What Is Corten Steel?

You may have noticed that shipping containers are almost always made of corten steel. Corten steel is a weathering steel, and is generically recognised worldwide by its branded trademark name, COR-TEN steel.

The steel uses a chemical composition that oxidises over time to create its own protective film instead of corroding or rusting. It’s often used for its decorative finish as the oxidation gives a unique rust-colour appearance.

Steel shipping containers are built to transport cargo around the world. They are transported by boat and are exposed to all outside elements. Because of this, manufacturers use corten steel for containers so the units have an additional layer of protection to prevent them corroding. Over years, containers may appear to be rusty but this “rust” won’t cause corrosion thanks to their self-preserving properties.

Corten Steel Explained

Corten steel has the ability to resist corroding in a vast range of extreme weather conditions, such as rain, snow, or ice. It does this by creating a dark brown oxidised coating over the metal.

The oxidised layer protects the steel and prevents any outdoor elements from penetrating the metal further, which in turn prevents corrosion.

The oxidised coating not only prevents damage from corrosion, but in the long term needs very little maintenance. The oxidised appearance means that painting the steel is optional. If the steel does need to be painted to blend into landscaping, it can easily be powder-coated in any RAL colour.

History Of Corten Steel

Corten steel was developed by the United States Steel Corporation in the 1930s, when a patent was created for a steel with good mechanical resistance and ‘controlled corrosion’. Its trademark name, COR-TEN steel, was formed using a combination of the steel’s two properties – corrosion resistance and tensile strength.

Its intended use was for railway hopper cars, which were used to transport heavy bulk loads including coal, metal ores, mineral products and grain. Later that decade, painted corten steel was used for railroad passenger cars.

It became increasingly popular in construction and architecture due to it requiring little to no maintenance. In recent years, it gained further popularity for aesthetic reasons as it adds a unique, weathered finish to modern statues and sculptures.

How Is Corten Steel Made?

Corten steel is made by melting additional elements, such as copper, nickel and chromium, and adding them to the steel during the production process. The steel is then passed between high temperature rollers which moves any iron waste material to the surface.

The process can be used to create two different types of weathering steel – Corten A (Type 1) and Corten B (Type 2). The type created is dependent on the amount of phosphorus melted into the steel which alters the properties of the final product. Corten A is up to 12mm, and often used in sheets or coils. It has a higher level of phosphorus and copper, which helps produce the oxidised finish on the steel. Corten B is thicker, ranging from 15mm to 50mm, and is produced in plate form.

Most Common Applications For Corten Steel

Due to its strength and resistance to weather damage, there are a number of applications that corten steel lends itself well to.

Corten steel is ideally suited for shipping container manufacture as it ensures the container has longevity. As the oxidised layer forms, it protects the steel box and prevents the container becoming damaged no matter whether it’s on a cargo vessel at sea or being used outdoors as a storage unit.

The steel is easily modified too, so containers made from corten are a great base for container conversion projects as it can be cut down, painted and can withstand having fixtures added, such as doors and windows, without compromising the structural integrity.

Corten steel is also frequently used for outdoor projects and architecture. Popular landmarks, such as the Angel of the North in Gateshead and Broadcasting Tower at Leeds Beckett University, have utilised corten steel for the exterior of their buildings. This not only provides a strong, robust material to build with, but it also gives an aesthetically pleasing appearance that stands out against the landscape.

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