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<p>Si-enriched ferritic/martensitic (F/M) heat-resistant steel is a candidate material for Generation-IV reactors due to its excellent corrosion resistance. However, excessive Si addition inevitably promotes the formation of δ-ferrite in the martensitic matrix, resulting in degraded mechanical properties. Consequently, eliminating the δ-ferrite content is critical for its application. Generally, δ-ferrite dissolves and transforms to austenite in prolonged austenitizing, but its evolution behavior is still unclear in Si-enriched F/M heat-resistant steel. An in-house developed alloy 10Cr1Si steel with 1 pct Si (wt) was austenitized at temperatures ranging from 1000&#xa0;°C to 1200&#xa0;°C for durations of 0.25 to 8&#xa0;hours. Abnormally, at 1000&#xa0;°C, only localized coarsening of δ-ferrite occurs, with increasing area fraction from 6.9 to 18.3 pct; while above 1000&#xa0;°C, the process progresses to a two-stage sequence of coarsening and subsequent dissolution. Specifically, at 1150&#xa0;°C for 0.5&#xa0;hours, the δ-ferrite increased from 6.9 to 14.4 pct, but it completely dissolved after 8&#xa0;hours. This paradoxical phenomenon is attributed to the dissolution of Si-induced M<sub>23</sub>C<sub>6</sub>, which releases Mo and Cr atoms to adjacent δ-ferrite through downhill diffusion, resulting in the increase of δ-ferrite fraction. With increasing holding time, the system evolves toward a thermodynamically stable state, and δ-ferrite gradually dissolves. Meanwhile, the released carbon also accelerates this process.</p>

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Austenitization-Parameter-Controlled Ferrite Evolution in Si-enriched Ferritic/Martensitic Heat-Resistant Steel

  • 期刊论文

  • 发表日期：

    2026年7月19日

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  • Fanao Meng,
  • Jun Zhang,
  • Xiaoxin Zhang,
  • Decang Zhang,
  • Qianyi Zhang,
  • Gang Ran,
  • Qingzhi Yan

摘要

Si-enriched ferritic/martensitic (F/M) heat-resistant steel is a candidate material for Generation-IV reactors due to its excellent corrosion resistance. However, excessive Si addition inevitably promotes the formation of δ-ferrite in the martensitic matrix, resulting in degraded mechanical properties. Consequently, eliminating the δ-ferrite content is critical for its application. Generally, δ-ferrite dissolves and transforms to austenite in prolonged austenitizing, but its evolution behavior is still unclear in Si-enriched F/M heat-resistant steel. An in-house developed alloy 10Cr1Si steel with 1 pct Si (wt) was austenitized at temperatures ranging from 1000 °C to 1200 °C for durations of 0.25 to 8 hours. Abnormally, at 1000 °C, only localized coarsening of δ-ferrite occurs, with increasing area fraction from 6.9 to 18.3 pct; while above 1000 °C, the process progresses to a two-stage sequence of coarsening and subsequent dissolution. Specifically, at 1150 °C for 0.5 hours, the δ-ferrite increased from 6.9 to 14.4 pct, but it completely dissolved after 8 hours. This paradoxical phenomenon is attributed to the dissolution of Si-induced M23C6, which releases Mo and Cr atoms to adjacent δ-ferrite through downhill diffusion, resulting in the increase of δ-ferrite fraction. With increasing holding time, the system evolves toward a thermodynamically stable state, and δ-ferrite gradually dissolves. Meanwhile, the released carbon also accelerates this process.