日本刀の焼入れ時における応力・変形挙動に及ぼす加熱形態の影響

抄録

Japanese swords are an important traditional craft of Japan. Characteristic of Japanese sword has unique deformation and toughness. Quenching is carried out to give such properties. Generally Japanese sword is moved back and foward during heating. However, it is difficult to raise the temperature uniformly as the Japanese sword becomes longer. Therefore there is a method that Japanese sword is sinked into charcoal in order to heat uniformly. However, the effects of change in the heating form on the residual stress and deformation behavior of the hasaki has not been clarified. In this study, the effect of difference of heating form on stress and deformation of Japanese sword was investigated by quench experiment and numerical simulation. Therefore, heating method that moves forward and backward and method that uniformly heats were carried out. As a result, the deformation amount increased in uniform heating method by both experiment and simulation. Focusing on the temperature distribution, the moving heating method caused a temperature difference between the hasaki side and the mune side. However, with the uniform heating method, the temperature distribution was uniform. Compared with moving heating and uniform heating, tensile plastic strain more increased at the hasaki side in condition of uniform heating. Therefore, in the uniform heating method, increase deformation amount caused by increasing the difference in plastic strain. In addition, comparing with move forward and backward heating and uniform heating, residual stress distributions showed almost the same tendency. However, in the uniform heating, compressive residual stress on the hasaki side increased. It is conceivable that tensile plastic strain increased on the hasaki side as a cause. Therefore, it was suggested that uniform heating increases deformation amount and compression residual stress on the hasaki side.