Study of Metallurgy and Mechanical Property on Japanese Sword

Abstract

Japanese sword has finer grain size and lath martensite in the microstructure of sharp edge amazingly. Nowadays these structures are considered to be one of the ideal structure at which are greatly aimed to strengthen or improve toughness of steels. Though the carbon content of its sharp edge is 0.70 mass %, there are no lenticular martensite and no micocracking in that area. As a result of bending test by actual sword specimen, one sword was finally bent, the other sword was broken. However it is found the sharp edge in Japanese sword has such a large bending strength 2500, 4600MPa respectively as modern, high performance tool steels and the difference of crack propagation under bending depends on the microstructure distribution and the grain size in cross section of Japanese sword.

Automatic Reconstruction Approach to Characterization of Prior-Austenite Microstructure in Various Japanese Swords

“…Japanese sword Hardness measurement and a four point bending test had been set up by Yaso et al 5,6) to measure the strength at the sharp edge of the same old and modern swords used in the present study. It was reported that the hardness of the two swords is similar (830870 HV), 5) but the strength of the modern sword is about 2 times higher than that of the old sword (4645 and 2552 MPa, respectively).…”

“…It was reported that the hardness of the two swords is similar (830870 HV), 5) but the strength of the modern sword is about 2 times higher than that of the old sword (4645 and 2552 MPa, respectively). 5,6) Without knowing the PAM, the difference in strength of the two swords was explained by thicker hardening region in the modern sword (5 mm) compared with the old sword (1 mm of peak hardening and 5 mm of transition). 5,6) Because of thin hardening region observed, the old sword was probably repolished several times in its life in order to recover the sharpness of its cutting edge.…”

“…5,6) Without knowing the PAM, the difference in strength of the two swords was explained by thicker hardening region in the modern sword (5 mm) compared with the old sword (1 mm of peak hardening and 5 mm of transition). 5,6) Because of thin hardening region observed, the old sword was probably repolished several times in its life in order to recover the sharpness of its cutting edge. With the result of PAM analysis in this study, it is reasonable to suggest that fine PAM of the modern sword also has contribution to its high strength.…”

A novel approach to study the effect of heating temperature on prior-austenite microstructure of a Japanese sword

“…The chemical composition, microstructure and mechanical properties of this sword have been investigated by Yaso et al [8][9]. According to their reports, the microstructure near the sharp edge of the sword is mainly lath martensite with 0.71 mass% of C, measured by electron probe micro-analysis (EPMA).…”