::Actually, I agree with Andy in that the carbon content is probably about dead on. Give me a day or so to go through my sources, but I'm know I have it around here somewhere... 

 ::The thing to understand about the Japanese swords is that they were made from different kinds of steel all assembled together in the same sword. The smiths were very careful in choosing the correct steel from the kera. The hocho iron typically contains about 0.00 to .05% carbon. The tamahagane contains about 1.0 to 1.5% carbon (not a very high-carbon steel) and the nabe-gane is cast-iron at between 3 and 4% carbon. The final product is produce by combining the nabe-gane with the tamahagane, to increase its carbon content through diffusion. Depending on how much carbon was added to the tamahagane, and how much diffusion (folding) occurred, the final, refined steel could range from pure iron for the core to very high cartbon steel for the edge. Even the WWII swords were often made by forging both high and low carbon steels together, resulting in a visible mokume (wood-grain) pattern. They used regular mill steel for this, not tamahagane. The Japanese farmed out this work to forgers all over the country, but I believe as much as 80% of the WWII swords were made in the town of Seki.