IRON CARBON EQUILIBRIUM DIAGRAM BASICS AND TUTORIALS

IRON CARBON EQUILIBRIUM DIAGRAM BASIC INFORMATION
What Is Iron-Carbon Equilibrium Diagram?


The iron-carbon equilibrium diagram in Figure below shows that, under equilibrium conditions (slow cooling) if not more than 2.0% carbon is present, a solid solution of carbon in gamma iron exists at elevated temperatures.


This is called austenite. If the carbon content is less than 0.8%, cooling below the A3 temperature line causes transformation of some of the austenite to ferrite, which is substantially pure alpha iron (containing less than 0.01% carbon in solution).

Still further cooling to below the A1 line causes the remaining austenite to transform to pearlite—the eutectoid mixture of fine plates, or lamellas, of ferrite and cementite (iron carbide) whose iridescent appearance under the microscope gives it its name.

If the carbon content is 0.8%, no transformation on cooling the austenite occurs until the A1 temperature is reached.

At that point, all the austenite transforms to pearlite, with its typical ‘‘thumbprint’’ microstructure.

At carbon contents between 0.80 and 2.0%, cooling below the Acm temperature line causes iron carbide, or cementite, to form in the temperature range between Acm and A1,3. Below A1,3, the remaining austenite transforms to pearlite.

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