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

Re-heat Treating Ss

Discussion in 'Heat Treating' started by Nieman Knives, Sep 17, 2020.

  1. Nieman Knives

    Nieman Knives New Member

    Likes Received:
    3
    Trophy Points:
    3
    Hi all,

    I’m having trouble finding an answer to this.

    Long story short my AEB-L SS came back from the HT place warped. I am sending it back to be annealed, straightened and re-HT’d.

    Will this in anyway effect the steel?

    Side note/more info:
    This is the second time this exact thing has happened with this company. With both these batches, the knives were all warped the same way in the same places. With the last batch that they fixed for me they came back so straight the second time that I was quite happy with them and was informed they had all the details figured out so why not go back with them (especially considering the price). Unfortunately it has happened again so I assume whoever did them the first time did the same thing that caused the problem with the first batch. This batch was 20 knives. Many of which I have orders for so I’m kinda crushed as a newbie just getting started and dying to get working on them as I work in a tarp shed and...winter is coming.

    Anyways, now it’s got me questioning the quality of the steel.
     
  2. Griff

    Griff Active Member

    Likes Received:
    215
    Trophy Points:
    43
    I’ve had a good look around for you bud, but most HT conversations about AEB-L don’t specifically mention any issue reheat-treating it when it has warped.

    Most grind post HT with AEB-L (Depending on the thickness of course) because of its tendency to warp. Were you sending the knives out just profiled, or did you sen them out fully ground, bevels and all?

    My only other thought is if this is an industrial HT company and not completely versed in knives, they may have a tendency of following a HT process for thicker cross-sections.

    Anyway good luck :beer::beer:
     
    Nieman Knives likes this.
  3. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    1,092
    Trophy Points:
    113
    Should be no issues. I had one where the tang cracked when I was flexing it (dumb) after hardening. I made it into a hidden tang and repeated the same heat treat with no problems. It was unbelievable hard to work as I didn't anneal it. I just blew through a ceramic belt. Hahaha.

    AEB-L is pretty easy to heat treat of the temps are right. Do you know if they are air quenching or oil quenching? I sometimes just take a soaked blade out of the oven and hang it on a nail and shoot compressed air at it. You can hear it hardening over the twenty or so seconds. Pretty cool.
     
    Nieman Knives likes this.
  4. Nieman Knives

    Nieman Knives New Member

    Likes Received:
    3
    Trophy Points:
    3
    Griff:
    The knives were all just profiled with a small (and very even) Scandi grind which I’ve heard helps extend belt life when doing your post HT bevel grinding. And yes, it is an industrial HT place.

    Dancom:
    My understanding of their process is that they are using a vacuum oven and quenching by pumping gas nitrogen into the oven. They then do temper by putting them in some type of “fixture” that gets thrown into the temper oven with the blades “squished” in this fixture.

    The thing is as I stated above, the first batch of 12 and second batch of 20 knives all had warps in the exact same places, same direction so it’s not just a “normal warp” it’s clearly something in their process, like they are sitting a rack of some sort???
     
  5. John Noon

    John Noon Well-Known Member

    Likes Received:
    620
    Trophy Points:
    113
    At tempering temperatures a rack should not cause issues with warping unless clamped into a overbend situation for straightening.

    I have found AEB-L is the most sensitive steel to asymmetrical cooling, place on a chill plate flat then place another plate on top and it will warp. Another condition is bumping the blade before it reaches zero degrees Celsius or applying pressure in a jig.
    Once below room temperature or freezing you can feel the material lock up as martensite forms.
     
    Nieman Knives likes this.
  6. dancom

    dancom Dust Maker Best Shop Tool

    Likes Received:
    1,092
    Trophy Points:
    113
    I have experienced what John mention about asymmetrical cooling. I initially used quench plates in the horizontal position...once. I placed the hot blade down on the bottom plate and by the time I put the top plate on she was wowed. I changed this to vertical plates sitting slightly open in a carpenter's vise, open just enough to slip the hot blade in and crank them together. More recently, I am air quenching and oil quenching as these seem to result in the least distortion.

    In Nieman's case I think it must be happening at or before the nitrogen quench when the steel is fairly plastic, perhaps the blades are placed on a shelf or something. I have always loaded my oven with the blades sitting point in and spine down. I wonder what effect laying the blades flat in the oven would have. Any tempering fixture would need to have flat surfaces if applying pressure during tempering.

    Sorry we can't be of much help.
     
    Nieman Knives likes this.
  7. Nieman Knives

    Nieman Knives New Member

    Likes Received:
    3
    Trophy Points:
    3
    As my question really was about doing another HT and the effect on the steel I think you’ve answered that. I have no control over the HT process so I’m just hoping they get that right this time without the warping.

    Thanks for all the replies!
     
  8. Scott Kozub

    Scott Kozub Member

    Likes Received:
    30
    Trophy Points:
    18
    I work a lot in AEBL. The stuff warps if you look at it funny. I made a peening hammer with a carbide drill bit and straightening has become way easier and faster and avoids broken knives. However youre sending it out specifically so you don't have to deal with it so you would expect it to come back straight. Even normalizing doesn't keep it from warping.

    I have retreated AEBL in the past without issue.
     
    Nieman Knives and dancom like this.

Share This Page