Mechanism of Carbon Diffusion in the Iron Sheet During Gas–Solid Decarburization

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To investigate the diffusion of carbon in the iron sheet during gas–solid decarburization in a weak oxidative atmosphere (Ar + H2 + H2O), the microstructures of iron sheets following decarburization were observed through SEM. The carbon gradient following decarburization in the iron sheet along the thickness direction was detected in this study. The results showed that the iron sheet along the thickness direction following decarburization consisted of three layers: the L1 layer (ferrite phase) that was near the surface, the L2 layer (cementite phase) that was between the L1 + L3 layers, and the L3 layer (cementite + ferrite + graphite phase) that was in the center of the sample. The depth of the decarburization layer (L1 + L2) showed a good linear relation with the square root of the decarburization time. The carbon gradient in iron sheet along the thickness direction was of ladder type during decarburization. The carbon content in the center of iron sheet was influenced by the decarburization time or the temperature. The carbon migration in iron sheet consisted of stable carbon decomposition and free carbon diffusion. The carbon migration in the S2 stage of iron sheet was the controlling step of the entire decarburization process.