The study of oxygen and water adsorption on iron surfaces using DFT calculations, along with the investigation of iron and steel passivation and depassivation mechanisms via ReaxFF-MD simulations, has yielded valuable insights into the corrosion process. DFT calculations can explore how surface oxidation states and coverage affect surface reactivity and corrosion mechanisms. The passivation of iron involves a multi-step mechanism, beginning with water dissociation that leads to the formation of iron hydroxides and the gradual thickening of the passive layer due to the formation of oxides and hydroxides. In alkaline environments, stable surface-Fe(OH)2 species limit iron dissolution, ensuring stable passivation. However, chlorideinduced depassivation destabilizes the passive layer by catalysing the formation of localized acidic sites.