In the construction world, steel is one of the most used materials versatilethanks to his resistence, ductility And ability to adapt to architectures required at the design stage. However, exposure to the external environment makes it susceptible to corrosion and, without adequate protection and maintenance over time, the product progressively weakens until it loses the resistance it needs to perform its task. Corten (or Cor-Ten) allows you to eliminate these problems. Where is the peculiarity? This alloy has a color and consistency similar to rust, which is the waste product formed by corrosion reactions. It would therefore seem to be dealing with a rusty materialbut strangely enough functional, which deserves a theoretical study and a description of the possible practical applications.
The characteristics of Corten steel
Patented in the 1930s, the Corten it is nothing more than a steel alloy whose name derives from the two main characteristics of the alloy:
- COR stands for corrosion resistance and indicates the ability of this alloy to have high resistance to corrosion by itself, that is, without the need for additional coatings;
- TEN stands for tensile strength and indicates the high mechanical resistance of the alloy, which makes the product useful for structural applications.
So how does the alloy recipe of this particular steel change? In addition to iron and carbon, the alloy is made up of copper, chromium And phosphorus. These components, in contact with the atmosphere, react and form oxides which, spontaneously, create a surface patina to the element that protects against corrosion. The process is spontaneous, but it takes time to occur (about 6 months). For this reason, it is usually accelerate with special chemicals that reduce the oxidation time by up to 2 hours. The color of the patina therefore changes over time because it is strictly linked to the time of exposure to the atmosphere and atmospheric agents, such as rain. Furthermore, since the external patina is linked to the presence of the alloy elements, it can self-regenerate if it were to be removed over time for some reason.
So, although of the same color, the spontaneous coating that forms around the Corten element It is not identifiable as rust in the chemical sense of the term, although it still remains an oxide. The latter, in fact, should be formed using Iron and not these additional elements present in the alloy.
The main types of Corten alloys
There is no single type of Corten alloy. Steel products are divided into three types:
- CORTEN-A: it is the one that protects the most from corrosion and is the alloy that is least resistant among all the others. For this reason, it is usually used for architectural applications;
- CORTEN-B: It has a slightly lower degree of corrosion protection than type A. It allows high mechanical characteristics to be maintained even with high thicknesses and is therefore mainly used in structural applications.
- CORTEN-C: more recently produced than the other two, it has significantly higher mechanical resistance but less protection from corrosion. It is therefore used in conditions where the need for resistance becomes binding.
The advantages of Corten steel
What are the advantages of using a Corten alloy compared to a classic steel alloy? The material’s ability to self-protect from corrosion phenomena brings great long-term benefits, especially of a economic. In fact, the elements made of Corten will not need protection against corrosion (normally, steel elements are galvanized or chromed). In addition, this patina – self-regenerating – alone guarantees that minimum of routine maintenance, necessary instead in structures formed by ordinary steel alloys. In the canonical cases, in fact, one could witness the degradation of the protective coating itself or, in other cases, its removal induced by external causes of various nature. It therefore requires a worker who, when necessary, goes to restore what has been removed or degraded.
In many cases, the use of Corten can even lead to a reduction in the material needed for the construction of the work. In fact, to compensate for the reductions in thickness that will occur in the elements over time due to the formation of rust, the designers considering increased thicknessesalready aware of the fact that some material will be sacrificed over time.
