QT700-2球墨铸铁发动机曲轴失效分析

Failure Analysis of QT700-2 Ductile Iron Engine Crankshaft

目的某厂生产的QT700-2球墨铸铁曲轴在路试过程中出现断裂,需寻找失效原因并提出解决措施。方法通过应用金相组织分析、化学成分分析、表面残余应力测试和力学性能测试等方法,对该曲轴的失效原因进行了分析。结果测试后分析结果表明,曲轴是在较大扭转循环载荷下,在第四连杆颈滚压圆角边缘多点萌生裂纹而导致疲劳断裂是其失效的主要原因。结论建议改进热处理工艺,保证组织的均匀性;改进加工工艺,减少应力集中;并强化表面残余应力以提高曲轴的疲劳寿命。

The work aims to find out the failure analysis and propose the solution for fracture of QT700-2 ductile iron crankshaft produced by a factory during the road test. The failure analysis for crankshaft was carried out by the examination of metallographic microstructure, chemical composition analysis, surface residual stress test and mechanical property test. The test results showed that the fatigue fracture was the main cause of crankshaft failure due to multi-point initiation of cracks at the corner edge of the fourth connecting rod neck during rolling under large torsional cyclic load. It is suggested to improve the heat-treating process to ensure the uniformity of microstructure and improve machining process to reduce stress concentration and then enhance the surface residual stress to improve the fatigue life of crankshaft.