Traditional Japanese Sword Making from a Tatara Ingot As Estimated from Microstructural Examination

Abstract

This paper has examined the progressive development of microstructures in the iron and steel samples taken at several different stages in the traditional Japanese sword making from a Tatara ingot. The results show that the use of a particular input material, Tatara steel, and the adoption of the manufacturing technique, repeated cycles of forging and folding, may be the major factors characterizing the sword making. The undesirable aspects of both the heterogeneous Tatara ingot and the labor-intensive forge/fold operation are found complemented in their combination. It is shown that this combination provides an effective control over the compositional and microstructural variations inherent in the Tatara steel while it is shaped into a sword. The finished sword comes thereby to achieve fairly uniform structures, at least, macroscopically with the earlier variation still retained in the form of fine layered microstructures. The present study shows that the key role of forging in achieving the desired effects can be understood only if the dynamic evolution of microstructure from one stage to another is carefully examined because majority of the structural developments in the forging process have only a transient existence. Besides, they often hold crucial information relating the Japanese sword making to the general technical traditions of East Asia where cast iron has been playing an important role since the inception of iron-working. This article will detail the continuous microstructural development in the entire process of the traditional Japanese sword making, without which its technical and historical facets cannot be properly recognized.