Abstract: Aiming at the crucial role of surface carburization in reducing the melting point of scrap steel, thereby promoting its melting and increasing the carbon content of the molten pool during its melting process in converters or electric arc furnaces, an Fe-C diffusion model was constructed based on the unsteady diffusion-mass transfer theory in media. The diffusion process of carbon on the surface of the iron matrix and the variation pattern of the melting point at the carburized locations were investigated using numerical simulation methods. The effects of factors such as carburization time, temperature, carbon particle size, and the rust layer on the iron surface on the carburization effectiveness were also explored. The results show that the interfacial carburization reaction is weak within the lower temperature range (500–900 ℃), and the migration ability of carbon atoms is poor. When the temperature rises to 1 200 ℃, the carburization depth increases significantly by 67% compared to that at 1 100 ℃. Carbon particle size has a notable impact on the carburization effect: smaller particle sizes favor carburization, but when the particle size is refined to 100 μm, further reduction in size leads to only a limited increase in carburization depth. In addition, the rust layer significantly promotes carbon migration; the presence of a rust layer on the iron-based surface increases the carburization depth by more than three times compared to the condition without a rust layer. This study provides a theoretical reference for developing efficient scrap preheating carburization and rapid-melting briquette processes, which can directly reduce smelting energy consumption and carbon emissions by improving scrap melting efficiency, and offers clear guidance for promoting the green transformation of the steel industry.