【摘要】 利用OM,TEM,SEM,显微硬度仪,AFM,磁力显微镜(MFM)和扫描Kelvin探针(SKPFM)等微观分析手段,分析了先进压水堆核电站反应堆压力容器安全端异种金属焊接接头低合金钢A508/镍基焊料52M/奥氏体不锈钢316L的金相组织、显微硬度、主要合金元素、晶界类型以及残余应变的分布,并对比了整个焊接接头不同厚度上的组织和性能.结果表明,焊缝厚度方向上组织和硬度没有显著差别,底焊位置出现一层未熔焊料形成的细小等轴晶,在316L母材热影响区(HAZ)内残余应变较焊接件其它位置高,熔合线附近具有复杂的微观结构、显微硬度、晶界类型、元素成分和残余应变分布.TEM和MFM分析表明,母材316L基体内有富Cr,Mo元素的颗粒状析出相,SKPFM的结果显示该析出相Volta电势较基体更负,因而更不耐腐蚀.更多还原

【Abstract】 The dissimilar metal weld joint(DMWJ) in primary water system of pressurized water reactors(PWRs) has been proven to be a vulnerable component owing to its proneness to different type of flaws. Thus,maintaining integrity of such joint in case of defect presence is of great importance to the design and safe management of nuclear power plants(NPPs). For a reliable integrity analysis of DMWJ, it is essential to understand the microscopic characteristics in all regions of the joint. In this work, OM, TEM, SEM, durometer, AFM, MFM and SKPFM were utilized to investigate the microstructure, micro- hardness and the distribution of main elements, grain boundary characteristic and residual strain in the A508/52M/316 L DMWJ that used for connecting the pipe safeend and the nozzle of reactor pressure vessel in PWRs, and a comparative analysis about the microstructure and property along the radical direction of the DMWJ was obtained. The results showed that there was no region that differed from the other part of the weldment in terms of the microstructure and micro-hardness dramatically. A layer of fine grain resulting from unmelted filler metal was found in the backing weld part of the joint. The residual strain in the heat affected zone(HAZ) of 316 L was higher than that in other regions. Meanwhile, drastic variations in the microstructure, chemical composition distribution and grain boundary character distribution(GBCD) in both the 316L/52 Mw and the 52Mb/A508 interface regions were observed. The analyses using TEM and MFM test showed that a large number of chromium and molybdenum- rich precipitates particles distributed both along the grain boundaries and inside grains in the 316 L base metal, which were identified to be precipitates with complex elementary composition rather than the normal string delta ferrite in 316 L austenitic stainless steel. The SKPFM test result indicated that these precipitates were more prone to be corroded than the base metal. Therefore, further investigation about the cause of deformation and the impacts to the corrosion resistance, particularly the stress corrosion cracking(SCC) sensitivity of the precipitates needs to be carried out.更多还原