ZDP-189 and Cowry-X: Overrated or Super Steel?

Discussion in 'General Knife Discussion' started by Larrin, Dec 30, 2019.

  1. ace

    ace Gold Member Gold Member

    May 3, 2000
    There is no argument that lamination is used for these to increase toughness of the blades, this is what the website says. The point being that the steel itself at this hardness is not tough. The main point being that you cannot or at least should not refute the findings of a well done and explained study based on personal experience. These are not equivalent, one is a well setup and researched paper on steel properties and the other is anecdotal, personal account of particular knife use that contradicts a multitude of opposite personal accounts.
  2. chiral.grolim

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

    Dec 2, 2008
    That is excellent! Are most of those tool-steel blades for saws, chisels, wood planers...?

    There are two aspects i am interested in, at least some of which you may be able to satisfy:
    1) personal experience utilizing these different high-Rc steels - what behaviors have you observed comparing similar edge geometries, specifically with reference to edge-degradation and edge retention as well as sharpening, and finally corrosion resistance. Questions for this would include:
    a) how are you using the blades? What type of cutting? In what environments (specifically is there any reason to be concerned about corrosion)?
    b) what edge geometries are you aiming for?
    c) what sort of edge-finish do you give the blades (grit, etc.)?

    2) Testing the edges in a consistent and relatively controlled fashion - establishing similar edge geometries and subjecting them to the same types of stress with the intention of causing at least some measureable amount of edge damage, doesn't need to be totally destructive, just enough to cause a "brittle" steel to chip noticeably. Then testing the steel (finished to a similar polish on each to minimize the impact of corrosive elements) - is ZDP any more or less rust-prone than these others? Which can take a patina well vs not?

    I am always interested in comparisons of high-RC blades because the increased strength allows for thinner usable apex diameters than is achievable with softer (60 Rc) materials - it is why we employ glass and sintered carbide blades for fine cutting. It is also worth noting that saws, lathes, and other machining blades often employ high-Rc tool steel if not sintered carbide for the actual cutting edges despite the known "brittleness" of the material because, in such use, a strong/hard very fine edge that breaks when subjected to extreme loads is FAR preferable to a softer edge than loses shape much sooner under lesser loads even if it is "tougher" i.e. doesn't fracture when stressed. "Tough" only matters when your use exceeds the strength of the blade - a stronger edge doesn't need to be as "tough" in the first place. This is why we prefer 60Rc edges to 50Rc for most cutting tasks and why steel makers are always pushing the boundary of strength and carbide content against the barrier of toughness - we want a knife that is as strong as possible and as wear-resistant as possible while retaining sufficient toughness for the task at hand. "Toughness" is what we may be able to sacrifice to improve performance on the other side.
    That doesn't mean I don't love me some INFI and well-done 3V! That is the flip-side. But even 3V gives away toughness to achieve what it does - crucible didn't need it to be as tough as S7. Compared to S7, CPM-3V is "brittle". ;)
  3. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    I agree in the case of an applied load. However, when an impact is applied ("high strain rate") the behavior is different, and it looks like impact toughness testing instead. Bending and lateral stresses can be relatively high in high hardness materials but with an impact the behavior is different.
    chiral.grolim likes this.
  4. chiral.grolim

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

    Dec 2, 2008
    "Tough" is a relative term. The assertion being made by a plethora of users and manufacturers is that ZDP189 is tough enough for its intended use and its other qualities - namely high Rc and wear-resistance - make it excellent for knife use. Nothing in Larrin's testing refutes that. Larrin did not compare ZDP to other high-Rc, high-carbide steels. He did not compare it to other high-Rc Japanese steels like White 1 and Super Blue which are also commonly used in laminated blades.
    What Larrin presented is that ZDP-189 has high hardness (known) and explained ways in which it may achieve that (excellent information) and how that makes it unique, and ALSO how that makes it less resistant to corrosion than other steels with high chromium content. Larrin's own final conclusion in his article is:
    That's all - because it was advertised as "stainless" and really doesn't perform at the level of steels normally considered "stainless" in Larrin's tests. His results are not surprising, which is good :thumbsup: but they also aren't the end. His testing was very limited (only one surface finish, not compared to steels at similar Rc). It would be great if Larrin could report on the corrosion resistance of the high-Rc CPM-154 as well as a high Rc tool steel to give a good comparison what happened with the ZDP and try different surface finishes... But Larrin is not made of money: https://www.patreon.com/Knifesteelnerds

    I do take issues with one particular point in Larrin's article:
    The word "significantly" in an academic environment indicates that a statistical test for significance was employed to compare multiple measurements taken from replicate samples of each group. Larrin hasn't presented raw data indicating that there were multiple samples run on each steel being compared at that hardness, which makes me doubt the accuracy of the statement. But perhaps he intended "significant" in a colloquial sense, i.e. that the toughness of one is noticeably higher than the other in actual use... but that is ALSO not evident in the article - a few users calling a steel "chippy" in use vs some saying that it has performed fine is not enough to make any such call. So for me, this part of the article is not supported by fact, it is anecdotal. Larrin can prove me wrong on that. If he has raw data on a bunch of specimens subjected to Charpy tests, i will gladly put in the time to plug them into my stat software and produce comparison graphs detailing statistical comparisons.

    I really really like that he went through the effort of suggesting alternatives to ZDP189 which may provide better performance in various aspects - heck, running the HT's for a higher CPM-154 and then trying its toughness is great :thumbsup: As mentioned previously, I like to see folk push for higher and higher Rc hardness and wear-resistance in knife steels while working to maintain a sufficient level of toughness for usability in knife tasks. I see ZDP as trying to do that. For me, that steel goes in this article and with this chart: https://knifesteelnerds.com/2019/12...ed-steels-maxamet-rex-121-and-more-explained/

    Great work, Larrin!!! And I still like ZDP189 :)
  5. Larrin

    Larrin Gold Member Gold Member

    Jan 17, 2004
    I already tested CPM-154 at lower hardness with the same finish. Using the high hardness heat treatment would improve corrosion resistance compared with the heat treatment I already used. As far as other finishes, etc. I am certainly not opposed to testing other finishes, or seeing how much the corrosion resistance could be improved. However, the finish used is consistent with the previous tests to compare relative material performance, not to see how much the corrosion resistance of ZDP-189 could be improved. For example, perhaps a mirror finished, passivated specimen of ZDP-189 could pass a distilled water test without rusting. I cannot say, but it wasn't the question I was attempting to answer. The "standard" test of a 400 grit finish with distilled water has done well for differentiating whether a steel exhibits "stainless" performance and so I like it. Then of course I have used the 1% saltwater test for differentiating between steels that passed the straight water test.
    insta9ves, ace and chiral.grolim like this.
  6. Sergeua

    Sergeua Gold Member Gold Member

    May 1, 2016
    You gotta give the piece of zdp steel to @DeadboxHero and we might have proper testing :)
    Btw my zdp endura is .63 mm bte and my m4 mantra is .43mm. So the endura is not that thin to begin with to be chipping all over the place.
  7. DeadboxHero

    DeadboxHero Triple B Handmade, Custom Knives Knifemaker / Craftsman / Service Provider

    Mar 22, 2014
    Facts are what they are, It doesn't have alot of Chromium in soultion and its not very tough because it has 30% carbide volume at high hardness.

    Yet, because of these draw backs it can get crazy hard, takes a sexy aggressive edge, sharpens like a champ on softer abrasive stones and is not as reactive as carbon tool steels.

    Everything is a trade off.

    I love the stuff but it's really really expensive and not really available at all.

    So I'll use other steel.

    But if I had a chance to use zdp at a good price I'd be all over it.

    I own two gyutos in zdp189. Very lovely edge.

    WValtakis and Sergeua like this.
  8. brownshoe

    brownshoe I support this site with my MIND

    Sep 6, 2002
    Personal experience is just as emperical as science, facts are facts.

    If a conclusion based upon limited testing can be easily reversed by multiple users, with years of use, with different makers, different heat teats i.e., more data points, then the conclusion is incorrect and the testing not really relevant to an actual knife. Some makers have trouble with ZDP some do not, this is good evidence supporting a common fact about knives...heat treat, finish, edge geometry and experience make a difference in performance.

    Matt Conable of William Henry is an expert cutler who has been making knives a very long time and has revolutionized the high end knife game in the domestic and international market. If ZDP didn't perform, he wouldn't use it.
  9. ace

    ace Gold Member Gold Member

    May 3, 2000
    Where did anyone say that zdp-189 doesn't perform in a small folder? Where did anyone say that Matt Conable doesn't know how to make knives. Where in the article did you see a knife being tested? You are arguing with conclusions of steel testing and comparison to other steels based on your experience with a particular knife design, small folder. You don't know what the heat treat is, you didn't say what the geometry is, you didn't tell us what you cut or how you cut it, no mention of finish or the environment you use the knife in or how you sharpen. All you said was I've been using zdp-189 in small folders for 20 years and it doesn't chip or rust, therefore the conclusion of the steel testing must be wrong.
    insta9ves likes this.
  10. T.L.E. Sharp

    T.L.E. Sharp Oatmeal Pecan is better than Chocolate-chip. Platinum Member

    Jun 30, 2016
    Just to sum up this thread and @Larrin's article: ZDP-189 ain't stainless but is otherwise the single greatest steel ever created and all knives should be made of it henceforth.

    I think that pretty well sums it up. Great job everyone.
    Larrin and WValtakis like this.
  11. jpm2


    Nov 19, 2014
    The home made M3 knives are made from Starret power hacksaw blades. M35/M42/T42 knives are made from 80's/90's era US made parting tools with 5/8/10% cobalt.
    One of the M2 knives (66hrc) is from Bluntcut. The rest are production Benchmades and Spydercos.

    The knife steel I judge all others by is the little T42 I made in '85, specifically for separating 3-phase motor leads in an industrial environment.
    This involves cutting through cambic/rubber/plastic tape, sometimes 1/2 inch thick and into nuts/bolts used to fasten the leads. The tape needs to be pryed away from the connection as its being cut, that means prying against the bolts. Sometimes the tape is no longer pliable, it's hard and brittle from years of heat.
    Other destructive uses are scraping corroded wire and electrical connectors, ringing sealtite conduit, reaming steel tubing cutting steel shields & braids, scraping metal ID tags, basically anything needed when another tool is not available, and sometimes when there are other tools available but because a knife just works better.

    Sharpening angle is not exact because I've always free handed on bench stones, but over the years muscle memory has somewhat locked in. I have taken the trouble to randomly measure some of my edges. The presentation side is about 14 degrees, the other side about 17, usually +/- 1 degree, with some convex. For some reason this is just how they turn out unless I make a conscience effort to change it.

    Up till recently, finishing was always on a fine Eze-Lap diamond plate unless experimenting. This seems to give the best all around utility edge for me and a little better edge life for my hss blades. I do keep a couple knives with 1 micron diamond paste finish for specialty purposes.

    There's no steel that has held up with my use without damage, but some suffer less than others.
    The ZDP I have does excellent when making straight cuts, even when the edge gets into other steel like nuts and bolts, but starts to falter more than HSS as the edge gets stressed off center. If I'm going to scrape or pry against other hard metals, I have to go easy.

    I feel sharpening anything is mostly a non issue with diamond abrasives. All steels touch up quickly and easily, if that's all they need, and can take a good while if damaged or blunted.

    I don't intentionally oil any of my blades, just wipe them down after use, or when I think to, sometime with a fresh water rinse, but they do pick up oils in the work environment. The flip side is, they also pick who knows what else, some stuff highly corrosive.
    Haven't had any corrosion problems with ZDP, just turns kinda dull grey and splotchy, no pitting.
    M2 and M3 get a light dusting at times but mostly wipe off with no pitting.
    M4 does well unless it's sweat soaked in my pocket all day. I've experienced pin hole pitting with it.
    M35/42 & T42 seem to be very corrosion resistant for non stainless. My little T42 lives in a leather scabbard in my fly vest on 1-2 week fishing trips, wet most of the time with very little staining. There's no telling how many hundreds of trout it has processed over the years, maybe the fish oil helps.

    I'm not equiped to do any kind of controlled testing like others here, just using different blades for the same/similar tasks. For work, I always go back to hss for its overall performance and minimal edge maintenance.

    My observations hold no weight when it comes to conclusions, and don't expect them to, but I always like reading other experiences whether from just use or formal testing. When it differs from mine, I try to learn and understand why.

    I would like to fill in a lot of gaps here, but already made this reply too long. To summerize, ZDP is a great steel I like for reasons already stated here, holds an edge much longer than most steels, sharpens well without super abrasives, has good edge stability for most normal uses, high hardness, reasonably stainless for me... but prefer mid to high hardness hss over it for MY work use.
    chiral.grolim likes this.

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