The modified HR3C austenitic heat-resistant steels for applications of ultra-supercritical (USC) power plants were developed and investigated. As the C content breaks through the limitation of the HR3C composition range (>0.1 wt%), the evolution of carbides and mechanical properties after isothermal aging at 700 °C have not been understood. In this study, two modified HR3C with different C content were studied by tensile test and Charpy impact test at room temperature after long-term aging up to 10,000 h. The M₂₃C₆ carbide is rapidly precipitated at the interface (GBs, TBs or NbC/γ), and these carbides at grain boundaries (GBs) are gradually changed from a continuous distribution to a semi-continuous distribution, then finally agglomerate and coarsen near the GBs. Moreover, a new morphology type lamellar M₂₃C₆ carbide forms in the grain. The effect of lamellar carbides on mechanical properties at room temperature (RT) is not obvious because the strength of GB is rapidly weakened. Besides, the Larson-Miller parameter was obtained and the creep strength of the modified HR3C was extrapolated, by conducting creep rupture experiments on un-aged sample. The creep tests reveal that the rupture lives decrease with increasing C content. Lamellar carbides are precipitated and weaken the strength of grain during high temperature creep.

开发并研究了用于超超临界（USC）电厂的改性HR3C奥氏体耐热钢。由于C含量突破了HR3C组成范围（> 0.1 wt％）的限制，因此在700°C等温时效后，碳化物的演变和力学性能尚未得到了解。在这项研究中，通过在室温下长期老化达10,000 h后的拉伸试验和夏比冲击试验，研究了两种具有不同C含量的改性HR3C。M ₂₃ C ₆碳化物在界面（GBs，TBs或NbC /γ）处迅速析出，这些晶界（GBs）上的碳化物逐渐从连续分布变为半连续分布，然后在GBs附近逐渐聚集并粗化。此外，一种新的形态学层状M ₂₃ C ₆碳化物在晶粒中形成。层状碳化物对室温下机械性能的影响并不明显，因为GB的强度会迅速减弱。此外，通过对未老化样品进行蠕变断裂实验，获得了Larson-Miller参数，并推断出改性HR3C的蠕变强度。蠕变测试表明，随着C含量的增加，断裂寿命降低。层状碳化物在高温蠕变过程中会沉淀并削弱晶粒强度。