All metals react with oxygen in the atmosphere to form oxide films on the surface. Unfortunately, the iron oxide formed on ordinary carbon steel continues to oxidize, causing the corrosion to expand and eventually form holes. The carbon steel surface can be guaranteed by painting or electroplating on oxidation resistant metals (e.g., zinc, nickel and chromium), but, as is known, this protection is only a thin film. If the cover is damaged, the underlying steel begins to rust.
The corrosion resistance of stainless steel screws depends on chromium, but because chromium is one of the components of steel, the protection methods are not the same.
The results show that the atmospheric corrosion resistance of the steel increases significantly when the chromium content reaches 10.5%, but the corrosion resistance can still be improved when the chromium content is higher, but it is not obvious. The reason is that when the steel is alloyed with chromium, the type of surface oxide is changed to be similar to that formed on pure chromium. This tightly adhered chromium rich oxide protects the surface from further oxidation. This kind of oxide layer is very thin, through which you can see the natural luster of the steel surface, so that stainless steel has a unique surface. Moreover, if the surface layer is damaged, the exposed steel surface will react with the atmosphere to repair itself, re form this "passive film", and continue to protect the stainless steel screws.
Therefore, all stainless steel screws have a common characteristic, that is, the chromium content is more than 10.5%.
