Effect Of Post-weld Heat Treatment Research Articles

Effect of post-weld heat treatments on strength and toughness behavior of T-250 maraging steel welded by laser beam

This paper elucidates here the strength and toughness behavior of T-250 maraging steel welded by laser beam under different approaches of three post-weld heat treatments, i.e. aging (A), solutionizing+aging (SA) and homogenizing+solutionizing+aging (HSA). The microstructures of the weld metals with A and SA processes both comprised of finely dispersive Ni3(Ti, Mo) precipitates, small martensite lath and reverted austenite along the grain boundary. However, in the weld metal with HSA process, it exhibited the same Ni3(Ti, Mo) precipitate with the large martensite lath and the absence of reverted austenite. The ultimate tensile strength and static toughness of the welded joint with HSA process were 1350.6MPa and 63.8MJm−3, respectively. The static toughness has been remarkably improved from 71% to 91% of the applied parent metal compared with that of the welded joint with A process. The present study underscores that the Ni3(Ti, Mo) precipitate and martensite are significant to ensure the high strength of welded joints. Due to its inconsistent deformation with the matrix of martensite, the reverted austenite has a notable influence on the toughness of welded joints. It shows that the post-weld heat treatments of HSA process can influence the mechanical behavior of welded joints by eliminating the reverted austenite.

Effects of Various Post-Weld Heat Treatments on Austenite and Carbide Formation in a 13Cr4Ni Steel Multipass Weld

Multipass welding procedures are common methods for 13Cr4Ni steels' fabrication and repairs. Compared to a single-pass weld procedure, the weld microstructure in a multipass weld is more heterogeneous due to the complex local thermal cycles imposed by adjacent weld passes. Furthermore, the final microstructure and mechanical properties of these steels are very sensitive to their thermal history which increases the microstructure heterogeneities. Thus, post-weld heat treatments are performed to reduce heterogeneities and produce a relatively homogenous weld. It has been found that the best option to improve mechanical properties of 13Cr4Ni steels is forming a “room temperature stable austenite” phase by heat treatments. This study focuses on the effects of these post-weld heat treatments on the austenite phase and carbide formations and the related evolutions of microhardness distribution. The study shows that nanometer-size carbides form at martensite lath interfaces and sub-block boundaries, and then at higher temperatures austenite lamellae appear at these locations. Results also show that the highest percentage of stable austenite achievable by a single-stage tempering was obtained at 610 °C. When the heat treatment temperature is lower than 610 °C, longer holding time produces softer steel while longer heat treatments at temperatures higher than 610 °C, produces harder steel. Still, double-stage heat treatments are more effective and produce the highest percentage of austenite and the lowest hardness of all heat treatments.

Effects of post-weld heat treatment on microstructure and mechanical properties of laser welds in GH3535 superalloy

In this study, the microstructure and mechanical properties of laser welds before and after post-weld heat treatment processes were studied. The results show that the tensile strength of the joints can be increased by 90MPa by a post-weld heat treatment process at 871°C for 6h, exceeding the strength of the original state of the base metal. Besides, elongation of the joints are also increased to 43% by the process, whereas the elongation of as-welded joints are only 22%. In addition, the Charpy impact properties of laser welds almost do not change. Second phase precipitates, which were identified as Mo–Si rich M6C-type carbides by transmission electron diffraction and scanning electron microscope, were observed at solidification grain boundaries and solidification subgrain boundaries. These carbides can pin dislocations during the following tensile deformation, hence are responsible for the strengthening of tensile properties of the joints.

Effect of Post-Weld Heat Treatment on the Microstructure and the Cryogenic Mechanical Properties of Electron Beam Welded Cast Inconel 718

Effect of Post-Weld Heat Treatment on the Microstructure and the Cryogenic Mechanical Properties of Electron Beam Welded Cast Inconel 718

Effects of post-weld heat treatment on microstructure and mechanical properties of linear friction welded Ti2AlNb alloy

Linear friction welds of a Ti2AlNb-based alloy were subjected to post-weld heat treatment (PWHT) at 815°C×1h (PWHT1) and at 1000°C×1h+815°C×2h (PWHT2) followed by air cooling. The microstructure and mechanical properties of the joints under as weld and PWHT conditions were investigated. The results indicate that in the as weld joint, the weld zone mainly consists of B2 phase while the quantity of α2 and O phase is relatively small, and most O phase gradually turns into B2 phase when the amount of α2 phase reduces as well in thermo-mechanically affected zone (TMAZ). After PWHT1, O precipitates within recrystallized B2 grains can be found in weld zone and the decomposition of α2 phase caused by niobium diffusion is found in TMAZ. PWHT1 have significantly enhanced the mechanical properties due to the O phase precipitation hardening and refined grain strengthening. And the coarsening of the microstructure in weld zone under PWHT2 is evident, which consequently reduces the elongation.

The effect of post-weld heat treatment on the microstructure and notched tensile fracture of Ti–15V–3Cr–3Al–3Sn to Ti–6Al–4V dissimilar laser welds

A CO2 laser was applied for dissimilar welding of Ti–15V–3Cr–3Al–3Sn (Ti–15–3) to Ti–6Al–4V (Ti–6–4) alloys. The microstructures and notched tensile strength (NTS) of the dissimilar welds were investigated in the as-welded and post-weld heat treatment (PWHT) conditions, and the results were compared with Ti–6–4 and Ti–15–3 homogeneous laser welds with the same PWHT. The results indicated that predominant α″ with a few α and β phases was formed in the as-welded fusion zone (FZ). Furthermore, the FZ hardness was susceptible to the PWHT and showed a plateau for the specimens aged in the temperature range from 426 to 482°C/4h. In comparison with the homogeneous Ti–15–3 weld under the same PWHT conditions, the dilution of Ti–15–3 with Ti–6–4 caused a slight increase in the Al equivalent (AlEQ) of the FZ, resulting in a further rise in FZ hardness. With the PWHT at/below 538°C, the dissimilar welds were associated with low NTS or high notch brittleness.

Influences of post weld heat treatment on tensile properties of friction stir welded AA2519-T87 aluminium alloy joints

AbstractAA 2519-T87 is an aluminium alloy that principally contains Cu as an alloying element and is a new grade of Al-Cu alloy system. This material is a potential candidate for light combat military vehicles. Fusion welding of this alloy leads to hot cracking, porosity and alloy segregation in the weld metal region. Friction stir welding (FSW) is a solid state joining process which can overcome the above mentioned problems. However, the FSW of age hardenable aluminium alloys results in poor tensile properties in the as-welded condition (AW). Hence, post weld heat treatment (PWHT) is used to enhance deteriorated tensile properties of FSW joints. In this work, the effect of PWHT, namely artificial ageing (AA) and solution treatment (ST) followed by ageing (STA) on the microstructure, tensile properties and microhardness were systematically investigated. The microstructural features of the weld joints were characterised using an optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The tensile strength and microhardness of the joints were correlated with the grain size, precipitate size, shape and its distribution. From the investigation, it was found that STA treatment is beneficial in enhancing the tensile strength of the FSW joints of AA2519-T87 alloy and this is mainly due to the presence of fine and densely distributed precipitates in the stir zone.

Effect of post-weld heat treatment on the fatigue strength of HFMI-treated mild steel joints

Welding as a thermo-mechanical joining process generally induces residual stresses and distortion in welded components or structures. Mechanical post-treatment methods as the high-frequency mechanical impact treatment (HFMI) reduces the geometrical notch and introduces compressive stresses in the locally treated weld toe area, whereas post-weld heat treatment (PWHT) globally affects the whole structure. In this paper, the fatigue strength of HFMI-treated transverse non-load-carrying attachments and cruciform joints made of structural mild steel S355 before and after PWHT is investigated. Comprehensive tumescent fatigue tests and evaluation of notch topography, residual stress and distortion show the influence of the investigated post-treatment methods. To analyse the effect of distortion on the resulting stress condition during the fatigue tests, simulations and strain gauge measurements are carried out for different load cases. Finally, a local fatigue assessment based on the effective notch stress approach shows that an additional PWHT is not beneficial for fatigue strength. As an increase in distortion of the samples, and an influence on the base material properties, caused by the heat-treatment is not observable, the decrease in fatigue is mainly caused by the entire relieve of manufacturing induced (as-welded/HFMI-treated) prior compressive residual stresses to an almost zero stress value.

Estimation of residual stresses in an 800 mm thick steel submerged arc weldment

Assuming plane strain conditions and taking phase transformations into account, finite element analysis was carried out using a bead-by-bead deposition model as well as two different lumped models. The effects of post-weld heat treatment at 600°C were also studied. Predicted residual stresses were verified using X-ray diffraction method. While both bead-by-bead and lumped models were found to overestimate the maximum residual stress in as-welded condition, the latter facilitated a safer upper-bound estimate of the residual stress. The net tensile stress in the weld metal was found to decrease as a result of solid-state transformation of austenite to ferrite. Further, a significant part of stress relief was found to occur in the first half hour of the holding time during post-weld heat treatment. A formula was developed for estimating the maximum residual stress in post-weld heat treated condition.

Effect of post-weld heat treatment on the mechanical properties of CLAM/316L dissimilar joint

Dissimilar welding between China low activation martensitic (CLAM) steel and 316L austenitic stainless steel was investigated to achieve the reliable connection between test blanket modules (TBMs) and piping system in the international thermonuclear experimental reactor (ITER). The dissimilar joints were welded by tungsten inert gas (TIG) welding process with a filler material type-309. In order to stabilize the microstructure and improve the strength and toughness, post-weld heat treatments (PWHTs) of tempering at 740°C, 780°C and 820°C, respectively, for 2h were performed. The microstructure observation showed that tempering at 740°C for 2h was the preferable PWHT rule in this work. After the treatment, the hardening in heat affected zone (HAZ) on the CLAM steel side decreased remarkably. The tensile strength of the joint was roughly the same as that of the base metal. The impact toughness of HAZ on the CLAM steel side was 77% of that of the base metal. The absorbed energy of HAZ of 316L steel decreased by 93J, and that of weld metal (WM) was 110J after the treatment.

Effect of post-weld heat treatment on friction welded joint of carbon steel to stainless steel

1045 carbon steel was joined to 304 stainless steel by friction welding, and the joint was heat treated at different post-weld heat treatment (PWHT) temperature. The weld interface of as-welded joint was straight and obvious, whereas, it became indistinct after PWHT characterized by severe element diffusion. Chromium carbides such as (Cr, Fe)7C3 and Cr7C3 formed at the weld interface, the amount of which increased with the PWHT temperature increasing. In thermo-mechanically affected zone (TMAZ), the microstructure at carbon steel side of as-welded joint was quite heterogeneous, while it became homogeneous after PWHT at 400°C. Analyses of fracture surfaces showed the amount of chromium carbide and the heterogeneous microstructure in TMAZ at carbon steel side were crucial factors in influencing fracture mechanism and properties of joints. Tensile strength and elongation of the joint were improved substantially after PWHT at 400°C, which could reach up to the equivalent strength of stainless steel and elongation of carbon steel, because the microstructure became homogeneous to some extent and the amount of chromium carbides barely increased. The fracture mode also altered from quasi-cleavage fracture in as-welded joint to the combination of dimple fracture and quasi-cleavage fracture after PWHT.

Effect of post-weld heat treatment and neutron irradiation on a dissimilar-metal joint between F82H steel and 316L stainless steel

A dissimilar-metal joint between F82H steel and 316L stainless steel was fabricated by using electron beam welding (EBW). By microstructural analysis and hardness test, the heat-affected zone (HAZ) of F82H was classified into interlayer area, fine-grain area, and coarse-carbide area. Post-weld heat treatment (PWHT) was applied to control the hardness of HAZ. After PWHT at 680°C for 1h, neutron irradiation at 300°C with a dose of 0.1dpa was carried out for the joint in Belgian Reactor II (BR-II). Compared to the base metals (BMs) and weld metal (WM), significant irradiation hardening up to 450HV was found in the fine-grain HAZ of F82H. However, the impact property of F82H-HAZ specimens, which was machined with the root of the V-notch at HAZ of F82H, was not deteriorated obviously in spite of the significant irradiation hardening.

Effect of Post-weld Heat Treatment on Properties of Friction Welded Joint Between TC4 Titanium Alloy and 40Cr Steel Rods

Dissimilar metal joining of Ti–6Al–4V (TC4) titanium alloy to as-rolled 40Cr steel rods was conducted with friction welding, and the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of the resultant joints was investigated. The average tensile strength of the as-welded joints reached 766 MPa and failure occurred in 40Cr steel base metal. However, after PWHT at 600 °C for 0.5, 1, 2 and 3 h, the tensile strength of the joints decreased and fracture happened through the interface with quasi-cleavage features. The bending angle of specimens was improved from 9.6° in as-welded state to 32.5° after PWHT for 2 h. The tensile strength of the joint was enhanced by martensitic transformation near the interface in as-welded state. Sorbite formed near the interface in PWHT state and improved the bending ductility of the joint. TiC brittle phase formed at the interface after PWHT for 0.5 h and deteriorated the tensile strength and bending ductility of the joint. After PWHT for 2 h, no TiC phase was detected at the interface. The microhardness on the interface in as-welded state was higher than that after PWHT, indicating that the decrease of microhardness around the interface could be accompanied by degradation of tensile strength but improvement of bending ductility of the joints.

Effect of Post-Welded Heat Treatments on Microstructure and Mechanical Properties of Friction Stir Welded Joints of 7A04-O Aluminum Alloy

Effect of post-welded heat treatment (PWHT) on the microstructure and mechanical properties of friction stir welded 7A04-O aluminum alloy was investigated. Solution heat treatment (ST) and artificial aging (T6) were given to specimens to improve the mechanical properties of the joints. The results show that defect-free joint was obtained via FSW and the microstructure of nugget zone was characterized by fine and equiaxed grains. After ST, most second phases dissolve in the matrix and the α-Al grains became coarse. Second phases precipitated in the α-Al matrix uniformly after T6 treatment. The Vickers hardness test shows that PWHT made the hardness distribution of the joints more evenly. The tensile test results indicate that the tensile strength of the joint increased from 228 MPa (in as-welded condition) to 440 MPa and 528 MPa after ST and T6 treatment respectively, but the elongation decreased to a certain extent. SEM fracture morphologies indicate that the joint failed through ductile fracture for the as-welded and ST states, and failed in a mixture mode of brittle fracture and ductile fracture for the T6 state.

Study of Hydrogen Cracking and PWHT of Dissimilar Materials for Elevated Temperature Application

s. On construction sites many challenges and premature failures are being encountered in welded joints of creep strength-enhanced ferritic (CSEF) steels. The primary reason of these premature failures is found to be the dissimilar material joints, having strength mismatch, or improper heat treatment that is mandatorily carried out to achieve the required weld hardness. This study aims at determining the impact of post welding heat treatment (PWHT) on dissimilar alloy steels joints, between ASTM A335 Gr. P-22 and ASTM A335 Gr. P-91 steels, welded by gas tungsten arc welding (GTAW) using ER 90S-B9 filler wire. The PWHT, at 745°C for 1hr., was applied to attain the required hardness. The effect of PWHT was investigated on the weld metal and the heat affected zones (HAZ) by hardness testing. Due to the martensitic microstructure, the hardness values of HAZ of P91 steel are over 350 HV. However, the hardness value of the P22 HAZ less than 350 HV. P91 HAZ has a higher hardness value than P22 HAZ because of its higher hardenability and due to phase transformation from martensite to ferrite. The interaction between the too high hardness microstructure with hydrogen can result in the hydrogen induced cracking (HIC) initiation in the HAZ. Therefore, the PWHT is needed to reduce this high hardness HAZ.

Effects of post-weld heat treatment on fracture toughness of linear friction welded joint for dissimilar titanium alloys

The effect of post-weld heat treatment processing parameters on the microstructure, fracture morphology, fracture toughness and crack propagation direction of the linear friction welded joint for dissimilar titanium alloys was investigated. Results show that weld zone and one side of thermo-mechanically affected zone are weak zones for fracture toughness of linear friction welded joint for dissimilar titanium alloys after welding; post-weld heat treatment can effectively improve the fracture toughness of the weak zones, but has less effect on that of the other side. During the heat treatment process, the fine acicular and equiaxed microstructures in the weak weld zones grow and partly transform into lamellar microstructure which can increase the total length of the crack along with energy consumption and relieve the residual stress, resulting in enhancing the fracture toughness of the joint. Meanwhile, the fracture morphology gradually transforms from intergranular fracture to ductile–brittle mixed fracture and dimple fracture.

Effect of post-weld heat treatment on microstructures and properties of friction stir welded joint of 32Mn–7Cr–1Mo–0·3N steel

In this study, the microstructures and mechanical properties of friction stir welded and post-weld heat treated joints of 32Mn–7Cr–1Mo–0·3N steel were investigated. Significant microstructural and mechanical property gradients were found along the transverse directions of the as welded joint. These gradients led to overmatching characteristic with higher strength but lower ductile than base material. The post-weld heat treatment effectively reduced the gradient characteristics in the as welded joint. Consequently, the mechanical property of the joint was nearly restored to the level of base metals. However, the abnormal grain growth was observed in the heat affected zone of the post-weld heat treated joint. The possible mechanism was discussed in term of the evolution of atom segregation at grain boundaries.

Effect of Post-Weld Heat-Treatment on the Stress-Corrosion Cracking Behaviour of Laser-Welded Shape Memory NiTi Wires in Hanks' Solution

Effect of Post-Weld Heat-Treatment on the Stress-Corrosion Cracking Behaviour of Laser-Welded Shape Memory NiTi Wires in Hanks' Solution

Effect of Post-Weld Heat Treatment on Microstructure and Mechanical Properties of X52 Linepipe HFIW Joints

In the present paper, influences of normalization heat treatment on microstructural and mechanical properties of high-frequency induction welded (HFIW) joints of X52 steel have been investigated. HFIW joints were post-weld heat treated at different times and temperatures. The microstructure and mechanical properties of the heat treated joints were then comprehensively investigated. Based on the results, a proper normalization of the primary fine grain steel caused the grain size to increase; but because of converting brittle microstructure into ductile microstructure, it caused the toughness to increase also. In addition, the ductility of the joints was enhanced. Nevertheless, tensile strength, yield strength, and hardness were reduced. The results showed that 950 °C was the optimum normalization temperature from the standpoint of fracture toughness for the X52 steel joints. At 1050 °C, the carbides and/or nitrides in the steel dissolved, and excessive grain growth occurred. Hence, the maximum allowable temperature for normalization was found to be 1000 °C.

Effect of post-welding heat treatment on wear resistance of cast-steel die with surfacing layer

The wear resistance capability of die surfacing layer under different Post-Welding Heat Treatments (PWHT) was analysed by Finite Element (FE) simulation and experiments. Taking hot forging process of a crankshaft as an example, a wear model of the hot forging die coated with surfacing layer was established using FE software DEFORM-3D. The simulation results indicated that the wear resistance capability of the die surfacing layer is optimal when tempering temperature and holding time are 550 °C and 4 h respectively. To verify the wear computational results, 16 groups of PWHT orthogonal wear tests were performed at a temperature of 400 °C, which is a similar temperature to that occurs in an actual hot forging die. The wear-test result showed a good agreement with the FE simulation. SEM observation of the wear debris on 16 specimens showed that oxidative wear is dominant when the temperature was in 400 °C. Furthermore, when tempering temperature and holding time were 550 °C and 4 h respectively, the carbide alloy dispersively distributes in the metallographic structure, which helps to improve the wear resistance of the surfacing layer.