Study of Microstructures on Cross Section of JAPANESE SWORD

Abstract
An old, famous Japanese sword has been studied metallurigically to observe its microstructure by optical microscopy and scanning electron microscopy. The microstructure in the sharp edge of cross-sectional part is fine martensite and the morphology is lath type martensite. The other parts of sword, side and central part, of cross section show the structure of fine pearlite or coarse pearlite dominantly. The hardness of the sharp edge is high enough to possess the sharp cutting property. SEM-EDX observations indicated that several kinds of non-metallic inclusions exist in the sword which are considered to be originated from the slag smelting reaction in Tatara process. The amount of non-metallic inclusions in the sword is 50-100 times more than that of the ordinary steel. In the sharp edge the amount of inclusions is fewer and the sizes are finer in comparison with side and central part of the sword. It is considered that repeatedly forging and folding operations in making sword process are responsible for that.