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<p>This study addresses the toughness deterioration in the heat-affected zone (HAZ) of EH420 thick steel plates during high-heat-input welding (296&#xa0;kJ/cm) by pre-placing an SW-5NiLT Ni alloy coating (8 ± 0.5&#xa0;mm) on the groove face via flux-cored arc welding, followed by electrogas welding. The influence of Ni on microstructure evolution and low-temperature toughness was systematically investigated using tensile, impact, and hardness tests, along with scanning electron microscope, electron backscatter diffraction, and X-ray diffraction. Results show that the Ni-coated group achieved a HAZ impact energy of 211&#xa0;J at − 40&#xa0;°C, a 258&#xa0;pct increase over the control group (59&#xa0;J), approaching the base metal level (238&#xa0;J). Ni diffusion (<i>D</i><sub>eff</sub> ≈ 3.0 × 10⁻<sup>11</sup>&#xa0;m<sup>2</sup>/s) refined the effective grain size from 44.5 to 13.5&#xa0;<i>μ</i>m via solute drag, increased high-angle grain boundaries (HAGBs) from 44.1 to 78.2&#xa0;pct, and introduced ~ 5.7&#xa0;pct retained austenite. Toughening mechanisms include grain refinement (contribution: 21.4&#xa0;J), HAGB optimization (45.3&#xa0;J), strain homogenization (22.1&#xa0;J), and the TRIP effect (54.2&#xa0;J). Their synergy elevated toughness to 211&#xa0;J, closely matching the theoretical estimate (203.5&#xa0;J). The proposed “diffusion-refinement-phase transformation-toughening” model provides a theoretical basis for high-efficiency welding of high-strength thick plates.</p>

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Effect of Pre-placed Ni Alloy Coating on Microstructure and Toughness of HAZ in Thick Steel Plates Subjected to High-Heat-Input Welding

  • 期刊论文

  • 发表日期：

    2026年7月27日

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  • Jiajian Huang,
  • Li Zhao,
  • Zexin Jiang,
  • Dongyue Cheng,
  • Ting Yu,
  • Chao Peng,
  • Yukuo Tian,
  • Lulu Cheng,
  • Xiang Wang,
  • Jinjun Ma

摘要

This study addresses the toughness deterioration in the heat-affected zone (HAZ) of EH420 thick steel plates during high-heat-input welding (296 kJ/cm) by pre-placing an SW-5NiLT Ni alloy coating (8 ± 0.5 mm) on the groove face via flux-cored arc welding, followed by electrogas welding. The influence of Ni on microstructure evolution and low-temperature toughness was systematically investigated using tensile, impact, and hardness tests, along with scanning electron microscope, electron backscatter diffraction, and X-ray diffraction. Results show that the Ni-coated group achieved a HAZ impact energy of 211 J at − 40 °C, a 258 pct increase over the control group (59 J), approaching the base metal level (238 J). Ni diffusion (Deff ≈ 3.0 × 10⁻11 m2/s) refined the effective grain size from 44.5 to 13.5 μm via solute drag, increased high-angle grain boundaries (HAGBs) from 44.1 to 78.2 pct, and introduced ~ 5.7 pct retained austenite. Toughening mechanisms include grain refinement (contribution: 21.4 J), HAGB optimization (45.3 J), strain homogenization (22.1 J), and the TRIP effect (54.2 J). Their synergy elevated toughness to 211 J, closely matching the theoretical estimate (203.5 J). The proposed “diffusion-refinement-phase transformation-toughening” model provides a theoretical basis for high-efficiency welding of high-strength thick plates.