Pearlite

Pearlite is often said to be a two-phased, lamellar (or layered) structure composed of alternating layers of alpha-ferrite (88 wt%) and cementite (12%) that occurs in some steels and cast irons. In fact, the lamellar appearance is misleading since the individual lamellae within a colony are connected in three dimensions; a single colony is therefore an interpenetrating bicrystal of ferrite and cementite. In an iron-carbon alloy, during slow cooling pearlite forms by a eutectoid reaction as austenite is below 727 °C (1,341 °F) (the eutectoid temperature). Pearlite is a common microstructure occurring in many grades of steels.