某工程机械传动系统用主轴的正常使用周期为0.5 a（年），但是在使用70 d（天）后就发生了断裂。通过宏观分析、化学成分分析、金相检验、硬度测试、微观分析及能谱分析等方法，对主轴的断裂原因进行了分析。结果表明：该主轴的断裂模式为疲劳断裂，主轴和轴套的偏磨使得主轴表面磨损严重，磨损造成的温度升高超过奥氏体化温度，冷却后形成了局部未回火马氏体的白亮区。白亮区周围的回火区域萌生的裂纹成为疲劳源，在主轴高速旋转过程中裂纹扩展直至发生疲劳断裂。

The normal service life of the driving system main shaft of a construction machinery is half a year, but it fractured after 70 days. The fracture causes of the main shaft were analyzed by means of macro analysis, chemical composition analysis, metallographic examination, hardness test, micro analysis and energy spectrum analysis. The results show that the fracture mode of the main shaft was fatigue fracture. The eccentric wear of the main shaft and the shaft sleeve caused serious wear on the main shaft surface. The temperature rise caused by wear was higher than austenitizing temperature, and the white bright area of local untempered martensite was formed after cooling. The cracks in the tempering area around the white bright area became the fatigue source. During the high speed rotation of the main shaft, the cracks propagated until the fatigue fracture occurred.