"Carbide" can refer to any number of types/grades of cutting tools. Based on 40 years as a manufacturing engineer, mostly in the machining area, as of today the best replaceable inserts for cutting most cast irons are something like Sandvik GC3210 or GC3225 CVD-coated cemented carbide. It can go by different names, made by different tool companies, but the tools are basically carbide. The only other tool material to consider for cast iron is ceramic, and it's doubtful any of your machines can run fast enough to make that type of tooling work.