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Something Weird Going On

Discussion in 'Heat Treating' started by dancom, Dec 12, 2020.

  1. dancom

    dancom Dust Maker

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    I have always been a big fan of AEB-L. I recently bought a bar of 3/32" AEB-L and every knife I made from it, four in total, didn't harden properly.

    Suspecting the thermocouple in the oven, I replaced it with my spare. I verified the temp with Tempilstik 1950°F and blades were coming out of the oven that familiar yellow colour. But none fully hardened after quench. One air, two oil and one plate quench. I cleaned and re-coated them and loaded them in a second time. The results were the same, then I gave up. Baffled. It's like the carbon is missing.

    The weird part is along with the AEB-L blades I had one 154CM blade and it came out perfectly hard

    I don't have a hardness tester, only a calibrated file set. All the AEB-L came out between HRC40 and HRC45. The 154CM was giving the HRC60 file a hard time.

    Anyone else observed this before?

    So I am four knives behind. Christmas orders in jeopardy. :(

    Dan
     
  2. Joelsund

    Joelsund Member

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    Very weird. Does it spark like normal when you grind it?
     
  3. dancom

    dancom Dust Maker

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    Yes, the sparks appear complex as usual, but it's much easier to grind. Normally post heat treat it takes a bit of pressure to get sparks like this. I am one-handing it to take the photo.

    [​IMG]

    I have some 154CM make up blades going in the oven--hopefully tonight. I will give it one more shot and see if anything improves, but I am pondering Einstein's definition of insanity.

    Dan
     
  4. Joelsund

    Joelsund Member

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    do you have other aebl you can try hardening at the same time? also have you checked its corrosion resistance?
     
  5. Scott Kozub

    Scott Kozub Member

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    I've never had ussue with aebl but when checking with my hardness tester I do grind a small divit in the tang first. Without it I sometimes get mid 50s. Then I check the divot and get 63 to 64 as quenched. My first temper is always low and it jumps up to 66 ish after first temper.

    Grind a hollow in the tang and check that. If it seems better grind a bevel and put a quick edge on. Do the brass rod test. If you haven't tempered yet it will chip.

    You can also look for a local heat treater and see if they'll test it.

    Final suggesting. I have a plate of .1 AEBL. not sure what thickness you have but if you want to send me a scaled dwg I can rip out some blanks and courier them to you. Hardness checked of course. If get them done today you should have them early next week hopefully in time to clean up and mount handles. No charge. Consider it a thank-you for your website.
     
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  6. dancom

    dancom Dust Maker

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    Thanks for the generous offer Scott, but I have already made new blades in 154CM. I have tons of scraps of AEB-L from bars before, so I will put a piece or two in when I do the run.
     
  7. John Noon

    John Noon Well-Known Member

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    Had the same thing happen to me, blade was so soft it bent when I bumped the tip.
    Put them in your freezer overnight or if -20C and colder outside will work. Leave them overnight and test them again.
     
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  8. dancom

    dancom Dust Maker

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    Thanks John,
    I hope you are right man. I am going to give that a try.

    Dan
     
    Last edited: Dec 16, 2020
  9. dancom

    dancom Dust Maker

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    Well John...I put them in the freezer overnight, Ours is at -19°C according to my IR thermometer. Checked them quickly this morning. I can't believe it. Hardness seems to be way improved. I flexed the tip of a boning knife and it sprang right back as I would expect it too. I won't be able to check against the files until I get home from work tonight.

    Any ideas as to what is going on? I usually put AEB-L in the freezer between tempering cycles, but I did not do that for these four blades. I was kind of rushing around getting things done for Christmas and didn't think it made a whole lot of difference. After all, room temp to -18°C is less than 40°C drop right? Does Martensite conversion have some kind of curve which increases as you move further away from the Martensite start point? I might have to study Dr. Larrin's book a bit closer.

    Moving along, I heat treated 154CM, some different AEB-L and one Nitro-V last night. Air and plate quench. All appear to be HRC60+ on the file test before going into tempering.

    Feeling thankful,

    Dan
     
  10. dancom

    dancom Dust Maker

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    I did a file test last night. It would appear that the AEB-L hardness is up to somewhere between HRC55 and 60 now. I was aiming for around 58 post tempering, so it's in the ballpark. I am asking Santa for Rockwell hardness tester, but I think he's pretty busy with toys and stuff for the kids.

    For sh!ts & giggles, I left some more knives outside overnight. We got down to -22°C at the farm, too bad wind-chill doesn't count. LOL
     
  11. John Noon

    John Noon Well-Known Member

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    When AEB-L does this I use minimum tempering temperature twice.
     
  12. Joelsund

    Joelsund Member

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    Larrin does have a cooling to hardness curve in his book somewhere showing that even -20 has a pretty noticeable increase in hardness over room temp. If you file test at room temp right after quench I've found that AEBL-L and nitro V don’t even seem to be hard at all and files cut easily, but after cryo a file won’t do anything.
     

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