某产线变速箱齿轮发生断裂。采用宏观观察、化学成分分析、扫描电镜和能谱分析、金相检验以及硬度测试等方法，分析了齿轮断裂的原因。结果表明：齿轮化学成分不符合产品设计标准GB/T 699—2015的要求，且断裂轮齿组织为粗大的魏氏体，并存在大量以氧化铝为主的非金属夹杂物，导致齿轮的韧性和耐磨性大幅降低。在服役过程中，齿轮在传递动力时长期受弯曲疲劳应力以及异常组织和夹杂物的影响，最终发生断裂。

The gear in the gear-box on a line was fractured. The causes of gear fracture were analyzed by macroscopic observation, chemical composition analysis, scanning electron microscopy and energy spectrum analysis, metallographic examination and hardness test. The results show that the gear chemical composition did not meet the requirements of the product design standard GB/T 699-2015, and the microstructure of the fractured gear tooth was gross widmanstatten tissue, and there were a large number of non-metallic inclusions dominated by alumina, resulting in a significant decrease in the toughness and wear resistance of the gear. In the service process, the gear was affected by the bending fatigue stress and abnormal microstructure and inclusions for a long time in the transmission of power, resulting in the fracture of the gear at last.