Pearlite

For the amorphous volcanic glass see perlite. Pearlite is 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. It forms by a eutectoid reaction as austenite is slowly cooled below 727°C. The eutectoid composition of Austenite is approximately 0.77% carbon [1]; steel with less carbon content will contain a corresponding proportion of relatively pure ferrite crystallites that do not participate in the eutectoid reaction and cannot transform into pearlite.
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Noun
1. a lamellar mixture of cementite and ferrite formed during the cooling of austenite; a micro-constituent of steel and cast iron
(hypernym) lamellar mixture
(hyponym) granular pearlite, globular pearlite
(substance-holonym) steel
(substance-meronym) cementite, iron carbide

(n.)
Alt. of Pearlstone
  

A mixture of ferrite and cementite forming distinct layers or bands in slowly cooled carbon steels .

PERLITE