Correlation between corrosion rate and composition of crystalline corrosion products formed on weathering steels

Abstract

The correlation between corrosion rate and compositions of crystalline corrosion products formed on weathering steels exposed to different amount of air-borne sea salt particles has been investigated by the X-ray diffraction method. The mass ratio (α/γ) of crystalline α-FeOOH to γ-FeOOH, in the rust formed on the weathering steels exposed at an industrial environment increases with an increase in exposure duration. The ratio α/γ is closely related to the corrosion rate in environments when the amount of air-borne salt is less than 0.2 mg NaCl/dm2/day. However this is not the case in seaside environments with higher amount of air-borne salts. The mass ratio (α/γ*) of crystalline α-FeOOH to the total mass of γ-FeOOH, β-FeOOH and Fe3O4, in the rust formed on the weathering steels is related to the corrosion rate even in seaside environments certainly more than 0.2 mg/ dm2/day of air-borne sea salt particles. When the ratio α/γ* is more than 1, the higher corrosion rate more than 0.01 mm/y is not observed. The ratio α/γ* is expected to be an index for evaluating the corrosion resistance of the weathering steels even in atmosphere containing higher salt content.