United States Capitol dome: Characterization of cast and wrought materials

► The microstructure and the mechanical properties of the cast and wrought materials used for the dome at the United States Capitol are documented. ► The cast iron skin of the dome is a ferrite-pearlite gray iron that comes close to meeting current requirements for a class 20 gray iron. ► The microstructure has a good distribution of Type A and B graphite. ► Fatigue data indicate good performance can be expected for many years to come.