发罩锁钩断裂失效分析

Failure Analysis of Fracture of the Hood Lock Hook

本文对某款在研车型腐蚀耐久试验中发现的发动机罩锁钩异常磨损,敲击断裂失效原因进行分析,对化学成分、金相组织、硬度、渗碳层深度等方面进行试验验证。结果表明,两种材质锁钩的化学成分符合技术标准要求。20#钢的心部组织均为铁素体+珠光体,10B21的心部组织为回火索氏体。1~3号试样表面硬度均超过技术要求(35~44)HRC,4号试样硬度为38HRC。根据以上结果,推断出锁钩敲击断裂可能原因为,20#钢的三种热处理工艺制定不合理或者工艺执行不到位,没有进行回火处理或者回火不充分,导致表面硬度过高,残余内应力未去除,敲击时断裂。

The causes of abnormal wear and percussion fracture of engine hood lock hook found in corrosion durability test of a certain model were analyzed,and the chemical composition,metallography,hardness and depth of carburizing layer were tested and verified.The results show that the chemical composition of the two materials meets the technical standard.The core structure of 20#steel is ferrite+pearlite,and the core structure of 1oB2l steel is tempered soxite.The surface hardness of sample 1-3 exceeds the technical requirements(35~44)HRC,and the hardness of sample 4 is 38 HRC.According to the above results,it can be inferred that the possible reasons for the fracture of the lock hook by percussion are that the three heat treatment processes of 20#steel are unreasonable or the process is not executed in place,the tempering is not carried out or the tempering is not sufficient,which leads to the surface hardness is too high,the residual internal stress is not removed,and the fracture during percussion.