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Thread: Why is D2 so toothy?

  1. #1

    Why is D2 so toothy?

    Why does D2 take such a toothy edge? It's often the go-to for people cutting rope and whatnot, and I'd like to know the specifics of why.

    Does it perform like this regardless of how the steel is handled? And does the "toothiness" of it buff out?

  2. #2
    This is relevant to kitchens because I'm considering making a kitchen knife in D2.

  3. #3
    Delbert Ealy's Avatar
    Join Date
    Feb 2011
    Indian River, MI Just under The Bridge
    D2 is considered toothy because of the chromium carbides it contains. There are several elements added to steel that have an affinity for carbon, iron is one, but it is not a strong carbide former and will form carbides, but if there are other stronger carbide formers, they will take the carbon and not leave much for the iron to form carbides. Chromium, tungsten, molybdenum, and vanadium are all strong carbide formers. Of these chromium has several characteristics that the others do not have. When present in high enough concentrations, along with some carbon, it will produce stainless steel, and when enough chromium and carbon are present the chromium carbides will clump together. The chromium carbides themselves have a great affinity for each other, they like to get together and throw a party
    This is where the carbide clusters can cause a problem, since many of you are familiar with the micron scale, I will use that as an example; I have seen micrographs of chromium carbides in D2 that are 50 microns long and 25 microns thick. If you are using a .25 micron spray for the final edge or even a 1 micron spray, think of the huge difference in the fine edge you are trying to produce and the size of these carbides.
    The toothyness of D2 is caused by these carbides being torn out of the edge during the sharpening process. They are very hard, if I remember correctly they are about 70 Hrc, and they will tear out of the surrounding matrix rather than being worn down.
    There is a way to control these characteristics in D2 and that is to use CPM D2, this version of D2 is made by taking the finished alloy and while it is molten; spraying it out of a fine nozzel in to a cool vaccum, and that makes a very fine powder. That powder is then compressed and heated until it forms a single solid piece again. The temps here are pretty high, but not molten, and it gives a much finer distribution of carbides, so they can't get together and party.
    In other alloys it can be controlled by lowering the carbon, such as in AEB-L , or by adding a carbide former that has a stronger affinity for carbon than chromium does.

    Laminated metals specialist, Kitchen knife and gadget maker
    "Build a man a fire and he will be warm for a day, set a man on fire and he will be warm for the rest of his life"

  4. #4
    So will the carbides last on the edge a while? Say, longer than a vg-10 or cpm154 that are sharpened to a really toothy edge?

    Just like on cheap steel I put toothy edges on them(cause they cut better), I also put toothy edges on my VG-10 Gyuto when I am cutting up something crusty, like grilled chicken, or tough, like beef round. But the teeth break off fairly quickly. Does the naturally occurring large carbide structure improve edge retention on intentionally toothy edges like that?

  5. #5
    I used to cut a lot of rope and swiched from VG-10 to a D2 steel edc. The D2 won’t take an edge as fine as VG-10 (the edge sortof crumbles) but with a less acute, more toothy edge, does have a longer edge retention. It also take longer to resharpen.

  6. #6
    Senior Member
    Join Date
    Mar 2011
    Gothenburg, Sweden
    Honestly, try borrowing a SKD11 or D2 kitchen knife before you start down this road.
    I have the Yoshikane 240 and it resides mostly in it's box because, quite frankly, apart from having good edge retention i really do not care for the steel. Especially sharpening.

    I would take pretty much any decent carbon or VG10, AEB-L etc any day before the SKD11

    just my 2c

  7. #7
    just my 2 cents... i have 4 skd 11 knives from 4 different makers (and a couple of skd 12 knives too), and they all feel noticeably different... some i dont care for that much and some i love

  8. #8
    Hey, I'd love to borrow a knife in D2 or SKD11, but I don't know anyone who has any sharp knives, let alone one that "oddball". Sounds strange, but it's true. There's 8 million people here in DFW and I don't know any of them personally that know jack crap about knives. I'm sure they are here, but I don't know them!

  9. #9
    Senior Member
    deanb's Avatar
    Join Date
    Feb 2011
    Wow Delbert. Now THAT is what I call an explanation! Nice post.
    It is better to remain silent and be thought a fool than to open your mouth and remove all doubt.

  10. #10
    I have a SKD11&12 blades and i love both of them.I really don't get into toothy-nontoothy edges.Also i can't say i had any trouble sharpening my yoshikane,the only issue is it's so thick behind the edge and can be fixed with some thinning.

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