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Having Problems With Ht

Discussion in 'Heat Treating' started by krash-bang, May 4, 2017.

  1. krash-bang

    krash-bang Active Member

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    I'm having trouble with heat treating CPM 154 steel, I had the same issue last year and I can't figure out the trouble.

    Here's what I did:

    Wrapped my blade in SS foil, 2 inches of slack on both ends and maybe 1.5" lenghtwise. Put a little piece of paper 1"sq. Single wrap.

    Into the kiln then started the program, afap to 1950F, then held there for 30 mins. Air quench with 3/4" aluminium plates.

    When I took out the pouch, it was as if it had been vacuum sealed, thankfully the foil wasn't stuck to the blade but I still get blemishes on the blade that are nearly impossible to get off.

    Here's a pic of the pouch after I cut all around.

    [​IMG]

    You can see where the foil "bubbled" around the ricasso area. I have the same pattern on the blade and that is the hard part to remove. I've had blades sent out for HT that came back and I cleaned them up with 800g sandpaper. Not this one.

    I thought the pouch should expand a little during HT but I seem to get the opposite.

    Any suggestions would greatly help.

    Thanks,

    Serge
     
  2. John Noon

    John Noon Well-Known Member

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    You will find the heat treating temperature of the blade and forging temperature of the foil have overlapped , excess pressure at the beginning of quenching can cause foil to stick.
    Also ran into staining from the paper I was using and started making sure it stayed at the handle end.
     
  3. dancom

    dancom Dust Maker

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    Hi Serge,
    How hard are you squeezing the plates? Hopefully just enough to make good contact, say 5kg (10 lbs) or so.

    Dan
     
  4. John Noon

    John Noon Well-Known Member

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    I have on a couple of occasions run a significant size of paper, about half handle length and one wrap. Only once was there any amount of material left after cutting open. This is one of the reasons I gave up on foil and went with Condursal which has been far more predictable over the last ten blades.
     
  5. krash-bang

    krash-bang Active Member

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    I may have put a little bit more then that, say a 25 lbs barbell weigh. And I may have been leaning on it a bit some.
     
  6. krash-bang

    krash-bang Active Member

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    I'm not sure I understand what you're saying. Could you elaborate, I want to make sure I get it. Thanks.
     
  7. John Noon

    John Noon Well-Known Member

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    Instead of thumb size I used a quarter sheet. My thought was maybe some air was left after a small piece burnt off
     
  8. krash-bang

    krash-bang Active Member

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    Did you find that when you used a bigger piece, the pouch would puff up more? I'm thinking of going to a 2" sq. or maybe even two.

    I'm thinking that if I can get the pouch to puff up, it would cool off somewhat fast, since its so thin, while going from the oven to the plates and it would mitigate the overlapping that you mentionned earlier. Does this even make any sense?

    Maybe I'm overthinking this.
     
  9. John Noon

    John Noon Well-Known Member

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    Not sure if the pouch puffs up more or not but come to think of it I did have a couple inflate to the point they jammed in the knife rack and broke two pegs trying to get the knife free.

    I think best practices for foil is to have as tight as possible and the titanium in the foil is the oxygen absorber. Also found one reference for the use of a wood sliver, paper pops up on knife making sites as the most popular method.

    The idea of loose foil cooling faster seems logical and might be worth a try
     
  10. krash-bang

    krash-bang Active Member

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    I'm going to try a couple of pieces of paper on my next attempt. I will also lighten up some on the pressure I apply to the plates.

    I appreciate you guys sharing your insight on this.

    Thank-you very much.

    Serge
     
    John Noon likes this.

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