I have been having trouble casting GX120MnCr18-2 with Mn content at 17.5% due to porosity defects-blowholes (probably gas porosity due to hydrogen solubility). The mold humidity as well as the sand's too were tested and are in given range. The same molds were casted with Mn content of 12$ and had no problem in the final product. This is where it gets tricky, when added Mn to 18% the castings had blowholes (pumped up instead of dragged as seen on the surface of the feeder). Casting temperature was methodically tested and never exceeded 1500 degrees C. Based on current research the more you increase temperature above casting temperature the more hydrogen dissolves and diffuses in the melt and when solidifies it makes those porosity defects. But when you increase Mn content hydrogen solubility should decrease.
As I said earlier 12% castings had no problem at all. Any ideas??
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