22/07/2026
Iron- Iron Crabide Phase Diagram
📘 Key Phases in the Diagram:
1. Ferrite (α-Fe):
• Solid solution of carbon in BCC iron (Body-Centered Cubic).
• Stable below 912°C.
• Very low carbon solubility: up to 0.022% C at 727°C.
• Soft and ductile.
2. Austenite (γ-Fe):
• Solid solution of carbon in FCC iron (Face-Centered Cubic).
• Exists between 727°C and 1493°C depending on carbon content.
• Higher carbon solubility: up to 2.14% C at 1147°C.
• Stronger than ferrite but less magnetic.
3. Cementite (Fe₃C):
• Iron carbide, a hard and brittle compound.
• Fixed composition: 6.67% C.
• Forms in steels and cast irons when carbon content exceeds solubility limits.
4. Pearlite:
• A lamellar (layered) mixture of ferrite and cementite.
• Forms at eutectoid point (0.76% C, 727°C).
• Strong and tough, key constituent of many steels.
5. Ledeburite:
• Mixture of austenite + cementite, or cementite + γ/α, depending on temp.
• Found in cast iron (carbon > 2.14%).
📍 Important Points:
🔸 Eutectoid Point:
• 0.76% C at 727°C
• Austenite → Pearlite (ferrite + cementite)
🔸 Eutectic Point:
• 4.3% C at 1147°C
• Liquid → Austenite + Cementite (Ledeburite)
🔸 Peritectic Point:
• 0.16% C at 1493°C
• Liquid + δ-ferrite → Austenite
