Gray Iron or Grey Cast Iron Posted on 13th November 20152nd September 2020 by ThePD (The Project Definition) Gray Iron, or Grey Cast Iron is a type of cast iron that has a graphitic microstructure as a result of the presence of flake graphite. Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window)Click to share on LinkedIn (Opens in new window) Related Posted in Substance and tagged metal, substance. ThePD (The Project Definition) ThePD has been developing the Preferred Project Definitions based on the actual project execution and operation experiences and knowledge with the Project Language, and sharing with you daily basis.