High vanadium/carbide tear-out questions

[DeadboxHero]

3 micron finish would be required to prevent the carbides from hiding within the cuts, iirc.

Definitely recognize and appreciate that people will prefer varying levels of finish. Very cool with that. I generally use a 1k apex, but I’ll never begrudge anyone for their own preferences.

The edges with higher vanadium steels just get crisper, have less fatigue and more longevity with diamond/CBN abrasive since the apex can be shaped with cutting rather then burnishing.

People that know this tend not to speak up about it because we have to write a book about all the intricacies and caveats involved.

I don't touch the subject for that reason.

I'm busy doing it.

We'll have to get together and show you.

 

[HeavyHanded]

It's not a big deal, but at some point you have to recognize that the differences between this steel and that matter.

The dif between diamond and SiC or AlumOx doesn't really come into play with regular steels - in fact the more traditional abrasives (IMHO) do a notably better job. But VC at above 4 % or even Chromium carbides in large % (about 10 or above) play by a different rule. It is at this point that burnishing, grinding, RC value, abrasive potential at lower PSI all come into play along with the actual size of the carbides...

Not to get mysterious about it, but matching the steel type to the abrasive matters if you want to really nail it, there is no getting around it.

 

[Haffner]

Unfortunately, there EEF DMT stones for the KME don’t seem to exist. It looks like it stops at EF.

Buy a DMT 6-in. Extra-Extra Fine (D6EE) and cut it to the size you need.

 

[Mo2]

Buy a DMT 6-in. Extra-Extra Fine (D6EE) and cut it to the size you need.

Or just get some basswood cut to size and use some diamond spray/paste. They also make 3m diamond Lapping films iirc, just cut them to size and apply in the clear blocks.

 

[tomhosang]

Now since it only happens at sub-3 micron, I believe that's sub-3 micron apex width. Not abrasive size. You can jump from a 200 grit diamond plate to stropping with 0.1 micron compound and it won't matter because the apex is not refined enough to be under 3 microns. Vanadium carbides are 2 to 3 micron so the apex width has to be smaller than that for tearout to happen.

 

[Mr.Wizard]

You can jump from a 200 grit diamond plate to stropping with 0.1 micron compound and it won't matter because the apex is not refined enough to be under 3 microns.

I don't think this is correct. See https://scienceofsharp.wordpress.com/2015/03/01/the-diamond-plate-progression/

10000x magnification of the apex cross-section after honing on the DMT Coarse (325). Edge width is less than 100nm.

 

[tomhosang]

I don't think this is correct. See https://scienceofsharp.wordpress.com/2015/03/01/the-diamond-plate-progression/

Hmm. That's interesting. Still, apex width is what matters and not the size of the abrasive particles.

 

[HeavyHanded]

I don't think this is correct. See https://scienceofsharp.wordpress.com/2015/03/01/the-diamond-plate-progression/

All sharp edges are sub micron, even if done with coarse abrasives. The difference for the most part is how much lateral and in-line deviation the edge has.

Also, most abrasives are only 10-15% proud of their bond layer (plated diamonds a little more), so a 30 micron abrasive is only making a 3-5 micron scratch depth.

 

[Blues]

We can tell without exhaustive testing that an edge apexed with conventional abrasives and honed with diamonds will have properties of all-diamond sharpened edge, while the edge apexed with diamonds/CBN but honed with conventional compounds like Totmek honing paste will have properties of all-Al2O3 sharpened.
This is because weakening of the steel matrix happens during fine honing, not bevelling.

wootzblade , since I can never seemingly get enough of this discussion...if I were to take a modern folder with a content of >2 or 3% vanadium carbide content and sharpen it, (for argument's sake), on a medium Spyderco ceramic bench stone...as long as I finished on diamond, (fine, x-fine, xx-fine, etc), it would be good to go?

But, alternatively, if I started and finished the job on the ceramic bench stone, the edge would be less than ideal and would dull more quickly in use due to having not shaped the carbides with the diamond hone, regardless of whether there was tear out or not?

Fascinating topic.

 

[wootzblade]

Yes, this is how I see it.
As Todd S. has seen in his SEM, and shown us mere mortals, silicon based abrasives (and ceramic is one of them) that are less hard than vanadium carbides, still can abrade them (wear off), and you can put an edge on a high vanadium blade with them, BUT they abrade the surrounding steel matrix at a higher rate, and because of that you see on the SEM bumps and nodes of the vanadium carbides raised above the abraded matrix. Off your non-diamond/CBN stone you get what people call "fatigued" edge.

CBN/diamond "superabrasives" remove material in a unique way; due to their super hardness the whole process is quite similar to the milling operation, while conventional abrasives are more akin to sanding.

 

[HeavyHanded]

The one question I have re this topic is what happens when sharpening with a coarse stone, be it diamond or otherwise. Having a large abrasive excavate metal and carbides seems to maybe crack the carbides(?!) instead of burnishing them as with a smaller abrasive - they maybe do not come out whole and as a result are sharper than they might be from abrasion alone.

Based on the observation you can get away with a rough stone and make a very sharp, long lasting edge, whereas with a finer hone you really need diamonds or CbN.

 

[Blues]

The one question I have re this topic is what happens when sharpening with a coarse stone, be it diamond or otherwise. Having a large abrasive excavate metal and carbides seems to maybe crack the carbides(?!) instead of burnishing them as with a smaller abrasive - they maybe do not come out whole and as a result are sharper than they might be from abrasion alone.

Based on the observation you can get away with a rough stone and make a very sharp, long lasting edge, whereas with a finer hone you really need diamonds or CbN.

Good question, HH. How would sharpening, at 320 grit for example, differ if it were the only grit utilized for sharpening via a diamond hone vs. silicon carbide vs. alox?

Would the diamond hone in this instance (still) provide a superior edge in terms of longevity as well as shaping the carbides? Would there be any rounding or tear out of the carbides with the SiC and alox hones at this grit?

Or is there no practical / discernible difference?

 

[HeavyHanded]

Good question, HH. How would sharpening, at 320 grit for example, differ if it were the only grit utilized for sharpening via a diamond hone vs. silicon carbide vs. alox?

Would the diamond hone in this instance (still) provide a superior edge in terms of longevity as well as shaping the carbides? Would there be any rounding or tear out of the carbides with the SiC and alox hones at this grit?

Or is there no practical difference?

My own experience says "no practical difference" until you get above 400 grit or so. Still makes a good edge up to about 600, and then really falls away.

 

[David Martin]

Since we are giving our own experience, I'll comment toward post 51 & 52. preface: I don't own a SEM microscope but have access to one and will take my knives over and give them a look. Which will allow me to know what's going on... When I sharpen s30v or s90v on a Norton India,
it takes longer working the bevel and is difficult to remove the burr. Same steel on my JUM-3 fine (280 grit SiC) I notice the steel works quicker and removes the burr. A nice edge. Then on the coarse diamond it works a step easier and the edge comes out a touch more crisp.
Cuts paper nice, over comes wrinkles and maybe cleaner. Burr removal responds better. Now, did any of them grind a vanadium carbide?
Maybe. As the VC % increases they could encounter a diamond protruding from the stone. Does shaping or flattening a few VC matter on the bevel? I doubt it. On the very edge? Maybe. I don't sharpen beyond a coarse diamond or fine SiC. For guys that take their s90v blade up to 1200-1500 grit, they are shaping VC if they use a diamond that fine. DM

 

[wootzblade]

The one question I have re this topic is what happens when sharpening with a coarse stone, be it diamond or otherwise. Having a large abrasive excavate metal and carbides seems to maybe crack the carbides(?!) instead of burnishing them as with a smaller abrasive - they maybe do not come out whole and as a result are sharper than they might be from abrasion alone.

Based on the observation you can get away with a rough stone and make a very sharp, long lasting edge, whereas with a finer hone you really need diamonds or CbN.

Exactly what I think. That is why I draw attention to that "CBN/diamond "superabrasives" remove material in a unique way; due to their super hardness the whole process is quite similar to the milling operation."
By sharpening on even coarse CBN/diamonds we "mill" the bevel through the carbides and matrix uniformly; the carbides do not fall behind the steel matrix, and the matrix does not get overabraded.
I have no SEM data to support that though, but we can tell that by better holding/stability of edges sharpened exclusively by diamonds.

 

[HeavyHanded]

Exactly what I think. That is why I draw attention to that "CBN/diamond "superabrasives" remove material in a unique way; due to their super hardness the whole process is quite similar to the milling operation."
By sharpening on even coarse CBN/diamonds we "mill" the bevel through the carbides and matrix uniformly; the carbides do not fall behind the steel matrix, and the matrix does not get overabraded.
I have no SEM data to support that though, but we can tell that by better holding/stability of edges sharpened exclusively by diamonds.

With CbN there is definitely a bit of milling depending on how the grains are oriented. When used in a slurry on a wheel, supposedly they can actually self orient to shave with the long edges of the abrasive instead of digging with the corners.

With diamonds they remove metal in much the same way as other mineral abrasives via scratch removal. The biggest difference IMHO is the depth to which they can cut per pass and of course they don't really blunt. What they hit, gives. Whereas other minerals shed as they hit those harder carbides. This is why SiC works better than alumox on high carbide steels, again just my opinion.

 

[wootzblade]

With CbN there is definitely a bit of milling depending on how the grains are oriented. When used in a slurry on a wheel, supposedly they can actually self orient to shave with the long edges of the abrasive instead of digging with the corners.

With diamonds they remove metal in much the same way as other mineral abrasives via scratch removal. The biggest difference IMHO is the depth to which they can cut per pass and of course they don't really blunt. What they hit, gives. Whereas other minerals shed as they hit those harder carbides. This is why SiC works better than alumox on high carbide steels, again just my opinion.

I will echo you, again.
Because of this difference, CBN is preferred for grinding, while diamonds for fine honing - and this is how we use them in our workshop. We bevel and set edge on CBN wheels, then hone and deburr on paper wheels with diamonds.
Compared to diamonds, the CBN crystals have better crushing resistance. Under workload, the CBN crystals gradually micro-chip maintaining sharp facets, while diamond crystals macro-fracture, turning into a finer grit. For example, our 5-micron diamond honing wheel, with use will also have, along with the nominated 5-micron crystals, a fraction of smaller 3-micron and 1-micron diamonds from the crushed original crystals, eventually giving better polished surface.