Can carburization be avoided in a propane fired furnace?

[jimhokie]

We have a requirement that certain castings be heat treated in a vacuum and/or inert gas atmosphere furnace. However, one casting is too large for the supplier's atmosphere controlled furnace, and is proposing to use a propane fired furnace instead, stating that this is effective at avoiding excessive carburization as well as the atmosphere controlled furnace. They provided a propane certification citing low sulfur content (8 ppm by weight) for partial justification. The casting material is CA6NM.

Is there a significant difference between using the vacuum/inert gas furnace vs. the propane furnace? Also, what does the sulfer content have to do with it? I have found no reference to sulfur regarding carburization during heat treatment. Thanks in advance for any assistance with this question.

 

[arunmrao]

Can you please let me know the need for vacuum heat treat when the castings are sand cast? Any surface carburization should be of concern .

 

[jimhokie]

As for the technical reason it is specified, I don't know for sure. At this point I just have a specification that our supplier has to follow, and it stipulates the vacuum and/or inert gas atmosphere furnace for heat treatment to the desired mechanical properties. I suspect the reason is that it is a high-pressure pump casing that will be shock qualified, and thus the hardened casing may be less shock resistant. Yes, surface carburization is the concern, but will the propane fired furnace allow more carburization to take place that the specified method?

 

[arunmrao]

How large is the casing. Alternate to a vacuum furnace an electric furnace with a neutral atmosphere can be attempted.

 

[EdStainless]

The propane furnace should be set to run with excess air. You will get some oxidation but the carbon potential will be too low to get any C uptake. S is a concern because sulfidation can also hurt you corrosion resistance.
These parts would need to be pickled after anneal in order to clean them.
The parts annealed in the propane furnace will probably see faster cooling rates, which may actually help the properties.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[jimhokie]

arunmrao: The casing size exceeds the capacity of their largest controlled atmosphere furnace, thus the request to deviate from the specification.

EdStainless: What is the purpose of the excess air--does this just ensure complete combustion minimizing CO?