Austenitic ductile cast iron

An austenitic ductile cast iron alloy composition comprising:

• about 2.2% to about 2.4% by weight carbon;
• about 3.5% to about 6.0% by weight silicon;
• about 28% to about 29% by weight nickel;
• about 2.5% to about 3.0% by weight chromium;
• about 0.9% to about 1.1% by weight molybdenum;
• less than about 0.0001% by weight tin and antimony;
• and
• greater than about 50% iron,
• wherein percentages are based on the overall weight of the composition, and
• wherein the cast iron has an austenitic structure having graphite that is essentially spheroidal, with a combined amount of Form I and II graphite according to ASTM A 247 at a level of about 70% or greater based on total graphite weight, and at least about 87% of the combined amount of Form I and II graphite comprises Form I, according to ASTM A 247 and based on total graphite weight.