Why is stainless steel resistant to corrosion?

The corrosion resistance of stainless steel depends on chromium, which is one of the components of steel. When the chromium content reaches 10.5%, the atmospheric corrosion resistance of steel increases significantly, but when the chromium content is higher, the corrosion resistance can still be improved, but the effect is not obvious.

The reason is that when the steel is alloyed with chromium, the type of surface oxide is changed to the surface oxide similar to that of pure chromium metal. This tightly adherent chromium rich oxide maintains the appearance and avoids further oxidation. The oxide layer is very thin, through which the natural luster of the steel surface can be normally seen, so that the stainless steel has the same appearance.

In addition, if the surface layer is damaged, the exposed steel surface will self repair with the atmospheric response, and form the "passivation film" from the beginning, thus maintaining the effect continuously. Therefore, all stainless steels have one characteristic, that is, the chromium content is more than 10.5%.