AEB-L Heat Treat Problem?

"Actually, you are partially wrong. The dry ice is never in contact with the blade because there is a layer of CO2 gas between the two caused by sublimation. Gas is a poor conduit for heat. Using a liquid allows the liquid to transfer the heat much more efficiently. Denatured alcohol is a better liquid than acetone."

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Excellent observation, Stacy.
 
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Stacy E. Apelt - Bladesmith said:
Actually, you are partially wrong. The dry ice is never in contact with the blade because there is a layer of CO2 gas between the two caused by sublimation. Gas is a poor conduit for heat. Using a liquid allows the liquid to transfer the heat much more efficiently. Denatured alcohol is a better liquid than acetone.
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OK well, I'll defer to greater knowledge than I have. I've never heard a legitimate reason proffered previously. How important is efficiency when you've got no curve to beat as in austinization?


I never doubted the heat transfer efficiency of the liquid medium, but are you saying that due to this gas separation the blades will never reach temp when submerged in inches of crushed dry ice, or simply that it'll take longer?


If the latter, my point remains valid. Regardless, I have a hardness tester and have observed RC change using this method, so I know it's at least partially effective, and I'm hitting max potential RC with my routine. Whether or not there's still some RA, I lack the means to test.
 
Also thanks samuraistuart for the pointless meme. I thought we decided to do away with that stuff around here?
 
Don't get worked up.

Efficiency and quality are always important. Liquid is a far better bath than a gas. It is basic physics and good metallurgy. Just because something will "work" does not make it a recommended process.
 
Hey guys I'm definitely not getting worked up. I know it's difficult (impossible) to infer tone or sentiment in this medium, but this is not the case.


I'm simply questioning something that I've seen repeated as dogma, with nary and explanation any time I've seen it mentioned. I know many things repeated in such a way (and lets be honest, there's a lot of people just repeating what they've heard, without knowing the why), have merit and reasons behind them. However, not all of them do, and many things get promoted as if they're the only way of doing things, and that culture has driven a lot of very competent makers away from these boards.


I'm more than happy to be wrong about something, if it can be explained why.


I agree completely that efficiency and quality are always important. Although the pragmatist in me believes that doing something quickly, which is what i think what efficiency means in the case of what we were talking about, may be arbitrary, if the result (quality) in the end is the same, and instead of investing active time in one thing, I can do something else with that time, with less direct effort (time, efficiency) and cost efficiency.


So I'm still uncertain whether I'm being told that using acetone or alcohol in dry ice is *necessary* to achieve the same results, when it comes to sub-zero quenching AEB-L (or D-2, or any other steels that need temps within the realms afforded by dry-ice alone), but I will be happy to know, and concede the answer. If it will work, and the extra step is simply idealistic process, why would the other be more recommendable unless there is some actual change to the end result? I understand that gas is a poor conductor, but even in still air temperatures will equalize, albeit slowly right? This is an issue for beating the cooling curve for austinizing, for many steels, although not all, but is this a legitimate concern for sub zero quenching these steels where dry ice temperature is effective?


I'm honestly trying to understand. Not trying to start some emotional debate.



Samuraistuart, I apologize for being snarky, I wasn't offended, it just seemed like you were piling on for no reason. As I mentioned, I don't want to promote a culture of "don't ask questions, just do what you're told" here. I know we've had some topics get out of hand where "conventional wisdom" has been questioned, but that's not my intent here. I quench in Parks, for the record. :P
 
In the interest of disclosure I'll admit, that the reason I tried using straight dry ice in the first place, before getting LN2, was because someone told me that using acetone in dry ice raised the potential temperature of it, that sounded plausible, so I just used crushed dry ice, before researching and realizing they were wrong about what they told me.


Still, it worked, and not just that I felt it work, but rather that testing verified. So I asked "is the acetone, etc., necessary"?


Now I use liquid nitrogen because it's more convenient, obviously the results are the same.
 
Does anyone know what Peters, etc. (the Big Kidz) use for subzero?
I'm assuming LN bath, but it would be interesting to find out. I could call them, but it's idle curiosity that may come in handy one day, and I hate to pester them.
 
elementfe said:
Does anyone know what Peters, etc. (the Big Kidz) use for subzero?
I'm assuming LN bath, but it would be interesting to find out. I could call them, but it's idle curiosity that may come in handy one day, and I hate to pester them.
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I would assume it's liquid nitrogen also. I'm under the impression that many high alloy/stainlesses require temps colder than what can be supplied by dry ice. From an industry standpoint I'm sure it's more convenient also.
 
Parenthetically, I quench in oil rather than plates for the very reason Stacey cites: efficient transfer. Plates can't carry heat away as efficiently as oil, especially with a shape that's all thick 'n' thin.
It really doesn't matter, though, because if we watch the times and temps and curves, we're all going to get the same results, because Metallurgy.
 
In one way this is a glass "half full-half empty" situation.

"It really doesn't matter", depends entirely on whether you are trying to get the minimum required or the maximum available. Metallurgically, it is always the latter, and that is why a wet slurry is better.

Another reason to do the sub-zero quicker, is that it is the finish of the martensitic transformation. Unnecessarily delaying conversion from austenite into martensite should be avoided.
 
As always, Stacey has the straight dope.
Last night, for no good reason, I thought I'd quench a fairly long (8.5"x.110) butcher knife in D2 on dry ice cakes without solvent. I had it nice and straight out of the quench, and darn if it didn't warp a bit on the dry ice. Back to alcohol slurry bath, I never seem to see warpage when the subzero quench is liquid, I.E. even all over the blade.

All I was saying about oil vs plate quench is, if you're staying inside the curve on either one, how could it matter? Makers I respect say, "AEB-L benefits from quick cooling" so I cut open the ends of the packet and dunk it in medium oil. Others get great results from plate quench, which is pretty much the standard.
 
Stacy E. Apelt - Bladesmith said:
In one way this is a glass "half full-half empty" situation.

"It really doesn't matter", depends entirely on whether you are trying to get the minimum required or the maximum available. Metallurgically, it is always the latter, and that is why a wet slurry is better.

Another reason to do the sub-zero quicker, is that it is the finish of the martensitic transformation. Unnecessarily delaying conversion from austenite into martensite should be avoided.
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I hope you're not implying that I'm irreverent about getting the best results, as that's definitely not the case. I'm merely questioning the redundancy of one piece of the overall process. Yet I still haven't been given a clear answer to whether or not using a "wet slurry" does in fact give or guarantee better results. Honestly I don't know if we're talking 5 minutes longer to temp or an hour, I have no idea, but nobody else seems to be giving specifics either.


I'm willing to concede it does, if you're willing to say it does definitely and why. That's exactly why I was challenging this often proffered yet rarely explained methodology. We take a lot on word of mouth around here, I'd like to know if this is one of those cases. If it's not, that's fine, I'm more than willing to accept that and admit being wrong.


You guys have given me whats obviously a legitimate reason to use a slurry, thank you (as I had never heard one offered before), however, I still haven't been given a definite "yes it's necessary for the best results in this case". If we don't know one way or another, but it's probably smart to err on the side of caution, I'll accept that also.



Regardless I use LN2 for sub-zero on AEB-L now, but in all honestly, I've seen zero difference in performance, or hardness from the knives quenched in powdered dry ice or LN2. As I admitted though, there may be some difference in RA percentage beyond my testing abilities.

Anyway, I hope you guys accept this for the constructive conversation in the spirit of full understanding, that my intent in it is. Thanks for participating.


FWIW elementfe, I've never had warp manifest in the sub-zero, but I always quench first in plates specifically for straightness, and then to oil to finish cooling. I sub-zero immediately after without any snap temper. My experience with AEB-L says you better get it straight from the get go because at 62-63+ RC in very thin cross section (i.e. my pairing knives are 0.045ish at the spine above the choil, and tapered from heel to tip), it doesn't respond well to conventional straightening methods, and I've broken more than a few attempting to.


Edit: Re-reading this i realize it seems I'm implying I don't do redundant things, which in actuality is completely untrue. I do redundant shit all the time in the shop. I admit I had a misconception about the reason for the dry-ice slurry, but I'm genuinely just in pursuit of understanding at this point. I concede that it's probably best practice to mix dry ice with an appropriate liquid.
 
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Javan,
No, I wasn't saying you are scrimping on quality. It is just that you are looking at it from one side and the metallurgists look at it from the other. Both sides are often looking at a very similar result.

Another way to justify the slurry is that if it is partly insufficient in the dry ice to alcohol/acetone mix, it will still be more than sufficient in reaching the Mf. If the dry ice only is insufficient, it may not properly reach the Mf. Since the slurry is really fool-proof as far as sufficiency of reaching -95F, it is the hands down winner.

I agree with you that in the real world, your way would be of little worry if the dry ice quantity is large enough and you leave the blades in it for a couple hours.
 
I took that AEB-L and ground it down to .015 and slapped a handle on. It cuts just fine and holds an edge fine. Did some like batoning and some wood shaving and the edge was not effected. Guess I had to grind through the decarb. Ok you guys can have the thread back.
 
This forum is actually pretty easygoing that way, 30-06.
There are other forums where if you aren't interested in the results of controlled, repeated, scientific testing you're asked to get lost- if modern metallurgical science doesn't interest you, they tell you to stick to the bushcraft sites.
Yeah, sometimes we go a long way chasing that extra little bit of performance, but some people are trying to do the best they can, while for others good enough is plenty good.
 
Some cant follow simple directions!
elementfe said:
This forum is actually pretty easygoing that way, 30-06.
There are other forums where if you aren't interested in the results of controlled, repeated, scientific testing you're asked to get lost- if modern metallurgical science doesn't interest you, they tell you to stick to the bushcraft sites.
Yeah, sometimes we go a long way chasing that extra little bit of performance, but some people are trying to do the best they can, while for others good enough is plenty good.
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