The eutectoid phase transition in the iron carbon system takes place at 727 C. The three components in equilibrium at this temperature are Austenite, g, with the composition Fe - 0.77 wt % C, Ferrite, ...

The transition that determines the micro-structure of the alloy is a solid-state process: Austenite <-> Ferrite + Cementite Austenite is stable above 727 C and is an interstitial solid solution of ...