Chromium

Element, chemical symbol Cr. This alloying material, which helps form ferrite and improves hardenability, is very easy to passivate. A thin yet dense oxide layer with good adherence is spontaneously formed on the metal surface in contact with air. This passive layer provides improved wet corrosion and high temperature attack. A steel alloyed with more than 12% chromium is classified as a stainless steel, which itself can be influenced by other alloying elements, especially nickel, molybdenum and carbon. The chromium steel, however, has no resistance to diluted non-oxidizing acids such as sulfuric acid and hydrochloric acid. See entries for Chromium Plating and Passivate.