Cementite

Cementite, also known as iron carbide, is a chemical compound of iron and carbon, with the formula Fe₃C (or Fe₂C:Fe). By weight, it is 6.67% carbon and 93.3% iron. It has an orthorhombic crystal structure. It is a hard, brittle material, normally classified as a ceramic in its pure form, though it is more important in metallurgy.