Japanese sword's excellence

  (1) : https://www.youtube.com/watch?v=5vaYfd0fekI (2) Sword making secrets of the Japanese sword: https://www.youtube.com/watch?v=qUwagkhCjDM Watch both the videos and understand the mystery of the Japanese sword's excellence based on the commentary made by the materials scientists in the second video and the lecture (the first video) given by Prof. R. N. Ghosh, Department of Metallurgy and Materials Science at IIT-Kharagpur, India.