I got interested Japanese swords, because I discovered they are superior to any of the European swords. The materials engineering is amazing for a pre-industrial society.
The secret of the metallurgy is the laminated structure. The sword consists of an inner core of softer, lower carbon steel, which imparts toughness and flexibility to the blade. The jacket and edge are of high carbon steel, which allows the razor edge, but is too brittle to be useful for complete fabrication of a blade.
The blade begins by folding layers of higher carbon steel from 10 to 16 times. The a core of lower carbon steel is inserted into a V that has been forged into the jacket steel. The blade is then hand forged to rough shape, and then filed to final demensions
The blade blank is coated with clay. The layer of clay is thin at the edge and thick for the back of the blade. The blade is then heated in the forge to a specific temperature, actually eye-balled by the sword-smith. The hot sword is then plunged into water.
The blade cools rapidly at the edge, but more slowly at the back of the blade. The result is a very hard edge, but a softer, more resilient back of the blade. The softer back shrinks more, on cooling. The result is the curved shape of the katana.
One of the most beautiful aspect of the sword is the hamon, the boundary between the softer back and the hard edge. The hamon becomes apparent with the final polishing of the blade.
A limited number of katanas and other swords are being made in the tradional manner (in Japan). The production is strictly controlled by the government, to assure the quality of the blades. These blades are museum quality, they are not intended for competitions, even though they are razor sharp. They are simply too expensive, well over $10,000 per blade. After all, they take at least 6 months to build.
Competitors buy lower priced blades, many of which are mass produced. They are still razor sharp and quite lethal. Some blades are of folded construction, with differential hardening (similar to the real Japanese swords).
Others are through hardened monosteel construction. The most durable may well be the monosteel beaters made by Cheness Cutlery, the ones made of 9260 spring steel. They will certainly cut every bit as well as the authentic folded blades.
I watched a program on one of the cable channels not too long ago about how a traditional Japanese sword is/was made. It was absolutely fascinating! It truly is more art than a manufacturing process.