1. Conclusion : It is presumed that the inspected product suffered ductile failure due to a pre-crack that had occurred on the inner periphery of the pipe at the rear of the engine. ・Element (S), which is thought to be derived from alumite treatment, was detected on the fracture surface, and galling was observed on the inner circumferential surface near the fractured part, indicating that galling occurred during mold release during the casting process (prior to surface treatment). It is assumed that the load caused a pre-crack to occur on the inner periphery of the rear side of the engine. Since no casting defects were observed in the cross section of the precrack starting point, it is unclear whether the casting quality influenced the occurrence of precracks. However, since multiple fracture chills were observed around the fracture, it is necessary to improve the casting quality.