Ed, if you look inside a carbide die, you'll see that the sizing portion is small compared to the length of the die (usually around 1/2" or so). For a steel die, on the other hand, the sizing portion is the entire length of the die in most cases and is finely polished. Therefore, as Mike pointed out, carbide dies can't be used for any bottle necked or tapered cases. I suppose a die could be made of carbide in the same configuration as a steel one, but it would be very expensive. In addition, although carbide is extremely hard it is also brittle and I doubt that a full length die made of it would last nearly as long as a steel die.