All metals react with oxygen in the atmosphere to form an oxide film on the surface. Unfortunately, the iron oxide formed on ordinary carbon steel continues to oxidize, expanding the corrosion and eventually forming holes. Paint or oxidation resistant metals (e.g., zinc, nickel and chromium) can be used for electroplating to ensure the appearance of carbon steel, but as is known, this maintenance is only a thin film. If the maintenance layer is damaged, the steel below begins to rust.

　　The corrosion resistance of stainless steel depends on chromium, but because chromium is one of the components of steel, the maintenance methods are different.

　　When the chromium content reaches 10.5%, the atmospheric corrosion resistance of steel is significantly increased, but when the chromium content is higher, although the corrosion resistance can still be improved, it is not significant. The reason is that when alloying steel with chromium, the type of external oxide is changed to an external oxide similar to that formed on pure chromium metal. This tightly adhered chromium rich oxide maintains the appearance and prevents further oxidation. This oxide layer is very thin. Through it, you can see the natural luster of the steel surface, which makes the stainless steel have a special appearance. Moreover, if the surface layer is damaged, the exposed steel surface will be self repaired with the atmospheric response to re form this "passive film" and continue to maintain the effect.

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