Ledeburite

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Iron alloy phases
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Ferrite (α-iron, δ-iron; soft)
Austenite (γ-iron; harder)
Spheroidite
Pearlite (88% ferrite, 12% cementite)
Bainite
Martensite
Ledeburite (ferrite-cementite eutectic, 4.3% carbon)
Cementite (iron carbide, Fe3C; hardest)

Steel classes

Carbon steel (≤2.1% carbon; low alloy)
Stainless steel (+chromium)
Maraging steel (+nickel)
Alloy steel (hard)
Tool steel (harder)

Other iron-based materials

Cast iron (>2.1% carbon)
Ductile iron
Wrought iron (contains slag)

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 steel solidify.

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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