What is Corten Steel And What is it Used For?

Corten steel, sometimes known as weathering steel, is a unique and innovative building material that has seen steadily rising popularity in recent years. But what exactly is Corten steel, what properties make it so useful, and why should you consider using it? Read on to learn all about this distinctive steel alloy.

Originally developed in the USA by United States Steel Corporation in 1933, Corten steel gets its name from two of its best-known properties - corrosion resistance and high tensile strength. The trademark name COR-TEN stands for CORrosion resistance and TENsile strength.  

Once the patent for Corten steel expired in 1971, other manufacturers around the world started producing their own version of this unique weathering steel, adding to its global popularity across several industries.

Unlike regular steel, Corten steel forms a stable rust-like appearance when exposed to the weather for several years, acting as a protective layer that shields the underlying steel from corrosion and eliminating the need for painting. This distinctive patina makes it perfect for outdoor applications.

Other properties like high strength, durability, and low maintenance requirements even in wet or cold UK climates add to the usefulness of Corten steel. It also costs less than more exotic stainless steel over the longer term, given that it does not require repeated painting, coatings, or special maintenance.

The weathering capacity of Corten steel comes from its chemical composition - it has high copper content along with chromium, nickel, silicon, and carbon in lower proportions. Together, these elements enable the formation of an outer rust layer that adheres tightly to the base steel when exposed to air and moisture.

Over the first few years, this layer builds up as the oxides respond to weather, eventually stabilising to form a rust-coloured protective shield. This is what gives Corten its famous weathered appearance.

There are many reasons why Corten Steel is gaining popularity with architects, designers, and builders across sectors:

The rustic earthy tones and textures make it ideal for creating visually striking sculptures, façades, surfaces and architectural features. The changing patterns from the weathering process can be an aesthetic advantage.

Corten steel lasts for decades even in harsh outdoor environments like marine settings or cold climates thanks to its corrosion-slowing patina layer. It has comparable or even better strength than common structural steels according to many tests.

Once the stable rust layer develops over the first 3-5 years of weathering exposure, very little additional maintenance is required over the lifetime of Corten steel products. No painting, coating or other protection is needed.

Though more expensive initially, when used on buildings the rust layer eliminates the need for repeated paint jobs or anti-corrosion coatings over decades. This makes Corten steel cost-effective in the longer term.

Corten steel has exceptional resistance from environmental factors like rain, snow, ice, solar radiation, salt exposure, and more - retaining its strength and durability.

Corten steel lends itself beautifully to building materials that will stand the test of time. Some common applications include:

• Outdoor Architecture: Façade cladding, walls, entryways, roofing, frames, bridges and more to add depth.
• Landscape Design: Planters, sculptures, garden features, and street furniture add elegance.
• Marine Settings: Harbours, ship hulls, docks, and bridges near oceans utilise their resistance to saltwater.
• Building Structures: Chimneys, towers, storage tanks, silos, and container lifts rely on high strength.

Are you still unsure if Corten Steel is the right choice for your next project? Here are answers to some frequently asked questions:

No, Corten steel does not rust through over time. The outer layer forms a protective patina that weathers when exposed to the elements, acting as a shield to prevent further corrosion of the inner steel. This rust layer is stable, tightly adhered and prevents full corrosion.

Unlike more common building materials like untreated carbon steel or wood that require frequent repainting, sealing or other protective measures when used outdoors, Corten steel does not need any special maintenance once the rust patina layer forms. The stable rust finish that develops eliminates the need for painting, coatings or other maintenance.

On the contrary, Corten steel matches or outperforms regular carbon steel in strength and durability. The addition of alloying elements like copper, chromium and nickel imparts added protection and boosts the mechanical performance to withstand decades of outdoor exposure.

Initially, Corten steel is more expensive than plain carbon steel when you first purchase it. However, as a building material for structures, over decades, using Corten steel is far more cost-effective since you avoid the need for frequent repainting, anti-corrosion treatments and other maintenance required for ordinary steel. The rust patina finish saves significantly on costs over the lifetime of the Corten steel.

On average, it takes between 3 to 5 years of continual exposure to the weather for Corten steel to develop the characteristic rust patina finish. Depending on environmental factors like the amount of rainfall, pollution, salt exposure, humidity levels and temperature fluctuations, it can take a bit longer or shorter for the protective rust layer to fully stabilise.

With its signature rustic appearance, high resilience, tensile strength and low maintenance, Corten steel has secured its status as a reliable and sustainable building material. If you’re looking to create durable, environmentally resistant structures with effortless beauty, Corten steel could be the perfect choice. You can find Corten steel sheets on our site in 3mm and 6mm thicknesses, cut to size. Reach out to us at [email protected] if you need help ordering your sheet.