Neutron Diffraction Study on Full-Shape Japanese Sword

Abstract A mapping measurement using pulsed neutron diffraction with time-of-flight method is performed on a full-shape Japanese sword made in Keicho era (1596–1615) to elucidate the manufacturing process. The obtained diffraction patterns are analyzed by the Rietveld refinement and a line profile analysis. The constituent phases in the area closer to the back of the blade (ridge) are found to be ferrite and cementite, composing pearlite, while the area close to the edge is composed by martensite and austenite. The distributions of constituent phases are well explained with the distributions of dislocation density and crystallite size. The carbon contents in the area closer to the ridge side estimated from the phase fraction of cementite and in the area closer to the edge side considered from the phase fraction of austenite are similar, 0.9–1.0 mass%, expecting that the Japanese sword used in this study was created by the technique of maru, i.e., the use of a single type of high-carbon steel for the whole volume. The residual macroscopic stresses are estimated from the obtained lattice parameters of constituent phases. The distributions of residual macroscopic stresses in the width and thickness directions are small. The stress in the longitudinal direction is compressive at the ridge side, turns to quite large tensile at the middle part of width, then drastically decreases to be quite large compressive at the edge side of about −650 MPa.