Corten steel (a.k.a. weathering steel) is an ideal metal material for many outdoor applications.
Civil structures, load-bearing structures, and general outdoor construction components and parts are made from corten steel since they can withstand and remain durable in harsh environmental conditions.
The material can last a long time.
Its ability to last for years and in some cases, decades, when exposed to outside elements is largely due to its capacity to regenerate a protective and highly corrosive-resistant coating within a few months to a few years of exposure.
This occurs without having to go through wet and dry weather cycles typically required by other types of non-alloy metals.
The information on corten steel provided below will be particularly relevant for businesses which require metal parts that will be used in outdoor construction and architectural projects.
The specific topics that will be covered include how it is made, its unique physical properties, the advantages, and disadvantages of using it for metal parts.
Some of its more common industrial applications and uses will also be listed.
Corten steel is a group of combined steel alloys that exhibit a high degree of corrosion resistance and tensile strength.
It was developed and introduced in the 1930s by the U.S. Steel Corporation (USS) to assist in the development of railroad coal wagons.
While typically written as corten, the official trademark name is COR-TEN, which refers to its specific qualities and properties, namely:
The alloys which make up corten are primarily copper and chromium.
The way they are combined allows the steel to retain a high degree of strength and create natural rust (patina) that protects it from atmospheric elements that commonly cause corrosion and structural damage.
The rust-coating it develops also gives it a natural-looking and ruggedly beautiful appearance.
Its anti-weathering, high-strength, and aesthetically pleasing properties make it an ideal metal for outside construction and landscaping projects.
These same properties also diminish the need for regular maintenance and painting—once a project is completed, it can usually be left alone for years without any additional work needing to be done to it.
The corten steel manufacturing process begins with a blending of three primary plates of steel—copper, chromium, and nickel—along with other alloying elements like phosphorus, silicon, and manganese.
Very little carbon is used during the mixing process—less than 0.2-0.3 percent—to ensure pliability, strength, and toughness.
Combining these specific metals and elements results in a 1/4th inch thick sheet that is ductile enough to be formed into almost any desired shape.
The real magic of the corten steel process, however, occurs after the initial mixing takes place and during its natural weathering cycle.
Alloy steels and other structural steels tend to rust when they are exposed to moisture and air.
The rusting of structural steel is usually porous (full of holes) and often detaches from the metal surface, causing the process to occur repeatedly, at a significantly higher rate each time.
With corten steel, the rusting process begins in the same way but instead creates a layer of stable rust (i.e., patina) that adheres to the metal instead of detaching from it.
This helps reduce the number of porous gaps within the metal and also reduces the amount of oxygen and moisture which often penetrate those gaps, thus eliminating further rusting.
The result of corten steel’s weathering process is a stronger and less-corrosive structure that requires less upkeep than other structural metals can normally provide.
Several factors affect the time it takes for the protective patina to form on corten steel.
The specific environment, humidity, and the distance between moisture particles affect the rate at which the patina is formed.
One thing is for sure, though: the more environmental cycles that corten steel is exposed to, the quicker it will form the desired protective rust on its surface.
For those who don’t want to wait for wet and dry environmental cycles of the weather, saltwater can be used to speed up the process.
Simply spray the saltwater across all sections of your corten steel panels and repeat the process every day until an even orange color appears across the entirety of their surface.
You can expect to see the patina forming in as little as a month (2-3 months is standard), depending on the amount and size of panels you are using.
Two kinds of welding procedures are used for corten steel: metal inert gas welding and arc welding.
MIG welding uses an electric arc and filler wire to join two pieces of corten steel together.
The electric arc flows between corten metal and the filler wire while producing enough heat to melt and join them together.
The arc welding process is a bit trickier and more complicated than MIG welding.
While an electric arc is also used in arc welding to run heat between a filler electrode and corten steel, the welder must hold the electrode and torch simultaneously so that the arc can melt the materials together.
Arc welding requires more manual labor than metal inert gas welding.
However, it also offers more flexibility, as different sizes (thickness) of corten steel can be welded without having to adjust the electrodes or change the general process in any way.
Whichever welding process is used, filler metals must be chosen cautiously for both technical and safety precautions.
This is because the final product will most likely be used for private and public structures and other service-related applications.
First, the following design requirements need to be considered:
Aside from these considerations, national steel welding codes must also be adhered to when welding corten steel.
The two most common steel welding codes in the U.S.A. include the American Welding Society (AWS) D1.1 and D1.5.
Both these codes provide guidelines for all the appropriate uses of corten steel and the welding methods that should be used for the structure being built and the environment it will be located in.
As was discussed earlier, the unique property that separates corten steel from other steels is its weathering capability.
Weathering (corten) steel naturally undergoes a chemical process that creates a new surface composition that offers more atmospheric-corrosion protection than other steels can provide.
In other words, the unique composition and distribution of alloying elements within corten steel form continuous self-regenerating rust that protects the surface from oxidation and corrosion.
Aside from its weather-resistant property, weathering steel also provides the following properties:
As you can see, such qualities are particularly useful for outdoor projects.
It should be noted here that weathering steel comes in two grades – Corten A and Corten B – which to a larger or lesser extent exhibit some or all of the above properties.
This version contains added phosphorus making it more suitable for flue gas applications.
Corten A is not recommended for heavy-load bearing applications as the added phosphorus reduces its tensile strength.
Corten B is the more common of the two kinds.
It is the one that forms the protective rust coating and maintains a high degree of tensile strength along with enough malleability for welding.
Corten B is especially useful for steel parts needed for heavy, load-bearing structures situated in harsh outdoor environments.
Depending on your specific requirements, your metal manufacturer will guide you as to which of the two versions is best suited for your particular project.
Weathering steel’s anti-corrosive properties are what separates it from other steels and make it a better choice for outdoor metal parts and structures.
Its natural-forming rust can lengthen the life cycle of any structure and so reduce maintenance and replacement costs.
Nevertheless, these are not the only advantages to using corten steel.
Below you will find a list of major benefits provided by this unique metal alloy.
The patina that forms on corten weathering steel reduces, and in most cases even eliminates, the need for paint.
This not only helps cut down on maintenance and material costs but also helps to avoid using dangerous and volatile compounds found in some paints.
Corten’s high tensile strength and durability (Corten B) make it very useful for heavy-duty, load-bearing structures.
Weathering steel is four to eight times more durable than traditional steel.
The reddish-brown rust that naturally forms on its surface makes it a popular choice among architects and design engineers who work with artistic and contemporary structures and applications.
Due to its chemical composition, corten steel can withstand wet and moist climates and heat that would cause corrosive damage to other forms of steel.
Corten’s melting point is around 1450-1510 degrees Celsius.
Structures made from corten weathering steel can maintain their integrity for many years. Little to no maintenance is required, which also means less money is spent on upkeep.
Corten steel retains a high degree of flexibility despite it being so sturdy. This means that it can be cut, shaped, curved, and welded to customized specifications.
Weathering steel can be cold and hot-formed, gas-cut, and welded utilizing almost any type of welding method in use today.
Since it is made of ecological materials that are 100% recyclable, it remains in compliance with most structural standards and codes.
Therefore, it offers an attractive option for those looking for environmentally-friendly building material.
Since corten weathering steel has so many advantages, it would seem like it is an ideal building material for just about any outdoor project.
However, some factors should be considered before choosing it for your next project.
For one thing, certain environmental conditions, such as high-chlorine environments, can reduce its corrosive-resistant and durability properties.
Also, wet environments, especially those located underwater, can impede its corrosion-resistant capabilities.
Some of the other disadvantages of corten steel are as follows:
While corten’s rust color tends to be an even orange-brown, there are no guarantees that it will stay that way over time.
This could pose a big challenge should a portion of a panel need to be replaced, and an exact match color reformed.
Aside from chlorine, other substances can interfere with weathering steel’s oxidation (rust-producing) process, such as oil, grease, cement, mud, and mortar.
Therefore, corten steel must constantly be kept clean so that it does not come into contact with such agents.
Corten steel does not always work well with other metals, especially when they are situated in certain types of environments.
Galvanic corrosion often occurs when two metals with different electrolytic properties and potentials are combined in the presence of water.
Oftentimes when such problems occur, extra material is needed, such as waterproof fasteners and nylon spacers to avoid the two different metals from touching each other.
Corten steel is widely used within the building and construction industry for large-scale projects as well as with medium to smaller projects where a high level of aesthetics is required (i.e., architecture, sculpture, home and garden).
A summary of its more popular applications is given below:
Building & Architecture: outdoor load-bearing buildings, bridges, and ships, as well as architectural structures of an aesthetic nature, such as beach homes and museums.
Art, Sculpture, & Garden Design: outdoor art projects, especially those that include sculptures, as well as landscaping and garden structures exposed to damp and moist environments.
Visual Screens: cladding material for surrounding, dividing, and protecting structures like fences, gates, and wall panelings.
Aside from the above common uses, corten weathering steel is also utilized to create lesser-known and uncommon outdoor structures and applications.
These include:
As can be seen from the above lists, weathering steel is a flexible material that can be used for large-scale construction projects, as well as medium-sized art and sculpture designs.
It is equally suitable for public service applications, and small and personalized home and garden hobbies.
Corten weathering steel is best known for its atmospheric corrosion-resisting properties.
Those properties result from a natural and automatic protective layer of rust that forms on its surface when exposed to the elements.
Aside from its rusting capabilities, it also comes with a high degree of tensile strength, weldability, and machinability properties.
That makes it a good fit for large outdoor construction and architectural projects.
Its rustic appearance is also prized by artists, sculptures, architects, and design engineers who need a natural-looking material for their work.
If you are looking for a corrosive-resistant, high-strength, and flexible material that is easy on the eyes, does not require a great deal of upkeep and maintenance, while being environmentally friendly and compliant, then corten steel is your best bet.
For further information about our machining and metal surface treatment capabilities, contact us directly via the convenient website form or request a quote here. We welcome your inquiries.