50Mn回转齿圈在加工过程中出现断裂，超声波探伤发现断口处的回转齿圈内部存在大量微裂纹，沿周向呈现出疏松状+林状的波形分布。为分析缺陷原因，利用低倍检验、扫描电镜、金相显微镜对回转齿圈断裂缺陷进行了相关检测。结果表明，回转齿圈工件内部裂纹本质上为白点裂纹，是导致回转齿圈在加工过程中断裂的主要原因。

The fracture of 50Mn slewing ring gear occurred in the machining process， and the ultrasonic flaw detection found that there were a large number of micro cracks in the fracture section of the slewing ring gear， which were distributed in the waveform with loose shape and Lin shape along the circumference direction. In order to analyze the cause of defect， macroscopic examination， scanning electron microscopy (SEM) and metallographic microscope were used to detect the fracture defects of the slewing ring gear . Results showed that the fracture in the inner of the slewing ring gear was essentially the white dot crack， which was the main reason for fracturing of the slewing ring gear in the machining process.