Iron-Iron Carbide Phase Diagram

Iron-Iron Carbide (Fe-Fe₃C) Phase Diagram

The Iron-Iron Carbide (Fe-Fe₃C) phase diagram is one of the most important phase diagrams in metallurgy. It describes the phase transformations and microstructures of iron-carbon alloys (steels and cast irons) as they cool and solidify.

Key Features of the Fe-Fe₃C Phase Diagram

• Carbon Content: The diagram covers 0–6.67% C, where Fe₃C (cementite) is the highest carbon phase.

• Phases Present:

  • Ferrite (α-Fe): Soft, ductile phase, low carbon solubility (~0.022% C).

  • Austenite (γ-Fe): FCC structure, can dissolve up to 2.14% C, stable at high temperatures.

  • Cementite (Fe₃C): Hard, brittle iron carbide compound (~6.67% C).

  • Pearlite: Alternating layers of ferrite and cementite, formed from austenite at 727°C.

  • Ledeburite: Eutectic mixture of austenite and cementite, found in cast irons (>2.14% C).

Regions of the Diagram

1️⃣ Hypoeutectoid Steels (0.022% - 0.76% C)

• Composed of ferrite and pearlite.

• Used in structural applications due to good strength and ductility.

2️⃣ Eutectoid Steel (0.76% C)

• Composed entirely of pearlite.

• Used for railway tracks, tools, and gears.

3️⃣ Hypereutectoid Steels (0.76% - 2.14% C)

• Composed of pearlite and cementite.

• High wear resistance, used in cutting tools.

4️⃣ Cast Irons (>2.14% C)

• Contain ledeburite, cementite, and graphite.

• Used in engine blocks, pipes, and heavy machinery.

Applications of the Fe-Fe₃C Diagram

✅ Heat Treatment: Guides processes like annealing, quenching, and tempering.
✅ Welding & Manufacturing: Helps select suitable steel grades for welding and machining.
✅ Material Selection: Determines steel and cast iron properties for different engineering uses.