This work presents an oxidation model that integrates high-temperature steel oxidation kinetics with CFD simulations to predict oxide scale formation during steel reheating under varying combustion atmospheres in the temperature range of 800–1200 °C, over residence times in the rage of 60–160 min. The model accounts for the water vapor content in the furnace atmosphere and evaluates scale thickness under both natural gas and hydrogen combustion, using air or oxygen as oxidizing agents. Oxide scale growth is described using a combined linear–parabolic approach to capture mixed growth mechanisms. Simulation results were validated against experimental measurements of scale thickness obtained for two low-carbon steel grades. The model predictions show good agreement with experimental measurements, with average deviations of approximately 10%, while maximum deviations of up to approximately 17% are observed for specific cases and operating conditions. The model captures scale growth trends under non-isothermal conditions and highlights the impact of water vapor and combustion atmosphere on oxidation behavior.