Quenching full flat grind stainless blades on alum quench plates

JG Custom Metal Works

JG Custom Metal Works

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Nov 27, 2013
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When quenching a stainless steal knife, with a full flat grind, on aluminum quench plates, is there any need to worry about the plates not reaching the very edge of the blade? On a double bevel(not chisel ground) knife of course. For instance I just ground a large .270” 3v chopper, with a relatively thin full flat grind. I left the edge at around .040”-.030” prior to the heat treat. I would guess there’s probably a gap of around .100” on each side of the edge between the quench plates and the edge. The quench plates of course rest on the flats of the knife.

Does anyone try and push their quench plates down at an angle so they lay across the bevels of a blade? I would also think you would need to have the edge of the plates right in front of the plunge so that the tilt/angle wouldn’t be prevented by the flats. Then you might need to worry about warping of the tang as it would be hanging out in the air, instead of being in between the plates.

This wouldn’t be an issue with knives that were heat treated/quenched prior to being ground.

Am I over thinking this? Do I need to just throw the blade in between the two damn plates and be done with it?

Oh and I am using stainless steel foil as well.
 
Well, since other folks haven't chimed in yet, I'll make a comment. The following is based on phone conversation with engineer with Sandvik steel. For their steels (and AEB-L I'm sure) as long as the temp is dropped below 1200F in less than 2 minutes, you're getting a full quench. With a beveled blade the edge isn't touching the aluminum plates, but with rest clamped tight, the edge will be below 1200F in well less than required 2 minutes. I'll also mist some water over and thru the plates for a faster quench. Since the blade in inside SS foil preventing water from hitting the edge directly I've never seen any issues with cracks.

I've not had problems with warping either with beveled blades clamped in plates.
 
What I've seen some makers do is blow air between the aluminum plates after the knife is clamped between them. A small compressor should do the trick.
 
When I quench my blades I put them in between the plates and stand on them. It might be possible to hose some air in between them while standing on them. It could be a little like a game of twister. :D
 
Stand on plates? Do you not clamp them also with C-clamps? They really need a good bit more pressure than just your weight.
 
Explain to me how plates "need a good bit more pressure than just your weight" in order to quench a blade? I outsource my SS knives, so don't have any experience quenching SS, but if contact is made with the aluminum plates and the steel blade, I would "assume" that is all you need for the heat transfer to happen. 1lb of pressure vs 180lbs of pressure vs 500lbs of pressure....I don't see how one is better than the other. If warp is the concern (and not just hitting the PN in time), I would think that a person's body weight (or MUCH less) would suffice.

I also would think the "best" way to quench a pre ground blade with plates is having the plates contact the bevels, and not the flats. Requiring the edge of the plates to ride in the plunge line, and the other edge of the plates right at the edge, then clamp on bevel. That's how I would do it anyway. In all reality, tho, because the edge is already ground and thus relatively thin, a simple air cool without plate contact would probably be enough. 2 minutes would be plenty of time for an air cool on an edge that was .020" thick (I would think).
 
Well, I am certainly not an expert on heat transfer, but I'd suspect aluminum plates pressed tight would transfer more heat than the same plates just lightly laying against blade. Also, remember the blade is inside a SS pouch that is usually "puffed" out a bit due to heat air inside sealed pouch expanding with heat. The "pressed tight" would make sure as much metal to metal contact as possible. Perhaps it would work just fine with only weight of plates laying on top, but I think I'll continue to clamp plates together.
 
Lightly laying against the blade? Probably good enough, as long as the contact is there.
Someone's weight? Yeah.....good enough.
Clamps? Overkill, but most common/easiest approach.
 
I’m 215lbs and when I stand on the plates I reach up and press off the ceiling as hard as I can. This adds at least another 100lbs of downward pressure on the plates.

Ken H, are you basing your comments off of actual experience or just theory? Clamping seems to work for you, but have you tried other methods to substantiate your claim that they don’t work? I’m not trying to be argumentative. I just want to make sure I’m not missing out on something. If you look at heat treating videos online you’ll find that a LOT of the people on them simply put the blade in between the plates and just press down on the top plate. I’ve done this before and it works fine. I hardness test everyone of my knives and have never had one not reach high levels of hardness. Usually the target hardness. So I’m not really sure what you’re basing your assertion off of.

My main concern is the very edge of a beveled blade. There isn’t really and adequate way to test out on the edge as it not flat for the penetrator to punch into. I thought about propping it up with some shims or a piece of thinner steel but haven’t yet...
 
My comments on clamping are based on 3 things, personal experience, theory of heat transfer, and what it seems "most" folks are doing. It seems you're getting 300+ lb of pressure, and since it's working just fine for you, wouldn't worry about changing anything.

As I mentioned before the Sandvik knife steels (and AEB-L I'm sure) only require getting the metal below 1200F in 2 minutes. With the thin edge losing its heat quickly, and the heat sink effect of the aluminum plates - you won't have any issue of the beveled edge being at full hardness after quench. Of course there's no way for me to test a beveled edge, but the Sandvik engineer assured it there were no problems with using aluminum plates on a beveled blade. He says I could always spray some water thru the plates if I wished to cool even faster - said it wouldn't hurt, but didn't really think it would improve anything.
 
I suspect if a blade is going to warp between the plates, there is nothing you can do about it. The blades will remain straight with as little as 10 lbs pressure, some people even do 2 blades to a boil packet [AEB-L]. Once you remove the blades form the plate they will take whatever shape the metal tells it to. My relatively inexperience may be showing here, but, the good things I can straighten before heat treat.
 
check steel makers data sheets. for some air hardening steels, like CPM3V & 4V, AEB-L, 13C26, 440C, 154CM, S30V, and S35VN, oil quench to black(1000*F) then cool in air or between plates is an option for maximum hardness.
 
I don't do a lot of stainless, mainly a few CPM 154 now and then. I've got aluminum quench plates set up on a metal wood worker's vise. It's got just enough slop in it to find it's own level and evenly apply pressure. I tighten the blade in the pouch between the plates and blow compress air in the gap until cool enough to touch. I snug the plates up pretty good, but don't get crazy with it, mainly want good solid even contact. Never had an issue getting full hardness yet.
 
Will52100 said:
I don't do a lot of stainless, mainly a few CPM 154 now and then. I've got aluminum quench plates set up on a metal wood worker's vise. It's got just enough slop in it to find it's own level and evenly apply pressure. I tighten the blade in the pouch between the plates and blow compress air in the gap until cool enough to touch. I snug the plates up pretty good, but don't get crazy with it, mainly want good solid even contact. Never had an issue getting full hardness yet.
Click to expand...

How far do you grind your bevels prior to heat treat though?

The chopper that made me question all this was a s3v chopper that was .270 thick stock and 2” wide blade(10” long). It has a full flat grind and the fact that the center of the edge, when heat treated, is around .03-.04” thick with .120” of space between it and the quench plates. I’m wondering if anyone else has thought about this or done any testing.
 
When 2 "flat" surfaces are in stable contact, they actually touch on 3 high points. All the other points of the surface are in contact with air gaps.
More pressure will deform the mating surfaces allowing more metal to metal touch surface area, hence more efficient heat transfer.
If a wrinkled foil gets in between i suppose you should squeeze even more.
Given the mild speed requirement from quenching stainless, i presume most of the benefit of pressure comes from the more even cooling granted by the extended contact surface along the entire piece.
Since i won't be able to get HRC from the bevels i'd be more comfortable by quenching flat parallel and then grind under coolant.
I won't swear you would be totally free from mixed structures with an air quench in the bevel area.
 
So I guess I’ll pose a question to those who grind stainless steel blades partially before heat treat. Do you have any issues with heat treating? Do your blades reach full hardness at the edge? Even though the aluminum quench plates might not be in direct contact with the very edge.

I’m trying to figure out if I’d just be better off heat treating prior to grinding, even with thicker stock. I usually HT everything under 1/8” thickness prior to grinding. What I’m wondering is if I should with steels that are 3/16” or 1/4” thick...
 
I used to pre grind to about 90%, but last few times I've done stainless I've waited until after heat treat to grind in the bevels. Use good belts and it's a pleasure to grind.
 
To be sure of the results is not so easy.
taking reliable edge hrc readings is not possible with a Rockwell, due to the sloped surface. The risk is getting mixed structures, probably not pearlite but upper and lower bainite, martensite and RA... plus added risks of distortion in the quench
Able to skate files, doing cuts, but not the top of that steel's capabilities in terms of edge holding and stability.
 
I have not been able to tell a difference in performance between pre or post heat treat grinding. As Stezzan mentioned it’s hard to get accurate readings on the bevel. Do one of each and do a performance test to see which one performs better. I clamp on my drill press and use forced air. After 1 minute or so they’re cool enough to hold. I almost all of my grinding post heat treat now as I prefer how it grinds.
 
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