Stainless steel obtains its corrosion resistance by a very thin, firm and fine stable chromium-rich oxide film (protective film) formed on its surface, which can prevent oxygen atoms from continuously infiltrating and oxidizing. Once this film is constantly damaged for some reason, oxygen atoms in air or liquid will continuously penetrate or iron atoms in metal will continuously separate out to form loose iron oxide, and then the metal surface will be corroded continuously. There are many forms of damage to this surface mask, and the following are common in daily life:1. Dust containing other metal elements or attachments of dissimilar metal particles are deposited on the surface of stainless steel. In humid air, the condensate between the attachments and stainless steel connects them into a micro-battery, which initiates electrochemical reaction and damages the protective film, which is called electrochemical corrosion.
2. Organic liquid (such as liquid from melons and vegetables, noodle soup, sputum, etc.) adhere to the surface of stainless steel, which will form organic acids in the presence of water and oxygen, which will corrode the metal surface over time.
3. Acid, alkali and salt substances are adhered to the surface of stainless steel (such as alkali water and lime water splashing in wall decoration), can lead to local corrosion.
4. In polluted air (such as atmosphere containing a large amount of sulfide, carbon oxide and nitrogen oxide), condensed water will form sulfuric acid, nitric acid and acetic acid liquid spots, causing chemical corrosion.
