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United States Capitol Dome:Characterization of Cast and Wrought Materials



Christopher N. McCowan, Thomas A. Siewert, David Olson, Joseph D. McColskey


Restoration of the cast iron dome at the United States Capitol is needed because moisture is leaking into interior areas of the building due to corrosion damage. Microstructure, composition, and tensile properties of cast and wrought samples from the dome are discussed in this report. The cast iron skin of the dome is a ferrite-pearlite grey iron with strength consistent with the carbon and silicon content. By current compositional and strength requirements the grey iron alloy comes close to meeting requirements for a class 20 grey iron. The microstucture shows good morphology and distribution of Type A and B graphite flakes that are appropriate for the intended service of the castings. In 20-20 hindsight, the decisions made concerning composition of the iron, and the details of the molding and casting conditions were all quite good. Fatigue data indicate that good performance should be expected to continue for the dome for many years to come.
Materials Characterization


cast iron dome, grey cast iron, microstruture, Office of the Architect of the Capitol, wrought iron, United States Capitol


McCowan, C. , Siewert, T. , , D. and McColskey, J. (2011), United States Capitol Dome:Characterization of Cast and Wrought Materials, Materials Characterization, [online], (Accessed April 15, 2024)
Created January 2, 2011, Updated February 19, 2017