How does the fold count add to the strength of a katana?

Walking Man

Walking Man

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It makes sense to me that a folded katana might be stronger than one that is not folded. However, I am wondering if the number of folds really makes a big difference. I ask this because of the difference in price of last legends 400 folds vs. their 800 folds. I am not really interested in buying either one right now, but they are cool, and their is a pretty big difference in price.
Let's take this one step further: Is there really a difference in strength between a sword made out of 100 layers vs. 2000, everything else being equal?
Thanks.
 
Basically old Japanese swords were folded to remove impurities in the steel.
The usual was between 8 and 15 folds. Of course they were also laminated with
different types of steel for skin, core, etc. The numbers of folds "roughly" determines
the number of layers by the formula #layers = 2 to the nth power, where "n" is
the number of folds. The stories of 100 folds is crap. Given the material loss with
each fold a swordsmith would have to start with a 5 ton billet to make a sword.

Rich S
 
There is nothing inherently tougher about a folded steel sword as far as I know, rather the folding today is done fore aesthetic reasons. If you are using traditional Japanese methods as Mr. Stein pointed out the folding is to remove impurities in the steel Folding is not however necessary when using modern steel.
 
Just to add my little piece to the stream of wisdom flowing here...

There was this Japanese trivia show that put a katana against a .50 BMG. Pretty fun to watch bullets getting cut in half. In the part of the show where they got around to actually trying to break the sword, they had a close-up of the broken blade - the blade had broken, as you would expect, but you could also see the laminations coming apart. It was kind of pretty, like a metal flower, but it seems to me that it's also evidence that folded steel really isn't any stronger than a homogeneous mill steel.
 
It doesn't. Japanese iron ore is very impure, so they had to fold it many, many times to get any quality steel. Now it's mostly done out of respect for tradition.
 
wow Rich Stein!

I would suggest that if you want to study the japanese sword, Rich Stein's site is the way to go.

:thumbup:
 
Folding steel is for consistency than improving inpurity. Japanese swordsmith had to shape a blade with hammer at a low temperature, which could not melt iron / steel.
If you want to have consistent blade along whole length, you might also iterate folding, and re-forge process for some times.

As for iron / steel quality, the traditional Japanese method to get tamahagane is a good way to have a good quality steel with minimum inpurity at the cost of VERY low yield rate. This explains the ridiculous price of tamahagane. Swordsmith still follow the same way because of legal constraint, which says a katana is a katana only if it is made under traditional process.
 
That met article is nice (as good museum articles generally are) but it's still promulgating the largely discredited (at least among American smiths) idea that a soft iron core increases the durability of a blade. There are many convincing arguments that lamination methods from kobuse on up are more economizing processes than optimizing processes.
 
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