Special Weathering Steel, A Contribution
To Environmental Protection
Author(s)
E. S. Ayllón
Abstract
The term weathering steels describes a class of low-alloy structural steels that
develop an adherent protective rust layer, called patina, during exposure to the
atmosphere. As a result of this, weathering steels, unlike ordinary plain carbon
steels, do not require painting, which means important advantages: avoiding
associated costs of initial painting, periodic repainting, containment and disposal
of blasting debris during repainting.
The development of the protective patina depends on the steel microalloying
elements which it contains, consequently, the corrosion process destroys a
certain amount of steel in order to supply the microalloying elements. However,
only part of all the Fe involved in this process gets into the patina. In fact, a
percentage of Fe in the form of soluble corrosion products is swept away by the
rainwater or dew, staining other materials with rough surfaces on the structures.
The completion of the protective patina takes at least several years.
In order to analyse the influence of non-metallic inclusions morphology and
composition on the initial stages of the corrosive atmospheric attack, an
experimental steel called PA (P: patina-A: acceleration) was designed.
A great quantity of non-metallic inclusions with spherical morphology, great
chemical reactivity and very small size was chosen. Considering the structural
behaviour, this morphology is advisable since it produces a greater isotropy of
the mechanical properties.
Experimental samples of PA steel were tested in outdoors exposure
producing, in only one year, a very effective passive patina. Consequently it can
be observed that these tests clearly showed a vanishing effect of all staining
contaminant products, which means an outstanding advantage towards the
environmental protection.
Keywords
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