1. 上海交通大学 核科学与工程学院， 上海 200240; 2. 中国核动力研究设计院， 成都 610041
Effects of Potential on 508III-52M-690 Dissimilar Weld Joint
WANG Jiamei1，SU Haozhan1,HE Kun2，ZHANG Lefu11. School of Nuclear Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; 2. Nuclear Power Institute of China, Chengdu 610041, China
摘要/Abstract
摘要： 通过慢应变速率拉伸和高温电化学试验相结合的方法，研究了外加电位对压水堆核电机组安全端 508III-52M-690合金异种材料焊接接头在含氯离子的高温高压水中应力腐蚀开裂(SCC)倾向的影响规律.结果表明，在温度为300℃高温高压水环境下，当氯离子的含量为50mg/kg、除氧时，焊接接头的SCC敏感性随电极电位升高而增大，即随着溶解氧浓度增加而增加.存在一个介于－500～－400mV(相对标准氢电极)的SCC临界电位，低于该电位时，焊接接头SCC敏感性较小，未见明显沿晶开裂，断裂为由力学性能主导的塑性开裂，与焊接接头不同冶金组织的硬度密切相关，硬度越低，越容易断裂，断裂位置均为硬度最低的52Mb处；高于临界电位时，SCC敏感性急剧增加，并出现明显的沿晶开裂和穿晶开裂断口，断裂为腐蚀主导的脆性开裂，断裂位置均为腐蚀性能最差的低合金钢 508III 热影响区.同时发现，焊接接头中52Mb对接焊和 508III 钢之间的热影响区对SCC最敏感.
关键词: 508III-52M-690异种焊接接头, 应力腐蚀开裂, 慢应变速率拉伸, 高温电化学
Abstract: Effect of applied potential on stress corrosion cracking (SCC) behavior of 508III-52M-690 dissi-milar weld joint of safe-end was researched with slow strain rate tensile (SSRT) tests and high temperature electrochemistry tests in high temperature (300℃) water containing 50mg/kg chloride. The results revealed that the SCC susceptibility increases dramatically with the applied potential, then the potential above a critical value exists between －500 and －400mV (versus standard hydrogen electrode). The SCC susceptibility is low and no obvious intergranular or transgranular stress corrosion cracks can be found when the applied potential below the critical value which corresponds to deoxygenated water chemistry. It means the fracture is dominated by mechanical properties and closely relates to the hardness distribution of welded joint. The lower the hardness is, the more easily fractures occur. Therefore, all ductile fractures are located at 52Mb (butt welded) with the lowest hardness. While, when electrode potential is higher than the critical potential, all brittle fractures are located at 508III heat affected zone (508III HAZ) with the lowest corrosion resistance, where exhibits significant SCC behavior with large area intergranular and transgranular stress corrosion cracks. Hence, the dissolved oxygen concentration need be controlled strictly to make sure the corrosion potential is below the critical potential. Besides, the 52Mb and 508III HAZ of this dissimilar weld joint are the most venerable sites to crack which need to be paid high attention to during the operation.
Key words: 508III-52M-690 dissimilar weld joint, stress corrosion cracking (SCC), slow strain rate tensile (SSRT), high temperature electrochemistry
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