High vanadium knives don't need diamond stones...

N

NeedItCheaper

Joined
Jun 17, 2012
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I've seen a few threads about this over the years. Something's off with thinking diamond stones are needed to get hair-popping, butter-smooth sharpness. I've been buying stones like crazy lately and brought my Benchmade Bugout (S30V) to a razors edge. All with Chosera stones and an leather strop (no compound). I shaved part of my leg to a butter-smooth point, which I didn't think possible with those stones. The theory, supposedly states vanadium is simply ripped out of the edge creating a jagged edge. This might be true on some level, but my edge isn't dulling any faster than it normally does when sharpening on Lansky's diamond stones. It feels like that whole idea is designed simply to convince people to buy diamond stones or to scare enthusiasts from ever buying any knife with high vanadium (3-4%). Instead, stick with; 1095, A2, O1, etc...



Thoughts?
 
I don't consider S30V to be "high" vanadium. at least not compared to S90V, 15V, M4, etc. more like a medium to low vanadium. and it's not all about percent of carbides but their size too. S30V has relatively small carbides compared to the others

my S110V knives just wear down my traditional stones without putting much of an edge on them. my diamond stones will put an edge on them in seconds
 
Backyard said:
I don't consider S30V to be "high" vanadium. at least not compared to S90V, 15V, M4, etc. more like a medium to low vanadium. and it's not all about percent of carbides but their size too. S30V has relatively small carbides compared to the others

my S110V knives just wear down my traditional stones without putting much of an edge on them. my diamond stones will put an edge on them in seconds
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^That bolded excerpt is what it comes down to, as to why diamonds are preferred for such steels.

The vanadium carbides in the steel are harder - sometimes much, much harder - than the grit in non-diamond/cbn stones. That brings two issues: (1) It'll glaze and prematurely wear the stones and (2) it'll limit how far an edge can be taken at higher finish, and how fast it can be done.

Regarding the Lansky mention: One of the best lessons I ever had in sharpening S30V, came in trying to reprofile an S30V blade using the standard XC and Coarse hones (aluminum oxide) in the Lansky set. Six hours later and two ruined hones later (both dished & glazed in the ONE job), I still couldn't finish that job until I switched to the one Lansky diamond hone I had (a medium). Ever since then, I can't help but notice how much easier it is to get the job done with a diamond hone on steels like these. The differences in how well they work are amplified in the use of smaller hones, especially. That's when it becomes obvious there's more to them than just marketing hype.
 
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Chuck_Nunface said:
3-4% V is one thing, 9-10% is another. Diamond is recommended for high V content steels. Mike Christy has a good video on s110v and carbide tear out on Youtube.
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The Science of Sharp guy has suggested that carbide tear out is a myth, and he has SEM images to back it up. OTOH, there is definitely a difference when sharpening vanadium carbides with diamonds/cbn vs softer abrasives. Dr. Kraichuk from Knife Grinders (RIP) did cut testing comparisons and he found that an all-diamond/cbn process results in superior edge retention with wear resistant steels.
 
In the world of high V steel, grinding troubles only start to get noticed at about 2%-3% and most stones can keep up with that. At 4% Vanadium the grinding curve jumps abruptly and pretty much skyrockets as makers add more and more Vanadium and Tungsten. Naniwa Chosera sharpening Benchmade S30V? Sure, BM runs their S30V a bit softer and the Chosera are high quality stones but still just hardly make the cut because they are still aluminum oxide. If the quality was any lower they would struggle, grab some King stones and you would see the difference. Shapton Glass is another high quality waterstone that can tackle some of the lower level super steels but overall its just not worth the effort compared to a diamond stone. Even the easier to sharpen M390 comes out so much better on the diamond plates when compared to my Shapton Glass. As for the whole carbide tear out thing, never believed it, the carbides being so much harder simply Glaze the sharpening stone which makes it start to polish the edge. So, if you found you got a better polish than the stones usually produce then you were experiencing Glazing from the carbides in the steel grinding away at the abrasive in the stone.

In the end you are only fighting the steel when using a stone that hardly makes the cut. Even if you don't notice it the fact remains that the steel is winning the fight, not the stone.
 
Evidence seems to point towards carbides fracturing rather than tearing out. But with high concentrations of them you start to get an odd effect where the wear-resistant carbide sort of forms a penumbra behind it that's shielded from abrasion. Compared to diamond, which cleanly cuts the carbides, it's not ideal, but will still produce an edge at least.
 
3D Anvil said:
The Science of Sharp guy has suggested that carbide tear out is a myth, and he has SEM images to back it up. OTOH, there is definitely a difference when sharpening vanadium carbides with diamonds/cbn vs softer abrasives. Dr. Kraichuk from Knife Grinders (RIP) did cut testing comparisons and he found that an all-diamond/cbn process results in superior edge retention with wear resistant steels.
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I think this depends on the carbides in question. Some seem to bond to the steel better than others. For instance, I made a blade from T15 once ( higher percentage of tungsten carbides) and had definite carbide tearout when using non-superabrasive hones. I could feel them grittily rolling on the hone surface on a Spyderco ceramic and see the pits where they used to be under the scope. I haven't seen that on Vanadium carbides though.
 
eKretz said:
I think this depends on the carbides in question. Some seem to bond to the steel better than others. For instance, I made a blade from T15 once ( higher percentage of tungsten carbides) and had definite carbide tearout when using non-superabrasive hones. I could feel them grittily rolling on the hone surface on a Spyderco ceramic and see the pits where they used to be under the scope. I haven't seen that on Vanadium carbides though.
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Tungsten in steel usually does not form carbides, I thought.
 
eKretz said:
I believe that is incorrect, but may be very dependent on the level of tungsten and other alloying elements present. Here's a good read I had bookmarked some time ago that talks about some interesting variables including carbide formation:

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That specific article doesn't deal much with it when you look at what it's really saying, but doing some more digging (Larrin has a good article over on knifesteelnerds about tungsten content) it does appear as though it can form in meaningful quantities in certain steels. Just the levels that are found in *more common* knife steels usually are more for grain refinement than for direct carbide formation.
 
FortyTwoBlades said:
That specific article doesn't deal much with it when you look at what it's really saying, but doing some more digging (Larrin has a good article over on knifesteelnerds about tungsten content) it does appear as though it can form in meaningful quantities in certain steels. Just the levels that are found in *more common* knife steels usually are more for grain refinement than for direct carbide formation.
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There is a section in there that mentions specific percentage of carbide formation in certain alloys - but it's admittedly a wall of text with only a small percentage that is about carbides.
 
Yeah if I remember correctly the issue with that section is that it's not talking about what kind of differentiated carbides so it's kind of useless for this context. It may be a certain percentage carbide, but of that percentage, how much of it is what kind of specific carbide? It didn't say. I'm saying this off the top of my head, though, so perhaps I merely missed such information when reviewing the mentions.
 
It's not that tungsten doesn't form carbides in some steels, it is that when chromium is present in ~4% or more it forms softer W6C carbides instead of WC carbides. In low alloy steels, 1.2562 for example very hard WC carbides are produced. The amount of tungsten doesn't seem to matter as long as enough chromium is present even something like T1 tool steel with ~18% tungsten doesn't have harder WC carbides.
 
My old Buck 301 pocketknife has 425M steel. It is so hard that my Arkansas stones won't even scratch it. I had to use diamonds stones to sharpen it. And my 65Rc file just skates right off of it.
 
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eKretz said:
I believe that is incorrect, but may be very dependent on the level of tungsten and other alloying elements present. Here's a good read I had bookmarked some time ago that talks about some interesting variables including carbide formation:

Click to expand...
knifesteelnerds.com

Carbide Types in Knife Steels - Knife Steel Nerds

A description of the major carbide types in steels, how they form, why they are there, and how carbides contribute to different properties of steel.
knifesteelnerds.com knifesteelnerds.com

Carbide Hardness Chart

I made a Carbide Hardness Chart for quick reference, useful for folks that are curious about which steels would be more wear resistant than others and what stones to use. I thought it would be fun for folks that are really geeked out to be on the same page and also a fun thread to discuss...
www.bladeforums.com www.bladeforums.com

Some good resources
 
000Robert said:
My old Buck 301 pocketknife has 425M steel. It is so hard that my Arkansas stones won't even scratch it. I had to use diamonds stones to sharpen it. And my 65HC file just skates right off of it.
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425M is essentially similar to 420HC in its makeup, with no significant hard carbide content at all. Not enough extra carbon in the steel to form hard carbides with other elements in it, like chromium. And just a tiny bit of vanadium (0.1%) for grain refinement. I have an older 4-dot Buck 112 in 425M, and it's essentially indistinguishable from Buck's 420HC in terms of how it sharpens up. I sharpen it on a Norton Fine India (aluminum oxide) most of the time, with occasional touchups on a medium Spyderco ceramic. Either stone type handles it easily and both leave a great finish on the edge, which is why I use those in particular. They're my favorites for that knife and for most of my others in 420HC and similar steels.

Sometimes, natural stones can be kind of marginal with stainless steels like these. But other synthetic stones of most any type should handle them without issue.
 
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