Cracks Analysis on Whirling Stand of Boring Machine

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.