Weathering steel is a kind of low alloy steel between common steel and stainless steel, a small amount of Cu, P, Cr, Ni and other elements is added into carbon steel, that forms a protective layer on the surface of the metal matrix, thus its atmospheric corrosion resistance is higher 2 to 8 times than of carbon steel. The weathering steel is an important raw material for the production of vehicles, steel bridges, containers and steel structures. According its different purposes, the weathering steel can be rolled into hot or cold coils, profiles, wire rod or other forms.
Generally speaking, the weathering steel divides into structural weathering steel and welding weathering steel. The former is mainly used for non-welding or welding requirements are not high in the structural parts, with excellent atmospheric corrosion resistance, which P content in 0.07% -0.15%, due to the high P content, so the yield strength of such steel is generally below 345MPa. The welding structural weathering steel, mainly used in large welded structure with excellent welding performance and low-temperature toughness.
Phosphorus is one of the most effective alloying elements to improve the atmospheric corrosion resistance of steel. Phosphorus in steel can be uniformly dissolved, help to form a dense protective film on the surface of the steel, so that its internal corrosion is not by the atmosphere.
Chromium can form a dense oxide film on the steel surface, slowing down the growth of the rust layer. When chromium and copper are added at the same time, the effect is especially obvious.
Nickel can make the steel self-corrosion potential change in the positive direction, increasing the stability of the steel.
Research results show that the addition of trace amounts of calcium in weathering steel can not only significantly improve the overall atmospheric corrosion resistance of steel, but also effectively avoid the rust hanging phenomenon when the weathering steel is used.
