ijzercarbiden

Ijzercarbiden, or cementite, is an iron carbide with the chemical formula Fe3C. It is an intermetallic compound that occurs in steels and cast irons and is known for its hardness and brittleness. Cementite is a key phase in the iron–carbon system and influences the properties of many steel microstructures.

The composition of Fe3C contains about 6.67% carbon by weight. Its crystal structure is orthorhombic, and it does not form a solid solution with iron. Cementite forms and persists across a range of temperatures and carbon contents, contributing to the mechanical behavior of iron alloys.

In the Fe–C phase diagram, cementite coexists with austenite or ferrite. During the eutectoid transformation at about 0.76% carbon and roughly 727 °C, austenite decomposes into ferrite and cementite to form pearlite. At higher carbon contents, cementite becomes a dominant constituent in microstructures such as ledeburite in cast irons, where it can appear with other phases formed during solidification.

Cementite's mechanical role is significant: it is among the hardest phases found in steel, increasing hardness and wear resistance but reducing ductility when present in continuous networks. The distribution and morphology of cementite, such as lamellae in pearlite or as precipitates, are strongly influenced by heat treatment and alloying, which in turn control strength, toughness, and machinability.

Overall, cementite is a fundamental phase in metallurgy for understanding steel and cast iron microstructures. Its presence helps explain hardness, wear resistance, and the effects of heat treatment on alloy properties.