Pearlite

Pearlite is a two-phased, lamellar (or layered) structure composed of alternating layers of ferrite (87.5% by mass) and cementite (12.5% by mass) that occurs in some steels and cast irons. This description of alternating layers is not strictly correct, each pearlite colony consists of a bicrystal of interpenetrating layers. A good analogy is a cabbage in a bucket of water, where all the leaves (cementite) are connected, but so is the water (ferrite). It is in two-dimensional sections that the appearance is of alternating layers. During slow cooling of an iron-carbon alloy, pearlite forms by a eutectoid reaction as austenite cools below 727 °C (1,341 °F) (the eutectoid temperature). Pearlite is a microstructure occurring in the vast majority of structural steels.