Benchmade Vex: another not-quite-right cheap knife

[HoB]

Like crumbling as it is sharpened, before it actually forms a burr you would notice?

Yes precisely, just like Cliff has observed happening to the edge of a certain severely thinned out blade made from S30V that is know to be run relatively soft.

Not exactly. If you look at burrs under high mag you can see they are very jagged, often highly irregular. They are deformed to plastic and just barely holding on, which is why you can easily scrape them off with your finger nail.

Your are not addressing the issue. If they are that fragile, they should hardly be able to form a stubburn burr. I think we have all had the experience that there are some burrs that are NOT simply drawn off by running the edge over some wood or plastic. Obviously they are irregular but I don't see how that would affect the issue at hand. Cohesiveness does not imply regularity.

those steels need a lot of force to abrade but have little ability to resist the force and thus they deform without getting cut.

Well, if these steels can deform that easily, especially considering the lower strain rate at smaller cross sections, thin edges made out of such a steel should not simply fall apart on you, as you have experienced yourself. Or are you saying that the edge geometry of even thin edges is that much thicker than a burr, that the strain rate is sufficiently larger.

Finally, as I said, while the highly alloyed steels may exhibit similar problems, my personal experience with bad burrs has been mainly with low carbon content stainless steels, which are not overly hard to abrade. Sure they are often really soft. I don't know, it is hard to judge for me by feel whether a soft lower end HC steel like 1060 or even 5160 is really that much easier to machine than a soft low carbon stainless steel like 420J or even 420HC to account for the difference in burring.

Just compare the following: I know from experience that 420HC can burr much worse than S30V. Nominally they were supposed to have very similar hardness, but lets say the 420HC slipped a few points. to may be 56-57 while S30V may be assumed to be 59Rc. Now the 420HC is significantly softer, but S30V is significantly more abrasion resistant. Which one would you have predicted to be worse. By your argument it would be a difficult call, yet in practice they were not even close in burr formation.

Sorry, everyone. I realize that this thread has been badly hijacked .

 

[db]

Not at all HoB, you've brought up some very interesting points I haven't thought of. I've for a long time questioned the theory of carbide tear out and it's effect on edges. I personally think that what you use to sharpen with will make a difference in forming a burr, and how that may relate to carbides being pulled out or cut is something I don't have any idea on.

 

[Carl64]

Just compare the following: I know from experience that 420HC can burr much worse than S30V. Nominally they were supposed to have very similar hardness, but lets say the 420HC slipped a few points. to may be 56-57 while S30V may be assumed to be 59Rc. Now the 420HC is significantly softer, but S30V is significantly more abrasion resistant. Which one would you have predicted to be worse. By your argument it would be a difficult call, yet in practice they were not even close in burr formation.

I have a Spyderco Paramilitary (s30v) and a Buck 110 (420hc at 58rc).

Neither is free of burr potential. The Paramilitary is much more likely to have a burr that won't go away. As long as I sharpen carefully, the Buck only has an annoying burr if a big one is formed during use.

But on the other hand, the Buck steel will wear down much faster. Even if it gets a big burr, it takes a lot less time of careful, light sharpening strokes to completely remove the bent steel. To get rid of the burr on the Paramilitary, I have to do the same thing for a long time.

Also, since we don't yet have a complete theory on exactly what proportions of all steel characteristics would result in specific levels of unwanted steel behavior, it's really hard to be sure of what to expect when changing two or more variables at once.

 

[Cliff Stamp]

If they are that fragile, they should hardly be able to form a stubburn burr.

This doesn't follow. A blade of grass is very weak but easily bends back and forth in the wind.

I think we have all had the experience that there are some burrs that are NOT simply drawn off by running the edge over some wood or plastic. Obviously they are irregular but I don't see how that would affect the issue at hand.

You were wondering if there are carbide tearouts then why isn't it seen in the burr, I was pointing out it is evident that the burrs are jagged and nonuniform as would be expected.

Cohesiveness does not imply regularity.

In one aspect it does, in others it does not. Lack of it will obvious induces an irregularity as well.

Well, if these steels can deform that easily, especially considering the lower strain rate at smaller cross sections, thin edges made out of such a steel should not simply fall apart on you, as you have experienced yourself. Or are you saying that the edge geometry of even thin edges is that much thicker than a burr, that the strain rate is sufficiently larger.

It isn't simply the thickness but the geometry. A properly formed edge is about 0.1 micron thick at minimum (to date on steel) but it thickens immediately due to the triangular cross section. This of course prevents (well strictly minimizes) focus micro-loading of the very edge itself.

A burr on the other hand may be thicker, some are 0.1+ mm, but they are constant in thickness and thus subject to point overloading. This is made worse as they havea huge fault line at the base and there are torque/leverage issues on extended burrs. A properly formed edge has essentially no specific lever arm at all.

I know from experience that 420HC can burr much worse than S30V.

As I said, there are issues with grain structure and similar properties as well. The steels you describe with burring problems are found on the cheapest knives made and thus they have the worst heat treatments possible. Try 420HC from Wilson and see how it burrs.

What you are seeing isn't steel specific, you are just seeing a bad heat treatment. Of course a steel with a huge and irregular grain structure with lack of proper relief and internal stresses is not going to respond well to a very fine geometry. Unfortunately the perception of those steels has been destroyed when in fact they are actually optimal choices for some types of knives.

-Cliff

 

[Last Visible Canary]

So, for the sake of the uninitiated (me):

The burring that your talking about sounds as though it relies on a two basic elements to be in place,

1) carbide tear out wich causes irregularies in the material present in the burr
2) a steel matrix wich has the ability to plastic deform


The idea being that the steel matrix is able to be pushed forward and away from the main edge bevel, out beyond the end of the triangles tip (wich makes up the edge geometry) without being sheered off, or "broken" off, implying a level of facturing along the fault line.

From the various descriptions in this thread, it almost sounds like the matrix is acting like playdough, making it very difficult to sharpen because the steel is not being removed entirely from the matrix by the abrasive action of the stone/grit, but rather its being pushed forward away from the edge bevel by deformation.

does that sound about right?

If it does, is the plastic deformation caused specifically by the thin cross section of the edge/burr? Is it present because the carbides have been knocked out, leaving the reletively meleable matrix?

 

[kel_aa]

A properly formed edge is about 0.1 micron thick at minimum (to date on steel)

Can I ask where is figure is from? I've read about techniques for viewing submicron (greater than 0.5 micron) edges. Commerical Stanley blades were measured to be 2 microns*.

*Clarification: I misqouted the above, it was 2 microns radius, so effectively 4 microns thick.

 

[Cliff Stamp]

Can I ask where is figure is from?

Verhoeven measured the irregularity in the apex of highly polished edges and the lowest he could achieve was about 0.1 microns. If you check Lee's pictures in his book they appear to be about the same.

The idea being that the steel matrix is able to be pushed forward and away from the main edge bevel, out beyond the end of the triangles tip (wich makes up the edge geometry) without being sheered off, or "broken" off, implying a level of facturing along the fault line.

That is one case, the common deformation burr. It is immediately obvious when sharpening as it flipps back and forth with each pass on the stone. There is also a facture burr which is more rare where the edge never forms due to excessive brittle failure or carbide tearout.

From the various descriptions in this thread, it almost sounds like the matrix is acting like playdough, making it very difficult to sharpen because the steel is not being removed entirely from the matrix by the abrasive action of the stone/grit, but rather its being pushed forward away from the edge bevel by deformation.

Yes, it is a combination of the abrasive not being aggressive enough and the steel being too weak. This is why you see it worse on stones which are loaded, edges which are highly used, etc. . You can minimize it a great deal with a couple of passes right into a stone before sharpening to remove the weakened metal.

If it does, is the plastic deformation caused specifically by the thin cross section of the edge/burr? Is it present because the carbides have been knocked out, leaving the reletively meleable matrix?

Carbide tear out can be a problem, but isn't always the critical issue, some of the high burr steels have little to no primary carbide. It is just due to a highly fatigued steel deforming rather than being abraded in most materials. This is why you see it readily for example if you press exceptionally hard when shaping an edge.

-Cliff

 

[HoB]

This doesn't follow. A blade of grass is very weak but easily bends back and forth in the wind.
-Cliff

For that to happen the steel would have to have very high ductility, which is hardly the case. The comparision is nonsense anyways, but I know you know that. I also understand what you want to say, but I don't think it applies here and the grass analogy paints a very wrong picture. We are talking about a burr that is not fibrous but contains in the ledeburitic steels you are talking about chunks of carbides which in themselves are not overly stable. Again we have to go back to the fact that you observed edges in this steel crumbling on you. Again I ask: If a thin edge can not be supported why do you think an even thinner burr would be. You just said in a different post that the edge literally exploded, why would you expect such a steel to form a stubburn burr? If you can not bend the edge back and forth like your blade of grass, why would you suddenly be able to do that with a burr. No I don't buy it.

You were wondering if there are carbide tearouts then why isn't it seen in the burr, I was pointing out it is evident that the burrs are jagged and nonuniform as would be expected.
-Cliff

You would expect the burrs to be ragged and non-uniform independent of the steel. This has nothing to do with carbide tear out. Yes, some burrs may look a bit more formed than others but none will be well formed.

It isn't simply the thickness but the geometry. A properly formed edge is about 0.1 micron thick at minimum (to date on steel) but it thickens immediately due to the triangular cross section. This of course prevents (well strictly minimizes) focus micro-loading of the very edge itself.

A burr on the other hand may be thicker, some are 0.1+ mm, but they are constant in thickness and thus subject to point overloading. This is made worse as they havea huge fault line at the base and there are torque/leverage issues on extended burrs. A properly formed edge has essentially no specific lever arm at all.
-Cliff

Here I can not tell which way you want to argue. In the first paragraph it sounds as you would an edge to "crumble" first. In the second it seems you are saying that a burr should fall apart before the edge goes? Also, I very much that what you experienced on the Sebenza was only occuring at the very edge. When an edge crumbles like you describe, this phenomenon must take already way back from the edge. If only the last 0.1 micro would crumble (which, as I would like to point out is not so easy to achieve for the average sharpener. Most of Verhoevens images indicate 0.6 microns on the better edges, and most decent sharpeners will rather produce a 1 micron edge, but I know that with great care 0.1 micron edges are achieveable) you would still have maybe a 1 micron edge left which would still be pretty sharp and if I am not mistaken, this is not what you have experienced? So the effect must propagate further inward from the edge, which is likely to bring the edge and the burr in a similar size regime.

What you are seeing isn't steel specific, you are just seeing a bad heat treatment. Of course a steel with a huge and irregular grain structure with lack of proper relief and internal stresses is not going to respond well to a very fine geometry. Unfortunately the perception of those steels has been destroyed when in fact they are actually optimal choices for some types of knives.
-Cliff

Well, sure, but what I really was after and I am still not any closer than before, is how I would predict from the hardness of the steel and the steel composition, how that steel burrs. Essentially you are saying here that there is no simple correlation because neither hardness nor composition will tell you how the steel was heat treated. And if you read back you will see that this is in essence what I said earlier. That this is not just dependent on hardness or carbide volume. I did some more speculation, but I indicated that I was doing exactly that: speculating. However from your last paragraph I have to wonder how you come to declare that 59Rc is way too soft for a steel with as high a carbide volume as S90V with regards to burring?

 

[Cleve Loga]

Benchmade- They'll RAPE YA AND ROB YA TO!

 

[Joe Talmadge]

Cleve, if you're going to make statements like that, could you add in some detail. If you don't like BM, I'm good with that, not everyone likes every company. But contentless all-caps insults should really be backed up a bit

 

[Cliff Stamp]

For that to happen the steel would have to have very high ductility ...

No, anything is inhernetly ductile in low cross sections because the strain is dependent on the cross section in a given extent of deformation. This is why the brass rod test is useless for example. I have knives with 66+ hrc edges that will readily take a set, this doesn't mean they are ductile.

t said in a different post that the edge literally exploded, why would you expect such a steel to form a stubburn burr?

Because they are both signs of weak steel. The edge broke apart at a thickness much higher than the burr. Makers use this fact to distort reality to customers all the time. Take a blade with a distal taper and very thin stock and bend it all over creation.

You would expect the burrs to be ragged and non-uniform independent of the steel. This has nothing to do with carbide tear out. Yes, some burrs may look a bit more formed than others but none will be well formed.

That is circular logic because it is how you are defining a burr. However a steel with the proper edge stability won't burr which is the point I was making.

...what you experienced on the Sebenza was only occuring at the very edge

No it was into the visible, past the micro and into the primary edge angle.

So the effect must propagate further inward from the edge, which is likely to bring the edge and the burr in a similar size regime.

Even at a similar thickness they won't react the same due to geometry, as I said, just try a physical demonstration with a much larger scale model. As well, a burr is formed of damaged and weakened steel and is far weaker than an actual edge of similar thickness.

Essentially you are saying here that there is no simple correlation because neither hardness nor composition will tell you how the steel was heat treated.

When you speak of steels in general you assume proper heat treatment. Carbide volume for example will increase wear resistance, D2 has a greater wear resistance than A2. This isn't the case if the heat treatment on D2 is blown of course, similar logic holds for burr formation.

I have to wonder how you come to declare that 59Rc is way too soft for a steel with as high a carbide volume as S90V with regards to burring?

Experimentation with sharpening along those lines. That level of carbide needs a higher hardness to produce crisp edges, as the grindability is very low and thus you need a much higher strength. S90V is way beyond it, even ATS-34 and similar steels are too soft at that hardness. Yes of course you need proper hardening as well. You could for example have it at 62/63 with the edge heavily microcracked and the edge would fracture burr heavily and be all but useless as a knife.

-Cliff

 

[Last Visible Canary]

Yes, it is a combination of the abrasive not being aggressive enough and the steel being too weak. This is why you see it worse on stones which are loaded, edges which are highly used, etc. . You can minimize it a great deal with a couple of passes right into a stone before sharpening to remove the weakened metal.



Carbide tear out can be a problem, but isn't always the critical issue, some of the high burr steels have little to no primary carbide. It is just due to a highly fatigued steel deforming rather than being abraded in most materials. This is why you see it readily for example if you press exceptionally hard when shaping an edge.
-Cliff

So, from this I gather that the type of burr you see that can be moved from side to side without being stripped away from the edge is made of fatigued or weakened steel.

But from this statement: "As well, a burr is formed of damaged and weakened steel and is far weaker than an actual edge of similar thickness." I'm unsure as to wether the weakened steel is created by the act of abrasion, or if it's inherent in the knife itself given its heat treatment and steel composition. It seems like your description of properly heat treated steels being burr resistant indicate that its inherent in the entire knife.

Is this a correct assessment of whats been said?

 

[Cliff Stamp]

So, from this I gather that the type of burr you see that can be moved from side to side without being stripped away from the edge is made of fatigued or weakened steel.

Yes. You can see this directly on some knives as the burr will be 1-2 mm in width and will visibly flop from one side to the other because as soon as the abrasive hits it, it moves out of the way like a blade of grass and isn't cut. Compare this for example to a stiff reed which will be cut under the same knife which just bends the grass.

I'm unsure as to wether the weakened steel is created by the act of abrasion, or if it's inherent in the knife itself given its heat treatment and steel composition.

Both. As a trivial example, take any freshly sharpened knife and steel it 5-10 times and you will have created a significant deformation burr that you can feel readily. When sharpening it is effected by the method of honing and the abrasive used. For example very heavy pressure and loaded abrasives will produce extensive deformation burrs.

Usually no matter how bad the steel you can compensate for it with enough skill and patience. I can sharpen the CRK&T AUS-4A blades for example to a very crisp edge which stays even push cutting fine paper to a very long time while slicing cardboard (reviews for details). In order to get that finish takes very fine pressure on the hone and very clean hones and a careful prep before sharpening and care not to oversharpen a side to the point of producing a heavy burr.

-Cliff