柴油机连杆断裂失效机理分析及改进
焦明裕1,2，李成艳1,2，蒋丽媛1,2，孔龙1,2
1.内燃机与动力系统全国重点实验室，山东 潍坊 261061；2.潍柴动力股份有限公司，山东 潍坊 261061
摘要：为解决某柴油机连杆在疲劳试验中出现的断裂故障，观察断口的宏观及微观形貌，对连杆进行金相组织分析、能谱分析、非金属夹杂物化学成分及含量等级检验，确定连杆断裂原因，提出改进措施，并对改进后连杆进行疲劳试验和整机耐久试验。结果表明：连杆原材料钢棒中心存在疏松缺陷，经下料切割及高温锻造后在连杆小头顶部产生氧化铁，氧化铁在交变载荷作用下成为疲劳源，导致连杆产生裂纹；连杆中硫化物夹杂含量过高、长度超限且具有方向性，使裂纹向外扩展，加速连杆断裂过程。采取降低钢棒连铸过热度、提高超声波探伤等级、降低硫元素和硫化物含量等改进措施，改进后连杆顺利通过疲劳试验和整机耐久试验，未再发生连杆断裂失效故障，改进措施有效。
关键词：连杆断裂；疲劳；疏松缺陷；非金属夹杂
Analysis of fracture failure mechanism of connecting rod for a diesel engine and its improvement
JIAO Mingyu1,2, LI Chengyan1,2, JIANG Liyuan1,2, KONG Long1,2
1. State Key Laboratory of Engine and Powertrain System, Weifang 261061, China;
2. Weichai Power Co., Ltd., Weifang 261061, China
Abstract: To solve the fracture failure of a diesel engine connecting rod during fatigue testing, the macroscopic and microscopic morphologies of the fracture surface are observed, and metallographic structure analysis, energy spectrum analysis, non-metallic inclusion chemical composition and content grade inspection are carried out on the connecting rod to determine the cause of the fracture. Improvement measures are proposed, and fatigue and overall durability tests are conducted on the improved connecting rod. The results shows that there is a loose defect in the center of the steel rod used as the raw material for the connecting rod. After cutting and high-temperature forging, iron oxide is produced at the top of the small head of the connecting rod, which becomes a fatigue source under alternating loads, leading to cracks in the connecting rod; the sulfide inclusion content in the connecting rod is too high, the length exceeds the limit, and it has directionality, which causes cracks to propagate outward and accelerates the fracture process of the connecting rod. After taking improvement measures such as reducing the overheating of steel bars during continuous casting, improving the ultrasonic testing level, and reducing the content of sulfur and sulfides,the connecting rod successfully passes the fatigue test and the overall durability test, and there are no more incidents of connecting rod fracture failure.
Keywords: connecting rod fracture; fatigue; porosity defect; non-metallic inclusion
