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 be oxidized, so that the rust is continuously enlarged, and finally a hole is formed. The carbon steel surface can be ensured by electroplating with paint or oxidation resistant metals (e.g., zinc, nickel, and chromium), but as is known, this protection is only a film. If the protective layer is destroyed, the underlying steel begins to rust.
The corrosion resistance of stainless steel hoses depends on the content of chromium. When the amount of chromium added is 10.5%, the atmospheric corrosion resistance of steel is significantly increased, but when the chromium content is higher, although the corrosion resistance is still improved, it is not obvious. . The reason is that when chromium is used to alloy steel, the type of surface oxide is changed to a surface oxide similar to that formed on pure chromium metal. This tightly adhering chromium-rich oxide protects the surface from further oxidation. This oxide layer is extremely thin, through which you can see the natural luster of the stainless steel surface, 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, and the "passivation film" is reformed to continue the protection.