Degradation of impact toughness in cast stainless steels during long-term thermal aging

JOURNAL OF NUCLEAR MATERIALS

卷:542

Article

Byun, Thak Sang¹  Collins, David A.¹  Lach, Timothy G.¹  Carter, Emily L.² 

[1] Oak Ridge Natl Lab, 1 Bethel Valley Rd, Oak Ridge, TN 37831 USA

[2] Pacific Northwest Natl Lab, 902 Battelle Blvd, Richland, WA 99352 USA

关键词: Cast stainless steels;    Charpy impact energy;    Ductile-brittle transition temperature;    Aging parameter;    Thermal embitterment;    Delta-ferrite content;   

DOI  :  10.1016/j.jnucmat.2020.152524

来源: Elsevier

【 摘 要 】

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 d-ferrite content ranges from similar to 2% to 33%. These stainless steels have been thermally aged at two light water reactor (LWR) temperatures (290 and 330 degrees C) and at two accelerated-aging temperatures (360 and 400 degrees C) for up to 30,000 h; these include both under-aged and over-aged conditions relative to the extended service life-time (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 d-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 delta-ferrite content (F). Finally, the critical aging parameter for embrittlement (A(C)) was evaluated and compared with the existing delta-ferrite content criteria. Published by Elsevier B.V.

【 授权许可】

Free