反应堆内17-4PH马氏体不锈钢阀杆材料长时间服役后的热老化脆化行为与断裂机制

核电站主蒸汽系统中的阀杆等关键部件常用材料为17-4PH马氏体不锈钢，在300 ℃左右的高温环境下，该材料会随服役时间的延长发生热老化脆化，具体表现为韧脆转变温度（DBTT）升高、上平台能量降低和硬度增加，对反应堆的安全运行构成潜在威胁。本文针对热老化后的17-4PH马氏体不锈钢阀杆材料，通过扫描电子显微镜（SEM）、电子背散射衍射（EBSD）等微观分析手段，研究其热老化脆化行为和断裂机制。结果表明，17-4PH马氏体不锈钢热老化后，马氏体板条束长大，晶界总数增多，冲击断口上微裂纹数量增多，且尺寸近似于马氏体板条束尺寸。结合其冲击性能等进一步分析了材料的脆性断裂机制，结果显示，小角度晶界与Cu相互作用产生的硬化导致脆化，是17-4PH马氏体不锈钢发生热老化脆化的主要原因。

Thermal Aging Embrittlement Behavior and Fracture Mechanism of 17-4PH Martensitic Stainless Steel Serving for a Long Time in Nuclear Power Plant

The valve stem used in the main steam system of nuclear power plant (NPP) is usually 17-4PH martensitic stainless steel. When it serves in 300 ℃ for a long time, the thermal aging embrittlement of valve stem will be significant, and the performance is that the ductile brittle transition temperature (DBTT) and the hardness increase, and the upper stage energy (USE) decreases. It will seriously affect the safety and economic operation of nuclear power plant. The 17-4PH martensitic stainless steel valve stem after thermal aging was studied by scanning electron microscope (SEM) and electron backscattered diffraction (EBSD). The thermal aging embrittlement behavior of the 17-4PH martensitic stainless steel and the brittle fracture mechanism of the material were further analyzed. The results show that the size of martensite plate bundle and the number of grain boundary increase. The number of microcracks increases on the impact fracture, and the size is similar to that of the martensite plate bundle. Combining with the impact properties, the brittle fracture mechanism of the material was analyzed. The results show that the interaction of the small angle grain boundary and Cu leads to hardening embrittlement, which is the main reason for the thermal aging embrittlement of 17-4PH martensitic stainless steel.