Advantages of stainless steel jewelry
Stainless steel is not free from rust, but also produces an oxide on the surface. The rust mechanism of all stainless steels currently on the market is due to the presence of Cr element. The root cause (mechanism) of stainless steel corrosion resistance is the passive film theory. The so-called passive film is a thin film mainly composed of Cr2O3 on the surface of stainless steel. Due to the existence of this film, the corrosion of the stainless steel substrate in various media is hindered, and this phenomenon is called passivation. There are two cases for the formation of this passivation film. One is that stainless steel itself has the ability of self-passivation, and this self-passivation ability is accelerated with the increase of chromium content, so it has rust resistance; A more extensive formation condition is that stainless steel forms a passivation film in the process of being corroded in various aqueous solutions (electrolytes), which hinders corrosion. When the passivation film is damaged, a new passivation film can be formed immediately. The reason why the passive film of stainless steel has the ability to resist corrosion has three characteristics: the thickness of the passive film is extremely thin, generally only a few microns under the condition of chromium content > 10.5%.
The specific gravity of the passivation film is greater than that of the substrate; these two characteristics indicate that the passivation film is both thin and dense, so it is difficult for the passivation film to be broken down by the corrosive medium to rapidly corrode the substrate; it is the chromium of the passivation film. The concentration is more than three times higher than that of the substrate; therefore, the passive film has high corrosion resistance. Stainless steel will also corrode under certain conditions. The application environment of stainless steel is extremely complex, and the simple chromium oxide passive film cannot meet the requirements of high corrosion resistance. Therefore, elements such as molybdenum (Mo), copper (Cu), and nitrogen (N) need to be added to the steel according to different use conditions to improve the composition of the passivation film and further improve the corrosion resistance of stainless steel. The addition of Mo strongly promotes collective passivation due to the proximity of the corrosion product MoO2-to the substrate, preventing the corrosion of the substrate.
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