Welding in the World最新文献

In response to the high standards demanded by marine engineering equipment for the strength and toughness of high-strength steel welded joints, this study systematically explores the effects and synergistic interactions of key alloy elements such as Mn, Ni, and Cu on the microstructural evolution mechanism, phase transformation behavior, and comprehensive mechanical properties of submerged arc welding deposited metal in 440 MPa grade high-strength low-alloy marine steel. Three welding wires with gradient variations in Mn, Ni, and Cu contents were designed and fabricated, followed by deposition experiments combined with OM, SEM, and TEM characterizations to analyze macroscopic morphology, microstructural constituents, and their evolution. Complementary JmatPro simulations of CCT curves and transformation temperatures further elucidated the relationships between alloying, microstructure, and properties. Mechanical testing revealed that increasing Mn, Ni, and Cu contents effectively promoted acicular ferrite (AF), significantly reduced proeutectoid ferrite (PF), ferrite side plates (FSP), and brittle M-A constituents, while refining and optimizing ferrite lath morphology, resulting in a denser and more homogeneous structure. Thermodynamic analysis indicated enhanced austenite stability and increased hardenability due to the alloying additions. The weld metal produced by wire #3 exhibited superior properties, including a yield strength of 523 MPa, tensile strength of 615 MPa, yield-to-tensile ratio of 0.85, and a high absorbed impact energy of 163 J at -40℃, with fracture mode transitioning to ductile dimples and quasi-cleavage. Overall, moderate additions of Mn, Ni, and Cu synergistically refined the microstructure and enhanced toughness, enabling wire #3 (Mn = 1.27%, Ni = 1.17%, Cu = 0.15%) to achieve optimal strength-toughness matching with the base metal, thereby fulfilling the demanding safety and reliability requirements of welded joints in harsh marine environments.

Wire and arc additive manufacturing (WAAM) facilitates the production of substantial near-net-shape components by layer-by-layer deposition. This work examines the effects of post-heat treatments (PHTs) on the microstructure, elemental distribution, and mechanical properties of pulsed-WAAM Hastelloy C-276 thin walls. Characterisation was performed using SEM/EDS, XRD, and EBSD on as-deposited (AD) and PHTed samples. Solution annealing (SA) yielded regenerated equiaxed grains, in contrast to the AD and double-ageing (DA) conditions. SEM/EDS of SA-1 showed a homogeneous Mo distribution devoid of coarse Mo-rich precipitates, whereas EBSD indicated a significant decrease in low-angle grain boundaries (68.3% in AD). Microhardness reached a maximum of 336 HV (SA-1) and 326 HV (SA-2), in contrast to 302 HV (AD) and 260 HV (DA). SA-1 had the most significant enhancement in strength, increasing from 790 ± 16 MPa (AD) to 892 ± 6 MPa. The fracture morphology under all conditions was primarily ductile, with infrequent transgranular and intergranular characteristics.

A novel powder-feed underwater laser metal deposition (ULMD) technology was developed for the in situ repair of the damaged components in an underwater environment. In this research, the Ti6Al4V block was fabricated by the powder-feed ULMD process in an underwater environment. A developed drainage device was used to generate a local dry cavity to realize the interaction between the laser and materials. The morphology features, microstructure, and mechanical properties of the ULMD block sample were investigated. The results show that the ULMD-produced Ti6Al4V presents a continuous and uniform surface, and no pores or incomplete fusion defects are observed in the deposited parts. The acicular α′ martensite within the columnar prior-β grains is formed due to the rapid cooling rate caused by water and gas flow. The tensile test demonstrates the ULMD sample has a higher strength and lower elongation compared with in-air LMD or wrought material.

This research investigates the effect of process parameters on AA5083/CeO2/TiO2 nanocomposites, focusing on microstructure, hardness, tribological properties, and corrosion resistance. Additive-manufactured aluminum alloy-matrix hybrid nanocomposites were produced using a combination of six different rotational and vertical speeds through modified friction stir deposition, and an additive-manufactured non-composite sample as a reference was produced to be compared with manufactured nanocomposite samples. This study investigated microstructure evolution, characteristics, phase distribution, corrosion resistance, hardness, and tribological behavior of samples. Grain refinement improved by 28.8% to 36.6% compared to the reference (6.28 μm grain size) due to the addition of nanoparticles, shear of friction stir rotation, and heat generation. Decreasing the vertical speed from 35 to 15 mm/min and the rotation speed to 700 rpm caused higher shear and suitable nanoparticle distribution, which resulted in 4% and 10.9% grain size improvement, respectively. Decreasing the grain sizes and the addition of hard nanoparticles caused hardness to increase from 8.75% to 14% compared to the reference (89.4 Hv). Wear rates improved from 0.2 × 10^–3 to 0.1 × 10^–3 mm³/N·m, compared to the reference wear rate of 0.25 × 10^–3 mm³/N·m due to nanoparticles addition, the samples' higher hardness, and the nanoparticles' suitable distribution.

High‑strength steels (HSS) are increasingly used in modern structural engineering due to their improved strength‑to‑weight efficiency and sustainability benefits. This study presents an extended formulation of the regular inclined shell element model (RISEM) through the incorporation of a Eurocode‑compatible plastic strain limit for predicting the resistance of fillet welded connections. The enhanced model employs equivalent plastic strain (PEEQ) as the ductile failure indicator, aligned with EN 1993‑1‑5 Annex C, enabling strain‑based verification without dependence on fracture calibrations. A comprehensive mesh sensitivity study and strain‑limit evaluation demonstrate that RISEM achieves stable predictions using mesh sizes between a/15 and a/20, with weld resistance variations remaining below 8% for the full 2–6.4% strain‑limit range. Verification against analytical design resistances confirms that the strain‑limited RISEM is accurate, computationally efficient, and suitable for design applications. The study delivers practical design recommendations for engineers using HSS welded connections under ULS verification conditions.

The challenging problem of quantitatively regulating friction rolling additive manufacturing (FRAM) process parameters to optimize forming quality and morphology is addressed in this study. A quadratic regression orthogonal combination method is employed to establish the relationship between process parameters, deposition height, and forming quality, thereby constructing a theoretical model of single-pass cross-section deposition. The results indicate that during FRAM multilayer deposition, the deposition height tends to stabilize as the number of layers increases. Among the process parameters, tool head speed has the most significant impact on deposition height. Additionally, the lift-off amount should be smaller than the deposition height to effectively prevent the formation of interlayer defects. This research facilitates stable control of FRAM deposition morphology and layer height and provides valuable guidance for selecting process parameters.

The directed energy deposition-arc (DED-Arc) process, using high-strength low-alloy (HSLA) feedstock wire, presents a promising solution for fabricating large-scale steel connectors in civil engineering. Due to the use of carbon steel feedstock wire, corrosion protection of the 3D-printed components is necessary. Therefore, this study investigates low-pressure cold spray (LPCS) as a method for applying zinc-based coatings. Two sets of thin walls were 3D-printed: one set uncoated and one set coated with LPCS Zn + Al₂O₃ coating. This LPCS coating was successfully deposited on untreated and on grit-blasted DED-Arc surfaces. Coating thicknesses exceeding 300 µm as well as electrochemical polarisation analysis confirmed sufficient corrosion resistance of the coated as-built specimens. To evaluate the influence of the surface condition and the coating process on the mechanical behaviour, dog-bone tensile specimens were extracted from the walls, 3D-scanned, and subsequently mechanically tested. Structured-light scanning of the geometry revealed different scatter of the specimens’ thickness based on their orientation with respect to the build direction. Uniaxial quasi-static tensile tests, combined with a four-camera digital image correlation (DIC) system, were performed both on specimens with machined surfaces and with LPCS Zn + Al₂O₃ coating on the as-built surface. While the machined specimens exhibited nearly isotropic behaviour, the coated as-built specimens showed pronounced anisotropy with comparable mechanical properties to uncoated as-built specimens from literature when excluding the coating thickness from the load-bearing cross-section. The LPCS Zn + Al₂O₃ coating led to a reduction of the corrosion rate by two thirds compared to uncoated HSLA DED-Arc.

FeCoNiCrAl high-entropy alloy (HEA) coatings were fabricated on the surface of 9Cr18 bearing steel using laser cladding technology. A total of nine experiments were conducted based on an L9(3⁴) orthogonal array with three selected factors at three levels. Range analysis and signal-to-noise (S/N) ratio analysis were employed to investigate the effects of laser power, scanning speed, and powder feed rate on microhardness and dilution rate. Cross-sectional defects were observed using a super-depth-of-field microscope. The microstructure, crystallographic orientation, and elemental distribution of the cladding layers were systematically characterized by metallographic analysis, electron backscatter diffraction (EBSD), and energy-dispersive spectroscopy (EDS). The results showed that the powder feed rate had the most significant effect on microhardness. The maximum microhardness of 597.86 HV was achieved under the condition of 1.3 r/min powder feed rate, 6 mm/s scanning speed, and 2100 W laser power. Scanning speed was the dominant factor affecting dilution rate, which reached a minimum of 28% at 1.3 r/min powder feed rate, 5 mm/s scanning speed, and 1800 W laser power. The cladding layer exhibited a gradient microstructure, with equiaxed grains in the upper region, mixed grains in the middle, and fine columnar grains near the substrate. EBSD analysis revealed that the cladding layer was mainly composed of a BCC phase, while the heat-affected zone (HAZ) consisted primarily of an FCC phase. A local BCC/FCC mixed-phase region was also observed, which may increase the risk of stress concentration.