Abstract This study explored the transformation of austenite to ferrite and precipitation behavior during the isothermal annealing of heat-resistant steel based on Fe-9Cr-1.5Mo-1.25Co-0.1C-0.2 V-0.05Nb (wt%). For this purpose, the samples used here were initially reheated to the full austenitization temperature and thereafter directly annealed at 710 °C and 730 °C, a temperature range in which the transformation to ferrite takes place, for up to 196 h. In addition, we modified the prior austenite grain size (PAGS) by changing the reheating temperature and then analyzed the effect of PAGS on the kinetics of the isothermal transformation to ferrite. In the early stage of annealing, Cr-enriched M23(C,B)6 carbides initially precipitated along the prior austenite grain boundaries (PAGB). As annealing progressed, the ferrite began to nucleate at the PAGB and then grew into the austenite. The initial stage of the transformation to ferrite was then accompanied with the cellular precipitation of M23(C,B)6 particles. Interestingly, we also found the interphase precipitation of V- and Nb-enriched MX particles resulting from the partitioning of the C concentration at the moving austenite/ferrite interface during the austenite to ferrite transformation. The transformation was finished after annealing for more than 48 h. The time taken to complete the process was prolonged with an increase in the PAGS, indicating that the kinetics of the transformation decreased with an increase in the PAGS.

中文翻译：

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9Cr-1.5Mo-1.25Co-0.1C-VNb耐热钢奥氏体向铁素体等温转变及析出行为

摘要 本研究探讨了基于Fe-9Cr-1.5Mo-1.25Co-0.1C-0.2 V-0.05Nb (wt%) 的耐热钢等温退火过程中奥氏体向铁素体的转变和析出行为。为此，这里使用的样品最初重新加热到完全奥氏体化温度，然后在 710 °C 和 730 °C（发生铁素体转变的温度范围）下直接退火长达 196 小时。此外，我们通过改变再加热温度来改变原始奥氏体晶粒尺寸 (PAGS)，然后分析了 PAGS 对铁素体等温转变动力学的影响。在退火的早期阶段，富铬的 M23(C,B)6 碳化物最初沿原奥氏体晶界 (PAGB) 析出。随着退火的进行，铁素体开始在 PAGB 处成核，然后成长为奥氏体。转变为铁素体的初始阶段伴随着 M23(C,B)6 颗粒的细胞沉淀。有趣的是，我们还发现了在奥氏体到铁素体转变过程中移动奥氏体/铁素体界面处 C 浓度分配导致的富含 V 和 Nb 的 MX 颗粒的相间析出。退火48小时以上，转变完成。完成该过程所需的时间随着 PAGS 的增加而延长，表明转化动力学随着 PAGS 的增加而降低。有趣的是，我们还发现了在奥氏体到铁素体转变过程中移动奥氏体/铁素体界面处的 C 浓度分配导致的富含 V 和 Nb 的 MX 颗粒的相间析出。退火48小时以上，转变完成。完成该过程所需的时间随着 PAGS 的增加而延长，表明转化动力学随着 PAGS 的增加而降低。有趣的是，我们还发现了在奥氏体到铁素体转变过程中移动奥氏体/铁素体界面处 C 浓度分配导致的富含 V 和 Nb 的 MX 颗粒的相间析出。退火48小时以上，转变完成。完成该过程所需的时间随着 PAGS 的增加而延长，表明转化动力学随着 PAGS 的增加而降低。