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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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Old 07-19-2004, 01:54 PM
Don Halter's Avatar
Don Halter Don Halter is offline
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equipment-microscopes

What kind of set-up is needed for viewing grain patterns? I remember placing a sample in a phenolic block, polishing, then etching, then viewing. Is this still standard methodology? How polished and how etched? I've picked up some varied equipment over the years here at surplus auctions at the university. I have some high powered medical microscopes used generally in transmission viewing. Is it possible to rig a light to shine down on a metallic sample to view grain, or is a whole different set-up reuired? I realize oil-adaption lenses for really high powered viewing won't work like this, but it looks like other standard lenses could. Anyone here familiar with microscopy in this?

I suppose I could just "try it and see" .


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Old 07-19-2004, 07:38 PM
Quenchcrack Quenchcrack is offline
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Microscopes

Don, I have been using metallographs (metallurgical microscopes) for 30+ years. You can use either a normal or an inverted stage scope as long as it is set up for reflected light. A scope set up for transmitted light will not work. You can still find an occasional bargain in used scopes, especially the brand name Jena, which came from East Germany but was identical to Zeiss in West Germany. New scopes get pretty pricey, I just got a new one at work. It was a stripped down Zeiss, 5 objectives to 1000X, with color digital imaging. $23K.

Polishing is just like knifemaking but the surface needs to be flat, which is why it is usually mounted in phenolic. Start with 80, 180, 320, 400, 600, then go to 5 micron alumina or diamond paste, then to .05 micron. Rinse between each grit, rotating the piece 90 degrees each time you change grit. Etch with 5% Nitric acid in methanol.

Now all you need is a book illustrating the bazillion or so microstructures possible with steel and you're all set!


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Old 07-20-2004, 08:11 AM
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Hmmm...with only 1000x I might can rig mine for reflection. We used to look at bug eyes and such with lower power lenses (more open space under the objective lens) by remounting the light source. Of course looking at metal surfaces, the light angle may be more of a factor. I'll have to keep an eye out for some more scopes. Last Spring they had about 8 microscopes from a materials lab go up for auction. Unfortunately I wasn't able to make the auction. None had lenses...but they went for $15-25 each! They also had a large tensile/compression testing, charpy impact , and rockwell hardness testing machine. I never saw how much the last two went for, but the tensile machine almost didn't sell (too big for most home shops!). It went for $25 and included all the other left over crap in the lot. I got my 2200* ovens there last year for $40. They weren't even scratched. The refractory looked as though the interior had never been over 400*.

I've been really curious about the structures formed during Japanese blade heat treating. Especially some of the effects seen in the hamon due to interrupted quenching and such. I was doing some testing on one last weekend and broke it in several places. There were lots of very subtle differences in the grain patterns, but they were all fine and almost impossible to make out with just a pair of eyeballs! I'd love to find a camera joined system...but those tend to be pricey even at auction! Hmmm...maybe some duct tape and a digital camera hooked up on a standard microscope?


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Old 07-20-2004, 11:49 AM
Quenchcrack Quenchcrack is offline
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Microstructures

Don Fogg is sending me some sword pieces for microstructure analysis. I will take some photomicrographs of different areas (edge, hamon, spine) in hopes we can explain why oil bends the tip down and water bends it up. The photos will be posted on Don's Forum.

I thought about making a series of micros of high carbon steel in various states of heat treatment and posting them somewhere. It might help understand what all the "metal heads" are talking about.


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