The corrosion resistance of stainless steel depends on chromium, but because chromium is one of the components of steel, the protection method is not the same.

When the addition amount of chromium reaches 10.5%, the atmospheric corrosion resistance of the steel significantly increases, but when the chromium content is higher, although the corrosion resistance can still be improved, it is not obvious. The reason is that the alloying treatment of steel with chromium changes the type of surface oxide to a surface oxide similar to that formed on pure chromium metal. This tightly adhered chromium-rich oxide protects the surface from further oxidation. This oxide layer is extremely thin, through which the natural luster of the steel surface can be seen, giving stainless steel a unique surface. Moreover, if the surface layer is damaged, the exposed steel surface reacts with the atmosphere to repair itself, and this “passivation film” is re-formed to continue protection. Therefore, all stainless steels have a common characteristic that the chromium content is above 10.5%.