8 Common Questions About Cor-ten & Weathering Steel

building constructed with weathering steel

8 Common Questions About Cor-ten & Weathering Steel

As a trusted provider of cor-ten and weathering steels, we field countless questions from customers about weathering steel, its properties and how it can be used. Below, we answer 8 common questions about corten steel. 

What is cor-ten steel? 

COR-TEN® is the U.S. Steel’s trade name for atmospheric, corrosion resistant steel while weathering steel and corrosion-resistant steel are the generic terms.  The name is a combination of its two main features: “cor-rosion resistance” and “ten-sile strength.” Today, while the terms “corten” and “weathering steel” are used interchangeably, COR-TEN® remains a trademarked product of U.S. Steel, but is now only produced in Europe under a license agreement with U.S. Steel. Typically, customers are using the ASTM A606-4/A588/A827/A242 grades when referring to “corten” in the U.S.. Read more

Is cor-ten steel rust-proof? 

Cor-ten steel is allowed to rust in order to form the protective patina coating. While this results in a much lower corrosion rate compared to other steels, it does NOT mean corten steel is rust proof. Read more

How long does it take for cor-ten steel to develop its patina? 

Cor-ten, or weathering steel, is silver in its original state – just like standard steel. The rate at which the patina forms depends on the environment the steel is in as well as various factors, such as humidity and proximity to bodies of water. In our experience, the patina forms quicker when the steel is exposed to more environmental cycles. Likewise, cold-rolled materials (18 GA sheets or thinner) form the patina quicker than hot-rolled materials (16 GA sheets or thicker). We documented two samples of corten-equivalent weathering steel over the course of 6 months (December 2019-May 2020) to illustrate how the patina forms and changes color over time. The smaller square is 16 GA hot-rolled sheet and the larger square is 18 GA cold-rolled sheet. Read more

How long does weathering steel last? 

The lifespan of weathering steel depends greatly on the local climate and the conditions the steel is exposed to as well as how it is used and treated. Climate plays an impactful role in the lifespan of weathering steel and how long it takes for the patina to develop. Under ideal circumstances, weathering steel can last for decades. In fact, properly designed weathering steel bridges have achieved lifespans up to 120 years with minimal maintenance. Read more

Can weathering steel be purchased pre-rusted?

The probably more correct answer is no, and yes! Weathering steel is produced and supplied from producing mills “as rolled,” which means just raw steel — not further treated or pre-weathered and left to develop a patina naturally. Treatments can be applied to accelerate the patina process. If you are working on a smaller scale project, you can expedite the process as described below. If you are working on a larger scale project, there are some companies that professionally pre-weather and seal or just pre-weather weathering steel. Read more

Does climate impact the rate in which weathering steels form a patina?

Yes, the rate at which the protective patina forms varies and depends on the climate the steel resides in. In our experience as a high-strength weathering steel distributor, we’ve found that the patina forms quicker when the steel is exposed to more cycles of wet and dry weather. In more consistent (mostly dry or mostly wet) weather environments, it can take longer for the patina to form. Read more

What’s the difference between hot rolled and cold rolled weathering steel? 

The difference lies in how the material is processed. Hot rolled weathering steel is roll-pressed with additional heat at temperatures above 1,700 degrees Fahrenheit. This step makes the steel easier to form and shape and results in a wider size range. Hot-rolled steel can be prone to shrink, and there is less control over its final shape and dimensions. Cold rolled steel starts off by being processed the same way as hot rolled steel; however, once the steel has cooled to room temperature, it is re-rolled at room temperature. This additional processing results in more precise dimensions and enhanced surface qualities. Read more

What type of welding rod or wire should be used to match the color of weathering steels?

For welding on corten/weathering steels, we recommend our Cor-Match™ products. Cor-Match™ is a weathering steel wire and electrode, which features excellent mechanical properties and serves as a weld metal that matches the corrosion resistance and the patina color of weathering steels. Cor-Match™ 80-CW is a composite, metal-cored electrode for FLAT AND HORIZONTAL welding of weathering steels while Cor-Match™ 810-W is a gas-shielded, flux-cored electrode for ALL POSITION welding of weathering steels. Learn more about our Cor-Match™ products here

Contact Central Steel Service for answers to questions about cor-ten and weathering steel

Do you have more questions about cor-ten steel? Contact one of our experienced sales associates. As a trusted supplier of weathering steel, we are committed to providing customers with an exceptional level of service and making your buying experience easy.