The electrochemical behavior of the weld metal, heat‐affected zone (HAZ), and base material of super duplex stainless steel (SDSS) welded joints, made with the application of flux‐cored arc welding ...(FCAW) and submerged arc welding (SAW), were investigated with the use of metallographic examinations (optical microscopy and scanning electron microscopy), potentiodynamic polarization measurements and total hydrogen content determination in the initial state and after hydrogen charging. The obtained results revealed that the effect of hydrogen depended on the microstructure and type of the region of a welded joint. The highest amount of hydrogen penetrated the welded joint charged at 1 mA cm−2. It was observed in case of the FCAW‐welded joint, made with lower heat input. The electrochemical measurements showed that the base material was the most corrosion resistant part of the welded joint while the hydrogen charging strongly changed pitting and general corrosion susceptibility of HAZ and weld metal of both welded joints.
The electrochemical behavior of the weld metal, heat‐affected zone and base material of super duplex stainless steel (SDSS) welded joints, made with the application of FCAW and SAW, were investigated with the use of OM and SEM, potentiodynamic polarization measurements and total hydrogen content determination. The obtained results revealed that the effect of hydrogen depended on the microstructure and type of the region of a welded joint.
•The three regions of the welded joint present different hardening behavior under the same irradiation condition.•He bubbles are the main reason for the different hardening behavior of welded joints ...after He ions irradiation.•The different structures of intrinsic dislocation lines in the welded joints affect the nucleation and growth of He bubbles in the grain.
Irradiation damage due to helium embrittlement impacts the safety and integrity of welded structural materials in power reactors. To understand this helium effect, in this study, GH3535 welded joints were irradiated at 650°C with 500 keV He ions at various doses to investigate the effects of He bubbles on the weld, heat-affected zone (HAZ), and base metal. The three regions exhibited different hardening behaviors. The hardness of the weld and HAZ after irradiation increased proportionately with the ion dose. The hardness of the base metal gradually saturates at a dose of 2 × 1016 ions/cm2. At the highest dose (1 × 1017 ions/cm2), the degree of hardening in the three regions was as follows: weld (92.9%) > HAZ (91.3%) > base metal (72.7%). The microstructures of the samples revealed that the mean diameters of the He bubbles in the weld, HAZ, and base metal were approximately 2.74, 2.80, and 2.36 nm, respectively, with corresponding number densities of 15.4 × 1023, 10.8 × 1023, and 9.69 × 1023 m−3. Furthermore, the yield strength increment was calculated using the dispersed barrier hardening model, which suggested that the helium bubbles played an important role in the different hardening behavior of the welded joint. The nucleation and growth of helium bubbles was influenced by the structures of the intrinsic dislocations in the weld, HAZ, and base metal.
The different helium bubble microstructures are the main reason for variations in the hardening behavior of welded joints under identical conditions Display omitted .
•The welding deformation and residual stress of thin aluminum alloy welded structure are accurately predicted.•Fatigue tests of typical thin-plate aluminum alloy welded joints were carried out.•The ...influence of welding defects on the fatigue strength of thin-plate aluminum alloy welded joints is quantitatively analyzed.
With the transformation and upgrading of shipbuilding industry, aluminum alloy shipbuilding will gradually develop towards energy saving, light weight and environmental protection. As a new generation of trustworthy aluminum alloy structure, 5059 aluminum alloy material has better mechanical properties and corrosion resistance. However, two prominent shortcomings of aluminum alloy welding structure are large welding deformation and low fatigue strength. In order to accurately consider the influence of welding defects, the temperature field simulation program of thin plate welding structure is designed to predict the welding deformation and residual stress. The simulation results of temperature field and welding deformation of typical welded joints are in good agreement with the test results. Moreover, taking welding deformation and residual stress as initial conditions, the fatigue strength class curves of 5059 aluminum alloy welded joints are renewed based on the hot spot stress.
This article deals with the dissimilar joining of two different grade Cr-Mo steel (2.25Cr-1Mo: P22 and modified 9Cr-1Mo: P91) for power plant application. The dissimilar butt-welded joint was ...produced for conventional V groove design by using the gas tungsten arc welding (GTAW) process with the application of an ERNiCrMo-3 Ni-based super alloy filler. A microstructure characterization was performed to measure the inhomogeneity in the microstructure and element diffusion across the interface in a welded joint. The experiments were also performed to evaluate the mechanical properties of the dissimilar welded joint in as-welded (AW) and post-weld heat treatment (PWHT) conditions. An acceptable level of the mechanical properties was obtained for the AW joint. After PWHT, a significant level of the element diffusion across the interface of the weld metal and P22 steel was observed, resulting in heterogeneity in microstructure near the interface, which was also supported by the hardness variation. Inhomogeneity in mechanical properties (impact strength and hardness) was measured across the weldments for the AW joint and was reduced after the PWHT. The tensile test results indicate an acceptable level of tensile properties for the welded joint in both AW and PWHT conditions and failure was noticed in the weak region of the P22 steel instead of the weld metal.
•Aluminium welded joints are considered in three-dimensional numerical analysis.•The fatigue behaviour of aluminium welded joints was analysed by means of the implicit gradient approach.•For ...aluminium arc welded joints a general fatigue scatter band has been proposed.•The characteristic length for aluminium alloy reduces to 0.15 mm (0.2 mm for steel joints).
In this paper, the numerical implicit gradient approach already validated for steel welded joints is also used for aluminium joints. Some peculiarities of aluminium joints are discussed and a general fatigue scatter band for arc welded joints has been proposed. The analysed experimental data taken from the literature range from the simple butt-welded joints with a thickness of 2 mm up to the extruded I-beam with a length of about 2 m. The obtained SN behaviour has an inverse slope of 3.7 and, at high cycle fatigue, the strength is about half that of steel joints.
In this study, fracture behaviors of base metal and weld metal of ferritic steel welded joint in the thick wall pipeline for hydrogen transportation were investigated and the effects of hydrogen and ...specimen thickness (B) on fracture toughness were comprehensively considered in detail. A series of single edge notched tensile (SENT) tests for base metal and weld metal with B/W (width) ratio of 0.5, 1 and 2 were conducted with and without pre-electrochemical hydrogen charging, and crack tip opening displacement (CTOD) of δm value was obtained by the double clip gauges method. It was found that fracture toughness (δm) of base metal and weld metal decreased with increasing specimen thickness or hydrogenating, and δm of hydrogenating specimen with B/W ratio of 2 was smallest. It was believed that large specimen thickness decreased fracture toughness by constraining plastic deformation at crack tip and restricting dislocations movement, while hydrogen promoted embrittlement by reducing cohesive energy of fracture. In the hydrogenating specimen with larger thickness, there was lower dislocation density near crack tip, leading to a decrease in trapped hydrogen and intensifying the cohesive energy reduction effect, which resulted in reduced δm and the worse fracture toughness, and it means that hydrogen and specimen thickness synergistically affected fracture toughness. In addition, effect of thickness and hydrogen on decreasing fracture toughness was more pronounced for weld metal than base metal, which could be attributed to poorer plastic deformation ability of weld metal and lower dislocation density at crack tip. It is concluded that the hydrogen and thickness effects should be taken into account for the structural integrity evaluation of welded joint in hydrogen transportation pipeline.
•Hydrogen coupled with specimen thickness severely deteriorated fracture toughness of base metal and weld metal.•Significant hydrogen embrittlement in thicker specimen was due to hydrogen, plastic deformation and dislocation interaction.•The hydrogen embrittlement effect was more pronounced for weld metal than base metal.•Structural integrity evaluation for welded pipelinemust take hydrogen and thickness into account.
•The crack occurred in the overheating zone of the basic material at a distance up to several hundred µm from the fusion line.•The crack was intergranular along the boundaries of the expanded grains ...of the prior austenite.•Metallography showed the presence of precipitates of secondary carbides located along the prior austenite grain boundaries.•The most likely cracking resulting from reheating of the joint, otherwise known as annealing or reheating cracking.
The article concerns a pressure vessel operated for forty years at elevated temperature in in an ammonia production installation. During the planned control tests, unacceptable defects were detected in the circumferential welded joint of the vessel, using the ultrasonic method. In the repair process, a fragment containing a crack located in the heat-affected zone was cut out of the welded joint. The cut fragment of the joint was subjected to tests, the results of which are discussed in this article. On the basis of chemical composition, hardness, macroscopic and microscopic tests, it was determined which factors had a negative impact on the formation of the crack. The most important of them are: an increase in the hardness of the base material and grain growth in the overheating zone, as well as the formation of numerous precipitates and their segregation at grain boundaries. The reheating of the joint during its subsequent repairs should be considered a negative factor.
A dissimilar autogenous laser welded joint of AISI 430F (X12CrMoS17) martensitic stainless steel and AISI 304 (X5CrNi18-10) austenitic stainless steel was manufactured. The welded joint was examined ...by non-destructive visual testing and destructive testing by macro- and microscopic examination and hardness measurements. With reference to the ISO 13919-1 standard the welded joint was characterized by C level, due to the gas pores detected. Microscopic observations of AISI 430F steel revealed a mixture of ferrite and carbides with many type II sulfide inclusions. Detailed analysis showed that they were Cr-rich manganese sulfides. AISI 304 steel was characterized by the expected austenitic microstructure with banded δ-ferrite. Martensitic microstructure with fine, globular sulfide inclusions was observed in the weld metal. The hardness in the heat-affected zone was increased in the martensitic steel in relation to the base metal and decreased in the austenitic steel. The hardness range in the weld metal, caused by chemical inhomogeneity, was 184–416 HV0.3.
Interfacial creep failure was strongly affected by the solidified grain boundary (SGB) for steel/nickel dissimilar metal welded joints, especially at higher temperatures and lower stresses. Short, ...long, and mixed length SGBs were found as three distinct characteristics adjacent to the interface. These characteristics were attributed to the heterogeneous nucleation, multi-layer thermal cycle, and pre-solidified macrosegregation inducing local cooling rate differences, respectively. Because of the diffusion of elements C and N across the interface, short SGBs were more likely to be occupied completely by coarsening granular carbides (M23C6 and M6C) and acicular nitrides (AlN and TiN), which promoted the relative sliding of SGBs. This resulted in a large number of cavities at the interface with short SGBs, while few cavities were observed for long SGBs. Besides, the shorter side of mixed length SGBs also tended to form cavities in macrosegregation. These findings indicated that controlling the presence of short SGBs and macrosegregation could improve the creep life of the dissimilar metal welded joints.
•Three distinct SGB characteristics were found.•The effect of SGBs on two modes of interfacial failure behavior were discussed.•Mechanism of SGBs induced interfacial failure was revealed.•The relationship between macrosegregation and interfacial failure was clarified.
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