Were all of them of cast iron?
Sort of. Often 'malleable' iron, which is cast.
. Ductile iron is the best of both, again imho.
Chilly
Are some wrenches made of ductile iron?
Yes, as far as I know, but only modern and mostly import. Some socket type head wrenches come to mind. Reminds ne, I need to throw some of those in the head wrench pile I have been collecting for a member here.
Our suppliers even supply ductile threaded fittings. They look similar to malleable. My trade, fire protection, uses mostly cast in 1"-10" threaded and flanged. Ductile in 1" to 2" threaded is common more and more, but mostly foreign. Malleable, like pipe-fitters use for gas lines, isn't used much for threaded. Grooved end systems (think Victaulic) are often ductile. And domestic. Other divisions of fire protection use malleable - special hazards (clean agent gasses, refineries with galvanized.) Steel conduit fittings for A&D. Unions are malleable along with some bushings, a few other fitting types, too.
Cast cannot be used for gas piping because it is porous.
Chilly
