Ancient high-carbon steel from southern Tamil Nadu, India: microstructural and elemental analysis

Abstract

There have been claims of early use of high-carbon steel in South India. Still, the antiquity, elemental composition and steelmaking process have not been explored adequately. The high carbon steel was known in the Iron Age or early historical period. However, the large-scale use of such steel was prevalent only in the medieval times. This article examines the presence of steel and its metallographic features in the iron artifacts retrieved from two archaeological sites, namely Ambal and Vallam, Tamil Nadu, India, with occupational evidence from the Iron Age to the medieval period through a number of scientific tests. Metallographic as well as mechanical tests were performed to identify the morphology and measure the strength respectively. Similarly, the chemical composition was determined to quantify the alloying elements in the material. The slag was exposed on the etched surface of the sample cut from axe. Microscopy and chemical composition analysis showed very fine bright dendrites of wüstite in the iron slag. The deterioration of samples was confirmed in microscopic and composition analysis. The result shows that the inhabitants of ancient Ambal and the Vallam were equipped with iron smelting technology and had the knowledge of steelmaking in the Iron Age.