HT'ing in an oven-question

J

Justin King

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Nov 8, 2009
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I just finished my oven build and will be HTing my first blade in it today. I have previously done all of my HT'ing in a forge, and have never used an oven. How does one know/calculate when the blade has equalized to the oven temp?
The temp. of the blade will lag behind the temp. that the TC/controller is reading to some extent, so how to you judge when the blade itself has come to temp, if/when treating a blade that needs minimal soak time? Soak it a few minutes at a lower temp. first, then ramp up slowly to hardening temp?
 
I preheat the kiln for an hour to my hardening temp them put the blade in and allow it to soak for 20 minutes-half hour. I suppose that now that I have a couple hundred thermocouples I could make a thermal penetration test rig with a blade shaped piece of steel with thermocouples on the surface, in the center, and halfway in, then time how long it actually takes to get to equilibrium.

-Page
 
I assume that the lag is absorbed into the soak time when Ht'ing a steel that calls for it, but I wondered about how to deal with it when doing a steel that does not call for or need soak period. Many HT specs say to heat and equalize and/or ramp and equalize but the equalizing part itself is never addressed.
I guess one can place the TC so that the blade can be brought into contact with the tip, if there is a considerable temp. differential the PID readout should indicate it, but I am not sure how precise this would be.
At any rate the oven itself seems to work perfectly, if not at the speed of light. I fired it up to 850 last night without autotuning the PID just to cure out the satanite on the oven door, it swung about 15 degrees over temp. initially and the temp. bounced a bit after that, but once I let the PID autotune itself this morning it will hold at 1525 within a degree.
 
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Weird, I can't get this thread to post a reply?

OK, now I can????

Soak time is more of a not enough thing than a too much thing.
Equalizaton time is a problem with anvils, not blades.
Fully pre-heat the oven for half an hour at target before putting in the blade.
Allow the oven to rebound to the target temp and start timing.
All carbon steel gets 2-5 min soak
Short soak steels get 5-10 min.
Full soak steels get 20-30 min.
 
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