The metal reacts with atmospheric oxygen to form an oxide film on the surface. Iron oxide formed on ordinary carbon steel continues to be oxidized, causing the corrosion to continuously expand, finally forming a hole. The carbon steel surface can be secured by electroplating with paint or oxidation-resistant metals such as zinc, nickel and chromium, however, as is known, 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 hoses depends on the content of chromium. When chromium is added to 10.5%, the atmospheric corrosion resistance of steel is significantly increased. However, at higher chromium contents, although corrosion resistance is still improved, it is not obvious . The reason for this is that when the 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 adhering chromium rich oxide protects the surface against further oxidation. This oxide layer is very thin, through which you can see the natural surface of stainless steel, so that stainless steel has a unique surface. Moreover, if the surface is damaged, the exposed steel surface will react with the atmosphere to self-repair, re-form this "passive film" to continue to play a protective role.