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Hardening air hardened drill rod

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  • Hardening air hardened drill rod

    I bought a piece of air hardened drill rod. I thought all I needed to do was heat it red and let it cool, and it will be hard, Wrong. Is this possible in a home shop to hardened this drill rod, with a torch? Stan

  • #2
    Air Hard

    You need to know what Air Hard steel you have for the project. One typical steel, A2, has to be heated to 1725-1775 deg F and allowed to cool in air. It should be drawn at 400 deg F. You may not have taken it to the required high temperature.

    JRW

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    • #3
      Tool Steel

      When heat treating with a torch, you have to get the metal to a temp. where it starts to have little spots that are extra bright. Hold that temp. for about 30 seconds, trying to make sure it is evenly heated where you want it hard.
      Quench quickly while it is at this temp. For A2, just let it air cool. For O1, quench in oil. etc. The bright spots on the metal tell you when it's the right temp. for that particular steel. Once it cools, knock off the black outer coating. Don't sand it. If the metal is a gray color, it's hard. Then you can clean it up and draw back to a gold color.

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      • #4
        Remember that when heat treating steel you are actually allowing mircrostructure changes of the steel to happen while still in a solid state. This doesn't happen very fast with A2.
        Although it depends on which data sheet you read, but IIRC the general rule for A2 is 1 hour per inch of thickness at the Austenitizing temperature (~1750F). You can't really over cook it so its better to soak it longer than too short. Then don't forget to temper the steel at 300-500F to toughen it up after its fully cooled in still air. A temper of 300F will produce Rc values of around 58-62 or so and 500F will produce Rc values in the 45-50 range. Again soak time is important here and leads to the variability in the Rc values noted above.
        I've had great results with A2, but I've always used an oven to soak it. I'v experienced very little warping and little to no scale if done in a foil wrap with a little piece of paper to burn off the excess oxygen.

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        • #5
          The OP said he was using a torch. It's not very practical to stand there holding a torch for an hour.

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          • #6
            A2 MUST BE PROTECTED from AIR while heating it up,or it will have a soft skin at least 1/32" deep.

            I use it all the time. You can't use a torch,because A2 must be wrapped in an airtight stainless steel foil,and put into an electric furnace. The quick,localized heat of the torch will burn a hole through it.

            You need to follow my advise,I use it a lot. Jungle is also right.

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            • #7
              A straight forward explanation on heat treating all the common tool steels is available in Bryson's book: Heat Treatment, Selection, and Application of Tool Steels ISBN 156990376X

              It's pretty much a cookbook of sorts, but lacks detailed explanations of why some of the steps in the process are necessary or what would happen if not followed; although other metallurgical texts fill this void at the cost of generally requiring a much deeper knowledge of material science.
              Bryson's book is an easy and accurate read and I keep a copy next to my furnace for reference.

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              • #8
                Originally posted by Toolguy
                When heat treating with a torch, you have to get the metal to a temp. where it starts to have little spots that are extra bright. Hold that temp. for about 30 seconds, trying to make sure it is evenly heated where you want it hard.
                Quench quickly while it is at this temp. For A2, just let it air cool. For O1, quench in oil. etc. The bright spots on the metal tell you when it's the right temp. for that particular steel. Once it cools, knock off the black outer coating. Don't sand it. If the metal is a gray color, it's hard. Then you can clean it up and draw back to a gold color.
                Why not sand it?

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                • #9
                  Because you want to see if it's gray or silver first. Then you can sand it or Scotchbrite it or whatever to clean it up. You will need to clean it off and make it silver again before you draw it back to see what color it is when you heat it the second time.

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