What is Corten Steel?
Corten steel (also known under the trademark COR-TEN or as weathering steel) represents a key innovation in the production of shipping containers and other structures exposed to extreme weather conditions. Its development began in the 1930s in the United States at United States Steel Corporation (USS), where it was first used on railway wagons for the transport of coal, ore and grain. Its unique properties soon found application in shipping, construction and architecture, where it is valued for its long lifespan and aesthetic appearance.
Corten steel is designed to be significantly more resistant to weathering than conventional carbon steels. Its unique ability lies in the formation of a protective layer of oxides, called patina, which forms on the surface of the material by the action of air humidity and atmospheric influences. This patina serves as a natural shield against further corrosion, eliminating the need for regular painting or complex maintenance. The result is a steel with high mechanical strength, long life and minimal maintenance requirements – ideal properties for shipping containers that face extreme stress at sea and on land.
Composition and production of Corten steel
History and development
Corten steel was developed in the 1930s with the aim of creating a material with increased resistance to weathering and mechanical stress. The name “COR-TEN” was created by combining the words COR -rosion resistance and TEN -sile strength, which captures the two most important properties of this alloy.
Chemical composition
Corten steel is a type of low-alloy steel, the chemical composition of which is precisely designed to promote the formation of a protective patina and increase corrosion resistance. Main alloying elements:
- Copper (Cu): Increases resistance to atmospheric corrosion, accelerates patina formation.
- Chromium (Cr): Improves the stability and cohesion of the patina, prevents further rust penetration.
- Nickel (Ni): Contributes to increasing the strength and toughness of the material.
- Phosphorus (P): Improves corrosion resistance, especially in thin sheets.
- Manganese (Mn), Silicon (Si), Carbon (C): Additional elements to improve mechanical properties.
Typical chemical analysis of Corten steel (e.g. Corten A and B):
| Element | Content [%] |
|---|---|
| Copper (Cu) | 0.25–0.55 |
| Chromium (Cr) | 0.40–1.25 |
| Nickel (Ni) | up to 0.65 |
| Phosphorus (P) | 0.07–0.15 |
| Manganese (Mn) | 0.20–0.60 |
| Silicon (Si) | 0.25–0.75 |
| Carbon (C) | max. 0.12 |
Each element has a specific role: copper, chromium and nickel promote the formation and stability of the protective layer, phosphorus accelerates the formation of patina, especially in thin profiles.
Production
The production of Corten steel takes place in large steel mills, where the mentioned alloying elements are added to the basic carbon steel. The mixture is then rolled at high temperatures, which allows the removal of impurities and the achievement of the required internal structure. The result is steel sheets or profiles that can be further shaped by welding or pressing.
Generally, we distinguish two main types of Corten steel:
- Corten A: Higher phosphorus content, suitable for thinner sheets and decorative use (architecture, sculpture).
- Corten B: Lower phosphorus content, higher strength, standard for the production of shipping containers and structures with high demands on mechanical resistance.
Corten steel is still manufactured under the supervision of United States Steel Corporation (USS), but similar alloys are also produced by other global manufacturers under the name “weathering steel”.
Scientific basis: Why is Corten steel resistant?
Corrosion resistance and self-healing patina
The key property of Corten steel is the process of so-called controlled atmospheric corrosion. After exposure to external conditions, the surface of the material begins to corrode, but – unlike ordinary steel – this corrosion:
- Does not create flaky, peeling rust.
- Forms a solid, cohesive layer of oxides (patina) that prevents the penetration of oxygen, water and salts into the core of the material.
This protective layer is stable, dense and adheres well to the substrate, which dramatically slows down further corrosion. If the surface is mechanically damaged (e.g. scratched), the patina is spontaneously renewed – the steel thus “heals itself”.
Patina formation
The process of forming a protective patina usually takes 6–12 months depending on the environment. The patina forms fastest in a mild, alternating humid climate (cyclic drying and wetting), where there is enough oxygen, but it is not permanently dry or long-term exposure to water.
Protective properties of patina
Patina is a mixture of iron, copper, chromium and other alloying element oxides. Its composition and structure are key to achieving the “stopped corrosion” effect – the rusty layer is not porous, but dense and practically impermeable to water and oxygen.
Advantage over ordinary steel
In ordinary carbon steel, rust gradually penetrates into the depth of the material, which leads to loss of strength, the formation of holes and the need for frequent repairs or replacement. In Corten steel, corrosion is limited only to the surface – the core remains intact even after decades of operation.
Use of Corten steel in shipping containers
Why Corten?
Shipping containers are exposed to extreme mechanical and climatic stress:
- Salty atmosphere at sea (highly corrosive environment)
- Alternating temperatures, humidity, UV radiation and other atmospheric phenomena
- Heavy mechanical stress (repeated stacking, transport, handling by cranes, impacts, bends)
Corten steel was chosen as the optimal material for these purposes due to:
- High strength at low weight: Safe stacking of up to 9 containers on top of each other without the risk of deformation.
- Excellent resistance to atmospheric corrosion: Minimal need for protective coatings, longer life.
- Low maintenance requirements: Patina itself protects the surface, normal maintenance is only local.
- Long life: Standard 20–30 years of operation without major repairs even in demanding conditions.
Container construction
Containers are made of corrugated sheets of Corten steel, which ensures high strength and rigidity of the structure and better drainage of water and minimization of moisture retention on the surface. The floors are made of hard tropical wood (e.g. bamboo or teak), while all other load-bearing and protective elements (frame, walls, roof, door frames) are made of Corten steel.
Production takes place in specialized factories, where individual panels are welded into a compact unit. Thanks to the use of Corten steel, containers can be easily modified (cutting, welding, expanding openings, etc.) without loss of structural integrity.
Key properties and advantages of Corten steel for containers
1. Corrosion Resistance
- Thanks to its unique patina, Corten steel is highly resistant to corrosion, even in extreme marine environments with high salinity and humidity.
- Patina acts as a protective barrier that prevents the penetration of water, oxygen and salts into the depth of the material. Containers can thus be stored and used for a long time in ports, on ships or in tropical areas without the risk of rapid degradation.
- Compared to ordinary carbon steel, corten containers typically last 2–4× longer.
2. High Tensile Strength and structural integrity
- Corten steel has a higher tensile strength (typically 485–620 MPa), which allows safe stacking of containers in multiple layers.
- Thanks to its high toughness (resistance to impacts, bending and deformation), the container protects the load even during repeated transport and handling.
- The corten construction meets strict ISO standards, which specify requirements for strength, dimensions and resistance to external influences.
3. Resistance to extreme weather conditions
- Corten steel retains its properties even with long-term exposure to:
- Salty sea air and splashing water
- Rain, snow, ice, alternating temperatures
- Strong wind, UV radiation, thermal shocks
- The protective patina is constantly renewed even after damage, which is essential for shipping containers that are constantly exposed to harsh conditions.
4. Low costs for maintenance (Low/Minimal Maintenance Requirements)
- Corten steel containers do not need to be painted regularly (unlike carbon steel, which rusts quickly and requires frequent repainting).
- Maintenance mainly consists of periodic visual inspections and treatment of any deeper damage (for example, after an impact).
- In aggressive environments, special coatings can be used that do not interfere with the formation of patina, but increase protection in extremely salty or humid environments.
5. Long life (Longevity)
- The average lifespan of a Corten steel container is 20–30 years under normal operation, often longer (some containers serve for over 40 years with proper maintenance).
- Long life means lower operating costs and a higher return on investment.
6. Ecological and economic sustainability
- Longer life means lower material consumption and a smaller ecological footprint (less waste, less consumption of raw materials).
- Corten steel is completely recyclable – after the end of its life, the material can be reused in the production of new containers or other steel structures.
7. Possibility of modifications and recycling
- Corten containers can be easily cut, welded and modified (for example, for the construction of mobile offices, residential modules, warehouses or restaurants).
- Thanks to the rigidity and resistance of Corten steel, structural integrity is maintained even after modifications.
8. Aesthetic value (Aesthetic Appeal)
- The characteristic rusty brown surface of Corten steel is now sought after in architecture and design (facades, sculptures, parks).
- Patina is constantly evolving – containers and buildings thus acquire a unique look over time.
Comparison of Corten steel with other materials used for containers
| Container material | Corrosion resistance | Strength | Maintenance | Lifespan | Purchase price |
|---|---|---|---|---|---|
| Corten steel (weathering steel) | very high | high | low | 20–30 years | higher, but balanced by lifespan |
| Carbon steel | low | medium | high | 5–10 years | lower, high maintenance costs |
| Aluminum | high (does not corrode, but oxidizes) | lower | low | 15–20 years | high |
| Stainless steel | very high | high | very low | 20–40 years | very high |
Note:
Corten steel is a compromise between purchase price, lifespan and easy maintenance. Aluminum is light and corrosion resistant, but has lower strength and is more expensive. Stainless steel offers extreme lifespan, but at the cost of several times higher investment.
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