Not sure if it’s the same thing, but from here:
http://atomic-fungus.livejournal.com/
“This “nanopaper” can withstand roughly 31,000 PSI of pressure without tearing. This is for a sheet 0.05 millimeters thick—approximately normal paper thickness. Ordinary paper can only withstand about 145 PSI.”
And more here:
Don’t know about cast iron. Seems like a brittle thing to work with. Mild steel is easy to work with: fast, strong, cheap.