Hand Tools

Subject:
What does this suggest?
Response To:
Photos for bill.. *PIC* ()

David Weaver
Well, for 26c3, the micrograph showed particles that are (non round, it's not a PM) carbides ranging from a fraction of a micron to perhaps 5 long). But they're fine particles. On 1095, those don't show up at all, but there's much less surplus carbon.

Interesting side note - you can actually dissolve way more than the eutectoid limit into solution if you're willing to soak carbon steel at a really high temperature, but that kind of thing comes with coarsening grain, and larrin's statement about that is that when the carbon is kept in solution instead of allowed to form carbides, the steel toughness suffers (so trying to eliminate these carbides by getting them in solution quickly and quenching them in place doesn't improve things, even though it would make a prettier micrograph).

Larrin has my samples - who knows when they'll be tested. If I'm doing bad work, we should know that unless my hand made samples aren't good enough for the test equipment.

But what else it suggests is that if we see bits coming out of an edge and they're not in the material being planed, they're either large grains (doubtful) or they're carbides. If the grain was that large, I don't think the steel would hold an edge. But if the chunky peanut butter matrix allows a peanut to escape once in a while and leave a line in the peanut butter, it is what it is.

I think the conclusion is that it's more likely that this is carbides escaping, but proof to me is a heavy burden and it doesn't actually prove anything other than to suggest the clear diamonds seen in the 600x picture look to be individual particles (else there'd be a line).

I have heard more than once that anything under 3 microns can't be seen in visible light ( not from bill) and that because of that, we wouldn't be able to see sharpening differences between an 8k stone and a 30k stone. That's definitely not true. I don't know who wrote that 3 micron thing somewhere, but when they wrote it, they said light wavelengths are longer than that amount, because that's what people parrot when they tell me.

I like bill's method of getting a ballpark estimate better - ask a guy who uses a scope as part of his living (you can see 2 micron particles, but they may be little smudges).

I suspect all of these things also cast some shadow under the toplight, and what we see may be the particles plus a small shadow. These are crisp little particles that on average, don't pass light that well, so they're a little easier to see. The see through ones are pretty nifty, though. I would guess the difference is that the facets on those (vs. the black ones) are lined up to let light through both sides at an angle favorable to the scope - or at least the top angle is favorable and another one is letting reflected light come in.

And just because 1095 shows nothing but a smudge at the edge doesn't mean its' doing the same thing - it just suggests the carbides are too small to make visible damage.

This is, again, the micrograph page:
https://knifesteelnerds.com/2019/05/26/new-micrographs-of-42-knife-steels/

with the link to 1095 - you can just make out the carbides and compare them to the 20 micron scale at the bottom.

https://i2.wp.com/knifesteelnerds.com/wp-content/uploads/2019/05/1000X-1095.jpg?w=750&ssl=1

It's hard to tell a complete story from the micrographs, too - it's pretty much standard that any high carbide volume is going to be low toughness, no matter how good it looks (maxamet and anything with lots of small vanadium carbides looks great - but 3V is tough because the carbide volume is small. The others are not because even though they look great, the volume is too large).

All of the high carbide volume pMs are expensive, too, and would be resistant to easy sharpening - we would need a well-heeled person with deep pockets to get a sample of everything in various hardnesses and test in planes. And it wouldn't make anyone a better woodworker (I can't get any practical saved time between V11 and O1, and maybe not even water hardening steel, so what would the point be? planing brass?).

But this is interesting - transiently - for me as I"m trying to come up with a repeatable process.

Larrin's charts for O1 suggest that I would be lucky to come up with 60-61 hardness and decent toughness (that's "properly done" O1 from a furnace). Same with 26c3 - if I hit 63 hardness at 400F temper, I"d be very lucky.

So maybe I"d better lower my expectations!

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