The basic difference between Corten steel and ordinary structural steel is the addition of chromium, copper and nickel alloy elements, which gives corten steel enhanced corrosion resistance. Corten steel is also called "weather resistant steel" because steel forms a protective layer on its surface under the influence of weather. It is this protective layer that makes corten steel excellent in atmospheric corrosion resistance compared to other steels.
When affected by the weather, the layer that protects the surface will continue to develop and regenerate. The same process allows corten steel to "self-heal";. Therefore, if the surface is scratched, the exposed area will regenerate its protective layer, and, over time, the area will merge with the surrounding area and become essentially invisible.
Through repeated wet and dry cycles, the weathering of the corten steel surface and its ultimate life have been actively improved. This weathering process is not "rusting" in the true sense. It is more similar to the curing and rusting process. These processes can also protect other long-lasting metals such as zinc, lead, bronze and copper. Although corten's surface layer is visually similar to "rust", it is actually a stable controlled oxidation and forms a corrective layer on the entire metal rather than a destructive layer.
