ledeburite

White cast-iron is composed mostly of a microstructure called ledeburite mixed with pearlite.

The purposes of both tempering methods is to cause the cementite to decompose from the ledeburite, increasing the ductility.

This causes the cementite to decompose from the ledeburite, and then the carbon burns out through the surface of the metal, increasing the malleability of the cast-iron.

In iron and steel metallurgy, ledeburite is a mixture of 4.3% carbon in iron and is a eutectic mixture of austenite and cementite.

Since bainite (shown as ledeburite on the diagram at the bottom of this page) and pearlite each have ferrite as a component, any iron-carbon alloy will contain some amount of ferrite if it is allowed to reach equilibrium at room temperature.