Minerals and Metals in Ancient India v2.c45.s9.5

v2.c45.s9.5

We do not know when India started producing crucible or ‘wootz’ iron/steel which contained more than 1.7 per cent carbon. Probabaly this technology also was started before the Christian era, as inferred from the Greek and Roman travellers-cum-writers. Such a high percentage of carbon resulted in the cementite (Fe₃C) phase, which contributed to hardness as well as brittleness. The Wootz swords and implements could however be made ductile by careful forging at a not-too-high temperature of 650ºC-850ºC, when the coarse cementite grains were compressed and elongated in one direction, surrounded by pearlite and ferrite matrix. Reheating and quenching would result in some martensitic transformation. On selective etching, these ‘Damascus steel swords’ would show white cementite streaks. The finished product, a high carbon steel with cementite streaks in pearlite-graphite-martensite matrix possessed ideal combination of hardness (even at the edges) and ductility. These steel materials, sword, etc. were described as ‘of a dull blue colour, marked with ten millions of meandering lines’ which were the distinctive ‘damask’ or surface pattern of seggregated white cementite (Sherby and Wadsworth, 1985).