日本金属学会誌

J. Japan Inst. Metals, Vol. 65, No. 10 (2001),
pp. 922-928

Correlation between Corrosion Rate and Composition of Crystalline Corrosion Products Formed on Weathering Steels

Takayuki Kamimura1, Masato Yamashita2, Hitoshi Uchida2 and Hideaki Miyuki1

1Corporate Research and Development Laboratories, Sumitomo Metal Industries, Ltd., Amagasaki 660-0891
2Department of Mechanical Engineering, Faculty of Engineering, Himeji Institute of Technology, Himeji 671-2201

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.


(Received July 16, 2001)

Keywords:

weathering steel, atmospheric corrosion, FeOOH, rust constituents, corrosion product, air-borne salt


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