柴油发动机用排气歧管常用高温力学性能优良的GhSiMoRct球墨铸铁材料铸造而成，但由于铸造零件的加工工序较多，铸件质量不稳定，排气歧管在服役过程中发生了断裂。通过磁粉探伤、扫描电镜分析、化学成分分析、金相检验等方法，对柴油发动机GhSiMoRct球墨铸铁排气歧管的断裂原因进行了分析。结果表明：排气歧管组织中存在铸造缺陷，在外力作用下产生裂纹并不断扩展，导致零件强度大幅度降低，最终排气歧管发生断裂。

The exhaust manifold of diesel engine is usually made of GhSiMoRct nodular cast iron material with excellent high temperature mechanical properties. However, due to the many processing procedures of casting parts and the unstable casting quality, the exhaust manifold fractured during service. The causes of fracture on GhSiMoRct nodular cast iron exhaust manifold in diesel engine were analyzed by means of magnetic particle inspection, scanning electron microscope analysis, chemical composition analysis and metallographic examination. The results show that there were casting defects in the structure of the exhaust manifold. Under the action of external force, cracks produced and propagated continuously, which led to the decrease of the strength of the parts and the fracture of the exhaust manifold.