The corrosion resistance of stainless steel depends on chromium, but because chromium is one of the components of steel, protection methods vary. When the addition of chromium reaches 10.5%, the atmospheric corrosion resistance of the steel increases significantly, but when the chromium content is very high, although the corrosion resistance can still be enhanced, it is not very large. The reason is that alloying 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 so thin that the natural luster of the steel surface can be seen through it, giving stainless steel a unique finish. Moreover, if the surface layer is damaged, the exposed steel surface will react with the atmosphere to repair itself, re-form this "passivation film", and continue to play a protective role.
Therefore, stainless steel has a common characteristic, that is, the chromium content is above 10.5%.
The term stainless steel does not just refer to one type of stainless steel, each type of stainless steel has good performance in its specific application area. The key to success is to understand the purpose first, and then choose the right steel grade. At present, there are usually only six steel grades related to the application field of building construction. They all contain 17-22% chromium, and the better grades also contain nickel. The addition of molybdenum can further improve atmospheric corrosion resistance, such as resistance to chloride-containing atmospheres.
