What steel takes the keenest edge?

[caldwelr]

Well, the steels that I've had the best luck with getting great edges on are lionsteels D2, 1095, AUS 8a, M390/CTS 204P, and CTS-XHP. The one that I've been able to get the absolute sharpest, however, is CPM M4 (on the Spyderco Gayle Bradley). Despite its high hardness, and that it takes a second longer to get an edge, it ultimately ends up with a better edge than any other steel I've tried. The worst luck I've had has been S90V. I can get it sharp, but not as sharp as other steels.

 

[5thShock]

Something soft enough to take a torn tin can edge from a relatively coarse file. The little teeth on that kind of edge seem to start cutting just before they touch you.

 

[Bob6794]

Outside of going very technical and scientifical I think a lot depends on the sharpener and what steel they work well with. For me I can put a pretty good edge on the steel they use in swiss army knives, opinels XC90, AUS8, 01, and 440A used in Rough Riders.

 

[chiral.grolim]

Sandvik's protocol/chart for hardening 13C26 with approximate carbide-volume % included: http://www.smt.sandvik.com/en/mater.../strip-steel/sandvik-13c26-razor-blade-steel/

Correct me then if I'm wrong you're saying, "It's the indian and not the arrow" in this discussion. You're saying then that blade material is not the determining factor in getting "keenest" knife edge and that given a competent knife sharpener, he can get any blade material to the same degree of keenest as any other regardless of the material?

Yes... and no. The harder the material, the keener the edge can be made, but achieving that edge becomes trickier, requiring better technique and tools to accomplish the task.

Decent diamond, SiC, and CBN abrasives will cut through martensite and most carbides used in steel with relative ease, shaping the very carbides themselves... IF the carbides in the abrasive are sufficiently sharp and used with the appropriate level of force. This is exactly how we refinish the edges of ceramic diatome blades - >90% carbide and able to achieve edges ~100X keener than ANY steel due to the increased hardness.

What you don't want is large, dull abrasive carbides smashing into the carbides in the matrix - that will just loosen them from their binder and result in carbide tear-out. Carbide tear-out is good if you are removing a lot of material, but it is bad if you are trying to form a fine, polished, keen apex. For that, you want small, sharp abrasive carbides cutting through those in the steel matrix. This is sculpting on the microscopic level.

With finer carbides well distributed, it makes less difference if a carbide is jostled loose because the void is small and easy to polish over. With a lower percentage of carbides, there is less to worry about jostling loose, and with softer carbides they are easier to cut so less likely to be jostled in the first place. So low-carbide steels are great for producing inexpensive razor-blades - fewer carbides means easier to manufacture and get suitably sharp. But for blades needing to be MUCH sharper than a face-razor, you need a harder material from the outset = high (pure) carbide. Also low-carbide has poor wear-resistance in cutting certain materials, so high-carbide is preferable there. The low-carbide canNOT get any sharper than the high-carbide, but it CAN get suitably sharp with greater ease.

Finally, someone mentioned that it might be impossible to polish these high-carbide materials... I submit this:
http://www.bladeforums.com/forums/showthread.php/1277926-Polishing-S110V
Also this:
http://www.bladeforums.com/forums/s...om-in-Z-A11-Steel-(CPM-10V)-Full-Review/page3

K390 blade, 64 Rc, polished by Ondrej Sabol (his images, I'm just reposting them from the linked thread):

 

[Rey HRH]

Yes... and no. The harder the material, the keener the edge can be made, but achieving that edge becomes trickier, requiring better technique and tools to accomplish the task.

Decent diamond, SiC, and CBN abrasives will cut through martensite and most carbides used in steel with relative ease, shaping the very carbides themselves... IF the carbides in the abrasive are sufficiently sharp and used with the appropriate level of force. This is exactly how we refinish the edges of ceramic diatome blades - >90% carbide and able to achieve edges ~100X keener than ANY steel due to the increased hardness.

What you don't want is large, dull abrasive carbides smashing into the carbides in the matrix - that will just loosen them from their binder and result in carbide tear-out. Carbide tear-out is good if you are removing a lot of material, but it is bad if you are trying to form a fine, polished, keen apex. For that, you want small, sharp abrasive carbides cutting through those in the steel matrix. This is sculpting on the microscopic level.

With finer carbides well distributed, it makes less difference if a carbide is jostled loose because the void is small and easy to polish over. With a lower percentage of carbides, there is less to worry about jostling loose, and with softer carbides they are easier to cut so less likely to be jostled in the first place. So low-carbide steels are great for producing inexpensive razor-blades - fewer carbides means easier to manufacture and get suitably sharp. But for blades needing to be MUCH sharper than a face-razor, you need a harder material from the outset = high (pure) carbide. Also low-carbide has poor wear-resistance in cutting certain materials, so high-carbide is preferable there. The low-carbide canNOT get any sharper than the high-carbide, but it CAN get suitably sharp with greater ease.

Thank you for your post which DOES relate to the point of this thread that a blade material may be sharpened to a keener edge compared to another blade material. And that the ability of a blade to be keen corresponds with its hardness. What you're adding is there is a corresponding requirement in terms of technique and sharpening material associated with getting that harder material to it's keenest possible state. You further specify that you want small, sharp abrasive carbides in the sharpening material in order to achieve the keenest edge. I hope I understand you correctly.

If so, please allow me pose a related question to triangulate: That same sharpening material with the small sharp abrasive carbides that you need for the hard blade material, you can also use the same to sharpen softer material to their keenest possible state, right? And maybe the downside is just overkill or less efficient but efficiency isn't a stated target anyway, just the keenest.

 

[chiral.grolim]

...I hope I understand you correctly..... That same sharpening material with the small sharp abrasive carbides that you need for the hard blade material, you can also use the same to sharpen softer material to their keenest possible state, right? And maybe the downside is just overkill or less efficient but efficiency isn't a stated target anyway, just the keenest.

:thumbup: For softer materials, harder/sharper abrasives are not required. You don't need to use diamond-hones to sharpen softer low-carbide steels or even to polish wood, but you certainly can use them. Why wouldn't you? Because just like steel, some abrasives are more expensive than others, but they load-up and require cleaning just as often. Just because diamond is capable of honing an edge of pure carbide to an edge 100X sharper than any steel could ever achieve doesn't mean the user is capable of making that happen, nor that such an edge would be of much benefit to the user. Most folk get by with soft kitchen blades honed on a grooved steel (round file), this can produce a very keen edge. Others might demand ion plasma finishing
http://www.shinmaywa.co.jp/pbp/english/products/ionplasma.html

http://www.materials360online.com/newsDetails/10740

http://en.wikipedia.org/wiki/Abrasive#Choice_of_abrasive
http://www.uama.org/Abrasives101/101Types.html

 

[Rey HRH]

Great explanations, chiral.gromlin Thank you.

If I had a Wicked Edge then maybe I'd be interested in getting that ion plasma finishing attachment.

 

[me2]

What kind of probes are those?

 

[samuraistuart]

What kind of probes are those?

Alien Anal Probes! Sorry.....couldn't help myself.

 

[singularity35]

Cliff's cohorts strike again...

 

[chiral.grolim]

What kind of probes are those?

STM. I included a link above the image.

There are companies that use the same process for sharpening razor blades and needles ... but if you're expecting an apex that fine to last through many applications, you're kidding yourself!

 

[me2]

Yea, those needles seem like one use only type stuff. When I was into that sort of thing, Focused Ion Beam machining was the latest, which was mentioned inthe articles. What is the radius on the diatome blades you mentioned? Someone mentioned it, but I remember seeing a steel blade honed down to about 30 nm. Somewhere here I have an article on obsidian being flaked to 3nm.

 

[jeeper9010]

Well, the steels that I've had the best luck with getting great edges on are lionsteels D2, 1095, AUS 8a, M390/CTS 204P, and CTS-XHP. The one that I've been able to get the absolute sharpest, however, is CPM M4 (on the Spyderco Gayle Bradley). Despite its high hardness, and that it takes a second longer to get an edge, it ultimately ends up with a better edge than any other steel I've tried. The worst luck I've had has been S90V. I can get it sharp, but not as sharp as other steels.

I have no experience with s90v but my own experience echos yours. m390 is fantastically sharp, but the m4 I can bring to a by my hands, an unbelievable sharpness. M4 is something to behold.

 

[afishhunter]

Edge angle would be a significant variable.
In production knives, the "lowly" Opinel comes with and takes the keenest edge. Logical, since it is designed to be a slicer, not an axe or splitting wedge.

 

[chiral.grolim]

Yea, those needles seem like one use only type stuff. When I was into that sort of thing, Focused Ion Beam machining was the latest, which was mentioned inthe articles. What is the radius on the diatome blades you mentioned? Someone mentioned it, but I remember seeing a steel blade honed down to about 30 nm. Somewhere here I have an article on obsidian being flaked to 3nm.

Needles would be single use based on application anyway. But steel razor blades lack the strength in the binder-material (martensite) to hold such fine edges through much of anything, even when honed as fine as 30 nm. That said, 30 nm is impressive honing. Normally razor blades are honed down to 0.2 - 0.4 microns for use, so that is 10x thinner than normal already :thumbup:

The carbide diatome blades I've seen were certified to have a radius of curvature <21 angstroms (2 nm, hence the "100X" reference) and what is really crazy is that they keep that edge through hundreds of cuts (albeit on some very delicate material), something I've never seen steel achieve, the binder is just too soft. Using focused ions to "bead-blast" a steel edge to supreme sharpness is a waste of time unless you only need it to hold that geometry once, or unless you've already coated the edge with carbide to provide more strength/stability to the apex - steel itself just doesn't get hard enough to hold edges that keen, although increasing the carbide-content of the matrix may help...

 

[chiral.grolim]

Edge angle would be a significant variable.
In production knives, the "lowly" Opinel comes with and takes the keenest edge. Logical, since it is designed to be a slicer, not an axe or splitting wedge.

I disagree with the bolded part. Those ultra-fine diatome blades with keener edges than any steel is capable of achieving ... sharpened to 15-20 DPS (usually it's 30-40 inclusive, single bevel). Steel, any steel, cannot hold a keen edge at a lower angle than that without dependence upon a microbevel or microconvexity that increases the edge-angle near the apex. Opinels perform well NOT because of edge-angle but because of edge thickness, i.e. how thin the blade is behind that 15-20 dps bevel.

 

[me2]

If I'm not mistaken, aren't the diatome blades used in a cutting fixture? If so, they are not subject to the same kinds of stresses the steel blade of a knife will see in hand held cutting. Any idea of the forces used in the diatome cuts? Any information on the compressive and tensile strengths of the ceramics/carbide used for the blades?

 

[chiral.grolim]

If I'm not mistaken, aren't the diatome blades used in a cutting fixture? If so, they are not subject to the same kinds of stresses the steel blade of a knife will see in hand held cutting. Any idea of the forces used in the diatome cuts? Any information on the compressive and tensile strengths of the ceramics/carbide used for the blades?

Analysis of the forces is beyond my meager knowledge, but we're not talking about the "blade" being keen, we're talking about the apex and the first few microns behind it - THAT is what makes a blade "keen", everything behind that is just a "fixture" to hold the apex as it completes the cut. There are steel microtome blades made to the same angle and thickness, used for the same purpose, but they cannot achieve the same level of "keen" or keep it through the same use. I am comparing similar blades for similar purposes subjected to exactly the same stresses. These are THE blades to examine when discussing "keen" beyond a subjective standpoint. If a steel blade designed for the utmost keen edge cannot hold that keen edge in even the most delicate cutting, do you really think it can hold that edge in uses subject to greater stresses? Not a chance.

I'm not saying that a carbide edge would be a good choice for an axe or machete - on that scale the stresses are so much higher that the greatly reduced toughness of these blades would quickly take them out of use, they'd be stupid-expensive to produce in the first place, and those tasks do not require such a level of keen in use. We do use carbide or carbide-coated blades in drill-bits and lathes and saws, etc. We don't use them much in hand-held knives because the fracture toughness against lateral stress is so much lower (much less binder). While the keen steel edge will fold and flatten, the blade will just flex; the keen carbide edge will hold its shape but the blade will crack and fail. We use steel because of its low cost, greatly increased toughness, and its ability to take and hold a suitably keen edge that can be easily restored.

My apologies for derailing the thread from the OP's question - which steel for you takes the keenest edge, i.e. does steel type seem to impact your ability to sharpen it? Most folk I know choose cheap, soft kitchen steels because they sharpen so easily.

 

[DeadboxHero]

Just tried SR101 on swamp rat rodent 6. Amazing.
Keenest edge so far. How do the Gurus feel about this steel? Is it better, same, or worse then say infi or CPM 10v?

 

[VermontEdge]

Out of my whole collection I would say VG10 and A2 get the sharpest.