Fatigue fracture analysis on copper brazed joint of low-carbon steel fuel pipe

低碳钢油管铜钎焊接头疲劳断裂分析 Fatigue fracture analysis on copper brazed joint of low-carbon steel fuel pipe 孔德群 KONG Dequn 1 first-author 杨利 YANG Li 1 周建 ZHOU Jian 1 周晓炜 ZHOU Xiaowei 1 王志勇 WANG Zhiyong 1 北京奔驰汽车有限公司研发部材料实验室 北京奔驰汽车有限公司研发部材料实验室 R&D Material Laboratory, Beijing Benz Automotive Co.,Ltd. R&D Material Laboratory, Beijing Benz Automotive Co.,Ltd. 从断口分析、金相检验、化学分析等方面分析低碳钢油管断裂性质及其产生原因。油管与支架通过铜钎焊的方式连接在一起,由于钎焊温度控制不良,连接处的油管表面发生铜原子沿低碳钢晶界的偏聚与扩散,降低了其塑性与强度;另一方面,焊后冷速控制不良,导致焊缝附近的油管内部产生魏氏体铁素体。平台试验中油管钎焊区域承受较大的循环应力,焊缝外表面机械损伤处由于应力集中效应,在局部高应力作用下产生疲劳裂纹源,裂纹向油管扩展并导致服役早期开裂失效。 The failure mechanism and causes of a low-carbon steel fuel pipe were investigated via fractography,metallographic examination and chemical analysis. The steel pipe and bracket are connected by copper brazing. The seg-regation and diffusion of copper atoms occur along the grain boundaries on the surface of fuel pipe due to a poorly controlled brazing temperature,which reduces its plasticity and strength;on the other hand,the poorly controlled postweld cooling rate leads Widmanstatten-ferrite to generate inside the steel pipe. In the platform test,the brazed zone is subjected to periodic loading processes of large cyclic stress. Due to the stress concentration effect at the mechanical damage on the weld surface,a fatigue crack source is generated under the local high stress condition and the initial crack extends towards the fuel pipe,which leads to a cracking failure at the early stage of its service life. 汽车发动机 油管 焊后冷却速度 铜钎焊 应力集中 疲劳断裂 automobile engine fuel pipe postweld cooling rate copper brazing stress concentration fatigue fracture U464;TG454 2022-03-08 5 50