Graphitauflösung und Kohlenstoffdiffusion beim Laser-Umschmelzen von Gußeisen

The dissolution kinetics of spherical graphite inclusions in nodular cast iron during laser remelting is analyzed for the resting and the well-stirred melt using a semianalytical approach to the moving boundary problem. Carbon transport from the dissolving particle proceeds close to its surface by diffusion but farther away by convection, the size of the diffusion zone depending on the particle's speed and hence on the forces acting on it as well as on its current size. A particle of initial radius 20 micrometers is found to dissolve in an eutectic melt within less than about 0.1 s at 2000 Cel and about 0.6 s at 1500 Cel. Lower dissolution rates are possible if particles cluster together in regions with comparatively low convective fluxes. The computed dissolution kinetics is in satisfactory agreement with particle size and distribution observed in the melting zone of laser remelted nodular cast iron GGG 40.