A2 heat treating recipes.

J

Jared Dinwoodie

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Jan 1, 2014
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What are some of the heat treat recipes people use for A2? I’m interested in cryo and non cryo options. I have some hand plane irons to make and haven’t worked with this steel before. Thanks in advance!
 
Without knowing your equipment and method, it is hard to give an exact regimen. Simple answer - 1750F for 20-30 minutes, quench plates until cooled, immediately into sub-zero in Dry Ice and alcohol or cryo in LN, temper twice at hardness target (usually 350-450F)

Dr. Larrin Thomas' book, "Knife Engineering" has lots of info. His site KnifeNerds has most of it as well.
 
super easy and forgiving steel, I love it. Pretty narrow parameters, adjust the flavour with tempering temp. You'll get a little more hardness from a cold treatment, and I've had good success just adding some freezer time to the quench process. I use LN2 for everything now, but I wouldn't hesitate to make a dependable blade from A2 without it
 
Lorien said:
super easy and forgiving steel, I love it. Pretty narrow parameters, adjust the flavour with tempering temp. You'll get a little more hardness from a cold treatment, and I've had good success just adding some freezer time to the quench process. I use LN2 for everything now, but I wouldn't hesitate to make a dependable blade from A2 without it
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Can you elaborate a bit? Thanks
 
May I ask a question slightly off track but related to the cryo treatment.

Is there any advantage in mixing the dry ice with a solution (alcohol or acetone) rather than simply laying the heat treated blades in between dry ice blocks. I have tried both and have not really seen any difference. If the steel gets -110 simply laying on dry ice, why mess with the mix ?
 
bjansen said:
May I ask a question slightly off track but related to the cryo treatment.

Is there any advantage in mixing the dry ice with a solution (alcohol or acetone) rather than simply laying the heat treated blades in between dry ice blocks. I have tried both and have not really seen any difference. If the steel gets -110 simply laying on dry ice, why mess with the mix ?
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Dry Ice sublimates and has no liquid state at room temperature and pressure. The gas vapor barrier between the surface of the steel and the solid DI does not transfer the heat as well as a liquid. To a degree, the steel "floats" on a layer of carbon dioxide gas.
Consider a DI bath compared to direct DI chunks similar to the rate of water quench vs air quench. They both will reach room temperature, but the rate and length of time will be very different.

If it was equally efficient, you couldn't touch or pick up a chunk of DI bare handed (which is a bad idea). If you stuck your hand into the liquid DI bath you would instantly freeze the skin (which is a worse idea).

In practicality, if you broke up the DI slabs into powder and small pieces, or used DI pellets, and put them in an insulated cooler with the blades, the blades would drop to a low enough temperature to get sub-zero conversion. The difference is mostly speed/time not temperature. I would have to find the right tech book, but IIRC the temp difference of direct exposure to dry ice vs a bath is about 10°.
 
We use DI/acetone baths in chem labs routinely since the mixture efficiently cools a flask. It consumes some DI when you first set it up as it needs to bring the liquid down to temperature. Once it's cool you can maintain it by adding a few DI chunks periodically, sort of like tending a fire. Once it's finished and all the DI is gone you can pour it back into a jug for next time. You don't lose much acetone since it's pretty cold for most of the time.
 
I use denatured alcohol and do the same as Richard does. I have used the same gallon of sub-zero alcohol for years. Once all the DI has sublimated, I leave the cap a little loose for the first day to let the dissolved CO2 gas escape as it warms up to room temp, shake the can, and tighten the cap snug.
 
I use isopropyl alcohol because it's relatively inexpensive, less toxic than the other options I'm aware of, and it gets the slurry below -100F. Isopropyl also disinfects my cooler, doesn't damage or stink up plastic like acetone and kerosene.
 
I'll jump in for Lorien, when using a freezer or dry ice slurry, the idea is just to get it to that temp. The transformation we are after happens instantly, no need to hold for any lenght of time, but I like to keep it in a freezer or the dry ice slurry for an hour or so. Cryo is a little different, as there is some evidence that extended soaks in LN2 offer benefits that soaking in a freezer/dry ice don't.

And this is done right after the quench, prior to tempering.
 
Jared Dinwoodie said:
When you said freezer time at what point and how long?
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once the steel comes out from between the plates, I take it out of the envelope and run it under cold water til the steel's cool and then into the freezer for a couple hours. From what I understand most of the benefit of a cold treatment occurs as the steel reaches the lowest temperature, and in the case of A2 there's not much more to be gained past that point. A2 can make for a good knife even without any cold treatment, so I wouldn't worry about it either way.
 
I did a search and found this recipie on here 3 years ago when I first started using A2. It's a good starting point. A few adjustments I have made are I don't pre-soak. Just let the oven come up to temp then add your steel and let it come back up to temp then soak. Granted this has been with a 120v oven. I do 31 minutes soak because as stated oversoaking is less detrimental than undersoaking. I prefer LN but if I don't have any on hand A2 is my go to because it does quite well with an overnight stay in the deep freeze next to the beef and swine. Also play with your tempering temps. I'm currently getting 61 @ 400*. I was getting more like 59 @ 425 as stated in these instructions.

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Hi all! Thanks for all the great info!
How necessary is it to wrap A2 in SS foil in the kiln?
I’m about to do my first A2 blades and not wanting drop another $70+ on foil at the moment. But I guess I’d better just used to that as It seems like it’s just part of the game… also, where do y’all get your foil?
 
Yes, you need to wrap A2. If 6yoiu don't there will be severe decarb.

Most all the knife suppliers sell HT foil. Also, many industrial suppliers, like MSC and McMaster-Carr, sell it. It is readily available on Amazon and ebay by the foot or short section.
 
WoodenMonkey said:
Hi all! Thanks for all the great info!
How necessary is it to wrap A2 in SS foil in the kiln?
I’m about to do my first A2 blades and not wanting drop another $70+ on foil at the moment. But I guess I’d better just used to that as It seems like it’s just part of the game… also, where do y’all get your foil?
Click to expand...

You can get away with just a little decarb using a no scale treatment at A2 austenetizing temps.

For foil if you are in the knife game for the long term I would seriously considered buying in bulk.

I grumble a lot but buy 309 foil in 100 foot rolls, ends up being $1.40 per knife for most of the patterns I make.
 
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