Relationship between Residual Stress Distribution near Blade Surface and Cross Sectional Microstructure Japanese Sword
Yoshihisa SAKAIDA, Toshiyuki MURAI and Hajime YOSHIDA
Abstract:The Japanese sword gWAKIZASHIh used in this study was made by sword craftsman. The surface of blade was finished by rough grinding just before final hand polishing process. In this study, the sword was cut using a wire-electrical discharge machine. Using a cut specimen, microstructure, hardness and carbon content of cross section of blade were measured experimentally. Surface residual stress distributions from the front edge gHASAKIh to the ridge gMUNEh of blade were measured by x-ray stress measurement. The diffraction from 211 plane of ferrite or martensite by Cr-K¿ radiation was used. As a result, the edge of blade gHAh had martensite structure. The area of gHAh was 10% of the total cross-sectional area. Other part remained pearlite and ferrite structures. The carbon density between two different carbon steels, the surface layer and core materials, changed continuously by diffusion. The hardness distribution coincided with the carbon content distribution. Biaxial principal compressive residual stresses were found to be generated and have constant stress gradients in depth on the ground blade surface because the Õ-splitting was not observed and the measured 2Æ vs. sin2Õ relations could be approximated as a parabolic curve. Large compressive residual stresses more than -1.0 GPa were distributed from gHASAKIh to gHAMONh on the edge of blade. On the other hand, compressive residual stresses diminished gradually to -500 MPa from gHAMONh to gMUNEh. The surface compressive residual stress distribution directly depended on the cross sectional microstructure of sword. Additional compressive residual stress field induced by rough grinding was superimposed on the residual stress field after quenching and tempering process. Key Words:Japanese Sword, X-ray stress Measurement, Microstructure, Hardness, Carbon content, Traditional technique