Welding in the World最新文献

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.

In the pursuit of lightweight vehicles, third-generation advanced high-strength steels (3G AHSS) with increased mechanical properties are desired to be used for critical components. However, the exposure of these zinc-coated AHSS to the manufacturing conditions during resistance spot welding can trigger liquid metal embrittlement (LME), possibly compromising the mechanical properties. As the reproducibility of LME cracks in resistance spot welding is a challenge, the effect on the static and dynamic mechanical properties of the welds is not yet fully clarified and therefore a distinction between critical and non-critical cracks is not implemented in current standards. To achieve this, it is necessary to provoke LME cracks of a given size, for example by increasing the welding current, reducing the electrode force and hold time, or using manufacturing discontinuities. Due to its significant effect on the heat input and the tensile stresses during the resistance spot welding process, which impacts the LME crack propagation, the focus of this paper is on the electrode force. An expulsion-free decreasing force profile, which consists of a force run-in, force decrease, and force run-out time, has been derived in a two-stage Face-Centered-Central-Composite design of experiment for an electrogalvanized third-generation advanced high-strength steel (3G AHSS) DP1200 HD. The crack location, length, depth, and nugget geometries were investigated for each weld. With the decreasing force profile, it was possible to generate type A, B, and C cracks by parameter adaption, with type B and C cracks being the most dominant. The type C crack formation was investigated by aborting the welding process in defined time steps and the LME cracking mechanism was confirmed by welding dezincified samples. Based on the investigations carried out, the force profile was found suitable for generating different LME crack sizes to further investigate the mechanical joint properties as it was able to reproducibly generate defined cracks without expulsion and excessive electrode indentation while maintaining a minimum nugget diameter.

Additive manufacturing (AM) is a reliable advanced manufacturing technology for producing stainless steel (SS) parts. Laser powder bed fusion (LPBF) is an essential AM technique; it has a wide range of applications in healthcare, automobiles, aviation, and agriculture due to its ability to produce SS alloys with high corrosion resistance and strength. However, achieving minimal defects and comparable mechanical properties with traditional processes is challenging. Appropriate LPBF process parameters, including scanning speed, hatch spacing, laser power, and layer thickness, are selected to overcome these challenges. The cumulative influence of these parameters with this technique is a novel method. Meanwhile, the volumetric energy density (V_ED) is one of the essential factors to integrate with these four most important processing parameters. Hence, there is a significant need to review V_ED's effect on the morphology and properties of LPBF-manufactured (LPBFed) materials. This paper provides a comprehensive overview of ongoing studies on the impact of V_ED on LPBFed steel parts, highlighting significant discoveries, challenges, and research objectives. Furthermore, this article evaluates AM’s ability to handle various types of multi-materials, particularly steel-based components; in addition, this study also evaluates multiple techniques for optimizing process parameters. The result of this review concludes by presenting future research challenges and opportunities for LPBF-processed steel alloys. This paper aims to contribute to the progress of both research and practical use of LPBF-printed steels.

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.

Wire arc additive manufacturing (WAAM) is currently one of the most promising technologies for manufacturing large-scale structures; however, its surface quality and dimensional accuracy urgently need to be addressed. Currently, research on WAAM shape control focuses primarily on single structural parts. Therefore, this study analyzes multiple factors that affect the surface smoothness of complex structural samples using proportional-integral-derivative (PID) control for the dynamic adjustment of wire feed speed to achieve superior surface flatness and establishes corresponding layer height deviation models and parameter self-learning algorithms. By controlling the surface flatness, the surface height difference could be reduced from 8 to 2 mm in the four layers. By the 30th layer, the variation in height was reduced by 88.4% compared with uncontrolled samples. Based on the surface flatness control, a closed-loop height dimensional control system was established. Under closed-loop height dimensional control, the error of the inclined edge of the sample was reduced to 0.87 mm, a decrease of 74.9%, achieving surface smoothness and dimensional precision control for intricate samples. Moreover, the sample exhibited an increase of 48.3% in the maximum available weld bead width and 40.0% in the maximum available area proportion, which significantly reduced the material removal rate.

Resistance projection welding is predominantly performed using capacitor discharge machines, known for their short welding times, rapid current rise times, and high currents compared to medium-frequency inverter technology. The resulting joints are covered up during resistance welding, so that either destructive or non-destructive testing is required to evaluate the quality. Process monitoring is therefore essential in resistance projection welding. The requirement for this is process data that can be acquired and integrated into the process monitoring easily, cost-effectively, and contactlessly. This study investigates the use of low-cost condenser microphones to utilize the airborne sound generated during welding for process monitoring. It is shown that, acoustic data processed by the fast Fourier transform can be used to evaluate the quality of the connection. Only a minor influence of the microphone position could be determined. A machine learning model was also used to detect the batch of the welding nut. The machine parameters, welding nut geometry and material were kept constant. The results show a batch prediction of more than 90% using airborne sound.

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.