HT Oven vs. Forge for Thermal Cycling

J

joedhiggins

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May 31, 2016
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In the past I have used my forge for thermal cycles because I forge everything and it is convenient/quicker. My older muffle furnace was analog controlled so was a pain to get stable at a specific heat, so I didn't really bother.

My new HT oven is digital, and easier to use (than the old muffle furnace). Still, I coat the part in anti-scale between heats which definitely is a bit of a pain. In the forge I run a reducing atmo for thermal cycling, so I don't bother with any sort of coating.

What do ya'll think? Is the extra precision of the HT oven worth the pain or should I just use the forge?
 
In my opinion a forge shouldn't be considered inherently inferior to a kiln. So it really depends on the ability of your forge to hold an even temperature in the chamber. The benefits of using a forge you already mentioned.
 
As good as a nice forge is it does not hold a candle to a heat treat oven in terms of control and accuracy. If your having a problem with scale do like I did and pipe in nitrogen.
 
In one respect, the forge can be superior to an oven in that the forge will heat
faster. Grain refinement occurs as steel temp rises.

Learn to use decalescence to judge temps.
 
I can judge temp by color pretty well (at least at night, and I don't want to black out my shop for daytime precision). Decalescence is pretty good in the 1400ish range, but doesnt do much to diferentiate 1600 from 1700. There you just have to guess based on color and emissivity. And I am not quite good enough to tell. For my thermal cycles in the forge, I generally get it to the dull end of the orange colors for the first cycle, just past the decalescence point for the 2nd, and dull red for the third.

I never worried about the 1600-1650 soak for spheroidized steels as my forging temps are well above and the knife spends longer than 10 min at those temps (not saying there would be no benefit here, but I couldn't see one and never had trouble getting full hardness from Aldo's steels).

I guess my question was if there was any noticable/meaningful benefit to thermal cycling at very precise temps (with your low to mid alloy carbon steels). It takes a lot of time I could otherwise use for forging if I were to thermal cycle in the forge.

If the answer is that the grain refinement is noticeably better with ultra precise temp control, then I will use the oven. I will use the oven for sub critical anneals like I did my muffle because, as I understand it, decarb isn't a problem at 1200F, and I can't hold 1200F for 2 hours in a forge without a PID/solenoid gas valve (at least I haven't figured out how to).
 
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