ledeburit

Ledeburite, commonly written as ledeburite (and also found as Ledeburite in some texts), is the eutectic constituent of the iron–carbon system consisting of austenite (gamma-Fe) and cementite (Fe3C). It forms when iron–carbon alloys solidify at the eutectic composition, about 4.3 weight percent carbon, at roughly 1147°C. In cast irons with near-eutectic carbon content, the liquid transforms on cooling into a fine, interleaved mixture of cementite and austenite, known as ledeburite.

Microstructure and properties: Ledeburite appears as a network or lamellae of cementite within an austenitic matrix and is typically hard and brittle due to the cementite. As cooling continues, the austenite may transform to pearlite, bainite, or martensite depending on the cooling rate and overall composition, leaving behind cementite-rich regions. The distribution and amount of ledeburite influence the hardness, brittleness, and machinability of cast irons.

Occurrence and significance: The concept is central to the study of cast iron microstructures and the iron–carbon phase diagram. Ledeburite is most readily observed in high-carbon cast irons near the eutectic composition and serves to explain the characteristic hard phases seen in such materials. It is largely a feature of solidification behavior rather than a stable, single phase at room temperature.

Name and spelling: The term is encountered in two spellings, ledeburite and Ledeburite, both referring to the same microstructural concept.