Welding in the World最新文献

In this research, the effects of the welding angle on the behavior of the molten pool, keyhole, and welding defects in the laser-MAG hybrid welding process of 14-mm-thick AH36 high-strength shipbuilding steel are thoroughly analyzed. High-speed photography was used to observe the behavior of the molten pool and keyhole, while synchronized oscilloscope measurements revealed a strong correlation between arc voltage fluctuations and keyhole oscillation frequencies, demonstrating the dynamic interplay between arc plasma and keyhole stability. The results reveal that the welding angle significantly affects the quality of weld formation, molten pool flow, keyhole behavior, collapse, and bottom hump, as well as spatter phenomena. When the welding angle is 82.5°, optimal weld formation quality is achieved, characterized by a stable molten pool shape and regular keyhole behavior. At a 75° welding angle, the molten pool shape and keyhole behavior exhibit significant instability, leading to poor weld formation. This results in the periodic formation of the narrowest throat on the surface of the molten pool, presenting a wide-narrow-wide serrated characteristic, which triggers surface collapse and hump defects. Furthermore, at a 97.5° welding angle, intense unstable fluctuations occur within the molten pool, causing the molten metal to overcome surface tension and bulge beyond the surface of the molten pool, forming violent fluctuations and a raised liquid column that progressively detaches from the molten pool to form spatter. The research findings indicate that an appropriate welding angle can optimize the behavior of the molten pool and reduce welding defects.

This study deals with the validation of the fatigue design values given in the IIW Recommendations for the HFMI Treatment for HFMI-treated steel joints under bending loading. In total, ten data sets involving T-joint specimens under bending loading with varying specimen geometries and base material yield strengths are investigated. The load stress ratio was R = 0.1 in all test series. The corresponding FAT-classes are defined on the basis of the IIW Recommendations for the HFMI Treatment in dependence of the structural detail and the yield strength of the base material. Furthermore, the thickness as well as certain thinness effect is covered by an IIW-recommended factor f(t) in one case leading to a design curve HFMI-IIW with f(t). In another case, a factor k_tb based on the British Standard BS 7608 is additionally considered, which combines the thickness as well as bending effect. The corresponding design curve is denoted as HFMI-IIW with k_tb. A comparison of the fatigue test data points and the related statistically evaluated S/N-curve for each data set with the two approaches reveals that the design curve HFMI-IIW with f(t) leads to a conservative assessment for all data sets involved in this study. Also, a certain thinness effects is well covered and still a proper fatigue design should be ensured. Focusing on the design curve HFMI-IIW with k_tb, which additionally covers the bending effect, a conservative assessment is observed for almost all data sets. However, it is concluded that further test data especially for reduced plate thicknesses should be assessed to provide additional comparison results and ensure a conservative applicability for HFMI-treated steel joints under bending loading in any case.

The fatigue strength of steel structures can decrease significantly when corrosion occurs. Pitting corrosion, in particular, can lead to locally high stress concentrations and may interact with existing stress concentrations from weld seams. Particularly in the case of offshore support structures, which are exposed to a corrosive environment and include several welded connections, this issue becomes relevant. Hence, in this study, butt- and fillet-welded joints of structural steel were exposed to accelerated corrosion in a salt spray chamber and then tested for fatigue strength. In order to investigate the long-term behaviour, the specimens were stored for 12 months in a salt spray chamber. Base material specimens were investigated as reference. All specimens were clean blasted and 3D scanned prior to the fatigue tests. It was shown for all specimens that the fatigue strength decreased after 12 months compared to the uncorroded reference tests. However, the fatigue reduction was different for the different geometries. The greatest reduction was observed for the base material from 282 to 122 N/mm², followed by butt-welded joints from 215 to 147 N/mm², and fillet-welded joints from 168 to 144 N/mm². As the fatigue strengths showed only minor difference after 12 months, an equalization effect can be assumed. The results show that a generalized reduction of the fatigue strength, in accordance with the guidelines, is not appropriate and therefore should be revised for a more accurate design of offshore support structures. Finally, numerical analysis based on 3D scans of the specimens was conducted and compared with the test results.

Arc-based directed energy deposition (DED-Arc) is a promising manufacturing technology on the rise in the industry. On the one hand, convincing process advantages, such as the possibility of sustainably producing complex and large-volume component geometries with comparatively high building rates, favor further industrial interest. On the other hand, there are still challenges, like the difficulty of controlling heat input and the intricate thermal history. The resulting temperature gradients and heat accumulations lead to inhomogeneous component properties and reduced process efficiency, which delays further establishment in the manufacturing industry. Therefore, implementing and developing concepts for thermal management in DED-Arc is necessary. The study examines how controlling the substrate temperature can affect the dimensional accuracy, microstructure, and hardness of DED-Arc components. Different preheating and in situ cooling strategies were developed based on numerical investigations, including a water-cooled in situ cooling unit, a cobot-guided inductor, and classical preheating approaches. The findings indicate that substrate tempering significantly impacts the penetration zone and heat-affected zone dimensions, layer widths, microstructure, and hardness profiles. A special combination of preheating and in situ cooling resulted in enhanced substrate bonding, uniform layer widths (4.0 ± 0.1) mm, and consistent hardness values (142 ± 10) HV due to a more uniform microstructure. These results indicate that integrated substrate plate tempering can significantly improve thermal process control in DED-Arc, supporting its further industrial establishment.

Low transformation temperature (LTT) welding consumables represent an innovative approach to realize compressive residual stress in the weld seam and HAZ. LTT welding consumables use the volume-expanding martensitic phase transformation near room temperature to generate compressive residual stress during cooling. This article focuses on the weld geometry and its influence on residual stress reduction using an LTT welding consumable. For this purpose, layers with an LTT welding consumable were additionally applied to the front sides of conventionally welded longitudinal stiffeners. Different weld geometries of the second weld seam could be realized by varying the welding parameters. These samples were analyzed for geometric parameters, chemical composition, and residual stress. While the chemical composition and martensite start temperature (M_S) were only slightly influenced by parameter changes, a clear influence with regard to residual stress and weld geometry was observed. Depending on the shape of the second LTT weld seam, residual stress reductions of 200 to 500 MPa were achieved using the same LTT welding consumable.

The mechanical properties of P92 (9Cr-0.5Mo-1.8W-VNb) steel weld joints, fabricated through tungsten inert gas (TIG) and activated TIG (A-TIG) welding, were compared. The non-monotonous variations in tensile and creep properties across the heterogeneous microstructural regions of both the weld joints were obtained using small specimen testing techniques. The A-TIG weld joint showed higher tensile strength than conventional TIG weld joint. The weld metal of A-TIG showed better creep resistance compared to the other zones of the A-TIG as well as all zones of the conventional TIG weld joint. The activation energies under creep for both the weld joints were found to be in the range of 385–418 kJ/mol, indicating that dislocation creep is the governing creep mechanism under investigated conditions. The low cycle fatigue behaviour of both the weld joints were evaluated under the applied strain amplitudes between ± 0.25 and ± 0.6% at room temperature and at 873 K. Both the weld joints exhibited continuous cyclic softening before a drastic reduction in the stress value due to the macrocrack propagation and eventual failure. The A-TIG weld joint showed better fatigue life than conventional TIG weld joint.

There are several guidelines and standards for assessing the load capacity of welds in terms of static loading. The individual procedures – among other things – differ in the limit state considered, the characteristic stress calculation, the material data used and the critical region’s location. Therefore, they lead to different allowable limit loads. The question naturally arises as follows: What is the most accurate calculation? This paper offers an answer to this question for the case of a non-load-carrying weld specimen made of S235JRG2. The specimen under investigation was subjected to the static strength assessment via ČSN 05 0120, Eurocode 3, AWS D1.1/D1.1M:2020, AISC, FKM and the FEMFAT software. Subsequently, an experiment was carried out for a given geometry and a combination of base and weld materials. The methods best correlating with the experiment were uncovered. The rupture of the specimen did not occur near the notches of the weld seam but in the region of the largest plastic deformation. This was also confirmed by a finite element analysis.

High-speed laser cladding was utilized to deposit a stainless steel coating on an S890 high-strength steel shaft and a laser power range of 2400 to 4200 W. The microstructure, mechanical properties, and grain growth behavior of the coating were systematically investigated. As the laser power increases, coating thickness, the width of the heat-affected zone, and the dilution rate exhibit a gradual upward trend, whereas the surface roughness initially decreases and subsequently increases, the grain size initially decreases and subsequently increases, and the element distribution becomes progressively more non-uniform. The microstructure of the coating predominantly consists of fine equiaxed grains and columnar grains, with the major phase being α-Fe. Compared to the substrate, the coating demonstrates enhanced hardness and corrosion resistance, the maximum hardness of the coating increases by 131.3%, and the corrosion tendency of the optimal coating decreased by 81.8%. Crystal grain refinement, homogeneous distribution of elements, and a high content of high-angle grain boundaries contribute to impeding dislocation movement, thereby prominently enhancing the mechanical properties of the coating. The high-speed laser cladding technology not only facilitates the improvement of the coating’s forming quality but also reinforces its surface strength and comprehensive performance.

The use of biomedical titanium alloys is gaining more and more interest and attention. In this work, the Ti-Zr–Nb system alloy was produced and studied, as well as its powder, that was obtained by the hydrogenation-dehydrogenation method. Challenges associated with using powders obtained through this method are discussed. Based on the obtained powder, an experimental metal powder wire was made, which was used as filler material for TIG surfacing. As a result, a multilayer deposited detail was obtained, and its microstructure and properties (modulus of elasticity and microhardness) were investigated.

Offshore wind turbine support structures endure significant cyclic fatigue loads, causing peak stresses at welded joints, which can lead to crack initiation and structural failure. The fatigue performance of welded tubular joints is therefore critical in ensuring safety and extending service life. Challenges arise in assessing joints with varying overlap ratios and with or without hidden welds, as traditional methods often fail to capture the complexities of residual stress and welding deformations that influence fatigue behavior. In this study, fatigue analysis of tubular joints with or without hidden weld and with different overlap ratios was conducted to estimate the fatigue life and predict the crack initiation positions. The 3D fatigue FE analysis is based on constitutive equations, thermal elastoplastic analysis, and continuum damage mechanics. Residual stresses and welding deformations were modeled to simulate the weld’s initial state, providing realistic input for cyclic loading in the FE analysis. The study aims to estimate fatigue life and identify likely crack initiation sites in various tubular joint configurations under cyclic fatigue loads. S–N curves obtained through this analysis were compared with Eurocode 3 standards, validating the approach. The study offers refined insights into fatigue behavior across joint types, supporting safer, more reliable offshore wind turbine designs.