Ledeburite

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v • d • e Iron alloy phases
Austenite (γ-iron; hard) Bainite Martensite Cementite (iron carbide; Fe₃C) Ledeburite (ferrite - cementite eutectic, 4.3% carbon) Ferrite (α-iron, δ-iron; soft) Pearlite (88% ferrite, 12% cementite) Spheroidite
Types of steel
Carbon steel (≤2.1% carbon; low alloy) Stainless steel (steel with chromium) HSLA steel (high strength low alloy) Tool steel (very hard)
Other iron-based materials
Cast iron (>2.1% carbon) Wrought iron (contains slag) Ductile iron

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 is 4.3% carbon, Fe₃C:2Fe. Its melting point is 1147°C. At 4.3% carbon the metal becomes 100% ledeburite. Ledeburite is a phase mixture, of austenite and cementite.

Ledeburite has two forms: Ledeburite I and Ledeburite II.

Ledeburite I (close below 1147°C) is made of austenite and cementite.

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 faster cooling, bainite can develop instead of pearlite, and with very fast cooling martensite can develop.