Corten steel: everything you need to know
Corten steel, with its registered trademark name COR-TEN, is not just a material. It is a story of innovation, resilience and enduring appeal. From its humble beginnings in the transportation industry to its prominent role in modern architecture, this type of steel has proven its mettle over time.
Its ability to merge form and function, coupled with the distinctive weathered aesthetic, makes it a captivating choice for those looking to make a lasting impression in the world of design and construction.
What is Corten steel?
Corten steel, often stylized as COR-TEN, is not just a material but a trademarked name owned by U.S. Steel. This unique alloy has garnered increasing popularity among end-users in roll-formed products, particularly in architectural projects.
The distinctive appearance of Corten steel, characterised by its natural oxidising finish, has made it a preferred choice in the world of modern architecture.
Developed in the 1930s, Corten steel is a group of steel alloys crafted to eliminate the need for painting. Its standout feature is the formation of a stable rust-like appearance. It is the consequence of exposure to weather and atmospheric corrosion for several years
The layer protecting the surface develops and regenerates continuously when subjected to the influence of the weather.
This natural weathering process not only enhances its visual appeal but also contributes to the steel’s durability.
- The journey of weathering steels, commonly known as COR-TEN steel, began in the United States in the 1910s.
- The research evolved, and by 1926, it was discovered that the corrosion resistance could be enhanced with varying copper content.
- In 1933, the United States Steel Corporation patented Corten steel for its exceptional mechanical resistance, primarily for use in railroad hopper cars.
Originally designated as A242 (COR-TEN A) by ASTM International, newer grades include A588 (COR-TEN B) and A606 for thin sheets. All these alloys are currently in common production and use, proving their adaptability and reliability in various applications.
What is special about Corten steel?
The trademarked name COR-TEN encompasses the two defining properties of this steel—corrosion resistance and tensile strength. While U.S. Steel sold its discrete plate business in 2003, the COR-TEN brand persists in strip-mill plate and sheet forms.
- Corten steel resists the corrosive effects of various weather conditions by developing a coating of dark brown oxidation.
- This coating not only inhibits deeper penetration but also eliminates the need for extensive painting and rust-prevention maintenance over the years.
- Corten steel is designed to rust, forming a protective coating that significantly slows down the rate of future corrosion.
The oxidation of Corten steel typically takes six months, but innovative treatment can expedite this process, reducing it to as little as one hour. This way, architects and designers can achieve the desired aesthetic more rapidly.
- Corten steel found its initial applications in the construction of railroad hopper cars thanks to its toughness.
- Its corrosion-resistant properties were discovered soon after, leading to the trademarked name Cor-Ten.
- Over the years, its use expanded to bulk transport, intermodal shipping containers and bulk storage, attesting to its enduring relevance and reliability.
- Notably, Cor-Ten made its mark in architectural applications in 1964 with the construction of the Moorestown Interchange over the New Jersey Turnpike.
- This marked the first highway structure to use weathering steel.
- Subsequently, its adoption spread to other states and even crossed borders, with the University of York Footbridge in the United Kingdom in 1967.
What is the difference between steel and Corten steel?
In the world of construction and design, choosing the right material is crucial. Steel and Corten steel are two contenders that offer a plethora of benefits, yet they differ in some key aspects.
Aesthetic evolution
At first glance, both Corten and steel share a dark blue surface, creating a visually similar appearance. As exposure to the elements triggers the weathering process, their aesthetics diverge.
Corten steel undergoes a captivating transformation, developing an orange patina before settling into an appealing orange-brown hue. In contrast, steel tends to exhibit a darker orange-brown finish from the start.
Corrosion dynamics
While Corten and steel may look similar after weathering, their corrosion outcomes differ significantly. Corten steel, in its fully weathered state, forms a protective rust layer that acts as a barrier, slowing down the corrosion process.
This unique characteristic grants Corten an extended lifespan compared to mild steel. Without a protective coating, mild steel succumbs to faster corrosion, necessitating earlier replacement.
Composition insights
Looking closer at their composition, steel primarily consists of iron and a small amount of carbon. In contrast, Corten steel is an alloy with additional elements like chromium, nickel, copper, and phosphorus. These elements endow Corten steel with self-protecting properties, enhancing its longevity.
Cost considerations
The price point is a notable difference between Corten and steel. On average, Corten products cost about 50% more than their steel counterparts. However, the longevity and lower maintenance requirements of Corten make it a prudent long-term investment. While mild steel is a cost-effective alternative, the addition of protective coatings narrows the cost gap with Corten.
Sustainability
In the realm of sustainability, both Corten and steel share a commendable trait—they are 100% recyclable. However, Corten steel gains an edge by forming a protective layer that eliminates the need for additional coatings, contributing to environmental friendliness.
Expanded Corten mesh: design innovation
Corten is a valuable material for the production of expanded metal panels and meshes that find applications in architecture, building facades and design in general. This is possible thanks to its ability to stand out and ensure an aesthetic result over the years.
- Corten is an innovative material that, in many European areas, is suitable for use in historical urban contexts. The reddish and rusty tones evoke the colours of roofs and bricks that have been used for centuries in the construction of houses and buildings. In this way, Corten contributes to creating dynamism while harmonising with the surrounding environment.
- It complements various materials, including wood, stone and concrete. Therefore, it is not only an external element but also proves valuable for adding a distinctive touch to interior spaces through furniture that offers a combination of materials.
- Corten panels and meshes are highly appreciated and regarded by architects, designers and facade specialists, leaving an indelible signature on their projects.
Ceramica Globo headquarters in Viterbo, designed by architect Romano Adolini, embodies its potential.
The central building and showroom’s facade are clad with Corten steel expanded metal panels, covering a total area of 1,300 square metres. As a tangible result, a series of old buildings have been transformed into a modern structure.
The cladding transparency has been graduated according to the portion of the building to be covered:
- it is lighter in front of the windows;
- It is denser on the parts lying on the wall.
In this way, there is a wider diffusion of natural light where it is required and a better view in the glazed areas, hiding the masonry ones. And, most importantly, all the structure changes colour over the time, maintaining its unique profile.
