An alloy of Iron, Chromium, Manganese, Silicon and Carbon (May also contain Nickel and Molybdenum). The alloying elements, particularly Chromium, react with oxygen and water to form a thin film of oxides and hydroxides, which prevents further chemical attack. All stainless steels contain at least 10% Chromium. The most commonly available grades of stainless steel are denoted 'A2' and 'A4'. A2 stainless (also known as type 304) shows superficial rusting in the presence of seawater. A4 stainless (AKA type 316) is completely resistant to seawater corrosion and is the preferred grade for marine applications.