Assembled sprocket comes in segmented and ring types.
Segmented type
Tooth tips are of cast stainless steel and bosses are of ductile cast iron.
Ring type
The teeth rings are of stainless steel or plastic and bosses are of ductile cast iron.
Assembled sprocket also helps to achieve similar lifespan extension of stainless chain.
For stainless tip, the boundary between the tooth tip and the boss is treated to prevent electrolytic corrosion.