1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Carbide tear-out questions

Discussion in 'Maintenance, Tinkering & Embellishment' started by wvdavidr, Sep 10, 2018.

  1. wvdavidr

    wvdavidr

    348
    Mar 21, 2007
    I have read numerous comments on hard steels having vanadium carbide tear-out during sharpening. I had never heard of this until recently. Are these carbides unmelted steel, pieces added later that aren't melted, or formed during the heat treating? I always assumed that blades are made from homogenous steel.
     
    bucketstove likes this.
  2. Wowbagger

    Wowbagger

    Sep 20, 2015
    I'm no big expert and owe BladeForums for most all I know but yes; formed during heat treat. They are extremely fine (hopefully . . . if the heat treat is done right).
    Homogenous steel is mild steel (not heat treatable). Google some microscope metallurgical photos of high vanadium carbide steel. It looks like a jigsaw puzzle or a mosaic.
     
  3. Wowbagger

    Wowbagger

    Sep 20, 2015
    I couldn't find S110V quickly but here are some other similar examples :
    Optical-micrograph-showing-the-multiphase-microstructure-PF-polygonal-ferrite-AF.png
    1204234113-Bohler_N690_edge_2.jpg
     
  4. Vanadium & chromium carbides are actually first formed in the manufacture of the alloy, before it's ever heat-treated. Subsequent heat treat can change their properties somewhat (size, hardness to some small degree), but they exist in the steel from the time of it's manufacture, formed at temperatures up around 1000°C.

    Different manufacturing processes, like the powder metal (PM) process, can make a difference in how large they get and how uniformly distributed ('desegregated') they are in the manufactured steel. PM-process steels produce carbides that are typically pretty small, usually 2 - 4 microns or smaller, and they're more uniformly distributed throughout the steel, which helps it remain strong and tough overall. Non-PM processes would tend to allow the carbides to cluster together in large masses, the effect called 'carbide segregation', during manufacture. In such cases, the carbides may end up being 50 microns or larger in size. So, they'd still be there, but at potentially much larger size, which makes grinding such steels more difficult, and also can negatively alter steel properties such as toughness (resistance to breakage). As an example, the difference in ease of grinding or sharpening can be seen in comparing conventionally-manufactured 'ingot' D2 with it's huge chromium carbides (making it harder to grind easily), versus CPM-D2 and it's much smaller chromium carbides (easier grinding/machining), made by the powder-metal process.
     
    Last edited: Sep 11, 2018
    W. Anderson, steff27 and MolokaiRider like this.
  5. David Martin

    David Martin Gold Member Gold Member

    Apr 7, 2008
    I cannot recall the members name but he is educated in this area and has access to SEM and has taken very detailed photos of high
    vanadium steels sharpened at various stages. His conclusions are that vanadium carbide tear out does not occur. DM
     
  6. David Martin

    David Martin Gold Member Gold Member

    Apr 7, 2008
    PoorUserName likes this.
  7. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    It's something that seemingly can occur in some rare circumstances, but is extremely unlikely in most of the situations it's commonly thought to occur in.
     
    willc and David Martin like this.
  8. David Martin

    David Martin Gold Member Gold Member

    Apr 7, 2008
    Most of us do not sharpen the vanadium steels fine enough for the grit to begin touching the fine carbides. DM
     
  9. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    Not just that, but even when doing so, it doesn't generally result in carbide tearout, just blunting of the carbides.
     
  10. eKretz

    eKretz

    749
    Aug 30, 2009
    I think Todd would disagree that your statement is equivalent to his. I think a more correct statement would be that carbide tear-out did not occur under the exact parameters of his test.

    And I have seen it happen under certain circumstances quite frequently - namely at very high hardness levels with HSS. How much this happens and how severe it is will be pretty dependent on the circumstances - steel type, hardness and abrasive used.
     
    bucketstove and Mo2 like this.
  11. This is what I wonder about too. It seems, since a steel's toughness and hardness directly impact how easily it might break or be damaged, it could also impact how easily (or not) the carbides might be torn out of the matrix. In other words, with the matrix steel being variably tough or strong, according to specific manufacture and heat treat, it may in some cases behave like the binders in sharpening stones, having more or less tendency to break down and 'release' the carbides, as a stone releases grit from the binder.

    I've read at least one reference mentioning this type of wear (carbide tear-out) in tungsten carbide tools specifically, and how the 'matrix' material used in them (cobalt, usually) can be engineered differently in terms of it's toughness and strength, and therefore it's ability to hold the carbide grains themselves. And in the context of those tools, the size of the carbides themselves are mentioned as making a difference too, with smaller carbides less-prone to being pulled out.

    It just seems to me, there are probably too many variables to say definitively if it actually happens or not. Or put another way, proving that it NEVER happens, I think, would be exceptionally hard, with so many possible variables affecting it.
     
    Last edited: Sep 11, 2018
    Chris "Anagarika" and Mo2 like this.
  12. eKretz

    eKretz

    749
    Aug 30, 2009
    Oh it definitely DOES happen. I posted a series of microscope photos some time ago in a "super-steel" stropping thread showing a progression on a HSS blade where it was very clearly evident they were being torn out on lower grit Shapton stones. At higher grit they stayed put but were prominently exposed. @HeavyHanded will probably remember that thread.
     
    Chris "Anagarika" likes this.
  13. I do remember seeing at least one such thread, with a lot of input from HH. I'm inclined to believe it can happen, myself.
     
    Chris "Anagarika" likes this.
  14. ToddS

    ToddS

    271
    Jan 15, 2015
    It seems that some people think of carbides at analogous to smooth stones in cement. We have all seen broken concrete with those stones "pulled out" leaving a hemispherical void. The problem with this analogy is that the carbides in steel are actually securely bonded to the surrounding iron.

    Carbides are more brittle than the surrounding iron, so they will crack if they are subjected to the bending that a thin apex or burr experiences during sharpening.

    These images (S30V) show the spheroidal vanadium carbides (typically 1-2 microns in diameter)near the edge.

    The first one shows a couple of vanadium carbides right in the apex, thinned to a keen edge with no evidence that "tear out" can occur.

    [​IMG]

    The second image shows the vanadium carbides around a micro-chip with some cracking and one is possibly separating from the surrounding matrix. This is the closest I have seen to "tear out."

    [​IMG]
     
  15. FortyTwoBlades

    FortyTwoBlades Baryonyx walkeri Dealer / Materials Provider

    Mar 8, 2008
    It's a bit more like a bunch of pebbles mixed with warm chewing gum. :p
     
    Diemaker likes this.
  16. HeavyHanded

    HeavyHanded

    Jun 4, 2010
    Great pics!

    I am convinced it does happen to some extent tho more likely the larger the carbides as with D2 (it looks like several have blown out in the second pic above). But...far more common is the carbides blunting/glazing due to abrasive wear instead of abrasive shaping.

    Either way it can be minimized or eliminated with good practices.
     
  17. eKretz

    eKretz

    749
    Aug 30, 2009
    I think that the amount of sharpening on the lower hardness abrasives is a large determining factor too. Heavy bevel setting for a long while might tend to remove them. Of course the steel type and hardness (high hardness is more brittle, would tend to shed them easier). And the included angle of the blade as well. If one were to just kiss the edge after diamond sharpening I'm sure it would be just fine. I also think it's pretty self-evident that quite a few people are reporting worse edge longevity when some of these steels are sharpened on non-diamond abrasives. Size and variety of carbides is another factor - the ones in my images were about 4-5 microns, and I think they're tungsten carbides. An aside: many people use the term "tear-out" but it could well be just carbide fracture/breakage. Either way, the net result seems the same. Voids with no carbide and a ragged edge. The fine edge gets wiped out and the edge radius becomes larger until the carbides still in place are reached. The edge may still continue to cut quite well with a "sawing" motion, but push cutting is degraded.
     
    Last edited: Sep 12, 2018
    Chris "Anagarika" likes this.
  18. bucketstove

    bucketstove

    Sep 23, 2014
    Hi,
    This is what you want to read

    https://knifesteelnerds.com/2018/08/27/what-is-edge-stability/
    [​IMG]
    [​IMG]
    [​IMG]


    https://knifesteelnerds.com/wp-content/uploads/2018/08/schneiden.pdf
    [​IMG]
     
    steff27 and buckfynn like this.

Share This Page