AEBL heat treat test data

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
Knifemaker / Craftsman / Service Provider
Joined
Jun 11, 2006
Messages
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AEB-L always makes me alittle twitchy when I think about heat treating it. So I decided it was time once and for all nail it down and figure it out. The pic below is the result of a 5 coupon test and many days of testing. It answered a lot of questions but brought others to the surface.

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Questions like why did the hardness increase after tempering for some samples? Did I interpret that correctly?
 
Interesting test... but I think your sample size is too small to be conclusive.
 
All samples increased hardness after the first 300° temper. How is the sample size to small? Thy all went through the tempering at the same time so as to factor out any oven variance. Same with the hardening. Each coupon was tested around 10 times in different spots for each temper.
 
I'm following this very closely. I just got my (used) hardness tester and calibration block and was going to do the same test to make sure I have my temps at optimal. Problem is I have to wait for my diamond indented to come in from Jina until I can test in c.

What soak times did you use? Where's the aeb-l from?
 
JT, your first column says "As Quenched plus Sub" - is that plate quenched, then N2? Did you test for hardness before soaking in N2 (if you did)?

I soak for around 6 to 7 minutes @1975F per blade (time varies a bit with several blades), then plate quench, then soak in Dry Ice solution for 30 minutes or so. That usually gives me around 62 to 63RC before tempering. Tempering at 400F will usually provide 60 to 61 Rc. Since my HR150A clone specs say ±1 Rc point accuracy a reading of 61Rc would indicate somewhere between 59 and 61Rc, so I don't usually put a decimal in Rc readings. The repeatability is better than the accuracy specs, perhaps 1/2 point.

Good thread - AEB-L always perks my interest since that's become my main metal to use.

Ken H>
 
What was the soak time, quench, and cryo process?
 
Ok so let me explain alittle more about my testing. I have a bunch of little 1” circles of AEBL. thy are drops from a sheet (from aks) I had laser cut. The soak time was 8min from the time the door closed. I also ran nitrogen injection to keep the scale off. I then would snag them with the tongs and drop them between the quench plates and close them tight. I would then take the disk and drop it into the dry ice and alcohol slurry. I would leave it there till it stopped bubbling and it was at temp. Maybe a min or so total in the subzero. Then it came out and was dryied off and warmed up in my hands. I cleaned up the faces a little using a fine belt on the grinder. Then into the house and did the series of first tests. This entire time the oven is ramping up to the next soak level. After thy where all done and tested I let them set for about 12hrs. I then retested them to see if the hardness changed. It did not so I preheated the oven (kitchen) to 300 and let it set for an hr once at temp so it was stable. I have a big steel plate in it that I do all my tempering on. I then stuck all 5 disks on this plate and started the 2hr timer. After 2 hrs I pulled them out and water quenched them. Then stright to the harness tester. Each coupon got a TON of readings. I did not wright them down. I just watched as I tested all over the disk and made sure all the tests where the same. It’s normal to get flyers some times that’s why thy say do a minimum of 3 tests. After all the testing the 5 disks went back into the preheated oven at the next higher temp for 2hrs. I just continued this process till I hit 500 deg. I know kitchen ovens are not that accurate but the purpos of my testing was to nail down a solid base of numbers for my heat treating. In all reality I could care less what the numbers say on the oven it’s the results I’m after and the oven temps are just repeatable reference points.
 
You left the disks in the dry ice slurry for only a minute? That's pretty quick to come up totally to temp inside the metal disk. I know the disks are small and will come up to temp faster than full size blade.

Not saying it didn't have to to fully transform all the RA it's going to. I usually leave blades in for at least 30 minutes or so. Extra time doesn't hurt.
Ken H>
 
Hello everybody, this is my first post here, however I've been lurking for a "while".
Ken the transformation of RA to martensite is at the speed of sound, that means when the sample reach the right temp the transformation happen instantaneous, extra time doesn't hurt but either does nothing any further.
Nice work JT!
 
Ken is expressing his concern that the entire piece did not reach temperature in the time it was immersed.
 
I'm curious about the finer details of your procedure. You said soak time was 8 minutes from when you closed the door. Say your oven reads 2000˚ and you open the door to put the coupons in. The temp will drop quite a bit just from opening the door. Then the "room temperature" coupon will drop the temp a little more when it goes in the oven. Part of that 8 minutes from the moment the door closes will be spent getting the oven back up to 2000˚. So actual soak time at that temp will be significantly less. Can you clarify that for us?

Also can Larrin or someone else explain why hardness would increase by 2 or 3 points after tempering?
 
i4Marc said:
Also can Larrin or someone else explain why hardness would increase by 2 or 3 points after tempering?
Click to expand...

This intrigues me as well. I experience the same with other steels like 14C28N. I'd also be interested in understanding how this works.
 
Stromberg Knives said:
This intrigues me as well. I experience the same with other steels like 14C28N. I'd also be interested in understanding how this works.
Click to expand...
I’ve been seeing this with 8670! After first low temper, hardness jumped by 1-2 points!
 
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