利用TEM和HRTEM研究了400 ℃热老化2~10⁴ h后Z3CN20--09M不锈钢的微观组织, 用纳米力学探针研究了微区力学性能. 结果表明: 相比于原始状态, 经400 ℃热老化2~10⁴ h后, Z3CN20-09M不锈钢中的铁素体发生了调幅分解并且析出了G相, 导致铁素体的硬度增加和塑性变形能力下降. 利用原位疲劳试验机、SEM和电子探针研究了400 ℃热老化2~10^⁴ h后Z3CN20-09M不锈钢的微型平板试样拉伸行为. 结果表明: 热老化后, 不锈钢的屈服强度和断裂强度升高, 延伸率下降. 热老化不锈钢中铁素体发生解理断裂, 微裂纹萌生于相界并向铁素体内扩展; 奥氏体主要发生微孔聚集型韧性断裂, 并且在局部区域发生撕裂. 调幅分解是铁素体发生硬脆化和热老化前后Z3CN20-09M不锈钢拉伸断裂行为发生改变的根本原因.

Cast austenite stainless steels (CASS) were widely used in the primary circuit piping of pressurized water nuclear reactors (PWRs), for their excellent mechanical behavior, corrosion resistance and good weldability.CASS, however, were known to have a tendency of thermal aging embrittlement after long term service at mid-temperature (about 280-320℃). The microstructures, micro-mechanical properties and tensile fracture behaviors of Z3CN20-09M stainless steels, thermal aged at 400 ℃ for 2~10⁴ h, were studied in this work. TEM was utilized to observe the microstructure. A nano-indenter was used to investigate the micro-mechanical properties. The tensile tests were completed by an in situ fatigue tester. The tensile surface morphology was observed in SEM and the fracture of thermal aged CASS was examined by an electron probe micro-analyzer (EPMA). The results indicated that the spinodal decomposition and G-phase precipitation distributed in ferrite of the aged CASS. The nano-hardness of ferrite increased and the plastic deformation ability of ferrite phase declined. After long-term aging, the yield strength and ultimate strength increased but the elongation declined. Cleavage features were observed in the ferrite phase of thermal aged CASS. It was also found that micro-cracks initiated at phase boundaries and extended toward the ferrite phase. Ductile dimples and tearing at some areas were shown in the austenite phase in the thermal aged CASS. The spinodal decomposition was considered to be the primary mechanism for the change of the tensile fracture behaviors of Z3CN20-09M stainless steel before and after thermal aging.