某液压系统使用的大型圆柱螺旋压缩弹簧在运行20万次后发生断裂，采用断口形貌、显微组织观察，化学成分、硬度测试等方法对弹簧的断裂原因进行了分析。结果表明：弹簧的断裂为低周疲劳断裂，裂纹源区位于弹簧钢丝近表面位置的大尺寸夹杂物处；夹杂物的存在降低了弹簧钢内部的连续性，弹簧钢受到拉应力和扭转作用力时萌生裂纹，在后续服役过程中裂纹扩展，最终断裂；弹簧喷丸处理形成的硬化层深度不够，不足以抵消弹簧钢丝表面脱碳层对疲劳寿命的不利影响，导致疲劳寿命降低。

A large cylindrical spiral compression spring used in a hydraulic system was fractured after operating 200 000 times. The causes of fracture on spring were analyzed by fracture morphology, microstructure observation, and chemical composition and hardness test. The results show that the fracture of the spring was low cycle fatigue fracture, and the crack source region was located at the large inclusions near the surface of the spring steel wire. The existence of inclusions reduced the internal continuity of the spring steel, and cracks initiated when the spring steel was subjected to tensile stress and torsional force, and the cracks expanded in the subsequent service process, eventually fracture. The depth of hardening layer formed during peening was not enough to effset the adverse effect of decarbonized layer on fatigue life of spring steel wire, resulting in the reduction of fatigue life.