Yes, it is only the resizing effort that needs lube. Carbide sizing die rings are indeed made to eliminate the need for lube and it works. Sorta. Well, you can - many do - skip lubing forever if you wish, but your brass will eventually pay a price if you don't.
Thing is, any time we run two metals hard against each other it produces heat from the friction. While our cases won't get stuck in carbide dies if used dry, that pressure and friction does some bad things. Small, almost microscopic bits of brass will scrape off the cases and adhere to the carbide ring in a process called "galling". The galled bits will be as firmly attached as if they were welded! Understandably, those tiny bits continue to grow as successive cases are rubbed over them. Eventually, the galled sizer will be making clearly visible scratches on the cases, most people think they have scored the die surface with dirty cases but that's rarely true. As the galling continues to grow the scratches will eventually become so deep they weaken the cases and they will eventually split along the scratch lines.
Once galling starts the only cure is to polish, or grind, the brass off the carbide. That can be done by the maker or at home. Just use a short length of split dowel rod chucked in a high speed drill. Put a strip of fine grit black sandpaper, silicon carbide of 400 grit or finer, and spin it until the brass is removed. Or use a wad of 3M's green cleaning pad and do the same thing but slower. Or soak the die's bottom in a copper dissolving bore solovent.
The prevention of galling on carbide is much easier than cureing it after it happens. Just lightly lube some, maybe every 10th or 20th case.
