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Annealing hard metal in a fireplace?

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  • #16
    Originally posted by pcarpenter
    I am no metallurgist, but I know some alloys do not return to their annealed state well. It sounds like this may just be a medium to high carbon steel.
    I thought most (all?) steel alloys return to their annealed state, but the annealing temperature goes up according to the alloying elements. So carbon steel anneals at around 1300°F and tool steels anneal around 1600°F.
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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    • #17
      I've annealed a pile of steel in my woodstove. I have no idea how hot it gets.
      all I know...i leave it in all day.
      I keep lifting it to the top of the fire everytime I put wood in it.
      At the end of the day i pull it out and plop it into a bucket of cold water...LOL
      NO!!! Just kidding...I put it into a bucket of warm ashes that I scoop from the fire.
      Works every time.
      Russ
      I have tools I don't even know I own...

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      • #18
        I thought most (all?) steel alloys return to their annealed state, but the annealing temperature goes up according to the alloying elements. So carbon steel anneals at around 1300°F and tool steels anneal around 1600°F.
        Robert-- like I said, I am no metallurgist and the one thing I am thinking of may be a poor example, but I recall some experiments here with welding tool steel (cutting bits). It might have even been your experiment?? I think the premise was that they did loose hardness that might render them not so ideal as tool bits, but would not go back to a real soft pre-hardening state. It may be that some of the alloying elements (molybdenum, aluminum etc.) that are in higher than normal percentages in tool steel make it a rare bird that has nothing to do with old truck axles though

        Paul
        Paul Carpenter
        Mapleton, IL

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        • #19
          Originally posted by pcarpenter
          I think I would be tempted to make a little "tunnel" out of fire brick and sort of pack the thing in charcoal and light it up.
          I've used charcoal briquets many times with good results. I drilled a bunch of holes in an old steel bucket. I put a bed of briquets in the bottom, light them and let them start to ash over, put the part in, then cover with more briquets. When they're going pretty good I throw a piece of steel plate over the bucket and let sit until cool. This method has never failed me.

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          • #20
            I have annealed a lot of ball bearings in my Ashley wood burning fireplace by getting them red hot and dropping them in a coffee can full of ashes. I had no problem drilling and tapping them after that treatment.

            Gayle Hopson
            GHop

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            • #21
              While all of the usual alloys of iron can be annealed it isn't always just a matter of letting it cool slowly. Iron goes through phase changes as it cools and forms different allotropes depending on the cooling rate and the presence of other elements. Some alloys must be very carefully cooled at exact rates and held at certain temperatures before further cooling. Some alloys must be cooled no faster than a certain number of degrees per hour and can take days to reach a normal annealed state. Some alloys are partially quenched in molten lead to prevent the formation of iron carbides then cooled further.
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              • #22
                Evan, while you make a valid point, the fact is that anyone annealing a chunk of steel in the fireplace probably doesn't really know its exact alloy to begin with.

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                • #23
                  That is why I mentioned the differences in annealing conditions. It explains why just tossing a chunk of mystery metal in the fire, even if it gets red hot, may not result in an annealed specimen.
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                  • #24
                    I use this technique all the time, seems to work the charm on all the high carbon stuff I have tried it on. One question though, how much will this affect the metallurgical properties? I am mostly wondering about carbon content, because when stuff comes out of the stove it is as ugly as sin and usually has to have a fair amount of material removed to get below the skin. So far metals that I have tried it on, at least the ones that I know what they were, are 1040, 1080, and some 4140. So far none of the stuff I have tried it on seems to be hurt and has been hardenable after I finished the machining.

                    -brian
                    -brian

                    Hello, my name is brian and I'm a toolaholic.

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                    • #25
                      Sorry Mcgyver, my reply was based on the inferrence from Evan that the practice of Fireplace annealing didn't work, I then went onto explain that it had been common practice on this side of the pond. With regards to annealing a two and a half foot long piece of material, common sense would dictate that a suitable fireplace would be used.

                      If I was given a gallon of milk I wouldn't expect to fit it into an eggcup, not at one filling'

                      Regards Ian.

                      I also did mention that different metals have different annealing temperatures, seems Evan and I agree on that one.
                      Last edited by Circlip; 01-23-2009, 03:56 AM.
                      You might not like what I say,but that doesn't mean I'm wrong.

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                      • #26
                        Originally posted by pcarpenter
                        I recall some experiments here with welding tool steel (cutting bits). It might have even been your experiment?? I think the premise was that they did loose hardness that might render them not so ideal as tool bits, but would not go back to a real soft pre-hardening state.
                        Yep, that was me. I was trying to see if you could weld a HSS toolbit without ruining it, but even with a two TIG tack welds on the side, the toolbit turned cherry red, and the toolbit itself lost about 10 points of Rockwell hardness (from around 64 HRc to 54 HRc). It was somewhat harder than 4140 Prehard (~38 Rockwell) after welding:



                        But remember that the TIG arc is around 11,000° F, so the heat is very intense, but brief. It's very different than slow annealing in a furnace or fireplace, with the traditional 1 hour per inch of thickness that the tool steel manuals recommend.

                        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.

                        While all of the usual alloys of iron can be annealed it isn't always just a matter of letting it cool slowly.
                        Annealing tool steels is simple, as my welding experiment showed: hit the annealing temperature, and soak for 1 hour per inch of thickness so the insides get to the annealing temperature. The hard part with tool steels is re-hardening: with the exotic alloying elements you need multiple complex hardening and quenching methods, including salt baths and vacuum furnances, and triple tempering.

                        I have no idea how that works, but here's Carpenter's description for T-15, as an example:

                        Last edited by lazlo; 01-23-2009, 11:10 AM.
                        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                        • #27
                          worked great for me

                          I needed to turn down a pin from a truck walking beam rear axle. Must have been case hardened it was so hard a carbide insert would just slide across it.

                          I put the pin (3.5" x 16") in the wood stove along with a couple chunks of dry oak. and a chunk or 2 during the day.

                          The next day pulled it out. It was still warm to touch. I tossed in the lathe and it took .100 cuts like mild steel.

                          I used the pin to repair a broken grader mount.

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                          • #28
                            Originally posted by Ghop Shop
                            I have annealed a lot of ball bearings in my Ashley wood burning fireplace by getting them red hot and dropping them in a coffee can full of ashes. I had no problem drilling and tapping them after that treatment.
                            Gayle Hopson
                            Ok, now for the OT stupid question. What do you do with annealed, drilled, and tapped ball bearings?

                            -Mark
                            The curse of having precise measuring tools is being able to actually see how imperfect everything is.

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                            • #29
                              Originally posted by Evan
                              That is why I mentioned the differences in annealing conditions.
                              Thanks for the clarification, obvious now that I read it in that context. Please pardon.

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                              • #30
                                Originally posted by Wirecutter
                                Ok, now for the OT stupid question. What do you do with annealed, drilled, and tapped ball bearings?
                                Instant ball-handles, for one
                                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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