Hot corrosion mechanism of Sodium Borate was investigated on mild-carbon steel at 800 °C by multiple surface characterizations. In addition, effects of tribological exposure on the interface chemistry were also examined in details by mean of ball-on-disk testing. The occurrence of interfacial reaction is characterized by the formation of a Sodium-rich film on the borate melt/oxide phase boundary. The basic dissolution reaction is accompanied by fluxing action of the protective scale in the case of static oxidation. External stressed shearing profoundly modifies the interface chemistry by establishing a hierarchical boundary film with remarkably low Oxygen density which renders improved oxidation resistance.