The colors of the grain inside

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.
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Very interesting... I'll start by saying that I don't feel up to the task of explaining this one ;-) My knee jerk responce to the color differences is oxidation in the areas of the cracks but it sounds like you think there is something else at work and you may be right. I would NOT have thought the aluminum would change a thing. What I will say is that the over all symptoms suggest that whatever you've been doing you're not getting evenly distributed heating and/or cooling. When you are doing grain experiments you want to try and do clearly defined before and after examples. Keep in mind too that it's not just temperture but temperture and time together. In some cases this is fractions of a second and in others it will mean minutes or hours but don't discount time in what you do. As for your tempering, it sounds like you need to flip the blade over once during the process or better yet get an oven that will give more uniform heat.
GA

rack.
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Me neither. :/

<moved> What I will say is that the over all symptoms suggest that

We may not ever know, but anything else you guys can up with will be interesting as anything. :)

Other than Al conducting heat like it means business? :) (don't know for a second whether that applies here tho)

If a.c.b ever gets a faq that, as written, needs to be in it! :)

Get an oven thermometer ;) I use a mercury one but the cheap, coiled bi-metal ones give the same reading IME.
And place a cookie sheet on the rack that's below the rack the knives and thermometer are on, it acts as a baffle.
Alvin in AZ
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On Tue, 31 May 2005 18:45:52 +0000, alvinj wrote:

Yeah, I had one of those cheap coiled thermometers. I think it's down between the fridge and the oven... I have a pizza stone; thought that would make an excellent baffle, but I'll have to plan ahead to get it hot. The oven is a 1958 GE built-in.
Looks like I'll have to do the experiment. I can get maybe three samples from the handle-end of the doomed rabbet plane blade.
Thanks for the interest.
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Oh man, don't forget to be armed when you go off in search of it, if your kicthen is like my kitchen, you don't know what you might encounter in there. ;)

Cool idea, sounds better than my temper-drawing setup. :)

Early '70's Toastmaster toaster-oven here. ;)
The knife blades don't know the make and model of the heat produced tho, just how hot and how long. ;)

You know a guy could beat his head against a wall for years and still never get it figured out. I say, get a metallurgy book. :)
You can learn a thousand-man-years of steel metallurgy in a month and in the process prob'ly figure out what went wrong both. "But there's more ;)" You'll know how to avoid it in the future without going over board and causing another problem.
Just simple understanding. :)
"it's easy when you know how" -my best friend He also sez: "nothing is hard to do, just some things take longer than others"

It's hobby-talk... it's all good! :)
So heck... thank-you for the cool discription of a problem. ;)
Alvin in AZ
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On Wed, 01 Jun 2005 20:41:47 +0000, alvinj wrote:

Yeah. Right after I finish the Penrose tome I'm slogging through now. Best of all is a combination of books and messing around. Mens et manus. Tipping down another slippery slope just cuz I'm too cheap to buy aftermarket plane blades... :)
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