汽车排气管焊缝断裂的失效分析

某汽车用排气管使用不久焊缝处断裂。对失效排气管焊缝进行化学成分、金相组织和断口的微观分析。发现该排气管焊缝柱状组织粗大,断口微观形貌为沿晶断裂,柱状晶贯穿整个断裂面,断口有较明显的脆性特征。分析认为该排气管属于早期失效,是由于薄壁的排气管焊接时温度过高,导致焊缝柱状组织粗大,加之薄壁管冷却又快,致使焊缝产生较大的内应力。建议改进焊接工艺,控制较低的层间温度,使焊缝组织细化,解决焊缝断裂问题。

Failure Analysis of Fracture on Weld of Motorcar Vent-pipe

There had been fracture on weld of certain motorcar vent-pipe soon after used.The failure analysis of weld of motorcar vent-pipe was carried out by chemistry component analysis,metallographic microstructure examination and fracture inspection.It was detected that the columnar crystal was big in microstructure on the position of the weld of vent-pipe.It showed that the fracture was along the crystals on the microstructure appearance,columnar crystals run through fracture surface,fracture part had obvious brittle character.It was considered that the vent-pipe occurred forepart failure,because the temperature was high enough on weld of vent-pipe when welding to bring about big columnar crystal in microstructure and the cooling of the thin pipe was rapidly enough to produce big stress.It was suggest that the welding technique should be improved and the lower temperature of layer between weld and base metal should be controlled,to make the micro-structure of weld thinner,and solve the problem of weld fracture.