Post Weld Heat Treatment Time Research Articles

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.

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 (PWHT) on the intergranular corrosion of ENiCrFe-7 weld overlay cladding materials

Effect of post-weld heat treatment on the intergranular corrosion of ENiCrFe-7 weld overlay cladding materials was investigated. The results showed that Cr-rich precipitates occured in the dendrites and grain boundaries, and Cr-depletion areas appeared around Cr-rich precipitates. The degree of Cr-depletion in the dendrite was aggravated with the increase of PWHT time to 16 h, then it was gradually recovered with increasing PWHT time to 48 h. The results showed that as-weld Alloy ENiCrFe-7 was only susceptible to dendritic corrosion after EPR, the one heat treated after 615 ℃/16 h has more serious dendritic corrosion than that of as-weld Alloy, moreover, the less intergranular corrosion was also observed when the weld was heat treated at 615 ℃/16 h. Only the intergranular corrosion was exhibited in the one heat treated after 615 ℃/48 h. Howerver, Alloy ENiCrFe-7 has better corrosion resistant properties.

Effect of PWHT Larson–Miller Parameter on Mechanical Properties and Microstructure of Line Pipe Microalloyed Steel Joints

In this article, the effects of the postweld heat treatment (PWHT) on grain size and mechanical properties of X52 microalloyed steel joints have been investigated. The joints were welded by high-frequency induction welding (HFIW), and heat-treated at various temperatures and times. Then, the mechanical and microstructural evaluations were done on the heat-treated samples. To study the cumulative effects of PWHT time and temperature, the Larson–Miller parameter (LMP) of all the heat treatment cycles was calculated. Finally, the effects of LMP on the grain size and mechanical properties of the samples were studied. According to the findings, the grain size, toughness, strength and hardness show completely meaningful relationships with the LMP of PWHT for the HFIW welded joints. To achieve high impact energies and ductile fracturing, there was an optimum time and temperature condition for the PWHT, and it was obtained for the LMP range of 23,300 to 25,300.

Study on the Effect of Post Weld Heat Treatment (PWHT) Time on the Tensile Strength and Hardness of TIG Weld Joint of Motorcycle Crankcase

Postweld heat treatment (PWHT) is a common practice among building codes to reduce the residual stress, improve the ductility, and decrease the defects. This article describes the welding joint property of motorcycle crankcase material by taking tungsten inert gas (TIG) welding measures before PWHT on 200°C with holding time of 0,4,6, 8 hours. Test data were analyzed in relation to tensile strength, hardness and microstructure on the welding joint. The regions corresponding to the base metal (BM) and heat-affected zone (HAZ) were studied. The effect of holding time under PWHT on properties of joints can be investigated. The results demonstrated that micro-hardness in the weld and tensile strength decreased with PWHT time prolonging, while tensile strength increased with the extension of PWHT time. The microstructure before PWHT was coarse in the joint. With the extension of holding time under PWHT, the structure obtains fine grain and the characteristic becomes obvious.

Influence of Temperature and Time of Post-weld Heat Treatment on Stress Relief in an 800-mm-Thick Steel Weldment

Ferritic steel weldments are invariably post-weld heat treated for relieving the residual stresses. However, the long duration of post-weld heat treatment (PWHT) required for very thick weldments can adversely affect the mechanical properties and fracture toughness. Thus, there is a need to establish the relative importance of temperature and time of PWHT with respect to stress relief. Accordingly, in the present work, the phenomenon of stress relief (due to PWHT) in an 800-mm-thick steel weldment was investigated using finite element analysis and the results were validated against experimental measurements. An analytical study was also carried out to determine the relative influence of temperature and time of PWHT on stress relief. It was found that time of PWHT plays a more significant role in case of relatively lower PWHT temperatures. It was also found that, for a given value of Hollomon parameter, different combinations of PWHT temperature and time can be employed to achieve the same level of stress relief. A mathematical relationship has been established between Hollomon parameter and magnitude of residual stress after PWHT. It has been shown that residual stress is a monotonically decreasing function of the Hollomon parameter.

Modelling and optimisation of the post-weld heat treatment of γ′ precipitation and hardness on Inconel X-750 using the response surface methodology

This work describes a post-weld heat treatment (PWHT) for Inconel X-750. The following PWHT variables were examined: the solution temperature, PWHT temperature, and PWHT time. In this research, the application of the response surface methodology and Box-Behnken design in a mathematical model was investigated and optimised. The resulting materials were examined using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) in the fusion zone (FZ). The experimental results reveal that using a full quadratic model with the proposed mathematical model of the γ′ precipitation size and γ′ hardness in the FZ, the obtained correlation of the hardness and γ′ precipitate size showed a reasonable linear relationship.

Comparison Between Using Longitudinal and Shear Waves in Ultrasonic Stress Measurement to Investigate the Effect of Post-Weld Heat-Treatment on Welding Residual Stresses

ABSTARCTFusion welding is a joining process widely used in the industry. However, undesired residual stresses are produced once the welding process is completed. Post-weld heat-treatment (PWHT) is extensively employed in order to relieve the welding residual stresses. In this study, effect of PWHT time and temperature on the residual stresses of a ferritic stainless steel is investigated. Residual stress distributions in eight welded specimens were measured by using an ultrasonic method. Ultrasonic stress measurement is a nondestructive method based on acoustoelasticity law, which correlates mechanical stresses with velocity of an ultrasonic wave propagating within the subject material. The ultrasonic wave employed could be longitudinal or shear wave produced by the longitudinal (normal) or transverse (shear) transducers, respectively. Ultrasonic stress measurements based on longitudinal waves use longitudinal critically refracted (LCR) waves in this direction, while shear wave methods use an ultrasonic birefringence phenomenon. The results show that the effect of PWHT can be successfully inferred by both longitudinal and shear wave methods, but the former is found to be more sensitive to stress variation. Furthermore, the distribution of subsurface residual stresses is found to be more distinguishable when the LCR method is employed.

Investigation of non-equilibrium grain boundary segregation on CGHAZ in reactor pressure vessel steel

In order to explore the reasons for coarse grained embrittlement, post-weld heat treatment (PWHT) with different times was conducted on the coarse grained heat affected zone (CGHAZ) of A533B steel. The results reveal that the impact toughness of the CGHAZ at room temperature decreases with the prolongation of PWHT time from 0.5 to 4 h. As the PWHT time increases to 4 h, the fracture feature of the CGHAZ presents intergranular cleavage ruptures, and the impact toughness exhibits the minimum value. After PWHT for 4 h, the area of the intergranular cleavage fractures decreases, and the impact toughness gradually increases. Further research reveals that there is phosphorus grain boundary segregation in the CGHAZ. The theory of non-equilibrium grain boundary segregation (NGS) is proposed to explain the phenomenon. It is found that the PWHT time with minimum impact toughness is consistent with critical time of phosphorus NGS.

Investigation into the influence of post-weld heat treatment on the microstructure and hardness of Inconel X-750

This work describes a post-weld heat treatment for a precipitation-hardened nickel alloy. Inconel X-750 is a nickel-based superalloy for gas tungsten arc welding processes. The materials were heat-treated in two steps: solution and aging. The post-weld heat treatment variables examined in this study included post-weld heat treatment temperatures of 705°C, 775°C, and 845°C and post-weld heat treatment time of 2–24 h in 2-h increments. The resulting materials were examined using the full factorial design of experiments to determine the resulting material hardness and observed with optical microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy in the fusion zone and heat-affected zone. The results show that a longer post-weld heat treatment time corresponds to larger γ′ precipitates and a smaller amount of Cr23C6 at the grain boundaries, which can decrease the overall hardness. The post-weld heat treatment analysis indicates that an increase in the amount of γ′ results in better mechanical properties for particles with octagonal shapes and a small size. A factorial analysis, which was conducted on the relationship between the post-weld heat treatment temperature and time to the hardness of the fusion zone, had a 95% confidence level.

Application of Response Surface Methodology for Modeling of Postweld Heat Treatment Process in a Pressure Vessel Steel ASTM A516 Grade 70.

This research studied the application of the response surface methodology (RSM) and central composite design (CCD) experiment in mathematical model and optimizes postweld heat treatment (PWHT). The material of study is a pressure vessel steel ASTM A516 grade 70 that is used for gas metal arc welding. PWHT parameters examined in this study included PWHT temperatures and time. The resulting materials were examined using CCD experiment and the RSM to determine the resulting material tensile strength test, observed with optical microscopy and scanning electron microscopy. The experimental results show that using a full quadratic model with the proposed mathematical model is Y TS = −285.521 + 15.706X 1 + 2.514X 2 − 0.004X 1 2 − 0.001X 2 2 − 0.029X 1 X 2. Tensile strength parameters of PWHT were optimized PWHT time of 5.00 hr and PWHT temperature of 645.75°C. The results show that the PWHT time is the dominant mechanism used to modify the tensile strength compared to the PWHT temperatures. This phenomenon could be explained by the fact that pearlite can contribute to higher tensile strength. Pearlite has an intensity, which results in increased material tensile strength. The research described here can be used as material data on PWHT parameters for an ASTM A516 grade 70 weld.

Designing Experiments to Affect Post Weld Heat Treatment Parameters: Using the Full Factorial Design in Inconel X-750 Welds

Alloy X-750 also has excellent properties down to cryogenic temperatures high stability and strength at high temperatures. This reason the alloy is used in manufacturing of gas turbine hot components. The research was study the effect of post weld heat treatment (PWHT) parameter on hardness and microstructure. The specimen was Inconel X-750 grade sheet of 2.8 mm thickness. This 23factorial design was used in experimental various post weld heat treatment at 705 and 845°C for 20 and 24 hour including solution temperature at 1,000 and 1,150°C. The welded specimens were tested by hardness testing in fusion zone (FZ) and heat affected zone (HAZ). The result showed that both of solution temperature, PWHT temperature and PWHT time interaction on hardness of FZ and HAZ at 95% confidential (P value < 0.05). The PWHT temperature and PWHT time interaction effect was the largest. The factor showed in the hardness increase with the low level (-1) of PWHT temperature and PWHT time for the hardness while it trended decrease for the solution temperature. The microstructure was the γ amount and small size would result in high hardness. Experimental results showed that the solution temperature at 1,150°C, PWHT temperature 705°C PWHT time of 20 hours provided intensity of gamma prime (γ) and MC carbide resulting in higher hardness both in FZ and HAZ.

Application of Full Factorial Design for Post Weld Heat Treatment Parameters on Duplex Stainless Steel UNS31803

In this research, the post weld heat treatment (PWHT) of duplex stainless steel (DSS) was study. The PWHT process can be affected by differing parameters. The specimen was duplex stainless steel UNS31803 grade sheet of 10 mm thickness. The PWHT parameters were analyzed by application of full factorial design. The factors used in this study were PWHT temperature of 650, 750, and 850๐C with PWA time of 1, 2, 4 and 8 hours. The welded specimens were tested with micro vickers hardness and ferrite content testing according to ASTM E3-11 code. The result showed that both of PWHT temperature and PWHT time interaction on hardness and ferrite content for 95% confidential (P value < 0.05). The factor in most effect of hardness was the PWHT temperature of 850๐C and PWHT time for 4 hour at the hardness of 277.73 HV. The ferrite was the most ferrite content for 77.39% resulted in corrosion resistance due to suitable of PWHT temperature 750๐C and PWHT time for 8 hour. Finally, form PWHT process with the information was used choosing the appropriate for PWHT parameters to duplex stainless steel welds.

Effect of Post Weld Heat Treatment on Carbon Steel AISI 1050 in Heat Effected Zone

The research was study the effect of post weld heat treatment parameters on microstructure and hardness in heat affected zone. The specimen was carbon steel AISI 1050 which thickness of 6 mm. The experiments with full factorial design. The factors used in this study were post weld heat treatment(PWHT) temperature of 500, 550, 600, 650 and post weld heat treatment time of 10 and 15 hour. The welded specimens were tested by tensile strength testing and hardness testing according to ASTM code. The result showed that both of post welds heat treatment temperature and post weld heat treatment time had interaction on hardness at 95% confidential (P value < 0.05). A factor affecting the hardness was the most PWHT temperature 550 ๐C and PWHT time 10 hr. of 279 HV. Microstructure can be concluded that low PWHT temperature and time effect on temper martensite with a coarse grain and martensite scattered throughout. Martensite was a smaller and greater fine grain, the ferrite and the volume decrease due to a higher temperature.This research can be used as data in the following appropriate PWHT parameters to carbon steel weld.

Behavior of Cu precipitates during thermo-mechanical cycling in the weld CGHAZ of Cu-containing HSLA steel

The behavior of Cu precipitates in the weld coarse-grained heat-affected zone (CGHAZ) of 1.5 wt% Cucontaining high strength low-alloy (HSLA) steel subjected to a thermal/thermo-mechanical welding cycle and post-weld heat-treatment (PWHT) was evaluated. The welding cycles of CGHAZ and PWHT were simulated by the Gleeble system. The hardness was measured at each PWHT condition, and observation and analysis of the Cu particles were performed using HRTEM. The hardness decreased initially with an increasing PWHT time at 550 °C. However, the peak hardness resulting from precipitation of Cu particles occurred after about 60 min at 550 °C. In the thermo-mechanical cycle, the peak hardness appeared at an earlier PWHT time. These results correspond with the HRTEM observations in which Cu particles were observed at an earlier PWHT time and larger Cu particles were observed at the same given PWHT time after the thermo-mechanical cycle. Thus, this paper confirms that the kinetics of Cu precipitation can be accelerated by an intrinsic mechanical cycle during the welding cycle.

Variation of microstructures and mechanical properties in the post-weld heat-treated HAZ of Cu containing HSLA steel welds

The present study focuses on the effect of Cu and post-weld heat treatment (PWHT) on the microstructure and mechanical properties in the coarse grained heat affected zone (CGHAZ) of Cu containing high strength low alloy (HSLA) steel welds. For this study, HSLA steels with and without Cu were prepared in laboratory. Mechanical properties were estimated by Vickers hardness and Charpy impact tests. As a result, despite PWHT, the Vickers hardness did not change noticeably; however, the impact toughness deteriorated significantly with increasing PWHT time. In case of Cu added steel, intergranular brittle fractures occurred after PWHT, due to the strengthening of the grain interior by precipitation of Cu particles. Additionally, the formation of a soft denuded grain boundary zone also played a significant role in lowering the fracture toughness during PWHT.

Fatigue of Laserbeam Welded Joints of High-Carbon Steel Strips

The high-carbon steel strips are one of the most widely used base materials of bandsaw blade manufacturing. These materials have sufficient strength and ductility to cope with the high fatigue load of the bandsaw blades. These endless strips are produced by welding, and therefore the weld and the heat affected zone have different mechanical properties, like tensile strength and fatigue resistance, than the base material. These properties of the weld can be influenced by preheat and post weld heat treatment. Regarding to the latest industrial requirements, the application of laserbeam welding was examined to produce higher standard bandsaw blade. The laserbeam welded joints has lower heat input and narrower heat affected zone compared to metal inert gas (MIG) welding, which is currently used in bandsaw blade manufacturing. To assure the proper mechanical properties and sufficient resistance to fatigue, an examination was carried out to determine the effect of preheat temperature and post weld heat treatment time on the mechanical properties and fatigue behaviour of the laserbeam welded joint.

Use of the Master Curve to Investigate the Effect of Post-Weld Heat Treatment on ASTM A106B

ASTM A106/B is commonly used for pressure piping in alumina refineries. Due to the problem of caustic cracking in alumina refineries, piping must be stress relieved after welding, usually through a post-weld heat treatment (PWHT) process at a temperature of 635°C. However, multiple PWHT procedures tend to degrade the mechanical properties of steel and design standards have set limits on the length of time PWHT can be carried out before steel should be replaced. In this study, the effect of PWHT time on the properties of A106/B parent metal was examined, with particular emphasis on the effect on toughness. PWHT was carried out for 1, 8 and 40 hours and the results were compared with those for as-received material. Impact transition temperature and room-temperature tensile results were determined using standard tests. The reference temperature, To, was determined using ASTM E1921 with arc-shaped tension specimens. The results showed that the ductile-to-brittle transition temperature increased significantly as PWHT time increased and the implications of this to a fracture mechanics analysis of plant operations are discussed.

Disbonding of Austenitic Stainless Steel Cladding Following High Temperature Hydrogen Service

The influence of welding process, consumable type and postweld heat treatment (PWHT) on the phenomenon of disbonding was investigated. Small weld clad test blocks were thermally charged with hydrogen in an autoclave. A range of austenitic stainless steel consumables and an ERNiCr-3 alloy were used to make the claddings on 2.25Cr-1 Mo parent metal by submerged-arc strip and wire, electroslag, plasma hot wire, and manual metal arc processes. The effects of simple and multiple postweld heat treatments at 565–690 °C were determined and local hydrogen contents in clad materials were determined both by measurement and also finite element modelling. Examination of the interface microstructures and disbonding cracks showed that the cracks were located in the compositional/microstructural transition zone within about 100 μm of the fusion boundary. In this region, martensite was present after PWHT, giving rise to high hardness and susceptibility to hydrogen embrittlement. Some disbonding sensitivity was found with all consumable types, but the stainless steel overlays showed appreciably higher susceptibility than the ERNiCr-3 cladding. Disbonding resistance was higher with manual metal arc (MMA) welding than with the various high deposition rate methods. The microstructure of the bulk first-layer cladding exerted an influence on susceptibility with both high ferrite and high martensite being beneficial. Minimising postweld heat treatment time and temperature reduced disbonding, as did duplex postweld heat treatments with the second stage temperature at or below 650 °C. Computed and measured hydrogen levels indicated that a peak in hydrogen concentration formed near the interface on cooling.

Ｎｉ基ＯＤＳ合金とＮｉ基超合金の拡散接合と接合体の高温疲労強度

Dissimilar diffusion boning between an oxide dispersion strengthened (ODS) Ni-base alloy, MA758, and conventional casting Ni-base superalloy, CM-247LC, was studied by combining and controlling some bonding parameters: bonding temperature, bonding pressure, and the post weld heat treatment. The optimum bonding condition was filtered and refined on the basis of the microstructure and thickness of the diffusion layer, the hardness distribution across the welded interface, and the high temperature tensile properties of the joints. The experimental evidences indicated, the bonding temperature and the post weld heat treatment played an essential role. For example, the longer the post weld heat treatment time, the better the high temperature tensile properties were. The fatigue strength of the joints thus optimized was also evaluated at high temperature in air, and was compared with that of the base material, MA758. The fatigue strength of the joints optimized was slightly lower compared with that of the base material, MA758, however, it was high enough for engineering applications.