Weathering Steel Buildings in Our Life
Are there no such strange buildings around you: it is a solid steel structure, but it is covered with thick red and black rust, as if it has been standing in the wind and rain for hundreds of years. Can rust into such a building still work? is it safe? I can tell you categorically: safe! Not only is it safe, it is also more durable than ordinary steel, and it will not rust even if it is exposed to air for several decades. This kind of surface rust, in fact, durable material is actually a special kind of steel, called weathering steel. Don't look at it as "ugly", in fact, high-end.
Weathering Steel Has Special Applications
Weathering steel, also known as atmospheric corrosion resistant steel, is a low alloy steel between ordinary steel and stainless steel. It is made of ordinary carbon steel and a certain amount of copper, as well as corrosion-resistant elements such as phosphorus, chromium, nickel, titanium and vanadium. It not only has the characteristics of easy extension, high strength and fatigue resistance of ordinary steel, but also can achieve 2-8 times of corrosion resistance in terms of ordinary carbon steel.
Due to its excellent performance, weathering steel is expensive. The weathering steel with similar performance has a price of about 60% higher than that of ordinary steel. Therefore, don't look at the weathering steel is ugly, the general building can not afford it.
Weather-resistant steel is used only for structures such as containers, railway vehicles, oil derricks, and drilling platforms that have a harsh environment and require high corrosion resistance. For reinforced concrete used in ordinary buildings, because the steel bars buried in the concrete are rarely in contact with oxygen and water, engineers are reluctant to use weathering steel here!
Why can the weathering steel rust and not rot?
Why Weathering Steel is So Special
Pure iron is not easy to rust, but ordinary steel usually contains impurities such as copper and carbon. These impurities have lower activity than iron, and form a primary battery with iron in aqueous air (ie, a current generated by oxidation-reduction reaction). The device separates the oxidation from the reduction and provides a “highway” for the corrosion of steel.
The rust generated by steel corrosion is a loose porous structure in which many microcracks connect the pores to each other. In this way, rust, like a sponge, can continue to absorb moisture from the air, allowing the steel to rust further until it is completely rusted.
Weathering steel is different from ordinary steel. At the beginning, it will also rust on the surface like ordinary steel. Due to the high degree of alloying, this process is even faster than ordinary steel. However, due to the more complicated lattice inside the weathering steel, a dark black dense rust layer is formed under the loose rust on the surface. This rust layer consists of nanoparticles of α-FeOOH. In this uniform rust layer, the nickel atom replaces the position of a part of the iron atom, so that the rust layer has cation selectivity, and the corrosive anion permeation is suppressed.
It is this layer of dense rust that makes the weathering steel rust, but the interior will not continue to rust. In fact, as long as you carefully distinguish, you can see that the surface of weathering steel is not the same as ordinary rust: the rust of weathering steel is uniform and dense, and the steel surface protects the steel against the surface of the steel; while the rust is streaked and loose, A touch will drop the residue. Instead of protecting the steel, such rust "leads the wolf into the room" and sucks water and oxygen onto the steel surface.
