Linked from
The 8 pages that link to Cementite, each with the reason it gives.
SteelBroader topic: Cementite combines with ferrite in pearlite and contributes to steel's hardness.
Cast ironRelated: Its presence in white cast iron creates a hard, wear-resistant structure.
Pig ironRelated: It can form in pig iron as carbon combines with iron.
FerriteRelated: Ferrite rejects excess carbon that can combine with iron to form cementite.