Effect of electric current pulse on size of primary carbides in hypereutectic high chromium cast irons in different solidification stages

Abstract

To investigate the influence of electric current pulse (ECP) on the size of primary carbides in the hypereutectic high chromium cast irons, an ECP (peak density: 19.66 × 105 A m−2) was applied respectively to samples in different solidification stages (the pre-nucleation stage, the nucleation and initial growth stage, the late growth stage of primary carbides). Besides the latter two stages, the ECP can also refine primary carbides in the pre-nucleation stage. There are a few similar reports in the literature about other alloys. The samples were treated with ECP of different current density in the same stages to better study the refinement mechanism. The results show that the size of primary carbides decreased first and then increased as the ECP current density increased in the first two stages. The size continued to decrease in the last stage. The analysis shows that the main roles of ECP in different stages are different. The main roles of ECP are the free energy effect and the pinch effect both in the first two stages. That is the pinch effect in the last stage. The change of size of primary carbides is the result of competition between two effects of ECP.