Proeutectoid ferrite and cementite

Question

Give a brief explanation of the term proeutectoid ferrite and cementite?

Answer 1

When you are not acquainted with the Fe-C binary phase diagram, please strive to download it before reading the answer below, since without this prior knowledge, it may be tricky to figure out answer. Using keywords "Fe-C", "phase", as well as "diagram" in search engines like Google, you can simply find this diagram.

As you in all probability know, in iron-carbon binary phase diagram, which besides to some other purposes is employed to predict phase transformations in steels as well as cast irons, there, is a eutectoid reaction where in the austenite phase decomposes to the mixture of the ferrite and cementite on cooling. When there is no alloying element other than carbon, and when cooling rate is slowing sufficient (so that there is adequate time for diffusion transformations to occur), this reaction takes place at the temperature of ~723C and at a composition of the ~0.8wt%C; a Fe-C alloy with accurately 0.8wt%C is called a eutectoid steel.