A program is being conducted to investigate the significance of in-service embrittlement of cast duplex stainless steels under light-water reactor operating conditions. The existing data are evaluated to determine the expected embrittlement of cast components during the operating lifetime of reactors and to define the objectives and scope of the investigation. This presentation describes the status of the program. Data for the metallurgical characterization of the various cast stainless steels used in the investigation are presented. Charpy impact tests on short-term aged material indicate that CF-3 stainless steels are less susceptible to embrittlement than CF-8 or CF-8M stainless steels. Microstructural characterization of cast stainless steels that were obtained from Georg Fischer Co. and aged for up to 70,000 h at 300, 350, and 400/sup 0/C reveals the formation of four different types of precipitates that are not ..cap alpha..'. Embrittlement of the ferrite phase is primarily due to pinning of the dislocations by two of these precipitates, designated as Type M and Type X. The ferrite phase is embrittled after approx. 8 y at 300/sup 0/C and shows cleavage fracture. Examination of the fracture surfaces of the impact-test specimens indicates that the toughness of the long-term aged material is determined by the austenite phase. 8 figures, 3 tables.

/pdf/aging-of-cast-duplex-stainless-steels-in-lwr-systems-2sa8ltcccr.pdf

Aging of Cast Duplex Stainless Steels in LWR Systems

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.

/pdf/he-dian-zhan-dui-nei-gou-jian-yong-304bu-xiu-gang-han-feng-3r9zkex4ms.pdf

核电站堆内构件用304不锈钢焊缝热老化行为研究 Study on Thermal Aging Behavior of 304 Stainless Steel Weld for Nuclear Internals

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核电站堆内构件用304不锈钢焊缝热老化行为研究 Study on Thermal Aging Behavior of 304 Stainless Steel Weld for Nuclear Internals