Metallographic structures and corrosion: cross-section investigation of archaeological iron objects from the Qin-Han Yueyang City site in Xi’an, China
Xi’an Institute of Conservation and Archaeology, 710068, Xi’an, China
2 Shaanxi History Museum, 710061, Xi’an, China
Accepted: 30 December 2022
Published online: 21 January 2023
Iron corrosion is a complex process that occurs in buried artefacts. In this work, we studied thirteen iron artefacts excavated from the Yueyang City site in Xi’an, China, which was a capital city during the Qin and Han dynasties approximately 2000 years ago. Metallography, SEM–EDS, and micro-Raman spectroscopy were used for artefact examination, and the results indicated that these iron artefacts were made from indirect processes of white cast iron, mottled cast iron, cast iron with solid-state decarburization, and liquid-state decarburization. Preferential corrosion was closely related to the metallographic phase. Lamellar pearlite was more easily corroded than ferrite, while ferrite was more preferentially corroded than spheroidal pearlite. Slag inclusions readily initiated the corrosion of the surrounding metal substrate. The main corrosion products were goethite, magnetite, hematite, lepidocrocite, and akaganeite. The results of this work provide a deeper understanding of the corrosion mechanism of iron artefacts and can be used to evaluate the necessity of de-chloride conservation.
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