Pearlite

Pearlite is the low temperature thermodynamic equilibrium form
of the iron-carbon alloy. It has two distinct phases, Alpha-iron and
Iron Carbide, both of which contain carbon. In alpha-iron, the
carbon is in interstitial solid solution, in iron carbide it forms a
compound, Fe₃ C, with a given Fe/C ratio.

Pearlite has the laminar structure shown in the photomicrograph.
This structural form reduces the distance that carbon must diffuse
when forming Peralite from the high temperature Austenite single
phase.

Pearlite is a hard material (less hard than Martensite) and its
hardness and work hardening rate depend upon its grain size. Large grains give a more ductile material with a lower work hardening rate.