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What am I doing wrong?

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Tin.Man, Mar 17, 2017.

  1. Tin.Man


    Sep 5, 2010
    So did my second batch of o1. Kiln at 1475 equalized for 15 minutes. Placed the 6 knives in let temperature spring back to 1475, held for 30 minutes then quenched in canola oil. Tempered at 375 for 2 2 hour sessions quenching in cold water between.

    A good friend hardness tested them after I cleaned all the scale off and was getting 56-57. Feel like with that recipe I should have been in the 62+ ?

    Brand new paragon kiln, fresh canola oil, his hardness tester is lab grade. Anyone have any thoughts? I'm in northern Colorado could mile high affect these temps? Maybe go for 1500?
  2. Frank Niro

    Frank Niro Basic Member Basic Member

    Sep 10, 2000
    Perhaps a lower temper. Say 325?
  3. Kevin McGovern

    Kevin McGovern KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jul 31, 2015
    Seems like you should be in the 62 range with that regimen. Are you sure your temp reading is correct for the kiln and tempering oven?
  4. BartlettBlades

    BartlettBlades KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Mar 24, 2016
    Are you sure you're grinding off the decarb layer and actually testing the hardened steel?

    Sent from my SM-N915V using Tapatalk
  5. kuraki

    kuraki Drinks Pearl in a can. Knifemaker / Craftsman / Service Provider

    Jun 17, 2016
    Verify kiln temp
    Verify you're grinding through decarb
    Did you quench all 6 one after the other? Did they all test the same?
  6. J. Doyle

    J. Doyle Bladesmith/Knifemaker Dealer / Materials Provider

    Feb 17, 2008
    ^^^Agree with the two posts above. With 30 minutes of soak time at temperature, the decarb layer might be thicker than you think.


    Dec 1, 2008
    30 Mins is a long soak time and would have built up a heap of decarb . I would bet if you grind deeper you will get harder readings.
    Beat me to it. ")
  8. Tin.Man


    Sep 5, 2010
    Ground with sharp 120 on the tang to shiny silver steel. I quenched one till it was cool to the touch then the next etc.

    Should I soak less maybe? Actually wasn't that much decarb. I have no way of verifying that the thermocouple is accurate other than it being a new kiln :(
  9. nickandersonart

    nickandersonart Basic Member Basic Member

    Aug 5, 2014
    Tin.Man I just went through this with my newly built oven a couple months ago. I recommend testing your oven temperature readings using either tempilstix or something that has a distinct melting point like fine .999 silver. The nice thing about using tempilstix (essentially crayons that melt at a specific temperature) is that they have a whole range of temperatures, and you can buy the temperature that most closely matches what you'll be using the most often for HT (say around 1475 or so for simple high carbon steels). If you're also doing stainless I'd get one in the 1950f vicinity as well to do two separate tests so you know how far off your readings are at the separate temperature ranges you'll be commonly using.

    I didn't have access to tempilstix where I'm at so I used a piece of fine silver cut to about the same thickness as my TC (Thermocouple) wire, 1/8". I placed the strip of silver right next to the TC tip sticking out of a piece of firebrick, at an angle so I could see exactly when it melted. I did repeated tests this way, bumping up the temperature 5 degrees at a time and letting the oven soak in between increasing the temp, until the silver would melt. It worked perfectly. After some rounds of testing, removing connecting plugs from my TC line, and triple checking to make sure all wires had correct polarity, it turned out the silver melted right at its designated melting point. Majorly relieved. I installed a second TC as well at a separate point further inside the oven as an extra safety measure (safe for my knives and peace of mind) just to be completely sure that the temp is what it says. When I preheat my oven and let it soak, both PID's with separate TC's will show the exact same temp or within a couple of degrees...really helps me to be more confident in my HT which is, really, the most critical part of the entire knifemaking process. Took me a bunch of time in advance but so worth it in the end.

    This is maybe a separate issue, but I would recommend doing this for any steel you're considering using *regularly* because it will also give you a lot of additional peace of mind for any given steel: Take about 4 or 5 "coupons" or scrap pieces of the steel that you intend on using, and mark each one separately, as in A1-A2-A3-A4. For each of these numbers, test your heat treatment sequence using a different hardening temperature. If the HT range for 01 is between 1440 and 1500, then test like this:

    A1: 1440
    A2: 1460
    A3: 1480
    A4: 1500

    After quenching each, break off a piece and check out the grain size. Then grind off enough to make sure there is no decarb and test for HRC. Whichever hardened the best, that's your temp to go with for that steel. From there you can also dial in the tempering as well. Temper at 350, check HRC. Temper higher, check HRC etc etc. You can do all this without messing up one or more blades that you spent all your time grinding on.

    Though it's a good amount of extra work in the beginning, I think this testing sequence is invaluable for any steel. I'm completely over using fully ground knives as guinea pigs for HT regimens. Done that enough at this point!

    Here's a few images from when I was doing my rounds of testing for various steels, one of the general layout and a couple closeups I was taking with a macro lens to inspect grain size:

    Last edited: Mar 18, 2017
  10. nickandersonart

    nickandersonart Basic Member Basic Member

    Aug 5, 2014
    And one very last thing to consider: Some steels come in a heavily spheroidized condition from the mill which is good for drilling, milling, grinding etc but can cause issues for some people in HT because the carbon stays locked up and isn't available for getting optimal hardness. Most people run a normalization and thermal cycling sequence to account for this and dissolve the carbon evenly back into the matrix of the steel. Given that O1 has a long soak time at austenitizing temp, I don't think that it's as likely that this could be your issue, but certainly a possibility.
  11. kuraki

    kuraki Drinks Pearl in a can. Knifemaker / Craftsman / Service Provider

    Jun 17, 2016
    I think you need to verify your set temp first and foremost. The toolmakers at work were having similar issues with O1 actually, and by using 3 tempilstiks I found that there was a more than 25f degree gradient inside the chamber. Blocking parts up to reside next to the thermocouple resolved the issue.

    25 degrees makes a difference, even on steel with a reported larger range in temps. For example S7 at 1750 the hardest I could get was 54 RC, but dropping to 1725 on recommendation from the forum, I get 60Rc every time and that's as hard as S7 gets.
  12. nickandersonart

    nickandersonart Basic Member Basic Member

    Aug 5, 2014
    Kuraki just curious, was the temp difference that you're mentioning from front to back in the oven, or from top to bottom?

    After installing a second TC just 5 inches from the 1st, I found that after opening and closing the oven, there can be a huge temp difference just between the two TC's (one about 11" into the oven and the other at about 16)" as the temp re-equalizes after shutting the door.

    Because of this, after putting the knife in the oven, I let it equalize for about 30-60 seconds with no power going to the coils before turning them back on. Otherwise, the back part of the oven stays hotter than the front, and if it starts heating immediately based on the temp from the 1st thermocouple (which is the one linked with the heater), the back will become hotter than the middle/front of the oven, potentially overheating the tip of the blade.

    Interesting to see how much the temp can differ inside of the oven once you're measuring multiple areas inside of it. Definitely helps to do a long preheat, and allowing the interior to equalize for a bit after putting the knife in before re-activating the coils.
  13. Greenberg Woods

    Greenberg Woods Wood Fanatic and Rosewood Addict Dealer / Materials Provider

    Dec 27, 2013
    Lab grade salt "NaCl" also has a very precise melting point that happens to be very close to the transformation temp of steel.
  14. kuraki

    kuraki Drinks Pearl in a can. Knifemaker / Craftsman / Service Provider

    Jun 17, 2016
    In this oven, both. The TC is located near the roof and protrudes about a third of the way in, the temp drops the further you get towards the door and the floor, diagonally. I let the interior equalize for an hour when doing knives, and block them up so the blade is alongside the TC. I can only do 3 at a time this way (for a fairly large furnace chamber) but I know they're at the right temp at least.

    I also cycle mine on and off with door openings and temperature changes, for the same reason. It outruns the feedback loop and will over heat if I don't.
  15. Tin.Man


    Sep 5, 2010
    Guys I appreciate all the help!

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