Grey Iron is a type of cast iron that has a flake graphite microstructure. When grey iron is broken, the fracture occurs along the graphite, thereby accounting for the characteristic grey color. Grey iron tends to be brittle in thin sections, has limited tensile strength, and no ductility. The flake graphite structure, however, provides grey iron with unique properties such as excellent machinability, effective corrosion resistance, very good compressive strength, and outstanding vibration dampening.

Grey Iron is the most common and widely produced of the cast irons. Its uses include: pump housings, valve bodies, automotive engine blocks, machine bases, sheaves, and cookware. The most commonly specified grey iron is AS 1830/BS EN 1561/ASTM A48.