I too need this data but haven't had the time to track it down yet. I found a reference in a source but don't know how good it is.
J.F.Janowak, A.Alagarsamy, and D. Venugoplalan, "Fatigue Strength of Commercial Ductile Irons.", Transactions, American Foundrymen's Society, Vol 98, 1990, Paper #90-123.
I hope this helps. If you do find a source I would appriciate you letting me know what it is.
Thanks