History and Features of Tosa Knife
Tosa Yamada-cho, the birthplace of Tosa-Uchi-Hamono (Knives).
As for the production area, Shikoku in Japan produces forged knives of traditional crafts in Kochi Prefecture.
The history of Tosa-Uchi-Hamono is old, and the swordsmith Goro Saemon Yoshimitsu, who moved from Yamato country in the late Kamakura period and the first year of Tokuji (1306), thrived until the end of Muromachi. In addition, the “Chosogabe District Prosecutor's Book” written by Chosokabe Motochika who unified Tosa in 1590, records that there were 399 blacksmiths.
In the early Edo period, the reformer of the Gen-Na (1621) Tosa clan fiscal tightness led to a rapid increase in demand for cutting tools for agriculture and forestry in response to promotion policies such as securing forest resources and developing new fields.
From this time on, the blade production technology has been remarkably developed, the mass production system and quality have been improved, and Tosa-Uchi-Hamono has been established. It is said that Tosa-Uchi-Hamono was developed from the current swordsmiths in Tosayamada-cho and developed mainly as tools for farming and forestry, such as sickles, scissors, saws, and harpoons. It is still known as one of Japan's leading blade production areas.
The feature of Tosa knife is that it uses the same high quality knife steel as Japanese swords. By forging like a Japanese sword, the metal structure is refined, giving sharpness, wear resistance, and blade toughness.
In addition, the parts that require strength and weight are made thicker, and the blades are finished to an appropriate thickness so that they can perform their ideal functions.
Types of Cutlery Steel
Aogami Super
Alloy steel with W, Cr, V to improve heat-treatment properties and wear resistance.
High quality plane, other tipped tool, kitchen knife, and/or sickle
Aogami 1
Alloy steel with W and Cr to improve heat-treatment properties and wear resistance.
Highest quality plane, other tipped tool, razor, and/or kitchen knife
Aogami 2
Alloy steel with W and Cr to improve heat-treatment properties and wear resistance.
High quality plane, other tipped tool, kitchen knife, and/or sickle
Shirogami 1
Carbon steel with minimum impurities. Highest hardness.
Highest quality tipped tool, plane, chisel, and/or razor
Shirogami 2
Carbon steel with minimum impurities. High hardness.
High quality tipped tool, chisel, razor, sickle, ax, and/or graver
Reference: https://www.hitachi-metals.co.jp/e/yss/search/aogami_super.html
Heat Treatment Method
Heat treatment is a process that changes the properties of steel (hagane) by heating or cooling it to suit the purpose of the steel.
Typical heat treatment methods include the following four treatment methods.
Normalizing (Yaki-narashi)
Heating and air cooling the steel removes the strain in the steel, making the steel structure uniform and fine.
Annealing (Yaki-namashi)
This is a heat treatment that makes the steel soft and sticky. It is a method of heating and then cooling it as slowly as possible.
It also plays a role in making the structure uniform. If the processing is incomplete, the structure of the steel material will be uneven, causing bending and warping during processing, and unevenness in hardness when quenched.
Hardening (Yaki-ire)
Heat treatment to harden steel. A method of cooling steel quickly by using water or oil after heating the steel.
If it is left as it is, it becomes hard, but it becomes brittle, so a heat treatment called "tempering" is required.
Tempering (Yaki-modoshi)
The steel that has become hard and brittle after the "quenching" process is now stiffened.
Once again, after heating at an appropriate temperature and then cooling, you can have both hardness and stiffness. Basically, "quenching" and "tempering" are performed in one set, which is used to make hard and durable products.