采用宏观分析、化学成分分析、硬度测试、金相检验和能谱分析等方法对材料为STKM 12B的机械结构用碳素钢汽车防震器外筒在组装时发生开裂的原因进行了分析。结果表明: 外筒开裂为塑性开裂，装配应力过大是造成开裂的外部原因;另材料局部显微组织粗大、晶粒不均匀以及硬度偏低是导致防震器外筒组装时发生开裂的内在原因。

By means of chemical composition analysis,hardness test, microstructure examination and SEM/EDS analysis,the cracking reason of the tube used in anti-shock instrument of automobile during assembling process was analyzed.The result show that the tube cracking was plastic cracking, and too big assembly stress was the major cause for the cracking.Local roase microstructure, asymmetric grain size and low hardness were the other causes which resulted in the cracking when the tube was assembled.