Today, weathering steel is the most famous brand among all steels resistant to atmospheric corrosion. Atmospheric corrosion resistant steels are ordinary structural steels alloyed with copper and phosphorus. Such steel creates a protective oxide layer, which slows down the corrosion process in conditions where it can freely moisten and dry in the open air.
Previously this steel was mainly used in industrial structures. However, their popularity has recently increased significantly in facade solutions and landscape design, and architects find its color very attractive. In addition, weathering steel is an environmentally friendly material since it doesn’t require separate anti-corrosion processing, unlike galvanized coil.
History of Weathering Steel
Weatherproof steels were developed in the United States in the early twentieth century when it was noticed that copper alloyed steel sheet is much more resistant to atmospheric corrosion than conventional carbon steel sheets. Company U.S. Steel conducted extensive research, testing the physical properties and resistance to atmospheric corrosion of many sheets with different chemical compositions, which resulted in the development of weathering steel and patented in 1933.
Weathering steel was widely used in steel structures, in which normal carbon steel succumbed to premature corrosion due to the combined effects of weather, water, and impurities that appear in industrial production.
Today, weathering steel is used in transport containers, bridge structures, and technological equipment in the chemical and petrochemical industries. Weathering steel is also often used in power line poles, truck chassis designs, water tanks, chimneys, and the construction industry.
Weathering steel can be used on its own or can be painted. When used correctly, untreated weathering steel quickly forms a dense and hard oxide layer that prevents progressive rust. On the other hand, weathering steel painted structures have longer tinting intervals during maintenance, since the hard oxide layer appears on any damaged areas of the paintwork, and corrosion cannot progress under the paint (as it usually happens with painted carbon steel).
Weathering Steel Properties
Weathering steel is a highly active metal compared to, for example, stainless steel and copper. For this reason, any moisture or atmospheric oxygen gaining access to the surface of unpainted carbon steel quickly causes oxidation and the formation of iron hydroxide. This process is commonly called corrosion. As the surface of the steel is repeatedly wetted, rusting occurs, which can significantly impair the properties of the steel structure. Weathering steel also oxidizes in contact with air and humidity. However, the oxidation mechanism in weathering steels is different from the rusting of other types of steel. When weathering steel is repeatedly moistened and dries, a dense and very hard oxide layer forms on its surface. This layer prevents the development of corrosion in normal weather conditions, which is why weathering steel is called weather-resistant.
Since patenting weathering steel, more than 30,000 tests have been carried out to optimize the chemical composition of steel and achieve the best weather resistance. Chrome, nickel, copper, and phosphorus improve the steel’s resistance to atmospheric corrosion. And silicon, titanium, molybdenum, and vanadium further increase the density of the oxide layer by interacting with copper and chromium.
