2015 Volume 56 Issue 10 Pages 1639-1647
Each Japanese sword is unique by its microstructure resulted by the steel composition and heat treatment. In this study, the automatic reconstruction method was applied for characterizing the prior-austenite microstructure at the sharp edge of three Japanese swords made in different time periods. The reconstructed prior-austenite microstructure was compared with that of three carbon steels, in order to clarify the variations of carbon content and heating temperatures of the swords. It was found that in carbon steels, the austenite microstructure is probably affected by initial microstructures, which is predominantly determined by carbon content. The three swords have similar carbon content, but their prior-austenite microstructures are considerably different, probably due to their heating temperatures. The strength at the sharp edge of the modern sword is significantly higher than that of the old sword. It may be due to the fine-grained prior-austenite in the modern sword compared with the abnormally coarse grains observed in the old sword. In order to obtain fine-grained austenite along with high strength and hardness of the cutting edge, it is recommended that the carbon content of Japanese sword is 0.6–0.7 mass%, and the heating temperature is from 750 to 800°C.
