Abstract Welding structures of primary coolant pipes were subjected on a series of accelerated thermal aging test at 400 °C until 30,000 h to investigate the resulting microstructure, impact and nanoindentation properties change. The results indicated that after long-term thermal aging, a mottled structure and precipitated G-phases were observed in ferrite phases both of straight pipes and welded joints, leading to a decrease in impact energy and an increase in nanohardness. Moreover, until thermal aging saturation, impact energy of welding structures was still higher than initial design value (80 J), thus demonstrating a high toughness reserve, but saturated impact energy in welded joints was higher than that in straight pipes owing to lower ferrite content. Furthermore, there were higher-density spinodal decompositions and more precipitated G-phases in welded joints than those in straight pipes owing to micro-defects generated from welding process, resulting in a higher nanohardness in ferrite phases of welded joints.

中文翻译：

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核电站一次冷却剂管道焊接结构长期热老化性能

摘要 对一次冷却剂管道的焊接结构进行了一系列在 400 °C 至 30,000 h 的加速热老化试验，以研究由此产生的微观结构、冲击和纳米压痕性能变化。结果表明，经过长期热时效后，直管和焊接接头的铁素体相均出现斑驳结构和析出的G相，导致冲击功降低，纳米硬度增加。此外，直到热时效饱和，焊接结构的冲击能仍高于初始设计值（80 J），显示出较高的韧性储备，但由于铁素体含量较低，焊接接头的饱和冲击能高于直管. 此外，