This paper presents the experimental investigations of the effects of thermal aging on the embrittlement failure mechanism and fracture toughness of 16MND5 reactor pressure vessel (RPV) steel using clamped single edge notched tension (SENT) specimens with different sizes. In order to study the embrittlement induced by thermal aging, the 16MND5 steel was subjected to accelerated thermal aging for 1000 h, 3000 h and 5000 h at 425 °C, and then the Vickers hardness and tensile properties were determined. To investigate the combined effects of thermal aging and specimen geometric sizes, the fracture toughness of various thermal aged materials was studied using SENT specimens with different specimen thickness ratios, B/W, and crack depths, a/W. A total of 59 SENT specimens were tested covering a wide range of thermal aging time and geometric size combinations. Results showed that as the aging time increases, the material’s micro hardness and tensile properties change slightly, but the R-curves (J-R and CTOD-R) decrease significantly. The ductile fracture properties of thermal aged RPV steels depend markedly on the geometric dimensions (crack depth, a/W and specimen thickness, B/W) of tested specimens. Furthermore, the effects of geometric sizes and thermal aging on fracture behavior are shown to have a strong interaction. Specifically, as the aging time increases, the influence of the geometric sizes on the fracture toughness decreases, especially with the variations of a/W. Also, as the geometric dimensions increase, the effect of thermal aging on fracture toughness decreases. Finally, combined with fractographic observations, the influence of thermal aging on the embrittlement mechanism and ductile fracture properties of 16MND5 steel was discussed.

本文介绍了热老化对 16MND5 反应堆压力容器 (RPV) 钢的脆化破坏机制和断裂韧性影响的实验研究，使用不同尺寸的夹紧单边缺口拉伸 (SENT) 试样。为了研究热时效引起的脆化，将16MND5钢在425℃下进行1000h、3000h和5000h的加速热时效，然后测定维氏硬度和拉伸性能。为了研究热老化和试样几何尺寸的综合影响，使用具有不同试样厚度比、B/W和裂纹深度a/W 的SENT 试样研究了各种热老化材料的断裂韧性. 总共测试了 59 个 SENT 样品，涵盖了广泛的热老化时间和几何尺寸组合。结果表明，随着时效时间的增加，材料的显微硬度和拉伸性能略有变化，但R曲线（JR和CTOD-R）显着降低。热时效 RPV 钢的韧性断裂性能显着取决于测试试样的几何尺寸（裂纹深度，a/W和试样厚度，B/W）。此外，几何尺寸和热老化对断裂行为的影响显示出有很强的相互作用。具体而言，随着时效时间的增加，几何尺寸对断裂韧性的影响减小，特别是随着a/W的变化. 此外，随着几何尺寸的增加，热老化对断裂韧性的影响降低。最后，结合断口观察，探讨了热时效对16MND5钢脆化机理和韧性断裂性能的影响。