Iron-carbon alloy with low graphitization factor so that chill occurs forming a graphite-free structure.
The carbon is present bonded in the form of iron carbide, which is why the break surface of the material appears whitish instead of gray. The carbides of the unalloyed types are ledeburite and cementite (Fe3C) or austenite with eutectoid decay (perlite).
High-alloyed materials form carbides of chrome, molybdenum, vanadium or niobium (see Niobium carbide).
In order to achieve chilling, the silicon content is set to a low level depending on the wall thickness of the casting; the carbon content is approx. 2.5 to 3.8%. Carbide-stabilizing additives such as chrome, in particular, increase chill. Depending on the chemical composition, the metal matrix, the basic structure, comprises ferrite, pearlite, bainite, martensite, or austenite.