在对经调质处理的40Cr钢承重连接杆进行精加工时,发现其外表面发生横向开裂。采用宏观观察、化学成分分析、气体分析、金相检验及硬度测试等方法分析了该连接杆开裂的原因。结果表明:该连接杆开裂的原因是热处理工艺不当,导致组织未被淬透;在零件内槽变形处的加工精度不足,产生了应力集中,导致弧形裂纹延伸至表面。采用调整淬火工艺参数、将冷却介质改为水基淬火液、优化工件车削精度、将过渡区域改为圆角等方法可以提高产品的合格率。

During precision machining of the quenched and tempered 40Cr steel load bearing connecting rod, the transverse cracking was found on its outer surface. The causes of cracking of the connecting rod were analyzed by macroscopic observation, chemical composition analysis, gas analysis, metallographic examination, and hardness testing. The results show that the reasons for the cracking of the connecting rod were due to improper heat treatment process, which resulted in the microstructure not being quenched thoroughly. Insufficient machining accuracy at the deformation of the inner groove of the part resulted in stress concentration, led to arc-shaped cracks extended to the surface. By adjusting the quenching process parameters, changing the cooling medium to water-based quenching liquid, optimizing the turning accuracy of the workpiece and changing the transition area to rounded corners, the qualification rate of the product could be improved.