When it comes to determining the "strongest" steel for katanas, it's essential to consider various factors, including hardness, toughness, and overall performance in cutting applications. Different types of steel can offer different combinations of these properties. One widely recognized and highly regarded steel type for katanas is known as "Tamahagane."

Tamahagane is a traditional Japanese steel that was historically used in the production of katanas and other Japanese swords. It is a type of high-carbon steel that is smelted using traditional methods, typically from iron sand (satetsu) and charcoal. Tamahagane steel contains varying amounts of carbon, generally ranging from 0.5% to 1.5%, along with trace elements and impurities.

The specific qualities of Tamahagane steel, such as its hardness, toughness, and overall performance, are influenced by various factors, including the specific smelting and forging techniques employed by the swordsmith. Skillful smelting and forging processes, as well as the careful manipulation of heat treatment, contribute to the quality and performance of the resulting sword.

It's important to note that the availability of Tamahagane steel can be limited, and the traditional methods for its production are highly specialized and often closely guarded secrets. As a result, modern swordsmiths may use alternative steels that aim to replicate the qualities of Tamahagane.

Other types of steel, such as modern high-carbon steels like T-10, L-6, or different types of tool steels, are also used in the production of katanas. These steels can offer excellent hardness, toughness, and cutting performance, although they may have different characteristics compared to Tamahagane.

Ultimately, the "strongest" steel for katanas depends on various factors, including the specific requirements and preferences of the user, the skill of the swordsmith, and the overall craftsmanship involved in the sword's production.