Problems with gas in Material P91 1

[FoundryB]

We are currently having problems with large amounts of gas forming in casting when using the material P91 (ASTM A217 C12A).
We use chemically bonded sand to produce our moulds.

We have tried increasing the aluminium content without to much succes.

Is there a another way of degassing this material?

 

[sdjvar]

I think the problem you have is the coating material that applied to the sand mold, try different one with black graphite. Other suggestion is making sure to fire the mold after coating so there is no moisture in the mold.
I hope these suggestion will help.
SDJVAR

 

[GRoberts]

I'm not sure about the gas problems, but be carefull with the aluminum since the nitrogen is added to improve creep properties. Tying it up with Al will reduce the creep strength