What is Corten Steel?

Corten or Weathering Steel is a version of low carbon steel that forms a thin layer of rust on the outside of the metal, thus preventing further corrosion. It is used for both its appearance and its corrosion protection.

In this article we’ll take a look at what makes Corten steel work, the disadvantages of using it, and discuss some of the common uses.

How is Corten’s Chemical Composition Different from Mild Steel?

Corten steel is similar to regular mild steel, except for the addition of higher amounts of Copper, Chromium, phosphorus and Nickel. These alloying elements help to prevent more than a thin layer of oxidation from forming on the surface of the metal.

This allows Corten to be used in an uncoated state without the risk of corrosion affecting the structural integrity of the part, something that mild steel usually requires galvanising or painting to achieve.

What Does Corten Mean?

The name Corten is a shortening of Corrosion – Tensile, as the material has good corrosion resistance and tensile strength. This trademark name is officially written COR-TEN, however, and you may also hear it called weathering steel.

How Does Corten Work?

One of the biggest drawbacks of using normal mild steel in components that will be subject to the weather is that they rust. This happens because the iron, which forms the majority of the material, oxidizes with oxygen in the air and rain, corroding the material and eventually disintegrating it altogether.

Corten steel minimizes this to only the outer surface by the addition of extra Copper, Chromium and Nickel. In a similar fashion to stainless steel and aluminium, forming an outer layer of protective oxide material, corten is protected once a thin outer layer of iron oxide forms.

However, in order to achieve this, the material has to be allowed to dry after being wetted by the weather. If the corten cannot dry out, the patina will not have sufficient time to form, and can continue to rust.

Advantages of Corten Steel

• Protected from rust – in the right conditions, Corten will form an outer protective layer of iron oxide, which prevents the inner material from rusting
• No need for paint – because Corten can protect itself from corrosion, extra painting, galvanising or plating steps are not needed, cutting costs and lead times during production

Disadvantages of Corten Steel

• Cannot be painted – in order for the patina to form, Corten needs to be exposed to the elements. Painting or otherwise covering it will not allow this, and the corrosion protection will be lost
• Expensive – Corten is anywhere from 30% – 70% more expensive than regular mild steel, depending on the grade and thickness

Workability of Corten

Thankfully, Corten is very similar to mild steel in workability terms, it can be welded, drilled, bent and formed using just the same techniques as low carbon steel.

When welding Corten, it is advised to select a Corten welding wire. This will allow the welds to receive the same weather protection over time. Using regular welding wire can cause the welds to rust at a faster rate than the Corten.

Uses of Corten Steel

Since it was brought to market by the United States Steel Corporation in 1933, Corten has found many uses, from architectural facades and structures to shipping containers.

Bridges and Infrastructure

There are numerous bridges around the world that utilise Corten steel, including the New River Gorge Bridge in West Virginia and overpasses on the New Jersey Turnpike. Various other pedestrian and vehicular bridges around the world also use weathering steel for aesthetic and practical reasons.

In the UK, Corten steel has been used on sheet pilings beside motorways, and in Denmark, the structures supporting the electrified cables for railways are made from Corten.

Transportation

In 1971, the St Louis Car Company used Corten to replace stainless steel on railcars destined for the Central Railroad. The use of Corten was cheaper than stainless steel. Unfortunately, the painting is thought to have prevented the steel from forming its protective patina, and the cars began to rust.

Container ships that travel the world holding all sorts of cargo are often made from Corten steel, which protects them from the harsh environments of months at sea.

Architecture

Countless examples of Corten architectural fabrications exist around the world, from the Barclays Centre in New York, the Broadcasting Tower in Leeds, UK, to various artistic sculptures all over the world.

One of the most notable large scale sculptures is the Angel of the North in Gateshead, UK. This sculpture stands 20 metres tall with a wingspan of 54 meters, it features a striking exoskeleton design capable of resisting 100mph winds.

Find Steel For Your Next Project at Metals Supermarkets

Whether you want to make a weathering steel sculpture or a stainless steel fabrication, Metals Supermarkets covers a wide range of metal products. Choose from hundreds of shapes, sizes and materials, and benefit from a cutting service nationwide.

Find a local store here.