I’ve done a bit of extensive Googling and haven’t come across anything that says yes or no. Anyone have any thoughts or experience doing this with AEB-L or 440C?
Both AEB-L and 440C have pretty high hardenability and reach full transformation if cooled in about a minute or less to under 200C. My assumption would be that you'd see only a very slight difference in hardness between edge and spine. Larrin has an article going in-depth on hardenability https://knifesteelnerds.com/2019/02/25/how-fast-do-you-have-to-quench-hardenability-of-steel/ The charts show there is only a marginal difference in hardness in 440C with faster cooling. It would be interesting to test though. It would also be interesting to test using clay on the spine along with the edge quench to slow cooling even further.
One of the benefits of stainless is that you don't get uneven hardness. Also if you plan on experimenting you should know many stainless steels have a critical temperature range you do not want to be in for any length of time where it is very brittle.
Likely an unperceivable difference in hardness. You would get uneven rate of cooling between the edge and the spine (oh not that again!) but the spine will still be near full hardness after being air quenched. To toughen the spine, one possibility would be to draw the spine back way further than the edge. You'd need treatment with a torch along the spine while keeping the cutting edge cool. According to tempering charts, one should be able to get the spine below 55HRC if you draw it in the 500°C range. No one seems to publish tempering curves above 500°C. So what happens at 600°C or 700°C is who knows. I would not assume linear extrapolation. Air cooled steel poses its own set of issues. Who wants to try annealing AEB-L? Hahaha Dan
600-700 critical temperature, goes crack AEB-L specs, "No Annealing" it has been tried though. You can plan on programming for a 24 hour cool down cycle.
A lot of high alloyed steels get tempered martensite embrittlement at high temp tempers, making it weaker. Not sure specifically what happens on aebl or 440C though. I’d just be careful going too crazy with a torch
Same as noted above. Plus AEBL is so stinking tough already. You may have better luck putting it in water and blue backing with a torch.
Never mind it seems there’s no benefit. Also I wasn’t going for a differential effect in my upcoming culinary knives, I was thinking of ways to lower the risk of warping. Anyway as Jay Fisher wrote (seemingly having documented it) *a 440C knife blade will lose 85% of its latent heat energy in less than 30 seconds, and that's a lot!* At the cross sections we deal with, especially the thinness of culinary knives, it seems that - even though most are not doing it - 440c should be left to harden in still air. References to Oil quenching 440c in thicknesses above 1” seems to be where ‘oil quenching,’ became acceptable. Even though I understand a lot of makers oil quench 440C with seemingly no issues, it does rapidly cool this particular steel, possibly too fast in cross sections under 1”.
When I pull AEB-L 3/32" out the of the oven it's a bright yellow color, almost hard to look at. By the time I get the oven door closed and start up the camera to snap a picture it's quickly going orangy-red. Maybe eight seconds later it's gone dark. If I recall correctly, "dark" should be about 500°C. Although I haven't measured it (as my hands are usually full at this part of the operation), to get under the nose in 30 seconds seem perfectly doable with thin cross sections like we work with. I watched Ray Rogers' video tutorial on making a chef's knife from 440C. He'd pull it from the soak and hang it on a nail in still air. That was how he quenched it. At that time I was like "what???" Dan
Same thing with T1 18%, that stuff hardens real fast and forget straightening unless it is still orange
