Iron-carbon diagram

The iron-Carbon diagram (Fe-C diagram) or iron-carbon phase diagram for Steel and cast Iron is the (metastable) Equilibrium diagram (phase diagram) for the binary system of the elements iron and carbon. It shows which phases are present based on temperature and carbon content. The Fe-C diagram is used to evaluate steel and cast iron, for example with regard to their suitability for Hardening, welding, Forming, etc.

The temperature is plotted on the Y axis and the carbon content on the X axis. Carbon contents higher than 6.67 percent by weight are not technically relevant, since at 6.67 percent only the carbidic phase Fe₃C (cementite) is present.

Steel covers carbon contents up to a maximum of 2.06 percent and Cast iron contents higher than this. Pig iron has a carbon content of 4.3 percent.