Samurai swords, such as the katana, are traditionally forged through a meticulous and intricate process that requires the skill and expertise of a trained swordsmith. Here are the general steps involved in the forging of a samurai sword:

1. Material Selection: The swordsmith begins by carefully selecting the raw materials for the blade. This typically involves using different grades of iron and carbon steel, such as tamahagane or modern steel alloys, to achieve the desired properties.
2. Smelting: If tamahagane is used, the swordsmith will undertake the labor-intensive smelting process. Iron sand (satetsu) and charcoal are placed in a clay furnace called a tatara. The tatara is heated for several days to melt the iron and create tamahagane steel.
3. Shaping the Blade: The steel is heated and hammered into a rectangular bar, which is then repeatedly folded and hammered to remove impurities, refine the grain structure, and distribute carbon evenly throughout the steel. This process of folding and hammering is typically repeated multiple times, resulting in a blade with numerous layers.
4. Forming the Blade: The swordsmith uses a combination of heat, hammering, and shaping techniques to transform the folded steel bar into the rough shape of the sword blade. This includes gradually tapering the blade from the hilt to the tip and establishing the curvature (sori) of the blade.
5. Differential Hardening: The blade is then prepared for the differential hardening process, where the edge is heated and coated with a heat-resistant clay mixture. The blade is then quenched in water or oil. This differential hardening creates a distinct hard edge (yakiba) and a softer, more flexible spine (mune) on the blade.
6. Tempering: The blade is heated again, this time at a lower temperature, to temper the steel. This process relieves internal stresses and further refines the blade's hardness, toughness, and flexibility.
7. Polishing: The swordsmith meticulously polishes the blade to remove any remaining imperfections, revealing the beauty of the grain patterns (hada) and creating a mirror-like finish.
8. Mounting: Once the blade is complete, it is fitted with a handle (tsuka), guard (tsuba), and other fittings to create the complete sword. This process is known as mounting or habaki.

The forging process for samurai swords is a complex and labor-intensive craft that requires years of experience and skill to master. Each swordsmith may have their own variations and techniques, contributing to the uniqueness and quality of their swords.