Minerals and Metals in Ancient India v1.c27.s1.t1.2

v1.c27.s1.t1.2

Today, a key procedure followed for steel-making is hardening by quenching, which produces martensite needles — highly stressed α- iron supersaturated with carbon — with adequate hardness (BHN 200-400). The hardened steel is usually tempered (heated to a temperature below the lower critical temperature and then cooled at a desired rate) to relieve the internal stresses, and improve ductility with slight reduction in hardness. We reported in chapter 12 that a couple of Indian iron samples belonging to third and second century BC showed martensitic structure, proving thereby that the quenching procedure was known to the Indians during the pre-Christian era.