Pearlite

SEM micrograph of etched pearlite, 2000X.
Atom probe tomography of pearlite. The red dots indicate the positions of carbon atoms. Iron atoms are not shown. The nanotube is shown for size reference.
Pearlite occurs at the eutectoid of the iron-carbon phase diagram (near the lower left).

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.

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