Why the Japanese sword is folded?

Published: 15/09/2021 Comments: 0

What is Folded Steel?


Folded steel isn’t a steel type like carbon steel. Folded steel is a forging technique applied to mostly carbon steels. In the process, the metal is forge-welded, folded, and welded again. Katanas are usually folded between 8 and 16 times. Folding swords is part of the traditional Japanese katana-making process for samurai swords. While ancient, this swordsmithing tradition is critical to the creation of durable, high-quality blades.




Why are Swords Folded?


Remove impurities

Most Japanese swords were folded. Most iron deposits in Japan contain ore with a very high carbon content. This iron was called Tamahagane or pig iron.

As this steel contains 4-5% of carbon it is unsuitable for blade forging. In feudal Japan, swordsmiths used this material during the katana making process which comprised iron sands and charcoal smelted in a clay Tatara furnace. This blade material was very impure, with gaps in the steel, less desirable elements, and an uneven distribution of carbon throughout. This carbon content would make every sword break extremely easily.
Thereby, they could remove the impurities in the steel and reduce the carbon content.

Alternating hardened layer

By folding the steel, the swordsman can achieve alternating layers of different hardenability. Every time the steel is folded you create more and more overlapping layers. These alternating layers greatly enhance the toughness of the blade.

Folded pattern

Furthermore, they add to the unique design of a katana. Everyone can spot a katana by one of its prominent features, one of it being the layers created by the folded steel. swordsmen pride themselves on their ability to create unique patterned particles. Shita-kitae is the key stage in the formation of these patterns.


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