All metals react with oxygen in the atmosphere and form oxide film on the surface. Unfortunately, the iron oxide formed on the ordinary carbon steel continues to oxidize, causing the corrosion to continue to expand and eventually form voids. It can be galvanized with paint or oxidation resistant metals (e.g., zinc, nickel and chromium) to ensure the surface of carbon steel, but, as people know, this protection is only a thin film. If the protective layer is destroyed, the steel begins to rust. The corrosion resistance of stainless steel depends on chromium, but because chromium is one of the components of steel, the protection methods are different. When the addition of chromium reached 10.5%, the atmospheric corrosion resistance of the steel increased significantly, but the corrosion resistance of the steel could be improved although the chromium content was higher, but it was not obvious. The reason is that alloying of steel with chromium changes the type of surface oxide into a surface oxide similar to that formed on pure chromium metal. This close adhesion chromium oxide protection surface, prevent further oxidation. This oxide layer is very thin, through which you can see the natural surface of the steel surface, so that stainless steel has a unique surface. Moreover, if the surface is damaged, the exposed steel surface will react with the atmosphere to repair itself and re form the "passivation film" of the oxide, and continue to play a protective role. Therefore, all stainless steel elements have a common characteristic, that is, chromium content is more than 10.5%.