| MadSci Network: Science History |
Well, the hardness of the metal makes the sword stay sharp. It also allows a very thin piece to be strong, as on the edge. The real question is how it is made so hard. Carbon steels can be hardened by "working" it. This cold work is done by bending, hammering, folding, etc., and results in the formation of martensite, the strenghtening structure. Under a microscope, and polished and etched properly, this structure lookes like a mass of needles. I have heard that the blades were sometimes folded nearly 100 times, and of course, pounded thin between foldings. One other thing, the steel must be annealed between workings to prevent brittleness. Heating to a temperature well below the melting point, but hot enough to reduce the stresses allows the material to remain strong without becoming brittle. The metal can be cooled in air, or dropped in water or oil. Another note... Except for a very recent alloy, sharp knives are never stainless steel because it does not have enough carbon to be able to be hardened.
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