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<p>To reveal the influence of inclination angles on the microstructural characteristics of welded joints in mountainous pipeline steel, this study employed electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques to systematically investigate the evolution patterns and mechanisms of weld zones and heat-affected zones in X70 pipeline steel welded joints with varying inclination angles under simulated mountainous environmental conditions. Specimens with 0°, 15°, 22°, and 30° welding angles were analyzed. EBSD results show increased high-angle grain boundaries (HAGBs) in weld zones with ascending angles, primarily modifying grain misorientation distribution without altering phase composition. TEM observations reveal enhanced dislocation density and complex configurations in weld zones. The TiN proportion in NbC-TiN precipitates progressively increased with inclination angles, while NbC content initially rose, then declined. These variations stem from inclination-induced alterations in thermal flow direction and temperature gradients during welding. Steeper angles promote thermal flow alignment along the weld axis, disrupting original grain orientations and intensifying defect formation (slip bands and dislocations). This work systematically reveals the inclination-dependent microstructural evolution mechanisms in mountainous pipeline welded joints.</p>

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Microstructural Evolution of X70 Pipeline Steel Welds

  • 期刊论文

  • 发表日期：

    2025年5月26日

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  • Jiayao Liu,
  • Junjie Huang,
  • Zihao Sui,
  • Hao Li,
  • Jia Xu,
  • Mei Yang,
  • Zheng Lei,
  • Yang Li

摘要

To reveal the influence of inclination angles on the microstructural characteristics of welded joints in mountainous pipeline steel, this study employed electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques to systematically investigate the evolution patterns and mechanisms of weld zones and heat-affected zones in X70 pipeline steel welded joints with varying inclination angles under simulated mountainous environmental conditions. Specimens with 0°, 15°, 22°, and 30° welding angles were analyzed. EBSD results show increased high-angle grain boundaries (HAGBs) in weld zones with ascending angles, primarily modifying grain misorientation distribution without altering phase composition. TEM observations reveal enhanced dislocation density and complex configurations in weld zones. The TiN proportion in NbC-TiN precipitates progressively increased with inclination angles, while NbC content initially rose, then declined. These variations stem from inclination-induced alterations in thermal flow direction and temperature gradients during welding. Steeper angles promote thermal flow alignment along the weld axis, disrupting original grain orientations and intensifying defect formation (slip bands and dislocations). This work systematically reveals the inclination-dependent microstructural evolution mechanisms in mountainous pipeline welded joints.