某型发动机增压器304不锈钢回油管在与法兰钎焊部位出现了批量开裂失效现象。采用扫描电镜(SEM)及能谱仪(EDS)分析、金相分析及硬度测试等方法对开裂件进行了失效分析。结果表明: 回油管钎焊缝开裂为高周疲劳开裂, 钎焊时出现了铜钎料对304不锈钢母材的熔蚀, 疲劳裂纹正是起源于这一钎焊缝熔蚀部位; 同时钎焊工艺不当导致的母材基体奥氏体晶粒粗大、大量碳化物沿晶界连续析出和不锈钢基体硬度偏低等因素促进了疲劳裂纹的产生与扩展。

The turbocharger oil return pipes made of 304 stainless steel and used in a certain type of engine, cracked in batches at brazing part with the flange. SEM and EDS analysis, metallographic analysis and hardness test were performed to analyze the cracking parts. The results show that the cracking of the oil return pipes was high cycle fatigue cracking. When brazing, the copper brazing filler eroded the 304 stainless steel substrate, and fatigue cracks just originated from the brazing erosion site. Meanwhile, coarse austenite grain, a large amount of carbides precipitating along the grain boundary and inadequate hardness of stainless steel substrate due to the improper brazing process promoted the generation and expansion of the fatigue cracks.