Metallurgy Interview Question:

What is proeutectoid ferrite and cementite?

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If you are not familiar with the Fe-C binary phase diagram, please try to download it before reading the answer below, because without such prior knowledge, it might be difficult to figure out my answer. Using keywords "Fe-C", "phase", and "diagram" in search engines like Google, you can easily find this diagram.

As you probably know, in the iron-carbon binary phase diagram, which in addition to some other purposes is used to predict phase transformations in steels and cast irons, there, is a eutectoid reaction wherein austenite phase decomposes to a mixture of ferrite and cementite upon cooling. If there is no alloying element other than carbon, and if cooling rate is slow enough (so that there is sufficient time for diffusion transformations to take place), this reaction occurs at the temperature of ~723C and at a composition of ~0.8wt%C; a Fe-C alloy with exactly 0.8wt%C is called a eutectoid steel.
Submitted by: Administrator