A Multi-Scale 3D Model of the Vacuum Arc Remelting Process

A multi-scale model of the VAR process was developed to simulate unsteady phenomena within the ingot melt pool due to arc motion and resulting effects on dendritic microstructure. External magnetic field and surface current measurements were used as boundary conditions, to determine the trajectory of the arcs between electrode and ingot and between ingot and sidewalls. The interactions between magnetic field, turbulent metal flow and heat transfer were modelled using CFD techniques and this "macro" model was linked to a micro model, to resolve the evolving dendritic microstructure, and establish a relationship between operational parameters and microstructure defects. Arc-driven solute convection in the mushy zone led to local remelting and changes in local Rayleigh number provided an indicator of when fluid flow channels (freckles) will initiate within the mushy zone. Particle tracking was further used, to characterise the trajectory and dissolution of inclusions entering the melt, causing "white spot" defects.