Rockwell hardness of talonite talon

CYA

CYA

Joined
Jul 21, 1999
Messages
105
Does anyone know what the Rockwell hardness of the talonite talon is? On knifeart's web site they claim it's 91! Is this true? Wouldn't that make talonite brittle like a ceramic knife?
 
Background:
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Rockwell hardness testers work, briefly, by applying a known load to a small diamond tipped probe of known surface area. They make a small dimple in the test piece. Based on the depth of the dimple (really, the measured amount of deflection of the probe once load is applied), they can gauge the relative resistance to deformation of the underlying material...i.e. the "hardness" is related to how much it deforms or dimples during this test.

Ok ...

Talonite is very similar to Stellite.

Stellite was the original, but not made readily available in sizes and at prices for knife makers.

Both rely on a "tough" but relatively "soft", in knife terms, matrix made of Cobalt and Chromium. The matrix is a sort of tough carrier or support structure for hard carbides in this alloy matrix.

You'll see them referred to as CoCr alloys. This matrix is in the Rockwell 42-48 range on the "C" Rockwell scale, which by itself is well below the Rc range of 55-60+ needed for decent edge retention. The Rockwell testers will essentially give you the "hardness" reading on the underlying matrix of Talonite.

But that's not the whole story...

These CoCr alloys also contain enough carbon and enough other "carbide forming" elements such that very hard carbides exist in the alloy when produced. Here are the major carbide formers and their relative hardnesses per Crucible Services:

60-65 hardened steel
66-68 Rc for chromium carbides
72-77 Rc for molybdenum and tungsten carbides
82-84 Rc for vanadium carbides

With that background, here is a relative range of alloy composition for either Talonite or Stellite (my notes don't indicate which, but it could be Stellite 6K... Stellite 6K is the one usually used for knife blades, Stellite 6BH might get some use also):

Carbon: 0.9% - 2.0%
Chrome: 28% - 32%
Cobalt: 49.5% - 56%
Manganese: 2%
Nickel: 3%
Tungsten: 3.5% - 5.5%

Ok, see this link for further info on Talonite:
http://www.geocities.com/mdpoff/talonite.html

From that link, here is what MDP says is in Talonite:

Nickel 3% max
Silicon 2% max
Iron 3% max
Manganese 2% max
Chromium 28%-32%
Molybdenum 1.5% max
Tungsten 3.5%-5.5%
Carbon 0.9%-1.4%
Cobalt: the balance

Here is where some educated speculation on my part comes in: I think it is the Tungsten and Molybdenum carbides that gives the Talonite the heavy duty wear resistance, but Chrome Carbides very likely play into this very heavily as well. I'm making another educated guess that nickel and silicon may help with alloy toughness. (any metallurgists out there who know better, chime in!). A Rockwell hardness tester will in essence push these carbides to the side, or impact them into the CoCr matrix, and so their contribution to Talonite's abrasion resistance, or wear resistance (which translates to longevity of a slicing edge) will be unmeasured by this hardness test.

For sure, Talonite/Stellite will not corrode under any kind of reasonable thing you'd get your hands into. It takes strong acids or bases to really start to corrode this stuff. Arguably, Talonite would make the perfect salt-water knife, and salt water won't really touch it.

Drawbacks, only two or maybe three really:
1. cost... very pricey for raw stock so blade prices are high
2. The edge can roll sooner than other steels, but is easy to straighten up with a steel or on ceramic rods. It may loose it's "as sharpened" wicked-sharp quicker than other premium blade steels, but a very good underlying edge is retained so it will continue to slice and slice for long periods.
3. It won't take quite as wicked-sharp an edge as many other materials will, from simple carbon steels to 420V etc.

I have a couple of kitchen paring knives make of 6K. They are very thin, flexible, work great for paring. They hold a good edge, but it rolls easily if you cut into say a cutting board, but I'm tellin' ya', it only takes 2 to 4 very quick swipes on a steel to straighten the edge back up. Super easy to maintain.

I have no idea where a hardness level of 91 comes from. Can't even think of anything that is that hard, maybe some ceramics...but I'm not sure. I think diamond may be the Rc scale limit at 100, and none of the usual materials are at Rc 91. There may be some metal nitrides (Titanium carbonitride, or some other stuff... might try the Buck Knives page) that might go that hard.

Also try using the search engine on this forum for "Talonite" and "Stellite"...this ground has been covered, probably find a thread that is more detailed.


[This message has been edited by rdangerer (edited 05-27-2001).]
 
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Geez, I was just gonna say - no.

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C.R. Specialties
Your #1 Source for CUDA, Camillus, Western, and Becker Knife & Tool Cutlery!
 
What I should have typed was:

"91? That's BS. It's more like Rc42-48 but the tungsten, moly, and chrome carbides make it cut MUCH better than that. Use the search engine for more..."




[This message has been edited by rdangerer (edited 05-28-2001).]
 
Geez, this is so complicated.
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It bends easier than steel, but holds a better edge. It's softer than steel, yet it's hard to grind. It just doesn't make sense.

[This message has been edited by CYA (edited 05-28-2001).]
 
CYA,

Think of it this way:

I have a piece of oak and a piece of pine; which is harder to sand? The oak, of course, because it is a denser wood. The oak is like a steel without heat treat and the pine is like talonite without the carbides.

Now if I drive a handfull of nails into the pine so that every half an inch or so, there is an 8 penny nail buried, then which is easier to sand? Well, the oak is now because the nails are HARD compared to oak. The nails represent the carbides present in the Cobalt-Chromium matrix that makes up talonite. The reason the RC doesn't work so well to measure hardness is that the matrix is soft, so if the diamond tip acts like a hammer would when the pine board filled with nails is hit...it will make a dent...the nails don't help prevent it denting very much. There is simply not enough of them.

I must also point out that when grinding steel, the carbides have not formed because the steel has not been heat treated. After heat treat, steel is also very hard to grind. Talonite does not require heat treatment, the carbides are already present. So, it's not really a comparison when you talk about how difficult each is to grind.

Jeff
 
I dont have the exact info in front of me right now but the hardest carbides formed in Talonite are Tungsten Carbides. They have an RC in the high 70's low 80's if I remember correctly.
 
Darrell Ralph;

The Rockwell "B" scale is primarily used for testing aluminum and the "C" scale is used for testing steel and harder materials. The "B" stylus is usually a small ball and the "C" stylus is a diamond.
Trying to compare the "B" scale to the "C" scale is like apples and oranges. You can cross reference the Brinell scale to the "C" scale.
Hope this is of some help.
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Ron,
Bremerton, Washington
0071.gif
 
Found a chart in a text book:

Rockwell 91 B-scale is below the Rockwell C chart. If I extrapolate (very dangerous), RB 91 would be about Rc=8.

Rockwell 100 on B-scale is about 20 Rockwell C, which is about 220 Brinell.

Rockwell C 60 is around 650 Brinell.

Past 100, Rockwell B is badly non-linear compared to other methods.... e.g. Rockwell C, Brinell, Vickers, or the Scleroscope hardness. It may be because the the 1/16" steel ball in Rockwell B must deform when it comes to the other hard materials (guessing that ball must be Rc65 or so).

Point is the claim is bogus that Talonite is Rc 91, must be typo or a braino.

Buck's home page indicated diamond was Rc 80, but Vanadium carbides are supposed to be Rc 82-84. Go figure.

Ok, that's more than anyone wanted to know. I will cease gazing into my navel for blue lint...

Ciao.



[This message has been edited by rdangerer (edited 05-29-2001).]
 
Roughly a year or so ago, I read some article somewhere that placed the Rockwell hardness of vanadium carbides at 91%. That is apparently in error, but I've seen the error repeated at least a couple times. I'm pretty sure that is where that # came from. Hell, I'm sure I wrote it once or twice. I might be the problem?? Sorry if that is so. Doubt it, but stranger things have happened.

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Asi es la vida

Bugs
 
If you want to play with a material that is up above 80 on the RC scale, try one of the Buck knives with the IonFusion coating. They use both Titanium Nitride and Zirconium Nitride coatings on blades (a trick used on some machine tool bits). I got one of the Buck Vanguard hunting knives with the Zirconium Nitride coatings and while I was fooling around with a sharpening steel I had trouble since the edge would shave metal off my RC65 steel.
 
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