Stropping wear resistant steels (S30V, S90V, CTS204P, etc)

eKretz said:
Interesting. I've seen the same effect as I've shown on the Suehiro 20k when using brand new AlOx lapping films from 9u up to 1u in progression (9u to 5u to 3u to 1u). I will try to get that 20K to strop test done in the next day or two.
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Hmm, I might have to dust off the old microscope too...Can you recall a point where the Suehiro stones by grit value, can be seen leaving carbides proud of the stone and prior to that they are either cut clean/excavated or lost in the overall noise of the scratch pattern?

Speaking just of the larger carbides (D2 excavation can be seen with a 10-12x loupe and almost the naked eye), I cannot recall seeing this effect off a waterstone or other hard stone, but again at 8k and down. Makes sense that at very small abrasive sizes it would become more prevalent and something you've already proven possible.

Was able to eliminate this with D2 and 440c (haven't tried any other) by using the honing compounds on 3 mil poly instead of my usual copy paper, both over a Washboard surface. This does have the effect of increasing the unit pressure considerably, so the finish values tend to drop a bit compared to use over a more conformable surface (and in some cases even compared to a waterstone) - the 3 mil poly I'm using is still compressible but less so than a sheet of copy paper - hence my advice re strop "hardness". I am confident a thin enough sheet of paper would have the same effect as the poly but also more likely to have the paper tear or give out, especially over repeated reconditioning.

I am confident I could add more layers to the strop and replicate the excavation of carbides effect, using poly or paper, even with diamond. I have not run any of these tests with CbN.
 
I actually haven't tested hardly at all on other AlOx stones except for the 20k as I was already expecting trouble (I tried using a Chosera 1k to set the bevel and was getting nowhere fast) so I went with diamond up to the 8k. It may be that the combination of increased hardness of HSS along with the carbides could be a deal killer for getting a whole lot done with the AlOx stones.

I only tested on the lapping film because someone else asked me to. I can add a few more tests easily enough though. I'll try taking the edge up on Shaptons through 12k and image every step, then go to the SG20k, image that and hit the diamond on leather to see what happens.

It strikes me that the carbides could be any of three that could be formed by alloys in M2 - not sure which are the hardest or if they're similar - but it likely contains chromium, tungsten, and vanadium carbides. The carbides shown in my image are about 4 microns in diameter on average.
 
eKretz said:
I actually haven't tested hardly at all on other AlOx stones except for the 20k as I was already expecting trouble (I tried using a Chosera 1k to set the bevel and was getting nowhere fast) so I went with diamond up to the 8k. It may be that the combination of increased hardness of HSS along with the carbides could be a deal killer for getting a whole lot done with the AlOx stones.

I only tested on the lapping film because someone else asked me to. I can add a few more tests easily enough though. I'll try taking the edge up on Shaptons through 12k and image every step, then go to the SG20k, image that and hit the diamond on leather to see what happens.

It strikes me that the carbides could be any of three that could be formed by alloys in M2 - not sure which are the hardest or if they're similar - but it likely contains chromium, tungsten, and vanadium carbides. The carbides shown in my image are about 4 microns in diameter on average.
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What you are describing is going to be a very interesting and I'd expect very useful bit of work!

I am not all that familiar with many of the HSS steels, but IIRC the AlumOx should be capable of cutting for sure the Chromium carbides and most likely the tungsten - though some form of AlOx might have trouble. The vanadium carbides it can gouge/abrade but not effectively by any means, so these would be the deal breaker for any finish close to or under the micron size of the carbides. The Molybdenum shouldn't be a direct factor as far as grinding.

One can do an etch to reveal the carbides, but not sure how to distinguish one form from the other (or if it even matters in this context).
 
Aluminum oxide (a.k.a. 'AlOx', 'alumina', Al[sub]2[/sub]O[sub]3[/sub]) = ~2100 Knoop hardness
WC (tungsten carbide) = ~1800 Knoop
Chromium carbide = ~1700-1800 Knoop
Molybdenum carbide = ~1800 Knoop

I'd not worry at all, about AlOx not being able to cut chromium carbides; AlOX is often my favorite stropping compound for D2, 440C and similar steels, for example. Harder abrasives like diamond would be faster and likely cleaner cutting (minimizing burrs or rounding), certainly; but AlOx can still get it done. And as shown above, I don't think I'd worry about WC either.

Vanadium carbides are about ~2600 Knoop; I don't even consider using AlOx for steels containing very much vanadium (S30V and beyond) for this reason. I've revisited my assumptions about this occasionally, still attempting at times to refine an edge of S30V/90V on an AlOx or SiC stone, but it never works as cleanly as using diamond for the same task. I always immediately follow with the diamond to 'fix' the damage left by the lesser grits.


David
 
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Good info guys, thanks. Yeah when I said I was expecting trouble I just meant speed of cutting. I didn't want to spend all day as I knew the AlOx would cut but could immediately tell it was going to be slow going due to barely any swarf forming on the 1k. Hence, switched to diamond right off the bat.
 
eKretz said:
Good info guys, thanks. Yeah when I said I was expecting trouble I just meant speed of cutting. I didn't want to spend all day as I knew the AlOx would cut but could immediately tell it was going to be slow going due to barely any swarf forming on the 1k. Hence, switched to diamond right off the bat.
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A big part of this is seeing how the abrasive is mechanically anchored and the result it has on steels with significant carbide content. In this case, even if that abrasive is physically harder than the carbides or not.

The other factor is Tungsten carbide (as well as vanadium carbide) comes in a range of hardness values. I have seen WC rated from 1300 all the way to 2100 knoop, and AlOx from 2000 - 2200.

My King waterstones use AlOx but they would be a poor choice against D2, let alone a HSS with a variety of carbides. That said, I have seen in post-etch s30v evidence of scratch marks on V carbides from AlumOx waterstones, including the King 4k. To be sure they were very shallow compared to the ones in the D2 I posted, but present anyway.

What brand of 1K waterstone are you using?
 
Some of the apparent variability/range differences in Knoop hardness ratings are due to the materials being referenced to different scales. With diamond used as the indenter and therefore the default reference for hardness comparison, some Knoop scales assign diamond's default value at the top to 7000; this is the reference to which the values I posted were compared. Other scales assign diamond a value of 7500, 8000 or sometimes even 10,000, which shifts the whole scale upward. Proportionally, when comparing all values within one particular scale though, the relative hardness differences between the listed materials (carbides and abrasive types) remain essentially the same, and the order of progressively harder materials is always the same within each scale (i.e., VC being harder than SiC, and SiC being harder than AlOx, which is harder than chromium carbide/WC/MoC, and CBN being harder than all of them, with diamond being the hardest at the top of the scale).


David
 
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I am not sure this jibes with my understanding. There are different grades of tungsten carbide that have a range of characteristics, hardness being one of these, from Rockwell A low 80s all the way up to low 90s, putting it out of reach of AlumOx at least for cleanly finishing.

I have also come across references to VC hardness being influenced by carbon content and temperature, but that might be related more to the completeness of the conversion of Vanadium oxides to carbides, and not of the carbides themselves. Wouldn't surprise me either way, the crystal structure of some these carbides can change based on temp and presence of other elements, leading to changes in hardness.

Not to be picking nits, but when the relative differences between the abrasive minerals and the alloying carbides is somewhat close to begin with, small changes can have a big effect at the finishing level.
 
I have a Chosera 1k, a Shapton 1k and a Suehiro 1.5k. Although the Chosera is in fact closer to the Shapton 2k in abrasive particle size (have that also).

I can't speak to the actual hardness numbers for tungsten carbides, but I can confirm trying to cut at least some of them cleanly with AlOx is basically impossible. Before I hurt my back I was a machinist and toolmaker for almost 20 years, and some of the shops I worked at in the early days didn't have diamond grinding wheels except in the tool crib, leaving machinists to try to grind carbide tooling with bench grinder wheels. It was basically absolutely pointless to even try - the wheels basically disintegrated into huge clouds of dust and the edge left on the tool was terrible - lots of fracturing and very unclean grinds.
 
You learn something new all the time. I recently participated in a pass around with a handful of knives from BCMW for overall eval. The M2 gave my AlOx waterstones a bunch of trouble that I didn't expect. Was able to sharpen well using SiC, but that was only to an 800 grit finish.

To be sure this is not the same as a solid carbide cutting head and it did grind the steel, but the difference in the amount of steel showing up on the surface of my stone was considerably less than the other steels in the mix. It also came in way behind the curve for edge retention compared to the others off the same stone. Resharpened with SiC it improved its cut longevity by over 100%.
 
Okay, got this mostly done, I want to do a little more with the loaded strop, may add more later on. This is M2 HSS, and on each subsequent stone I changed from a straight stroke to an angled stroke so as to be able to see any scratches from the previous stone.

What I see is that after 8k the carbides are not being cut and remain seated in the steel matrix, but prominently exposed. Prior to that, I am not convinced they're being cut much either - I think they're being torn out.

The water stones don't do much of any cutting at all if the dull particles don't tear loose - which is why the Shapton 1k doesn't look like it did a whole lot. The problem I see is that once the dull particles tear loose, they create a slurry, which I'm pretty sure is just tearing those carbides right out. For all of these I used a very light touch so as not to influence tear-out of the carbides by being too aggressive with pressure.

The diamond on leather seems to have rounded the carbides, and I'm thinking more work on the strop might be able to bring them closer to the steel matrix. I'll update with another shot after some more work on the strop.

Here's the first in the progression, a DMT C (325) to ensure that the edge starts out clean:



Next, Shapton Pro 1k:



Shapton Pro 2k:



Suehiro Rika 5k:



Shapton Pro 8k:



Shapton Pro 12k:



Suehiro Gokumyo 20k:



1 micron diamond compound on leather:

 
Nice bit of work!

I agree with your assessment 100% so far. I am growing an appreciation for HSS and Tungsten carbide, it doesn't appear at any level the carbides were significantly worked until the diamonds came into the picture.

I wonder if SiC could do any better, wet/dry over a hard surface.

Keeping in mind Vanadium carbides are going to be substantially harder even than the WC, it will be interesting to see the effect of diamond strop played out a bit further - will it come into equilibrium before or after the carbides are worn down to the steel.

Thanks for doing this!

Martin
 
Thanks! I am pretty sure SiC would do better, as it is harder than AlOx, but how much better is anyone's guess. I can test that too though - I've got a very fine Carborundum SiC barber hone that should test it nicely.

First I'm going to go back to the strop with a bit coarser diamond compound - I've got some 5 micron also, I'll try hitting the present edge on that for a bit then going back to 1 micron and see what we've got. After that I'll take it to the SiC stone and see what that accomplishes.
 
OK, pretty much satisfied now that the carbides are being cut by the diamond loaded leather strop at about the same rate as the surrounding steel, but it seems that since this occurs in such a fashion there's no way that a soft substrate will bring the carbides back flush with the steel matrix if they are sticking out when stropping commences. I think that if the stropping follows a diamond stone that there needn't be any worries about the carbides being dug out during loaded stropping unless a very aggressive abrasive particle size is used.

Here's some further stropping done on the last edge from above with 5u diamond loaded strop:



Back to the 1u:



And here's the same edge after the finest SiC stone I have, a Carborundum 103. I see uncut carbides in there for sure. It has either knocked out or cut some others, not sure which. I'm guessing it wouldn't be super successful at cutting them either though.

 
Again, very nice work!

Looks like so far the DMT EEF is the only stone that really got it done. The SiC stone looks like a finish somewhere between the Shapton 2k and Suehiro 5K - maybe it did a better job on the carbides overall, but not enough to say 100%. The effect might be as much from the abrasive in a harder bond than from the abrasive doing a better job.

Now I wonder what the Spyderco fine or UF might do. Also wondering what my Washboard compound (SiC in hard binder) might do vs this steel. Also if a difference using diamond compound vs lapping film of same micron rating...
 
eKretz said:
I have a Chosera 1k, a Shapton 1k and a Suehiro 1.5k. Although the Chosera is in fact closer to the Shapton 2k in abrasive particle size (have that also).

I can't speak to the actual hardness numbers for tungsten carbides, but I can confirm trying to cut at least some of them cleanly with AlOx is basically impossible. Before I hurt my back I was a machinist and toolmaker for almost 20 years, and some of the shops I worked at in the early days didn't have diamond grinding wheels except in the tool crib, leaving machinists to try to grind carbide tooling with bench grinder wheels. It was basically absolutely pointless to even try - the wheels basically disintegrated into huge clouds of dust and the edge left on the tool was terrible - lots of fracturing and very unclean grinds.
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For three hours I grind by hand bevel in 4 inch long M2 steel blade with ALOx /used water/ .Price of stone is half a dollar ............
 
HeavyHanded said:
Again, very nice work!

Looks like so far the DMT EEF is the only stone that really got it done. The SiC stone looks like a finish somewhere between the Shapton 2k and Suehiro 5K - maybe it did a better job on the carbides overall, but not enough to say 100%. The effect might be as much from the abrasive in a harder bond than from the abrasive doing a better job.

Now I wonder what the Spyderco fine or UF might do. Also wondering what my Washboard compound (SiC in hard binder) might do vs this steel. Also if a difference using diamond compound vs lapping film of same micron rating...
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I was wondering the same, as I recalled Sal mentioned it's like Sapphire.
The diamond paste vs film also interesting ...
 
Natlek said:
For three hours I grind by hand bevel in 4 inch long M2 steel blade with ALOx /used water/ .Price of stone is half a dollar ............
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Yes but your edges are not as clean as they could be, and your edge retention will suffer also. You really should be using a diamond plate. On top of the other stated benefits, you'd be done in 5 minutes!
 
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