Evaluation of Residual Stress Field near Filed Surface of Nakago in Japanese Sword Hilt

Abstract

The core steel part “NAKAGO” in the hilt of the Japanese short sword “TANTO” was used. This sword was made by one sword craftsman. The surface of the core steel part was machined manually by him using some hardened files. After hand-filing, the filed mark lines were remained on the finished surface. In this study, the 2θ-sin²ψ diagrams as a function of φ-angle from Fe-211 plane using Cr-Kα radiation were measured near the filed surface. The residual stress field near the filed surface of “NAKAGO” was determined. As a result, the typical 2θ-sin²ψ diagrams from the filed and electrolytic polished surfaces show the ψ-splitting phenomena. The compressive residual stresses, σ₁₁, σ₂₂ and σ₁₂, of about -208, -235 and -8.11 MPa were found to be generated on the in-plane polished surface parallel and perpendicular to the average filed line. And the microscopic shear residual stresses having stress gradients, σ₁₃ and σ₂₃, of about 28.7 and 2.88 MPa were also generated on the out-plane. It was concluded that the surface layer of the core steel part "NAKAGO" could be strengthened by this biaxial compressive residual stress field induced by hand-filing.