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<p>L415/316L bimetallic composite pipes were welded using two sequences, conventional welding and post-inner welding, to analyze the influence of welding sequence on the fusion-zone microstructure and mechanical performance. The microstructural characteristics, element diffusion, hardness, and local mechanical properties of the fusion zone were systematically investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and instrumented indentation testing. Furthermore, a three-dimensional finite element model was developed in ABAQUS/Explicit to simulate tensile and bending behavior, enabling a quantitative correlation between local hard-zone features and macroscopic stress–strain evolution. Experimental results indicate that conventional joint produces a continuous martensitic–bainitic layer of about 5&#xa0;mm at the filler weld/transition weld fusion zone, resulting in sharp compositional gradients, localized hardening, and pronounced stress concentration. In contrast, post-inner joint yields a narrower martensitic–bainitic layer of about 20&#xa0;μm width. Finite element analysis demonstrates that the post-inner joint effectively reduces Von Mises stress peaks, enlarges plastic-area fraction, and delays damage initiation under tensile and bending loading.</p>

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Microstructure and Mechanical Properties of Fusion Zone in the Welded Joint of L415/316L Bimetallic Composite Pipe

  • 期刊论文

  • 发表日期：

    2026年7月20日

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  • Liying Li,
  • Yiming Xu,
  • Liwen Xu,
  • Jiahui Wen,
  • Bin Han,
  • Xueda Li

摘要

L415/316L bimetallic composite pipes were welded using two sequences, conventional welding and post-inner welding, to analyze the influence of welding sequence on the fusion-zone microstructure and mechanical performance. The microstructural characteristics, element diffusion, hardness, and local mechanical properties of the fusion zone were systematically investigated using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), and instrumented indentation testing. Furthermore, a three-dimensional finite element model was developed in ABAQUS/Explicit to simulate tensile and bending behavior, enabling a quantitative correlation between local hard-zone features and macroscopic stress–strain evolution. Experimental results indicate that conventional joint produces a continuous martensitic–bainitic layer of about 5 mm at the filler weld/transition weld fusion zone, resulting in sharp compositional gradients, localized hardening, and pronounced stress concentration. In contrast, post-inner joint yields a narrower martensitic–bainitic layer of about 20 μm width. Finite element analysis demonstrates that the post-inner joint effectively reduces Von Mises stress peaks, enlarges plastic-area fraction, and delays damage initiation under tensile and bending loading.