The metal reacts with oxygen in the atmosphere to form an oxide film on the surface. The iron oxide formed on the ordinary carbon steel continues to oxidize, causing the corrosion to continue to expand, and finally to form holes. It is possible to use paint or oxidation-resistant metals (such as zinc, nickel, and chromium) for electroplating to ensure the surface of carbon steel, but, as people know, this protection is only a thin film. If the protective layer is damaged, the steel underneath will begin to rust.

According to Stainless Steel Hose Fittings Company , the corrosion resistance of stainless steel hoses depends on the content of chromium. When the addition of chromium is 10.5%, the atmospheric corrosion resistance of steel is significantly increased, but when the chromium content is higher, the resistance can still be improved. Corrosive, but not obvious. The reason is that when steel is alloyed with chromium, the type of surface oxide is changed to a surface oxide similar to that formed on pure chromium metal. This tightly adhered chromium-rich oxide protects the surface and prevents further oxidation. This oxide layer is extremely thin, and the natural luster of the stainless steel surface can be seen through it, giving the stainless steel a unique surface. Moreover, if the surface layer is damaged, the exposed steel surface will react with the atmosphere to repair itself, re-form this "passivation film" and continue to play a protective role.