Most of us do not finish grinding our blades before HT. I do mine as directed by most professional heat treaters, about 80% finished and finish grind after full HT.
Now WBE says he finishes his blades before HT to 220 grit. I understand the separate equalize. Some makers do that. I also know that Cashen knows more about HT than I do, but I also was a heat treater and what I am specifying is by the best practice and book. No pro HTer would HT finished blades the way WBE does without charging extra for them or say not responsible for warp. I have probably checked and straightened as many HT parts as anyone here, but I never heard of doing them straight from quench, they would be hard as a file or harder or on it's way and I wouldn't relish having a blade pop apart in my press. I always straightened knives after final temper, but my blades barely warped if at all. D2 could be bad about it, but not O1. The only time I had a problem with O1 was when it had been precision ground from too thin of a sheet, ie. .250. Should be ground from mill bar stock or 3/8" sheet. 1/4" is too thin period. I will buy 3/16 sheet O1 and straighten it before grinding it and mill bar stock as I do not know what I am getting under that precision ground stuff unless I know the manufacturer.
So poor Irishknifeworks is getting contradicting information. O1 not ground enough before HT and O1 ground too much before HT? Oh and some makers do not grind anything but the profile before HT. What the heck?
I stand by what I said above, if your 80% ground knife warped during equalization @ 1200 either the steel is bad and I seem to be the only one to have encountered it, but it was a machine shop and they bought the lowest priced stuff, but it was 4.5mm x 50mm x 4 ft. PG for paper cutting blades, stuff warped before machining in equalize. Sent it all back, 200 parts cut to 120mm and the supplier is not responsible for wasted labor. Pro heat treaters are same way, they will just replace the material if it's their fault.
Other option is your oven is heating unevenly. Those are the 2 options unless your idea of 80% finished is different from mine, but it still shouldn't warp at 1200.