annealing cast iron

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FLtenwheeler
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annealing cast iron

Post by FLtenwheeler » Mon Jan 18, 2016 8:05 am

I need to anneal a gray iron casting. What temperature do I need to take it too? And for how long?

Thanks
Tim
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Harold_V
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Re: annealing cast impon

Post by Harold_V » Mon Jan 18, 2016 3:54 pm

An almost impossible question to answer, as you have not provided a reason for annealing, nor a description of the casting.

There are pitfalls that one faces when heating a casting, as internal stresses, both heat induced and residual, can lead to cracking. For that reason, the casting should be heated slowly and uniformly, at least up to 800° F.

Assuming one wishes to improve machinability, and that the casting is just normal alloy iron, the object can be heated to approximately 1,100° F. Hold heat for one hour per inch of casting section. One should not exceed 1,400° F.

It stands to reason that the piece should not be quenched, but allowed to cool slowly. If you use a furnace, allow it to cool with the furnace. You can also consider heating the piece in a wood fire, allowing it to cool in the ashes. With this option, you have little control over temperature.

Harold
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FLtenwheeler
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Re: annealing cast iron

Post by FLtenwheeler » Mon Jan 18, 2016 7:15 pm

Thanks Harold

It is a driver casting just over 7" in diameter. I have it in the kiln how taking it to 1350F and holding it for 2 hours. I will see if it works tomorrow.

Tim

Ferritizing Annealing.
For an unalloyed or low-alloy cast iron of normal composition, when the only result desired is the conversion of pearlitic carbide to ferrite and graphite for improved machinability, it is generally unnecessary to heat the casting to a temperature above the transformation range. Up to approximately 595°C (1100°F), the effect of short times at temperature on the structure of gray iron is insignificant. For most gray irons, a ferritizing annealing temperature between 700 and 760°C (1300 and 1400°F) is recommended.
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Harold_V
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Re: annealing cast iron

Post by Harold_V » Tue Jan 19, 2016 2:21 am

Many years ago I witnessed ductile iron pipe being poured (Mountain States Cast Iron Pipe). The 20' lengths were poured in a spinning water cooled mold, so the operation could be defined as spiral casting. The only core used was to form the seal area in the hub end of the pipe, with sizes from 4" up to and including 20" being poured. How rapidly the metal was poured and the spout advanced determined wall thickness.

Once set, the now chilled pipe was withdrawn from the mold and sent to an annealing oven. Annealing is often very much a part of such an operation, but the chemistry of the process is quite involved (which you apparently understand, as you quoted a good deal of the information I have at my disposal), depending on the desired results.

Your choice should yield good results and I'm anxious to read about the results you achieve.

Harold
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FLtenwheeler
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Re: annealing cast iron

Post by FLtenwheeler » Tue Jan 19, 2016 8:33 am

Hi Harold

The annealing worked. But I heated the wheel to fast and cracked 4 spokes. I am using this as an learning experience. If I have to do it again I will ramp the temperature slowly. Maybe 120F per hour.

But for now the wheel pattern is heading back to the foundry to have 2 more pored.

Tim
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Re: annealing cast iron

Post by Harold_V » Tue Jan 19, 2016 4:43 pm

Cast iron is really horrible in regards to cracking, as it has little tensile and little ductility. A lot of that goes away if you spec ductile iron instead, so give that some thought. It machines very much like gray iron, but has far better tensile strength and is not as sensitive to heat cracking due to greater ductility.

Sorry to hear you cracked spokes, but it confirms everything I have in print (Metals Handbook, volume 4, Heat Treat, Ninth Edition).

Harold
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BAdams
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Re: annealing cast iron

Post by BAdams » Tue Jan 19, 2016 10:39 pm

Tim and Harold,
Thanks for sharing and letting us learn through your experience.

Brook

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