Sword foldings

[plewis66]

I've just been playing with a little Java program, inspired by hearing things (not necessarily here) about swords being folded 'hundreds of times'.

I think the people don't realise that every time a sword is folded, the number of layers is doubled, and this very quickly leads to some stupendously large numbers.

It's certain that is someone says a sword is folded '500 times', they actually mean it has 500 layers. This means it is folded 10 times (giving 512 layers).

The very best swords might be folded 30 times, and this gives an incredible 1,073,741,824 (over 1 billion) layers.

The number of all atoms in the entire universe is something like 1,000,000,000,000,000,000,000,000,000,000,000,000, 000 (10 to the power 40).

If a sword really were folded 500 times, the layering would become meaningless. Each layer must be at least one atom thick (unless we get into nulcear folding - which I don't think even the best sword makers ever manged).

A sword folded 500 times would, if there were no physical limits, consist of this many layers:

327,339,060,789,614,200,000,000,000,000,000,000,00 0,000,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000,000,00 0,000,000,000,000,000,000,000,000,000,000,000,000!

[Khabbi]

Plewis66 ,Is your real name Stephen Hawking ?

[Neil Gendzwill]

The very best swords might be folded 30 times, and this gives an incredible 1,073,741,824 (over 1 billion) layers.
The steel was not normally (I'd say never but I'm not 100% sure) folded that much. Generally between 12-16 times. Also, the purpose was not to make layers but rather to make the steel homogeneous and to control the carbon content. If you're really curious, find a book called "Craft of the Japanese Sword" by Yoshihara and Kapp.

[ACRAWFORD]

10 folds would be 1024 layers.



2,4,8,16,32,64,128,256,512,1024

[plewis66]

10 folds would be 1024 layers.



2,4,8,16,32,64,128,256,512,1024
D'Oh! Schoolboy error!

[Raiza]

That's what happens when you use Java on a $2000 PC instead of a $20 calculator. :smiley:

Which means those shinken folded to create "30 thousand layers" have been folded 15 times. Cool.

[roar]

Modern swordsmiths who has approached this "million and billion and zillion layers"-issue, has found that there is no point in folding the iron-lump more than 15 times, there is no measured overall improvement in the quality of the steel after that. But gimmicks sell, you now, and a myth is often preferred to reality. :beard:

[roar]

That's what happens when you use Java on a $2000 PC instead of a $20 calculator. :smiley:

Which means those shinken folded to create "30 thousand layers" have been folded 15 times. Cool.

10 times 1024
11 2048
12 4096
13 8192
14 16384
15 32768

yes, I just had to check ;)

[Takamatsu]

Hello I am deshi to a Tosho here in Japan I always laugh when someone say a sword is folded so many times depending on the quality of the tamahagane used a tosho can fold as many as 20 times after this you lose to much carbon and you cannot make good hamon everytime the block is heated it loses carbon. The main reason for folding is to take the impurities out of the tamahagane when tamahagane is made it is made in the old way only this can be used to make Japanese sword but many impurities are left from the charcoal and becuase the steel does not become molten all the way. when it is done it looks like crystals and a tosho can look at each piece and tell how much carbon is there. So we do sakite with a big ha,mmer while sensei moves the block and we do this 12 to 15 times until the grain and color is right if this is not done well you will have many kizu when the sword is polished.

[chidokan]

Takamatsu,
would I also be right in saying that every time you hammer you lose some mass of the steel as well... I guess you would start with, say, 2kg and finish with 1.2 kg of steel after forging? I am curious as to the actual starting weight and final weight of the average blade, as iaido people like me only see finished ones!

[Optomitrist]

Yeah, you are only trying to get the impurities out.

[Takamatsu]

Yes as you hammer and fold the hagane become more compressed impurities are lost from hagane and it becomes smaller and lighter I will measure next time I start a sword with sensei and let you know how much for sure. Since there are two types of steel welded together to make sword this kawagane and shingane i will check both and all when finished. Can you post picture of sword here and how ?

Takamatsu Kenshin

[neko kenshi]

N00bish question:

I had read somewhere that there is a core peice in the katana and then another layer of metal wrapped around this. Now it may be that I just terribly misunderstood or don't correctly recall the article I read, but if I am correct, Which part of the sword is folded, the core or the blinketing metal? I also heard that sand was folded into the steel to distribute carbon and that was the purpose of folding it, is this true? And if so, is this the only reason it is folded, or is folded steel actually much stronger? Sorry for questioning so much, and for sake of not bothering everybody with stupid questions too much in the future, does anybody know a good online in depth article about the making of a shinken they could refer me to? Thank you very much for any information you could provide me with, and sorry again for asking silly questions.

[Ric Flinn]

N00bish question:

I had read somewhere that there is a core peice in the katana and then another layer of metal wrapped around this. Now it may be that I just terribly misunderstood or don't correctly recall the article I read, but if I am correct, Which part of the sword is folded, the core or the blinketing metal?
Hopefully Takamatsu-san will correct me if I'm wrong, but I believe it's both the core and outer steels that are folded. The core steel isn't folded as much, however, and is a softer, lower-carbon piece of steel. Lower-carbon steel is more forgiving of shock and stress, but doesn't hold an sharp edge very well; high-carbon steel is more brittle but will stay sharp. Japanese swords combine these properties (with differing steel types and unique heat-treating) to make a more durable but sharper sword.


I also heard that sand was folded into the steel to distribute carbon and that was the purpose of folding it, is this true?
I don't think this is quite right; maybe what you're thinking of is that the steel used (tamahagane) comes from iron sand originally? But by the time a smith sees it it has been turned into solid chunks in a smelter (I have no idea what this process is called or how it works).


And if so, is this the only reason it is folded, or is folded steel actually much stronger?
Mainly to remove impurities and make the steel more uniform. Read Takamatsu-san's posts again. I guess this would make the steel stronger, though, since the steel will have less imperfections. The process of folding the steel came about simply because the swordsmiths only had impure steel to work with. If they had modern steels available, they may never have folded the steel at all. But they didn't, so they learned to use what they had, and I'm glad they did it this way. Even today, true Nihonto must be made from the same tamahagane steel.

Again, sorry if I have any information wrong or forgot any major details.

[Takamatsu]

Hello I am sorry for not responding for such long time I have been on a trip and now I am going Kyoto for one week. when I come back I want to start sword manufacture talking It is my favorite thing Ric san you are right I will fill in small details when I come back home. Ganbate!!!!!

[tattooedasshole]

Carbon ditribution is probably the main reason for folding (along with purity of steel). Tamahagane, after the smelting of the sand, has huge "chunks" of carbon in it, you can actually see the purple or blue that are carbon deposits. The smith choses pieces based on the carbon he can see, then breaks them into small pieces. These pices are stacked, then welded into a billet. The billet is then forge folded/welded to distribute the carbon, and push out impurities. The forge welding process lowers the carbon content, starting with approx. 1.1%, you end up with approx .7% after forge welding (.8%-.5% is good for swords). There will only be 9-15 folds, past that, too much carbon migration.

The core steel is folded, not as much though (5-9times if memory serves), and the smith starts with a lower carbon content steel. There are many ways of forging nihonto, some have as many a 7 different pieces. Look up san-mai blade construction.

The folding process does not make the steel any stronger per-say, just distributes the carbon evenly so that when the blade is hardened you don't end up with soft spots or extra-hard spots.

The smelter is called a tatara (sp?), and the steel coming out is VERY nasty looking. Looks almost like a fabric, and that is how the smith gets it.

I'll try and get my copy of The Craft of the Japanese sword back from ChaShu and post some pics.
If you have any other questions, I may be able to help.

[Peegee]

Swordmaking Process by the late living National treasure

Miyairi Akihira (1913-1977)


http://www.jpsword.com/files/swordmaking/sword-making.html

Enjoy:wink: !!!

[shred_lord]

folding the steel also lengthens and repacks the crytal structure from something like this; (cue assci :) )

<><><><><><><><>
<><><><><><><><>
<><><><><><><><>
<><><><><><><><>
<><><><><><><><>

to something like this

<=====><=========><===========>
<============><========><=======>
<========><=========><=========>
<======><=========><=========>

This gives greater strength and flexibity.

I may be wrong but I'm fairly sure that normal forging doesn't do this as much.

[tattooedasshole]

With pure forms of steel, folding is not required. The forging and heat treating with change the grain structure of the steel. Heating and cooling of any type will increase grain size in the steel, this why most smiths will aneal a piece before heat treat. Normalize the grain structure before the change to pearlite and martensite.
Folding has NOTHING to do with the strength of the steel (unless you're making damascus, but that's another story....). A steal with the same alloys at the same carbon content is every bit as strong as a folded piece. The alloying metals, and the carbon content will determine the "strength" of the steel, but even the best steel can have a crappy heat treat, making a crappy blade.

[tattooedasshole]

http://www.iforgeiron.com/Blueprints/BP0078Metallurgy%20of%20HT/BP0078%20Metallurgy%20of%20HT%20w-pix.htm

It's kinda long, but explains grain structure.....

[tattooedasshole]

Ok, did some reading in The Complete Blade Smith by Jim Hrisoulas.

Any time you heat a piece past critical (austenite) the carbides in the metal melt, and the grain size in the peice increase. The welding process for forge folded blade requires that the piece be heat well past critical, almost to liquid state. When this happens the grain of the steel grows tremendously. The forging of the blade will make the grain smaller, but as you heat the piece for forging, or hardening, those grains begin to grow again. When the blade is quenched, th cooling rate will detemine the size of the grain/phase of the steel. This doesn't mean that cooling rates are the only thing involved. If you spend too much time at heat before quenching, the grain in the steel will get too large, and hinder hardening.
As per "grain" in a japanese sword. The hada that is visible on a nihonto is not the same as the grain in the steel. The hada is produced by the welding in the forge folding process. What you are seeing are the weld lines, not the actual grain of the steel.
And just to show that a non folded blade can be as good as a folded one, look into Haward Clarke's L6 katana, or at least the destructive testing of one. If you can find a stronger sword, I'll eat my hat.

[nahte123]

The more you fold a sword, to a certain extent (about 10-12 times) it makes the sword more flexible, but a tremendous amount of folding, as stated above, actually releases the carbon, so eventually it would turn back into iron, which isn't good. But then the coal puts some carbon back, but still, you get the point.

[tattooedasshole]

The more you fold a sword, to a certain extent (about 10-12 times) it makes the sword more flexible, but a tremendous amount of folding, as stated above, actually releases the carbon, so eventually it would turn back into iron, which isn't good. But then the coal puts some carbon back, but still, you get the point.
Folding will not increase flexibily. Where did you hear that it would?
The coal will only put carbon back into the steel at a specific spot in the fire(carburizing layer), wich is not where the steel sits for forging (on top for forging, has to work through the charcoal to the bottom to add carbon). The steel will lose carbon because of oxidation (oxidation occurs most at the top of the fire).
Guys, the folding of the steel was done for ONE (1) reason, even carbon distribution. Thats it. Nothing else. Even the idea that it is done to remove inpurities is not really true (yes it does do that too, but.....). Japanese steel, wheil in a very crapy state, is very pure (few impurities, such as sulphur), but the carbon, and other elements, are not evenly distributed. If the smiths of old had modern day steel, they would never have folded a single blade (unless they were going for a certain look).

The heat treat is what makes for a hard edge, soft/ductile body, and will determine if the sword is useable or not.