Nichrome (NiCr, nickel-chrome, chrome-nickel, etc.) is any of various alloys of nickel, chromium, and often iron (and possibly other elements). The most common usage is as resistance wire, though they are also used in some dental restorations (fillings) and in a few other applications.
Nichrome alloys are known for their high mechanical strength and their high creep strength. The properties of nichrome vary depending on its alloy. Figures given are representative of typical material and are accurate to expressed significant figures. Any variations are due to different percentages of nickel or chromium.
When heated in air, most metals oxidize quickly, become brittle, and break. However, when heated to red-hot temperatures, nichrome wire develops an outer layer of chromium oxide, which is thermodynamically stable in air, is mostly impervious to oxygen, and protects the heating element from further oxidation.