通过断口宏观观察、化学成分分析、力学性能检测、金相检验以及扫描电镜分析等方法对材料为ZG35CrMnSi的掘进机回转架裂纹产生原因进行了分析。结果表明：掘进机回转架裂纹的产生主要是由于零件基体内部存在大量的疏松孔洞缺陷和沿晶分布的夹杂物，加之零件没有经过热处理，其显微组织保留着粗大的铸态组织结构，使其塑性和冲击韧度都远低于技术要求；当掘进机在使用过程中受到外力作用时，就会在应力集中严重的回转架耳轴根部过早的萌生应力裂纹并迅速扩展。

Fracture macroscopic observation, chemical compositions analysis, mechanical properties test, metallographic examination, as well as scanning electron microscope observation were used to find the cracking reason of ZG35CrMnSi whirling stand of boring machine. The results indicate that the whirling stand of boring machine had massive loose hole flaws and inlusions distributed along crystal. In addition, it retained cast microstructure because it had not passed through any heat treatment, which caused the mechanical properties of the whirling stand were far below the technical requirements.Cracks would initiated and propagated quickly at the trunnion root fo the whirling stand where the stress concentration was the heaviest, under the external force in the course of working process.