Questions about plate quench heat treat of AEB-L

[Paul Carter]

Hi and thanks in advance for any tips or suggestions.

This will be my first S.S. knife and it's made from AEB-L for a chefs knife for my son-in-law. Actually there are two, one for my mother also. I have heat treated over 70 blades so far, but this is my first plate quench hardening. I have some SS foil to wrap the blades with and I am using an Evenheat heat treat oven. It's my understanding that the foil needs to be wrapped as tight as possible to remove as much air as possible.

Is there something I can put in with it to burn up any air left inside[like I use WD-40 for making Damascus instead of flux]?

Normally I grind my bevels in before heat treat, leaving just the final edge for after. I am assuming that because I am plate quenching, I should NOT grind the bevels first so the knife blank remains flat for the plate quench?

After heating it to temp, do I leave it in the foil during the plate quench? Or am I somehow supposed to get it out of the foil and into the plates before it cools down? And if I do need to remove it from the foil first, is there any tricks for that to do it quickly? A certain way to wrap maybe?

I am also assuming I need to blow compressed air between the plates as I'm quenching it. Or is that an invalid assumption?

 

Here is the heat treat recipe I have for it. What do you think about it? Thank you!

 

Preheat to 1560° and equalize.

Ramp to 1975° and hold for 5 minutes, plate or oil quench.

Temper twice for 2 hours and cryo.

300° = 62 RC

400° = 60 RC

500° = 58 RC

What is the desired working hardness for a chefs knife?

Thanks again!

 

[Paul Carter]

Well I went ahead and heat treated them wrapped in SS foil. What a PITA that was! I sprayed them down with WD40 to burn up the air inside. I followed the recipe I spelled out above and quenched them between two aluminum plates, 1" thick, and blew compressed air between them. They came out with no scale, and one skates the 65 file, but just barely. So I'm guessing it's probably around 64. The other skates a 60, but a 65 definitely grabs. Tempering at 400° for 2 hours right now. That should get me to around 60. Then I will take to work tomorrow and cryo treat them.

 

Today I also heat treated two Damascus blades I made. One was a short sword, raindrop, and the other one is a 7" blade, ladder pattern. I used satanite down the center of both blades, something I don't normally do with Damascus. I knocked the short knife off the anvil, and onto the concrete shortly after heat treat. Luckily it did not break. So maybe the clay on the spine did what I wanted it to do.

[Alan Longmire]

I didn't reply earlier because I haven't done plate quenching yet, but from what I understand, the WD-40 and compressed air is not a necessity. It doesn't hurt, though.   Glad it worked for you!

 

I will look it up later, but I think I read somewhere that for the cryo to be the most effective it should be done right after quenching and before tempering, but I am more than happy to be wrong.  I know it's much more important with the CPM steels than with AEB-L, so you should be fine regardless. 

[Alan Longmire]

So, after a little research, it seems that delayed cryo (done more than an hour after the quench OR done after tempering) does not reduce retained austenite, but does still provide better toughness.  I'm sure you've read the AEB-L article here :  https://knifesteelnerds.com/2019/03/04/all-about-aeb-l/ ,but here are the cryo articles:

https://knifesteelnerds.com/2018/12/03/cryogenic-part1/

https://knifesteelnerds.com/2018/12/10/cryogenic-processing-of-steel-part-2/

 

It would have been nice if Larrin had done the cryo articles using only one steel, or using several in comparison, because as it is those are some brain-bendingly difficult to understand fully ideas.  

[Garry Keown]

I dust my blades with talcum powder before they go in the SS foil. It stops any tendency for the foil to stick to the blade. I dont add anything else and the blades come out clean. I have two 1/2 inch alloy plates bolted to either side of the vise (set vertically) and have a pair of 3/4 inch movable plates that I can dunk in a bucket of water to cool between blades so the cold 1 1/4 in alloy either side of the blade is sufficient without using the air hose so I can get straight back to adding another blade to the forge.

[Paul Carter]

Thanks guys for your responses. Interesting reading Alan. Thanks for that. Here is a pic of one of the knives I hardened. This is for my Son-in-law. The handle shape is what he wanted. I would have done it different. It's also a little small for my hands, but just right for his. The colors it produced are pretty cool.

Edited September 30, 2020 by Paul Carter

[Paul Carter]

I plate quenched these two blades I did[both like the one pictured above] between two 1" thick aluminum plates and both blades came out warped quite a bit. ?. Is this common with plate quenching? Could it have been from uneven foil wrapping causing the plates to not clamp evenly? This is my first rodeo with foil wrap and plate quench. I figured the blades would come out flat.

[Paul Carter]

Well I got both blades straight and surface ground them. They both cleaned up with about .008"-.009" removed from each side. This AEB-L really grinds nice without developing a lot of heat. I completely ground each side without cooling it off once. Then, when done, it was barely too warm to handle without gloves. I'd say around 150°. Started grinding the edges, but got one side done and my belts are just too worn now to finish so I ordered new belts that will be here Wednesday so I can finish grinding.