Possibly stupid question about plate quenching.

mpcoppin

mpcoppin

Member
Background before the question:

I have been making kitchen knives lately. Mostly out of 80CrV2. I usually have a spine thickness around 0.10” and I grind the edge down to about the thickness of a dime (0.05”) pre-HT. I’ve been quenching in warm canola oil with pretty good results but I get the occasional warp.

I’ve heard the smart people taking about plate quenching and am wondering if it is something I want to try. Here are my questions.

1- Sometimes I will pull my blade out of the oil and stick it in the vise between a couple of lengths of angle iron “just in case” there are any warps. Is this actually doing any good? Is the steel still in a state where it can be straightened after it comes out of the oil (it is usually black and smoking)?

2- If I were to buy some aluminum plates and skip the oil… Are there issues with plate quenching when you have pre-ground bevels? Am I going to get a 0.05” air gap between the hot steel and the plate? Will it make a difference?

So far I’ve never had a warp that was so bad I couldn’t fix it on the grinder. But, it would be nice to not have to fix them at all.
 
Good evening, mpcoppin. Hopefully smarter folks will chime in with more detailed explanations, especially regarding specific alloys, but in general:
mpcoppin said:
Is this actually doing any good? Is the steel still in a state where it can be straightened after it comes out of the oil (it is usually black and smoking)?
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Yes, depending on your timing. Depending on the steel there is a period of time after cooling below the critical temp, where the steel is still transforming and clamping between the plates should help to keep the blade straight during this period. There is also a window where the blade is hot enough to straighten a warp and I'm sure you've seen smiths do this with gloved hands, and the angle iron can do the same thing to straighten a warp if the blade is still hot enough. For my damascus, I do 7-8 seconds in oil (blade should be ~700F at this point), then directly between aluminum plates for the remainder of cooling.

mpcoppin said:
2- If I were to buy some aluminum plates and skip the oil…
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Is 80CrV2 air hardening? The aluminum plates might not cool it quick enough to harden, but thin blades help. I have a friend who hardens his 1080/15N20 kitchen knives in aluminum plates, skipping the oil and he says they harden fine, so it might work, but I can't remember how fast aluminum is compared to Parks50 (medium speed oil). To avoid worrying about the air gap, just add some strong springs to the 2 bolts you use to attach the plates to a cheap harbor freight wood bench vice, This allows the plates to 'float' enough to conform to 2 tapers.
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I don't have any idea if plates will quench 80CrV2 but pulling it out of the oil while it is still a little warm and clamping flat can help with warping...sometimes.
 
billyO said:
To avoid worrying about the air gap, just add some strong springs to the 2 bolts you use to attach the plates to a cheap harbor freight wood bench vice, This allows the plates to 'float' enough to conform to 2 tapers
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Love this idea, but still trying to wrap my head around the plate to vise connection. Are the holes in the vise large enough to allow the 1/4-20 bolts to float a bit? Is the only compression from the aluminum plates to the billet made by the springs?

Thanks
 
I do not qualify for being one of the smart people but from my experience .100 thick will harden just fine between two one inch thick pieces of aluminum. I have done it many times. In that thickness though I do all of my grinding post HT. That will solve any trouble with air gaps in the plates. If you are doing multiple plate quenches in a row you will have to cool your plates in cold water or something in between.
 
latticino said:
Love this idea, but still trying to wrap my head around the plate to vise connection. Are the holes in the vise large enough to allow the 1/4-20 bolts to float a bit? Is the only compression from the aluminum plates to the billet made by the springs?

Thanks
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Yes the holes are usually big enough. If they aren’t, just drill the holes out.

I second the recommendation to do all grinding after heat treat for anything thinner than 1/4.
 
Looking at Aluminum, as with steel, there are various flavors; which aluminum am I looking for? 6061? 7075? 6013?
 
mpcoppin said:
Looking at Aluminum, as with steel, there are various flavors; which aluminum am I looking for? 6061? 7075? 6013?
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I took a look at what differences in thermal conductivity there might be between various aluminum alloys. I don't think it will make any difference which alloy you use. The minor AL alloy variations are well below the other more significant variables in the HT process.
 
mpcoppin said:
I never thought about that (whether I grind better on hard steel). It would certainly be harder to make the big screw ups.
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You more than likely already know this but for others reading this thread when we say "grind after HT" that means tempering too. I would not want to grind fully hardened FIF style blades though I am sure it can be done.
 
Chris Railey said:
You more than likely already know this but for others reading this thread when we say "grind after HT" that means tempering too. I would not want to grind fully hardened FIF style blades though I am sure it can be done.
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Ya… Figured that. I’ve had the unfortunate learning opportunity of thinking I was going to “just” do a little this or that after quench but before temper and seeing what happens when a blade gets knocked out of my hand or something.
 
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