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, ...

Before transforming to pearlite, this material phases through the two-phase zone (yellow) between austenite and ferrite. In cooling through this zone, ferrite is precipitated on the austenite grain ...