核岛冷却系统铜-不锈钢真空钎焊焊接工艺设计和性能研究

Welding procedure design and property study on vacuum brazing of copper-stainless steel in nuclear island cooling system

在核岛冷却系统中常可见到铜和不锈钢的复合结构。铜导热快,核反应产生的热量通过铜迅速传给不锈钢管,不锈钢管中通入的冷却介质即时带走热量,确保核电系统的安全。对T2纯铜和316L奥氏体不锈钢管的真空钎焊进行了焊接工艺设计。对高精度间隙的接头,采用银铜共晶钎料,在8×10^-3Pa真空下830℃保温30min进行钎焊。通过剪切试验、金相显微镜、显微硬度试验、热冲击试验、扫描电镜和能谱仪对钎焊接头进行显微组织观察和性能分析。结果表明,铜与不锈钢结合良好,钎缝致密。钎缝中的组织是铜基固溶体和银铜共晶。钎焊接头剪切强度可达176MPa。剪切断裂位置在钎缝,断裂形式为韧性断裂。

Composite structures of copper and stainless steel are often used in nuclear island cooling system. Copper conducts heat quickly,the heat generated by the nuclear reaction can be rapidly transferred to the stainless steel tube through copper. The cooling medium introduced into the stainless steel tube takes away the heat immediately to ensure the safety of the nuclear power system. Therefore,the welding quality of copper and stainless steel pipes plays an important role in the nuclear island cooling system. The welding procedure design of vacuum brazing of T2 pure copper and 316L austenitic stainless steel tube is conducted. For the joints with high precision gap,silver-copper eutectic solder is used,and brazing is carried out under vacuum of 8×10^-3 Pa with heat preservation of 830 ℃ for 30 min. Microstructure observation and performance analysis of brazed joints are studied by shear test,metallographic microscope,micro-hardness test,thermal shock test ,scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The result shows that stainless steel and copper are successfully joined together and the brazing seam is dense. The microstructures in the middle area of the brazing seam are copper-based solid solutions and silver-copper eutectic. The shear strength of brazed joints can reach 176 MPa. The shear fracture location is in the brazing seam,and the fracture type is ductile fracture.