The oxygen in the metal and atmosphere reacts to form an oxide film on the surface. The iron oxides formed on ordinary carbon steel continue to oxidize, which causes the corrosion to expand and eventually form holes. You can use paint or oxidation-resistant metals (e.g., zinc, nickel, and chromium) to insure the surface of the carbon steel, but, as people know, this protection is only a thin film. If the protective layer is damaged, the steel below begins to rust.
The corrosion resistance of stainless steel hose depends on the content of chromium, when the amount of chromium added to 10.5%, the corrosion resistance of steel significantly increased, but the chromium content is higher, although still can improve corrosion resistance, but not obvious. The reason is that when the steel is alloyed with chromium, the type of surface oxide is changed into a surface oxide similar to that formed on the pure chromium metal. This tightly bonded rich chromium oxide protects the surface and prevents further oxidation. This oxide layer is very thin, through it can see the natural luster of stainless steel surface, make stainless steel has unique surface. Moreover, if the surface is damaged, the exposed steel surface will be repaired with the atmospheric reaction, and the "passivation film" can be formed again, and the protective effect will continue.