When the chromium content of more than 11.7%, the significantly increased resistance to atmospheric corrosion of steel and high chromium content, although you may still increase corrosion resistance, but not obvious.
Because when alloyed with chromium on steel, changed into similar to the type of surface oxide formed on the surface of pure chromium metal oxides. This tight adhesion of chromium-rich oxide surface, preventing further oxidation. This oxide layer can be extremely thin, natural sheen on the surface of steel can be seen through it, making stainless steel flagpole has a unique surface.
And if the damaged surface, exposed steel surfaces and the atmospheric response to repair itself, forms the oxide "passivation", continues to play a protective role. Therefore, all stainless steel flagpole elements have a common characteristic, that chromium contents over 10.5%.
You can use paint or oxidation of metal (for example, zinc, chromium and nickel) plating to ensure the surface of carbon steel, but as you know it, this protection is only a film. If the protective layer is damaged, the following steel begins to rust. Stainless steel flagpole depends on the corrosion resistance of chromium, but because chrome is one of steel, so protection is not the same.