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Blade steels - what's wrong with improvement?

Discussion in 'General Knife Discussion' started by Comeuppance, Feb 26, 2014.

  1. me2

    me2

    Oct 11, 2003
    Its interesting you bring up that M2. Its still the best edge holding steel I've tested by a good margin. It beat everything from 1095 to S60V and S30V. As I've said in my testing threads, I test for high sharpness edge holding. That M2 held a treetopping edge longer than anything so far.
     
  2. me2

    me2

    Oct 11, 2003
    Any recollection of what happened? Did the O1 blade break, roll, chip, etc, or was it just a time lag thing?
     
  3. Big Chris

    Big Chris SAHD/Knifemaker Knifemaker / Craftsman / Service Provider

    Apr 1, 2010
    I really do not know any more than that. I would just be speculating to say this, but I bet that it just could not keep up with the M4 blades at the Championships in Atlanta.
    I thought about it while out plowing snow a while ago; Jose Diaz makes some competition choppers from 52100 and damascus. Not real sure if they are what his actual competition knife is made from but I am pretty sure I have seen a couple of videos about that as well.
     
  4. Shotgun

    Shotgun

    Feb 3, 2006
    Personally I think everyone is over thinking things. If buying the latest super steel is what you're into that's cool. Nothing wrong with that but there are reasons why I still use a SAK as an edc over my super steeled folders. It has better geometry and sharpens up easy. No matter how careful you are when working you WILL get edge damage eventually and it's much easier to sharpen that nick out of a SAK then it is s30v. I think people who focus on super steels and the latest engineered ball bearing system or whatever are overlooking the most important aspect, the geometry. I'm interested in the latest steels right up to where they're used in a knife with crappy edge and handle geometry. Then I pull my SAK out and cut stuff. :D
     
  5. Camber

    Camber

    Jul 13, 2011
    Pretty sure Jose uses M4 in his actual competition blade.

    I'm pretty sure Dan Keffeler told me 52100 is popular for practice blades as it is less fragile, less cost if it is damaged, and easier to grind back down to a thin edge. That conversation has been a while though, so I could have misunderstood or not remembered correctly.
     
  6. chiral.grolim

    chiral.grolim Universal Kydex Sheath Extension Knifemaker / Craftsman / Service Provider

    Dec 2, 2008
    Wow, this thread went far! Anyone mind if i back up a little?


    I eagerly await purchasing an English translation of Landes' "Messerklingen und Stahl" - is there one yet?

    Regarding the physics of cutting, i got these equations from Cliff Stamp:

    If Force against the blade is constant as a function of cut depth (i.e., K(h)=K), then W= (K/2)[tan(a)*h1^2 + tan(b)*h2^2 - tan(b)*h1^2]
    Here :
    W=work to make a cut to depth h2
    h1=height of edge bevel
    a=angle of edge (apex angle)
    b=angle above the edge (back-bevel angle)
    K=stiffness of material

    If h2 is actually smaller than h1, i.e. the material pulls away from the edge as it is cut by the apex, the force goes to zero before the edge bevel is even in the material:

    W= (K/2)*tan(a)*h2

    Now in both of these equations take note that apex angle is rendered via trigonometry to a ration of thickness:height and then multiplied by the height of either the cut or the edge itself such that the effect of the angle is reduced to THICKNESS. And this makes sense because "angle" is simply a convenient way of describing the space between two lines, i.e. thickness. THIS is why thickness is the most important factor per physics/math.

    Now Verhoeven's cites Leonard's "Complete Guide to Sharpening" for recommending 15-dps (30-inclusive) for ALL steel knives @ 60Rc for ANY use requiring greater strength than shaving, including everything from cutting veggies to chopping wood, stating that below 10-dps such knives experience "rapid edge deterioration ... in normal kitchen use." Verhoeven goes on to mention that inclusive angles of 10-15 degrees are so thin behind the apex than the act of sharpening can produce sufficient stress to bend and fracture the edge and that this issue becomes MORE evident in "Japanese blades containing a central high carbon strip with HRC values in the 64-65 range... extremely brittle." He tests this, finding that burr-formation is more pronounced when sharpening blades to 10-dps resulting in a rougher and thicker edge vs sharpening to 15-dps :eek: Imagine, greater angle (15-dps) but thinner and smoother apex (0.3-0.5 um), i.e. better for shaving and the like.


    Now that is simply in regard to edge-angle for 60 Rc blades of low carbide content in uses from simple shaving to heavy use.


    Could someone indicate what hardness ranges and type of cutting (i.e. what range of media and under what stresses) Landes was working with when he described his 3 classes (type I, II, III) and their stable edge-angles (degrees per side: 8-12, 12-20, 20-30)? I am reading folks advocating the fine-grained low-carbide for heavy chopping at nominal hardness (because the lack of carbides and fine grains allow for increased toughness) or for extremely light use (shaving only, or maybe ophthalmic surgery) at very thin angles and very clean apices and much higher hardness (where lack of carbides won't impede apex formation). Cutting rope, cardboard, meat, vegetables, etc. we know that a very clean, polished apex is less efficient than a coarse edge, chopping wood you need a thicker angle (15-dps) to provide the needed strength, so.... where is the advantage of AEB-L and 52100 other than shaving or surgery? Again, I'm not trying to dismiss these steels, but I want to know what makes them better...
     
  7. Camber

    Camber

    Jul 13, 2011
    Not disagreeing at all, but if angle is a convenient way of measuring space between two lines, then 20 degrees inclusive is thinner than 30 degrees inclusive. Regardless of whether this "thinness" has more of an impact with the primary behind the apex angle or not (and I agree that it probably does) a thinner apex is not going to reduce cutting efficiency...quite the contrary since it will be thinner...so if you can have one, why not use it?

    As I asked earlier, if thickness behind the edge is all that matters why not use 20dps or 25dps apex angles on very thin edges? My guess is because those dps increase the thickness too much, so why draw the line at 15dps if the steel can handle lower.

    So he's saying below 10dps there is more rapid edge deterioration? Roman only goes down to 8dps in his recommendations and he also recommends at least 60RC (more on this in a minute)

    Addressing the issue of edge stressing during sharpening...do you know how he was sharpening? Along those same lines, if advancements could be made in sharpening 10dps might be more viable.



    I can't provide hardly any specifics here as I have not read his book. I don't read German :(. I guarantee Cliff could tell you or as you can ask Roman on hypefreeblades.

    I did pull this quote from Roman off of hypefreeblade:
    With regard to Roman's recommeded RC's. Joe Mandt has noted several times that Roman told him for most normal cutlery applications you should not be letting blades leave your shop at less than 60RC.
     
    Last edited: Mar 3, 2014
  8. bluntcut

    bluntcut KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Apr 28, 2012
    By example/data. I spent over an hour of continuous cardboard cutting with a 3" 52100 paring knife. It started out with newsprint pushing edge. Cut about 600 meters of linear cardboard, where thickness range from 1mm to 6mm.

    http://www.bladeforums.com/forums/s...r-12-different-steels?p=13259645#post13259645

    Pardon an analogy. Steel-plated vest can stop a bullet (within reasonable scenarios). Kevlar vest can also be effective against a bullet. In knife world - it's carbide vs strong-transitional-matrix option. Sure, it would be cool to have both in one, e.g nano-alloy-carbide-uniform-distribution + fine grain .
     
  9. Big Chris

    Big Chris SAHD/Knifemaker Knifemaker / Craftsman / Service Provider

    Apr 1, 2010
    That makes sense that they would make practice blades. Dan told me that when an M4 knife goes it does not just chip a little spot on the edge they usually blow a rather large chunk out of the edge. I know that 5/16" M4 is not overly cheap, and then it takes a couple belts to make it look like a knife.
     
  10. Camber

    Camber

    Jul 13, 2011
    Ok, seems like I was remembering it correctly then, because that's what I was referring to by less fragile...that the M4 when it does finally goes, goes big essentially. Still, I always hate to reference spoken conversations as there's no way to go back and make sure I have it right.

    And yeah, I cant' imagine M4 is cheap!
     
  11. chiral.grolim

    chiral.grolim Universal Kydex Sheath Extension Knifemaker / Craftsman / Service Provider

    Dec 2, 2008
    The reason to not go much above 15-dps is because the thickness behind the apex gets higher than is easily remedied by lowering a single back-bevel (primary). However, if that back-bevel is quite short, transitioning into a lower-angle bevel - i.e. if you convex the edge, then your 20-25 dps edge-bevel is SO short that it doesn't have a chance to thicken the edge much to be detrimental (per the equations provided). Again, the importance of the micro-bevel cannot be overestimated. Keep in mind that a steel apex in these razor blades is ~0.3 - 0.5um in diameter... i.e. the apex is actually FLAT (no angle, a tangent to the apex is perpendicular to the force vector) but it is so thin that the angle isn't important until you need something thinner. And you absolutely CAN shave with those high angles.

    Why not go lower than 15-dps if you can? I would! But ONLY if you CAN do so consistently and still have the requisite strength and toughness for the task...

    Verhoeven's paper describes a bunch of different techniques to use. The most effective for achieving very thin angles was hand-sharpening on wide-face, high-grit waterstones, followed by gentle stropping with loaded leather.

    Yeah, if you could sharpen consistently at a fine enough grit-size, you could partly avoid this issue of insufficient strength to endure sharpening. And technology on improving sharpening technique continues to evolve with mixed success. Straight-razors worked to eliminate the inconsistency by being designed to have users lay the blade flat against the hone so that the edge was at the desired angle and the spine stabilized that angle. Modern razors solved the issue by simply being disposable ;)

    But this doesn't solve the issue of strength during actual use. Shaving (and ophthalmic surgery) doesn't require significant strength or toughness beyond achieving the cleanest possible apex prior to use and re-establishing it after use. What about in the kitchen? Most kitchen tasks seem to prefer a micro-serrated edge to achieve better penetration, the key is to keep those teeth very small and strong enough to not tear out or crumble on contact with a cutting-board. Outside of the kitchen, the edge needs to be strong enough to endure the occasional twist and wear-resistant enough to cut abrasive materials. Presumably harder would be better for all of these tasks, but there are other concerns. And again, most manufacturers aren't giving use blades harder than 60 Rc. Why not? Cost of production?

    Would we the consumers benefit more from razor-steels with increased hardness or wear-resistant steels with increasingly fine carbide aggregates? The latter seems to be the direction that the industry is taking...
     
  12. ericvar101

    ericvar101

    738
    Feb 24, 2012
    Add me to the blade geometry advocates, I used to think that S30V didn't hold a razor edge long, until I got a Sebenza with the hollow grind that makes the cutting edge very thin. I have used it several times and its still shave sharp. So far, I prefer it to my PM2 in M390 with a flat grind. (which is a great slicer by the way), but not as good as my CRK, becoming a fan of the hollow grind and the Sebenza.
     
  13. Camber

    Camber

    Jul 13, 2011
    You bring up a lot of good points (for instance, 10dps is not needed for shaving...that's very true) and a lot of things I need to look into further. My final thoughts on all of this though:
    1. Increasing the apex angle too much on a thin edge can transfer torque into the primary I believe, and thus put it at significant risk...however I don't know how much of this is dependent on a true secondary vs a microbevel.
    2. I would suspect that a lot of Verhoeven's problems may have come from the stropping and the issues it presents, but that's not another can of worms I don't care to open in this thread.

    3. Acting like 10dps is only acceptable for shaving or eye surgery is a bit dramatic. Ever measured the edge angle on a factory Mora (which come in one of two high edge stability steels [12c27 or 1095] that are far from optimally heat treated? Common measurements seem to range from 20 to 25 inclusive . I just measured the two I own,
    Standard .100 stock is at 23inclusive
    Robust .128 stock (a relatively new product for Mora) is at 27ish inclusive.
    While there are issues with Moras (as would be expected considering the mass heat treat to less than ideal conditions for the steel) 1000's of moras have survived cutting on a much rougher order than you are describing. My own .100 stock, 22 degrees inclusive edge, has done just fine cutting hard seasoned wood and doing light batonning.

    Along those same lines wood chisels often come in less than 25 degree angle edges and they obviously survive cutting the wood just fine.
     
  14. Shotgun

    Shotgun

    Feb 3, 2006
    This is one of the bigger misconceptions regarding "slicing ability" IMO. The problem is that you really do have to take into account other geometries going on and not just edge angle and thickness right behind the edge. Curved edges cut differently, how the handle is constructed will determine how well the force from your hand is transferred, the angle of the handle to the blade makes a difference...and so on and so forth. Any "test" out there is anecdotal at best when they don't take all of the variables into account. They're certainly not scientific by any stretch. I believe the only reason these two factors get talked about the most is that they're easier to quantify.

    I have a 5 dollar kiwi brand kitchen knife of unknown stainless steel and unknown HT. Hands down the best kitchen knife I've owned. I haven't sharpened it in over 2 years and it gets thrown in the dishwasher and then thrown in a drawer full of other knives. It's still a wicked slicer. I don't begrudge good steel and if I have the option I'll buy it, but only after the geometry is sorted out. ;)
     
  15. chiral.grolim

    chiral.grolim Universal Kydex Sheath Extension Knifemaker / Craftsman / Service Provider

    Dec 2, 2008
    1. Any torque is present already at the apex, you WANT to transfer that to the metal behind it to prevent twisting/fracturing out the apex.
    2. Verhoeven's experiments on sharpening are available online, just google "verhoeven knife edge". STEELING was a problem, as were motorized sharpeners, as both of these put too much stress on the apex, and even sharpening by hand without good wrist control to keep the angle consistent (the second most common problem when sharpening, first being sharpening at the actual apex). Stropping he noted to be the BEST technique to refine a poor edge. He knew what he was doing ;)
    3. Yes, it is a bit dramatic, but I keep reading people criticize 15-dps as obtuse when it is an angle at which you can accomplish EVERYTHING from chopping to shaving and not encounter issues with edge-fragility in use or in sharpening, it is the recommended angle for cutting implements whether they be made of 52100 or S110V. If you have to put the bevel below 15-dps and bring the hardness over 61 Rc in order to give 52100 an edge over S110V in a cutting task, it seems that you are limiting the scope of BOTH steels. If you are optimizing for a very particular task, GREAT! But for general utility.... :confused: The same would be true in reverse. If you need to bring the hardness below 59 Rc and the angle >25-dps (and thicker than 0.010") to give S90V the edge over 52100 in some cutting task, WTF?

    Regarding the Mora's or Opinels for that matter, I have worked with both and other "zero-edge" knives and quickly found that for my 'general utility' purposes they lose their apices quite quickly. Mora's are 12-15 DPS from the factory and are soft. I can carve soft wood with them, cut soft flesh with them, open letters... But in seasoned oak, the edge rolls; cutting cardboard and carpet, the edge is either squashing or rolling or wearing away. So what? Just put a true 15-dps microbevel on it and keep going. The steel is soft and not very wear-resistant so while it doesn't hold up all that well, it re-sharpens easily with a few swipes. If it were harder, it wouldn't squash or roll (a strength issue) but it might fracture out... unless it were thicker, where again 15-DPS might make all the difference. Batonning, as long as the apex doesn't experience too much twisting in the wood then stock-thickness gives the strength, hence axes being that same 15-DPS but maintain that angle further back from the apex, thickening to provide support. Wood chisels are similar - you can get chisels at lower angles than 30 degrees but need to be more aware of their limitations.

    All this talk of edge-angles and performance cutting makes me appreciate thin knives all the more - be they high or low carbide, they are easy to adapt at the apex for whatever purpose you need them (provided you don't need the strength of a thick spine).


    I really look forward to reading Landes' work because I'd like to see where these superiorities really fall. Previous work suggests that 60Rc knives should be 15-DPS. If Landes criticizes high-carbide steels at angles below that but sees no disadvantage above it, well then they must be REALLY bad at very low thickness because previous work criticized LOW carbide steels there. But if Landes is simply showing that for highly specialized cutlery where 15-dps is obtuse or 0.005" is too thick, tasks where edge-twisting is minimized/eliminated, where abrasion is unlikely but hard impact is very likely (?), where a highly-polished fine edge is key... What are all the qualifications to make these high-carbide steels poor performers?

    In general utility, how important is edge-strength from Rc hardness vs edge toughness? Wear-resistance vs apex brittleness (as that is the assumed issue with high-carbide steels)?
    If 52100 is made hard enough to prevent deformation but also brittle failure of the apex, the question should be, "How thin can we make it before such failures occur?" Make it that thin, then test it for wear-resistance.
    If your 52100 blade wears too quickly, what can be done to improve that? Harder won't give it vanadium carbides and might make it too brittle... more brittle than the vanadium carbides?
    If the higher carbide 52100 is less brittle than the harder 52100 (i.e. harder than necessary to prevent deformation) and can reach the same thin geometry needed to provide strength to the apex, it is superior. If it needs to be thicker, how much thicker? How much performance is lost in exchange for increased wear-resistance? Can that be mitigated by a coarser finish (i.e. performance of slightly thicker high-carbide blade is higher than performance of low-carbide blade at fine finish)? What about the thinner low-carbide blade at coarse finish - better or worse than high carbide blade?

    So many questions, so many mitigating factors. What I really challenge is the assertion that high-carbide steels are so limited in their superiority with regard to application, especially when the most common applications being discussed go well beyond shaving your face. Now whether or not they are worth the price increase for the supposed performance increase is entirely separate. Who cares?? This is about innovation. Are they or are they not helpful innovations for a wide variety of tasks? If not, drop them and go back to 52100 (Bussekin have stuck with SR101 and INFI in blades of all size, only dabbling in other steels). BUT IF they retain strength and toughness while adding wear-resistance for general use applications and beyond :thumbup: Again, whether we want razor-blades with longer wear-life or high-wear blades with lower fragility at thin cross-sections, powder-metallurgy is working in our favor. The narrower we need to make the qualifications that keep PM steels inferior, the better off we all are with the continued innovation.
     
  16. Bo T

    Bo T

    Feb 12, 2011
    Good points, chiral.grolim..
     
  17. singularity35

    singularity35

    Mar 1, 2010
    I've always aslked what you can't cut with 15dps edges on EDC knives?
     
  18. thombrogan

    thombrogan

    Nov 16, 2002
    Are you sure the powder steel process isn't too keep carbides from clumping up too much with the need for a very long soaking temperature? :confused:

    Why use an edge at all? Just push or swing harder.
     
  19. chiral.grolim

    chiral.grolim Universal Kydex Sheath Extension Knifemaker / Craftsman / Service Provider

    Dec 2, 2008
    Why are carbide-formers added at all? - To increase tool wear-life.
    Why use the PM-process? Because it allows for increased carbide-level without large carbide aggregation that compromises tool strength and toughness. Keep in mind that a vanadium carbide is simply V-C which is smaller than iron carbide (Fe3-C), but the affinity of vanadium to form carbides is so strong that the molecules tend to aggregate. If you can reduce that aggregation sufficiently, you could actually form a high-carbide steel that is stronger&tougher than low-carbide steel! But that is technically impossible. Instead of abandoning all hope, powder-metallurgy works toward that ideal - steel that is stronger and tougher and more wear-resistant for a variety of applications. THAT is innovation. It has not reached that point yet, but it is getting there. In Charpy tests, CPM-20CV has impact toughness in the range of tool steels like O1 rather than 440C or D2! Now that is not at the 0.5 micron level, but it is improvement.

    LOL. Remember that ANY steel edge is actually FLAT at the apex such that if you try cutting a thin enough material, you'll always end up just squashing the material instead. Does it take less effort to cut at 10-dps than at 15-dps? Of course... IF the apex has the strength to endure the stress of cutting and also IF you can actually achieve that 10-dps to begin with. You may need to limit that low geometry to special steels at high hardness and used in very specific low-stress tasks, OR you can just throw a 15-DPS microbevel on the apex and have at it! In the end, remember, the 15-DPS apex may be THINNER than the rolled/crumbled 10-DPS apex. THAT is the finding of Verhoeven and Leonard, and there are SEM images to prove it. So using your 10-DPS blade will require you to push/swing harder than a slightly more obtuse apex angle. Neat, huh?
     
  20. thombrogan

    thombrogan

    Nov 16, 2002
    Didn't ask that. Also, the steels of which I'm critical have large amounts of vanadium versus large amounts of Wolfram or moderate amounts of niobium and they also usually have very high ( > 1.25%) levels of carbon, too. Most of them are intended for use as die-cutters, extruders, and punches, not pocketknives or kitchen knife.

    So it does exactly what I guessed it was supposed to do and doesn't more than that. It is an improvement and it is valid, but that still leaves us at square, well, not square one, but square 'there are better carbide formers for knife steels than vanadium and better alloys for knives than the higher carbon higher vanadium ones being hyped like the second coming - even steels that predate their existence by decades.'

    Cool paradox. Will test it out on the Opinel this week. Thanks!
     

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