Carbide, such as those used on saw tips, are actually something called "cemented Tungston Carbide" aka "tungston carbide cobalt". What they do, basically, is take WC and press it together with red-hot, liquid cobalt. So effectively you get all the strength of the sand like WC, but as a somewhat workable metal.
the cemented carbide is not easily sharped, seeing as it has a Mohs hardness of 9 or 9.5. The most commonly used tool to sharpen carbide is a diamond grinder. This is basically a sharpening stone filled with very cheap diamonds (relative to jeweler's grade diamond).
Tungston Carbide Cobalt is basicly made of two of teh most expensive base metals: Tungston and cobalt. Tungston and cobalt cost at least $40/lbs. This makes carbide a very expensive thing to buy, so people usually don't make, for example, a whole saw blade out of carbide, just the tips of the teeth. Carbide recycling has also become a very big industry too!