Marcos de Campos

Abstract:

The Tatara furnace was the traditional method for steel production in ancient Japan. Tamahagane steel ("precious metal" in Japanese) obtained from the Tatara furnace was used for the manufacturing of Japanese swords.
These Japanese swords were produced with two types of steel: one with high carbon (kawagane) and another with low carbon (shingane). The high carbon steel was used for the blade region. The ductile low carbon steel was used for the interior part of the sword.
Japanese swords have a curvature, which is produced in the moment of the quenching. One of the interesting aspects of the Japanese sword is that the processing occurs in such a way that compression of residual stress is introduced on the side of the blade [1]. Thus, if a crack appears, it does not open. The Western swords with blades on both sides were much less reliable in combat. As for Western swords, existence of tensile residual stress on the surface of the swords makes them much easier to break.
Other details of the physical metallurgy of the steel employed in Japanese swords are also discussed.

[1] Tatsuo Inoue. Tatara and the Japanese sword: the science and technology. Acta Mech 214, 17-30 (2010)