relief of tensile residual stress due to grain refinement. As a consequence higher ductility but lower strength existed in PWHT samples. In comparison, EPP-treated samples revealed lower residual stresses, but no significant variation on the grain refinement. Consequently, EPP-treated specimens exhibited higher tensile strength but lower ductility and toughness for the martensitic formation due to the rapid heating and quenching effects. EPP was also applied on PWHT samples, but which did not reveal any substantial effect on the tensile properties after PWHT at 650°C. Finally the microstructures and fracture morphology are analyzed using scanning electron microscopy (SEM) and optical microscope to study the evolution of microstructures.

Effect of a post-weld heat treatment on the mechanical and microstructure properties of AA6061 joints welded by the gas metal arc welding cold metal transfer method

This work studies the effect of a post-weld heat treatment (PWHT) on the mechanical and microstructure properties of an AA6061 sample welded using the gas metal arc welding (GMAW) cold metal transfer (CMT) method. The CMT method was used because the method provides spatter-free welding, outstanding gap bridging properties, low heat input and a high degree of process flexibility. The welded samples were divided into as-welded and PWHT samples. The PWHTs used on the samples were solution heat treatment, water quenching and artificial aging. Both welded samples were cut according to the ASTM E8M-04 standard to obtain the tensile strength and the elongation of the joints. The failure pattern of the tensile tested specimens was analysed using scanning electron microscopy (SEM). A Vickers microhardness testing machine was used to measure the hardness across the joints. From the results, the PWHTs were able to enhance the mechanical properties and microstructure characteristics of the AA6061 joints welded by the GMAW CMT method.

Effect of filler alloy composition on post-weld heat treatment cracking in GTA welded cast Inconel 738LC superalloy

The effect of filler alloy composition on post-weld heat treatment (PWHT) cracking in Inconel (trade name of the Special Metals group of companies) 738LC (IN-738LC) superalloy was investigated. Five filler alloys (IN-625, IN-718, FM-92, C-263 and Rene-41), containing varying concentrations of Al and Ti, were used to gas tungsten arc (GTA) weld IN-738LC superalloy specimens which were given two different preweld heat treatments. Additionally, autogenous (without filler) welds were also made on the same two preweld heat treated materials. The preweld heat treatments consisted of the standard industrial solution heat treatment (SHT) at 1120°C for 2 h in vacuum followed by argon quenching and a new heat treatment (UMT), developed by the authors to improve the heat affected zone (HAZ) cracking resistance of IN-738LC. The latter heat treatment comprised of solution treatment at 1120°C for 2 h followed by aging at 1025°C for 16 h and then water quenching. The welded specimens were given a PWHT consisting of solution treatment at 1120°C for 2 h in vacuum followed by argon quenching and subsequent aging at 845°C for 24 h in vacuum. Intergranular cracking was observed in all the PWHT welds, regardless of the filler alloy; however, autogenous welds suffered the highest amount of cracking, and cracking susceptibility of the filler welds reduced with a decrease in concentration of the main hardening elements, Al and Ti, in the fillers. While cracks were observed only in the HAZ of the as welded samples, almost all the PWHT samples were found to have cracks in the fusion zone (FZ) and in the base metal (BM), in addition to those present in the HAZ. The severity of cracking in the SHT preweld heat treated material was, however, consistently higher than that observed in the UMT preweld treated material, in both autogenous and filler welds. The microstructure of FZ of the welds made with various filler alloys consisted of a unimodal distribution of small spheroidal γ' particles of 0˙10–0˙15 μm, while a bimodal distribution of γ' precipitates, consisting of large cuboidal particles of about 0˙5–0˙6 μm and fine spheroidal γ' particles of ∼0˙1 μm, was observed in FZ of the autogenous welds. Results of the microstructural analysis and crack measurements were correlated with the chemical composition and the precipitation kinetics of γ' in the filler alloys. It was observed that PWHT cracking in GTA welds of IN-738LC was reduced to a significant extent by using age hardenable fillers with (Al+Ti) concentration less than that in the BM. The PWHT cracking resistance of IN-738LC was further improved by the use of these fillers in conjunction with the UMT preweld heat treatment.