Iron-carbon phase diagram under atmospheric pressure

This diagram is limited by pure iron on the left and by iron carbide on the right. The mains phases are:

• α iron: ferrite, ferritic steel
• γ iron: austenite, austenitic steel
• iron carbide: cementite, Fe₃C.

We can see an eutectic and an eutectoid; these phases crystallise as a stacking of fine strips of pure phases (iron and cementite) in case of the eutectoid, or a pure iron containing small balls of cementite for the eutectic. Although it is heterogeneous, these phases behave like homogeneous pure bodies.

Steel is between 0 and 2 mass percent of carbon. Cast iron is between 1,7 and 6,67%.

Author : Christophe Dang Ngoc Chan