Cast austenitic stainless steels (CASSs) have been extensively used for the large components of nuclear reactor primary coolant systems. Since the cast steels inevitably contain degradable metastable phases and replacement of the large coolant system components is impractical, the thermal embrittlement of CASS components has been a serious concern in the extended-term operation of nuclear power plants. This study aimed to systematically measure and analyze the effect of long-term thermal aging on the Charpy impact toughness to provide a comprehensive understanding of thermal degradation behavior and a practical aging model to predict the degree of thermal degradation in the cast stainless steels. The materials tested in the research include eight CASS alloys (two CF3s, one CF3M, three CF8s, and two CF8Ms) and two reference wrought materials (304L and 316L), in which the nominal δ-ferrite content ranges from ∼2% to 33%. These stainless steels have been thermally aged at two light water reactor (LWR) temperatures (290 and 330°C) and at two accelerated-aging temperatures (360 and 400°C) for up to 30000 hours; these include both under-aged and over-aged conditions relative to the extended service lifetime (80 years). Charpy impact testing was performed for aged and non-aged specimens, and the impact (absorbed) energy parameters were correlated with a new aging parameter (A). Both the reduction of impact fracture toughness and the shift of ductile-brittle transition temperature were strongly dependent on the δ-ferrite content and degree of thermal aging. A linear relationship was found between the increasing rate of the index transition temperature T_41J and aging parameter A; base on which an empirical model was proposed for prediction of the transition temperature as a simple function of the aging parameter (A) and δ-ferrite content (F). Finally, the critical aging parameter for embrittlement (A_C) was evaluated and compared with the existing δ-ferrite content criteria.

铸造奥氏体不锈钢（CASS）已广泛用于核反应堆一次冷却剂系统的大型组件。由于铸钢不可避免地包含可降解的亚稳相，并且不可行更换大型冷却剂系统组件，因此CASS组件的热脆化一直是核电站长期运行中的一个严重问题。这项研究旨在系统地测量和分析长期热时效对夏比冲击韧性的影响，以提供对热降解行为的全面理解，并提供一种实用的时效模型来预测铸造不锈钢的热降解程度。该研究中测试的材料包括八种CASS合金（两种CF3，一种CF3M，三种CF8，两种CF8Ms）和两种参考锻造材料（304L和316L），其中标称δ铁素体含量在〜2％至33％之间。这些不锈钢已在两个轻水堆（LWR）温度（290和330°C）和两个加速时效温度（360和400°C）进行了30000小时的热时效处理；这些包括相对于延长的使用寿命（80年）而言的未成年人和过老人情况。对老化和未老化的试样进行了夏比冲击试验，冲击（吸收的）能量参数与新的老化参数（A）相关。冲击断裂韧性的降低和韧性-脆性转变温度的变化都强烈地依赖于δ铁素体含量和热老化程度。_41J和老化参数A; 在此基础上，提出了一个用于预测转变温度的经验模型，该模型是时效参数（A）和δ铁素体含量（F）的简单函数。最后，评估了脆化的临界时效参数（A _C），并将其与现有的δ铁素体含量标准进行了比较。