There are two available cast iron alloys: Cerodur (Ni4Cr2) & Nisodur (15CrMoNi)

Cerodur is the most commonly used material for the sealing rings of Enduro face seals
Cerodur is an extremely long wearing alloy that will give years of service under proper operating conditions.
In addition to its exemplary hardness, it is very resistant against corrosion, scoring, and seizing.
It is particularly well suited for use in heavy equipment axles and transmissions.

Nisodur can be selected for high speed applications.

Bearing steel (52100) is an option when economical considerations are most important. It is often selected when operating conditions will cause the other components in the assembly to fail long before the sealing ring itself. Consult a sales engineer for more details.

Cast Iron Alloy C Si Mn Cr Ni Mo V
Cerodur 2.8-3.6 1.0-2.0 0.3-0.9 2.5-3.5 3.5-4.5 0.3-0.5 <0.3
Nisodur 3.2-3.8 1.1-1.6 0.5-1.0 14-16 1.0-1.3 2.0-4.0 <0.3