Glossary

Pearlite is a lamellar (layered) microstructure found in steels and cast irons, consisting of alternating thin plates of ferrite (soft, ductile iron) and cementite (hard iron carbide, Fe₃C). It forms when austenite (γ-iron) of eutectoid composition (0.76% carbon) cools and transforms at about 727°C (1341°F) during the eutectoid reaction:

Austenite(γ) → Ferrite(α) + Cementite(Fe3​C)

Pearlite gets its name because the alternating light and dark layers resemble mother-of-pearl under a microscope. Its mechanical properties fall between those of its two components—stronger and harder than ferrite, but more ductile than cementite.

Key characteristics of pearlite:

- Formed through the eutectoid decomposition of austenite in steel.

- Appears as fine, alternating layers of ferrite and cementite.

- The spacing of the layers (lamellar spacing) determines hardness—fine pearlite is harder and stronger than coarse pearlite.

- Found in carbon steels, ductile irons, and some cast irons, often making up a large portion of their microstructure.

Mechanical significance:

Pearlite provides an excellent balance of strength, hardness, and toughness, so steels containing a high percentage of pearlite (like rail steels, prestressed wires, and springs) are used in applications demanding high wear resistance and moderate ductility. In contrast, steels with less pearlite and more ferrite are softer and more formable.