From a materials science perspective, what is the point to folded steel? How does the folding process affect the properties of the metal? The place I see this extensively is in Japanese swords, such as Katanas. They will say "hand folded X times" with X usually being anywhere from 150-750, with the upper end being vastly more expensive. I’ve taken an upper division course in basic materials science, and I can't figure out what could be accomplished by folding the steel. Id think that most of the austenite to alpha iron and Fe3C type properties can be controlled by cooling rates - resulting in the martensite, spherodite, perlite, etc. What happens during the folding process on the micro scale that makes this desirable?