One of the strongest and most highly regarded sword metals is a type of steel known as "tamahagane." Tamahagane is a traditional Japanese steel that was historically used in the forging of high-quality samurai swords.

Tamahagane is produced through a labor-intensive smelting process using iron sand (satetsu) and charcoal in a clay furnace called a tatara. The resulting steel has a relatively low carbon content but contains impurities that contribute to its unique grain structure and strength.

The forging process of tamahagane involves multiple cycles of heating, folding, and hammering to remove impurities, refine the grain structure, and create the desired shape and curvature of the sword blade. The blade is then differentially hardened to create a distinct hard edge and a softer, more flexible spine.

The strength of tamahagane is attributed to its composition, refining process, and the skill of the swordsmith in manipulating and shaping the steel. The resulting sword blades exhibit exceptional hardness, durability, and resilience.

It's important to note that tamahagane is a specific type of steel used in the traditional Japanese sword-making process. However, modern steels, such as various high carbon steels, tool steels, or alloys, can also be engineered to possess high strength and durability, making them suitable for producing strong sword blades.

The strength of a sword ultimately depends on various factors, including the specific type of steel used, the heat treatment process, the blade geometry, and the overall design and craftsmanship of the sword. Skilled swordsmiths and manufacturers utilize different materials and techniques to create swords that meet specific requirements for strength, sharpness, flexibility, and balance.