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<p>The microstructure evolution and mechanical property degradation of domestically produced C-HRA-5 steel reheater steam tubes were investigated after 4000&#xa0;h of service at 620&#xa0;°C. The initial state of C-HRA-5 exhibited an austenitic organization and a diffusely distributed strengthening phase NbCrN. High-temperature exposure resulted in a precipitation process. Cr-rich M<sub>23</sub>C<sub>6</sub> carbides with chain-like structures were mainly precipitated near grain boundaries. Creep cavities also accumulated and coalesced into microcracks at grain boundaries, indicating that the coarsened M<sub>23</sub>C<sub>6</sub> carbides on grain boundaries negatively affect the grain strength and are the main factor causing the reduction of steel plasticity and toughness. Within the grain interiors, NbCrN precipitation occurred, along with dislocation pinning. The hindering effect of the dispersed particles on the dislocations allows the steel to maintain strength properties comparable to the initial state after service. However, the gradual deposition of NbCrN reduces the strength properties.</p>

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Microstructure and Mechanical Properties Evolution of C-HRA-5 Steel After High-Temperature Service

  • 期刊论文

  • 发表日期：

    2025年5月8日

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  • Xiaochun Wang,
  • Zhibao Ma,
  • Guiyang Qu,
  • Jiang Lin,
  • Yonghui Zhang,
  • Jing Gao,
  • Hao Zhou,
  • Qingfeng Wang

摘要

The microstructure evolution and mechanical property degradation of domestically produced C-HRA-5 steel reheater steam tubes were investigated after 4000 h of service at 620 °C. The initial state of C-HRA-5 exhibited an austenitic organization and a diffusely distributed strengthening phase NbCrN. High-temperature exposure resulted in a precipitation process. Cr-rich M23C6 carbides with chain-like structures were mainly precipitated near grain boundaries. Creep cavities also accumulated and coalesced into microcracks at grain boundaries, indicating that the coarsened M23C6 carbides on grain boundaries negatively affect the grain strength and are the main factor causing the reduction of steel plasticity and toughness. Within the grain interiors, NbCrN precipitation occurred, along with dislocation pinning. The hindering effect of the dispersed particles on the dislocations allows the steel to maintain strength properties comparable to the initial state after service. However, the gradual deposition of NbCrN reduces the strength properties.