Traditionally, the steel used for crafting Japanese katana swords is known as Tamahagane. Tamahagane is a type of steel that is produced through a traditional smelting process in Japan. It is made from iron sand (satetsu) and charcoal, and the process involves multiple stages of heating, folding, and hammering to remove impurities and create a high-quality steel.

Tamahagane typically has a low carbon content, around 0.5% to 0.8%, which provides the blade with toughness and flexibility. The lower carbon content helps prevent the blade from becoming too brittle, allowing it to withstand impacts and flex without breaking. The unique properties of Tamahagane contribute to the distinctive characteristics of a well-crafted katana, such as sharpness, resilience, and the ability to maintain an edge.

In modern times, other types of steel may also be used for crafting katana swords. Various types of high-carbon or tool steels are often utilized by modern swordsmiths to achieve specific performance characteristics, such as improved hardness or durability. Common examples include AISI 1095, 1060, or different types of tool steels.

The choice of steel for crafting a katana depends on the intended use, the desired balance of properties, and the preferences of the swordsmith. A skilled swordsmith will carefully select the appropriate steel and employ traditional forging and heat treatment techniques to create a functional and high-quality katana.