针对某40Cr钢汽车半轴在装配过程中发生断裂的问题, 通过对半轴的化学成分、显微组织、力学性能、断口等方面进行分析, 查找出了导致半轴断裂的原因。结果表明: 半轴热处理时淬火温度过高或保温时间过长, 导致奥氏体晶粒粗大, 冷却时在材料心部形成魏氏体组织, 是导致半轴断裂的主要原因; 另外淬火温度偏高导致杂质元素在晶界聚集, 降低了晶界的结合强度, 也促进了半轴的断裂。因此, 优化冶炼工艺制度、并严格遵守热处理制度是避免汽车半轴断裂的主要措施。

Aiming at the problem of fracture of 40Cr steel automobile half-shafts during assembly, by analyzing the chemical compositions, microstructure, mechanical properties and fracture of the half-shaft, the fracture reasons were found out. The results show that the too high quenching temperature and too long holding time in the heat treatment process led to coarse austenite, and then widmanstatten structure was formed in the center of the half-shaft during cooling, which were the main reasons for the fracture. At the same time, higher quenching temperature led to the aggregation of impurity elements at the grain boundaries and reduced the grain boundary bonding strength, which also accelerated the fracture of the half-shaft. Therefore, optimizing of smelting process system and strictly complying with the heat treatment process system were main measures to avoid fracture of the automobile half-shafts.