OT? Rockwell Hardness

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Chris "Anagarika"

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Mar 7, 2001
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I am wondering what is the method of determining a blade's Rockwell Scale ..

and of course what is the best hardness for a general use knife?

Does it depend on steel alloy(i.e.440V or 420, can they both achieve same scale?), does the steel alloy bring different characteristic to the hardness?
 
Chris, rockwell hardness is measured by a machine that presses the tip of a diamond into the metal. This produces a small inprint as a result. The amount of pressure required to do this indicates the rockwell hardness.
Different alloys react differently. Most cutlery steels can get to around the same hardness, but will have different characteristics (sometimes negative results) after they are heat treated. I believe that is why some steels aren't hardened as much as others; because they will become too brittle.

This is how I understand it. I might not be 100% correct, but I'm sure other people here know a lot more about it.

Steve
 
<font face="Verdana, Arial" size="2">Originally posted by epigram79:
Chris, rockwell hardness is measured by a machine that presses the tip of a diamond into the metal. This produces a small inprint as a result. The amount of pressure required to do this indicates the rockwell hardness.
Different alloys react differently. Most cutlery steels can get to around the same hardness, but will have different characteristics (sometimes negative results) after they are heat treated. I believe that is why some steels aren't hardened as much as others; because they will become too brittle.

This is how I understand it. I might not be 100% correct, but I'm sure other people here know a lot more about it.

Steve</font>
Click to expand...
What he said!
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There are different Rockwell scales but the one used most by the knife industry is the "c" scale hence the "Rc" for Rockwell c scale.......
 
Hmm (a good food for thought).. Thanks a lot Steve and Dawkind!

Another question: the hardness relate to edge retention or sharpness achievable?
 
Cool, I never knew how they measured the Rc of a blade, does a company do this to just 1 knife out of their entire line or to each one?

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Cameron

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"Look deep, deep inside and you will find a place of anger, vengeance, and brutality. Go there. It is your last hope to conquer the truly wicked."
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Hardness does relate to edge retention. Aluminum is soft...you could sharpen it to an edge (not a very good one) but if you use it, the aluminum will wear very fast. At the same time, the aluminum would take an "edge" very fast because it is so soft. Same with steel. If the steel wasn't hardened at all, it would take an edge and lose it quickly. If you harden the steel too much, it becomes brittle.

Cameron, you can actually see an imprint on the steel when it has been tested by a rockwell tester. Most blades I see (which are all production knives) don't don't have these marks. I would guess that they through a whole bunch of them in the kiln and set it to the proper temperatures when both hardening and tempering. They know what temps they need so they just do it by mass.

 
Does the only one of the production that has the RC test imprint becomes more valuable as collectibles?

How do we see one when there is one?
 
That's a good question, whether or not they test one per batch. I don't honestly know. The companies know what temperatures to set the kilns for (some do it themselves, others send their blades out to have it done). If you repeat the same steps everytime, you should yield the same results with a good degree of consistancy. That would probably negate the need to test the blades. I would think that having a blade that was rockwell tested wouldn't have any more value than one that was not; at least I wouldn't pay more for one. I believe value is based on personal preferance. On a regular folder, the testing mark would not be visible. It would be on the tang where the handle would cover it. If you had one and were selling it, I would pay you less money because I know you've taken the knife apart and already voided the warrantee. Maybe someone with a custom balisong can point out if there is a recognisable mark on the blade where it was tested. Hope I've helped somewhat. I'd also appreciate it if someone could let me know if I am misinformed.


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Steve
(Third Mate for hire!)
 
Puma is the only manufacturer that I can think of that advertises and points out the spot on the blade where the test was made. Most of the custom makers I know eliminate the test spot when they finish the blade. On a carbon steel blade that has been differentiately heat-treated, the test is usually done near the cutting edge, the blade tip, the blade spine, and the tang area since all are different hardnesses to enhance/maximize performance.
 
I have an Auto blade with nothing but a capital "D" on it that I was told was from the Rc test. The knife resembles a BM AFO... Is this considered a Rc test mark?

I have yet to confirm positive identity of this knife.

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Sabo 29
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Sabo, a knife that resembles an AFO??? Lets see some pictures! At first I wanted to say Dalton, but he doesn't put just a "D" on it. I would suspect that the "D" isn't the rockwell mark...if it was, that would be really cool! But I don't think so. Lets see it!

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Steve
(Third Mate for hire!)
 
It is not valid to just test one spot on the blade. Because the blade varies in thickness and width, the hardness can also vary. Especially skilled makers actually do this deliberately making the edge hard for best edge but the spine less hard so as not to be so brittle. So, if a maker proudly points out one test mark, it means very little.

Most production manufacturers test a few samples from each lot. This is reasonably valid since they use very controlled processes and equipment.

Truth be known, many custom makers never test their blades since they don't own the equipment (which costs thousands of dollars). If they give a hardness, it's often just a typical number for similar blades they have had tested in the past.

A mark such as a "D" is not likely to come directly from hardness testing but could be an inspection mark added to indicate that the blade passed hardness testing or that it achieved some specific hardness. But, I've never heard of any standard for such markings, so what it might mean would be unique to that maker. Military knives sometimes have a series of small letter marks that indicate that they've pasted certain tests or inspections.


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Chuck
Balisongs -- because it don't mean a thing if it ain't got that swing!
http://www.balisongcollector.com
 
I really appreciate the different opinion voiced here .. we are all enriched that way, at least I am ..

I agree with you Steve: if the test is at the tang where it is covered by the handle, I would pay less for one as the warranty is void.

If a production knife is regularly tested (i.e. one per batch), then the mark would not add value either. However, if a production knife only being tested at the prototype / first production to ensure proper hardness and later one it is maintained by keeping the standard rigid, don't you think the marked blade should value higher (given the checking would not require knife to be disassebled)?

My personal opinion is: the final test is the user as hardness is only a factor among geometry, grinding, etc.. My original question was related only to the technicality as I am always a curios engineer.
 
Generally, production manufacturers like the products they sell to be uniform. So, the samples tested are generally either cleaned up or thrown away. They may also be subjected to additional quality testing that might be destructive.



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Chuck
Balisongs -- because it don't mean a thing if it ain't got that swing!
http://www.balisongcollector.com
 
I checked the rockwell hardness of my 42 today. The blade measured Rc 58, about what I expected. Now my blade, the flat area, has the diamond mark from the test.
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