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针对曲轴早期断裂失效的问题,通过宏观检验、化学成分分析、力学性能测试、金相检验、断口微观结构分析等手段对其断裂原因进行了分析。结果表明,轴颈油孔内壁异常粗糙的加工刀痕,因应力集中而诱发了材料的最初损伤;感应淬火过渡区低硬度铁素体与刀痕的叠加,明显加速了裂纹的萌生与扩展,是此次曲轴断裂的主要原因;心部上贝氏体的存在一定程度上弱化了材料的力学性能,最终曲轴在复杂交变应力作用下,发生高周疲劳而断裂。
According to the problems of failure of early crankshaft fracture, the causes of fracture were analyzed by macroscopic test, chemical composition analysis, mechanical property test, metallographic examination and fracture microstructure analysis. The results show that the abnormally coarse machining marks on the inner wall of the journal oil hole induce the initial damage of the material due to the stress concentration. The superposition of the low hardness ferrite and the knife marks in the induction hardening zone accelerates the initiation and propagation of cracks, Is the main reason for the crankshaft rupture. The existence of bainite on the heart part weakens the mechanical properties of the material to a certain degree. Finally, the crankshaft is fractured by high-cycle fatigue under complex alternating stress.