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DICKEYBIRD
01-21-2009, 09:33 PM
I've seen it mentioned on the forum that hardened steel can be annealed in a wood burning fireplace. After a few years of not using ours, SWMBO & I decided to fire it up this winter (friggin' cold!)

I have a 2 1/2 ft. piece of auto axle that I drug home a couple years ago, thinking I'd make something with it. The darned thing is hard as Superman's kneecap and I'd like to soften it. If I simply laid it on the bed of coals it seems to me that it would slowly settle down through the coals and end up too close to the fireplace floor to stay hot.

Do you just lay it across the top of the andirons, pile on the wood and forget about it for a day? Or do you tie it loosely to the bottom side of of the andirons so it'll stay close to the top of the coals? If so, what kind of wire?

garyphansen
01-21-2009, 10:16 PM
Let the fire but down to to a good bed of red hot coals higher than your grate. Lay the steel on the bed of coals and build a good fire on top. Let that buren down to a bed of coals and rake the coals up over the steel and leave it to cool down slowly. As long as you got the steel red hot after it cools slowly it should be fully annealed. If you did not get it hot enough you could repeat. Gary P. Hansen

Mcgyver
01-21-2009, 10:43 PM
I welded up an annealing box from 1/8" plate, filled it with ash from the fire place and it works perfectly. Get the material red hot, put it in the box and next day take it out......files etc come out very soft.

Now, at 2.5 feet you don't want to weld up a box, but the take away is 1) that ash provides a great insulator and isn't bother by the high temps and 2) as Gary said, it won't work if you can't get the metal hot enough....I can't see how the fireplace will get you there, especially for a 2.5' piece, then again i haven't tried so maybe its possible

can you torch into some manageable sizes ?

When i need to get a largish piece, like a foot long, red hot, I build a temp structure out of insulated firebrick, bottom, sides, roof and heat the item red hot there and drop it in the annealing box. Last one i did was a big ass file - with the IFB structure i was able to leave the O/A in the corner and got it done with propane, cheap sob that i am.

anyway, your challenges are getting it to temp and then having it cool slowly.....I'd be thinking the fireplace won't generate enough heat but the ashes you make could be very handy. maybe set up on a couple of pieces of brick in the fireplace (without the grate), lay the piece across the the brick more or less surrounded by ash and get to temp with a a torch then cover it over with ash. just an idea, maybe some domestic issues with wheeling the O/A cart into the house though :D

Evan
01-22-2009, 12:38 AM
I don't think a fireplace will do the trick either. It has too much airflow to get hot enough. I anneal my pieces in our airtight wood stove which is a great big old Fisher with a box about three feet deep and lined with firebrick on the bottom half. I build up a good fire and let it burn down the toss in the material and keep the fire stoked as usual. Then I let it burn out and cool overnight. Next am it is still pretty hot but below the quenching temperature so it can come out and be washed.

SGW
01-22-2009, 07:27 AM
I don't think you need to get it all that hot, relatively speaking. It's almost certainly just high-carbon steel. To anneal it, you don't need to get it as hot as you would if you were trying to harden it. In fact, just "dull red," then cooled slowly, ought to do it.

DICKEYBIRD
01-22-2009, 08:01 AM
Thanks all. I'll try Gary's method since it looks easy.:) As luck would have it, the temps are climbing and are supposed to be back in the 60's (!!) on Sat. when I was going to try. Never fails; plan something & the weather won't cooperate. I'm not going to complain too loud though.

McG I was hoping to get the middle soft enough to cut it in half in my bandsaw and then throw 'em back in again. I don't have a torch yet but do have my eye on a set.:)

As far as the heat goes, if I open my damper wide open and close the glass doors, leaving the little sliding vent at the bottom open, the coals get REAL hot. I've seen the middle bars on the grate glowing pretty red! I guess I could hit it with a hairdryer to stoke it up even more if need be.

Circlip
01-22-2009, 10:04 AM
Sorry, the fireplace trick does work. Fuel and location may change but the fireplace was the standard annealing furnace for Muddle Ingineers in the UK before the "Central Heating" brigade took over.

The fuel used was coal and the text of many articles in the ME were " Place in the burning fire and leave overnight "

Regards Ian.

Annealing temperature is dependent on material being annealed.

A.K. Boomer
01-22-2009, 10:16 AM
I think it all depends on this question --- "can you get it glowing cherry red"

If so then your fireplace will work just fine, some things to consider

hardwood creates hotter coals that last much longer -- something like pine will due for a piece thats not as thick but a fiery bed of hardwood coals will get some fairly large material cherry red hot.

GadgetBuilder
01-22-2009, 10:16 AM
I've annealed a car axle in my fireplace and there wasn't much to doing it. I laid the axle on the grate (about 4" above the bricks), built a fire using relatively small wood (so it would burn fast and hot) and kept it going for a couple hours. The fire was much hotter than I expected - the axle actually turned dull red.

I left it on the grate over night to cool slowly. The axle, which had been really difficult to cut before annealing, turned very nicely afterward and became several MT3's for my mill tooling. The axle spline is visible on the leftmost holder:
http://www.gadgetbuilder.com/MillTooling2.jpg



John

lazlo
01-22-2009, 11:52 AM
The fire was much hotter than I expected - the axle actually turned dull red.

Steel's annealing temperature (when the carbides go back into solution) is 1341 F, which is dull red :)

Anything below that temperature won't do much.

Fasttrack
01-22-2009, 12:00 PM
I used a wood burning forge, but I think a fireplace would work too. Like you mentioned, with the damper open, the doors closed and the vent open, you can get things going real well. You'll just have to work a little more at it.

Once I got my axle a nice cherry red, I dropped it in a bucket of kitty-litter. I came back 24 horus later and it was still warm! :eek: Anyway, it was soft as butter and easy to machine.

mwechtal
01-22-2009, 12:55 PM
I used a wood burning forge, but I think a fireplace would work too. Like you mentioned, with the damper open, the doors closed and the vent open, you can get things going real well. You'll just have to work a little more at it.

Once I got my axle a nice cherry red, I dropped it in a bucket of kitty-litter. I came back 24 horus later and it was still warm! :eek: Anyway, it was soft as butter and easy to machine.
I once shoveled ashes out of my woodstove after it had been out for a week. I could put my hand on top of the ashes and not feel any heat. I shoveled them into a plastic bucket, and melted it. The bottom of the stove was still quite warm. I've since switched to a galvanized steel bucket. ;)

Mcgyver
01-22-2009, 03:26 PM
Sorry, the fireplace trick does work. Fuel and location may change but the fireplace was the standard annealing furnace for Muddle Ingineers in the UK before the "Central Heating" brigade took over.

.

I can accept the fireplace gets hot enough, like i say, haven't gone the route before, but the point is not will it work for any annealing, but will it work for a 2 1/2' length ......that's a very big fire! It takes a fair bit of heat to get big chucks to red all over...not sure how you'd make a fire to engulf all 2 1/2' at temp as well as have it buried in coals for a slow cool.

pcarpenter
01-22-2009, 03:36 PM
I am glad to see a couple of folks addressed the specific question of whether a presumably forged axle shaft would anneal. 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 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. This scheme would allow you to heat it evenly and to use forced air (maybe a leaf blower at idle) at one end to generate the needed heat pretty quickly.

The only concern I might have (and maybe someone could address) is whether the charcoal might tend to provide enough carbon on the exterior to case harden it if left in there. I think after it reached red heat I would pull it and bury it in dry sand to slow cooling. I have done that with smaller parts and it seemed to work well.

Paul

Nick1911
01-22-2009, 04:21 PM
I once shoveled ashes out of my woodstove after it had been out for a week. I could put my hand on top of the ashes and not feel any heat. I shoveled them into a plastic bucket, and melted it. The bottom of the stove was still quite warm. I've since switched to a galvanized steel bucket.

My father caught the house on fire doing that once. Shoveled week old ashes into a metal bucket, then set it outside, next to the house.

The fire was contained before significant structural damage occurred. New siding and a few new studs were needed.

lazlo
01-22-2009, 04:46 PM
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 1300F and tool steels anneal around 1600F.

torker
01-22-2009, 04:58 PM
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

pcarpenter
01-22-2009, 05:37 PM
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 1300F and tool steels anneal around 1600F.

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 :D

Paul

x39
01-22-2009, 05:55 PM
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.

Ghop Shop
01-22-2009, 06:17 PM
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

Evan
01-22-2009, 08:09 PM
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.

x39
01-22-2009, 11:04 PM
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.

Evan
01-23-2009, 12:27 AM
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.

carlquib
01-23-2009, 01:16 AM
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

Circlip
01-23-2009, 03:53 AM
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.

lazlo
01-23-2009, 11:06 AM
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:

http://i164.photobucket.com/albums/u15/rtgeorge_album/HSSTIG.jpg

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:

http://i164.photobucket.com/albums/u15/rtgeorge_album/T15HeatTreat.gif

scott96088
01-23-2009, 11:24 AM
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.:)

Wirecutter
01-23-2009, 12:42 PM
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

x39
01-23-2009, 12:51 PM
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.

lazlo
01-23-2009, 07:08 PM
Ok, now for the OT stupid question. What do you do with annealed, drilled, and tapped ball bearings?

Instant ball-handles, for one :)

DICKEYBIRD
01-25-2009, 04:41 PM
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?

http://i57.photobucket.com/albums/g227/DBAviation/Annealedaxle.jpg

clutch
01-25-2009, 06:15 PM
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

Mcgyver
01-25-2009, 08:35 PM
way to go - now i've got to get me some axles!

Circlip
01-26-2009, 07:18 AM
And a bigger fireplace.

Evan
01-26-2009, 09:05 AM
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.

lazlo
01-26-2009, 11:15 AM
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...

ckelloug
01-26-2009, 12:23 PM
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.