Allotropes of iron
form different types of steel
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.