Service safety and maintenance costs of turbine components after overheating exposure are closely related to the initial microstructures and subsequent microstructural evolutions after overheating. However, comparative investigation about microstructural evolutions and corresponding mechanical properties of cast polycrystalline superalloys with different initial microstructures after overheating exposure has been rarely reported. In this paper, stress rupture tests at 975 °C/196 MPa, tensile tests at room temperature and microhardness measurements were conducted in both as-cast and standard heat-treated K424 alloy after overheating at the temperature range from 1000 °C to 1200 °C for 2 h. The microstructural evolutions and fracture features were then investigated. The results showed that the mechanical properties didn’t decrease for standard heat treated specimens and even increased gradually for as-cast specimens with increasing the overheating temperature. Microstructural characterization indicated that the grain structures, the morphologies of MC carbides and γ/γ′ eutectics showed no significant change after overheating at different temperatures. The mechanical properties were improved by the more cuboidal γ′ precipitates in the dendritic and interdendritic region, the sufficient re-precipitation of ultra-fine γ′ particles as well as the dissolution of γ′ particles along grain boundary. The initial microstructures had a significant influence on the microstructural evolution and corresponding mechanical properties after overheating exposure. In addition, the high temperature and room temperature fracture behaviors of overheated K424 alloy were also discussed.

暴露于过热之后的涡轮机组件的服务安全和维护成本与过热后的初始微观结构和随后的微观结构演变密切相关。然而，很少有关于过热暴露后具有不同初始微观结构的铸造多晶高温合金的微观组织演变和相应的力学性能的比较研究的报道。在本文中，对铸态和标准热处理的K424合金在1000°C至1200°温度范围内过热后进行了975°C / 196 MPa的应力断裂试验，室温下的拉伸试验和显微硬度测量。 C 2小时。然后研究了显微组织演变和断裂特征。结果表明，随着过热温度的升高，标准热处理试样的力学性能并没有降低，而铸态试样的力学性能甚至逐渐提高。显微组织表征表明，在不同温度下过热后，晶粒结构，MC碳化物的形态和γ/γ'共晶没有明显变化。通过在树枝状和树枝状区域中长方体的γ'沉淀，超细γ'颗粒的充分再沉淀以及γ'颗粒沿晶界的溶解，改善了机械性能。过热暴露后，初始的显微组织对显微组织的演变和相应的机械性能有重大影响。此外，