Allotropes of iron

Iron is the most often-used example of a metal with allotropes. These allotropes are α-iron, aka ferrite, γ-iron, aka austenite, and δ-iron, which doesn’t have another name. At higher temperatures, ε-iron exists, called hexaferrum. There is evidence for a fifth form, but it has not been proven to exist.

Delta Iron is Iron below 1538°C. Austenite is created when Iron cools further, to 1394°C. Beta ferrite Iron is the term for Iron that’s paramagnetic. Alpha Iron is all Iron below 912°C. Epsilon Iron is created above 10 GigaPascals and below 100°K.

Allotropes Of Iron Media

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  Low-pressure phase diagram of pure iron. BCC is body centered cubic and FCC is face-centered cubic.

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  Iron-carbon eutectic phase diagram, showing various forms of FexCy substances.

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  Iron allotropes, showing the differences in structure. The alpha iron (α-Fe) is a body-centered cubic (BCC) and the gamma iron (γ-Fe) is a face-centered cubic (FCC).

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  Molar volume vs. pressure for α-Fe at room temperature.

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  Figure 1: The beta field and A2 critical temperature on the iron-rich side of the iron-carbon phase diagram.