Mechanical Properties of Samurai Swords (Carbon Steel) Made using a Traditional Steelmaking Technology (tatara)

Okayasu M Sakai H

doi:10.4172/2169-0022.1000162

Abstract

The material and mechanical properties of samurai swords (Japanese swords), made using a traditional steelmaking technology (tatara), are investigated experimentally. The quality of these swords appears to be low because of the presence of a large number of inclusions, including oxide- and phosphorus-based structures; however, their mechanical properties are relatively good because of their fine-grained structure and high residual stress. The swords consist of several carbon steels, with a fine microstructural formation being obtained in the sharp edge of the sword (knife) as a result of the forging process. There is high residual compressive stress in the thick edge of the sword (mandrel), caused by bending due to the martensitic phase transition in the sharp edge. The carbon content of the sword varies depending on region: the sharp edge is found to have 0.55% C, which is more than twice the amount in the thick edge. The Vickers hardness and tensile strength in the sharp edge region are about 6 and 1 GPa, respectively, which are about three times higher than the corresponding values in the other regions of the sword. The hardness in the sharp edge region is almost the same as in a conventional carbon steel (Fe-C0.55) produced by presentday steelmaking technology. The tensile strength of the sharp edge of the sword is relatively high, but is slightly lower than that of the conventional Fe-C0.55 steel, despite the fine-grained structure and high residual compressive stress in the sharp edge region. This is caused by the presence of various inclusions in the sword.

Highlights

The samurai were a class of warriors in ancient Japan, originating more than 1000 years ago and having a relatively high social position
Because of the coating that was applied to the sword surfaces other than the sharp edge during quenching, there are no significant differences in microstructural characteristics between S2 and S3, whereas it is obvious that the heating process has led to a decrease in the amount of ferrite phase in S2 and S3 compared with S1
On the basis of the results obtained, the following conclusions can be drawn: 1. The tamahagane from which the sword is made is formed with fine microstructures with several residual inclusions: oxide- and phosphorus-based structures

Summary

Introduction

The samurai were a class of warriors in ancient Japan, originating more than 1000 years ago and having a relatively high social position. Samurai always carried Japanese-style swords, generally on the waist, as part of their role as protectors of society. They were often required to use these swords in battle, and there were a number of battles in ancient Japan in which many casualties were caused by these swords. There are still craftsmen making samurai swords in Japan, even though these are no longer intended for actual use. Because of their beautiful designs, these swords have acquired the status of aesthetic objects in Japanese society [1]

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