Rockwell Hardness Testing Question

W

WMW

Joined
May 23, 2005
Messages
6
Can anyone comment on whether or not it makes a difference when using a Rockwell Hardness Tester (3JR in this case) to check a blade in an area of 1200 finish versus a tang of around 220? Also, when looking at hardness readings, do you take the average of a few points to determine hardness?

.... trying to zero in on some variability in readings. :confused:

Herb
 
Either of those finish grits should provide a good reading. It should have enough surface removed post HT to make sure there's no HT oxide left and you're in fresh steel. You should always calibrate with a test block before taking readings. Also, unless it is a newer fancy machine with special anvils, the surfaces should be parallel to each other. Non-parallel surfaces will give specious readings. I usually check the tang immediatley behind where the guard will go. I always take multiple readings on both sides of the blade and average. Usually in a little triangle about 3 mm on a side. I have been known to have pecker tracks all over the flats on a blade if I'm stumped by the results. :)

I need to dig up tempering charts for your steel and try to think on your results some. With ATS34, I seem to remember there is a secondary hardening that can occur during tempering, and I can't remember the temps off the top of my head. That means that it will soften (temper) to a certain point, then harden more as the temp increases. After that, it will enter another zone where the hardness will start to drop again. I'm not certain I've described this in a way that will read like I'm trying to convey, so take this description as anecdotal.

One thing I would recommend is to either not temper at all before cryo (one school of thought for SS's only) or simply snap temper at about 250-300 degrees and then off to the LN. Tempering can stabillize retained austenite and I don't know what the exact ramifications are then for the final product. As I say, though, there are two schools of thought on this. Roger and I do it differently. Hopefully he will comment here. I value his knowledge; he does his homework and tests...

Hope this helps a bit. :)
 
The finish won't make a difference . I always get mine checked on the tang, where my slabs will go so you can't see the little divots that are made. The shop I take mine to to check and the shop I get my blades heat treated at usally check at least 3 time and take the average. I have never seen more that 1 point difference in any of the testing (eg, 59,58,58.5 ect).This would be a 58-59Rc


hope that helps
jimi
 
The rule of thumb for a rockwell tester is to take 3 readings within a small area. It takes 3 to get everything settled down and pressed together ie:the threads and nut on the bottom anvil, oil,etc.

Properly done, with clean surfaces, the 3rd. reading will be higher and the actual hardness.
 
At the risk of sounding dumb, when testing the tang, make sure that there aren't any burrs left from drilling. I found this out the hard way when an S30V blade that was actually 59 scored a 37 twice in a row before we noticed the burrs. After a touch up on the grinder the tang was 59.
 
One helpful hint is to use the smallest anvil possible that will hold the blade.
If you have a blade on a large anvil it may not be perfectly straight and will act like a spring in certain areas giving you false readings (similar to the burr story above). a 1/2 inch diameter anvil is enough for a blade.
 
Can't dissagree with much of the above.

The smoother the more precise. The flatter the more precise. An average of three readings is, I believe, normal practice. I, like Fitzo, usually read as close to the edge as practicable. Shollow hardening steels, such as the 10XX series, can be difficult to test and I find I must get VERY close to the shoulder in order to make a reasonable estimation of edge hardness, while testing further into the body reads much softer.

ATS-34 is a secondary hardening steel. Tempering around the 900 F area is common but I do not. Tempering at the higher end will decrease corrosion resistance. For blades I usually temper ATS-34 in 400 to 600 F range. I'll usually first temper at about 425 F then finally temper as high as 600 F, depending.

I cryogenically treat all the medium and deep hardening steels I so far use. I always snap temper 325 to 350 F one hour prior to minimum 10 hour deep (liquid nitrogen) cryo.

RL
 
Roger, do you by chance have the actual graph that`shows hardness versus tempering temp? I had the dang thing and haven't found it yet! :grumpy:

I can't remember who the maker was, but there used to be someone who left the triangle of HRc dots right on the ricasso next to their logo as a sign it had been tested. I always thought that was a neat touch.
 
I don't Fitzo. All I have to go by is the Crucible 154CM sheet. I don't have a ATS-34 data sheet at all.

Dimples in the ricasso seems pretty cool to me. Never did it though (came close a couple times :eek: ).

RL
 
You guys are great and I made an attempt at checking the cutting ability of an ATS hunter -w- 1950 + air quench + 400 room temp 2Hr , + cryo @ 2hrs + 400 @ 2hr for 64RC.... tempered again at 400 for 2 hours. (ended up at 61-63). RL pointed out it was high...I believe him. So the knife cut about 145 times before it began to labor. My enthusiastic son felt he could cut more. But his labor showed the effort. A quick sharpen on a water wheel and leather wheel made the blade shavable again. I was very happy at this point. Now I put the blade in a vice and proceded to bend it 90%. Well, it broke,,,in three places. The knife broke at the ricsso and across the guard pin holes. (not too surprising). Would you expect ATS to break in this fashon from a bend test? Is it appropriate to 90% flex an ATS blank?

HW
 
The high alloys won't bend without breaking like the simple steels can. I would guess 60 degrees would be pretty darn good. I haven't done much bend testing so hopefully someone more experienced will chime in about that.

RL
 
Thanks to all the responses. I learned a lot to try on my next set of experiments. If anyone has any further comments on bend testing ATS34 or CPM 440V I would appreciate it. :)

Herb
 
Just know that you are dealing with a deep hardening steel. It can't be expected to perform flex tests like a shallow or medium hardening steel and especially one that has been differentially heat treated.

RL
 
You must log in or register to reply here.
Back
Top