Dumb "Hardness" Question Of The Day...

V

Vess

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Oct 2, 2001
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What exactly does the "material hardness" 59-60 or 56-57 mean? The two blades in question are Cricket and Gunting. Which one is "harder"?
 
Those are Rockwell hardness numbers. The higher the number, the harder the blade. The rockwell test is done by pushing a diamond point at a certain load into the blade, and then measuring the indent. The size is the indent then maps to a hardness level.

Are you just curious, or is there something you're expecting out of the harder blade?

Joe
 
he one with the higher number is harder. These numbers come off of the rockwell scale for measuring steel and work especially well for blade steel. If a blade has a higher number it usually means that it will last a little longer i think.
 
I was just very surprised to find that something like a Cricket with ATS-55 is actually harder than a CPM440V Gunting. Somehow I always assumed that superior edge retention automatically implied a harder steel.
Oh, well... Live and Learn...:D
 
Originally posted by Vess
I was just very surprised to find that something like a Cricket with ATS-55 is actually harder than a CPM440V Gunting. Somehow I always assumed that superior edge retention automatically implied a harder steel.
Oh, well... Live and Learn...:D
Click to expand...

Yep, you learned! If you have two blades of the same steel, then the harder blade will usually have more wear resistance (though note that wear resistance does not always equate to edge holding). If you have two different steels, knowing that one blade is harder than the other tell you ... nothing. Steel is essentially a soft matrix within which there are very hard carbides. The Rockwell tests measures the hardness of the soft matrix, but does not measure the carbides. However, it's the carbides that really determine wear resistance. So 440V, which has a lot of well-distributed ultra-hard vanadium carbides, can be left soft, but still end up with better wear resistance than the harder ATS-55, which has fewer, relatively-softer chromium carbides.

Joe
 
Depending on the structure of the matrix, different steels perform differently at different hardnesses. While a higher rockwell number may imply a greater surface hardness, such a hardness may impart a structural weakness to the steel blade. 440V is notorious for it's instability at too high a hardness, leaving it too brittle, and subject to chipping and breaking. That's fine if you're not going to subject the blade to any lateral stresses or chopping, but for a general utility blade, such stresses may be common. Spyderco's heat treat on 440V leaves a very workable edge that lasts a long time, but remains durable.

Other steels may be able to go much harder, but then become very difficult to sharpen once they dull.

The key to hardness isn't finding the highest number, it's finding the right number for the steel you're using.
 
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