High-carbon steel and ancient sword-making as observed in a double-edged sword from an Iron Age megalithic burial in Tamil Nadu, India

Abstract

An iron sword from an Iron Age megalithic burial at Thelunganur in Tamil Nadu, India, was examined using metallographic techniques. The sword was made of ultra-high-carbon steel with a fairly uniform microstructure consisting primarily of fine cementite particles in a ferrite background free of notable non-metallic inclusions. The morphological control, however, was not perfect and frequently allowed cementite to precipitate in the form of a network along austenite grain boundaries. It was also observed that carbide particles of varying size and shape often caused microscopic layers to develop, forming a visible pattern to the naked eye on the polished and etched surface of the iron sword. This pattern likely inspired the later development of various surface markings such as the damask. This paper presents a detailed account of the analytical data to show that the iron sword under consideration was an early example of high-carbon steel employed in the manufacture of a functional object where the divorced eutectoid transformation technique, rediscovered recently, was used for the control of cementite morphology. It is also proposed that technologies for making and handling high-carbon steel were in existence at a much earlier date than previously supposed.