The secrets of Tamahagane steel Katana Sword

Tamahagane is widely known as the raw material for Japanese swords. Although it is said to be the purest steel in the world, its manufacturing process is limited and so are the products made from tama-hagane. We will now introduce why tama-hagane is considered the best raw material for swords, the origin of its name and why it is said to be of better quality than other types of steel.

Presentation of Tamahagane steelkatana en mains

Tamahagane, known as the material of swords, is a precious steel that can only be made in very small quantities by the direct steel-making method known as the "keraoshiho method" of tatara iron-making.

Although the name "tamahagane" did not take root until the middle of the Meiji period (1868-1912), the existence of a high quality steel called shirahagane (white steel), which is considered equivalent to tamahagane, was confirmed during the Tenmon period (1532-1554).

The Tamahagane appellation

Tamahagane has been valued since the Edo period (1603-1867) as an excellent steel that can be used as "hagane" (blade metal) simply by forging it, due to its extremely low impurity content and uniform quality of the material.

The name "tamahagane" existed as early as the late Edo period (1603-1867). At that time, tamahagane was a fine-grained round ball produced by grinding kera, a material derived from the manufacture of tatara iron.

Theories on the origin of the word "tamahagane

One theory is that this term comes from the word "tama" (=bijou).

Another theory is that when the army and navy arsenal asked for crucible steel material, they were given tamahagane. The latter was considered to be of inferior quality to crucible steel (the renowned steels of the time were tsukuri-hagane or tsubuhagane). Nevertheless, the evaluation of tamahagane by the arsenal was surprisingly high, and the term "tamahagane" was used to designate the better quality steel.

A third theory is that the name "tamahagane" comes from the fact that the arsenal made cannonballs (tama) from crucible steel.

The "brass pressing" method and the "cast iron pressing" method.

The raw material for tamahagane is masa iron sand, and charcoal is used as fuel during the steelmaking process. There are two main established methods of making tatara iron. The first is the kererae-oshi method, which refines steel into tamahagane and other ferrous materials known as mejiro (mejiro) and tsukuriko (tsukuriko).

Although not refined in large quantities, steel, unlike pig iron, has a low carbon content and can be beaten, drawn and forged, as well as hardened to make it harder.

Another method of making iron is the "pig iron pressing method" (zuukuoshi-bo). Pig iron is a ferrous material obtained by a pressing method. Because of its high carbon content and ease of dissolution, pig iron was mainly used as a raw material for mass production of items such as nails, pots and agricultural tools. This method is characterized by the use of "akome iron sand" as the raw material for iron making.

The term "Hitoyo" refers to the entire process of making tatara iron, from the beginning of the fire to the end of the process. It is said that about 2.5 tons of iron sand and 12 tons of charcoal are used in the first generation of tatara (also called "three-day pressing" because it takes three days and three nights in the case of the hite-oshi method), but only about 2.5 tons are made into tamahagane, and only about 2000 llbs scan be obtained as good quality tamahagane. This shows how valuable tamahagane is as a material.

What is the difference between tamahagane and ordinary steel?

homme avec deux sabres

In general, the word "iron" is often associated with "steel". For example, kitchen utensils. Spoons, forks, kitchen knives, pans, pots and other kitchen utensils are usually "steel products" made of iron.

Large vehicles and heavy machinery such as cars, airplanes and excavators are also steel products. Most of these steel products we see in our daily lives are alloys made primarily from iron ore, and steel balls are also alloys made from iron sand. Each type of steel differs in the amount of carbon it contains.

Toughness obtained by bending and forging

In refined iron, the higher the carbon content, the harder the iron, but the less tough it is in proportion. Toughness" refers to breakability, and the harder the iron, the more likely it is to break. Conversely, the lower the carbon content, the less hard the iron is, but the softer and easier to stretch. Ordinary iron can be deformed relatively easily when force is applied, but steel is so hard that it cannot be deformed without heat.

The Japanese sword was such a strong weapon that it was called "unbreakable, undeformable and sharp". Swords are treated in various ways during the manufacturing process. Tamahagane, the raw material used to make swords, is a very pure steel with a carbon content of 1 to 1.5%. Impurities, which are only slightly present, are gradually dispersed and refined by a process called "bending and forging", during which the steel is beaten, drawn, stacked, beaten, drawn and stacked again, repeated about 15 times.

The non-metallic inclusions (oxides, sulfides and other non-metallic substances in the metal) in tamahagane are extremely soft and stretchy, making it the perfect steel material for swords, as they make Japanese swords stronger through the bending and forging process, create beautiful patterns on the base iron, and improve sharpening. It is truly the perfect steel material for swords.

Types of Tamahagane by quality

Yasukuni Tatara et Nittoho Tatara

The Nittoho Tatara (Japanese Sword Preservation Association), which still operates every winter in Okuizumo City, Shimane Prefecture, produces about 1 ton of tamahagane per production cycle (one generation), and as the process is carried out three times (three generations) during this period, the resulting tamahagane is about 3 tons and is distributed to smiths throughout Japan. The fact that tatara iron making is still in operation today is due to the extraordinary efforts of our predecessors.

In the middle of the Meiji period (1868-1912), with the import of cheap steel from overseas, the demand for Japanese iron decreased considerably due to the rapid spread of "western iron", which is refined from iron ore and contains many impurities produced by modern western steel making methods. The few remaining techniques of iron pressing (mashi-oshi) were temporarily revived as "Yasukuni tatara" from 1933 to 1945 due to the wartime demand for military swords, but disappeared from the public scene again after the defeat of World War II.

The number of sword smiths decreased greatly after this period, but a few continued to make swords from the small stock of Yasukuni tatara.

The Association for the Preservation of Japanese Art Swords and Hitachi Metals (the only remaining special steel manufacturer) took the situation very seriously and in 1977 decided to close the Yasukuni tatara to allow swordsmiths to continue to make swords, believing that "Japanese swords are not weapons, but works of art." In 1977, the site of the Yasukuni Tatara, which had been closed, was renamed Nitto Tatara and restored to the present day.

Tamahagane Steel Grades

The manufacture of Tatara iron was revived after many ups and downs. It was not until modern times that grades were assigned to the rare and high quality tamahagane produced.

Yasukuni tatara and Nittoho tatara were graded according to different standards, with Yasukuni tatara having four quality levels: "crane", "pine", "bamboo" and "plum". In Nittoho tatara, the quality is divided into three levels: "1st grade", "2nd grade" and "3rd grade". The highest quality tamahagane, such as 1st and 2nd grade, is used for making swords.

The standard for grading the quality of tamahagane in Tatara Yasukuni was determined by the carbon content as well as the impurities. The highest quality tamahagane has a carbon content of about 1.5%.

As with Yasukuni Tatara, the criteria for classifying the quality of Nittoho Tatara tamahagane include carbon content and impurities, as well as the appearance of the material when refined into tamahagane.

The criteria for premium tamahagane are a carbon content of 1.0% to 1.5%, very small impurities and a uniform "fracture surface" (the cross section of the metal when crushed); for second grade tama-hagane, a carbon content of 0.5% to 1.2%, very small impurities and a slightly uniform fracture surface; and for third grade tama-hagane, a carbon content of 0.2% to 1.0%, very small impurities and a slightly uniform fracture surface. The third-grade products had a carbon content of 0.2% to 1.0%, and the fracture surface was rough. Although detailed component analysis was not available, it can be seen that the tamahagane used for sword making was selected based on the fracture surface condition after grinding.

The Nittoho Tatara produced about 2 tons of tamahagane per operation (one generation), of which about 1 ton was tamahagane, and only 20% was premium tamahagane, which shows how valuable the tamahagane used for swords was.

Why tamahagane is a high quality steel ?

grande lame de katana

Tamahagane, produced by the tatara process, is a material with very low impurities and carbon content, making it very easy to process.

The impurities present in the two raw materials, iron sand and charcoal, would normally have a negative effect on the appearance and properties of the finished product, but the very fine impurities in tamahagane increase the toughness and sharpness of the blade through bending and forging.

Because of its rarity, tamahagane is rarely used today except for Japanese swords, but there are a few products made from tamahagane other than Japanese swords, such as kitchen knives and shoehorns.

Japanese swords made from other materials than tamahagane

There are other reasons why tamahagane is considered the best material for Japanese swords. Its toughness means that it is easier to apply a beautiful "edge pattern" (hamon: the pattern that appears on the edge of a sword blade when it is tempered) to the base iron, and its improved sharpening properties make for sharper, more beautiful swords.

However, it is not true that a sword can only be made from tamahagane. In fact, there are imitation Japanese swords that do not use tamahagane. Swords made from stainless steel or western iron have been tested and found to be of almost similar quality in terms of sharpness.

However, research has shown that the beauty of the blade pattern and the base iron, as well as the strength of the sword itself, are not as good as those of tamahagane.

Obvious differences between Western steel and Tamahaganedeux lames de sabres

Pure iron with very few impurities produced by the traditional Japanese tatara iron making process is called wako (Japanese steel), while iron with many impurities such as phosphorus and sulfur produced by the modern western steel making process (a steel making process that uses iron ore as the raw material and produces a large amount of iron by applying a high heat treatment at one time) is generally called western iron.

Phosphorus and sulfur are considered harmful impurities that make iron brittle, even in minute amounts, and if iron contains large amounts of them, it rusts easily and becomes brittle.

For example, there is a record of a nail used in Horyu-ji Temple in Ikaruga-cho, Ikoma-gun, Nara Prefecture, since its foundation: "After more than 1,000 years, if the surface rust is peeled off, the iron inside is not rusted and can be used again if hammered again. The nails were Japanese steel "propeller nails". This is a valuable testimony that the nails were extremely pure, with minute impurities, and therefore rusted very little.

Tamahagane is also an iron with very few impurities, which explains why, unlike Western iron swords, the swords are found in their original state with almost no rust. This is the reason why tamahagane is considered to be a very high quality iron..

The "mystery" of tamahagane, which even modern science cannot solve

katana tenu dans mains

Japanese swords are made using the tatara iron method of manufacture that has been passed down to the present day. However, the process of making swords was originally passed down from one generation to the next, and many mysteries remain as to the manufacturing process and materials used.

It is said that ancient swords were made from different materials than modern swords, which is why it is said that no two swords can be made the same way, even with modern technology. The method of making tatara iron that has been passed down from generation to generation is based on a method developed by the blacksmiths of the late Edo period, "Suishinshi Masahide", who is considered the founder of the Shin-Shin-To style.

Japanese sabers whose hardness exceeds the theoretical values

The process of making a Japanese sword is called "Tsukurikomi", in which a hard high-carbon steel (kawagane) made by bending and forging is wrapped with a soft low-carbon steel (shintetsu) to unite them. The combination of two opposing materials, hardened by high carbon content and softened by low carbon content, is what makes the "unbreakable and undeformable" part of a Japanese sword possible. It is said that it is inexplicable that the hardness of the sword blade exceeds the theoretical value, no matter how much the sword blade has undergone the zokuri process.

It is also said that metallurgy cannot well explain how tamahagane "sticks" simply by being flattened, bent and tapped in the first place. The temperature in the furnace used to make tatara iron is below 1,500 degrees Celsius. In contrast, when processing ordinary iron, the temperature inside the furnace must be much higher for the iron to hold together, and it is too difficult to dent it even by tapping.

The iron work of Tatara has overcome the crises of existence and death, and each time it has been passed on to our days with slight changes in its form. Although science cannot explain it, the smiths have learned the techniques with their eyes, ears and bodies, and they continue to pass on their skills to future generations.

Swords are not weapons, but works of art that still fascinate people around the world. When you have the opportunity to see a sword up close, you should fully appreciate its beauty while imagining the appearance and thoughts of the smiths who created it.

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