Iron-carbon phase diagram, showing the iron-carbon phase diagram (near the lower left).

In iron and steel metallurgy, ledeburite is the eutectic that results when some forms of molten iron solidify. It is a type of metallographic structure in the Fe-C phase diagram, not properly a type steel as the C level is too high and in proper condition graphite would be formed and grey cast iron instead of a white cast iron.

It is named after the metallurgist Karl Heinrich Adolf Ledebur (1837–1916). He was the first professor of metallurgy at the Bergakademie Freiberg. He discovered ledeburite in 1882.

Ledeburite arises when the carbon content is between 2.06% and 6.67%. The eutectic mixture of austenite and cementite is 4.3% carbon, Fe₃C:2Fe, with a melting point of 1147 °C.

Ledeburite-II (at ambient temperature) is composed of cementite-I with recrystallized secondary cementite (which separates from austenite as the metal cools) and (with slow cooling) of pearlite. The pearlite results from the eutectoidal decay of the austenite that comes from the ledeburite-I at 723 °C. During swifter cooling, bainite can develop instead of pearlite, and with swift cooling martensite can develop.

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