Cast Iron for heat treat fixture?

[gearHTr]

I am considering making support for large gear during carburize cycle. Fixture is to be re-usable also. We normally used low carbon steel with decent success.

My question is whether there is any benefit to using cast iron instead, either by cost savings or durability.

Cylce will be 1700 F for approx 10 hours.
Support Ring will be 18.5" OD, 15" ID, 1.5" thick
Part weighs about 88 lbs.

Thanks

 

[gieter]

I have no experience with carburizing, but in standard heat treatments cast iron has the tendancy to "grow" when being subjected to temperature cycles. A bit like multiple layerd wood plates that have become wet. Moreover it will have no strength at those temperatures.

Depending on how many times you want to use the fixture, I would look at heat resistant steels like 25Cr-9Ni. They are much more expensive, but they will stand significantly longer. they will also have some remaining strength at the temperature you mentioned. The nickel is necessary if you have high temperature gradients. The higher the gradient, the higher the Ni-content, going up to 25Cr-20Ni or even the Incoloy 800 series in case of water quenching.

"There are easier ways of earning a living than in the casting industry. But few are as exiting"
After Prof. John Campbell

Gieter

 

[arunmrao]

Gieter, I like your signature and my experience also is the same.

Coming back to cast iron fixtures,never heard of them being used,though chromium containing cast irons are used as furnace furniture in lower temperature zones.

At carburizing temperatures of 850C and above and prolonged exposure to high temperature may cause failure.

The current practice of using steel fabrication is economical and simple. Distortion may be an issue. Many heat treaters in India use steel fabrications .

I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
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