Post-weld Heat Treatment Temperature Research Articles

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.

Postweld Heat Treatment of 15Cr-6Ni-2Mo-1Cu Supermartensitic Stainless Steel Welds

Supermartensitic stainless steels with 15Cr- 6Ni-2Mo-1Cu with 135 ksi minimum yield strength (15Cr-135 SMSS) offer high strength and good toughness through a complex hierarchical microstructure of nanoscale precipitates, tempered martensite, and reverted austenite. Upon welding and postweld heat treatment, substantial changes to heat-affected zone microstructure and hardness may occur. Here, we reveal spatially heterogeneous microstructure and microhardness in the HAZ of 15Cr-135 SMSS; correlate these changes to measured phase transformation temperatures; and demonstrate that HAZ hardness changes depend strongly on postweld heat treatment temperatures. Furthermore, we demonstrate that PWHT may lead to undesired reductions in base metal yield strength and formulate a design guide for PWHT that quantifies the trade-offs in desired reductions of HAZ hardness with undesired changes to base metal yield strength. These findings have important practical implications for welding procedure design and qualification.

Stress relaxation cracking susceptibility evaluation in 347H stainless steel welds

AbstractStress relaxation cracking (SRC) has been reported as a dominant failure mechanism for 347H stainless steel welds at elevated service temperatures, occurring in either the heat-affected zone (HAZ) or fusion zone (FZ). In this study, SRC susceptibility of physically simulated HAZ and cross-welded E347-347H stainless steel welds was studied using a four-step accelerated SRC test with a thermomechanical physical simulator. The stress and temperature range studied represents weld-induced residual stress at 150–600 MPa and post-weld heat treatment temperatures between 800 and 1050 °C. For all temperature conditions, the cross-welded samples failed at a lower critical stress threshold than the simulated HAZ. A finite element model of a 50.8-mm-thick single-V groove weld was used to generate the residual stress maps induced by a 40-pass welding procedure, which in combination with the experimental threshold stress map predicted potential SRC failure locations. Postmortem microstructural evaluations were performed to identify contributing characteristics to SRC. It was found that HAZ samples exhibited a combination of creep void development, secondary cracks with intergranular fracture near grain boundary carbides, and eutectic phases. FZ samples showed brittle fracture with cracks propagating along straight, non-tortuous interdendritic grain boundaries.

Influence of post-weld heat treatment on welding residual stress in U-rib-to-deck joint

Welding residual stress (WRS) significantly influences the fatigue life and safety of welded steel structures. Post-weld heat treatment (PWHT) is a common method employed to mitigate WRS. In present study, the WRS evolution law and relaxation mechanism of U-rib-to-deck joints was investigated during PWHT. High-temperature heat treatment tests with varying holding times were conducted on U-rib-to-deck joints to reduce WRS. The WRS distributions were measured using the hole-drilling method before and after PWHT. ABAQUS software, incorporating the Norton-Bailey creep constitutive model, was employed to simulate the WRS evaluation during both welding and PWHT processes. The simulated values were validated against the measured data, and the effects of different holding times, holding temperatures, and heating and cooling rates during PWHT on WRS relaxation were discussed. The results demonstrate that PWHT effectively reduces WRS and leads to a more uniform distribution. Extending the PWHT holding time from 0.5 h to 1 h and 2 h results in a gradual decrease in WRS relaxation at 600 °C, primarily occurring in the high-value stress region of the weld zone with a small amplitude. Elevating the PWHT temperature from 500 °C to 550 °C and subsequently to 600 °C amplifies the significance of WRS relaxation. Variations in heating and cooling rates (200 °C/h and 80 °C/h, 100 °C/h and 40 °C/h, 50 °C/h and 20 °C/h) lead to a gradual decrease in WRS relaxation across the entire model. Furthermore, considering the creep effect, the stress relaxation rate in the weld is approximately 70 %–80 %, which found to be about 2–3 times higher than that without considering the creep effect. By understanding the evolution law and relaxation mechanism, this study provides valuable insights for designing PWHT processes and assessing their impact on structural safety and fatigue life.

Enhancing Microstructural and Mechanical Properties of Ferrous Medium-Entropy Alloy through Cu Addition and Post-Weld Heat Treatment in Gas Tungsten Arc Welding.

This study investigates the impact of a high-entropy alloy filler metal coated with copper (Cu) and post-weld heat treatment (PWHT) on the weldability of a ferrous medium-entropy alloy (MEA) in gas tungsten arc welding. The addition of 1-at% Cu had an insignificant effect on the microstructural behaviour, despite a positive mixing enthalpy with other elements. It was observed that a small amount of Cu was insufficient to induce phase separation into the Cu-rich phase and refine the microstructure of the as-welded specimen. However, with an increase in the PWHT temperature, the tensile strength remained mostly consistent, while the elongation significantly increased (elongation of as welded, PWHT700, PWHT800, and PWHT 900 were 19, 43, 55 and 68%, respectively). Notably, the PWHT temperature of 900 °C yielded the most desirable results by shifting the fracture location from the coarse-grained heat-affected zone (CGHAZ) to base metal (BM). This was due to significant recrystallisation and homogenised hardness of the cold-rolled BM during PWHT. However, the CGHAZ with coarse grains induced by the welding heat input remained invariant during the PWHT. This study proposes a viable PHWT temperature (900 °C) for enhancing the weldability of cold-rolled ferrous MEA without additional process.

Interfacial microstructure and mechanical properties of rotary inertia friction welded dissimilar 422 martensitic stainless steel to 4140 low alloy steel joints

In this work, dissimilar rotary inertia friction welds between 422 martensitic stainless steel and 4140 martensitic low-alloy steel were made to fabricate prototype heavy-duty diesel engine pistons. The influence of the inertia friction welding process and post weld heat treatment (PWHT) temperature on the interfacial microstructure evolutions and corresponding effects on mechanical properties of the 422/4140 welds were evaluated in detail. Carbon diffused from the 4140 side to the 422 side during PWHT at 650 °C for 1.5 h, causing the formation of a hard carbide-rich layer on the 422 side, and a softer but discontinuous C-depleted layer the 4140 side. PWHT at 700 °C for 1.5 h greatly accelerated C diffusion across the interface relative to 650 °C, resulting in a thicker hard carbide-rich layer and a relatively thick and continuous layer of coarse C-depleted grains (ferrite) on the 4140 side. In addition, the PWHT temperature greatly influenced the tensile properties and fracture behavior of the welds, with the 650 °C PWHT-ed samples failing predominately in a ductile manner in the 4140 heat affected zone during tensile testing. Conversely, the 700 °C PWHT specimens exhibited a strength reduction compared with the 650 °C PWHT specimens because of additional coarsening of the interfacial ferrite layer and softening of the base materials during PWHT, with brittle fracture between the hard and soft layers the predominate failure mechanism. Based on the findings, a reduced PWHT temperature and/or time, minimizing the hardness differential of the base metals, and pre-heating the 422 steel prior to welding are the potential pathways to achieve a more optimal balance between desirable tempering and stress relief of the weld microstructure and undesirable C migration across the weld interface, and to reduce the strength mismatch across the weld.

Microstructure and mechanical properties evolutions of 9Cr heat resistant steel deposited metals with different Si contents during 550 °C aging process

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.

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Weld Heat-Affected Zone of 2.25Cr-1Mo Steel

The effect of post-weld heat treatment (PWHT) temperature on the mechanical properties of the heat-affected zone (HAZ) of 2.25Cr-1Mo steels was investigated. SA-387 Gr. 22 Cl. 2 steel was employed, and the specimens taken from the steel were thermally cycled using Gleeble to simulate the coarse-grained HAZ (CGHAZ), fine-grained HAZ (FGHAZ), and intercritical HAZ (ICHAZ). Before the PWHT, the simulated HAZs exhibited poor impact toughness as compared with the base metal. The base metal and simulated HAZ specimens were heat treated in a furnace at 610, 650, 690, and 730℃ for 8 h; their impact toughness improved significantly irrespective of the PWHT temperature. The microstructural changes owing to the PWHT were observed using scanning electron microscopy and correlated with the mechanical properties.

The Effects of Post-Welding Heat Treatment on the Cryogenic Absorbed Energy of High Manganese Steel Weld Metal

In this study, a post-weld heat treatment (PWHT) was proposed at high temperatures of 600 °C, 750 °C, and 900 °C for 30 min to significantly improve the impact absorbed energy of high manganese steel weld metal. Electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) were employed to characterize the production and study the deformation mechanisms in the high manganese steel weld metal. The impact absorbed energy is divided into crack initiation energy and crack propagation energy, which are divided by the value of Pmax. The cryogenic impact absorbed energy was 81 J. After PWHT at 600 °C, 750 °C, and 900 °C, it was 75 J, 69 J, and 88 J, respectively. The impact absorbed energies did not follow a proportional relationship with the PWHT temperatures. The increase in impact absorbed energy can be attributed to the narrowing of the dendritic region, which blocks the crack propagation path and efficiently prevents crack propagation. Conversely, the decrease in impact absorbed energy can be attributed to the presence of 100-nm-sized (Cr, Mn)23C6-type carbides at the grain boundaries, which facilitate crack propagation.

Post-Weld Heat Treatment of S690QL1 Steel Welded Joints: Influence on Microstructure, Mechanical Properties and Residual Stress

During the manufacturing of welded structures, some degree of residual stresses occurs. The classic approach to residual stress reduction is Post-Weld Heat Treatment (PWHT). In the case of structural grade mild steels, the thermal process is well established. In case of S690QL1 High Strength Steel (HSS), which is manufactured using the Quenching and Tempering (QT) process considered in this paper, only limited PWHT treatment is possible without deterioration of mechanical properties. Since this steel grade is susceptible to subsequent heat input, the challenge is to establish adequate PWHT parameters, achieving residual stress reduction while retaining sufficiently high mechanical properties. The paper considers X joint welded HSS steel plates with slightly overmatching filler metal. The welded coupon is prepared and subjected to PWHT treatment. The research on the influence of heat treatment was performed using the four different PWHT cycles and initial As-Welded (AW) material condition. The authors proposed those PWHT cycles based on available resources and the literature. Process holding temperature is considered the variable parameter directly related to the behaviors of material properties. The methodology of welded joint analysis includes experimental testing of mechanical properties, metallographic examination, and residual stress quantification. Testing of mechanical properties includes tensile testing, Charpy V-notch impact testing, and hardness testing in scope of complete welded joint (BM + HAZ + WM). Metallographic examination is performed in order to characterize the welded joint material in relation to applied PWHT cycles. In order to quantify residual stresses, all heat-treated samples were examined via the X-ray diffraction method. Mechanical properties testing determined that an increase in PWHT cycle holding temperature leads to degradation of tested mechanical properties. For specific zones of the welded joint, the decreasing trend from AW condition to Cycle D (max. 600 °C) can be quantified. Based on representative specimens comparison, strength values (BM ≤ 5.7%, WM ≤ 12.1%, HAZ ≤ 20%), impact testing absorbed energy (BM = 17.1%, WM = 25.8%, FL = 12.5%, HAZ = 0.6%), and hardness values (BM = 4.1%, WM = 3.2%, CGHAZ = 16.6%, HAZ = 24.2%) are all exhibiting decrease. Metallographic examination, using the light microscopy, after the exposure to PWHT thermal cycles, did not reveal significant changes in the material throughout all specific welded joint segments. Average relative reduction in residual stress in correlation with PWHT temperature can be observed (AW = 0%, Cycle A (max. 400 °C) = 72%, Cycle B (max. 530 °C) = 81%, Cycle C (max. 550 °C) = 93% and Cycle D (max. 600 °C) = 100% stress reduction). It can be concluded that S690QL1 HSS welded joints can generally be subjected to PWHT, while adhering to the limits of the material and process. In the authors’ shared opinion, it is advisable to use the PWHT Cycle C (max. 550 °C) with 93% RS reduction, while mechanical properties retain high values.

Retaining Mechanical Properties of GMA-Welded Joints of 9%Ni Steel Using Experimentally Produced Matching Ferritic Filler Metal

Motivated by the loss of tensile strength in 9%Ni steel arc-welded joints performed using commercially available Ni-based austenitic filler metals, the viability of retaining tensile strength using an experimentally produced matching ferritic filler metal was confirmed. Compared to the austenitic Ni-based filler metal (685 MPa), higher tensile strength in gas metal arc (GMA) welded joints was achieved using a ferritic filler metal (749 MPa) due to its microstructure being similar to the base metal (645 MPa). The microstructure of hard martensite resulted in an impact energy of 71 J (-196 °C), which was two times higher than the specified minimum value of ≥34 J. The tensile and impact strength of the welded joint is affected not only by its microstructure, but also by the degree of its mechanical mismatch depending on the type of filler metal. Welds with a harder microstructure and less mechanical mismatch are important for achieving an adequate combination of tensile strength and notched impact strength. This is achievable with the cost-effective ferritic filler metal. A more desirable combination of mechanical properties is guaranteed by applying low preheating temperature (200 °C), which is a more practicable and economical solution compared to the high post-weld heat treatment (PWHT) temperature (580 °C) suggested by other research.

Enhancement of tensile properties of gas tungsten arc welds using Cu-coated CoCrFeMnNi filler and post–weld heat treatment

This study investigated the gas tungsten arc (GTA) weldability of cold-rolled CoCrFeMnNi high-entropy alloys (HEAs) using Cu-coated HEA filler, specifically through the application of various post–weld heat treatment (PWHT) temperatures. The GTA weldability of cold-rolled HEA was evaluated by applying the optimum condition of full penetration, and the effect of PWHT was investigated in the temperature range of 973–1173 K. No macro-defects were detected in the weld metal (WM) to which the Cu coated HEA filler was applied. All the PWHT-applied specimens, including the as-welded specimens, were composed of the FCC phase. The Cu component was solid-solutionized over the entire area of the WM and did not form a precipitate. The tensile properties of the as-welded specimens deteriorated in the presence of CrMn oxides. As the PWHT temperature increased, the grain size in the base metal (BM) increased and inclusions in the WM were re-dissolved. Furthermore, by increasing the PWHT temperature, the hardness of the BM decreased significantly by grain growth, and the WM softened slightly owing to the re-dissolution of inclusions. Therefore, the WMs improved the tensile strength and elongation with increasing PWHT temperature. The application of PWHT significantly improved the weldability of the Cu coated CoCrFeMnNi welds.

Influence of PWHT Parameters on the Mechanical Properties and Microstructural Behavior of Multi-Pass GTAW Joints of P92 Steel.

The 9% Cr steels were developed for ultra-supercritical (USC) power plants to meet the requirements of high operating temperature and pressure. These steels are produced to operate at high temperatures where impact toughness is not a concern; however, it becomes important for the welded joints to have good impact toughness at room temperature for manufacturing. The present work investigates the effect of the post-weld heat treatment (PWHT) parameters, i.e., temperature and time, on the impact toughness of multi-pass gas tungsten arc welded (GTAW) joints of ferritic/martensitic grade P92 steel. The microstructural evolution in welded joints given varying post-weld temperatures and times was studied. The lath martensitic structure of the weld metal for the as-welded joints resulted in high hardness and low impact toughness. The weld fusion zone toughness was 12 J, which was lower than the minimum specified values of 41 J (ASME standards) and 47 J (EN ISO 3580:2017). The PWHT temperature and time were found to have a significant effect on the impact toughness of the weld metal. A drastic increase in the impact toughness of the weld metal was noticed, which was attributed to lath break-up, reduction in dislocation density and reduction in solid solution hardening. The maximum impact toughness of 124 J was measured for PWHT temperature and time of 760 °C and 120 min, respectively. The effect of PWHT parameters on tensile strength was also investigated, and test results showed that the joint was safe for USC boiler application as it failed from the region of the P92 base metal. The variation in microstructural evolution along the weldments resulted in hardness variation. PWHT led to homogeneity in microstructure and, ultimately, reduction in hardness value. According to the study, the optimum temperature and time for PWHT of a GTAW joint of P92 steel were found to be 760 °C and 120 min, respectively.

Effect of post-weld heat treatment on a friction stir welded joint between 9Cr-ODS and CLF-1 steels

Dissimilar-metals welding is essential to construction of a fusion reactor by using advanced blanket structural materials of oxide dispersion strengthened (ODS) steels. In the present study, Dissimilar-metals bonding between 9Cr-ODS and CLF-1 steels was carried out by friction stir welding (FSW). Effect of post-weld heat treatment (PWHT) on microstructure and bonding properties of the joint was investigated. The results show that, quenched martensite was found in the weld metal (WM) after FSW. PWHT at 740-800 °C can recover the microstructure of the WM to tempered martensite. Mid-size particles and nano-particles were observed and analyzed in the WM. Besides, in the WM on the CLF-1 side, recrystallization was found after PWHT. As the PWHT temperature increased, the recrystallization width and grain size grew up. However, the recrystallization in the WM did not degrade but may be beneficial to the bonding properties of the joint due to support ductile deformation during mechanical tests. The recommend PWHT temperature is 740-760 °C for keeping the mechanical properties of the CLF-1 base metal (BM) as that before FSW.

Test for stress relief cracking susceptibility in creep resistant chromium-molybdenum steels

An externally restrained stress relief cracking test was developed and demonstrated in testing susceptible and resistant to cracking welds in Cr–Mo steels. Compared to other externally restrained tests, it simultaneously applies stress and compensates thermal expansion during heating to post-weld heat treatment temperature and utilises digital image correlation for quantification of key characteristics of the stress relaxation and stress relief cracking phenomena. In contrast with resistant to stress relief cracking materials, susceptible materials experienced lower levels of stress relaxation, strain absorption, and sustained mechanical energy, with accelerated kinetics of strain accumulation and strain localisation leading to failure. The processes of stress relief cracking and stress relaxation were quantified as low strain – slow strain rate – low energy phenomena.

Analyzing the Effects of Heat Treatment on SMAW Duplex Stainless Steel Weld Overlays

Duplex stainless steel (DSS) has a reasonably high resistance to chloride stress corrosion cracking for offshore and marine applications. However, DSS weld overlay has not been successfully demonstrated due to some inherent problems in achieving pitting and crevice corrosion resistance. In this research work, isothermal heat treatments (350, 650 and 1050 °C) with and different cooling rates have been performed DMR249 Grade A by using shield metal arc welding (SMAW) with an E2209 electrode. Micrographs have shown two phase microstructures of the DSS weld metal, the amounts of austenite phase increased with increment of post-weld heat treatment (PWHT) temperatures. The dilution has maintained consistent values except solution annealing that has shown the disappearance of the heat affected zone in micrographs. The weld metal hardness values increased with PWHT temperatures and remained low at solid solution annealing temperatures. The major alloying elements (C, Mo, Cr, Ni, N, and Fe) were analyzed, as these elements can contribute to intermetallic phases. The results showed that C and Cr content slightly increased with PWHT except for solid solution annealing, Mo showed consistently low content due to dilution effects. Ni maintained higher content, although the heat-treated samples showed slight fluctuations. Nitrogen produced consistent values, as recommended to prevent critical involvement in nitride precipitation.

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Carbon Steel Base Metal

The effect of post-weld heat treatment (PWHT) on the mechanical properties and microstructure of carbon steel base metal was investigated. MDF A 105, 106-B, 216-WCB, 516-415, and 516-485 carbon steels were employed, and the steels were each subjected to heat treatment with holding temperatures of 610, 650, 690, and 730 ℃ for 8 hours for the simulation of PWHT. The tensile strength and impact toughness of the steels showed a tendency to decrease with increasing holding temperature; this behavior was mainly attributed to the spheroidization of cementite in pearlite and the precipitation of cementite at grain boundaries.

Precipitation behaviour of 20MnMoNi55 RPV steel in the temperature range of 630–670 °C

The precipitation behaviour of 20MnMoNi55 grade RPV steel while tempering and PWHT in the temperature range of 630–670 °C was characterised through microstructural observation and CALPHAD based thermodynamic calculations. Steel samples were tempered at 630 °C from 1 to 6 h and further subjected to simulated post weld heat treatment (PWHT) between 650 °C and 670 °C temperatures, which is relatively higher than the conventionally employed PWHT temperature range. Microstructural observations revealed that tempering and subsequent simulated PWHT of 20MnMoNi55 grade RPV steel resulted in precipitation of Fe3C and Ksi carbides as Mo lean and Mo rich precipitates, respectively. CALPHAD based computations also suggested that Ksi carbide and Mo2C could form as metastable carbides, whereas Fe3C and M7C3 as thermodynamically stable carbides while heat treatment in the temperature range of 630–670 °C.

Effect of the post-weld heat treatment temperature on the mechanical properties and microstructure of magnetic pulse welded Al/Fe tubes

Post-weld heat treatment (PWHT) can improve the microstructure and properties of welded joints. Here, the effect of the PWHT temperature on the microstructure and mechanical properties of Al/Fe tube joints manufactured by magnetic pulse welding (MPW) was investigated systematically. The results indicated that PWHT improved the distribution of the chemical composition in the thick transition layer (thickness >10 μm), with only a slight change in thickness. In contrast, the thickness of the thin transition layer (thickness ≤10 μm) increased significantly upon increasing the temperature. Micropores, radial cracks, and axial cracks were repaired to different degrees below 250 °C, but axial cracks propagated in the axial direction when the temperature exceeded 250 °C. The local shear strength 3 mm from the free end reached about 58 MPa, which was almost two times greater than that without PWHT at 250 °C. Once this temperature was exceeded, the shear strength decreased; thus, the optimal PWHT temperature was 250 °C, at which the microstructure and mechanical properties were improved better.

Effect of Post-Weld Heat Treatment Temperatures on Microstructure, Intergranular Corrosion Resistance, and Mechanical Properties of 4130 Steel with Inconel 625 Weld Overlay

Effect of Post-Weld Heat Treatment Temperatures on Microstructure, Intergranular Corrosion Resistance, and Mechanical Properties of 4130 Steel with Inconel 625 Weld Overlay