The traditional material used to forge a katana blade is a type of steel known as tamahagane. Tamahagane is a high-quality steel produced through a labor-intensive process in traditional Japanese swordsmithing.

Tamahagane is made from iron sand, specifically iron-rich sand known as satetsu, combined with charcoal in a clay furnace called a tatara. The iron sand is heated and smelted for several days, resulting in the production of tamahagane steel. This steel is then carefully refined, layered, and forged by skilled swordsmiths to create the katana blade.

The composition of tamahagane steel can vary, but it typically contains a combination of iron, carbon, and trace amounts of other elements. The layered structure and specific heat treatment techniques employed by the swordsmiths contribute to the strength, flexibility, and sharpness of the katana blade.

While tamahagane is traditionally used in the production of katana blades, it's worth noting that modern steel-making technologies have also introduced other types of steel that can exhibit excellent strength and performance characteristics. Contemporary katana blades can be crafted from different types of high-quality steel, such as tool steels or specialized alloys, which offer enhanced durability and cutting capabilities. However, the use of such materials may deviate from traditional Japanese swordmaking practices.