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Need Some Expert Advise On Heat Treating

Discussion in 'Heat Treating' started by RussGen, Mar 22, 2020.

  1. RussGen

    RussGen New Member

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    I just did my first heat treat in my new oven expecting perfect results and ended up with a much softer result than forge hardening. The steel was 1084. I know the tap controller is very exact so the problem is in my programming. I normalized 3 times 1600 (slow ramp), 1500, 1400. Then I hardened by heating fast to 1200, holding 5 min. to preheat. Then continuing to 1500 and soaking for less than a minute in 120 degree canola oil. I then tempered as soon as the oven cooled enough at 400 deg. for 2 hours. Result was file dug in like it was very soft metal. My temper produced a nice straw color. What gives. Is. There were 2 knives, same results. Is 1084 maybe better in the forge. Hoping that I can get some good pointers. I'm new at forging and using the oven and have more questions than answers.
     
  2. dancom

    dancom Dust Maker Best Shop Tool

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    Hi Russ,

    Not an expert, but have heat treated 1084 a couple of times before. Looks like your temps are ok. How quickly are you getting the steel from the oven into the oil? Like a couple of seconds or less if possible. Also, to be safe, let the blade soak at the 1500°F for a little longer. The air temp inside the oven can rise much faster than the steel. I notice that with mine.

    To be on the cautious side, I would do the file test right after hardening, before tempering. If it fails, you can give it a wipe and get it back in the oven (a little smokey) right away.

    As a sanity check, keep a magnet handy when you are normalizing. Take it up to 1500°F and whip the blade out and test for magnetic or not.

    Dan
     
  3. RussGen

    RussGen New Member

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    Hey Dan, thanks for the response I heat treated four more knives this morning and let them sit a few minutes longer with a much better result. This is a slow learning curve because of the time it takes to prepare the blanks so I try to tweak a few variables(or one) with each blade. I was surprised how fast the temp dropped when the oven was opened so I increased the temperature setpoint by 50 degrees for 5 minutes before quench time and it definately produced an added bit of hardness again. This stuff is fascinating. Thanks again. My next focus is the canola oil. Its a royal pain trying to get the temperature needed and keeping it. If real quench oils dont require heating I'm going to look into getting a good oil for high carbon steel and focus more on the oven. Cheers
     
  4. Griff

    Griff Active Member

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    Sorry did you say files dug in after tempering? They will, you’ve softened the blade down to a useable RC, which above all else allows you to sharpen the knife, as well as enhance its performance. Files only skate - or should only skate - directly out of the quench as that’s when the steel is at or close to its maximum hardness.

    If I read it wrong, my apologies. As for your heat-treat process I would say I cannot see anything wrong with it, but like Dan suggested let the knives soak a bit longer.

    https://knifedogs.com/threads/help-with-1084-heat-treat.44928/

    Great thread on 1084.


    Out of curiosity, how thick were the knives?
     
  5. dancom

    dancom Dust Maker Best Shop Tool

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    Good to hear. I have a homemade HT oven. The thermocouple is not in a ceramic shield and it exhibits a very fast response to heat increases. But I know the steel temperature won't move that fast. I always give a bit of extra time at soak to allow the steel to be equalized and I am comfortable that the steel is actually made it to the target temp. Thicker pieces = more time.
     
  6. Magnus

    Magnus New Member

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    The great thing about a heat treat oven is you start to really get a feel for the colour at the transformation temperature. That's usually my best check for if the knife has soaked long enough. With simple steels, though, I find it's best not to put the knife into the oven until it's at temp.

    Griff makes a pretty good point above, and also, you can't forget about decarb. If your knife has spent any amount of time at high temperature you might end up with a shallow soft layer on the outside.

    Magnus
     
  7. dancom

    dancom Dust Maker Best Shop Tool

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    Another reason to grind post heat treat. :p

    Dan
     
  8. RussGen

    RussGen New Member

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    There is so much good information I've taken from all your answers. As a newbie you can really speed up the learning curve on this forum. I've made some technical mistakes that I will correct but under the decarb the knife was not great but hard enough. I think my biggest mistake was put the knife in the oven and then started heating the oven. I'm assuming this from Magnus' advise to not leave simple steels in the heat too long.
     
  9. RussGen

    RussGen New Member

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    Yes, the file check was done only after temper and the blade was 1/8 thick.
     
  10. dancom

    dancom Dust Maker Best Shop Tool

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    Decarburization occurs around lower critical temp, 700ºC (1200°F) and higher. I prefer to start the oven cold with the load (knives) inside. This reduces the thermal shock in the steel as the steel is heated more gradually. Not everyone can do this if they are using stop-off coatings. For example, the coating I use, Condursal, has a recommended minimum temp of 860°C (1580°F ), so I load the oven shortly after reaching this temp.

    EDIT: I should mention I do mainly stainless, so 860°C is the start and the soak is at 1060°C.
     
    Last edited: Mar 28, 2020
  11. dancom

    dancom Dust Maker Best Shop Tool

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    I should point out too that many steel datasheets specify an equalization step. The idea is to rest just before critical temp so the steel is the same temperature throughout. It is meant for thicker steel where the inside temp lags behind the outer temp when the environment temp is rising. If your steel is thin and your oven ramps slowly, this equalization step is not required.

    I heat treated a repaired hydraulic crimp head which was 2" thick in places. I spent a good 10 minutes at equalizing temp before moving up to soak.
     
  12. RussGen

    RussGen New Member

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    Thanks Dan. So it sounds like there is nothing wrong with my having put the 1084 in the oven right from the beginning of heating the oven. I did set the ramp to AFAP but next time I can slow the ramp down. I hope to try stainless at some point but for now I think it best to get proficient at the 2 steels I've tried, 1084 and 80CRV2.
     
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  13. John Noon

    John Noon Well-Known Member

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    It is a good practice to get into of putting the steel in the furnace when it reaches 1200F then let soak for 15 minutes.

    This practice will get you into a habit needed for stainless steel work and if you choose to use ATP-641 then a minimum temperature would be 1200F do that it works properly
     
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  14. Griff

    Griff Active Member

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    I equalize O1 even though the tech sheets don’t mention it. Steel goes in cold, oven ramps to 1200F (649c) at about 400F (204c) per hour, and holds for 15 mins.

    I am not saying everyone should ramp so slowly. Some makers put the steel in an already hot oven. It’s just all the tech I’ve read on O1 says to ramp slowly to temperature, but they are of course talking about large industrial cross sections.

    Nevertheless I ramp slowly so the steel, the air around it, and the oven all get time to level off.

    Paragon Sentinel is then programmed to automatically ramp to 1475F - 1500 (802c -815c), you can go as high as 1500 with 01, but I’ve read lots correlating posts of makers that say over 1500F is not good for it.

    I typically soak a 0.250” (6mm+) knife anywhere from 7.5 minutes to 12minutes. O1 is 30 min for every inch. Though I’ve found I soak this thickness a bit longer on average at the 12min mark.

    That said I do soak my 0.125 (3mm) blades correctly at 3-4 mins tops, and for whatever reason it’s helped me avoid banana warping, and kept it to manageable warps, the kind easily corrected in the 2 tempering cycles.
     
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