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Annealing hard metal in a fireplace?

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  • ckelloug
    replied
    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.

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  • lazlo
    replied
    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...

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  • Evan
    replied
    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.

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  • Circlip
    replied
    And a bigger fireplace.

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  • Mcgyver
    replied
    way to go - now i've got to get me some axles!

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  • clutch
    replied
    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.

    Clutch

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  • DICKEYBIRD
    replied
    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?

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  • lazlo
    replied
    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

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  • x39
    replied
    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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  • Wirecutter
    replied
    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

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  • scott96088
    replied
    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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  • lazlo
    replied
    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.

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  • Circlip
    replied
    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.

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  • carlquib
    replied
    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

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  • Evan
    replied
    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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