核电站堆内构件用304不锈钢焊缝热老化行为研究

Abstract

压水堆核电站堆内构件用奥氏体不锈钢焊缝在长期服役过程中会面临着热老化脆化。本文开展了核电站堆内构件用304不锈钢焊缝在325℃、365℃和400℃下15,000 h的加速热老化试验，利用TEM和HRTEM研究了热老化后焊缝微观组织演变，采用冲击实验设备和纳米力学探针分别对热老化后焊缝冲击行为和纳米硬度变化进行了测试，并使用SEM观察了冲击断口形貌。结果表明：热老化后，焊缝内铁素体相发生了调幅分解；随着热老化温度增加，焊缝的冲击韧性显著下降，冲击断口呈现解理断裂特征；焊缝中铁素体相塑形变形能力不断下降，纳米硬度快速增加，而奥氏体相纳米硬度未发生改变。并以焊缝铁素体纳米硬度作为热老化程度指标，利用阿累尼乌斯Arrhenius方程得出304不锈钢焊缝在325℃~400℃内的热老化激活能约为80.4 kJ/mol。 The stainless steel welds used for PWR internals after a long service faces thermal aging embrit-tlement. In this study, the accelerated thermal aging experiments of nuclear internals 304 stainless steel weld were performed at 325˚C, 365˚C and 400˚C for 15,000 h. Microstructure evolution of weld after aging was observed by TEM and HRTEM. Changes of the Charpy impact energy and na-nohardness were studied by Charpy impact and nano-indenter test. The results indicated that Spinodal decomposition and G-phase precipitation in the ferrite was observed after aging. The impact toughness of weld decreased with the increase of aging temperature, and cleavage feature was observed after aging. The nanohardness of ferrite increased, plastic deformation ability of ferrite phase declined, and the nanohardness of austenite hardness had no change. Taking the nanohardness as the standard of thermal aging embrittlement, the thermal aging activation energy was determined for 304 weld in the temperature range 325˚C - 400˚C based on Arrhenius rela-tionship.