Zhang Jiale, Hu Zhengfei, Gao Ziyi
School of Materials Science and Engineering, Tongji University, Shanghai 202409, China.
Materials (Basel). 2025 Apr 11;18(8):1756. doi: 10.3390/ma18081756.
Creep tests of Super304H austenitic steel were carried out at 700 °C under different stresses. The samples were characterized by an optical microscope (OM), scanning electron microscope (SEM) and a transmission electron microscope (TEM). The results show that high-temperature creep promotes the precipitation of the MC, secondary MX carbide, σ phase, Cu-rich phase and Z phase. These fine precipitates improve both the matrix and grain boundary strength. Furthermore, the precipitation sequence of these second phases relates to the stress level during elevated temperature testing. The rapid precipitation of the σ phase is also observed at high stress levels, whereby fast growth at triangle boundaries notably deteriorates grain boundary strength. Conversely, the presence of dispersed fine MX precipitates under low-stress conditions during long-term creep should contribute significantly to microstructure stability and long-term creep strength. Despite the absence of homogeneous cavities observed on the grain boundary when subjected to creep for over 20,000 h, the decrease in grain boundary strength was explained from another aspect by analyzing the change in low angle grain boundary during creep.
在700℃下对Super304H奥氏体钢进行了不同应力水平下的蠕变试验。通过光学显微镜（OM）、扫描电子显微镜（SEM）和透射电子显微镜（TEM）对样品进行了表征。结果表明，高温蠕变促进了MC、二次MX碳化物、σ相、富铜相和Z相的析出。这些细小析出物提高了基体和晶界强度。此外，这些第二相的析出顺序与高温试验期间的应力水平有关。在高应力水平下还观察到σ相的快速析出，其在三角形边界处的快速生长显著降低了晶界强度。相反，在长期蠕变过程中，低应力条件下分散细小MX析出物的存在应显著有助于微观结构稳定性和长期蠕变强度。尽管在蠕变超过20000小时后，在晶界上未观察到均匀的空洞，但通过分析蠕变过程中低角度晶界的变化，从另一个方面解释了晶界强度的降低。
