Stainless steel was accidentally discovered by Brelier while searching for materials for military weapons. Later he discovered that the material was resistant to corrosion and high temperatures. With the extremely business-minded, he made it into tableware.
Though people extol the virtual of stainless steel and various models were manufactured later, they always rust in a few days? Why?
Actually, no matter what type of stainless steel, each of them exists 15%-30% of metallic chromium. Stainless steels with different properties also contain different elements such as nickel, molybdenum, nitrogen, etc.
Stainless steel, which holds a overwhelmingly thin, firm, fine and stable chromium-rich oxide film (protective film), formed on its surface to prevent the continuous infiltration and oxidation of oxygen atoms. and it obtain the ability to resist rust on account of the protective firm. Once the film is continuously damaged for some reason, oxygen atoms in the air or liquid will continue to infiltrate. Or the iron atoms in the metal will continue to separate out to form the loose iron oxide. And the metal surface will be affected and constantly rusting. Additionally, there are numerous forms of damage to the surface film.
On the surface of stainless steel, there are attachments which contains the dust of other metal elements or heterogeneous metal particles. In humid air, the condensed water between the deposits and the stainless steel connects the two into a micro-battery, which triggers an electrochemical reaction so that the protective film would be damaged, and this called electrochemical corrosion.
The surface of stainless steel is adhered by organic juices (such as vegetables, noodle soup, sputum, etc), and in the presence of water and oxygen, THE organic acids are formed. For a long time, the metal surface will be corroded by organic acids.
The surface of stainless steel is adhered by acid, alkali and salt substances (such as alkali water and lime water splashing on the decoration wall), causing local corrosion.
In polluted air (such as the atmosphere containing a large amount of sulfide, carbon oxide, nitrogen oxide), when encountering condensed water, it will form sulfuric acid, nitric acid, and acetic acid liquid points, causing chemical corrosion.
The stainless-steel cable tray is in contact and welded with dissimilar metals such as iron. The contact between them will cause iron contamination of stainless steel and result in a decrease in corrosion resistance and stainless steel will be more prone to rust.