船用柴油机连杆断裂失效分析

刘凯，仇立兵，朱奎，王树纲

中国船舶集团有限公司第七一一研究所，上海 200090

摘要：为解决某船用柴油机连杆断裂失效故障，分析连杆断口宏观及微观形貌、金相组织及非金属夹杂物、化学成分及力学性能，确定连杆失效原因，提出改进措施并进行验证。分析结果表明：连杆螺纹孔根部加工粗糙造成应力集中，连杆中非金属夹杂物较多，且存在与螺纹根部呈一定角度的带状偏析，导致非金属夹杂物在螺纹根部露头，加剧应力集中，在交变力作用下产生裂纹并扩展，使连杆断裂。采取降低连杆非金属夹杂物含量、变更连杆锻造工艺、提高连杆螺栓孔加工质量等改进措施后，进行约4 000 h实机运行验证，未再发生连杆断裂故障。

关键词：连杆；失效分析；非金属夹杂物；疲劳断裂

Failure analysis of connecting rod fracture for a marine diesel engine

LIU Kai, QIU Libing, ZHU Kui, WANG Shugang

Shanghai Marine Diesel Engine Research Institute, Shanghai 200090, China

Abstract: To solve the fracture of connecting rod in a certain marine diesel engine, the cause of connecting rod failure is determined through macroscopic fracture analysis, microscopic fracture analysis, metallographic structure and non-metallic inclusion analysis, chemical composition and mechanical performance analysis, some improvement are also introduced and verified. The analysis results show that rough machining at the root of the connecting rod thread causes stress concentration, and there are many non-metallic inclusions in the connecting rod, with strip segregation at a certain angle to the root of the thread. This leads to non-metallic inclusions exposing at the root of the thread, exacerbating stress concentration, and generating cracks and expanding under the action of alternating forces, causing the connecting rod to fracture. After taking improvement measures such as reducing the content of non-metallic inclusions in connecting rods, changing the forging process of connecting rods, and improving the machining quality of connecting rod bolt holes, the actual machine operation verification are carried out approximately 4 000 hours, and no connecting rod fracture fault occurres again.

Keywords: connecting rod; failure analysis; non-metallic inclusions; fatigue fracture