question about Japanese sword steel

[TimB]

I ain't been able to find anything on this yet, but I'm having fun looking through the BP's and threads. I heard once that the quality of the steel in an old Japanese sword was due to the steel being forged and folded 200 times. It has been my thought that work hardening metal by a repeated bending, is what causes it to break when a piece of coat hanger / welding rod / or tin is bent back and forth repeatedly. This "work hardening" effect can be canceled out by heating and slow cooling the metal, (as I do with hard drawn copper refrigeration pipe, in order to swage it)---conclusion : it isn't the act of folding the sword steel that creates the quality of the katana blade.

I have also heard, that carbon steel is created when heating iron in the presence of carbon, I assume, as in a coal fired forge. My conclusion then, is that the quality of the steel in a katana blade is due to the many hours it spends being heated in a coal bed.

I don't know if this is true though, it is just my speculation based on things I've picked up over the years. If it is true, it leads me to the question, is it possible then to turn a piece of mild steel black iron gas pipe, into a higher quality carbon steel by working it with a coal fired forge?


A related question would be if anyone has ever tried an oil fired forge? I have a few residential oil fired burners laying around and a commercial hot water tank firebox (200 gal. size, still with the ceramic fiber refractory in tact.) that I was thinking of converting to my first forge.

[Frosty]

You can make a forge out of one of your oil guns but I don't know how to size it like I do a propane burner. You'll need to experiment and let us know the particulars.

I'll let the blade buys address your blade questions except to say in general it's exaggerated to a great degree but there is a kernel of truth to most all of it. But JUST a kernel.

Frosty

[Steve Sells]

Traditional Japanese swords are cool but they started with junk steels. The repeated folding, aka Forge welding, was like working out wrought iron, and for the same reasons. to work some junk out of the metal in an attempt to get usable steel. Don't even bother trying to get black pipe into "good steel" as it wont happen, there is a lot more to it that just roasting iron in carbon.

Just buy good steel to start with. Since I am wearing my asbestos suit, Let the flames begin.:D

Edited April 8, 2009 by steve sells
typo

[Donnie]

Like Steve said, buy good steel to start with. New steel is very inexpensive compared to the time and effort involved in any project.

[ThomasPowers]

Well the traditional japanese sword starts at nearly 2% carbon and after the repeated folding and welding ends up at 0.5% carbon so that's right out.

You can carburize iron into steel in a forge---charcoal fuel is easier as you don't run the risk of putting sulfur in the steel as well; However if you are not carefull and skilled you will scale off the surface faster than you will soak carbon into it.

Carburizing to make blister steel was done in vessels sealed against O2 infiltration containing a carburizing agent, powered charcoal is the simplest one. My last run I did with a piece of pipe welded shut on one end, packed with charcoal and then had wrought iron strips shoved in the charcoal and the other end flattened and folded over. put it inside the Gas forge along one side and let it cook while doing my other forging, turing it every once in a while---20 hours was way too much as I ended up too near cast iron in carbon content.

I could probably do that with blackpipe; unless you really have the experience you probably could not.

Oil fired forges were quite common industrially but few smiths use them at "home"; they tend to stink. (I've seen on in use at a Museum in Germany at Lauf ADP).

Edited April 9, 2009 by ThomasPowers

[TimB]

Well the traditional japanese sword starts at neary 2% carbon and after the repeated folding and welding ends up at 0.5% carbon so that's right out.

Thanks for the responses guys.

I spose I should ask first, what was the quality of those swords that made them such a good blade, I guess I assumed it was a high carbon content that made them a hard steel.

Another question you brought up Thomas is the % carbon in steel. I ran into it in the BP's, I think...maybe somewhere else on this forum...but what does the % carbon have to do with steel hardness? I've seen some softer steels listed here with higher carbon content than harder steels. I guess I'm getting a bit confused, I always thought a "high carbon" knife blade was a better blade than another, not "high carbon" (I prefer blades that hold an edge well, even if it takes me a while to sharpen it.) I'm getting the idea that it's all relative, to other elements in the steel.

[Iron Falcon 72]

It has been my thought that work hardening metal by a repeated bending, is what causes it to break when a piece of coat hanger / welding rod / or tin is bent back and forth repeatedly. This "work hardening" effect can be canceled out by heating and slow cooling the metal, (as I do with hard drawn copper refrigeration pipe, in order to swage it)---conclusion : it isn't the act of folding the sword steel that creates the quality of the katana blade.

One other point. The repeated bending that results in failure is not work-hardening, it's fatigue failure.
http://en.wikipedia.org/wiki/Fatigue_(material)

My general reading says the repeated folding actually reduces the carbon content.
The story of the Japanese sword

[Frosty]

The Japanese blades were a super weapon because they were better than anyone elses. . . In Japan. Get close to India or the mid-east and they weren't so hot.

Carbon content makes a big difference, generally yielding a harder result with higher % content up to around 2%, then it turns to cast iron.

That however is for simple or low alloy steel, add half a % chrome, a % nickle, etc. etc. and it's a whole different ball game.

Even just steel metallurgy is far from simple, in fact it's a lifelong study.

Frosty

[MattBower]

The steel that comes out of a Japanese tatara smelter is very heterogeneous; some parts will be very low carbon, and others will be nearly cast iron. The bloom is forged down flat and broken into pieces, then sorted by carbon content (mainly based on a highly trained eyeball). The pieces are stacked together (I imagine the process of selecting the right pieces involves a lot of experience, too) and forge welded into a solid mass, then forged out into a billet and repeatedly folded and welded. (But not 200 times!) That homogenizes the carbon content and, as Steve said, helps work out impurities.

The result is hardly super-steel. Closer to 1050 without the manganese.

[Steve Sells]

TimB said:

Another question you brought up Thomas is the % carbon in steel. I ran into it in the BP's, I think..

 

See the knife sticky's Knife Making - Knife stickies here at iForge it explains how carbon and heat treating make steel hard, or not.

 

[CBrann]

As far as folding goes, 9 folds based on folding the billet once, gives 256 layers (2 to the ninth power)

Still amazes me how well they worked, and how well they lasted! no to mention their effeciency

[ThomasPowers]

While I think that japanese swords can be true works of art I do not consider them a superior sword for *use*. Don't fall for all the hype you see in the general media.

They have been optimised very well for a single use case and so don't do as well for most other ones.

eg: take a $50,000 historical japanese sword wielded by a master swordsman: it can make a marvelous cut; but and hit it sideways on a tree, (edge of shield, etc), they will often take a set (stay bent) and the edge may crack. (Ashi were put in to prevent the entire hardened edge from cracking off in such situations) Learning how to straighten your sword after a not-perfect cut is part of learing to use it.

I want a sword that has a spring temper and can take the hurly burly of the battle field rather than the comtemplation of the monestary.

[johnptc]

Thanks for the responses guys.

I suppose I should ask first, what was the quality of those swords that made them such a good blade, I guess I assumed it was a high carbon content that made them a hard steel.
.

the best swords are made of multiple pieces for forge welded steels each with its own purpose in the blade... maybe as many a 7 separate pieces

simplest case is a very hard edge piece surrounded by softer protective steel.

a fully hard sword would break and a soft sword wont cut.


pretty good swords :)

[ThomasPowers]

Note that the europeans were making swords out of multiple pieces; example:13 pieces with 5 of them being patternwelded billets back around the year 600 (The Metallography of Early Ferrous Edge Tools and Edged Weapons, Tylecote and Gilmour)

The katana is a great sword for some things; but remember that on the battle field that the Samurai code of chivalry was Kyuba no michi ("The Way of Horse and Bow") and not armoured combat with swords.

[ThomasPowers]

Odd the Europeansd were making swords with multiple pieces; exp 13 seperate pieces 5 of them being pattern welded billets around the year 600---"The Metallography of Early Ferrous Edge Tools and Edged Weapons", Tylecote and Gilmour.

And the Samurai code of chivalry was known as Kyuba no michi ("The Way of Horse and Bow")...

There have been quite a number of reports at how surprised japanese master swordsmen have been when they got to try cutting with *accurately* reproduced or original european swords and found that they cut very well indeed!
Thomas

[Charlotte]

Carbon makes steel hard by jumping into the middle of the crystal's molecules at a certain range to temperatures and locking them in a form that has difficulty shifting form or sliding along other crystals. We heat treat to make sure that we get the arrangements we want so we have the propeties appropriate to its use.

The folding of steel produces a lamination like plywood. It makes it strong and flexible. Having different kinds of steel lying side by side allows the best properties of each kind to cover the weakness of the other.

Laminated steels tend to be sharper than monlithic steels because, at the microscopic level, the soft spots wear away leaving sharp points of harder material sticking up. A very sharp blade is actually a narrow wedge with a sawtooth edge.

There are a number of videos available on the web and through ABANA that deal with the Japanese sword and its manufacture.

The legend of the Japanese sword is based in part on the skill of the users.
They trained extensively and precisely on the proper technique to produce the best cut possible.

Most of the the "Historic" Japanese world war two swords were produced in factories. I've see a number of these swords offered as master works that were less well made than civil war confederate swords, ( most made in britan any way).

True master work swords were assembled in a number of ways any where from 2 to 5 seperate pieces were forge welded. Only the cutting edge was given the 9 or ten forge folding treatment.

The master's sword makers first job was to select from the variety of bloomery products supplied by the master of the bloomery. The mixture of products used varied from master to master.

The way in which a sword is manufactured often determines the way in which they are used.

Most Japanese swords were a not as sharp as popular myth portrays, but they were very highly polished and the edge was very highly honed and precisely angled. Great polish and careful refinement of the microscopic edge makes for wonderful cutting. Japanese Swords were both tough and cut well enough slice through boiled leather, wood, cloth, and flesh with great ease. The Samurai, like European Chivalry spent most of their time killingthe "Cannon Foder"They were rarely used edge to edge because one or the other blade would suffer sever damage to the cutting edge. They did however often meet blade to cross hand guard. Most the training involved how to get in the first fatal cut without being touched your self.

The sharpest blades were made of indian wootz steel. They were truely
amazing and able to cult silk scarves thrown in the air.
The were produced in staggering number and cut at the slightest pressure.
They were "super carbon " steels produced by breaking down a mixture two different kinds of iron alloys that were in the same billet by hammering them into a more uniform state of alternating layers. This was done hot as soon as the billet was removed for the crucible. The hammering and folding continued until the master smiths judged it same to stop. If the billet was allowed to cool without hammering then the segration of carbon and iron would produce something resembling failed cast iron.
The technique in use was to again avoid making contact edge but to sweep around and evade until a telling blow could be landed. A sharp blow in the center of the blade would often shatter it.


European swords were made in wide variety of shapes, Styles, and material combinations. Of course since the swords were less dependable and prone to go dull on chainmail Large and heavy ruled the day. Which inturn lead to larger and heavier armor and bigger horses and so. One of the reasons that chain mail died out was that even a big dull sword that didn't cut through the mail could still break your your arm or smash your collar bone.

[johnptc]

when blocking a cut with a katana with another katana the swordsperson would turn their blade sideways or reversed so as not to shatter his own edge

never edge to edge if it could be helped

[Charlotte]

when blocking a cut with a katana with another katana the swordsperson would turn their blade sideways or reversed so as not to shatter his own edge

never edge to edge if it could be helped

Yes, that is exactly as it was demonstrated to me. I was already running to long to be really exact.

[Iron Falcon 72]

I was already running too long to be really exact.

Someone who makes such informative and well-written posts cannot run too long. Thanks for the info.

BTW, did I misread the article at The story of the Japanese sword that said in paragraph 1-3 that the folding reduced the carbon content? Or is that not correct?

[MattBower]

Laminated steels tend to be sharper than monlithic steels because, at the microscopic level, the soft spots wear away leaving sharp points of harder material sticking up. A very sharp blade is actually a narrow wedge with a sawtooth edge. . .

The sharpest blades were made of indian wootz steel. They were truely
amazing and able to cult silk scarves thrown in the air. . .

They were "super carbon " steels produced by breaking down a mixture two different kinds of iron alloys that were in the same billet by hammering them into a more uniform state of alternating layers. This was done hot as soon as the billet was removed for the crucible. The hammering and folding continued until the master smiths judged it same to stop. If the billet was allowed to cool without hammering then the segration of carbon and iron would produce something resembling failed cast iron.

Just to be clear, I know of no evidence whatsoever that there was any pattern welded aspect to genuine wootz/pulad/"Damascus" blades. I don't think you believe there was, but it's not completely clear from your description. (The word "lamination" usually implies taking two different materials and joining them in a solid state process, like plywood or modern pattern welding.) The papers I've read by Feuerbach, Verhoeven & Pendray, and others conclude that wootz was a crucible-melted monosteel, and the pattern was a the result of carbide banding having to do with the hypereutectoid nature of the steel, plus some combination of thermal cycling and the natural presence of carbide formers such as vanadium. E.g.,

Home Page
The Key Role of Impurities in Ancient Damascus Steel Blades
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"Segregation," rather than "lamination," would best describe what was going on in these steels. And the carbides in the carbide bands would've produced the microscopic sawtooth effect you're talking about, no lamination required.

The guys who're making this stuff today don't seem to have any problems letting it cool before they work it, although it needs to be worked in the right way and at the right temperature.

The idea that pattern welded steel allows one to take advantage of the properties of two types of steel is largely myth, particularly with respect to ancient steels that were composed almost solely of iron, carbon and impurities. Any serious degree of folding and welding quickly homogenizes the carbon content unless there's a barrier such as pure nickel between the layers -- and in ancient steels there wasn't. That may not be the case for san mai construction and other types where the layers are coarse and the welding minimal, but for typical layer counts in the hundreds it's certainly true.

[Steve Sells]

not exactly true. While I have posted many times about carbon migration, there are other elements to steel that do not migrate in the heat and time allowed in forge welding. So there is still differences in the layers that do work together, OR cause problems, one reason we must take care with which alloys we use. So while carbon variations are myth, the Chrome, Vanadium or Nickel are not.

[MattBower]

Notice that I said, "largely myth, particularly with respect to ancient steels that were composed almost solely of iron, carbon and impurities." Modern alloy steels may be a slightly different story (although selecting steels with significantly different properties can cause its own set of problems), but my main point was that in a world where even carbon content was somewhat hit-or-miss, and other alloying elements were there in very small amounts and largely by chance, the "best properties of two different steels" idea is nonsense.

Edited April 10, 2009 by MattBower

[Charlotte]

A couple of issues here I guess, mostly my fault.
Matt Bower is correct. yes Wootz steels are a segregated rather than "laminated in the fashion of plywood"

Yes, modern replicates have no problem with letting some of the cakes cool and solidify. The traditional smiths usually worked their billets immediately because they had less control of the content and the process than we do today. At that time, and using charcoal as the principal fuel, if it was hot they tried to keep it workable as long possible.
Archaeolgy in Syria and other near east locations has recovered a few uncut cakes that were appearently well hammered.

The trick with wootz is work it so that the carbides remain present in finely divided sheets seperated by relatively lower content steels. Working at the right temperature is require otherwise it crumbles.

As for laminated steels:

I belive that Steve Sells is correct in his remarks. In even the best made pattern welded the carbon content still varies from high to low through out the piece according the content of orgional. Carbon migrates to some extent. Most of the remaining metal stay put.

Homogenious pattern welded blade is an Oxymorn. As for cutting properties, you really want to have a blade that approaches the sawtoothed configuration of Wootz steel. Well laminated steel will display hard and soft areas as sharpened.

All of which discussion is a long way from my first intent of making a simple answer to initial posters question about Japanese swords.

Edited April 10, 2009 by Charlotte
Sentence left out

[MattBower]

In even the best made pattern welded the carbon content still varies from high to low through out the piece according the content of orgional.

I know we're getting pretty far off topic, but . . .

The forged samples (shown in cross section, Fig. 4 to 10) were annealed; therefore, the extent of carbon diffusion can be visually determined by the distribution of pearlite. In the four layer sample (Fig. 4 and 5) it is evident, based on the pearlite gradient between the two layers, that extensive carbon diffusion occurred after the first step in manufacture.

In the eight-layer sample it is observed that the pearlite concentration has almost equalized, however ferrite still decorates the prior-austenitic grain boundaries in the 203E layer (Fig. 6). By the time the material has reached 16 layers, the carbon content of the sample appears to be uniform as shown by both layers consisting of nearly 100% pearlite
(Fig. 7 and 8). . .

By means of light optical microscopy, it is apparent that carbon diffusion occurs rapidly during the manufacture of pattern-welded steel, and that the carbon content in the finished material is homogenous.

http://asmcommunity.asminternational.org/static/Static%20Files/IP/Magazine/AMP/V167/I02/amp16702p24.pdf?authtoken=cb31535fc425fd4bcb22e182921e2963ed861895

Of course it's true that metals don't diffuse nearly as rapidly as carbon, but I'm not aware that the component steels in ancient pattern welding often varied significantly in terms of alloying elements other than carbon. I'm willing to be enlightened, though.

[Charlotte]

Thank you for the link!! That is very nice work. Been a while since I was looking at these issues.

My only concern here is: On what scale? The level of examination just a little coarse. But still it does show that for these two alloys the diffusion rate is much greater than the studies I read several years ago lead me to belive

At any rate, or ancestors used the best available materials for their pattern welded weapons and so often had materials from a wide variety of sources.
In turn this produced results that varied form wonderful to awful.


We set out to build a sand box but finished up with a swiming pool.