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<p>To elucidate the cause of decomposition in martensite laths of T91 heat-resistant steel (T91 HRS) during long-term creep at 650&#xa0;°C, the microstructure of the steel after creep at 650&#xa0;°C lasting up to 12343&#xa0;h was investigated. X-ray diffraction (XRD) results show that the crystal lattice constant of the matrix alpha Fe declines after long-term creep. The hardness and average geometrically necessary dislocation (GND) density first increases slightly at the initial stage of creep and then decreases. The formation of polygonized subgrain occurs after long-term creep as systematically verified by transmission electron microscopy (TEM) image and electron backscattered diffraction (EBSD) mapping&#xa0;analysis. TEM and energy-dispersive spectrum (EDS) analysis reveal that the rodlike M<sub>23</sub>C<sub>6</sub> carbides containing more silicon elements exhibit accelerated coarsening behavior. The fraction of chromium increases, the fraction of iron decreases, and the fraction of molybdenum remains relatively stable in M<sub>23</sub>C<sub>6</sub> carbides after long-term creep at 650&#xa0;°C. Back-scatter electron (BSE) analysis shows that the coarsening rate of carbides varies at different locations due to the different diffusion rates of alloy elements at grain boundaries and lath boundaries.</p>

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The Decomposition Characteristics and Carbide Growth Mechanism of T91 Heat-Resistant Steel After Long-Term Creep at 650 °C

  • 期刊论文

  • 发表日期：

    2025年2月18日

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  • Zhen Zhang,
  • Bin Zhang,
  • Kejie Qu,
  • Yekuan Tu,
  • Zixuan Xu,
  • Yujun Han,
  • Baosen Zhang,
  • Yong Shen,
  • Zhengfei Hu

摘要

To elucidate the cause of decomposition in martensite laths of T91 heat-resistant steel (T91 HRS) during long-term creep at 650 °C, the microstructure of the steel after creep at 650 °C lasting up to 12343 h was investigated. X-ray diffraction (XRD) results show that the crystal lattice constant of the matrix alpha Fe declines after long-term creep. The hardness and average geometrically necessary dislocation (GND) density first increases slightly at the initial stage of creep and then decreases. The formation of polygonized subgrain occurs after long-term creep as systematically verified by transmission electron microscopy (TEM) image and electron backscattered diffraction (EBSD) mapping analysis. TEM and energy-dispersive spectrum (EDS) analysis reveal that the rodlike M23C6 carbides containing more silicon elements exhibit accelerated coarsening behavior. The fraction of chromium increases, the fraction of iron decreases, and the fraction of molybdenum remains relatively stable in M23C6 carbides after long-term creep at 650 °C. Back-scatter electron (BSE) analysis shows that the coarsening rate of carbides varies at different locations due to the different diffusion rates of alloy elements at grain boundaries and lath boundaries.