探讨了MoNb改性FeCrAl不锈钢(C35MN)在800℃、400 h时效过程中以及1000~1200℃、1 h退火处理后的组织演变及力学性能变化。结果表明,C35MN合金在800和1000℃具有优异的高温组织稳定性,然而在1100℃以上Laves相大量回溶至基体,晶粒尺寸迅速长大至310 μm；C35MN合金的组织稳定性由Laves相的热稳定性决定,而Laves相热稳定性又与其成分密切相关,形成Laves相的组元在bcc结构Fe基体中的固溶度越低,Laves相越稳定；晶粒尺寸显著影响C35MN合金的力学行为,当晶粒尺寸小于50 μm时,合金表现出韧性断裂特征,晶粒尺寸大于130 μm时则表现出脆性解理断裂特征。

MoNb-modified FeCrAl ferritic stainless steel (C35MN: Fe-13Cr-4.5Al-2Mo-1Nb, mass fraction, %) exhibits excellent comprehensive properties, including oxidation and corrosion resistance, as well as moderate mechanical properties, machinability, and neutron irradiation-resistance, making them potential accident-tolerant fuel (ATF) cladding materials for pressurized water reactors. However, the microstructural evolution and corresponding mechanical properties of C35MN alloys at the loss-of-coolant accident temperature have not been systematically studied. Herein, the microstructural evolution and mechanical properties of C35MN alloys during 400 h aging at 800^oC and 1 h annealing at 1000-1200^oC were systematically investigated. The alloy ingots were prepared by vacuum induction melting and cast into round bars, followed by 1150^oC hot-forging, 800^oC hot-rolling, and aging at 800^oC for 400 h. The samples annealed at 1000-1200^oC for 1 h were preaged at 800^oC for 24 h. The C35MN alloy exhibited excellent microstructural stability at 800 and 1000^oC, which is attributed to the precipitation of the Laves phase. The alloy showed a good combination of strength and ductility. However, when the annealing temperature increased above 1100^oC, a large amount of the Laves phase dissolved into the ferritic matrix, resulting in the coarsening of the matrix grains. Annealing above 1200^oC for 1 h, the grain size increased to 310 μm, severely degrading the mechanical property of the C35MN alloy below the requirement of ATF cladding materials. The microstructural stability of the C35MN alloy was influenced by the thermal stability of the Laves phase, which depends on the composition of the phase. The thermal stability of the Laves phase depends on the solid solubility of Laves phase forming elements in the ferritic matrix: the lower the solid solubility, the higher thermal stability of the Laves phase. The mechanical properties of C35MN were significantly affected by the grain size. The alloy exhibited ductile fracture when the grain size was less than 50 μm and brittle cleavage fracture when the grain size was above 130 μm.