ledeburite

Ledeburite is a eutectic constituent of iron–carbon alloys, consisting of intertwined phases of austenite (gamma-Fe) and cementite (Fe3C). It forms at the eutectic composition of about 4.3% carbon when liquid iron–carbon solidifies, at a temperature near 1147°C. The name honors the German mineralogist Carl Friedrich Ledebour.

In cast irons with very high carbon content, particularly white cast iron, solidification proceeds through L → gamma-Fe + Fe3C, producing a ledeburite microstructure. The cementite forms a network or needle-like (acicular) and blocky cementite within retained austenite. Upon further cooling or deformation, the austenite may transform to pearlite, bainite, or martensite, leaving behind cementite-rich regions.

Because it is a high-temperature eutectic phase, ledeburite is not a stable phase at room temperature; it is a microstructural feature rather than a stable compound. Today the term is used mainly in metallography to describe the eutectic mixture visible in cast iron microstructures; it has little relevance as a separate mineral.