Cementite is a connection of iron and carbon of the composition Fe3C (an iron carbide).

During long glow times or extremely slow cooling the metastable cementite disintegrates into iron and graphite.

The crystal structure of cementite is relatively complicated. In a orthorhombischen elementary cell are twelve iron and four carbon atoms, whereby the carbon atoms are surrounded by eight iron atoms relatively irregularly (doubly over-cuts trigonal prismatisch).

Cementite is very hard (HV=800) and verschleissfest, but inflexibly and therefore badly ductile. It has a smaller density than iron and is magnetic, when warming up is lost the magnetism with 215"°C.

When cementite designated primary cementite (Fe3CI), which came out by a crystallization from the melt (line CD). Secondary cementite (Fe3CII) results to Tertiary period cementite (Fe3CIII) from elimination from the austenite (line IT), by elimination from the ferrite (line PQ).

In the mineralogy cementite under the name Cohenit is well-known as meteoritisches nickel iron mineral in connection with cobalt ([Fe, Ni, CO] 3C).

See also: Iron carbide diagram

Articles in category "Cementite"

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