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Yaso M.,Wakoh Museum | Takaiwa T.,Wakoh Museum | Minagi Y.,Wakoh Museum | Kanaizumi T.,Hitachi Ltd. | And 5 more authors.
International Journal of Materials and Product Technology | Year: 2011

Several metallurgical properties of a traditional Japanese sword were investigated from sharp edge to core area in cross-section and on surface. The microstructure is found to be lath martensite at the sharp edge and the prior austenite grain size is observed to be very fine. Towards the inside from the sharp edge in the cross-section, the microstructure changes gradually from hard martensite to soft ferrite. Micro hardness along the centre line in the crosssection was measured. The sharp edge is very hard and the hardness decreases drastically with the detachment from the sharp edge. The hardness gradient on the hardness distribution curve, tan θ is defined here. The value of tan θ is estimated as an important factor for the explanation of mechanical properties of Japanese swords. Furthermore, residual stress was measured with XRD. Large compressive stress is consequently found on the surface including the sharp edge, which is effective for strengthening the Japanese sword. © 2011 Inderscience Enterprises Ltd.

Yaso M.,Wakoh Museum | Takaiwa T.,Wakoh Museum | Minagi Y.,Wakoh Museum | Kanaizumi T.,Hitachi Ltd. | And 4 more authors.
Journal of Alloys and Compounds | Year: 2013

Two Japanese swords produced by 70 years ago and 600 years ago were investigated. Four-point bending test has been performed to estimate the strength of sharp edge of Japanese sword for the first time. The strength of sharp edge with fine lath martensite microstructure was evaluated, taking the specimen geometry of bending test into consideration. The strength of modern sword is estimated as high as approximately 4500 MPa (by four point bend test) and is considered to be a great value along with high hardness, which is comparable with the value of high performance tool steels. The fracture surface showed that the crack propagation behavior is smooth around sharp edge and ductile like the zigzag morphology from wavy pattern region into the core region. © 2012 Elsevier B.V.

Das A.K.,The University of Shimane | Ohba T.,The University of Shimane | Morito S.,The University of Shimane | Yaso M.,WAKOH Museum
Materials Science Forum | Year: 2010

Field Emission Scanning Electron Microscopy with Electron Back-Scattering Diffraction (SEM-EBSD) and Optical microscopy were used to point out the microstructural features of a Japanese sword prepared from tamahagane steel using traditional method. A lath martensite structure, which is usually characterized by packet and block in a prior austenite grain, existed both on the surface and the cross-section of the sword. SEM-EBSD study revealed that the development of prior austenite grain and packet were not much distinctive but the blocks within the packets were fairly observed. It was found that the packet size increased with the prior austenite grain size but the increment was small. Vickers micro-hardness measurement revealed that the sharp end was comparatively harder than other sections of the sword. EPMA study showed that the average carbon content of the sword was around 1 mass% along with a variety of non-metallic inclusions. Formation of lath martensite structure in such high carbon steel is remarkable but comparable to 0.6 mass% carbon ordinary steel. It was realized that the traditional method of preparation using tamahagane as well as the higher content of carbon provided the extraordinary features to the Japanese sword different from the ordinary steel. © (2010) Trans Tech Publications.

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