Circles in steel after HT

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by TRAVIS R HENNINGER, Aug 12, 2017.

  1. TRAVIS R HENNINGER

    TRAVIS R HENNINGER

    36
    Jul 23, 2017
    Can someone tell me what causes these circles in the steel after HT. I am using a homemade forge burning lump charcoal.

    The steel is 5160 from Jantz.
    [​IMG]
     
  2. JTknives

    JTknives ABS Apprentice Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    From scale building up on the surface when you heat treated. this is why we remove all the decarb layer after heat treat.
     
  3. TRAVIS R HENNINGER

    TRAVIS R HENNINGER

    36
    Jul 23, 2017
    I do not recall seeing ut on my other blades. Is this a bad thing? I normallized 3 times then HT.
     
  4. JTknives

    JTknives ABS Apprentice Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    It's not a good or bad thing, it's a surface condition. Normalising is most likely what did it. Extended exposure to heat creates lots of scale and some times it forums in little round blister shapes. There is also a layer on the surface called decarb that has had the carbon burned out of it. This is why we normally grind or sand after heat treat. If you don't have a grinder then use a corse grit paper and start sanding till all the scale scaring and decarb is gone then move up in grit and finish the blade. But like I said as long as the heat treat was done right and everything is spot on then it's just a finish issue and not a structural problem.
     
  5. TRAVIS R HENNINGER

    TRAVIS R HENNINGER

    36
    Jul 23, 2017
    Thanks for the help. The heat treat went well, and the portable hardness tester I am using is showing around 57 Rockwell. Should be ok.

    I am hand sanding now.
     
  6. JTknives

    JTknives ABS Apprentice Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    Just remember to get an accurate hardness reading you have to remove the decarb becaus it is much softer the the hardened steel.
     
  7. 3fifty7

    3fifty7 Basic Member Basic Member

    414
    Dec 24, 2016
    As a side question, if the OP doesn't mind me jumping in here, how do I know when I am completely through the decarb layer?
     
  8. JTknives

    JTknives ABS Apprentice Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    If it's a simple carbon steel you can just give it a dunk in some ferric chloride. Steel with real low carbon content will etch much lighter color then the hardened steel.
     
  9. jdm61

    jdm61 itinerant metal pounder Knifemaker / Craftsman / Service Provider

    Aug 12, 2005
    I had that happened early on with some O1. It looked like beach sand when i broke it. I am voting for overheating.
     
  10. JTknives

    JTknives ABS Apprentice Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    +1^
    That's why I said "if" the heat treat was done correctly.
     
  11. TRAVIS R HENNINGER

    TRAVIS R HENNINGER

    36
    Jul 23, 2017
    Just finished it. Plan on abusing it tomorrow to see if it holds up. We will see. I am still figuring it all out. This is knife #4 i am not to worried about the mirror finish yet, until I get the basics down.
    [​IMG]
     
    Natlek likes this.
  12. JTknives

    JTknives ABS Apprentice Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    Do you have an edge bevel on that blade?
     
  13. TRAVIS R HENNINGER

    TRAVIS R HENNINGER

    36
    Jul 23, 2017
    I do. It is not a great picture. The bevel near the tip needs corrected. I will work on that tomorrow. I made a jig to help hold my angles. I am not real good at it yet. But I will keep practicing.
     
  14. JTknives

    JTknives ABS Apprentice Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    How thick is your blade?
     
  15. TRAVIS R HENNINGER

    TRAVIS R HENNINGER

    36
    Jul 23, 2017
    The blade is 1/4 inch.
     

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