Porosity in CA6NM Castings

[mahadhatu]

thread330-217250

The above thread references Nitrogen solubility in CA6NM. We are having porosity issues in casting with thinner walls (0.5"). I am having our heat tested for nitrogen content. In the mean time can any one comment about what percentage of Nitrogen would cause porosity in CA6Nm castings? Also, if the nitrogen in the heat is higher than desired, is there any way to remove this nitrogen during melting?

Thank you,

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There is always some thing better out there...
Mahadhatu

 

[metengr]

mahadhatu;
Could you describe your melting practice for these castings?

 

[mahadhatu]

Melted using air melt induction furnaces. We either use fresh materials (100% Chrome, Ni, 100% Mo and Low carbon steel) or ingots purchased from as master melter. According to the Certs from the Master melter, the average Nitrogen in the ingots is 0.02%. We do not have the capability of measuring Nitrogen in house so we have never measured it in our heats.

We use FeSi, Mn and Fe-Ti as deoxidisers.

--------------------------------------
There is always some thing better out there...
Mahadhatu

 

[EdStainless]

More likely it is moisture. These alloys will hold a lot of nitrogen in solution.
How are you shielding the alloy during melting?

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Plymouth Tube

 

[mahadhatu]

Ed,

This problem is evident in CA6NM castings with thinner walls (0.5") and not in thick wall castings. If the same configuration is cast out of something like 316SS we don't have this issue.
If moisture was the main cause, all of out castings should have the same problem which is not the case.

Thank you for your comments.

--------------------------------------
There is always some thing better out there...
Mahadhatu

 

[metengr]

mahadhatu;

Here is an interesting paper/book to review;

http://www.rastgar.com/rec/papers/Porosity in Castings.pdf

http://books.google.com/books?id=kW...=onepage&q=porosity in CA6NM castings&f=false