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<p>To address the escalating quality and safety imperatives associated with welded joints in offshore platform leg structures, this study compared multi-pass metal-inert gas (MP-MIG) welding and laser-metal-inert gas hybrid welding on 20&#xa0;mm plates, revealing the significant microstructure and mechanical differences produced by the two techniques and their post-weld heat treatment. The results showed that the microstructure in as-welded MP-MIG welding seams exhibited networked grain boundary ferrite, whereas laser-metal-inert gas hybrid (L-MIG) welding seams contained a large amount of martensite. The ultimate tensile strength and yield strength of as-welded MP-MIG welding joints were similar to those of as-welded L-MIG welding joints, but the elongation was significantly lower. After post-weld heat treatment (910&#xa0;°C/30&#xa0;min → water quenching, followed by tempering at 500&#xa0;°C/30&#xa0;min → air cooling). Electron backscatter diffraction analysis confirmed that post-weld heat treatment could refine grains within the weld seam, reduce grain size disparity, and eliminate grain anisotropy. Furthermore, the ultimate tensile strength, yield strength, and elongation of post-weld heat-treated (PWHT) MP-MIG welding joints increased by 11.9, 22.3, and 67.6%, respectively, compared to as-welded joints. For PWHT L-MIG welding joints, the ultimate tensile strength and yield strength in the laser zone increased by 47.4 and 73.3%, respectively, while those in the hybrid zone increased by 40.1 and 66.6%, respectively. Additionally, the average impact energy of laser-metal-inert gas hybrid welding samples exceeded that of PWHT MP-MIG welding samples by more than 20%, the mechanical properties have been significantly enhanced.</p>

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Microstructure and Mechanical Properties of EH36 Weldments: Comparing MP-MIG, L-MIG, and Post-Weld Heat Treatment

  • 期刊论文

  • 发表日期：

    2026年5月19日

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  • Yanfa Han,
  • Yingjie Kong,
  • Hongxi Jin,
  • Jiasi Cai,
  • Meng Wang,
  • Xuan Liu,
  • Kuijun Fu,
  • Yanhong Wei

摘要

To address the escalating quality and safety imperatives associated with welded joints in offshore platform leg structures, this study compared multi-pass metal-inert gas (MP-MIG) welding and laser-metal-inert gas hybrid welding on 20 mm plates, revealing the significant microstructure and mechanical differences produced by the two techniques and their post-weld heat treatment. The results showed that the microstructure in as-welded MP-MIG welding seams exhibited networked grain boundary ferrite, whereas laser-metal-inert gas hybrid (L-MIG) welding seams contained a large amount of martensite. The ultimate tensile strength and yield strength of as-welded MP-MIG welding joints were similar to those of as-welded L-MIG welding joints, but the elongation was significantly lower. After post-weld heat treatment (910 °C/30 min → water quenching, followed by tempering at 500 °C/30 min → air cooling). Electron backscatter diffraction analysis confirmed that post-weld heat treatment could refine grains within the weld seam, reduce grain size disparity, and eliminate grain anisotropy. Furthermore, the ultimate tensile strength, yield strength, and elongation of post-weld heat-treated (PWHT) MP-MIG welding joints increased by 11.9, 22.3, and 67.6%, respectively, compared to as-welded joints. For PWHT L-MIG welding joints, the ultimate tensile strength and yield strength in the laser zone increased by 47.4 and 73.3%, respectively, while those in the hybrid zone increased by 40.1 and 66.6%, respectively. Additionally, the average impact energy of laser-metal-inert gas hybrid welding samples exceeded that of PWHT MP-MIG welding samples by more than 20%, the mechanical properties have been significantly enhanced.