Yongdian Han

DH36/EH420 dissimilar‐steel welded joints (DSWJs) are increasingly used in lightweight marine structures, where fatigue performance is a critical concern. In this study, the fatigue behavior of DH36/EH420 DSWJs was systematically investigated by combining conventional stress‐life (S–N) testing with fracture‐mechanics‐based fatigue crack growth (FCG) analysis. For comparison, EH420‐EH420 welded joints (WJs) were also examined in the S–N tests. The results show that the DH36/EH420 DSWJs exhibited lower fatigue strength, with fatigue cracks preferentially initiating and final fracture occurring in the DH36 base metal (BM), consistent with the tensile fracture location. In contrast, FCG tests performed in five representative microregions showed that the highest crack growth rates occurred in the two heat‐affected zones (HAZs), followed by the DH36 BM, weld metal (WM), and EH420 BM. Microstructural characterization further supported the observed fatigue strength and crack growth trends. These findings indicate that, in the investigated DH36/EH420 DSWJs, the region controlling total fatigue life differs from the region most sensitive to long‐crack growth, corresponding mainly to the DH36 BM and the HAZs, respectively.

This study investigates the fatigue performance and hydrogen‐assisted failure behavior of X65 pipeline steel welded joints in a 10 MPa N ₂ /H ₂ mixed environment with hydrogen contents from 0 to 20 vol%. Through fatigue life testing, fractography, and electron backscatter diffraction (EBSD), the fatigue lives of base metal (BM), weld metal (WM), and heat‐affected zone (HAZ) were examined under different stress amplitudes. Results show that in the high stress range, hydrogen significantly accelerates fatigue damage. In the low stress range, hydrogen has negligible influence on fatigue life. The HAZ is the most vulnerable region due to stress concentration, higher hardness, and lower fraction of high‐angle grain boundaries. Crack‐tip deformation in hydrogen‐blended environments is stress‐level dependent, showing lower geometrically necessary dislocation (GND) density and narrower kernel average misorientation (KAM) distribution than N ₂ at lower stress amplitudes, but higher GND density and broader KAM distribution at higher stress amplitudes.

The investigation focuses on the microstructure, impact toughness, and pitting corrosion resistance of cold metal transfer and pulse hybrid welded joints of unified numbering system (UNS) S32750 duplex stainless steel. The results show that the filler pass exhibits the highest austenite ratio (47.9%), whereas the heat‐affected zone (HAZ) shows the lowest (32.3%). Notably, secondary austenite (γ₂) is present in both the backing pass and HAZ, but conspicuously absent in the filler pass, indicating that reheating from subsequent weld pass is a prerequisite for the precipitation of γ₂. Additionally, chromium nitride (Cr₂N) also precipitates in the HAZ and backing pass. Comparative analysis with the weld metal (WM) and base metal (BM) indicates that the HAZ displays lower impact toughness, primarily attributing to imbalanced phase ratio, coarse ferrite grains and the brittle Cr₂N. Owing to the lower austenite content and Cr₂N precipitation in the backing pass, its toughness (122.6 J cm⁻²) is found to be inferior to that of the filler pass (130.1 J cm⁻²). Furthermore, the HAZ with a lower critical pitting temperature compared to the WM (79.1 °C) and BM (87 °C), and exhibits the worst pitting corrosion resistance due to the abundant precipitation of secondary phases and excessive ferrite with low pitting resistance equivalent number.

Owing to the high optical reflectivity of copper powder, the high-performance fabrication of copper alloys in the laser additive manufacturing (AM) field is problematic. To tackle this issue, this study employs the remelting process during laser powder bed fusion AM to fabricate defect-free and high-performance CuCrZr alloy. Compared to the non-remelting process, the remelting process yields finer grains, smaller precipitates, denser dislocations, and smaller dislocation cells. It realizes not only the dense molding of high laser reflectivity powders but also excellent mechanical properties and electrical conductivity (with an ultimate tensile strength of 329 MPa and conductivity of 96% IACS) without post-heat treatment. Furthermore, this study elucidates the influence of complex thermal gradients and multiple thermal cycles on the manufacturing process under the remelting process, as well as the internal mechanisms of microstructure evolution and performance improvement.