History of Technology in India, Vol. I: From Antiquity to c. 1200 A.D. v1.c13.s4.38

v1.c13.s4.38

The classical Indian heat-treatment given to the steel swords was to heat the blade to red hot condition and then insert the blade from the cutting edge side into a green trunk of Plantain tree and allow it to cool there. During this process the organic fluid and water present in the cells of the trunk created a cooling rate fast enough to transform the Austenite of the edge into Martensite and in the latter period the dried wood helped in self tempering by acting as heat insulator. This typical heat treatment was called ‘watering treatment’ and it produced a typical flowery pattern on the sword blade as shown in Fig. 34. Recently Rakshit et al. (1991) have experimented on this technique of hardening steels and were successful in developing edge hardness of Rc 45 to 47 with decreasing hardness towards the thicker section of the blade. Archaeological evidence of hardened steel has been found by Ghosh and Chattopadhyaya (1982) dating back to 810 B.C. at Barudih in Bihar.