On Thursday I just got my first order of Magnacut. I'm planning on making a chefs knife for myself a skinner for a friend and a reverse tanto scandi for another friend. I'll be varying the hardness from 64 in the chef to 62 in the scandi. It's been a while since I've been excited about making a knife and even longer since making one for myself.
I managed to heat treat 5 knives today. 2 chefs knives, a hunter and two reverse tantos one as a scandi and 1 as a high saber grind to compare. Comming from mostly AEBL it was nice to grind the hunters while soft. They're in the liquid nitrogen right now. I did a check on one chef and it 65hrc. I wasn't sure if my DIY oven would get to 2175 but it perfect. I'm really looking forward to see how they perform.
My process is as follows. 1. Plate quench vertically between 2 aluminum plates in a wood workers vice 2. Bolt plates together with tapped holes in each corner 3. Dunk whole assembly in water or snow to get as cold as possible before going into LN 4. Unbolt the plates and put the knives in the LN overnight 5. Temper multiple times checking the hardness each time creeping up the temp till the ideal hardness is reached I've never done a snap temper. I usually heat treat in batches. I used to use compressed air in the plate quench. With AEBL I was getting a ton of warping. Since cooling in water or snow before going into the LN my warping has completely stopped.
Agreed, but in some steel supplier’s sites it does say cryo can be done after the first temper. I haven’t found any posts where a knife maker has tried both ways and if any differences were found.
Cryo after tempering is done to reduce the chance of cracking on large complicated part. This article from Knife Nerds is a good read on Cryo treatments. https://knifesteelnerds.com/2018/12/03/cryogenic-part1/
I believe in the article posted by Vladimir above, Larrin discusses that it reduces the effectiveness of cryo since tempering stabilizes the retained austenite making it harder or impossible to convert with cryo. This would reduce ultimate hardness and yield stress. But yes it would reduce the risk of cracking. In my experience, of only maybe 30 knives (10 in LN and 20 in dry ice) i've never had a crack.
So was compressed air leading to warps? Thinking about it now, that would make sense since it introduces faster cooling in certain areas at a time making the cooling overall more uneven. Ill have to try without.
Not sure if it was the compressed air or the knives not being quite as cold going into the LN. I think the issue was simply removing them too fast from the plates. I could remove them with bare hands but the blades would still be a bit soft. I'd straighten them before they'd stiffen up then toss in the LN just to warp again. I think maybe the extra couple minutes in the plates prevented the warping.
