The appearance of gray iron comes from the carbon that is precipitated
in the form of graphite flakes. Even the softer grades have good wear resistance.
Increased hardnesses (giving even better wear resistance) are obtainable byusing special foundry techniques, heat treatment, or additional alloying elements.
Because the graphite flakes markedly weaken cast iron in tension, the compressive
strength is three to five times as high. Advantage is often taken of this strength differential,
such as incorporating ribs on the compression side of a member loaded
in bending.
Typical applications of gray iron include gasoline and diesel engine blocks,
machine bases and frames, gears, flywheels, and brake disks and drums.