Reactive force field molecular dynamics is a powerful tool tosimulate large-scale reactive events such as catalytic reactions and metalliccorrosion, including the carburization or so-called metal dusting corrosion.Building on a vast set of reactive force field parameters, it aims to reduce the gapbetween computational and experimental observations. However, the productionof different versions of reactive force field parameter sets in the past 2 decadesdemonstrates the challenges faced by developers when attempting to describecorrectly and at the same time a broad range of environments, such as the kineticsof CO adsorption, dissociation, and carbon diffusion in iron systems. This haslimited the ability of these force fields to capture the competing phenomenagoverning complex evolution such as the carburization of iron responsible formetal dusting corrosion. In this work, we demonstrate that it is possible to treatvery different environments in an integrated way by expanding the ReaxFFparameter set, creating an environment-specific description. This approach enables us to capture both metallic surface-induceddissociation of carbon-containing gases such as carbon monoxide (CO) and atomic carbon bulk diffusion in iron systems within thesame simulation setup so far unreachable with previously available force fields. Employing this extended-ReaxFF to describe a cellcontaining a gas mixture of carbon monoxide and argon reacting with an Fe(110) surface, we fully capture at the same timecompeting carburization reaction/diffusion processes on both the surface and the bulk. Analysis of the radial distribution functionand charge density maps shows a variety of carbon bonds at different stages/layers, highlighting the diversity of the mechanismscaptured while using our extended-ReaxFF. Interestingly, at a CO coverage higher than 0.7 monolayers, the atomic arrangement ofthe iron atoms is sufficiently altered to cause surface reconstruction leading to a significant increase in carbon diffusion. Moreover,we are able to observe and quantify the diffusion of Fe from the bulk toward the upper coke layer, computationally elucidating theslow but continuous coke formation reported experimentally, opening a wide range of opportunities to model various stages of ironcarburization mechanisms.