Analysis of microstructure evolution during different stages of closed-open cross wedge rolling

Abstract

Due to metal different flow rate at the position of part’s surface and its internal, the end of shaft parts formed from traditional open cross wedge rolling (CWR) would produce concave heart. Therefore, the material processing allowance must be considered, which will affect the forming quality and material utilization of parts. In order to solve the problem, the closed-open CWR technology is proposed in this paper. An automobile oil pump shaft made of 42CrMo material was regarded as the research object, and the simulation on part’s deformation, heat, and microstructure structure evolution is performed using finite element software DEFORM. The average grain size and dynamic re-crystallization volume fraction distribution in the first closed rolling stage, the second closed rolling stage, and open rolling stage were analyzed, respectively. Compared to the open CWR, the dynamic re-crystallization volume fraction in the process of the closed-open CWR can reach 100%; the average grain size can decrease to 20 μm. Combined with the rolling experiment, the grain size distribution of the high-temperature austenite grain size was obtained with metallographic analysis method; the average grain size of the experiment is proximately consistent with the simulation results, so the reliability of the closed-open CWR is verified. The results provide a reliable theoretical basis for further improving the material utilization of CWR and the comprehensive mechanical properties of rolled parts.