AbstractThe corrosion of a 75Sn–25Pb coating on low‐carbon steel exposed to a vapor/condensate phase over a 1 mol/L HCl solution has been studied. The corrosion mechanism initiation was based on several steps. The presence of CO2 and lead involves the precipitation of cerussite PbCO3 crystals. Overtime, the cerussite evolved and transformed into PbCl2. This transformation was not direct and involved the creation of reaction intermediates whose chemical composition was variable. In parallel, tin formed oxides that were not stable in the HCl solution. These oxides dissolved and led to the formation of an electrolyte concentrated in Sn2+. When tin ions' saturation was reached, tin precipitated to form abhurite, Sn21Cl16(OH)14O6, or hydrated tin chloride, SnCl2.2H2O. This study highlighted the particularity of the corrosion mechanism. It also showed that the presence of tin promoted the oxidation of lead and consequently the formation of cerussite.