某装载机用内齿圈成品在搬运过程中意外跌落并发生脆断。采用宏观观察、断口分析、化学成分分析、低倍检验、金相检验等方法对其断裂原因进行了分析。结果表明：不当的辗环工艺导致内齿圈形变过烧，进而在其心部出现大量呈周向分布的细小孔洞和裂纹；机加工使材料心部的缺陷暴露出来，并在随后的渗氮处理中生成了大量的脉状组织，极大地增加了内齿圈的脆性，最终导致内齿圈在跌落时发生脆断。

The finished product of inner gear ring for a loader accidentally fell and brittle fracture occurred during transportation. The fracture reasons were analyzed by macroscopic observation, fracture analysis, chemical composition analysis, low power test and metallographic examination. The results show that the improper ring rolling process led to the deformation overburning of the inner gear ring, and a large number of circumferentially distributed fine holes and cracks appeared in the center of the inner ring. The machining exposed the defects in the core of the material, and a large number of vein structures were generated in the subsequent nitriding treatment, which greatly increased the brittleness of the inner gear ring, and eventually led to brittle fracture of the inner gear ring when it fell.