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<p>In this study, we conducted a comprehensive investigation into the microstructure and mechanical properties of submerged arc weld (SAW) joints in an API X65 steel pipeline. Our analysis revealed that the microstructural composition of the base metal consisted of a combination of ferrite and pearlite. In contrast, the fusion zone exhibited directionally solidified grains, primarily characterized by the presence of acicular ferrite as the dominant phase. To evaluate mechanical performance, we performed hardness measurements across various weld zones, uncovering that the fusion zone exhibited the highest hardness value, reaching 260 HV. Additionally, we noted a softening effect in the heat-affected zone (HAZ). We also quantified the impact toughness through Charpy V-notch (CVN) tests conducted at different temperatures. The results showed that the fusion zone demonstrated the lowest absorbed energy values, measuring 219.5&#xa0;J at 0&#xa0;°C and a mere 3.2&#xa0;J at -196&#xa0;°C. To further elucidate the fracture behavior, we examined the fractured surfaces using scanning electron microscopy (SEM). Furthermore, Electron Backscatter Diffraction (EBSD) analyses indicated the presence of high-angle grain boundaries within the fusion zone, which were more pronounced than in the base metal and HAZ. The combination of elevated hardness and widespread grain boundary intersections likely serves as a precursor for crack initiation, contributing to the fusion zone’s reduced toughness. Overall, our experimental findings substantiate the intricate relationships among microstructure, hardness, toughness, and misorientation angle across the various zones of the welded pipeline joint, providing valuable insights into the performance characteristics of API X65 steel welds.</p>

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Microstructure and mechanical properties of weld joint in submerged arc welded API X65 steel pipeline

  • 期刊论文

  • 发表日期：

    2026年6月15日

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  • Ali Tahaei,
  • Behrouz Bagheri Vanani,
  • Mahmoud Abbasi,
  • Matia Merlin,
  • Chiara Soffritti,
  • Argelia Fabiola Miranda Perez

摘要

In this study, we conducted a comprehensive investigation into the microstructure and mechanical properties of submerged arc weld (SAW) joints in an API X65 steel pipeline. Our analysis revealed that the microstructural composition of the base metal consisted of a combination of ferrite and pearlite. In contrast, the fusion zone exhibited directionally solidified grains, primarily characterized by the presence of acicular ferrite as the dominant phase. To evaluate mechanical performance, we performed hardness measurements across various weld zones, uncovering that the fusion zone exhibited the highest hardness value, reaching 260 HV. Additionally, we noted a softening effect in the heat-affected zone (HAZ). We also quantified the impact toughness through Charpy V-notch (CVN) tests conducted at different temperatures. The results showed that the fusion zone demonstrated the lowest absorbed energy values, measuring 219.5 J at 0 °C and a mere 3.2 J at -196 °C. To further elucidate the fracture behavior, we examined the fractured surfaces using scanning electron microscopy (SEM). Furthermore, Electron Backscatter Diffraction (EBSD) analyses indicated the presence of high-angle grain boundaries within the fusion zone, which were more pronounced than in the base metal and HAZ. The combination of elevated hardness and widespread grain boundary intersections likely serves as a precursor for crack initiation, contributing to the fusion zone’s reduced toughness. Overall, our experimental findings substantiate the intricate relationships among microstructure, hardness, toughness, and misorientation angle across the various zones of the welded pipeline joint, providing valuable insights into the performance characteristics of API X65 steel welds.