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Annealing cast iron

in a woodburner

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Bazyle17/12/2013 14:10:10
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5688 forum posts
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I have some small castings in my small woodburner at the moment. They are small and max thickness about half inch. They only get to a dull red and i'm not going to thrash the fire to get hotter but time is not a problem.

So how long? Will it be enough at dull red as I read suggestions of more like bright red for an hour or so.

I have in the past tried a bit of sash weight in this fire and it didn't make any difference but that may just have been the cruddy nature of the sample.

jason udall17/12/2013 14:39:51
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Dull red to me seems a bit low...but why not cycle and test ( file? )...

I think soak time won't help if not above critical temp...all soaking really does is allow the whole sample to attain temp.
The phase change chemistry happens at a critical temp...and no amount of soaking below that will help...
Nicholas Farr17/12/2013 19:37:34
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Hi Bazyle, I agree with Jason that dull red is a bit low.When I had a Parkray I used to get it burning fairly well and then get any cast iron into the middle of the fire, so that I could get as even as possible heat all around. I would keep an eye on it and watch for it to be a reasonably red to bright red but not cherry red, I would then leave it like that for a short while, depening on the size, and that pull it to the top of the fire and then dampen the Parkray down to the normal use level. Once the piece had gone back to black I would then pull it out of the fire and bung it in the ashpan untill morning. All the pieces that I did like this would machine very nicely.

Below are a couple of scans that I've dug out of my old college notes when I was doing my C&G advanced welding, which may help you.

graph01.jpg

graph02.jpg

Regards Nick.

JasonB17/12/2013 20:04:01
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20mins at this colour allowed me to complete this part which is probably a bit above dull red.

Bazyle17/12/2013 20:43:18
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5688 forum posts
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Thanks, I keep forgetting it needs the actual temperature not just time like some diffusion based transformations. Might try a couple of firebricks to condense the size of the fire then I can run it hotter without overheating the rest of everything.

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