I'll heat treat up to five blades at a time. They are individually wrapped in foil. The seams are folded, rolled and folded again. The seams are outside of the blade, meaning the seams will not come between the blade and the plates, and they are thinner than the blade so they will not prevent the blade from making good contact with both plates.
I have one heavy plate on my bench with another suspended above it with a chain. I pull out one blade and put it between the plates and lover the upper plate on it. It weighs about 75 lbs. A lighter plate will work just fine, but you'll need to apply pressure so it irons out the blade, otherwise areas that are touching will cool faster than areas that are not, the weight flattens out little bends that prevent even contact. This reduces warping.
Once the blade has cooled to 400-600 degrees I pull it out and remove the foil and straighten it. Things like the tip and the edge that don't touch the plate are free to move and need to be corrected if they are thin (I'll go as thin a .010). Once it starts to "set up" you need to stop, even if you don't break it, you can weaken it. I continue to let the parts cool to room temp. A2 might should get a snap temper. Stainless and D2 go directly into cryo.
A2 will benefit from cryo if you're making a hard thin type of blade that utilizes a lower tempering temperature and you're wanting fine edge stability. If you're making a chopper some RA probably isn't a bad thing, and the higher tempering temps will probably decompose it anyway.
But, back to plate quenching: After I pull the blade out of the plates, I'll stick in the next. I only left the oven open for a second while I pulled out the first blade, but things did cool down a little bit. There is a misconception that blades must be quenched from austenitizing temperature, so as soon as they start to cool down the quench must proceed. That is not the case. Things only need to progress quickly while you're near the nose, and with simple steels, but if you're austenitizing at 1850, and it drops to 1800 deg, the clock isn't ticking. The time and temp you soaked at are what counts, not the temp of the steel when it is quenched (within reason).
I have metal drops on the plates from the steel I'm quenching. Because they don't have foil on them they're a few thou thinner than the blade I'm quenching, so they don't hold the plates off the blade, but they do prevent the top plate from rocking on the blade, acting like stops. They keep the plates parallel.
My plates have a lot of thermal mass, but they still get fairly warm to the touch. As they warm, the heat transfer out of the blade is lowered. I don't know where the line is that you would no longer achieve an adequate quench. It would depend on the blade steel too, but at some point you would need to let your plates cool. quenching only 5 at a time, I will never find that point.
