Microstructural analysis of a steel tool rescued from historical site in RIO de Janeiro state

摘要

The present work has as its objective a metallographic analysis of a metallic archaeological artifact using methods of optical microscopy (OM) and scanning electron microscopy (SEM). The object of study is a scythe from the Brazilian colonial period, dated beginning of XVII century, removed from an archaeological site, Sitio Cruzeiro, in excavations conducted by researchers of the Brazilian Archaeological Institute. Sample preparation required a meticulous procedure in view of the fragility of the object. The scythe has been suffering the action of oxidation-corrosion for over 300 years, allowing the impregnation of mineral sediments. A detailed metallographic analysis coupled with spectroscopic SEM measurements concluded that of the object was made of steel with a carbon content of the order of 0.4%. The equi-axed microstructure together with the alignment of inclusions strongly suggest a metal working procedure followed by heat treatment and a slow cooling rate as the method used for fabricating the artifact.