Oven Tempering?

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  • Nail Gun

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    Out of boredom I decided to make an ulu for the wife out of an old saw blade. It’s shaped up and ready for a temper.

    I’ve heard of folks using a kitchen oven for the temper. Has anyone tried it? Any success?

    I’ve googled it but only found arguing and butthurt from other forums.
     

    shrxfn

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    My first thought was you can't get it hot enough to temper it but after a quick Google search without knowing the exact type of steel it seems tempering is around 450F to 550F so you could theoretically do it in an oven that goes to at least 500. I haven't done it so can't say if it works or not but it seems feasible on paper at least.
     

    Nail Gun

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    My first thought was you can't get it hot enough to temper it but after a quick Google search without knowing the exact type of steel it seems tempering is around 450F to 550F so you could theoretically do it in an oven that goes to at least 500. I haven't done it so can't say if it works or not but it seems feasible on paper at least.

    That was my thought as well.
     

    Bangswitch

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    If you have a spare oven so that you didn’t have to quench it in your kitchen. I’m no expert but I think you would want to quench it.
     

    Nail Gun

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    If you have a spare oven so that you didn’t have to quench it in your kitchen. I’m no expert but I think you would want to quench it.

    I’m just going to wait until a night my wife has work. She’ll never know unless the kids rat me out. I have a cast iron frying pan that needs to be seasoned, so two birds with one stone...

    Should I use oil or water? No clue what steel the blade is...
     
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    Gus McCrae

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    Lol. You probably need to ask someone who actually does this stuff. When you are quenching, the faster the steel cools, the harder and more brittle it will be. You want the right amount of hardness.... to much and it will chip, crack, and break, too little and it won't hold an edge.
     

    Bangswitch

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    Lol. You probably need to ask someone who actually does this stuff. When you are quenching, the faster the steel cools, the harder and more brittle it will be. You want the right amount of hardness.... to much and it will chip, crack, and break, too little and it won't hold an edge.

    Very good point. Post weld heating is often used to prevent certain metals from becoming brittle. But honestly I’m not sure how much hardness 550F would get you.
     

    Bangswitch

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    I’m just going to wait until a night my wife has work. She’ll never know unless the kids rat me out. I have a cast iron frying pan that needs to be seasoned, so two birds with one stone...

    Should I use oil or water? No clue what steel the blade is...

    Just a suggestion if you use an oil high smoke and flash points. You really don’t want that smell in the house.
     

    shrxfn

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    Nail Gun

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    Thanks for the articles. Looks like I need to heat it, quench it and then bake it. Now I need to figure out how to get good even heat to it.
     

    Bangswitch

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    You don't want to quench the steel when tempering you do that after the initial forge and that has to be super hot way hotter than an oven will get. From what I read you will want to temper the steel at 400F for a few hours then let it air cool. quick Google article find.

    https://www.instructables.com/id/Make-a-Knife-From-a-Saw-Blade-Using-Basic-Tools/

    https://feltmagnet.com/crafts/Making-Knives-from-Old-Table-Saw-Blades

    Ok I’m not all that boned up on my terms. So I was thinking hardening but tempering sounds a lot like a post weld heat treatment. I’m an amateur welder (emphasis on amateur) but the purpose of a post weld is to keep the metal from getting brittle. Tempering would probably weaken steel that hasn’t been through a hardening process.

    So if you can’t fire and quench it, I wouldn’t bother tempering it.
     
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    3fifty7

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    I’ll try to help where I can, I hope you enjoy the project.

    Old saw blade; meaning circular saw, cross cut, or industrial bandsaw from a lumber mill?

    Tempering is the last step involved in heat treatment. To essentially slightly reduce the hardness and remove some of the brittleness.

    Depending on the steel used you will need to heat to 1450*-1550*,(generally a bright orange but not quite yellow) then quench it in oil, brine, or water(again depending on the steel). Canola is the standard for diy, preferably heated to 120*-130*, allow the blade to cool in the oil for at least 10 seconds, say a quick prayer that it remains straight, then wipe clean and temper in an over at 400* for two 1 hour cycles, allowing it to cool to the touch in between.

    The blade should be fully shaped while leaving the edge about as thick as a dime prior to heat treating. Then you will have to do some cleanup the scale and decarb then sharpen.


    You can heat treat the entire knife or just the cutting edge.
     

    Nail Gun

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    I’ll try to help where I can, I hope you enjoy the project.

    Old saw blade; meaning circular saw, cross cut, or industrial bandsaw from a lumber mill?

    Tempering is the last step involved in heat treatment. To essentially slightly reduce the hardness and remove some of the brittleness.

    Depending on the steel used you will need to heat to 1450*-1550*,(generally a bright orange but not quite yellow) then quench it in oil, brine, or water(again depending on the steel). Canola is the standard for diy, preferably heated to 120*-130*, allow the blade to cool in the oil for at least 10 seconds, say a quick prayer that it remains straight, then wipe clean and temper in an over at 400* for two 1 hour cycles, allowing it to cool to the touch in between.

    The blade should be fully shaped while leaving the edge about as thick as a dime prior to heat treating. Then you will have to do some cleanup the scale and decarb then sharpen.


    You can heat treat the entire knife or just the cutting edge.

    Thanks, that’s helpful. I used a 14* diamond rimmed blade for cutting concrete.

    I ended up joining a FB group of knifemakers. They suggested starting out with a snap test by taking a scrap, heating it, quenching it and seeing if I can snap it in a vise. If it snapped, there is enough carbon for a good edge. They suggested heating it until the magnetism is gone.

    I tried it using a torch that puts out a blue flame similar to a crawfish pot. I ran it until the regulator developed ice. I simply couldn’t get enough heat to remove the magnetism. I still tried the snap test and the scrap bent like a nail...
     

    shrxfn

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    If you look at the links I posted you may want to build a brick oven to keep the heat in the enclosure and not let it escape using an open flame. That may solve your issue with the initial fire and quench.
     

    Nail Gun

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    If you look at the links I posted you may want to build a brick oven to keep the heat in the enclosure and not let it escape using an open flame. That may solve your issue with the initial fire and quench.

    Yup. That’s the next step. I was hoping that torch directly on the small scrap would be enough. Apparently not.
     

    3fifty7

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    Yeah, nearly all tipped blades either diamond or carbide are on mild steel that won’t have enough carbon to properly harden.

    A *two brick forge* is small but effective.

    Depending on how far along you are with the blade and considering an ulu will slice and rock cut you can finish it out without any heat treatment. Upsing a wooden cutting board and hand washing will go a ways to helping.
    You won’t have much edge retention but think of it as dipping your toes in the water.
     

    Bangswitch

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    If you look at the links I posted you may want to build a brick oven to keep the heat in the enclosure and not let it escape using an open flame. That may solve your issue with the initial fire and quench.

    Yup. That’s the next step. I was hoping that torch directly on the small scrap would be enough. Apparently not.

    Enclosing the fire will help get you some more heat also may consider fuel source if you are still struggling. Ferriers often use coal I guess it gets hotter.
     

    Any 22

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    Out of boredom I decided to make an ulu for the wife out of an old saw blade. It’s shaped up and ready for a temper.

    I’ve heard of folks using a kitchen oven for the temper. Has anyone tried it? Any success?

    I’ve googled it but only found arguing and butthurt from other forums.

    Iv used my wifes oven for over 20 years. NO PROBLEMS!!!! if your leery it can only be temp variation Get an extra Oven thermometer at walmart or a laser thermometer at Harbor freight I have both but heat is heat it just has to be the right temp And I dought very seriously 10 degree would change a thing
     

    Magdump

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    Old thread, I know.
    Just posing the question. When the saw blade was made, the steel was most likely tempered. Cutting and grinding and shaping shouldn’t change anything that drastically that would beg you to re-temper and especially heat quench the new blade, seeing as there was no forging going on. Especially if you take care when cutting, not to rush things with a side grinder to the point of bringing the temp up to molten orange, lol. Grinding the edge on a wheel shouldn’t be done so fast that you get a glow from the steel either. Again, if you’re not forging anything, the steel should make for a nice edge as it is.
    I made a machete from an old, quality framing square just using a belt sander and fine grinding wheel. After I got the edge where I wanted it, there was nothing more to do but use it. The edge has held up fine over the years.
     
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