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<p>Uniaxial creep tests coupled with comprehensive microstructural characterization were conducted on both pre-service and after-service P92 steel welded joints to elucidate their microstructural evolution and fracture mechanisms under creep conditions. The creep life of after-service joints exhibited a remarkable 50% reduction compared to pre-service counterparts, primarily attributed to (i) progressive coarsening of M<sub>23</sub>C<sub>6</sub> carbides, (ii) precipitation of Laves phases, and (iii) pre-existing creep cavity networks. Distinct failure mode transitions were observed: Under low-stress, welded joints predominantly failed via Type IV cracking in the fine-grained heat-affected zone (FGHAZ), whereas high-stress conditions induced ductile fracture in the base metal (BM). The Laves phase evolution followed a sequential precipitation pathway, initially forming (Fe, Cr)<sub>2</sub>(Mo)-type phases, which later evolved into hybrid (Fe, Cr)<sub>2</sub>(Mo, W)-type structures, thereby accelerating microstructural degradation. Long-term service exposure significantly reduced both the critical stress threshold and Larson–Miller parameter (LMP) values, directly correlating with FGHAZ embrittlement. Coarsened carbides and Laves phases collectively degraded grain boundary cohesion while promoting cavity nucleation at martensite lath boundaries.</p>

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Microstructural Evolution and Fracture Mechanisms of After-Service P92 Welded Joints in Ultra-Supercritical Units

  • 期刊论文

  • 发表日期：

    2025年9月23日

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  • Qingfeng Wang,
  • Hao Zhou,
  • Lei Zhao,
  • Xin Chen,
  • Shuai Liu,
  • Haifeng Jiang,
  • Kang Shen,
  • Derui Guo

摘要

Uniaxial creep tests coupled with comprehensive microstructural characterization were conducted on both pre-service and after-service P92 steel welded joints to elucidate their microstructural evolution and fracture mechanisms under creep conditions. The creep life of after-service joints exhibited a remarkable 50% reduction compared to pre-service counterparts, primarily attributed to (i) progressive coarsening of M23C6 carbides, (ii) precipitation of Laves phases, and (iii) pre-existing creep cavity networks. Distinct failure mode transitions were observed: Under low-stress, welded joints predominantly failed via Type IV cracking in the fine-grained heat-affected zone (FGHAZ), whereas high-stress conditions induced ductile fracture in the base metal (BM). The Laves phase evolution followed a sequential precipitation pathway, initially forming (Fe, Cr)2(Mo)-type phases, which later evolved into hybrid (Fe, Cr)2(Mo, W)-type structures, thereby accelerating microstructural degradation. Long-term service exposure significantly reduced both the critical stress threshold and Larson–Miller parameter (LMP) values, directly correlating with FGHAZ embrittlement. Coarsened carbides and Laves phases collectively degraded grain boundary cohesion while promoting cavity nucleation at martensite lath boundaries.