Unexpected thermal aging effect on brittle fracture and elemental segregation in modern dissimilar metal weld

IF 4.8 2区材料科学 Q1 MATERIALS SCIENCE, CHARACTERIZATION & TESTING Materials Characterization Pub Date : 2024-09-30 DOI:10.1016/j.matchar.2024.114419

Andrea Fazi , Pedro A. Ferreirós , Yanling Ge , Song Lu , Mattias Thuvander , Zaiqing Que

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Abstract

A full-scale dissimilar metal weld safe-end mock-up, precisely replicating a critical component of a modern nuclear power plant, was investigated. The brittle fracture behavior, carbide evolution and nanoscale elemental segregation in the heat-affected zone (HAZ) of low alloy steel (LAS) were analyzed under both post-weld heat-treated and thermally-aged conditions (400 °C for 15,000 h, equivalent to 90 years of operation) using analytical electron microscopy and atom probe tomography. The observed increase in grain boundary (GB) decohesion and intergranular cracking on the fracture surface and the decrease of fracture toughness are primarily attributed to P and Mn segregation to GBs and the coarsening of carbides upon long-term thermal aging. The direct observations of significant elemental segregation to GBs and the consequent reduction in fracture toughness in the HAZ are unexpected for modern low-phosphorus LASs, highlighting potential concerns for evaluating the structural integrity of modern nuclear power plants.

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热老化对现代异种金属焊缝脆性断裂和元素偏析的意外影响

对精确复制现代核电厂关键部件的全尺寸异种金属焊接安全端模型进行了研究。利用分析电子显微镜和原子探针断层扫描技术，分析了低合金钢（LAS）在焊后热处理和热老化（400 °C，15,000 小时，相当于运行 90 年）条件下的脆性断裂行为、碳化物演变和热影响区（HAZ）中的纳米级元素偏析。所观察到的晶界（GB）脱粘和断裂表面晶间裂纹的增加以及断裂韧性的降低主要归因于 P 和 Mn 在 GB 上的偏析以及长期热老化后碳化物的粗化。对于现代低磷 LAS 而言，直接观察到大量元素偏析到 GB 以及 HAZ 断裂韧性随之降低是意料之外的，这凸显了评估现代核电站结构完整性的潜在问题。

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来源期刊

Materials Characterization 工程技术-材料科学：表征与测试

CiteScore

7.60

自引率

8.50%

发文量

746

审稿时长

36 days

期刊介绍： Materials Characterization features original articles and state-of-the-art reviews on theoretical and practical aspects of the structure and behaviour of materials. The Journal focuses on all characterization techniques, including all forms of microscopy (light, electron, acoustic, etc.,) and analysis (especially microanalysis and surface analytical techniques). Developments in both this wide range of techniques and their application to the quantification of the microstructure of materials are essential facets of the Journal. The Journal provides the Materials Scientist/Engineer with up-to-date information on many types of materials with an underlying theme of explaining the behavior of materials using novel approaches. Materials covered by the journal include: Metals & Alloys Ceramics Nanomaterials Biomedical materials Optical materials Composites Natural Materials.