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Morgan Boes





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PostPosted: Fri 05 Jan, 2007 8:16 pm    Post subject: question about folded-steel forging         Reply with quote

I know the Japanese practiced(and still do) the special forging technique called "folding", where they would heat a blade, fold it, pound straw into it to add carbon, fold again, etc. Are there any other cultures that used this method or something like it?
moo
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Dan Howard




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PostPosted: Fri 05 Jan, 2007 11:41 pm    Post subject:         Reply with quote

In order to add carbon to steel you have to heat the metal in a carbon rich environment for a long time. Pounding straw won't do it. Regarding folding/forge-welding. The La Tene Celts are believed to be the first to practice this technique and it has been used ever since by many iron working cultures. A good book on the subject is "The Celtic Sword" by Radomir Pleiner.
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Joshua Connolly




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PostPosted: Sat 06 Jan, 2007 2:52 am    Post subject:         Reply with quote

Also, Europeans didn't use Folded steel after a while because generally the techniques used for folding steel are only effective in areas where there is a small amount of available iron.
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Fabrice Cognot
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PostPosted: Sun 07 Jan, 2007 6:44 pm    Post subject:         Reply with quote

I don't think the straw was added to raise carbon content - it was rather straw ash, used as a flux to facilitate welding.

folding/welding helps giving the object a more homogenous structure/carb content/properties. Several la Tènhe swords show such a structure, with the steel having been folded at least 4 times. Also, same structure (of sorts) was found in a 13th cent. blade.

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Shawn Shaw




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PostPosted: Sun 07 Jan, 2007 7:17 pm    Post subject:         Reply with quote

That book doesn't look like it's an easy one to track down.

Does anyone know of a place to get it?
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Dan Howard




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PostPosted: Mon 08 Jan, 2007 12:43 am    Post subject:         Reply with quote

You will have a hard time finding a copy of Pleiners book to purchase but many university libararies will have a copy.
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Jeroen Zuiderwijk
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PostPosted: Mon 08 Jan, 2007 3:56 am    Post subject:         Reply with quote

All steel was folded, it's the only way iron or steel could be made until bloomery steel was introduced. When you smelt iron, basically all you get is a big spongy lump of iron, slag, charcoal and other stuff. Before you get a piece of iron you can do something with, you have to forge it down, fold it, forge it down, fold it etc. until enough of the slag and other impurities have been forged out, so you get a solid piece of iron. Then you can go further to introduce carbon by placing the iron in a reducing fire for a good a mount of time. The carbon will only enter a thin surface layer, so if you want to get a fairly homogenous steel, you have to fold it various times. During that process, you can carburize it again to introduce more carbon.
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Jason Dingledine
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PostPosted: Mon 08 Jan, 2007 5:26 am    Post subject:         Reply with quote

Morgan Boes wrote:
I know the Japanese practiced(and still do) the special forging technique called "folding", where they would heat a blade, fold it, pound straw into it to add carbon, fold again, etc. Are there any other cultures that used this method or something like it?


The raw steel in block form (never as a finished blade) is folded back on itself and "Forge Welded" in order to homogenize the carbon content that naturally varies from piece to piece, due to the production methods of the orginal bloom. Carbon is actually lost with each fold and weld, not introduced and is carefully controlled by the experience of the smith.

Joshua Connolly wrote:
Also, Europeans didn't use Folded steel after a while because generally the techniques used for folding steel are only effective in areas where there is a small amount of available iron.


The use of "Forge-folded" (which is exactly the same as "Pattern-welding") ceased to be used in Europe because the smelting processes that develop increased the quality of the blooms that they were able to produce. This created a more consistent base product that require less refinement.

Brian VanSpeybroeck has a couple of movies that display this exact process. He filmed them at our mutual friend's (Mike Blue) shop and at a smelt that Mike conducted at a hammer-in.

http://home.mchsi.com/~galloglas/movies.html

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Matthew Parkinson
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PostPosted: Mon 08 Jan, 2007 6:45 am    Post subject: rough history of steel in Europe         Reply with quote

Disclaimer: I am simplifying some of this to avoid writing a book...further details are encouraged.

Until the invention of the Huntsman Process (otherwise known as Sheffield or crucible steel) in Sheffield, England in 1740, all steel used in European blades started off as either 1) bog iron, 2)meteoritic iron, or 3)a wrought iron bloom. Wrought iron was initially produced by REDUCING iron ore in an appropriate furnace. When reducing an ore, it never becomes molten, but instead the oxygen is stolen from the metal by carbon monoxide gas...a reducing fire produces carbon monoxide gas. Later in history processes such as PUDDLING developed which were more efficient. In all cases, what you got was a lump of iron which had many voids and impurities, silica being the chief among them. In the earlier reducing processes, the carbon content of the bloom varied depending on how much exposure a particular portion had to the air draft. Thus a bloom made through reduction could be broken up into "steel" portions and "iron" portions, and could be used accordingly. This BLOOM of iron needed to be forged, folded, and reforged several times to remove the voids and homogenize the material...thus the name WROUGHT IRON. The more times that material was folded, generally speaking, the higher the quality (and selling price) of the final product. Does this sound a bit like the Japanese process to anyone?

Once PUDDLING became the main way of making wrought iron, the carbon content was homogenous throughout, so the secondary process of making BLISTER STEEL was developed. Blister steel is made by packing bars of wrought iron into sealed boxes filled with such items as charcoal and bone fragments...carbon sources...and "baked" at a high heat in a furnace for several days. During this time, carbon diffused into the iron, making it into steel. The carbon content could be affected by the time and temperature involved. Blister steel had higher carbon content close to the surface, and less at the core. It was called blister steel, because the carbon sometimes reacted with impurities in the wrought iron, creating blisters of gas. In order to re-homogenize the material, blister steel was often forged out, sheared into pieces, restacked and forge-welded several times to create SHEAR STEEL. Again, the number of re-stackings affected the quality of the end process, thus SINGLE SHEAR, DOUBLE SHEAR, and TRIPLE SHEAR designations.

The CRUCIBLE STEEL process initially used blister steel as its starting material, but later evolved to used a mixture of wrought iron and cast iron as the raw materials. Basically, the ingredients were placed in a sealed crucible, and brought to a molten state in a furnace. The molten steel was poured into ingot molds and forged out. It was already homogenized, and therefore needed no folding and reforging before use. Those of you familiar with WOOTZ probably have noticed a few similarities here.

All of the earlier wrought iron producing processes became obsolete with the invention of the BESSEMER process, which created mild steel directly from cast iron through blowing oxygen through the molten material to burn out the excess carbon and impurities. All modern steelmaking is based on Bessemer's process. Most alloy and tool steels are made through remelting of mild steel (and scrap) and adding the desired alloying elements and carbon to the melt. This is then poured into ingot molds and rolled into bar, sheet, etc. The secondary melt to create alloy and tool steels can be considered a modern version of the crucible process.

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Kjell Magnusson




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PostPosted: Mon 08 Jan, 2007 2:36 pm    Post subject:         Reply with quote

According to The Craft of the Japanese Sword, by Kapp and Yoshihara, the steel used for Japanese swords actually start out at a higher carbon content than the finished sword has (should the carbon content from the smelting be on the low side, it will first be carburized in a separate step before the forging begins), with the excess being burnt away during the forging. The straw and clay mixture would instead be used to limit the rate of this decarburization (by simply keeping the oxygen of the atmosphere from coming in contact with the steel), as the final carbon content could otherwise be too low.
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Bruno Giordan





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PostPosted: Tue 09 Jan, 2007 12:18 pm    Post subject:         Reply with quote

This is the european traditinal method explained by a top notch maker.

http://www.templ.net/english/making-welded_steel.php

English translation is a bit rough.
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