Abstract
The role of manganese sulfides as inclusions on the rust formation process of the steel sheet was investigated by the microscopic observation and the electrolytic isolation method. The obtained results are as follows.
(1) The first stage of the rust formation process is the dissolution of α(Mn, Fe) S inclusions into dew water on the steel surface.
(2) The second stage is the one owing to the oxygen contained in dew water; the manganous ions of the dissolved α(Mn, Fe) S reprecipitate as the fine colloidal particles of γ-Mn2O3 (Mn3O4) in the surround ings of the α(Mn, Fe) S inclusions.
(3) The third stage is the one in which the fine colloidal γ-Mn2O3 (Mn3O4) particles remarkably absorb water and this accelerates the wet corrosion. The brown rust is thus initiated around the γ-Mn2O3-(Mn3O4) particles.
