Possibly this is old hat to many readers here, but I just saw Nova on TV
(online at http://video.pbs.org/video/1150578495/
)about how samurai swords are made. Very cool. Stuff about the amounts of carbon mixed in with the iron when forging the steel, how steel with different amounts of carbon is layered in the blade to combine hardness and toughness...
I've heard that the opposite layering is used in a power hacksaw blade, where the tougher steel is the outside layer and the harder one is the inside. I guess it's less important to hold a fine edge than to be flexible in that use.