船用柴油机活塞连接螺栓断裂失效分析

采用光学显微镜、扫描电镜和能谱分析等检测手段对船用柴油机活塞头和活塞裙的连接螺栓断裂原因进行了分析。结果表明：该连接螺栓的断裂属多疲劳源引起的疲劳断裂，疲劳源均位于螺纹牙根表面，是由车削螺纹表面加工精度不高而引起的；此外，显微组织中网状、块状铁素体的存在以及螺纹表层脱碳使连接螺栓疲劳强度下降也是造成断裂的重要原因。

Fracture Failure Analyses of Piston Connecting Bolt of Diesel Engine for Ship

The fracture reasons of connecting bolt of piston head and piston skirt in a diesel engine for ship were analyzed by OM, SEM and EDS etc. The connecting bolt was fractured by fatigue with many fatigue sources, which entirely located at the fang surface of screw threads and resulted from the low surface machining precision of screw threads, The existence of reticulation and mass shape ferrite, decarbonization at the screw thread surface layer which induced decline of fatigue strength of connecting bolt were also the important reasons of fracture.