Stainless steel is a high ally steel of more than 60% of the iron matrix and chromium, nickel, molybdenum and other alloying elements.
When the steel contains more than 12% chromium, the steel in the air and dilute nitric acid rusts difficultly. The reason is the formation of chromium in the steel surface layer of chromium oxide film is very close to effectively protect the steel from corrosion. The chromium content of stainless steel is generally more than 14%, but not absolutely stainless steel does not rust. In coastal areas or some areas with serious air pollution, when the chloride content in air is large, exposed stainless steel surfaces in the atmosphere may have some rust spots, but only surface rust, will not erode the inside of stainless steel substrate.