we want reducing Carbon content of initial electrode of VAR furnace, electrode composition prepared for VAR is (FSX-414: 52Co 29Cr 10Ni 7W) but Carbon is higher than limited composition (about 0.2% exceeded). which technical parameter most modify to obtain correct composition?
The pressure/temperature conditions near the arc control removal of carbon (higher vacuum after accounting for leak rate is desirable). In addition, the ingot size (larger may be better) and the electrode gap (too small a gap makes the arc unstable and introduce glow, which can increase carbon contamination) are secondary parameters. There may be others as well, such as melt/cooling rate.
These documents may be useful:
(1) http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.471.7698&rep=rep1&type=pdf
(2) https://pdfs.semanticscholar.org/1757/122619699506f35fdebb47bc9cbe3ed88107.pdf
Practically no carbon is lost during vacuum arc remelting.If lower carbon is desired in your cobalt base super alloy , use virgin metals and controlled amount of low carbon Ferro-chromium to meet the the final requirement.
Modify you pressure and clean your raw metals properly via effective etchant. Rinse in ultrasonic condition in high purity ethanol as well. Your Argon pressure will determine the Arc condition. Purge three times before melting.
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