Materials
Iron-Carbon Diagram
5 self-contained study topics — notes, diagrams, formulas, and worked examples for exams and GATE.
Topics
- Phases in Fe-C DiagramThe Fe-C diagram's phases are ferrite (α, soft BCC), austenite (γ, FCC), cementite (Fe₃C, hard), and their mixtures pearlite and ledeburite. Key lines are A₁ = 727 °C (eutectoid) and A₃ (varies with %C), per physical-metallurgy texts.
- Invariant ReactionsThe Fe-C diagram has three invariant reactions: eutectoid γ(0.76 %C) → α + Fe₃C at 727 °C, eutectic L(4.3 %C) → γ + Fe₃C at 1147 °C, and peritectic at 1493 °C. Each occurs at fixed T and composition, per physical-metallurgy texts.
- Cooling Curves of SteelCooling curves plot temperature versus time; arrests (plateaus/inflections) mark phase transformations. Faster cooling shifts transformations to lower temperatures, and section size affects cooling rate (Chvorinov analogy), per physical-metallurgy texts.
- TTT and CCT DiagramsTTT (isothermal) and CCT (continuous-cooling) diagrams show which product forms at a given cooling path. The nose of the curve is the minimum time to start transformation; missing it (fast quench) gives martensite, per physical-metallurgy texts.
- Heat Treatment SelectionSelecting a heat treatment matches the required property to a cycle: austenitise hypoeutectoid steel above A₃ + 30 °C, hypereutectoid between A₁ and A_cm, then choose cooling for the target structure, per physical-metallurgy texts.