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Annealing hard metal in a fireplace?

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  • #31
    Well, here's the rest of the story.

    A cold front came through yesterday and I felt justified in firing up the heat-treating furnace, erm, fireplace and see what happened. I had to work 1/2 day and used the shop O/A torch to whack the axle in half. When I got home, I used Gary's method; after I had a solid bed of coals in place, I drug the logs aside, placed the 2 pieces onto the grate and piled the logs back onto them. I just kept putting wood on as I normally would and after a couple hours I raked the logs aside to look at the metal. They were hot, a dull red I'd say; a bit duller than the coals. I piled up the remaining logs and left them 'til this morning.

    Before I started, a file would mar the surface but not bite. Today, a file would bite into the metal fairly well. They're still harder than plain mild steel but will now machine nicely with HSS. It's usable stock now and the price was right!

    My only complaint is that one of the pieces warped about 3/32" or so. Ain't nuthin' perfect. eh?


    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton


    • #32
      I've never tried to anneal an axle but I've taken fairly large boring bars, either the good end or the end we cut off to clear the turret and annealed them in a patio burner.

      Seems to work fine.



      • #33
        way to go - now i've got to get me some axles!
        in Toronto Ontario - where are you?


        • #34
          And a bigger fireplace.
          You might not like what I say,but that doesn't mean I'm wrong.


          • #35
            Originally posted by Lazlo
            I still have these test pieces, and I'd love to split them down the middle and test the hardness of the insides, but I don't know how to do that with affecting the current hardness.
            Clamp the end in the vise and snap it off by striking with the hammer. Wear safety glasses. If you want to split it lengthwise you need a rock saw or a slow speed grinder like mine to expose the center.
            Free software for calculating bolt circles and similar: Click Here


            • #36
              Originally posted by Evan
              Clamp the end in the vise and snap it off by striking with the hammer. Wear safety glasses.
              Oooh, that's a great idea Evan. They're 5/16" bits, so that might need to be a Hell of a whack, but I think I should be able to gently notch the heat affected zone with a Dremel diamond cut-off blade.

              I don't know how my hardness tester is going to like a rough (cracked) surface. I have one of those portable (~ 20 lbs) Rockwell-brand testers with the spring-loaded tester point -- it's not one of the giant, 700 lb cast iron lab testers...
              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


              • #37
                I don't know about rockwell hardness testers but I needed to do a microhardness measurement some years ago in college and I was chewed a new one by the materials engineering professor for not polishing the thing to some small number of microns. It's difficult to measure and interpret the indentation properly on a part that isn't flat and polished doing microhardness. YMMV for macrohardness but the same principles sound applicable.

                I will also point out that a snapped piece will have work hardening that could easily render the measurement completely dubious.