Higher RC steels hold lower edge angles better?

Steel130

Steel130

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I have been wondering if the some of these newer steels, CTS-XHP, M390, CPM-M4, ZDP-189 ect. are some of the best for holding low edge angles? For example, I had my M390 Paramilitary 2 reprofiled to 12* secondary bevel, and then I put on a 30* micro bevel. It has been holding up great even in some harder tasks, even coming in direct contact with metal ( accident ). Are some of these newer steels able to do this better because they can get a higher rockwell hardness thus increasing lateral strength?

I have also been trying to figure out why edges that are thinner behind the edge are said to hold their edges longer, is this because there is less force required to push through the material, thus decreasing the pounds of force being pushed into the edge apex? I am also assuming carbide distribution, and grain refinement can also play a part in both of my questions.
 
M390 is really nice stuff. M-4 is also incredible. At a higher rc I found that m-4 at 63 rc and 12 degree edge will continue slicing until my arms and hands are cramping. That's badass in my book.
 
Steel130 said:
I have also been trying to figure out why edges that are thinner behind the edge are said to hold their edges longer, is this because there is less force required to push through the material, thus decreasing the pounds of force being pushed into the edge apex? I am also assuming carbide distribution, and grain refinement can also play a part in both of my questions.
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Yes. As the apex wears the width of the apex geometry will depend on the blade geometry and the thinner that geometry is the better is will continue to cut as it wears. A narrow edge angle reaches an arbitrary apex width less rapidly than a broader edge angle would. Carbides will play a role in terms of wear resistance, but given the question we can discard that variable and presume that we're talking about identical steel and heat treatment with only a variation in geometry.
 
Thanks fellas. This topic seems like one that isn't discussed much.
 
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Yes, the better the steel, the thinner the blade and the finer the angle can be to perform a desired cutting task. It really is all about the steel (and, of course, heat treatment). It is possible to take a Chinese-made Ikea kitchen knife and thin it down and put a 10 degree angle on it. But it would quickly be obvious how poorly the knife would perform.

I've seen this topic discussed several times in the knife-making sections of BF but not very often here. Japanese kitchen cutlery performs so well -- and there has been a large migration of chefs from German-style to Japanese-style knives in the cooking world -- for example, because the blades are so thin and hard with very acute angles; they just cut better. They are able to get that sort of performance out of their knives by using exceptional steel that can take such a geometry without compromising on edge-retention and strength. That's why you see steels like the Hitachi super steels being used in those knives.

One would think that with the advent of modern steels, we'd be seeing a change in knife designs universally. But that hasn't been the case. I, for one, don't understand the new tactical folders that use modern, high-wearing super steels but haven't changed the blade design, at all, to milk the increased performance out of these steels. Why build the blades so thick? It increases weight, and it's not like you can baton with a framelock anyway, so I really can't think of a reason why a folder should be 1/4" thick.
 
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Someone did baton with SRM710, framelock but thin. It was posted here in BF too, but forgot which thread.

Sorry, can't help it ;). I do agree though, just reprofiled my EL08, the bevel is now about 2mm wide :D but it'll cut better.
 
It took me a while to digest & indigest the lengthy thread in spydercoforumes linked by razoredgeknives. Cliff went a great depth discussed on many 'whats' and 'empericals', without going much into 'whys' therefore not much correlation to this thread.

Thinking steel RC from an analogous perspective of ceramic, spyder silk and plastic fibers. Ceramic has super high hardness but total lack of ductility, i.e. mainly high compression strength but low in stretch, lateral, torsion, displacement, etc. properties. Plastic is opposite from ceramic. spyder silk strikes balanced on properites except low plastic flow (displacement). Each type can be thin and strong depend on its targeted purposes.

Clean steel+alloy molecules bonds & grains(molecular structured growth boundaries) bonds dictate the minimal sustainable/practical thinness of an edge for its intended uses. Choose a high RC HT - in the optimal range - to serves sustain type of impact. Lower RC for impulse type of impact (chopping). Wear resistant aspect is just a time variable.

Adding to FortyTwoBlades and others mentioned about geometry. Catra results are emperical data points supported thin-behind-edge yielded higher endge retention (for certain cutting/dulling material) - why so? ahh the 'why' is always more tricky than the 'what'.

For me - thicker behind the edge dull faster because
1. I suspect material compression+twist+stretch (from wedging) increased the hardness & tensile of material.
2. For cutting near the material edge (think wood whittling), forced steering to keep the blade from exiting the material asserted extra lateral force lead to premature edge roll.
3. Impact with material may not be continuous, so impulse impacts occured which is exponentially more damaging than sustain (slice) impact.
4. Inadverdent blade twist & steer when you put so much into cutting force, especially at and near exiting point.
5. :confused: and curious just like you.
 
Makes sense. From what I could tell on the Spyderco thread. After sifting through all of Cliffs scientific talk. It seemed he was basically saying what others have before. That alot of people won't notice the wear resistance advantage of a steel until they take it to a really low level of sharpness. I mean I can tell at my job the difference between how much cutting I can do with S30V, CPM154 ,CTS-XHP, and M390 for example. It also seems that since either rolling or chipping is going to be the two main reasons your edge dulls, finding the balance in a steel is the trick. What Cliff is talking about confuses me some, but if I understand correctly, he is saying that overall edge geometry, blade geometry, and edge finish can all be factors in wear resistance between two steels?
 
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Chris "Anagarika";11718577 said:
Someone did baton with SRM710, framelock but thin. It was posted here in BF too, but forgot which thread.

Sorry, can't help it ;). I do agree though, just reprofiled my EL08, the bevel is now about 2mm wide :D but it'll cut better.
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STR did a test a while back and found that no framelock could hold even 68 pounds of free weight suspended from the blade. Linerlocks fared a little better at around 100 pounds. The force you subject a lock to by batonning through hardwood is immense. A framelock will always fail if it's subjected to that kind of force, guaranteed. I see a lot of posts occasionally, where people claim total confidence in their (insert name of expensive status folder here) to do anything, up to and including batonning. I have yet to see the videos of them batonning. I'd wager that the lack of such videos is due to the inherent knowledge of the owners that this will be the result (and the manufacturer will say, "You did what?" when they submit the knife for warranty repair):

Emerson+HD7.jpg
 
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Steel130 said:
Makes sense. From what I could tell on the Spyderco thread. After sifting through all of Cliffs scientific talk. It seemed he was basically saying what others have before. That alot of people won't notice the wear resistance advantage of a steel until they take it to a really low level of sharpness. I mean I can tell at my job the difference between how much cutting I can do with S30V, CPM154 ,CTS-XHP, and M390 for example. It also seems that since either rolling or chipping is going to be the two main reasons your edge dulls, finding the balance in a steel is the trick. What Cliff is talking about confuses me some, but if I understand correctly, he is saying that overall edge geometry, blade geometry, and edge finish can all be factors in wear resistance between two steels?
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Buck Knives wised up to thinner blade & edge geometries, based on CATRA testing. Even with seemingly 'ordinary' steel (420HC), they found that decreasing the factory edge angle to a thinner grind resulted in better edge retention. They adopted their "Edge2000" grind as a result, which specs the factory edge angle at 13-16°/side (26-32° inclusive). I think even Case modified their edge grinds in post-2000 years (this is my perception; I have a lot of those knives). Their edges seemed to get a bit thinner as well, also using 420HC at lower RC than Buck's, and still cut correspondingly better with little or no loss in durability. There's a noticeable 'step up' in cutting performance at or below 30° inclusive, I've noticed. Cutting takes a lot less downward force then, due to the thinner geometry, and I think that helps preserve the edge at thinner angles. I've even noticed this after using a cheap, imported, grocery-store paring knife that I re-bevelled to a very thin edge (and assumed it would fold fast). When using it as a steak knife on a stoneware plate, I noticed there's ZERO need to lean into a cut (blade goes through a steak like it's warm butter), and therefore no reason to drive the edge into the plate underneath the meat. Contrast that with a seemingly 'stronger' and thicker edge grind, which doesn't slice worth a darn, except under much greater force. Better cutting efficiency can alter the way the blade gets used, and therefore the forces subjected to it, and that alone can make a difference in how long the edge will last.


David
 
Mag,

Spyderco Tuff is frame lock & MBC rated. Let's discuss this on different thread. Sorry, I took this Off Topic.
 
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To be honest, MBC doesn't mean anything to me because its not an industry standard; it's Spyderco's own standard. Not to knock Spydercos; I own several and they are excellent. But baton-worthy? You know how I do things, Chris. There are a lot of wild claims made by knife makers, and even wilder claims made by the fans. If someone will post of vid of themselves batonning through a cord of cured hard wood with their Spyderco Tuff, with a before and after comparison of the lock and mechanical operation, that would settle it. If there's no damage, then I will retract my statement. The edge will suffer; that is a given and not a problem. But if there is damage -- even slight damage -- to the opening mechanism, the lockup, and the general operation of the knife, well...

EDIT: And I don't mean baton through one or two pieces of soft wood. There are a few vids of that (with about half of them failures anyway), which don't prove anything. I might be able to lightly baton through one or two pieces of soft wood with my Ikea kitchen knives with relatively little damage. I mean pound through knots in hardwood. Do a whole cord. Really subject that lock to stress.
 
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For holding low edge angles, steels can roughly be grouped into categories. Steels like D2, 440C, ATS-34, etc, would need to have the most obtuse edges, as they have a coarser structure with a lot of chromium carbide or other carbides. The next group would be the powder/particle metallurgy steels, like CPM D2, M390, S30V, CPM S90V, etc. These also have a lot of carbides, but generally speaking, they are smaller and more evenly distributed than the first group. These steels will handle a lower edge angle at higher hardness than the first group.

If you want to get extreme, you need to go to high hardness on steels with low carbide volume. This group of steels is stuff like 1095, 52100, AEB-L, 13C26, 1084, 50100B, 15N20, etc. The steels have low carbide volumes and are capable of very high hardness, in the case of 1095, 1084, 52100, and 50100B, they can reach 66 HRc or above.

Higher hardness prevents the edge from rolling, allowing a lower edge angle before the edge rolls or collapses. Lower carbide volume prevents the edge from becoming too brittle at lower angles. The real advantage of the lower carbide, higher hardness steels becomes more apparent at what most would consider ridiculous edge angles, like razor blade edge angles of 5 to 7 degrees per side (dps).

With regard to carbide volume and individual carbide size, here is an analogy I've used before. Think of trying to roll clay into a thin sheet. Then mix into the clay a bag of marbles and a bag of sand. Which one can be rolled the thinnest? Well, you can roll them both equally thin if you're willing to crush the marbles. You can take something like 440C to a nice thin edge, if you can cut and break the rather large chromium carbidess that are present. However, as with the clay, get too thin and some of the marbles will just fall out or be torn out rather than be cut or crushed. You need a little carbide, but too much, or too big, will ruin things. For some steels like the very high wear resistant, high carbide content CPM steels, imagine mixing in so much sand there is barely enough clay to hold things together at a thin edge. The carbides aren't big and clumpy like the first group or clay with marbles. This is why I grouped these steels in the middle. They are better than the first group, but can have a little too much carbide to go to the super thin angles the last group can take. This is all academic for most people, since the edge angles commonly used (15-25 dps) are supported no problem by all all three groups. Few knife nuts sharpen knives down to less than 10 dps. I have 2 I've been testing in the kitchen; so far no trouble. These are at 7-8 dps with a 10 dps microbevel.
 
Me2,

Depending on the microbevel size, the 7 dps bevel with 10 dps micro likely would not be affected by the carbide size, if my understanding of your analogy is correct. (?)
 
Thats the idea more or less. A very sharp edge is less than 1 micron wide. The question here is how fast does it thicken beyond that very edge. The faster it thickens (higher edge angle) the larger the carbides it can hold and the more there can be. However, cutting ability is decreased as the edge angle limit becomes greater. Most people dont use their knives with a small enough edge angle to notice. 20 dps is kind of the standard. Most knives see more than just cutting use, which would destroy very thin edges in short order.

Its interesting to note that in Richard Burton's "The Book of the Sword", he recommends such angles for 2ft long swords, and I've seen experienced axe users recommend even lower edge angles for dedicated felling axes.
 
me2 said:
This is all academic for most people, since the edge angles commonly used (15-25 dps) are supported no problem by all all three groups. Few knife nuts sharpen knives down to less than 10 dps. I have 2 I've been testing in the kitchen; so far no trouble. These are at 7-8 dps with a 10 dps microbevel.
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I'm very glad you added this part. I've personally found that 10 dps is about as low as I like to go and that is alot lower than most. I've also found no problems with 10 dps and up. Sometimes these forum threads get into theory and unreal examples. The best advise I ever got was go very thin with my edges and behind the edge as well. If it chips or rolls then put a little thicker edge on it. keep doing this until you get an edge that doesn't deform easily. We all use and cut with a knife differently and a 10 dps edge may work for one of us wile the same knife may need a thicker edge to work for someone else. Just as an example a few years ago I was in a arguement on the forums about thin edges. I put a very shallow convex edge on a SAK,and cut wire. Those wires like you find holding toys in the package. The angle was very low and with a controled cut I could easily cut the wire with no damage to the edge. However if I tried to cut the wire like you would normaly do to get a toy out of the package the edge would be easily damaged. SAKs have fairly soft steel and they can hold a realy thin edge if you are careful enough. And even at something like 12dps you don't even have to be very careful with them.
 
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Excellent explanation me2. As db stated above, and Murray Carter, take your edge as low as it can handle the task at hand. If it rolls or chips, take it thicker. M390 has been doing fine at 12* per side except for direct metal contact :o.
 
Ultimately the lower carbide steels will withstand a lower edge angle than the higher ones. However, I only know of a hand full of people willing to run 10 to 15 degree inclusive (5-10/side) edges, so the practical limit for most people is well above this. I would like to try for myself, but that would require customs or homemade knives. Given the high influence of edge angle for CATRA testing, one could make a good case that 1095 has the potential to far outperform something like D2. However, we all know CATRA isnt perfect, at least IMO.
 
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