Post-weld Heat Treatment Temperature Research Articles

Effect of post-weld heat treatment on microstructure and mechanical properties of welded joints of 6061-T6 aluminum alloy

Abstract 6061 aluminum alloy T-joints were welded by double-pulsed MIG welding process. Then, the post-weld heat treatment was performed on the welded T-joints. The weld microstructure under different aging temperature and time was investigated by transmission electron microscopy and scanning electron microscopy. The mechanical properties were examined by hardness test and tensile test. The results showed that the micro-hardness was sensitive to heat treatment temperature and time. Increasing temperature was beneficial to the shortening of peak aging time. There were a large number of dislocations and few precipitates in the welded joints. With the increase of post-weld heat treatment temperature and time, the density of dislocation decreased. Meanwhile, the strengthening phase precipitated and grew up gradually. When the post-weld heat treatment temperature increased up to 200 °C, large Q' phases were observed. And they were responsible for the peak value of the micro-hardness in the welded joints.

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.

Effect of PWHT Conditions on Toughness and Creep Rupture Strength in Modified 9Cr-1Mo Steel Welds

Abstract We clarified the effect of post weld heat treatment (PWHT) conditions on the toughness and creep rupture strength of modified 9Cr–1Mo steel weldments used for high temperature components of ultra-supercritical power plants. Fracture appearance transition temperature (FATT) decreased as PWHT temperature increased, and for all of the weld metals of tungsten inert gas welding, submerged arc welding and shielded metal arc welding, FATTs were lower than 293 K when the PWHT temperature was higher than 1,008 K. In contrast, in the uniaxial creep test with a loaded stress of 108 MPa, the creep rupture strength of the specimen on which PWHT was carried out for a holding time of 7.2 ks was significantly decreased when the PWHT temperature was more than 1,033 K. Therefore, the appropriate PWHT temperature range to maintain the toughness and creep fracture strength was 1,008 K ≤ T ≤ 1,033 K.

Effects of post-weld heat treatment on microstructure and mechanical properties of Hastelloy N superalloy welds

The effects of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of Hastelloy N superalloy welds were systematically investigated. Eutectic-like M6C carbides and nano-sized M2C carbides were observed in the interdendritic region of the as-welded specimens, with finer granular M6C carbides precipitating at the dendrite boundaries. With the increase in the PWHT temperature, the nano-sized M2C carbides dissolved, while the M6C carbides at the dendrite boundaries coarsened. When the PWHT temperature increased to 950 °C, the nano-sized M2C carbides completely disappeared. Consequently, the weld with the PWHT at higher temperatures exhibited lower micro-hardness, lower yield strength, and higher elongation. In particular, the elongation increased by 63% after applying the PWHT at 950 °C for 6 h.

Effect of post-weld heat treatment on the microstructure and mechanical properties of the 2205DSS/Q235 laser beam welding joint

Embrittlement of the 2205DSS base metal occurred at 500 °C, 700 °C, and 800 °C as the “475 °C embrittlement” and precipitation of the σ phase. The high-hardness quenched martensite in the as-welded welding seam became low-hardness tempered martensite at 500 °C and 600 °C. It contributed to the improved toughness of the welded specimen at 500 °C and 600 °C. The toughness of the welded specimen decreased at 700 °C and 800 °C because of the generation of high-hardness normalized martensite. A carbon-depleted layer and carbon-rich layer formed on the welding seam-Q235 interface following post-weld heat treatment because of the diffusion of carbon atoms. A carbon-depleted layer and carbon-rich layer formed at 600 °C, 700 °C, and 800 °C. The thickest carbon-depleted layer was obtained at 700 °C, as the fastest diffusion of carbon atoms occurred in the Q235 BM. The ferrite grain of the carbon-depleted layer also rapidly coarsened owing to the lack of a hindering effect from Fe3C on the grain boundary migration. The optimal post-weld heat treatment temperature was determined to be 600 °C.

Effect of post weld heat treatment on weldability of high entropy alloy welds

ABSTRACTThe effect of post weld heat treatment (PWHT) temperature on laser beam welds in high-entropy alloys (HEAs) using a cold-rolled cantor system (CoCrFeMnNi) was investigated. Laser welding of low heat input was applied to reduce thermal distortion. The cold-rolled HEA welds indicated larger grain size and inferior tensile/hardness properties as compared to the base metal (BM). By applying PWHT, the welds showed superior hardness to the BM with no variation in the face-centred cubic phase and a decrease in the size and fraction of CrMn oxide inclusions. As the PWHT temperature increased (800–1000°C), the variation in the grain size decreased between the weld metal and heat-affected zone, thus resulting in approximately the same tensile strength and elongation of the transverse welds as compared to the BM.

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Simulated Weld Heat-Affected Zone of SA-516 Grade 70 Carbon Steel

Effect of Post-Weld Heat Treatment Temperature on the Mechanical Properties and Microstructure of Simulated Weld Heat-Affected Zone of SA-516 Grade 70 Carbon Steel

Microstructural evolution of dissimilar welded joints between reduced-activation ferritic-martensitic steel and 316L stainless steel during the post weld heat treatment

In the present study, electron beam welding (EBW) was used to join reduced-activation ferritic-martensitic (RAFM) steel to 316L stainless steel. Microstructural evolution and mechanical property variation in the heat-affected zone (HAZ) and weld metal (WM) during the post weld heat treatment (PWHT) was investigated. The results suggested that the hardness of RAFM-HAZ decreased with increased PWHT temperature, while the hardness of WM decreased to minimum at 620 ℃ and then increased at higher PWHT temperatures. This was consistent with strength variation in the WM during PWHTs. Microstructural observations and corresponding phase diagram calculation indicated that blending of two types of base metals increased nickel content of WM, enlarged the two phase-region and lowered A1 (start of transformation of ferrite to austenite) point of WM, as compared with similar ferritic-martensitic steel weld joint. Thus, reversed austenite transformation and subsequent martensite transformation occurred in WM of sample subjected to higher temperature heat treatment, while there was no transformation in the HAZ. This effect explained the changes in hardness and strength of WM corresponding to PWHT. The optimized properties of both HAZ and WM in the dissimilar weld joint were obtained by a two-step post weld heat treatment.

Tempering effect on the fusion boundary region of alloy 625 weld overlay on 8630 steel

The NACE standard MR0175 requires that the HAZ hardness of AISI 8630 steel overlaid with Ni-base Alloy 625 cannot exceed 250 VHN, requiring a postweld heat treatment (PWHT) to decrease the as-welded HAZ hardness. However, PWHT results in the diffusion of carbon from the steel into the overlay and may lead to interface embrittlement. To understand the effect of PWHT on the microstructure and hardness of the regions near fusion boundary, a wide range of PWHT conditions were investigated. The regions of interest include the coarse-grain HAZ (CGHAZ), the partially-mixed zone, the “swirl” structure, the planar growth zone (PGZ), and the Alloy 625 weld metal. The microstructure and hardness were evaluated using optical metallography, SEM, Vickers hardness testing, and nanoindentation. With an increase of the Hollomon-Jaffe parameter (HJP), the CGHAZ hardness decreases, the PGZ hardness increases, and the weld metal hardness also increases but at a much lower rate. At HJP > 19,300, carbide precipitation was observed in the PGZ. Following PWHT, the partially-mixed zone was found to contain fresh martensite since the PWHT temperature was above the A3 temperature of this region. Reducing the cooling rate from the PWHT temperature did not eliminate the untempered martensite in this region. Finally, the behavior of the 8630/625 overlay is compared and contrasted to the F22/625 overlay behavior which was reported previously. This work builds a foundation for future studies on hydrogen-assisted cracking and sulfide stress cracking in Alloy 625 overlay on steels used in the oil and gas industry.

Effect of post weld heat treatment on microstructure and mechanical properties of Hot Wire GTA welded joints of SA213 T91 steel

There is an increasing interest in understanding the processing and properties of alloys such as 90Cr-1No-V steels. Of these steels, the modified 9Cr-1Mo steel known as T91/P91 has a wide range of industrial application. During welding this grade undergoes change in microstructure, increase in hardness and decrease in impact toughness. The present study is concerned with the comparative study of the effect of post weld heat treatment (temperature and soaking time) on the metallurgical and mechanical property of hot wire GTA welded SA213 T91 alloy steel tubes. The results of hardness and impact strength measurements suggest that post weld heat treatment of 2h at 760°C is optimum to re-establish the strength of T91 steel after welding.

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.

Effect of post-weld heat treatment on fusion boundary microstructure in dissimilar metal welds for subsea service

Abstract Microstructural features at the fusion boundary in dissimilar metal welds significantly influence the susceptibility to local hydrogen embrittlement under subsea service conditions. Two subsea dissimilar metal welds using nickel-based filler metal on low alloy steel substrate were studied in this work in order to investigate the nature and microstructural evolution of the dissimilar interface during post-weld heat treatment (PWHT), and to determine resistance to hydrogen embrittlement. The delayed hydrogen cracking test (DHCT) was utilized to determine hydrogen-assisted cracking (HAC) susceptibility. Thermokinetic modeling was conducted to study phase formation and carbon diffusion across the dissimilar interface. Diffusion calculations incorporated initial compositional gradients after welding and the nonmoving phase boundary during PWHT. Resistance to HAC was in good agreement with previously obtained DHCT results for the tested dissimilar metal welds. Tempered martensite in the heat-affected zone of the steel substrate was observed as a function of PWHT temperature. Fresh martensite with high local hardness formed during cooling in highly diluted weld metal regions. The cell model incorporated in DICTRA effectively predicted differences in carbon concentration profiles across the dissimilar interface and type of carbide precipitation as a function of PWHT procedure and steel substrate.

Numerical studies of post weld heat treatment on residual stresses in welded impeller

The temperature filed was simulated by use of the established moving heat source model of TIG welded impeller. The obtained computational temperature can be treated as thermal load for the computation of the residual stress near weld. The comparison with experimental data in published literature can validate the proposed models. The effect of the post weld heat treatment (PWHT) was studied by the Norton creep law model. Results indicate that the circumferential residual stress in blade is obviously higher than the vertical residual stress. The final residual stress in the impeller can be greatly decreased by the PWHT. The PWHT temperature is the most important factor in the PWHT process. Higher PWHT temperature can be beneficial to the decrease of the residual stress. But when the PWHT temperature is higher enough, stress concentration occurs at the corner of blade. PWHT process can obviously decrease the residual stress intensity factor.

Improved properties of friction stir-welded AZ31 magnesium alloy by post-weld heat treatment

Mechanical properties and microstructure of friction stir-welded AZ31 based on variety post-weld heat treatment (PWHT) temperatures were evaluated, and an optimal PWHT condition was identified. At rotational speed of 1200 rev min−1 and welding speed of 300 mm min−1, the average yield tensile, tensile strength and elongation of friction stir-welded joints was 92.5 MPa, 199.1 MPa and 7.3%, respectively. It was found that (300°C – 1 h) heat treatment after welding was more beneficial than other heat treatments in enhancing the mechanical properties and homogenising grain size. The maximum yield and tensile strength was 139.9 and 238.4 MPa, respectively, tensile longitudinal and compressive transverse residual stress could be effectively eliminated, and the fatigue strength increased 34.2% comparing with as-welded joints.

Reheating cracking susceptibility in the weld heat-affected zone of a reduced activation ferritic-martensitic steel for fusion reactors

Reheating cracking susceptibility in the weld heat-affected zone of reduced activation ferritic-martensitic steel was explored by stress-rupture tests. The HAZ samples were experimentally simulated using Gleeble simulator with heat input of 30kJ/cm. After HAZ simulation, the samples were reheated to three different temperatures which correspond to post-weld heat treatment temperature, and stress-rupture tests were carried out. After the samples ruptured, fracture morphologies and cross-sectional microstructures were carefully observed by scanning electron microscopy and transmission electron microscopy. The results revealed that reheating cracking occurred in the vicinity of intergranular Cr23C6 carbides, due to the formation of soft denuded zone along the grain boundary. In addition, the reheating cracking susceptibility increased with increase in PWHT temperature.

Effect of Post-Weld Heat Treatment on the Mechanical Properties and Microstructure of P-No. 1 Carbon Steels

This study aims to investigate the suitability of requirement for post-weld heat treatment(PWHT) temperature when different P-No. materials are welded, which is defined by ASME Sec. III Code. For SA-516 Gr. 60 and SA-106 Gr. B carbon steels that are typical P-No. 1 material, simulated heat treatment were conducted for 8 h at 610°C, 650°C, 690°C, and 730°C, last two temperature falls in the temperature of PWHT for P-No. 5A low-alloy steels. Tensile and Charpy impact tests were performed for the heat-treated specimens, and then microstructure was analyzed by optical microscopy and scanning electron microscopy with energy-dispersive spectrometry. The Charpy impact properties deteriorated significantly mainly due to a large amount of cementite precipitation when the temperature of simulated heat treatment was 730°C. Therefore, when dissimilar metal welding is carried out for P-No. 1 carbon steel and different P-No. low alloy steel, the PWHT temperature should be carefully selected to avoid significant deterioration of impact properties for P-No. 1 carbon steel. Key words: P-No. 1 carbon steel, Post-weld heat treatment, Impact toughness

Local Postweld Heat Treatment of Heterogeneous Welded Joint

A concept of heterogeneous welded joint is proposed for researching and describing the characteristics of local postweld heat treatment (PWHT) temperature field for asymmetric thermal conductivity welded joint. Its three types have been classified according to thermal conductivity direction around the weld, separately, welded joint with transverse unidirectional thermal conductivity, transverse bidirectional thermal conductivity, transverse and longitudinal thermal conductivity. Compared with the temperature field of symmetric thermal conductivity welded joint, the highest temperature point of heterogeneous welded joint deviates from the heat device center, and uniform temperature area shrinks. In addition, longitudinal temperature difference and dramatic temperature change zone have arisen for the third type heterogeneous welded joint. In order to improve the temperature distribution, two PWHT methods called temperature compensation method and power compensation method have been put forward and developed. Several engineering applications of two methods are illustrated as examples.

Phase Transformation Behaviour in P91 During Post Weld Heat Treatment: A Gleeble Study

Grade P91 is a creep strength enhanced ferritic steel used widely at high temperature applications in thermal power plants. P91 weldments are subjected to post weld heat treatment (PWHT) at a typical temperature of 760 °C for stress relieving purpose and to obtain optimal mechanical properties. In general PWHT temperature is about 30–50 °C lower than the lower critical temperature (Ac1). Depending on the chemical composition (particularly Ni + Mn), heating rate and prior austenite grain size, Ac1 temperature can vary from 780 to 860 °C. In this investigation an attempt was made to understand the effect of surpassing the typical PWHT temperature of 760° and approaching Ac1 of the material. The investigation was based on physical simulation conducted using 3500 Gleeble thermo mechanical simulator. The study was performed on cylindrical specimens which were extracted from weld metal and parent metal. Specimens were subjected to normalizing treatment at 1050 °C for achieving austenitisation and to determine the Ac1 temperature and then to different PWHT temperatures in the range of 790–850 °C at suitable intervals. American Society for Testing and Materials (ASTM) A1033-10 based procedure was used to find Ac1 temperature for the parent metal and weld metal at slow heating rate condition to compare with practical heat treating condition. Dilatometry plots, microstructure and hardness tests performed on the specimen were used to analyse the phase transformation. Results indicated that alpha ferrite phase and fresh untempered martensite could be formed in P91 steel when PWHT temperature was about 12 °C less than the Ac1 temperature. It was also seen that the heating rate had strong influence on the Ac1 temperature. At the heating rate of 28°/hr, Ac1 was about 792 °C for weld metal, while Ac1 was about 812 °C for the heating rate of 220 °C/hr.

Effect of post weld heat treatment on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel weldments

The effect of postweld heat treatment (PWHT) on the microstructure and mechanical properties of ITER-grade 316LN austenitic stainless steel joints with ER316LMn filler material was investigated. PWHT aging was performed for 1h at four different temperatures of 600°C, 760°C, 870°C and 920°C, respectively. The microstructure revealed the sigma phase precipitation occurred in the weld metals heat-treated at the temperature of 870°C and 920°C. The PWHT temperatures have the less effect on the tensile strength, and the maximum tensile strength of the joints is about 630MPa, reaching the 95% of the base metal, whereas the elongation is enhanced with the rise of PWHT temperatures. Meanwhile, the sigma phase precipitation in the weld metals reduces the impact toughness.

Study of Dissimilar Header Welding Between 2.25Cr–1Mo Steel and 9Cr–1Mo Steel with 9018 B9 Electrode Under Various Conditions of Post Weld Heat Treatment

Headers are an integral part of the power plant equipment which serves as junction for receiving and distribution of fluid. Headers are routinely used in high temperature applications in which various combinations of steels are used to achieve weight and cost savings thus optimising the use of steels. This paper intends in studying the evolution of microhardness and microstructure in a dissimilar header fillet welding between the base materials 2.25Cr–1Mo steel and 9Cr–1Mo steel when welded using 9018 B9 electrode and a constant preheat of 220 °C. The post weld heat treatment (PWHT) is varied at temperatures from room temperature to 770 °C and the soaking duration is kept at 1 h. The changes in microstructure and microhardness are examined with the help of micrographs, electron dispersive spectrum and scanning electron microscopy analysis. As the PWHT temperatures changes, the variation in microstructure and microhardness becomes very much evident which is detailed out in this paper. Also, carbon migration phenomena and its relation with the PWHT temperatures has been studied in this paper.