I've never personally worn out a die, but I have broken one. It was a carbide sizing die I managed to crack the carbide ring on. I don't know how I managed that. It was awhile ago (early 80's. give or take).
dahermit said:
I suspect that the dies for commercial ammo production are coated with titanium nitride or some other ceramic.
I don't know whether they feel a need to do that or not. The resizing dies you buy in from the usual suspects are made of fairly mild, easy machining steel that is machined and then subjected to gas nitriding to give it a hard, wear resistant surface. The mild steel is less expensive than tool steel. It is less tough and easier to machine. The gas nitriding doesn't tend to warp the shape the way heat treating and quenching of carbon tool steel often does.
The commercial cartridge case makers use dies made from a proper tool steel and maybe some solid carbide for some operations. I think a lot of cartridge cases are extruded by stamping a brass slug to force it to flow up around the die ram to form the cups. Unlike the older process that starts with brass discs cut from a sheet, the slugs are cut from wire or rod so there is much less scrap involved.
Slug extrusion is the way seamless aluminum beer and soft drink cans are made, all in one step. A die maker who'd worked on the dies for the cans told me they used high impact S-7 air hardening tool steel for that, so I imagine the cartridge case manufacturers do for that kind of operation, too. It retails for about five times what oil hardening tool steel does. I don't think its surface wear characteristics are anything special, though. so perhaps nitriding is used, too.
