Grain Structure in Metal

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Forgentro, Apr 20, 2019.

  1. Forgentro


    Apr 6, 2019
    I've only been able to fine hit or miss information on what the grain structure should look like after a proper heat treat and temper.
    Here is a link to my pics.
    It would be helpful if someone can give me any information on my failure of heat treating this throwing knife or a critique of the grain pattern on what it should look like for properly quenched and hardened throwing blade.
    Many hours to make, less than a second to brake.

    Throwing Knife, 5160, Stock Removal, Heat to non-mag, hold for 10 minutes, Veg oil quench, temper 450 / 1.5hrs,
    ...After about 10 throws, a good smack on the side and WHAMO!! See link below.
  2. DevinT

    DevinT KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 29, 2010
    Yup, not good grain size. It should not sparkle, should be smooth like velvet. Looks like you over heated it. Non-magnetic is a very large range of hot.

    DeadboxHero and Forgentro like this.
  3. Ken H>

    Ken H>

    Dec 31, 2011
    For comparison break an old file that is high carbon steel (not a new file that's surface hardened) and you'll see a good example of what grain should look like. maybe an old broken drill bit? The grain should look almost like a gray end with almost no visible grain.
    Forgentro likes this.
  4. Natlek


    Jun 9, 2015
    You don t need to hold for 10 minutes this steel, and I think that you should temper it twice............
    Forgentro likes this.
  5. Rhinoknives1

    Rhinoknives1 KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jul 1, 2013
    AFAIK,!Most throwing knives aren’t harden steel! You want them soft so that they won’t break or chip when hitting something hard. As far as HT, Devin is the one to listen to..
    Ken H> likes this.
  6. R.C.Reichert


    Jul 26, 2008
    Holding at non-magnetic for 10 minutes will do this? This looks more like something that was heated to way past non-magnetic and held for 10 minutes then quenched.
  7. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    While your grain isn't optimal, I suspect the main culprit was a bad HT.

    Austenitization for 5160 is 1525F. That is 100 degrees hotter than "non-magnetic".
    How was it held at "non-magnetic". If it was in a forge it was surely overheated. It really takes a HT oven to do a hold of more than 60 seconds. If you use a forge, just hold 5160 for 30 to 60 seconds and quench.
    You want two tempers on any steel.
    A throwing knife in 5160 should be tempered at 600F for a mid-50's Rockwell hardness. 425F temper is way too hard.
    Many throwing knives only have a hardened tip … if any hardening at all.

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