核级304L不锈钢钎焊接头组织及耐腐蚀性能研究

核级304L不锈钢与BNi 7钎料真空钎焊接头存在晶间腐蚀行为，但工艺与钎缝耐腐蚀性能的关系尚未得到充分研究。为充分评估压水堆燃料组件结构件中不锈钢真空钎焊接头的晶间腐蚀和应力腐蚀敏感性，降低腐蚀失效风险，采用定量金相方法分析了钎缝中的化合物相含量，采用硫酸 硫酸铁法和双环动电位再活化（DL EPR）法评价了钎缝耐晶间腐蚀性能，并采用高温高压水应力腐蚀裂纹扩展试验评价了钎缝的耐应力腐蚀性能。结果表明，钎缝中化合物相含量越高，耐晶间腐蚀性能越好。且钎缝在高温高压水中存在明显的应力腐蚀开裂行为，但其与钎焊工艺的关系尚需进一步试验研究。

Structure and Corrosion Resistance of Brazed Joint of Nuclear Grade 304L Stainless Steel

The vacuum brazed joints of nuclear grade 304L stainless steel and BNi 7 filler metal show obvious intergranular corrosion behavior, but the relationship between the brazing process and the corrosion resistance of the brazed joint was not fully studied. In order to fully evaluate the sensitivity of intergranular corrosion and stress corrosion of stainless steel vacuum brazed joints of the structural parts of PWR fuel assemblies, and reduce the risk of corrosion failure, many trials and studies were conducted. In this paper, the quantitative metallographic method was used to analyze the content of the compound phase content of brazed joints by different brazing processes. The sulfuric acid ferric sulfate test method and the double loop electrochemical potentiokinetic reaction (DL EPR) test method were used to test the intergranular corrosion resistance. The high temperature and high pressure water stress corrosion crack growth tests were used to study the stress corrosion resistance of brazed joints, respectively. The results show that increasing the brazing temperature, prolonging the holding time and decreasing the clearance of the brazed joints can reduce the content of the compound phase content in the brazed joint. This might be related to the increase in diffusion of P element. But meanwhile, with the reduction of the compound phase, the intergranular corrosion rate will also significantly increase. Metallographic photographs show that all the corrosions are caused in the nickel based solid solution phase of the brazed joint. Both the sulfate ferric sulfate test method and the DL EPR test method show such a trend. Firstly, the stress corrosion cracking behavior in high temperature and high pressure water was also confirmed by the high temperature and high pressure water stress corrosion crack growth tests. But the relationship with the brazing process needs further experimental research. Therefore, under the condition of ensuring the strength of the brazed joint, the brazing temperature should be increased, the holding time should be extended and the clearance of the brazed joints should be reduced to reduce the compound phase content, thereby increasing the content of nickel based solid solutions in the brazed joints and reducing the tendency to the intergranular corrosion. In addition, within the range of test parameters, the obvious tendency to intergranular corrosion in all the brazed joints was observed. The lower the compound phase content in the brazed joints, the more obvious the intergranular corrosion tendency, which is related to the fact that intergranular corrosion is mainly caused by the dissolution of the solid solution phase of the lean Cr. This study also confirmed that there is a stress corrosion tendency of brazed joints in the PWR water environment, and the area where stress corrosion is generated is mainly the solid solution phase. But the correlation between the degree of stress corrosion and the brazing process needs to be further studied.