Traditionally, the blade of a katana, the iconic Japanese sword, is made from a type of steel known as tamahagane. Tamahagane is a specific type of steel produced through a traditional smelting process using iron sand (satetsu) and charcoal in a tatara furnace.

Tamahagane steel has a unique composition and properties that are highly valued in Japanese swordmaking. It typically consists of a combination of low-carbon steel (called shingane or soft iron) and high-carbon steel (called kawagane or hard steel). The layering and differential heat treatment of these two steels create the distinctive hamon, the visible line or pattern along the blade's edge.

The tamahagane steel used in katana production undergoes a rigorous smelting process, which involves several stages of heating, folding, and forging to purify the steel, remove impurities, and achieve a refined and uniform grain structure. This process is critical for creating a blade with desired strength, flexibility, and sharpness.

It's important to note that the production of tamahagane steel is a specialized and time-consuming process, and traditional swordsmiths who specialize in traditional Japanese swordmaking techniques continue to employ this method. However, in modern times, alternative steel types may also be used to create katana blades, including various high-carbon steels, tool steels, or Damascus steel, depending on the preferences and goals of the swordsmith or the specific requirements of the blade.