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My 2 cents....I've never had O1 warp on me....ever.
I've been told by metallurgists and guys that know infinitely more than I that with low alloy steels (higher alloy stainless is a different story...because of the high amount of alloying).....that the only time a steel like O1 "needs" a 1200?F pre hardening soak is if it's a complicated cross section...which our knives are not. I've used the 1200?F stress relief on other steels that did warp, with success sometimes, others not.
Kiln should be AT the hardening temp before placing the knife inside. 1475?F ideal for O1 and most all hypereutectoid steels. Once kiln is at 1475?F (and I wait maybe 15 minutes to be sure there is not temp overshoot and that the atmosphere inside the kiln, and not just the thermocouple reading, is 1475?F), insert the knife, allow the readout to rebound to 1475 and begin a 15 minute soak. The blade will not be AT 1475 once the readout rebounds....but it is within 2 minutes.
The blade warping.....when is this actually happening? After the quench? If so, it may be bad quench technique, although you stated this does not happen with your forge. Most O1 comes precision flat ground, and is one of the most stable carbon oil quenching steels out there.
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