Chemical Vapor Deposition (CVB) of SiC in a vertical cold-wall rotating-disk reactor is modeled in a wide range of precursor (silane and propane) flow rate variation. It is found that SiC growth rate is limited by the gas mixture depletion in silicon atoms due to gas-phase nucleation. The secondary phase (graphite and silicon) formation on the growing surface is analyzed. The SIC growth window depending on the precursor flow rates is calculated, and a significant influence of the gas-phase nucleation on the window is demonstrated.