Ferriittipearlite

Ferriittipearlite, also known as ferrite–pearlite, is a common two-phase microstructure found in steel and cast iron. It consists of ferrite, a relatively soft, ductile phase of iron, and pearlite, a lamellar mixture of ferrite and cementite (iron carbide) that forms as the austenite transforms.

Pearlite forms during the eutectoid transformation, when austenite cools through the eutectoid temperature near 727°C (Ac1). The resulting structure is a layered, alternating arrangement of ferrite and cementite within pearlite. In steels with carbon content near the eutectoid composition (about 0.77% C), the microstructure after complete transformation is predominantly pearlite. In hypoeutectoid steels (lower carbon), proeutectoid ferrite appears before pearlite, while in hypereutectoid steels (higher carbon), proeutectoid cementite forms ahead of pearlite; in all cases, ferrite and pearlite coexist in the final microstructure.

The properties of ferrite–pearlite steels depend on the relative amounts and the spacing of the lamellae. Pearlite strengthens ferrite and increases hardness compared with pure ferrite, while still offering ductility greater than that of cementite-rich phases alone. The spacing of the pearlite lamellae (finer vs coarser pearlite) is influenced by the cooling rate and heat-treatment history; finer pearlite generally yields higher strength and hardness but lower ductility.

Ferriittipearlite is a central concept in steel metallurgy, used to tailor mechanical properties through controlled cooling and heat treatment. It serves as a reference state for understanding subsequent transformations toward bainite, martensite, or spheroidized structures.