The Microstructure and Residual Stress Analysis of Gray Iron Castings by Ultrasonic Technique

Abstract

Currently, the precision demand of machine tool has reached to the micrometer level. The precision stability of the equipment is more important than ever. Instability of the dimensional precision of the structural component is usually caused by the unstable microstructure of materials and the residual stress. In this study, we perform the residual stress analysis by CAE method on ASTM 300 gray iron castings and use the XRD and ultrasonic methods to perform the certification, respectively. The martensitic microstructure significantly has lower wave speed and the smaller size of the graphite tends to reduce the longitudinal wave speed. However the effect of gray iron microstructure is higher than the graphite size. It is acceptable to use ultrasonic inspection method to perform microstructure identification and residual stress analysis. Once the residual stress of castings has not suitable relief, serious dimensional variations will induce the distortion of the castings.