某型车20MnB5 钢座椅调节器齿轮在强度试验中断裂.对失效和未失效的调节器齿轮进行了化学成分分析、宏观检查、断口分析、金相检验和硬化层深度检验.结果表明:失效齿轮有严重的机加工划痕,在外加载荷的作用下裂纹易在划痕处萌生并扩展;失效齿轮热处理工艺不当因而心部有较多大块状铁素体,导致其强度降低、最终断裂.
The seat angle adjuster gear of a type of car,made of 20MnB5 steel,broke during strength test.The chemical composition analysis,macro check,fracture testing,metallographic examination and test for hardened layer depth were performed on the failed and the undamaged gears.The results showed that(a)the failed gear exhibited serious machining scratches from which the crack is easy to originate under the action of applied load,and(b)the failed gear displayed more massive ferrite in core due to improper heat treatment,resulting in its lower strength and eventual fracture.