Carbides and cutting edges

I think you have to look at the size and distribution of the carbides in the steel, as well as the grit size and hardness of the sharpening stone.

In powder steels, the carbides are going to be evenly distributed and very small, usually smaller than the apex of the typical edge. In that case, you can sharpen with SiC, which is softer than the vanadium carbides. You will tear out some of the carbides and expose others, but the exposed carbides are so small that you will still produce a sharp, slightly toothy edge that works exceptionally well with some media, such as rope or tomatoes.

With a fine-grit diamond stone, you can sharpen both the matrix and the carbides in that matrix, if you use light pressure.
 
Twindog said:
I think you have to look at the size and distribution of the carbides in the steel, as well as the grit size and hardness of the sharpening stone.

In powder steels, the carbides are going to be evenly distributed and very small, usually smaller than the apex of the typical edge. In that case, you can sharpen with SiC, which is softer than the vanadium carbides. You will tear out some of the carbides and expose others, but the exposed carbides are so small that you will still produce a sharp, slightly toothy edge that works exceptionally well with some media, such as rope or tomatoes.

With a fine-grit diamond stone, you can sharpen both the matrix and the carbides in that matrix, if you use light pressure.
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The stone I finish with is 40 micron.

Took a S35VN kitchen knife that's .006" behind the edge and 15 DPS and it will pass the typical straight razor test, that's cutting free hanging hair.

No I wouldn't shave with it or would I sharpen a straight razor to 40 microns, but you get the idea.
 
Ankerson said:
The stone I finish with is 40 micron.

Took a S35VN kitchen knife that's .006" behind the edge and 15 DPS and it will pass the typical straight razor test, that's cutting free hanging hair.

No I wouldn't shave with it or would I sharpen a straight razor to 40 microns, but you get the idea.
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Definitely not questioning the performance of your edges, just trying to get a sense of what is going on.

So what happens when a 40 micron SiC grit plowing through a soft steel matrix hits a harder, 1-micron vanadium carbide? Seems like it would tear out the carbide.

On the other hand, with a ton of tiny, well-distributed carbides, many will be left exposed, and they are so small that they won't degrade the edge's performance in many kinds of media, especially when the serrations are just what some media are most susceptible to.
 
Twindog said:
Definitely not questioning the performance of your edges, just trying to get a sense of what is going on.

So what happens when a 40 micron SiC grit plowing through a soft steel matrix hits a harder, 1-micron vanadium carbide? Seems like it would tear out the carbide.

On the other hand, with a ton of tiny, well-distributed carbides, many will be left exposed, and they are so small that they won't degrade the edge's performance in many kinds of media, especially when the serrations are just what some media are most susceptible to.
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I end up with a smooth edge, can't feel anything running it on my thumb nail, that's what really matters TO ME.

For the rest of it, I don't care because I keep things simple, I found stones that work for me in how I sharpen and I have been using them for awhile now. :)
 
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Here is my s90v tomato slicing edge, sharpened with 320-400 SiC stone.
Sharpened:
1. Flattened the apex (light reflected to naked eyes for entire edge)
2. Sharpen 15dps with 320-400 SiC stone, start with heavy pressure until almost apex. Gradually reducing pressure until apexed, whence pressure less than 0.5oz.
3. Use very light edge-leading strokes to deburred

Nital etched. I don't have picral or alike, nevertheless you can clearly see a lot of Vanadium Carbide. There are a few 2um VC along/near apex.
It's a bevel face view. Too hard to capture edge-on look due to shallow field of view.
rWqdyUJ.jpg
 
bluntcut said:
Here is my s90v tomato slicing edge, sharpened with 320-400 SiC stone.
Sharpened:
1. Flattened the apex (light reflected to naked eyes for entire edge)
2. Sharpen 15dps with 320-400 SiC stone, start with heavy pressure until almost apex. Gradually reducing pressure until apexed, whence pressure less than 0.5oz.
3. Use very light edge-leading strokes to deburred

Nital etched. I don't have picral or alike, nevertheless you can clearly see a lot of Vanadium Carbide. There are a few 2um VC along/near apex.
It's a bevel face view. Too hard to capture edge-on look due to shallow field of view.
rWqdyUJ.jpg
Click to expand...


Can you describe what the vanadium carbides look like in that photo?

If I'm seeing it correctly, the sharpening grooves are so deep relative to the size of the vanadium carbides that it wouldn't matter whether the SiC is harder or softer than the carbides because they are just being plowed out of the matrix.

When you make your final, very-light sharpening strokes, how long are the strokes? A leading edge stroke should cut off the old burr quickly, but then begin creating a new burr if you don't stop the stroke once the burr is gone.
 
Spherical & oblong bounded(ring around) objects (5um or less in dia size).

OK, perhaps only applicable to my sharpening skills (or lack of)

You are right, carbide shaping wasn't relevant when abrading depth/magnitude is much larger than carbide size.

I mostly use long strokes (lead & trail). With this 12" long stone, my strokes were extra long. 15dps edge leading at this low grit will hardly producing burr. Edge in pic was off the stone, i.e. no strop, no cut into material, etc... Note: my stone surface was rinse with water often when deburring. I've another of this stone but oil instead, quite messy & collecting dust now.

Twindog said:
Can you describe what the vanadium carbides look like in that photo?

If I'm seeing it correctly, the sharpening grooves are so deep relative to the size of the vanadium carbides that it wouldn't matter whether the SiC is harder or softer than the carbides because they are just being plowed out of the matrix.

When you make your final, very-light sharpening strokes, how long are the strokes? A leading edge stroke should cut off the old burr quickly, but then begin creating a new burr if you don't stop the stroke once the burr is gone.
Click to expand...
 
So the carbides are not sharp and make up a large amount of the cutting edge. Wouldn't that mean that sharpening them is pretty important for performance?
 
dkb45 said:
So the carbides are not sharp and make up a large amount of the cutting edge. Wouldn't that mean that sharpening them is pretty important for performance?
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I think that's a good question, but it probably has the largest affect on large-carbide steels like D2 or 440C.

The typical apex of a sharp edge is 1 or 2 microns for most of us. The carbides in Sandvik's fine-carbide 13C27 tend to run 0.5 microns in size, so they probably don't need to be shaped, even if we could.

But a lot depends on what you're cutting.

http://smt.sandvik.com/en/products/...ge/different-steel-types/fine-carbide-steels/
 
Ah so vanadium carbides are actually the size of the apex (roughly) and make little difference if they are shaped, depending on the distribution near the edge? I know chromium carbides don't matter much to me, because all of my stones will shape them, so even though the carbide is huge it will be worn down like the matrix.

If it doesn't show, I have a decent amount of rudimentary knowledge, but in terms of the actual technical and mechanical aspects, I need a lot more.
 
Good discussion.


And why I keep things simple and use diamonds.


1095 or M4. All the same on my stones
 
Yes, it's matter a lot because edge quality/durability rely on matrix foundation. Carbide volume (proportionally) is a large liability for about 1.5*avg carbide size of edge thickness.

Most abrasive types will abrade matrix faster than carbide (stating the obvious). Even with diamond/cbn, surface carbides always be raise/stick-out of the surface at some level - amt (% of its dia) depend on carbide type & size. I won't go into excess matrix recess/abraded would undermine carbide footing/binding.

W/o an effective ability to shape carbide, mean abrading matrix + mostly-impacting carbides. If chunk of matrix is much bigger than carbide than carbide get ploughed along. When matrix is much thinner than carbide, impacted carbides will result with combination of [ status quo, displacement, tear out, loosen, etc. ]. For abrasive size range from very coarse down to 1/2 carbide diameter, (result) exposing carbides that still embeded to surface either 'status quo'/strong or compromised/weakened. Smaller grit than that will just polish (whatever reachable) sunk matrix surface.

Whereas abrasive can shape carbide will result with less 'compromised' exposing carbides. Notice the 'less' because impacts still taken place, they are: bounce off, push down, over-committed bite size, partial abrasion, etc..

Mitigating carbide durability issue is knowing what taken place in sharpening interaction between abrasive and matrix+carbide. Understand abrading mode [plow, cut, burnish, etc.] at when and why, so appropriate abrasive surface and forces (note: velocity is important). Aware that sharpening stroke where abrasive run into the edge/apex (edge leading), will has more apex plowing than edge trailing. If you want a very high edge durability -> when apex radius is about 1.5*avg carbide dia width, must avoid impacts that can compromise embedded surface carbides. By switch to fixed (plate or film) diamond/cbn with dia size smaller than 1/5 carbide dia. So abrasive size should stay ahead smaller than 1/5 of carbide size and apex radius.

You spend this careful sharpening progress to shape high alloy nano edge for long lasting(wear) low impact(no chop & soft landing cut) usages.

For rough usages - shape edge & surface features/irregulaties with lowest possible 'promised' carbides & features.

dkb45 said:
Ah so vanadium carbides are actually the size of the apex (roughly) and make little difference if they are shaped, depending on the distribution near the edge? I know chromium carbides don't matter much to me, because all of my stones will shape them, so even though the carbide is huge it will be worn down like the matrix.

If it doesn't show, I have a decent amount of rudimentary knowledge, but in terms of the actual technical and mechanical aspects, I need a lot more.
Click to expand...
 
I thought vanadium carbides were uniform in particles steels for size? Obviously I am meaning everything from S30V to M390, and those kinds of vanadium rich stainless steels.

I guess I'm just really looking for what is best to get the most out of those steels. My S30V Volli lost its razor edge in moments from thick cardboard cutting, but I was able to strip it right back with black compound. Does that mean the razor edge is all in the matrix, because I didn't use diamonds for stropping? The more I delve in, the more questions are being raised, and the less I apparently know.
 
Crucible PM process create carbide around 2-5um in size. Avg size indeed around 2um but not uncommon to see aggregated (in micrograph) carbide 3-5um. CPM drop/particle size around 500um. Bohler Particle size around 250um and carbide still avg around 2um however a slight less variance toward 5um because of smaller particle size.

What is your blade hrc & edge geometry? Stropping (loose and partially embedded abrasives) topic is too complex to cover here. Black compound is SiC. oh heck, even with diamond most likely that your edge will be weaken by stropping.

Definitely most razor edge is by the matrix and some carbide peaks. Although, these protruding carbide and feature probably have receeded/eroded/weakened footing. Cardboard attr/variable has big impact on edge wear/tear. Perhaps, try slice a stack of thinner cardboard to see if dulling is about the same as thick cardboard.

dkb45 said:
I thought vanadium carbides were uniform in particles steels for size? Obviously I am meaning everything from S30V to M390, and those kinds of vanadium rich stainless steels.

I guess I'm just really looking for what is best to get the most out of those steels. My S30V Volli lost its razor edge in moments from thick cardboard cutting, but I was able to strip it right back with black compound. Does that mean the razor edge is all in the matrix, because I didn't use diamonds for stropping? The more I delve in, the more questions are being raised, and the less I apparently know.
Click to expand...
 
Bluntcut thanks for going to the trouble of etching the blade and posting that excellent photo with description. You guys are turning this into an excellent thread.

Joe
 
The hardness of all of my blades is around 60 (all production S30V, Elmax, and M390), and I tried to keep the edge angle consistent around 17 dps. I sharpen all of my knives with my DMT aligner from XC down to XXF, using decreasing pressure and finishing with edge trailing strokes. Of course I match the edge angle with the strop, and reload the strop when it gets glazed. I scrape it off with ceramic every 2 or 3 full loads.
 
Push Cutting tomato with S125V, 400 grit SIC

[video=youtube;o1QSk-fcHbg]https://www.youtube.com/watch?v=o1QSk-fcHbg[/video]
 
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