The casting method is a key method for large-scale production of multi-crystalline silicon for use in highly efficient solar cells in the photovoltaic industry. Since the efficiency of solar cells depends on the quality of the multi-crystalline silicon, it is important to optimize the casting process to control temperature and iron distributions in a silicon ingot. We developed a new transient global model for the casting process and carried out simulations to study the temperature and iron distributions in a silicon ingot during solidification. Conductive heat transfer and radiative heat exchange in a casting furnace and convective heat transfer in the melt in a crucible are coupled to each other. These heat exchanges were solved iteratively by a finite-volume method in a transient way. Time-dependent distributions of iron and temperature in a silicon ingot during the casting process were numerically studied.