Hoss,
I would also start over. I may keep the knife and use/test it untill it breaks to get an idea of what I may have done to the steel. But the fact of the matter is that heating a peice of metal way above normal HT range doesn't damage it in a way that can't be fixed as long as it doesnt crack in the subsequent quench.
The problems it creates:
Grain growth (this is assured, but can be remedied as previously discussed)
Micro fractures from the quench (no simple fix, but etching in ferric would let you know)
Significant decarb (this is possible but unlikely in a coal flame)
Not reaching an ideal hardness from having been austenitized at too high a temp prior to quench (also assured, but fixed by redoing a HT)
Steel doesn't have a function where it says: "You brought me to forging temperatures during austenitization, I will never be the same." Furthermore, if the quench was into one of the slower oils, I suspect that the chance of microfracturing is low. He was using O1 and it is pretty forgiving.
Practically we are essentially talking about him quenching from a temperature in the 1800-1900 F range. That doesn't make for an ideal HT by any stretch, but it doesnt make the resulting block of metal something other than O1. Normalizing, refining the grain, etc should fix it.
The big deal that I see is that O1 really likes a longish soak at austinitizing temp prior to the quench, and it doesn't sound like the OP has the tools to do it. So until he has an oven or pot, it seems to me he would be much better served by using one of the simple steels.
