7-11-2026

the KME sharpening system -- when is diamond needed?

Steels with a lot of vanadium carbide require diamond stones. Some people say if the steel has more than 3-4 percent diamond, you need carbide.

With interest, I read a comment that this accounts for the reputation that S30V has of taking a mediocre edge, but holding it for a long time. Diamond stones would change that story.

Some hardness numbers

Various scales exist to measure hardness: 
Diamond -- Mohs 10   Knoop 70,000  Vickers 7000 to 10000
CBN     -- Mohs 9.5  Knoop 45,000  Vickers 4700
Si-carbide Mohs 9+   Knoop 26,000  Vickers 2200 to 2800   Rockwell 83-85
Al-oxide - Mohs 9    Knoop 20,000  Vickers 2100 to 3000
V-carbide  Mohs --   Knoop ------  Vickers 2500 to 3330   Rockwell 82
W-carbide  Mohs --   Knoop ------  Vickers 1700 to 2600   Rockwell 72
Cr-carbide Mohs --   Knoop  1820   Vickers 1350           Rockwell 69
So sharpening a high vanadium steel with Al-oxide ceramic would be somewhat of a losing battle. Silicon carbide is only slightly harder. Maybe. People claim that silicon carbide will sharpen S30V for example, while use of aluminum oxide is discouraged, with the warning that attempting to do so will be slow and frustrating. Given the numbers above, it is hard to believe SiC will be any different.

Vanadium content of some popular steels

These steels are "easy to sharpen" with essentially no V content. 
52100 -- no V (Cr provides the carbide)
440C  -- no V (Cr is 16 percent)
VG-10 -- 0.30 percent (Cr is the main carbide here)
VG Xeos  0.40 percent
ATS-34 - no V (Cr is 14 percent)
154CM  - 0.40 percent or less
And now the "super steels" 
Cruwear - 2.4 percent (PD1)
Rex45   - 3.05
HAP40   - 3.0
M4      - 3.75 to 4.5
S30V    - 4.0 percent
M390    - 4.0 percent (20CV, CTS-204P)
S90V    - 8.75 to 9.0
S110V   - 9.0 percent
K390    - 9.0 percent
PMA11   - 9.25 to 10.25
A have seen the comment "20CV is famously difficult to sharpen and requires diamond stones." 20CV has very fine comments and does yield an excellent edge. S30V is not as hard to sharpen.

It is easy to see why I have found Cruwear fairly easy to sharpen.

Of course vanadium is not the whole story, but I am finding this study useful and enlightening.

Feedback? Questions? Drop me a line!

Tom's Knife Info / tom@mmto.org