THE LONG-TERM GROWTH OF THE PROTECTIVE RUST LAYER FORMED ON WEATHERING STEEL BY ATMOSPHERIC CORROSION DURING A QUARTER OF A CENTURY

The rust layers formed on weathering and mild steels by atmospheric corrosion in an industrial region for a quarter of a century have been characterized using various analytical techniques. In particular, analysis of a local portion of the rust layers by means of Raman spectroscopy gives important information on the structure of the layers. It is elucidated that the inner stable and protective rust layer which covered the surface of weathering steel mainly consists of nano-particles of alpha-FeOOH containing a considerable amount of Cr. The relative change of the amount of rust constituents for low alloy steels supports well a newly proposed schematic progress of long term alteration in stable and protective rust layer formed on a weathering steel in an industrial environment, i.e. the gamma-FeOOH, as an initial rust layer, is transformed into a final stable rust layer of alpha-FeOOH, probably via an amorphous oxyhydroxide substance, during the long term atmospheric corrosion of a weathering steel.