To put it simply, the main material of Japanese swords is "Tamahagane". However, the materials and manufacturing methods used in the "ancient sword" period have been lost. Current technology can analyze the chemical composition of the finished sword, but it cannot accurately calculate the material composition before the furnace treatment and the temperature, time, frequency, quenching method and other data of the furnace treatment. The earliest knife-making techniques that can be handed down mainly come from the records of the "Edo" period. Different knife-making schools and in different eras have different knife-making methods. The following can only briefly list the typical knife-making steps:

The first step. "Water Frustration" (Mizuheshi)< /p>

Also known as "water reduction". That is, "jade steel" is heated and hammered into thin sheets with a thickness of about 5mm. It sounds like a very simple process, but it is not... In order to control the carbon content of the steel (retention/loss of carbon content), the number of times of heating is strictly limited; and the hardness of "Jade Steel" gradually increases as it cools There will be changes from time to time. Only experienced knifemakers can accurately grasp the changes in hammering force and temper "jade steel" into thin slices of uniform thickness under a limited number of heatings. After the steel sheet is formed, the knifemaker rapidly cools it with water. The parts with sufficient carbon content will naturally break down and be used as materials for making knives. The knifemaker needs to have a very accurate grasp of the temperature of the steel sheet and the amount of water in order to collect materials with the right carbon content. The remaining part will be saved by the knifemaker for future use. From the perspective of modern material science, this step can be regarded as the knifemaker's method of controlling the carbon content of the steel.

Step 2. "Kowari"

Crush the steel into thin pieces of 2 to 3 cm in length. The unbreakable part has too low carbon content, and some swordsmiths will use this to make the "core iron" of swords.

Step 3. Make the burning platform

The burning platform will become a part of the blade, so it must be made of high-quality "jade steel". (The burning stick is not part of the blade and can be made of any steel material.)

The fourth step. "Tsumikasane" (Tsumikasane)

Crush the pieces obtained from the "small cutting" process The steel blocks are welded layer by layer on the burning table so that the heat can be transferred evenly. The thermal viscosity of the steel block has a decisive influence on the welding effect, and the thermal viscosity depends on the purity and carbon content of the steel. Therefore, it is necessary to select "Jade Steel" and perform the first step of "water rolling" process. . Different swordsmanship schools have different welding methods... Parallel arrangement of welding is called "Tanshu Forging", staggered arrangement is called "Pai Mu Forging", and cross-shaped arrangement is called "Konoha Forging" or "Jumonji Forging" ”. Taking the forging of a "knife" ("打刀") as an example, it is necessary to accumulate about 2 to 3 kg of steel.

Step 5. "Tsumiwakashi"

Put the materials completed in the "Tsumiwakashi" process back into the furnace to ensure that the steel materials can be completely welded. In order to ensure that the steel is completely isolated from the air (to prevent the fire from consuming the carbon content in the steel) and to allow for slow and even heat treatment, the cutter will cut the steel with a knife filled with mud and straw ashes before placing it in the fire. The paper wraps the steel material tightly. The knifemaker must carefully control the temperature of the fire and the heating time.

Step 6. Return training

Japan has never had the opportunity to develop the technology of high-temperature furnaces in ancient times, so it is very difficult to make homogeneous swords. In order to overcome such problems, the only way to apply the technique of "return exercise" is to apply it. Fold the steel material that has been completed in the "accumulation boiling" process and weld it again. By repeating it 10 times, you can create a steel material with 1024 layers (2 to the 10th power); the more layers there are, the less carbon in the steel. The various ingredients will be more uniform, the iron crystals will be more refined, and the strength of the finished product will be higher. (Note: However, if there are too many layers, it means that the steel has been in the furnace for too long and the carbon content in the steel will be lost too much. The hardness of the finished product will be affected and the sharpness will also be limited. Generally speaking, Japanese swords usually do not go through more than 15 retracements.) During the "reentry training", the constant hammering will cause a large part of the impurities in the steel to fly away into sparks. Impurities are the "strength weakness" of steel. Damage often starts from the "strength weakness" and slowly spreads to the entire material, becoming comprehensive damage. The smaller the number of "strength weaknesses", the smaller the chance of destruction. Therefore, the purer the steel, the higher its strength and toughness will be. Swords made in high-temperature furnaces around the world will have problems with iron crystal enlargement after being formed. According to the interpretation of thermodynamics, during the high-temperature refining process, in order to reduce their number (reduce the total surface area), the fine iron crystals will combine with each other and reorganize into smaller iron crystals with a smaller number and larger volume. As a result, the strength of the steel will be affected. Therefore, after quenching the swords made in high-temperature furnaces (that is, throwing the white-hot steel into water/oil to cool down), they must be put back into the low-temperature furnace for several hours to allow the fine iron crystals to form in the original crystals. Recrystallize between them to restore strength and toughness. However, long-term fire exercise will cause excessive loss of carbon content, affecting the surface hardness and sharpness of the finished product.

Compared with Western swords, Japanese swords are made in low-temperature furnaces (less than 1000 degrees Celsius). The iron crystals can always be kept in a fine and dense state, so there is no need to temper them after quenching, further reducing the loss of carbon. Hardness, strength and toughness are maintained. In addition, swords that have undergone "return training" will have a surface texture ("ground texture") like pine wood grain, which is extremely beautiful. (Note: There must be advantages and disadvantages. The steel in the high-temperature furnace is softer and easier to shape; the steel in the low-temperature furnace is harder and more difficult to shape, and may not even be handled by an individual's physical strength. If the return layer cannot be completely welded If they are combined, they will become potential cracks and become flaws in the finished product. Therefore, during the general making process, the swordsmith will hold the steel tightly and give instructions, while two or three strong disciples will use long-handled swords. Hammering. In other words, making Japanese swords is a labor-intensive work, a great art that exchanges blood and sweat for quality)

Step 7. "Making the edge"

Japanese sword blades. Being sharp and not easy to bend means it has the characteristics of "hardness".

At the same time, Japanese swords are not easy to break, that is, they have "flexible" properties. Combining strength and softness, how does a Japanese sword achieve this? Different from swords in other countries around the world, Japanese swords are not made of a piece of steel, but are made of a layer of hard "Kawatetsu" wrapped around another flexible "Core Iron" (Shintetsu) and welded together. become. "Skin Iron" is made of "Jade Steel" with a higher carbon content after 10 to 15 times of "return exercise", while "Core Iron" is made of "Paoding Iron" (or low-carbon steel) with a lower carbon content. Carbon pig iron, or "jade steel" with low carbon content) is made after 5 to 6 times of "return exercise". With such a combination, the Japanese sword can be both strong and soft. Different knife-making schools use different steel material distribution methods. Some will add higher-hardness "Hatetsu" (Hatetsu), lower-hardness "Munetetsu" (Munetetsu), or use folded but not welded steel. The combined double-layer "core iron".

Step 8. "Su Ting"

Form the mixed steel prepared in the "edge making" process into a long strip, which becomes the basic shape of the blade.

Step 9. Create the "Qie Xian"

To ensure that the "Qie Xian" has the same mixed steel distribution as the blade, and to obtain a smooth surface texture, the knifemaker will Cut off a section of the tip diagonally (the sharp corner is at the winger's position), and then use a small hammer to shape the sharp corner into a backward arc, which becomes the "cut first". When the knife maker forges the "cut head", the steel is in a high temperature state. After quenching (that is, placing the blade in water to cool), the "pick" part shrinks when it is cold, but the crystal of the "blade" will expand, so the "blade" will shrink in the direction of the "brick". The production of "Kirsen" is the most exquisite craftsmanship, so the "Kirsen" of the finished product can reflect the skill of the knife maker.

Step 10. "Fire Making"

Use a small hammer to shape and modify each part of the blade.

Step 11. "Burning in"

The final fire forging process. The swordsmith prepares "Yakibatsuchi" (Yakibatsuchi) using clay, charcoal powder and whetstone powder (different schools have different ingredients and preparation methods), and then encapsulates the shaped blade with "Yakibatsuchi". The soil used in the area of ??"Blade" is thinner, while the soil used in the area of ??"Pickaxe" and "Building" is thicker. Basically, the distribution of "Burning Blade Earth" can be seen a little bit from the "Blade Text" of the finished product. The mud-sealed blade is placed in a fire at 750 to 760 degrees Celsius. The knifemaker confirms the temperature by the color of the furnace fire. If the temperature is higher than 800 degrees Celsius, the iron structure of the finished product will become enlarged, affecting the strength. After a specific heating time, the knifemaker will remove the blade from the fire and then place it in water to cool rapidly, which is "quenching". (The water temperature, water source, techniques, additives, etc. of quenching are all regarded as the biggest secrets by various sects of swordsmen.) Because of the different thicknesses of the "burning blade soil", the cooling speed of the "blade" is much faster than that of the "pickaxe ground" and "pickaxe ground". "Building" is faster, so the hardness of "Blade" will be much higher than the hardness of "Pickaxe" and "Building". Also due to rapid cooling, the iron crystals of the "blade" will mutate and become larger in size, so the blade will bend further backwards after quenching. This situation is different from the "crystal hypertrophy" problem mentioned above. After quenching, the number of iron crystals in the "blade" remains unchanged, but the volume of each crystal becomes larger. The situation is like the density of clear water becoming smaller and the volume increasing after it freezes.

Step 12. Others

After the preliminary polishing, opening of "nail holes", filing of "eyes", and engraving of "inscriptions", the responsibility of the knifemaker can be Said that was the end of it. Generally speaking, the "grinding", sheath making, gold and silver decoration, rolling handle and other processes of Japanese swords are handled by dedicated personnel and are not the scope of the swordsmith's work.