Minerals and Metals in Ancient India v1.c20.s1.12

v1.c20.s1.12

The solubility of carbon in iron is small at room temperature, but it increases greatly above 910°C. The hot spongy mass of iron when kept in prolonged contact with charcoal, absorbed carbon into the surface layers and thus became surface-hardened. The iron with the absorbed carbon is arranged in a two-phase structure called pearlite, which consists of alternate layers of soft and ductile iron (ferrite) and hard and brittle iron carbide (cementite). The hardness of the carburized sample depends upon the relative proportions of the two phases. Careful microscopic studies permit identification of pearlite structure relics even in a totally corroded iron object. (Knox, 1963)