An Experimental Study on Blade Curving due to Quenching in the Japanese Sword

Japanese swordsmiths have recognized that Japanese sword (JS) blade curves initially downward and then upward during quenching. In the late 1920s, Hattori concluded based on his experimental studies using cylindrical specimens that the sword curving is induced from not only martensitic transformation expansion in the cutting edge side but also non-uniform plastic strain distributed in the section. We prepared straight JS type specimens made of the same steel and processes as JS, and machined model JS type specimens with the same shape as the JS type from commercial carbon steel and stainless steel bars. All specimens quenched by a Japanese swordsmith using the traditional way had a usual curved shape with different curvatures. Video recordings during the quenching and residual stress measurements for the specimens were performed for our future simulation works.