Guide for weathering steel
Guide for weathering steel

Guide to weathering steel

High strength, low alloy weldable structural steel with exceptional corrosion resistance.

What is weathering steel?

Weathering steel definition: steels that are chemically formulated to develop a protective patina layer – rust-like in appearance – that eliminates the need for paint. The dense oxide patina layer of weathered steel seals it off from the atmosphere. If a weathered steel panel is scratched, its patina will self-heal. The weathered steel is only not protected against further corrosion: it also delivers a unique finish that is an aesthetically pleasing – a warm, dark-brown, textured appearance that needs low or no maintenance.

The patina formation process of weathering steel

the patina formation process of weathering steel

Once it’s exposed to alternating wet and dry conditions, weathering steel begins to rust in the same fashion as non-weathering steel. However, as time passes, the rust layer transforms into a patina layer, and its color changes from a fresh, newly developed orange-brown to a light or dark brown.

The speed of change and the final color of a weather-resistant steel sheet are dependent on the atmospheric conditions of a site and the level of pollution. Sulfur-dense atmospheres will speed up the oxidation process and result in a darker patina. Frequent cycles of wet and dry conditions will also speed up oxidation. The entire oxidation process for this corrosion-resistant steel usually takes between 2–6 years.

chemical composition of weathering steel
Rusted weathering steel

Rust – the perfect protection

Weathering steel’s patina process has no effect on the steel’s mechanical properties, including its strength. As a result, structures made from SSAB Weathering steel require low- to no-maintenance for as long as the structure stands. Weathering steel from SSAB is strong, reliable, and guaranteed to last, as will its vivid natural appearance.

Weathering steel sheets, heavy plates, strips, tubes and sections

SSAB offers weathering steel in a large selection of strengths – from 345 to 960MPa YS – and configurations, including weathering sheets, hot- and cold-rolled strips, tubes, and sections. To save time when selecting grades, contact us so we can mutually determine the most appropriate configurations, grades, and thicknesses.
weathering steel sections

SSAB offers three types of weathering steel


COR-TEN® steel is known for its striking use in art and architecture, providing long-lasting beauty to housing, museums, headquarters, galleries, visitor centers, mixed-use buildings – even power plants. SSAB distributors are the exclusive licensed COR-TEN® suppliers for Europe, offering a wide range of sheet and tube products.

SSAB Weathering

SSAB Weathering steel offers a comprehensive selection of low- to no-maintenance solutions for industrial uses, such as bridges, railcars and shipping containers. And its ability to withstand sulfur-rich, high-temperature gases makes it suitable for chimneys/exhaust stacks, heat exchangers, air preheaters, and gas-to-gas heaters.

Strenx® Weathering steel

Low- to no-maintenance loadbearing steels with yield strengths of 700 and 960 MPa. These products can be ideal for long-term, corrosion-resistant structural use in trailer chassis, containers, railcars, cranes, and more.

Choose the right type of weathering steel for your industry

weathering steel for structures and bridges

Structure and bridges

Weathering steel for heavy transport

Heavy transport

Weathering steel for process industry

Process industry

weathering steel for buildings


weathering steel for arts and parks

Arts and parks

FAQ about weathering steel

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What is the definition of weathering steel?

Weathering steel (sometimes called by the brand name COR-TEN®) is designed to develop a protective oxide layer – its patina, a tightly adhered, dense, textured seal that is rust-like in appearance. The patina is very resistant to further corrosion in environments with alternating wet and dry conditions, and it never needs to be painted.

Where is weathering steel used?

Weathering steel is used on houses, buildings, bridges, structures, heavy transports (containers, trailer chassis), and in process industries, including heat exchangers. Weathering steel edging is even popular in landscape design. Weathering steel use is driven by both the need for strong, low- to no-maintenance building materials and its aesthetics – its warm, dark-brown patina.

How long does it take for patina to form on weathering steel?

Weathering steel from SSAB typically takes 2 to 6 years to reach its final appearance. Sulfur in the atmosphere speeds up the oxidation process and gives a darker patina. In fact, SSAB Weathering steel is suitable for sulfur-rich applications, such as exhaust stacks.

What is the chemical composition of weathering steel?

The key elements in weathering steels are small amounts of copper, chromium, nickel, silicon, and phosphorus. These elements, when exposed to alternating wet and dry conditions, develop the protective oxide layer – the weathering steel’s patina.

Can weathering steel be welded?

Weathering steel is easily welded. If you wish to have the weld’s patina quickly match the surrounding steel’s patina, pick a low-alloy steel-filler metals that will aid in color matching.