I'd would either get a second opinion on that or have my machinist cut it for a new seat. If he's any good he'll know as soon as the cutter makes contact whether your heat treat "expert" is full of it or not.
Kevin
Because we welded a circumference around where the old seat was, the material was the rod (4340?) which was harder than the alloy casting. The casting where the fire ring on the headgasket seats was the soft point as the chamber had some extra fill put in this area so it could be ground back to look like it did originally I had done all the work only to see his test point out the soft zone next to the weld. His call was it'll always blow head gaskets because of this. His son was a serious racer so i trust his call on this.
