Yeah, I was thinking about a lot of those different things especially like flex and vibration resistance. I found a site that has some pretty cool info :
basically Ductile Iron is twice as strong as Grey Cast iron but Steel is twice as strong as Ductile Iron.
Quoted from the site :
Material Hardness Tensile Strength Fatigue strength :
Grey cast iron 22-23 HRC 45,000 psi 30,500 psi
Ductile iron 38-40 HRC 180,000 psi 87,300 psi
Steel (SAE9254) 44-53 HRC 240,000 psi 138,600 psi
Like ductile iron, steel is not compatible with cast iron cylinder walls, so it must be coated with either chrome or moly -- or gas nitrided.
The amount of machining that’s required to finish a steel ring is far less than that which is required to finish grey cast iron or ductile iron rings, so steel rings are actually less expensive to manufacture.
Just some more tech info. This was from a site that was talking about rings though but I thought it would be related, considering my initial conjecture.