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Multiblade Stacked Quenching of AEB-L?


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I've been profiling knives from AEB-L for a few weeks now, and I'm about ready to heat treat them, that said I have a lot of them to do. 24 chef's knives, 14 petty knives, and 14 paring knives. Looking at the cycle times it would take me ages to do these individually, so a thought occurred to me-namely just to stack them on top of each other and do multiple at once. Then I got to thinking that air quenching a stack of blades 1" thick (if I tried to do the petty and paring knives all at once and the chef's knives 12 at a time), might take too long even with compressed air, and that the blades in the center wouldn't harden, or that there would be variable and inconsistent hardening throughout.

Now, I remember reading that AEB-L can be quenched in a slow oil, so I had another idea, what if I stack them, wrap them in foil, bring the stack to temperature, then when I take it out of the oven I put it between two 1/4" steel plates with holes so that I can bolt them together, tighten everything down and put the stack into canola oil? That should eliminate most of the potential for warping, ensure a quick enough quench for more uniform hardening throughout, and save me two days of heat treating.

What are your thoughts and concerns with this idea? Have I overlooked something potentially catastrophic? I wouldn't be so concerned about the time it will take me to harden everything, just that they need to go into the subzero stage of the quench within an hour of the plates and I don't know how long a tub of acetone laden try ice will keep for. Not to mention I have to drive an hour to pick up the dry ice on top of everything too.

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On 11/18/2021 at 8:08 AM, Matt S said:

Have I overlooked something potentially catastrophic?

Yes. You have made too many blades.  :P  Now you are scrambling to figure out how to get them HT'd  and the task seems monumental.

If I were in your shoes, I would try to figure out a system to do multiple types of quenching  and set up an assembly line. Air quenching station, plate quenching station, etc. Decide which knives get what type of quench and cook them in mixed batches, Maybe the paring knives all get the air quench, the chef's knives get the plate quench and the petties get the oil. Place them in your oven so you can get to the three different types easily. Grab a paring knife and hang it in front of a fan, grab a chef and put it between the plates, grab a petty and oil quench it. collect these three and place them on a rack. Lather rinse repeat.

With 52 knives to do, I see you getting through this in 2 days.

 

The other obvious option, is send them out and let someone else worry about how to accomplish it. Look locally for a heat treater in your area. These folks do this all day long and with 52 knives, you could probably get into a price discount zone.

Edited by Joshua States
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The important thing to think about is the risk to profit ratio. You are already realizing that doing this yourself is going to take a huge time investment and comes with the distinct probability of losing some, or all, of your work due to not being in a comfortable process. Sending them out to have them profesionally done accomplishes much, and comes with a price. So, my advice is to contact a heat treatment outfit and get a ball park price or even a quote. Then weigh that cost against having certainty that every knife will be within the hardness specs you give them, and you get two extra days to start preparing the handle materials.

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Too many blades? Heresy! 

 

Outsourcing is a no go for me, I need to incorporate heat treating stainless into my domain of competence. I think I may end up trying out my theory on the paring knives and see if I can get the HRC checked on at least 5 of them. To my, admittedly inexperienced mind, heat treating a bundle of AEB-L knives should amount to the same thing as heat treating a 1" thick knife. I may need to up the soak time some, but if it isn't so long as to be detrimental to the steel, I don't see why it wouldn't work out. 

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I have a bad feeling about that...

 

AEB-L does air harden, especially when thin.  A thick stack is not going to harden evenly or all the way through, as this stuff is right on the edge of air hardening to start. Oil will do it if you have some space between the blades, but the risk of warps goes up.

 

Experimentation is great, but not when it comes to customers.  Figure it out on your own dime, that's cheaper than getting a bad reputation for your stainless blades. 

 

I would send this batch out, if there's still time before Christmas, which is doubtful.

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12 hours ago, Matt S said:

I need to incorporate heat treating stainless into my domain of competence.

Then you need to spend the time to do it the right way. If you don't have the time and money to do it the right way the first time, how are you going to find the time and money to fix it? There are no shortcuts here, at least none that change the laws of physics.

 

Your last reply made it obvious to me that you are not actually seeking advice, you just want confirmation of what you have already decided to do. So go for it. Let us know how it works out for you.

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13 hours ago, Matt S said:

To my, admittedly inexperienced mind, heat treating a bundle of AEB-L knives should amount to the same thing as heat treating a 1" thick knife.

Maybe, in theory, but my question is how do you cool the a 1" thick piece of steel fast enough to prevent the re-transformation of the atomic structure in the center of the piece but slow enough so that you don't crack/damage the steel closer to the surface?

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That was one of my qualms about it too. My answer to that was a slow oil. Of course I don't know what my upper and lower limits are on the cooling rate to avoid both of those things, if that's even possible, or if it's just one or the other with a block that that. In all honesty though I don't expect to be able to do them all in one shot. Even 4 at a time would be a tremendous increase in working speed, at at 1/16th thick per knife that only brings me to 1/4". People have made bowies and camp knives out of AEB-L about that thick.

 

Mostly I was hoping for an answer along the lines of "I've tried this, and it didn't work because X", or "don't try it, it won't work because X" 

 

I can see why, if a person's sole source of income is their blades, they'd be disinclined to experiment and why it might be better to dispense with the notion entirely. If I can't get this done more quickly by doing multiple blades at a time, and it has to be a two day event that requires me to do two runs of dry ice, so be it. 

 

Offhandedly do any of you know how long dry ice will last in a cooler full of methyl hydrate? As in how long the slurry solution is good for? 

Edited by Matt S
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1 hour ago, Matt S said:

how long dry ice will last in a cooler full of methyl hydrate?

 

I'd say it depends entirely on the cooler.  As for how to tell if it's getting too warm, I guess if it's not a slurry anymore?  I haven't tried it.  

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1 hour ago, Matt S said:

Even 4 at a time would be a tremendous increase in working speed, at at 1/16th thick per knife that only brings me to 1/4". People have made bowies and camp knives out of AEB-L about that thick.

 

There's a huge difference in heat transfer in a solid block of steel and a stack of steel, even if clamped tight.  That slight air gap is most likely going to keep the middle two blades from hardening right.  I can't say I've tried it, but it just doesn't seem like it would work very well.  

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When I have done multiple (NitroV) blades I will take a strip of the foil (1/2 in wide) and wrap the two blades handle to blade tip and that stops the top one from trying to fall over the lower one when they are foil wrapped and in the forge. My quence plate are wide enough for cooling this way. I do the cold quech in liquid nitrogen and at first I would string them all (or as many as would fit into the neck of the dewar at one time) but found there was some warping of them so now I will put a couple of washers between each blade to make sure the instant cooling of the liquid nitrogen has clear access to both sides of each blade similtaenously and that made a difference.

I definitely got warping when stacking them of top of each other in the quench plates which was why I changed to the handle to blade setting..

With the 7 minute 1955f soak I can get through quite a few blades in short order by using a timer to make sure the blades come out of the quench pates at the 3 minute mark so the plates can sit in the water bucket (to cool) for 2 mintes and then have 1 minute to dry and replace them in the vice just in time for the next lot to come from the forge. 

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