KnifeMaker / Machinist / Evil Genius
Knifemaker / Craftsman / Service Provider
- Feb 13, 2007
I got a question-
Nathan, would you be so kind as to walk us(me) through the heat treatment process for a thick and large knife, (looks to some like a khukuri) of A2 please?
Preheat your oven 100 hotter than your austenitizing temperature
Wrap your blade in stainless foil. Double fold the seams and roll them. Place them where they won't interfere with the plate quench
Make a heat shroud out of foil to help reflect IR from the coils.
Once your oven is at temp for an hour, turn it off and put your work in. Place the heat shroud over the work.
Close the door and turn the oven on at your austenitizing temperature. If you've timed it right it will be pretty close so the exposed coils aren't on a long time burning your shit. Don't worry if you're a little over, the blade takes a few minutes to get up to temp.
Soak the correct amount of time for your application
Turn the oven off. Pull from the oven and quench between two metal plates to pull the heat out quickly. Ideally you want it under 100F in about a minute. This prevents the carbon from leaking back out of solution on the way down reducing certain carbides and maximizing strain energy to reduce RA. Don't worry about pearlite in A2 at this point. Any structures of that nature won't be formed here, it will be from decomposing retained austenite remaining when going into temper.
Once under 100 cut open the foil, hang it above the liquid nitrogen in a large dewer for enough time to get under -300F (an hour works). You can use dry ice in a pinch, you'll get most of the benefits at -100F
pull from cryo and warm until the frost starts to thaw. Clamp it straight and put it into temper. Temper two times (min) for an hour.
^ This is good basic HT for A2
Off the top of my head I'd guess for this application I might soak at 1725 for 30-40 minutes and my tempers might be 475 for a target hardness of around 58. You'll want to double check those numbers.
If you're just doing design development work you can skip a lot of that. Just get it hard and don't worry about a perfect HT.