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My own dumb question

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  • #37523
    Readheads
    Participant
    • Topics: 28
    • Replies: 304

    After reading two of Verhoven’s works on sharpening and then blade metallurgy, I’ve wondered about the following:

    What is the impact of the stresses imparted to an edge during the metal abrading process of sharpening ?

    Given all the heat treating done to balance toughness et al. to a piece of metal, when we sharpen over a very small thin section, you would think that the stresses are very large. Without relief (and given also sort of strange theories about metal not forgetting, etc) you would expect that we change the baseline blade properties somewhat. I would not expect any phase transformations but as we know bending a paper clip just 2-3 times will not only break it but will change the metal properties in the metal in the vicinity of the break.

    What might be the techniques to minimize this and also verify it ?

    #37539
    tcmeyer
    Participant
    • Topics: 37
    • Replies: 2030

    It’s my understanding that steel has internal stresses created through the forming and hardening processes.  From my former life in machine design and manufacturing, when final dimensions were critical, the steel was first sent out for “stress relieving,” which is effectively a drawn-out annealing process.

    When you remove material from stock that has not been stress-relieved, you effectively are weakening the structure which is containing those stresses.  I see this frequently when I rip lengths of wood to narrower widths.  Where the original board had been relatively straight, now the resulting two narrow boards have become badly bowed.  I haven’t added stresses, I’ve actually cut the connection which was holding them straight.  They are now free to relax into their most natural shapes.

    Bottom line is that I don’t think you add any stresses through the sharpening process.  The internal stresses already in the blade are probably hundreds or maybe thousands of times higher than any effect you could produce with the stones.

    Here’s a photo of an IKEA chef’s knife – a Damascus blade with a VG10 center I sharpened a few years ago.  The photo shows one of three cracks I found in the blade when inspecting it with my USB ‘scope.  They happen during the quenching process when the thinner edge cools faster than the rest of the blade.  It wants to get shorter but is not allowed to as it is held fast by the thicker parts of the blade which cool more slowly.  The result is extremely high stresses in the edge steel.  In this case, it actually created tensions so high that the steel parted in three places.  Usually, you can hear it happen.  On “Forged in Fire” it’s referred to as the “dreaded ping.”

    IKEA  Crack No 3 compressed

    Or maybe I didn’t understand your question?

    #37541
    wickededge
    Keymaster
    • Topics: 123
    • Replies: 2936

    Readheads,

    It sounds like you might be talking about work hardening happening at the edge through sharpening. Cliff Stamp talks a lot about this and recommends periodically removing the compromised metal from the edge by filing the edge flat. I’ve read from others that they’ve tried this approach and it’s let to better durability. I haven’t tested it myself.

    -Clay

    #37564
    NotVerySharp
    Participant
    • Topics: 33
    • Replies: 56

    TC what camera did you take that photo with?

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