New to Air Hardening Steels

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TheEdge01

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Apr 3, 2015
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I recently received an oven and want to try it out on some air hardening tool steels such as A2 or D2. I bought some a stainless foil and aluminum plates that are 1” thick and 8” in length. The maximum overall length I can fit into my oven is 7” if I place the knife in at an angle, leaving about a 1/2” of the plate clearing the knife on each end during heat treat. Would this be enough clearance to properly harden, or would it hurt to move the handle closer to the edge and focus more on hardening the blade?
 
It will harden just fine as long as the blade is covered I don't think much overhang is necessary. Smaller plates will just heat up faster so you can't run multiples.
 
I agree, you will be fine.

You will read about putting the plates in the freezer. Realistically, this does almost nothing as far as making the quench better or faster. The blade is at around 1750°F/955°C the drop to 80F/27C° is not much different than the drop to 0F/-18°. The quench speed difference would be less than 5%, which makes no difference for an air hardening steel.
 
Stacy E. Apelt - Bladesmith said:
I agree, you will be fine.

You will read about putting the plates in the freezer. Realistically, this does almost nothing as far as making the quench better or faster. The blade is at around 1750°F/955°C the drop to 80F/27C° is not much different than the drop to 0F/-18°. The quench speed difference would be less than 5%, which makes no difference for an air hardening steel.
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Just to add to that, if you're doing a whole bunch of blades in a row and your plates end up 200˚F or more then the quench speed will slow down more noticeably. Some steels will quench fine regardless but it's something to keep in mind.
 
Stacy E. Apelt - Bladesmith said:
I agree, you will be fine.

You will read about putting the plates in the freezer. Realistically, this does almost nothing as far as making the quench better or faster. The blade is at around 1750°F/955°C the drop to 80F/27C° is not much different than the drop to 0F/-18°. The quench speed difference would be less than 5%, which makes no difference for an air hardening steel.
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How important is cryo with A2? Being a low chromium steel, would dry ice or putting the blade in a deep freeze help, or do I need a dewar and LN?
 
Mf is -120°F/-85°C
Dry ice slurry (alcohol and crushed dry ice) is sufficient to convert most all the RA.
The freezer will not do much for A2.
 
just curious- why do they call it an air hardening steel when everyone clamps them between plates ? i heard a rumor a well known knife maker would just hang his cpm-154 blades in the air and they would harden. i told this to a knife maker friend, he did a comparison between air hardened and quench plate hardened blades and he said they ended up with the same rockwell reading in his shop.
 
TheEdge01 said:
How important is cryo with A2? Being a low chromium steel, would dry ice or putting the blade in a deep freeze help, or do I need a dewar and LN?
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I've been using an A2 recipie posted by RJ Martin that I pulled from this forum with excellent results. I do not cryo my blades. My target hardness is 59 - 60 HRC and I am hitting that consistently. I use precision ground stock and quench between 1" thick Al plates and have not had a blade warp yet (folder blades). I've kept 2 of my builds for myself and use them often to get a sense for how well the steel is performing and am genuinely surprised at edge retention. Long story short, you don't need to cryo A2. Just follow this recipie and you'll be gtg.
The only deviations for me is I throw my packets in the oven as it comes up to temp and I let them soak a wopping whole extra minute before quenching just for good measure. Pretty simple.

Screenshot_20201110-122011_Chrome.jpg
 
Signalprick said:
I've been using an A2 recipie posted by RJ Martin that I pulled from this forum with excellent results. I do not cryo my blades. My target hardness is 59 - 60 HRC and I am hitting that consistently. I use precision ground stock and quench between 1" thick Al plates and have not had a blade warp yet (folder blades). I've kept 2 of my builds for myself and use them often to get a sense for how well the steel is performing and am genuinely surprised at edge retention. Long story short, you don't need to cryo A2. Just follow this recipie and you'll be gtg.
The only deviations for me is I throw my packets in the oven as it comes up to temp and I let them soak a wopping whole extra minute before quenching just for good measure. Pretty simple.

View attachment 1626995
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Thank you!!!!
 
john april said:
just curious- why do they call it an air hardening steel when everyone clamps them between plates ? i heard a rumor a well known knife maker would just hang his cpm-154 blades in the air and they would harden. i told this to a knife maker friend, he did a comparison between air hardened and quench plate hardened blades and he said they ended up with the same rockwell reading in his shop.
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Actually, I read something Larrin Thomas posted in his KnifeSteel Nerds website about A2. He said it hardened very consistently. Even blowing air between the aluminum plates didn’t make a difference. The plates will help prevent warping though, so they will see some use in my shop.
 
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The answer to the question on why knifemakers use quench plates is to prevent warp. A2 (and most air hardening steels) will warp unless there is very even cooling from both sides.
 
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