History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s2.t4.163

v1.c13.s2.t4.163

In the first process steel was made by packing about 350 gms of small pieces of wrought iron into a clay crucible with 1/10th of its weight of chipped dry wood and leaves of specific plants e.g. Avaram (Casia auriculata) etc. and the crucibles mouth was sealed with clay. Fig.35 shows the branch, leaves and flowers of Casia Auriculata. Sometimes a hole was made in the crucible cover for the escape of the gases produced inside the crucible. During heating 20 to 25 or some times more number of such crucibles were heated in a specially designed furnace where the central crucible could attain a temperature of more than 1550°C. The furnace as described by Buchnan(1807) and others gives an idea how the crucibles were shifted in a fixed order to the hottest zone of the furnace where the steel reached the molten state. After this crucible was either cooled slowly or it was water quenched. The process details and the time of one such operation have been summarized by Bronson (1986). The wrought iron charge could be carburized in about 2 to 6 hours and the extent of carburization was controlled by adjusting the proportion of wood chips in the charge and the residual amount of the FeO rich slag remaining in the wrought iron.