The microstructural evolution and its effect on mechanical properties of 27Cr-4Mo-2Ni super ferritic stainless steels during intermediate temperature aging treatment were investigated. Experimental results demonstrated that Laves phase started to nucleate at dislocations and sub-grain boundaries before chi and sigma phase, while the chi phase and sigma phase precipitated at grain boundaries. Laves phase was partially dissolved into the matrix to provide additional Cr and Mo atoms for the rapid coarsening of sigma phase with increasing aging time during 800 °C aging treatment. Meanwhile, the average grain size increased from ~ 68 to ~ 111 µm. Mechanical properties such as RT impact toughness, tensile properties and micro hardness were significantly influenced by the brittle intermetallic and grain coarsening. When the alloy was aged at 800 °C, the rate of microhardness increase was accelerated by the formation and coarsening of sigma phase, and the value of Vickers hardness was positively correlated with the volume fraction of sigma phase. Impact toughness was much more sensitive to brittle precipitates than both the tensile properties and hardness. Precipitation of sigma phase induced brittle fracture during impact testing, especially in the situation where the grain boundaries were completely covered by sigma phase.

研究了中温时效处理过程中27Cr-4Mo-2Ni高铁素体不锈钢的组织演变及其对力学性能的影响。实验结果表明，Laves相在chi和sigma相之前在位错和亚晶粒边界处开始形核，而chi相和sigma相则在晶界处析出。Laves相部分溶解在基体中，以提供额外的Cr和Mo原子，用于在800°C时效处理中随着时效时间的增加而使sigma相快速粗化。同时，平均晶粒尺寸从〜68增加到〜111 µm。机械性能，如RT冲击韧性，拉伸性能和显微硬度，受到脆性金属间化合物和晶粒粗化的显着影响。当合金在800°C时效时，σ相的形成和粗化促进了显微硬度的增加，维氏硬度值与σ相的体积分数呈正相关。冲击韧性对脆性沉淀物的敏感性比拉伸性质和硬度都高得多。在冲击试验期间，σ相的析出会导致脆性断裂，尤其是在晶界完全被σ相覆盖的情况下。