某排气支管采用QTRSi4Mo耐热铸铁一体铸造成型，在运行约2 000 h后发生开裂。利用直读光谱仪、拉伸试验机、扫描电子显微镜、光学显微镜等设备，对排气支管的开裂原因进行了分析。结果表明：排气支管开裂主要是由于材料内部存在较多的疏松缺陷，降低了材料的强度，在服役过程中的振动力作用下，排气支管于缺陷处发生了开裂。

An exhaust branch pipe was integrally casted with QTRSi4Mo heat resistant cast iron, and cracking occurred after about 2 000 h of operation. The cracking causes of the exhaust branch pipe were analyzed by direct reading spectrometer, tensile testing machine, scanning electron microscope, optical microscope and other equipments. The results show that the cracking of the exhaust branch pipe was mainly due to the existence of much shrinkage defect inside the material, which reduced the strength of the material. Under the vibration force during service, the exhaust branch pipe cracked at the defect.