Heat treating procedure in barrel furnace vs forge vs kiln?

[Leon Husock]

So I'm building a Don Fogg-style heat treating barrel with a thermocouple and pyrometer, where previously I've always used a forge. I've been reading Larrin Thomas's articles on forge heat treating, and I'm wondering whether this type of barrel furnace should be treated as more similar to a forge or to a kiln in terms of procedure?

On the one hand, a reasonable degree of precision can be achieved with this sort of setup which wouldn't be too dissimilar to a kiln I would think. You definitely can't do things like anneal something at 1200 degrees for 16 hours or anything like that to achieve a DET spheroid anneal, but Thomas says that after normalizing and several grain-refining cycles you can achieve a structure pretty similar to that, and with a barrel furnace you can certainly hold at austenitizing temperature for 10-15 minutes as is recommended in many heat treating procedures for hyper-eutectoid steels.

Note: this is for forged knives not stock removal, so there's no option to heat treat them in the annealed state that they come in when purchased.

 

[Larrin]

What I call the “fast DET” anneal isn’t difficult to do without a furnace. For many simple steels you heat to non-magnetic and then place the steel in vermiculite.

Edit: the “fast” refers to the cooling rate which is much faster than the typical 25-50F/hr listed in datasheets. Typically something like 250-650F/hr which works for vermiculite. The slow rate is also DET, it is sometimes called a “transformation” anneal or not referred to by any name at all.

 

[A.McPherson]

Hey Larrin would adding a big chunk of steel to the vermiculite in hopes of slowing the cooling down be helpful at all?

 

[Larrin]

Hey Larrin would adding a big chunk of steel to the vermiculite in hopes of slowing the cooling down be helpful at all?

If you need a slower cooling rate then potentially yes. It would be more important with thin blades and/or high hardenability (O1 for example).

 

[A.McPherson]

Larrin thanks!

 

[Leon Husock]

My current plans involve chef knives and 52100, so the chunk of steel might not be a bad idea. Thanks for chiming in in person, Larrin! Very much appreciated. It seems like given the level of available precision in a barrel furnace and that fast DET anneals aren't as finicky as I'd thought, I might be best off following your recommended heat treat as if I were using a kiln rather than a forge.