Many metals will form an oxide film on the surface during the process of reacting with oxygen in the air. But unfortunately, the compounds formed on ordinary carbon steel will continue to oxidize, causing the rust to expand over time, and finally form holes. In order to avoid this situation, we generally use paint or oxidation-resistant metals (such as zinc, nickel, and chromium) for electroplating on the surface of carbon steel.
This type of protection is just a plastic film. If the protective layer is destroyed, the underlying steel will begin to rust. Where there is a need, there is a solution, and the use of stainless steel can perfectly solve this problem.
The corrosion resistance of stainless steel depends on the "chromium" element in its composition, because chromium is one of the components of steel, so the protection methods are not the same. When the chromium content reaches 10.5%, the atmospheric corrosion resistance of steel increases significantly, but when the chromium content is higher, although the corrosion resistance can still be improved, the effect is not obvious.
The reason is that when chromium is used for fine-grain strengthening treatment of steel, the type of outer oxide is changed to a surface oxide similar to that formed on pure chromium metal. This tightly adhered chromium-rich metal oxide protects the surface from further oxidation by air. This kind of oxide layer is very thin, and the natural luster on the outside of the steel can be seen through it, making the stainless steel have a unique metallic surface.
Moreover, if the surface layer is damaged, the exposed part of the surface will repair itself with the atmospheric reaction and re-form this "passive film" to continue to play a protective role. Therefore, all stainless steels have a common characteristic, that is, the chromium content is above 10.5%.
Post time: Dec-19-2022