Greetings, Took GreyAngel's advice and messed around with normalizing. The blade turned out to have nasty cracks in it, so I had fun whacking it with a hammer. The grain size had come way down. What I found interesting were the zones of color. I tempered the piece in the kitchen oven. I set the dial to "425", having found by experiment that that's where I get good tempering of my O1. Dunno what the actual temperature is, however. I set the piece on a scrap of aluminum foil so it wouldn't fall through the rack.
On to the vice and hammering. The face of the piece that laid on the foil is way hard. The rest of the piece behaves like it tempered properly. The cracked-off surface is gray for most of the stuff. There's a thin band of black with brownish highlights (0.3 mm thick) and a thinner (0.1 mm) band of light brown. The grain size appears larger in these colored bands. (5X loupe and .5mm pencil lead for comparison.) The colored bands appeared where the piece laid on the foil.
Am I seeing perlite, martensite and friends, or is the color just due to the grain size? Heated a fragment in a propane torch; the colors went away, but the relative grain sizes didn't change.