Hardness testing...

Phillip Patton

Phillip Patton

Knifemaker / Craftsman / Service Provider
Joined
Jul 25, 2005
Messages
5,362
A couple months ago I bought a nice Rockwell tester off of ebay, and recently got a test block and adjusted the tester to agree with it.
So I'm wondering, how do you guys who have a tester use it? By that I mean, what part of the knife do you test? Whenever I test the edge, it's always way softer than the ricasso or tang (assuming I hardened the whole knife). Is this because it just doesn't work well on an angle, or is the edge really softer?
Thanks,
 
Did you purchase a Rockwell "B" or "C" tester? Are you doing the test after you temper? Is the edge deforming when you test it ? You have posed an interesting question. I would like to know why also. Fred
 
you can check only on surfaces parallel to the table. otherwise the diamond wont ge enough resistance => "lower hrc"
there are lists with correction factors for different angles :rolleyes:
 
I make test blocks out of the same material as I use for my knives. Take the blocks through the same thermal cycling and heat treating steps as the knives and then check the hardness levels at various stages.

I surface grind the test blocks to about 1/8" and grind off the de-carb layer before any hardness tests. I keep a chart of each steel I use with hardness levels at the annealed stage, after the quinch and various levels at different drawing temps. A lot of other factors can come into play such as soaking time and quinchant temp but it does give me a good idea of where the hardness level is. As I try different processes I can really narrow down the treatment for a particular steel. But I never really stop experimenting.

Daniel
 
Fred.Rowe said:
Did you purchase a Rockwell "B" or "C" tester? Are you doing the test after you temper? Is the edge deforming when you test it ? You have posed an interesting question. I would like to know why also. Fred
Click to expand...


My tester will do A, B, or C. The edge doesn't deform, but a few have had big chunks crack and fall off. :eek: I think I can safely say that those were hard. ;)
Usually I test after tempering, because I'm afraid the diamond might start a crack in the highly stressed condition of un-tempered steel. MAybe it doen't matter.
 
kababear said:
you can check only on surfaces parallel to the table. otherwise the diamond wont ge enough resistance => "lower hrc"
there are lists with correction factors for different angles :rolleyes:
Click to expand...


That's kind of what I figured. Seems like the diamond would tend to "drift" "downhill" and give a false reading. Do you think I could make an angled platform, so the surface of the blade being tested would be horizontal?
 
DWinkler said:
I make test blocks out of the same material as I use for my knives. Take the blocks through the same thermal cycling and heat treating steps as the knives and then check the hardness levels at various stages.

I surface grind the test blocks to about 1/8" and grind off the de-carb layer before any hardness tests. I keep a chart of each steel I use with hardness levels at the annealed stage, after the quinch and various levels at different drawing temps. A lot of other factors can come into play such as soaking time and quinchant temp but it does give me a good idea of where the hardness level is. As I try different processes I can really narrow down the treatment for a particular steel. But I never really stop experimenting.

Daniel
Click to expand...


Sounds like a good idea. As soon as I get some free time...
 
Phillip Patton said:
My tester will do A, B, or C. The edge doesn't deform, but a few have had big chunks crack and fall off. :eek: I think I can safely say that those were hard. ;)
Usually I test after tempering, because I'm afraid the diamond might start a crack in the highly stressed condition of un-tempered steel. MAybe it doen't matter.
Click to expand...
Phillip,
Being able to tell the customer the working hardness would be one importance of testing after tempering, or if you are measuring to test different quenches, then testing for; as hardened Rc. would also be of interest.
So, it only matters in that way. I wish I had one. I send my stuff out to be tested.
No way that diamond tip will harm the steel in its hardened state. IMHo

Fred
 
I diagree, Fred.
In full hard state, the 150kgf load on a concentrated spot near an edge might indeed crack the steel.
Also, the minimum sample thickness to test at HRC60 is about .03"...
Measurements should be made perpindicular to the test surface.
 
howiesatwork said:
I diagree, Fred.
In full hard state, the 150kgf load on a concentrated spot near an edge might indeed crack the steel.
Also, the minimum sample thickness to test at HRC60 is about .03"...
Measurements should be made perpindicular to the test surface.
Click to expand...

I would tend to agree with you, when we are talking about edges. Fragile indeed, when the rc is up around 62 or so. As you pointed out, you really can't get a correct read on the slanted surface that a blade presents. I have seen test done on blades where the blade was shimmed to make the top level. I think if you set the stylest just below the temper line, with the surface level, you could take a safe reading that would be correct. I would want to stay away from the edge for all the obvious reasons. With the Rockwell superficial hardness test [15n 30n or 45n] which is addapted to the testing of thin sheets and to surface layers on steel, the test could be done without damage to the blade.
I new after I posted this originaly that someone would give that statement a challenge, I thought about editing, but new I would get back to it. Thanks for keeping me honest and letting me explain myself. Fred :cool:
 
Fred,
In shimming a blade on an angle to make the surface level would work fine for a flat grind, but may pose a problem on a hollow grind, as the surface sitting on the anvil should be in solid contact, but the bottom surface will be hollow, and allow flexing, causing the readings to be lower than actual.
If it's not one thing, it's another, huh?
I think Daniel offered the most correct way to assure the process yields the desired results on single hardness testing.
Differentially hardened surfaces have to be measured on the blade, though.
 
I had not considered a hollow ground blade. That would be a challenge!
It would be nice to have a Rc tester in the shop. I test all my blades with a flex test on the edge, [after tempering] and sharpening. I just built a digitally controlled heat treat oven to further my control of the steel through the processes. The knife shop is always a challenge and that keeps it interesting.

Fred
 
Phillip, a couple of obserations after reading the posts here. As already stated you can't get a good reading on an angle. If you still want to try with shimms ect. there is a good chance you can break the diamond styliss(?sp). A new one from Wilson Rockwell will cost you about $200. The std test block is very important, Dan Winkler has a very good method. The only thing there to watch out for is if you really have a std. test block made and certified by Wilson/Rockwell/Instrom. you would think that some where in Washington there would be std. test block but the fact is that Wilson--maintains it and you can only get it from them. I have seen some offshore test blocks that were as much as 2 pts off the real std. I bought a test block from Wilson, they are expensive, about $150. I got it in the range needed (60RC) and I use it like Daniel to make and calibrate all the different steel types I use. I checked my block against the ones in Crucibles lab in New York when I was there a few years ago and we checked within .5 pt, --as close as you can hope to measure. I have offered before --and do it now-- again to calibrate your test block against my std to be sure you are on the right path. The actual measurement can easily be off .5 to one full point plus or minis and add that to a test block that is a point off and you can easily have a 2 pt or more error. When we are talking hardness we should all be on the same sheet of music. You can contact me through my website www.seamountkniveworks.com PHIL
 
Hi Phil,
A couple weeks ago I bought a test block from Qualitest. It was $70.
That would be great if you would compare mine with yours. I'll send you an e-mail.
But, what good does that do if you can't get a good reading off the edge bevel? Do you test the tang and hope it's the same hardness as the edge?
Today I hardened a blade of 1095, and tested the edge straight out of the quench, and it was 62. The tang was 64.
 
Phil, yes the edge bevel is going to be the same as the tang with most steels. As long as you get it cooled before the "nose " on the time temp curve. I haven't worked with 1095 so can't be positive with it but for all the air hardening steels I use this is the case. I did an experiment that you can do to prove that to your self. Make a test piece with thickness steps in it. Go from the tang thickness to the edge, maybe like .020 or so. You will have to make the piece perfectly flat and best to surface grind it to make sure. I found with this experiment that all the thicknesses were the same within 1 pt which is the normal error you can expect with a hardness tester. Yes give me an email and coordinate a check on your test block. Phil
 
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