Pearlite is a lamellar mixture of which phases?

• A. Ferrite and Cementite
• B. Austenite and Cementite
• C. Ferrite and Austenite
• D. Martensite and Cementite

Answer: (A)

Pearlite forms when austenite in steel transforms at the eutectoid temperature into a fine, alternating stack of two phases: ferrite and cementite. Ferrite is a relatively soft, nearly pure iron phase with very little carbon, while cementite is iron carbide (Fe3C), which is hard and brittle. The transformation happens by diffusion at about 727°C, and the carbon partitions to create long, interleaved plates of ferrite and cementite. That lamellar arrangement is what gives pearlite its characteristic look and combines a balance of strength and ductility. Other potential combinations don’t produce this distinct layered structure; pearlite is specifically ferrite plus cementite.