Zone Of Welded Joints Research Articles

The microstructure and mechanical properties of the laser-welded joints of as-hot rolled AlCoCrFeNi2.1 high entropy alloy

AlCoCrFeNi2.1 hot-rolled eutectic high entropy alloys were welded by laser welding, yielding a free-defect laser-welded connection. With the use of optical microscopy, EDS, EBSD, and XRD, the microstructure of the base metal (BM), fusion zone (FZ), and heat-affected zone (HAZ) of the joint was examined. The produced joint underwent tensile and micro-hardness testing as well as a fracture morphology examination. A similar tensile strength in the FZ and BM is measured, while a decrease in the elongation. The typical layered lamellar structures, in particular an FCC + BCC dual-phase structure, were all visible in the HAZ, BM, and FZ zones. The α-fiber and γ-fiber as well as other textures are determined by the ODF figure, indicating a potential orientation distribution of the as-hot rolled AlCoCrFeNi2.1 joint. A clear grain refinement characteristics in the fusion zone as a result of the uneven thermal cycling during the welding process. The results of the mechanical test demonstrate the base metal has the highest hardness value, i.e. 500–550 HV0.2, within the welded joint zone. The welded joint has a tensile strength ∼1200 MPa, which is marginally higher than ∼1150 MPa in the base metal, and an elongation that decreases by 20 % from base metal to welded joint, indicating a decrease in the plasticity of the welded joint. A combination of brittle and ductile fracture occurs in welded joints during tensile failure. This study may give possibilities for the engineering application of laser welding of AlCoCrFeNi2.1 eutectic high entropy alloy in the future.

Tensile testing of S690QL1 HSS welded joint heterogeneous zones using small scale specimens and indentation methods

Abstract The welded joints are structures with significant heterogeneity, indicated by their fundamental segmentation into base metal (BM), heat affected zone (HAZ), and weld metal (WM). The heat affected zone, having width in millimeter scale for fusion welding processes, is further segmented into several characteristic regions, having differences in grain structure and size. The microstructural heterogeneity results in significant differences in mechanical properties of individual welded joint zones. Mechanical testing of such small material volumes is inconvenient, or even impossible, using the standard size specimens proposed in testing standards. Requirement to precisely position the specimens, even ones with subsize dimensions, and investigate mechanical properties of specific narrow HAZ regions presents certain challenge. This work investigates the X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The material tensile properties are tested, using small scale specimens and indentation methods. Small scale specimens are ASTM E8 round tensile subsize and flat sheet mini tensile specimens (MTS). The indentation methods include hardness testing and profilometry-based indentation plastometry (PIP) method, to gain additional insights into material stress–strain behavior. Finally, paper evaluates the testing methods, comparatively processes the collected experimental data, and provides guidelines for heterogeneous structures testing.

Macroscopic and microscopic element distribution in transition zones of GTAW Alloy 52M weld joint and its PWSCC growth behaviour

The microstructure and element distribution in the transition zone (TZ) of Alloy 52M buttering (52Mb) layer near the fusion boundary to the SA508III low alloy steel in a dissimilar metal weld joint with post-weld heat treatment (PWHT) is characterized. Two macroscopic TZs in the heat-affected zone have lower Cr and Ni contents than the bulk Alloy 52Mb. The first TZ near the fusion boundary has the lowest Cr and Ni compositions, accompanying the highest Fe content. Cr depletion and Ni enrichment along with slight Fe enrichment at the dendrite boundaries in the TZs, are more significant than those in the bulk Alloy 52Mb. The number and the maximum depth of local oxidation penetrations at the alloy-inner oxide interface based on the oxidation tests, the number and the maximum length of locally interdendritic cracks, as well as the average crack growth rate (CGR) in terms of the stress corrosion cracking (SCC) band based on the SCC tests in the first TZ are higher than those in the second TZ. The average SCC CGR is enhanced by macroscopic element dilution, while local oxidation penetration, as well as locally interdendritic SCC, are thought to be enhanced by both the macroscopic dilution of Cr in the TZs and the microscopic Cr depletion at dendrite boundaries.

Measurement of strengths and fracture initiation strains of weld metal and HAZ in steel joints using miniature coupons

This paper investigates the strengths (fy, fu) and fracture initiation strains (εf) of the weld and heat affected zone (HAZ) of welded joints. Miniature coupons were extracted and tested using a custom-built jig. The weld metal was generally isotropic with the highest and lowest εf in the longitudinal and transverse directions, respectively. The HAZ had higher fy and fu than the base metal but smaller εf in the transverse direction under low stress triaxiality, indicating possible fracture through the weld and HAZ when loaded transversely. The strengths of the weld metal and HAZ can be approximated to within 7%-10% using empirical hardness-strength correlation functions.

Methods and means of ensuring the accuracy of bending deformation measurements of connecting pipe between the VVER reactor and the steam generator in the conditions of a fuel campaign

The welded joint zone (WJ) No. 111 is a welding unit for the "hot" collector of the primary coolant to the DN1200 steam generator nozzle. The experience of operation of steam generators PGV-1000M of NPP power units with VVER-1000 shows that the WJ zone No. 111 is prone to the formation and development of operational defects. According to the results of periodic non-destructive testing of the WJ No. 111 zone performed at the PG of various power units of the VVER-1000 NPP, cases of detection of extended planar-type discontinuities, including through ones, were repeatedly recorded. Thus, this zone is one of the most critical zones of the reactor plant (RU) with VVER -1000. The root cause of the formation and development of operational defects has not yet been identified. Solving the problem of cracking of WJ No. 111 steam generators of nuclear power plants with VVER-1000 is one of the priority areas for improving the safety of operation of the power unit during the over-design service life. This problem is determined by a complex combination of temperature conditions, mechanical and corrosive effects, is relevant and has not yet been definitively solved. Therefore, it is very important to ensure the collection of reliable data on the actual stress-strain state of the WJ No. 111 zone in various operating modes (pressure loading of steam generators, heating/cooling of the power unit, hydraulic testing of the 1st and 2nd circuits). The article reveals the approaches and stages of creating and applying a strain gauge installation to ensure metrological suitability in the conditions of a campaign fuel company at an NPP power unit by using an adequate physical model to obtain additive and multiplicative correction coefficients.

Study on the microstructure and properties of spray formed 7055-T76 aluminum alloy joints by rotating magnetic field assisted friction stir welding

This study explores an electrically-magnetically-assisted friction stir welding (EMAFSW) method, conducting butt welding experiments on T76 tempered spray-formed 7055 aluminum alloy. Compared to traditional friction stir welding (FSW) processes, the EMAFSW method maintained basically consistent weld hardness, while tensile strength and elongation increased by 13.1% and 72.3%, respectively. The rotating magnetic field enhanced the mechanical stirring action of the welding tool, reduced the size of precipitates, promoted dislocation pinning, and increased the mobility of dislocations. The stirred zone (SZ) and thermo-mechanically affected zone (TMAZ) of EMAFSW weld joint showed significant grain refinement and increased recrystallization proportion, enhancing the weld joint toughness. The joint's fracture behavior shifted from brittle to ductile fracture.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ СКОРОСТНОЙ ЭЛЕКТРОТЕРМИЧЕСКОЙ ОБРАБОТКИ НА СТРУКТУРУ СВАРНОГО СОЕДИНЕНИЯ ИЗ НИЗКОЛЕГИРОВАННОЙ КОНСТРУКЦИОННОЙ СТАЛИ

The studies’ results of the high-speed electrothermal treatment effect on the structure and hardness of various zones of welded joints made of low-alloy structural steel 10ХСНД (10KhSND) are presented. It is shown that carrying out high-speed electrothermal treatment at 950–980 °C leads to the formation of a homogeneous, fine-grained ferrite-perlite microstructure with practically unchanged hardness values in all zones of the welded joint except for the weld root, where slightly higher values of microhardness are registered.

Experimental evaluation of the short and long fatigue crack growth rate of S355 structural steel offshore monopile weldments in air and synthetic seawater

Welded steel structures used in the offshore wind industry are exposed to harsh marine environments, which can result in corrosion-induced fatigue damage. Of particular concern is the heat affected zone (HAZ) of welded joints, a region known for its altered microstructure and mechanical properties, which can significantly influence the initiation and propagation of fatigue cracks. This study investigates the short and long fatigue crack growth rates, and the effect of seawater exposure, for the HAZ in S355 steel weldments. Single-edge notch bend (SENB) specimens are used, with a shallow notch in the HAZ. A series of specimens is immersed in synthetic seawater that is continuously circulated at a controlled temperature to assess the synergistic effects of corrosion and fatigue. The experimental method integrates a novel application of front face strain compliance for monitoring short cracks, alongside an extended back-face strain compliance approach for monitoring long crack propagation. It is concluded that the short fatigue crack growth rate of the HAZ is 2.7 to 3.5 times higher in seawater as compared to air. As the crack propagates and enters into the long crack regime, the ratio decreases to 2.2 times at the transition point of the two-stage crack growth curve and further decreases to 1.5 times when the notch advances towards fracture. The findings indicate that the fatigue crack growth rates documented in standards tend to be on the conservative side. This study significantly enriches the fatigue crack growth data available in literature, which will contribute to a more accurate lifetime assessment offshore wind turbine structures.

Enhanced mechanical properties of thermo-mechanically affected zone of friction-stir welded AZ61 magnesium alloy joint

Friction-stir welded (FSW) magnesium alloy joints frequently fracture at thermo-mechanically affected zone (TMAZ), and the joints exhibit unsatisfactory welding efficiency and ductility. The TMAZ is considered as the weakest region of the entire joint. Enhance the mechanical properties of TMAZ can improve the performance of the welded joint. In this work, subsequent aging treatment and pre-strain of 3% along the weld seam were conducted on the FSW AZ61 magnesium alloy joint. The microstructure of the TMAZ is characterized by abundant nanoscale second phase particles and {10–12} twins. The reduced basal texture intensity decreased the anisotropy of plastic deformation. The welded joint showed a good synergic of welding efficiency (96%) and ductility (20%). The enhanced strength is attributed to the blocking effect of nanoscale particles and grain/twin boundaries to dislocation movement. The increasing of twin boundaries is the main reason for the improvement of work hardening ability and ductility during tensile deformation. This work demonstrated that introducing {10–12} twins and nanoscale particles into TMAZ is an effective way to improve the balance of strength and ductility of the welded joint due to the synergistic effect of multiple strengthening and toughening mechanisms.

Physical and Mechanical Properties of Butt Welded Joints of Aluminum Alloys

Along with the improvement of joining technologies with argon arc, plasma and laser welding for aluminum alloy elements, high efficiency of joints made with the use of friction stir welding (FSW), which has low energy consumption and is almost equally strong as base metal, has been achieved. However, the processes of friction stir welding have not been sufficiently studied and can lead to softening of aluminum alloy welds up to 0.65 of base metal strength. When studying the effect of friction stir welding and mechanized electric arc welding in argon medium, welded joints of aluminum alloys of Al-Si-Mg (AD35T1, 6082-T6) and Al-Zn-Mg alloying systems (1915T) were subjected to tensile and impact tests. The values of strength, elastic and plastic characteristics of argon arc welded specimens of 1915T, AD35T1 and 6082-T6 alloys were obtained. For alloy 6082-T6, the same characteristics are presented for FSW welded specimens. Decrease in strength and ductility in the zones of welded joints for both welding methods is observed. At the same time, the highest relative values of strength and offset yield strength of the welded joint are fixed for friction stir welding. Slight decrease in modulus of elasticity obtained for argon-arc welded specimens was recorded. The impact strength is constant for each welded joint zones in the temperature range of +20 – -60оC and increased in weld metal of FSW butt joints of alloy 6082-T6.

Effects of magnetic field and post-weld heat treatment on microstructure and properties of laser welded joints of 22MnB5-TRIP590 steel

Laser welding without and with an auxiliary magnetic field (B = 30 mT) is performed on 22MnB5-TRIP590 steel. Subsequently, post-weld heat treatment, involving quenching at 800 °C followed by tempering at 200 °C, is carried out on the welded joints prepared by these two welding processes (B = 0 mT, B = 30 mT). This study examines the improvement of microstructures and mechanical properties of the welded joints by applying the magnetic field (B = 30 mT). Furthermore, this research investigates whether these enhanced characteristics of the welded joints persist after post-weld heat treatment. When the magnetic field is applied, the overall width of the welded joint is significantly reduced, and the microstructure of the weld is changed mainly from proeutectoid ferrite, granular bainite, and upper bainite to lath martensite and lower bainite. Furthermore, the grains in the coarse grain zone are refined, and the plasticity and overall hardness of the welded joint are considerably improved. After post-weld heat treatment, the weld and coarse grain zone of both welded joints (B = 0 mT, B = 30 mT) are mainly tempered martensite, and the tensile strength and overall hardness are significantly improved compared to those without post-weld heat treatment. Although the plasticity of two welded joints is lower than that of two unheated-treated welded joints, the fracture positions are all at the base metal and are both ductile fractures. The improved characteristics, such as optimized macro-morphology, refined grain morphology, improved plasticity, welded joint efficiency, and weld hardness of magnetic field-assisted laser welded joint, are all retained after post-weld heat treatment. A thorough comparison reveals that the magnetic field-assisted laser welded joint with post-weld heat treatment has better comprehensive mechanical properties.

Influence of physical properties of weld metal on hydrogen diffusion into the heat affected zone of heterogeneous welded joints

The paper presents the analytical solution of one-dimensional problem on hydrogen diffusion in butt heterogeneous welded joints. Such parameters as welded joint thickness, weld thickness, diffusion coefficients, solubilities and initial concentrations of hydrogen in the weld metal and base metal have been taken into account. The effects of microstructure on hydrogen kinetics in homogeneous and heterogeneous welded joints are considered. It is shown that hydrogen concentration in the heat affected zone (HAZ) to a great extent depends on the ratios of the initial concentrations, hydrogen diffusion coefficients and solubilities in the weld metal to those in the base metal. The concentration of hydrogen in the HAZ decreases by three orders of magnitude when welding martensitic steel with austenitic electrodes as compared to homogeneous joints.

The Influence of Centerline Segregation on Impact Toughness in Welding Heat-Affected Zone of X70 Pipeline Steel

The influence of centerline segregation on the low-temperature impact toughness of the heat-affected zone (HAZ) of welded joints was studied by welding experiments on X70 steel plates rolled from continuous casting slabs with segregation grades of class 2 and class 3. The experimental results show that the impact toughness at HAZ from class 2 slab steel plate is more stable and has excellent low-temperature toughness than that of class 3 slab steel plate. The impact toughness of the HAZ of the class 3 slab steel plate is low to 100 J at −40 °C and has a severe fluctuation range (~150 J), and the delamination phenomenon is also observed in the fracture cross-section. The reason for this phenomenon is due to the enrichment of C and Mn elements in the centerline segregation zone. The formation of abnormal microstructure (martensite/bainite) in the segregation zone leads to stress concentration, which easily weakens the low-temperature toughness of the joint.

Microstructural characteristics of different heat-affected zones in welded joints of UNS S32304 duplex stainless steel using the GMAW process: analysis of the pitting corrosion resistance

Abstract The influence of specific microstructural characteristics on the properties of single-pass welding joints was assessed by optical processed images, transmission electron microscopy, microhardness measurements and corrosion tests conducted in various regions of the heat-affected zone (HAZ) in a lean duplex stainless steel. The welded joints were obtained with heat inputs of 1.5 and 2.5 kJ/mm using a gas metal arc welding (GMAW) process with a shielding gas enriched in Ar. Three selected regions in the HAZ showed different ferrite grain sizes and austenite fractions. The place in the welded joint where the HAZ was narrowest, and therefore experiences the highest cooling rate, is most prone to the formation of cubic CrN metastable nitrides. Conversely, the place where the HAZ was wider promotes the precipitation of stable Cr2N nitrides with more coalesced intragranular austenite (IGA) particles, where presumably random interfaces predominate. The HAZ region where the cooling rate was the highest presented more pitting corrosion resistance.

Сравнительный анализ химического состава и механических свойств различных участков сварного соединения дюралюмина, полученного сваркой трением с перемешиванием

Friction stir welding is an advanced method of joining various metals and alloys in the aircraft and mechanical engineering industries. This type of welding is used to join materials that are difficult to weld or not weldable by conventional methods. The high-strength D16 aluminum alloy is difficult to weld by fusion, which is associated with the formation of a dendritic structure in the fusion zone leading to a decrease in the mechanical strength of the joint. In the work, the microstructure and microhardness of a welded seam of the D16 aluminum alloy produced by friction stir welding was studied. Using scanning electron microscopy and optical metallography, the authors identified the presence of three zones: the weld core, the thermomechanical impact zone, and the heat effected zone. In the central part of the welded joint (in the core), a laminated onion ring structure was discovered. A change in the chemical composition of the aluminum solid solution was identified in different areas of the weld zones, as well as the presence of a concentration gradient within each zone. In the upper part of the welded seam, the solid solution is silicon-enriched and depleted in copper. Due to the solid solution depletion in alloying elements, the aluminum content in the solid solution in the zone of the welded joint is higher compared to the initial state. The microhardness values in different areas of the welded joint correlate with changes in the chemical composition. In the welded joint zone, a significant decrease in microhardness was found compared to the initial state, and a change in microhardness associated with the chemical composition gradient within each zone was also observed.

Numerical validation of fatigue properties and investigation of local deformation of heat-affected zones in P91 steel’s weld joint

The low cycle fatigue (LCF) behavior of P91 steel weld joint (WJ), prepared by gas tungsten arc welding, has been investigated both experimentally and numerically. However, due to the smaller size and complex geometry of various zones of the WJ, the experimental investigation of the local fatigue behavior of different sub-regions of the heat-affected zones (HAZ) could not be made. Hence, the sub-regions of the WJ were reproduced at bulk scale by physical-thermal simulation (PTS) (i.e., heat treatment) to study the LCF behavior of the individual zones of P91 WJ. In the literature, the accuracy of such physical-thermally simulated bulk-scale specimens, which correspond to different sub-regions in the weld joint, is confirmed by comparing the microstructures and microhardness. In this article, a new method, based on the LCF experiment and finite element simulation, is proposed to validate the PTS method and the fatigue properties of the sub-regions of the weld joint. The simulation accurately predicted the failure location and also the most vulnerable sub-region within the WJ, as observed experimentally. Moreover, significant ratchetting and heterogeneous deformation were observed in the sub-regions of the WJ.

Experimental and Numerical Analysis of Fracture Mechanics Behavior of Heterogeneous Zones in S690QL1 Grade High Strength Steel (HSS) Welded Joint.

The heterogeneity of welded joints' microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth.

Improvement of the cooling control during electrofusion welding of polyethylene pipes at low temperatures

A method has been developed for determining the heater power at the cooling stage when welding polyethylene pipes for gas pipelines at low ambient temperatures (below those recommended by regulatory documents). Efficiency of the method is verified by studies of materials crystallization kinetics in the heataffected zones of welded joints

Microstructural aspects of fatigue strength of welded joints of medium carbon steels produced by rotary friction welding

The paper studies the resistance to fatigue failure of welded joints of steels 32Mn2-40CrNi2Mo, intended for the production of drill pipes for geological exploration. The connection of pipe billets for the purpose of manufacturing experimental samples was carried out by means of rotational friction welding at various process parameters. The assessment of resistance to fatigue loads was carried out on solid cylindrical samples with a welded joint under conditions of bending with rotation, which made it possible to identify the weakest zone in which the initiation and development of a fatigue crack occurred. The microstructure was studied using optical and electron scanning microscopy using the electron backscatter diffraction (EBSD) method. In the course of research, it was found that the greatest resistance to fatigue loads is provided due to the intensive development of strain hardening processes in the thermomechanical affected zone of welded joints, which depend on the parameters of rotary friction welding.

МЕТОД ИССЛЕДОВАНИЯ НАГРУЖЕННОСТИ КУЗОВОВ ПАССАЖИРСКИХ ВАГОНОВ С ДВУХСЛОЙНОЙ ОБШИВКОЙ БОКОВЫХ СТЕН

A method is proposed to estimate the loading capacity of passenger car bodies with two-layer side wall lining using the finite element method and mathematical modeling of the car movement along real track irregularities. The interaction of the side wall lining sheets connected by spot welding is described. Various types of two-layer lining are considered. The estimation is given to the influence of the method of the two-layer lining on the stress-strain state obtained by finite element calculation according to the dynamic parameters of the car when modeling its movement along real track irregularities. It is found out that when estimating the stress-strain state in the zones of welded joints, it is advisable to use detailed design diagrams with modeling of their geometry. When assessing the strength of the body bearing structure or the stress-strain state of large body components, it is advisable to use design diagrams describing welded joints with special rod finite elements. When assessing the dynamic characteristics of a car moving along the track irregularities using a hybrid dynamic model, design diagrams with the description of a two-layer lining with orthotropic materials are applied. Also, when using appropriate design diagrams in these types of studies, a sufficient degree of results accuracy obtained is ensured.