Welding in the World最新文献

This study investigates the influence of surface integrity and the localized fatigue phenomena on the initiation and propagation of short fatigue cracks in high-frequency mechanical impact (HFMI)-treated welded joints. The treated surface region, characterized by a compressive residual stress field, smooth notch geometry, and work hardening layer, improves welded joints’ fatigue strength. However, how these surface conditions influence the fatigue damage process zone during short crack initiation and growth is not yet well known. Therefore, this study systematically investigates the influence of different surface characteristics on fatigue life modeling of HFMI-treated welded joints made of high-strength steel. This is achieved using a non-local continuum damage mechanics-based approach of crack growth and elastic–plastic finite element simulation, explicitly modeling treated surface conditions. The simulated fatigue life is first verified with experiments and then applied to various surface conditions. The simulation results show that most of the fatigue life is spent until a crack size of 0.2 mm. The compressive residual stress field greatly extends both short crack initiation and propagation life, with its degree of contribution highly dependent on loading history and residual stress change. The role of the work hardening layer is mainly concentrated on improving fatigue life during short crack initiation and the very beginning of short crack growth.

This study investigates the friction stir butt of 2024 aluminum alloy with 6061-T6 aluminum alloy using both double rotating shoulder friction stir welding (double rotating shoulder friction stir welding, DRS-FSW) and conventional friction stir welding (FSW) techniques. The differences in joint structure and morphology and mechanical properties between DRS-FSW and FSW joints were investigated. Defect-free joints were obtained for both DRS-FSW and FSW at a rotational speed of 600 r/min and a welding speed of 30 mm/min. Compared to the cross-section morphology of the dissimilar aluminum alloy joints of FSW, the morphology of the shoulder-affected zone (SAZ) and weld nugget zone (WNZ) of the DRS-FSW joints is more complex. The longitudinal morphology of the DRS-FSW joints shows complex material flow variations. The microstructure of the weld nugget zone (WNZ) of DRS-FSW joints is dominated by recrystallization. The microhardness magnitude and distribution are approximately the same for both. The FSW tensile properties are higher than those of DRS-FSW. Both DRS-FSW and FSW tensile fracture locations are in the heat-affected zone (HAZ) on the retreating side (RS) of the joint, and both exhibit ductile behavior. This paper is a further exploratory study of the double stirring technique.

The weldability of stainless steels is largely controlled by the chemical composition, and alloys with ferritic or ferritic-austenitic solidification show the highest resistance to hot cracking. As the resulting phase balance also affects the final properties, it may be beneficial to both foresee and measure the weld metal ferrite content. The WRC ‘92 constitution diagram is currently the most accurate prediction tool available, but it does not take the cooling rate into consideration and the precision may be less accurate for stainless steels with high ferrite numbers (FNs). This study aims to assess the reliability of the WRC ‘92 diagram for weld metals with FN > 50. The chemical composition was altered through gas tungsten arc welding (GTAW) of UNS S32205 with ER347 filler wire that had been coated using physical vapor deposition (PVD) with either niobium (Nb), copper (Cu), nickel (Ni), manganese (Mn), carbon (C), or silicon (Si). The actual ferrite content was evaluated using image analysis, FeriteScope and X-ray diffraction (XRD). While predictions from the WRC ‘92 diagram were deemed acceptable for Ni, Si, and Mn, notable deviations were observed for Nb, Cu, and C. The FeriteScope exhibited a consistent trend with image analysis, albeit with slightly higher FN values, wider scatter, and the conversion factor from FN to vol% is open for discussion. The lowest accuracy and largest spread were obtained using non-contact XRD, rendering it unsuitable for ferrite measurements of welds. These findings underscore the need for improved prediction tools and appropriate measurement methods for assessing ferrite content in duplex weld metals.

Although laser-welded additively manufactured Inconel 718 joints find numerous high-temperature industrial applications, their strengthening and embrittlement mechanisms remain underexplored. To bridge this gap, we herein prepared such joints by the laser welding of the as-built material (built-LW), laser welding of double-aging heat-treated as-built material (DAT-LW), and double-aging heat treatment of laser-welded as-built material (LW-DAT). The microstructures of the joint fusion zones (FZs) were examined using scanning electron microscopy (electron backscatter diffraction and secondary electron imaging), while nanoscale features were probed by transmission electron microscopy, and mechanical properties were evaluated using microindentation hardness (H_IT) measurements and tensile tests. The FZs of the built-LW and DAT-LW joints contained no strengthening precipitates, such as the Laves phase and γ′ and γ″ nanoparticles. In stark contrast, the FZ of the LW-DAT joint contained spherical nanoparticles of the γ′ and γ″ phases responsible for precipitation hardening. The DAT-LW joint displayed base metal (BM) strengthening and FZ softening (H_IT = 6.47 and 3.6 GPa, respectively), whereas the LW-DAT joint demonstrated BM and FZ strengthening (H_IT = 6.2 and 6.5 GPa, respectively). The built-LW joint exhibited the lowest ultimate tensile strength (UTS) of 833 MPa, primarily because of the absence of strengthening precipitates. The DAT-LW joint, despite experiencing FZ softening, exhibited a higher UTS of 1086 MPa and a limited elongation of 2%, while the LW-DAT joint featured the highest UTS of 1440 MPa, primarily because of the enhancement of nanosized γ′ and γ″ strengthening phases facilitated by postwelding double-aging heat treatment.

The high mechanical stresses that may be linked to the operation of French Navy ships and in particular the operating conditions of submarines must be considered right from the preliminary design phases. The failure to define special requirements may expose large-sized parts or weld fabricated assemblies to the risk of sudden fracture in the presence of flaws or cracks, right from the phase of admission of the naval platform to active service. This risk needs to be ruled out through laboratory tests. As early as the 1950s, Pellini’s work led to the development of several tests aimed at preventing this type of risk. The best known of these tests is the eponymous test or drop weight test. While this test became fundamental to determining the characteristic brittleness temperature of ferritic steels, Pellini also developed other less well-known tests. The impact of preparing the test pieces for this Pellini test gave rise to numerous studies, the guiding principle being to consolidate the resulting reference nil-ductility transition temperature (RT_NDT), which is a key element in guaranteeing the service life of a nuclear reactor component in service. The work presented in this article focuses on fracture behaviour and the prevention of sudden fractures on nuclear propulsion components. The study is focused on the work of William S. Pellini in order to propose a “modified” Pellini test giving access to a toughness transition (type T0) with a test that costs less to implement and requires less material. This article presents an experimental strategy and makes a comparison between different test results obtained on several parts to give credit to the approach and build a strategy to standardise the method.

Stellite 6 hardfacing is deposited on Haynes 282 and Inconel 740H via plasma transferred arc (PTA) welding. The fabricated hardfacing specimens are subjected to different post-welding heat treatments, and then aged at 760, 815 and 871 °C for a time length ranging from 1000 to 30,000 h. The microstructures of the hardfacings before and after long-time aging are investigated with SEM/EDS/XRD. It is shown that the PTA welding process causes the hardfacing microstructure deviating from Stellite 6 alloy due to dilution. With participation of other elements from the substrate material, the compositions of both solid solution and carbide/intermetallic of the Stellite 6 hardfacing are modified. In the meanwhile, Ti–rich or Ti/Nb-rich new phases are generated. Long-time aging has an impact on the microstructures of the hardfacings, but at 760 °C, especially for an exposure time less than 20,000 h, the microstructures of the hardfacings do not show obvious change. However, when the hardfacing specimens are aged at 815 and 871 °C even for an exposure time of 1000 h only, Al-rich precipitates can occur, and the amount of the precipitates increase with aging time. These brittle precipitates generally have a detrimental effect on the performance of the hardfacings because they can deteriorate the ductility of the hardfacings. With the presence of Al-rich precipitates the hardness of the hardfacings decreases.

The welding of steel grades relies primarily on the interaction of the weld metal with doped oxygen components of the shielding gas. This mainly serves to decrease the viscosity and reduce the surface tension of the melt in order to achieve an adjusted material transition. Interference with the ambient atmosphere is undesirable in this context. In order to prevent material-related changes in the microstructure, slag initiators are admixed which promote the precipitation of low-density oxides on the weld seam surface. Manufacturing technology is increasingly striving to eliminate the interaction of atmospheric oxygen in the production process. It is primarily intended to counteract the negative effects of oxygen during manufacturing. For this objective, silane-doped gases for subtractive manufacturing processes and additive manufacturing via the PBF-LB/M process have been considered. Small amounts of silane in conventional inert shielding gases allow partial pressures of oxygen that are comparable to a high vacuum. In the scope of this publication on investigations for welding applications, blind welds on S355 substrate plates were performed using G3Si1 filler material. In addition to the recommended M21, an argon shielding gas with 1.5% silane doping and argon 4.6 are applied for welding. Apart from the observation of the resulting energy input, the weld seams are metallographically characterized. For this purpose, the formation of silicates on the weld seam surface and the development of the weld seam within the base material are investigated. The volume of the weld seam is reduced as a result of the silane doping compared to the M21 application. The composition of the weld metal is significantly influenced by the silane content, leading to an increased manganese content in particular. The silane doping results in an intensified formation of an acicular bainitic structure and an accompanying hardening within the weld metal.

Important variables such as temperature, time, surface quality, atmosphere, chemical composition, and interlayer thickness affect the quality of the transient liquid phase (TLP) bonding. The mentioned factors have an essential role in the behavior of the created joints by affecting the formation of intermetallic phases. In this research, the TLP joints of Hestalloy X (HX) superalloy were prepared by a Bni–2 interlayer with a thickness of 80 µm and at a bonding temperature (T_b) of 1070 °C. The joining process was done in different atmospheres, including air, argon, and vacuum (10⁻⁵ torr) for 40 min. Field-emission scanning electron microscope (FESEM), X-ray diffraction analysis (XRD), microhardness, and shear tests were employed to check the samples’ mechanical and metallurgical aspects. The results of microstructural investigations showed that joints prepared under argon and air atmospheres contain holes and porosities due to the partial oxidation of the joint-base metal (BM) interface. The results of mechanical tests prove that the joint made in the vacuum has the best shear strength (about 80% of the strength of the BM). This is attributed to the diffusion of the boron element into the BM and the reduction of harmful intermetallic borides in the bonding region.

In the underlying study, a method has been proposed to automatically extract finite element (FE) peak stresses of welded components to alleviate human errors and increase the calculation accuracy. The approach is based on the K-means and DBSCAN (density-based spatial clustering of applications with noise) methods as the unsupervised machine learning approaches. Data points, in this case, nodal coordinates and their corresponding stress magnitudes, are grouped within different clusters. The peak stress in each dense region (cluster) is then highlighted and reported automatically. Parametric and comparative studies have also been carried out in order to detect optimised parameters of the K-means and DBSCAN algorithms. The methodology will ultimately be used for more reliable stress analysis in fatigue assessment of welded structures.