Ok, I messed up the heat treatment of a couple of O-1 plane blades. Too hard, edges crumble. I, and others, keep coming back here for advice. Sometime back someone said the metal was done for, couldn't be recovered. Yet one can forge O-1. So if it's forged at orange or yellow, it's in the same condition as my blades which only reached bright red. Shouldn't annealing my wrecked blades fix them up? (I can see the crystals with a 5x loupe.) Is the problem that there are fractures in the metal that annealing heat can't fix?
I understand that it's a pita to anneal small bits of O-1. Red hot chunk of iron in the vermiculite to slow the rate of cooling, and so forth. Although that confuses me too: the book says 20 degrees per hour, or something like that. I once tossed a marking knife into the fireplace and fished it out the next morning. It re-hardened just fine even though it must have cooled more rapidly than the suggested rate. Just how much leeway is there in the cooling rate?
I took an O-1 chisel blank to my recent blacksmithing class and sneaked a couple of heats to draw a tang. I tried to keep the business end cool, but that blade will have to be annealed too.