Development of Microstructures in Iron—Carbon Alloys

The eutectoid composition of austenite is 0.8 wt %. When it cools slowly it forms perlite, a lamellar or layered structure of two phases: α-ferrite and cementite (Fe3C). Hypoeutectoid alloys contain  proeutectoid  ferrite  plus   the   eutectoid  pearlite.  Hypereutectoid  alloys  contain proeutectoid cementite plus pearlite. Since reactions below the eutectoid temperature are in the solid phase, the equilibrium is not achieved by usual cooling from austenite