I read some that say a ceramic stone won't sharpen S90V only diamond. Others write that SiC and ceramic will sharpen it. Ceramic is aluminum oxide fired hotter with different binders. Which the carbides come out not as hard as Crucible states their vanadium carbides at. This is why many write that only diamond is hard enough to cut these V carbides. Which I can see. But the flip side to this coin is that the vanadium carbides are very small 5u. Hence, a grit the size of XX fine diamond is needed to cut these. So, this beckons the question; are you using this fine of a diamond stone? Otherwise the vanadium carbides could be passed over by a more coarse stone and remain untouched. i.e. steel removed from the matrix and the V carbides not.
I own a X coarse, coarse and fine diamond stones and have no intentions toward purchasing a finer diamond stone. So, I can use these or my fine and X fine SiC stones (up to 500 grit). I have ceramic stones that will take it fine enough to encounter the V carbides but I don't care to take a everyday user knife that fine. And the ceramic stones are not hard enough to cut the V carbides anyway... So, this is the short of the equation on sharpening Vanadium carbide steels. DM