Pearlite

Iron alloy phases v • d • e
	Ferrite (α-iron, δ-iron; soft); Austenite (γ-iron; harder); Spheroidite; Pearlite (88% ferrite, 12% cementite); Bainite; Martensite; Ledeburite (ferrite-cementite eutectic, 4.3% carbon); Cementite (iron carbide, Fe3C; hardest)
Steel classes
	Carbon steel (≤2.1% carbon; low alloy); Stainless steel (+chromium); Maraging steel (+nickel); Alloy steel (hard); Tool steel (harder);
Other iron-based materials
	Cast iron (>2.1% carbon); Ductile iron; Wrought iron (contains slag);

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For the amorphous volcanic glass, see perlite.

SEM micrograph of etched pearlite, 2000X.

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 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 0.8% 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.

Bainite is a similar structure with lamellae much smaller than the wavelength of visible light and thus lacks this pearlescent appearance. It is prepared by more rapid cooling. Unlike pearlite, whose formation involves the diffusion of all atoms, bainite grows by a displacive transformation mechanism.