Traditional samurai swords, including katanas and tachis, were typically made using a type of steel known as Tamahagane. Tamahagane is a specific type of high-quality steel that was traditionally produced in Japan using a labor-intensive process.

Tamahagane is made from iron sand (satetsu) and charcoal, with the iron sand being smelted in a clay furnace called a tatara. The tatara process involves multiple stages of heating, melting, and hammering to remove impurities and create a high-carbon steel with a relatively low content of impurities.

The resulting Tamahagane steel has a carbon content ranging from 0.5% to 1.5%, which provides the blade with its hardness and sharpness. The steel also contains trace elements that contribute to its strength and resilience.

The process of making Tamahagane steel was highly valued and kept as a closely guarded secret by skilled swordsmiths. It required significant expertise and craftsmanship to produce steel of the desired quality, and the resulting blades were highly regarded for their cutting ability, durability, and beauty.

It's important to note that modern reproductions or replicas of samurai swords may use different types of steel due to various factors such as availability, cost, and manufacturing processes. Modern swordsmiths and manufacturers may utilize steels like high carbon steel or even modern alloys to create swords that replicate the appearance and functionality of traditional samurai swords.