Weathering steel, better known as Corten, is a beautiful cladding material that naturally rusts over time. Corten offers superior resistance to atmospheric corrosion because of its protective layer, which develops and regenerate.
Weathering steels form a compact rust layer during long-term exposure to the atmosphere. The compact rust layer gradually becomes denser over time and eventually protects the steel from corrosive environment & thus corrosion is inhibited by the corrosion product. Minor damage to the rust heals itself; therefore maintenance is greatly reduced. Due to such beneficial property, weathering steels have been used for many structural and engineering applications. It is well known that the protective rust layer of weathering steel consists of two layers; a compact, dense, amorphous and adherent inner layer, enriched with some alloying elements such as Cr, Cu, Ni, Mn, and P and a loose crystalline outer layer distributed with cracks and pores. The 1600-year old Delhi Iron Pillar is well known for its remarkable corrosion resistance. This exceptional corrosion resistance has been attributed to the presence of relatively high phosphorus content (0.25 wt.%) in the pillar which plays a major role by facilitating the formation of a protective passive film on the surface , the rust became more homogeneous and compact on increasing P content in cast strips. The P enrichment was observed at the interface between rust layer and substrate, which was believed to be responsible for the improvement of weathering resistance by retarding ingress of aggressive ions and moisture, phosphorus forms a thin and protective intermediate phosphatic layer between the outer and inner layer. Based on these literature findings, the use of higher amount of phosphorus in weathering steels seems to be worthful. The maximum specified value of phosphorus content in CORTEN steel, widely used for structural applications, is 0.15 wt.% with 0.65 wt.% max Ni and 0.55 wt.% max Cu.(15) As Ni is costly, the alternate steel with lower Ni and Cu content and higher phosphorus content will be economically more viable than CORTEN steel. This is the main focus of this paper.