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The Japanese sword is produced from a special kind of steel called tamahagane, using a forge-fold operation repeated several times. The purpose of this study is to clarify the development of microstructures with successive forge-fold operations using tamahagane. Specimens under several stages of sword making have been investigated with optical microscopy, scanning electron microscopy and electron probe micro analysis methods. Microstructures have been found to be a combination of ferrite and pearlite with a lot of nonmetallic inclusions. The ferrite bands become finer and among other inclusions Fe2SiO4 takes a spherical shape with increasing recurrence of forge-fold operations.

Abstract. Tatara is traditional iron making method developed around San-in area in Japan. Typical product of Tatara is Japanese sword, which is tough and strong and is also known as an art object. It is said that Japanese sword cannot be produced without Tatara iron. Thus microscopic observations of Japanese sword attracted researchers and were performed for example by Tawara with optical microscopy at the beginning of 1900s. Since then a few microscopic observations have been performed but not so many. A lot of knowledge of steels has been accumulated and new equipments have been also developed, which give information on atomistic scale. Thus the precise microstructural observations of Japanese sword using such as SEM/EBSD have been made and are compared with ordinary steel. The preliminary experiments indicated that the average martensite block thickness is little longer than that of ordinary steels and crystal orientation distribution is different from ordinary one.

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