Welding in the World最新文献

The object of the research reported in this study was a welded joint of Hardox Extreme steel, made using submerged arc welding (SAW) and subjected to thermal treatments involving isothermal hardening in various temperature–time variants. This treatment serves as an alternative to conventional hardening, enabling the achievement of high mechanical indices in selected cases due to the formation of fine-lath martensite or lower bainite microstructures. Heat-treated joints were analyzed macro- and microstructurally using stereoscopic, light (LM), and scanning electron microscopy (SEM). The study also determined selected mechanical properties, such as hardness, tensile strength, relative elongation, and reduction of area at break, as well as impact toughness at ambient and reduced temperatures. A separate section was dedicated to characterizing abrasion resistance in the presence of loose abrasive, along with determining the relationship between this parameter and the identified mechanical characteristics. Based on the analysis of the microphotographic images obtained, the main wear mechanisms were also characterized. The analysis of the results allowed the conclusion that in the case of isothermal hardening, the factor determining the obtained microstructural and mechanical properties is the temperature of the performed thermal operations. Furthermore, after the conducted thermal treatments, the parameters characterizing the ductility of the welded joint improved by several percent compared to the state immediately after welding. Therefore, the main goal of the technological operations conducted on welded joints of high-strength steels can be defined as improving ductility, which is justified in applications considering alternatives even to structural steels.

The effect of process parameters of DED technology on elemental segregation and crystallographic orientation of alloys was investigated. The results show that the degree of elemental segregation decreases with the increase of scanning rate, and the degree of segregation rather increases with the increase of deposition height. The microstructure of all specimens consists mostly of columnar grains grown epitaxially along the build direction, showing a clear [001] orientation. The increase in scanning rate weakens the effect of epitaxial growth of crystals, leading to a significant weakening of the strength of the weave in the [001] direction texture. In addition, the actual growth direction of the dendrites is not strictly parallel to the building direction, but is tilted towards the laser scanning direction, resulting in a large deflection angle from the building direction. Based on the synergistic effect of the local temperature gradient and the optimal grain orientation, a composite temperature gradient model is established in combination with the numerical simulation of the temperature field, which reasonably explains this phenomenon. The fundamental reason for the deflection of the dendrite growth direction is that the direction of the composite temperature gradient deviates from the build direction, and the transverse temperature gradient is larger after the scanning rate is increased, resulting in a larger deflection angle.

Buried gas pipeline is subjected to a large axial load due to earthquake-induced ground flow. The deformability of the pipeline depends on the strength of the girth weld joint. Since the heat-affected zone (HAZ) of tempered steels is locally softened due to the heat input of girth welding, the strength of the girth weld may be affected by softened HAZ. In addition, as for gas pipeline, the effect of internal pressure on the strength of the girth weld joint should be considered. Therefore, this paper proposes a tensile strength evaluation formula for girth weld joint with softened HAZ under internal pressure. The formula is developed by modifying the existing tensile strength evaluation formula of the wide plate of weld joint with softened HAZ, considering the effect of internal pressure using the elastoplastic finite element analysis. In this modification, the effect of both internal pressures on the apparent tensile strength of pipe material and the shrinkage behaviour of pipe material are focused on. Furthermore, the validity of the modified formula is demonstrated by conducting full-scale pipe tension tests.

The constantly increasing demand for renewable energy sources leads to the necessity of transporting large amounts of hydrogen. Since pipelines enable a cost-effective way for the distribution of gaseous hydrogen, the interaction of hydrogen and the pipeline materials must be carefully investigated as hydrogen can cause a degradation of the mechanical properties under certain conditions. Especially welds, which are assumed to be more susceptible to the degradation enhanced by hydrogen, are of great interest. The aim of this study is to investigate the effect of gaseous hydrogen on the mechanical properties of an X65 pipeline, and the longitudinal submerged arc welding (SAW) welded joint. The tests are conducted using the hollow specimen technique on two types of specimens: one extracted from the base material (BM) and the other extracted as a cross-weld (CW) specimen consisting of BM and weld seam. The specimens are charged in situ under a pressure of 60 bar and tested using slow strain rate (SSR) tensile tests with a nominal strain rate of 10⁻⁵ s⁻¹. The properties obtained of specimens tested in hydrogen atmosphere are compared to the properties of comparable specimen in inert argon atmosphere as a reference. The performed tests showed a decrease of the reduction of area (RA) from 72% in inert atmosphere to 52% in hydrogen atmosphere for the CW specimen and a decrease from 73% in inert atmosphere to 51% for the BM. Metallographic analyses showed the crack initiation between fine-grained heat-affected zone (FGHAZ) and BM for the specimens tested in hydrogen atmosphere as well as for the reference specimens. This leads to the conclusion that the location of the crack initiation does not change due to the presence of gaseous hydrogen.

The weld seams of large liquefied nature gas (LNG) storage tanks are long, straight butt welds made of 9% nickel steel. The GTAW process, involving AC current, torch weaving, and filler wire feeding, introduces significant interference to traditional weld seam tracking methods such as arc sensing, acoustic sensing, and laser vision sensing. Consequently, welding has long relied on manual operation, resulting in inconsistent weld quality and high labor intensity. This paper proposes a passive vision-based weld seam tracking method to address the limitations of traditional methods under these working conditions. A series of algorithms, including pixel grayscale calculations, particle filtering, and summation-difference methods, were used to extract the arc, molten pool regions, and groove edges from the images. The average deviation and arc length over one torch weaving cycle, filtered through Kalman filtering, were calculated to achieve GTAW weld seam tracking under these conditions, effectively mitigating interference from the aforementioned factors in feature extraction. Real-time monitoring and control welding experiments were conducted on workpieces with preset offset trajectories, producing smooth and flat weld seams. The detection accuracy can reach up to approximately 0.019 mm, with an average processing time of 58.37 ms per frame. The detection accuracy and system response time meet the requirements for industrial applications.

Inconel 625 alloy, known for exceptional mechanical properties and corrosion resistance, is widely used in aerospace, power generation, and marine applications. Laser powder bed fusion (LPBF) excels in manufacturing complex geometries with good surface finish. However, LPBF printed microstructure is highly heterogeneous due to the rapid and complex thermal cycles, necessitating careful parameter selection to prevent the stabilisation of detrimental phases. Experimental parametric optimisation of LPBF is challenging due to the cost and complex inter-playing process variables. Therefore, mathematical modelling is advantageous for optimising LPBF parameters. A 3D heat source model was developed using finite element method (FEM) to analyse thermal cycles with bed-preheating and varying laser parameters in LPBF of IN625. The model focused on a simplified thermal cycle method, where all elements in a layer were set to melt at once to reduce the computational time. A multi-phase-field method (M-PFM) was developed to simulate the microstructural evolution as a function of FEM-generated thermal boundary conditions. The morphological and elemental segregation behaviour of evolving microstructure was simulated. The dendrite morphology predicted by simulations showed strong agreement with experimental observations. The primary dendritic arm spacing (PDAS) obtained from phase-field and analytical models matched the experimental trends, validating the adapted modelling approach. The segregation and the microstructural evolution were found to be strongly influenced by the prevailing temperature gradients and the cooling rates of the melt pool, along with the peak temperatures reached during the remelting cycles.

The use of laser powder bed fusion (LPBF) for faster and more customized manufacturing has grown significantly. However, LPBF parts often require welding to other components, raising concerns about their weldability due to differences in microstructure compared to conventionally manufactured parts. Despite its importance, research on the weldability of additive manufacturing materials remains limited. This study aims to evaluate the susceptibility of LPBF 316L stainless steel to weld solidification cracking using transverse varestraint testing and compare results with conventional 316L. Tests were conducted across strain levels from 0.5 to 7%, revealing a saturated strain of 4%, with maximum crack length (MCL), maximum crack distance (MCD), and total number of cracks (TNC) of approximately 0.36 mm and 31, respectively. Compared to existing literature, LPBF 316L produced with optimized printing parameters and low nickel equivalent content exhibited higher resistance to weld solidification cracking, reflected in lower MCL and MCD values. Cracks initiated at the solidus interface and propagated along the ferrite–austenite boundary under strain. Microstructural changes were observed after testing, transitioning from cellular austenitic solidification in LPBF to a skeletal ferrite-austenitic mode due to material remelting and slower cooling rates. These findings highlight that reduced nickel equivalent, alongside optimized printing parameters, contribute to enhanced weld solidification cracking resistance in LPBF 316L. This study advances understanding of the weldability of LPBF materials.

The Goodman-Smith (GS) diagrams are widely used for fatigue strength assessment of bogies as a common method for welded structures. The traditional GS diagrams proposed by the UIC ORE B12/RP17 standard suffer from the problems of too large a safety factor leading to optimistic assessment results and data scarcity. Therefore, an improved method of GS diagrams for base metals and welded joints was proposed. The traditional GS diagrams were improved by combining the IIW standard and the unilateral tolerance coefficient method. The design guidelines of the traditional GS diagrams were incorporated into the improved GS diagrams to obtain the improved design guidelines. Within this framework, the improved GS diagrams were validated by applying base metal specimens with three common welded joints. The results showed that the safety factor was reduced to 0.3–0.5 times the original factor for the same survival rate and confidence level. The accuracy of the fatigue strength assessment was improved. Finally, the improved GS diagrams were used for the fatigue strength assessment of the critical base metal and weld region of the bogie frame, which provided a new reference for the fatigue strength assessment research in the field of rail transport.

Additive manufacturing (AM) has contributed to significant advances in the production of aluminium alloys, particularly through powder bed fusion (PBF) and directed energy deposition (DED) processes. However, joining of conventionally and additively manufactured components remains essential. This work focuses on the weldability of AM aluminium alloys using fusion and solid-state welding processes. The study analyses the microstructural evolution and mechanical properties, revealing a relationship between AM technology and joining process. In particular, fusion welding of PBF-laser beam (LB) produced aluminium alloys presented a significant limitation due to the high porosity level, especially in the weld zone near the PBF-LB base material. This region of high porosity, known as the pore belt region, has an enormous detrimental effect on the mechanical properties of the weld. This phenomenon is not observed when the welds are carried out by solid-state welding processes, which makes this group of welding processes very suitable for this type of material. On the other hand, fusion welding of aluminium alloys produced by wire arc additive manufacturing (DED-Arc or WAAM) exhibits a good stability and repeatability, analogous to conventional aluminium alloy welding practices. Rotational friction welding of DED-Arc-produced components presented an unexpected challenge. Due to the difference in ductility compared to conventionally manufactured parts, the process window for optimal process pressure was found to be very narrow and sensitive. The findings are confirmed by metallographic examination, hardness profile measurement, tensile and bend testing.

New electrical machines for passenger cars are gaining popularity. These electrical machines which contain copper parts need to generate a magnetic field to generate the propulsion of the machine. Laser welding is a fast and an effective joining process for the copper parts. In order to determine the lifetime of the copper parts, it is necessary to assess the fatigue behavior of the laser weld seam. Current guidelines for fatigue assessment do not include copper parts or copper weld seams, hence a fatigue concept must be derived. This proceeding examines the applicability of the notch stress concept with a reference radius of 0.05 mm for copper weld seams and provides a complex and a simplified way of modeling the weld seams. The presented concept takes the geometry of the weld seams and the fracture area surfaces into account. This leads to stress results with a low scatter range and a flat slope of the S-N curve. Furthermore, the results indicate that the notch stresses are transferable.