Mikeeman
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Post by Mikeeman on Jan 30, 2015 21:17:08 GMT
This is something I've been thinking about for quite a while. I saw a thing a while back where this modern dude was recreating a viking sword trying to be as authentic as he could. So he get's some iron and, if I'm not mistaken, put some ground up charcoal in it to raise the carbon content. So when he put it in the crucible, it got all mixed around in the iron and made carbon steel. And, suddenly, these swords were legendary. Ufberts, I think they were called. Anyway, this seems to be something that got figured out all over the place. Yet I still here about how the Japanese iron sand is so low quality (because it is) and how they had to invent all these fancy ways to try to improve it. Am I missing something?(Most likely.) Did they just not figure it out? I'm not super familiar with ancient Japanese metalurgy, so I just wanted to ask.
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Paul
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Post by Paul on Jan 30, 2015 21:26:56 GMT
This link is kind of related;
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Mikeeman
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Post by Mikeeman on Jan 30, 2015 21:34:38 GMT
That was actually pretty insightful. What I got from the video was that even though they were lower carbon steels, they only quenched them (as I understand it) and got reasonably similar results to higher carbon steels that had been quenched and tempered. So I guess they just didn't add carbon because they didn't HAVE to?
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Post by randomnobody on Jan 30, 2015 21:55:12 GMT
The process, to my layman understanding, is not significantly different. A tatara is just a big furnace that melts down iron ore using carbon-rich fuels and what comes from it tends to vary in carbon content. Some bits will have more than others. It's the smith that takes these bits and combines them into a single billet that they will then fold several times in an effort to make things more homogenous throughout. Ulfberht swords, if I remember the documentary correctly, somehow managed a slightly better starting product that could be forged (or was it cast?) straightaway but was also often folded, twisted, or otherwise arranged into patterns. Then comes wootz, which is yet another take on a similar process that ends up with a chuck of steel ("bulat") that is then worked into whatever blade shape. Again, total layman, very basic understanding, using the word loosely. Japan DID, and to my knowledge does, still add carbon during forging, but the blades are not tempered like their western counterparts, which makes them less tolerant to bending.
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Mikeeman
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Post by Mikeeman on Jan 30, 2015 22:20:12 GMT
The way I understood it was that the Japanese would throw iron sand in to a huge fire box thing that was fueled by wood. Then they just kind of collected the chunks and forge-welded and folded them together. I guess the wood would turn in to charcoal and add carbon, but it's not very controlled, it seems like. Seems like you could get a lot of junk in there you wouldn't really want to be there pretty easy. The viking thing that I saw had the guy put the metal and charcoal (along with a couple other things) inside of a sealed, clay cup sort of thing. Keeping anything else unwanted out of it. Then they forged down the chunk thing. It seemed like a much more controlled process, to me. But then again, I don't know. That's why I'm asking.
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Post by randomnobody on Jan 30, 2015 22:40:14 GMT
I've read before, in many places, that the common tatara produces several grades of "steel" in the end. Most of it goes off to make basic stuffs like tableware, teapots, and other goods; only the "good stuff" gets turned into swords. Whether one considers this a flaw in the design or the design itself is up to each observer. The crucible used in the Ulfberht (I always think I'm spelling this wrong) is certainly more controlled, for starters it's usually a lot smaller. That makes things a lot easier to keep track of, and sealing the unit much easier. I think the same fellow in the Ulfberht doc also does wootz in the "middle eastern" style. If not him, then another big, burly fellow with a bushy beard. I think those are all requirements for old school western bladesmiths...\ Thought I submitted this post already but after several minutes of YouTube searching I find I had not. Been trying to find a good video on making wootz just for giggles, but can't seem to. Also, apparently the guy I was thinking of is different from the fellow in the Ulfberht doc. Tee hee.
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Post by Timo Nieminen on Jan 30, 2015 23:07:49 GMT
The tatara is a bloomery furnace, along the lines of bloomery furnaces in Europe, Africa, India, SE Asia, and elsewhere. Layer ore and charcoal (not wood), and light. The charcoal provides both energy and rips out the oxygen from the iron ore, reducing the iron oxides in the ore to metallic iron. The chemical reaction occurs in solid state - the iron doesn't melt at any stage. You need to hammer and fold and hammer and fold to get rid of the slag. The Japanese iron sand wasn't that bad an ore. Yes, they could have had a somewhat higher iron content by directly mining the ore bodies that eroded into the iron sands, but that would take hard rock mining.
The easy product is low carbon iron, but you can make steel directly in a bloomery furnace by raising the temperatures a bit, and keeping it hot for longer. The Japanese tatara was pretty good for making steel, compared to some other bloomery furnaces.
If you want to make crucible steel, first make iron using a bloomery furnace. Then charcoal + iron into a closed crucible, or iron + cast iron into a closed crucible. Stack the crucibles in a big kiln, and heat and keep at high temperature for 2 days or so. This takes more fuel, but gives more consistent steel, and can give higher carbon contents, than you'll get by making bloomery steel. Didn't spread outside Central Asia/India/East Asia until quite late (adopted in Europe during the Industrial Revolution), and the Chinese largely abandoned it in favour of decarburising cast iron (see below) about AD1.
The blast furnace is more efficient, mainly because it runs continuously. Higher temperatures melt the iron, which then dissolves carbon up to a saturated solution, and molten slag and iron are tapped from the bottom of the furnace. Meanwhile, dump more ore and charcoal in at the top. Traditional-style Chinese blast furnaces were seen running continuously for 40 days or so in the early 20th century. The problem is that the product is cast iron, with 3-4% carbon. Too much for many purposes. Mixing low carbon iron and cast iron to make crucible steel is one thing you can do with it (the usual Indian and Central Asian crucible steel method). The Chinese solution was to decarburise the cast iron. Break it into small chunks, heat it, and blow air over it. "Fried iron" was the Chinese term, since the heating was done in what looks like a giant wok. The relevance of the blast furnace to Japanese steel-making is as a potential source of carbon (as cast iron).
Note that it takes more fuel to make crucible steel (especially if not using cast iron from a blast furnace) than to make bloomery steel. Depending on wood resources (or availability of coal as an alternative), bloomery steel and/or importing crucible steel can be a sensible economic alternative.
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Post by Timo Nieminen on Jan 30, 2015 23:11:08 GMT
Japan DID, and to my knowledge does, still add carbon during forging, but the blades are not tempered like their western counterparts, which makes them less tolerant to bending. The forging is done in an oxidising atmosphere, not a reducing atmosphere. The carbon content goes down during forging (which is why they like to start with about 1-1.2% carbon, to end up with about 0.7% after forging).
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Post by Timo Nieminen on Jan 30, 2015 23:14:59 GMT
That was actually pretty insightful. What I got from the video was that even though they were lower carbon steels, they only quenched them (as I understand it) and got reasonably similar results to higher carbon steels that had been quenched and tempered. So I guess they just didn't add carbon because they didn't HAVE to? Similar carbon content to good European swords made from bloomery steel, on the cutting edge. It works. Lower carbon content compared to typical crucible steel/wootz swords. But quench those without tempering, and they'll break like glass (people break antique wootz swords by dropping them on the floor). Sometimes (often!) wootz swords wouldn't be quenched, but air-cooled, to avoid brittleness.
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Mikeeman
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Post by Mikeeman on Jan 30, 2015 23:18:08 GMT
I meant the Japanese steels had only been quenched where as swords elsewhere were quenched, then tempered. Seems like you would need to "water it down" so to speak if you have to let it air cool. That must have a looot of carbon.
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Post by Timo Nieminen on Jan 30, 2015 23:38:33 GMT
1.2-1.5% is not unusual for wootz swords (the wootz might have been 1.5-2% carbon before forging). They get good edge retention from carbides, even though the steel itself is relatively soft.
There are many swords other than Japanese that were quenched and not tempered (or just somewhat auto-tempered; i.e., residual heat from the quenching not cooling the whole sword down tempers the blade). Mostly differential quenched swords (where only part of the blade is quenched) or laminated construction, where only the edges (or centre plate in sanmei/sanmai) are high-carbon. Japanese swords combined both of these (differential quenching and lamination).
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Post by randomnobody on Jan 30, 2015 23:46:10 GMT
Japan DID, and to my knowledge does, still add carbon during forging, but the blades are not tempered like their western counterparts, which makes them less tolerant to bending. The forging is done in an oxidising atmosphere, not a reducing atmosphere. The carbon content goes down during forging (which is why they like to start with about 1-1.2% carbon, to end up with about 0.7% after forging). Whoops, thanks for the correction there, Timo. I had a feeling you'd be along shortly to clear everything up.
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Luka
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Post by Luka on Jan 31, 2015 0:41:52 GMT
Well, I won't go into japanese metalurgy, I didn't research it well enough, but I will go into Ulfberht swords a bit. ;) The documentary was made with a premise that Ulfberht swords with inlay spelled +VLFBERH+T were the original Ulfberhts and that they were made of crucible steel imported from Asia. This is quite controversial premise and not researched enough. The first problem is that the oldest Ulfberhts were inlayed +VLFBERHT+, not +VLFBERH+T. +VLFBERHT+ spelling appeared in 9th century and +VLFBERH+T in 10th. The second problem is that we don't know if Ulfberht is a kenning for a high quality sword, a smith's name that was inherited by future generations of smiths from that workshop or is it a name of a bishop who owned the sword making manufacture (because supposedly only bishops put crosses before and after their name). The third problem is that even for +VLFBERH+T's from 10th century that were analized and had structure of steel similar to crucible steel we can't be 100% sure they really were crucible and that their structure was not achieved with some other technique. If it is crucible, we can't be sure if it really is from Asia or from Europe and we just didn't know europeans of that era knew how to produce it. Too few of +VLFBERH+T's are analized to prove that majority of them had that steel structure or if they were made like older +VLFBERHT+'s and other swords of the period, with regular bloomery steel piled, refined with folding, sometimes forge welded from different grades of steel for the core and edges etc...
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Post by Timo Nieminen on Jan 31, 2015 1:03:55 GMT
Of the "crucible steel" Ulfberhts that have been analysed, crucible steel is likely. The 3 signs are uniformity of carbon content, high carbon content, and low slag. They tend to brittleness, too. Much more likely to be snapped than piled/pattern-welded Ulfberhts.
I don't see why import of crucible steel from Asia would be controversial. Viking/Rus were major traders with the Khazar Khanate, which was a major trader with Central Asia (Transoxiana, Afghanistan, Persia), which was a major exporter of crucible steel. Given the large number of coins from the region found in Viking sites, the trade was large scale. (The Vikings went further than the Khazar Khanate, e.g., raiding in the Caspian Sea, but the bulk of their Asian trade was with the Khazars, AFAIK.) Were the Ulfberhts predominantly Mediterranean, there might be a controversy as to whether the steel was imported from India or Central Asia, but given Viking/Rus trade routes, Central Asia looks good.
Controversies as to which Ulfberhts are oldest, whether groups of them are counterfeits of the "genuine" ones, what "Ulfberht" means, etc. - those make sense. Crucible steel from Central Asia looks like the best answer to the "crucible steel" ones. Not certain and thus we might change our mind given more information, but I don't see any reason why it would be controversial.
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Post by Jussi Ekholm on Jan 31, 2015 16:37:05 GMT
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Luka
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Post by Luka on Jan 31, 2015 22:16:54 GMT
Of the "crucible steel" Ulfberhts that have been analysed, crucible steel is likely. The 3 signs are uniformity of carbon content, high carbon content, and low slag. They tend to brittleness, too. Much more likely to be snapped than piled/pattern-welded Ulfberhts. I don't see why import of crucible steel from Asia would be controversial. Viking/Rus were major traders with the Khazar Khanate, which was a major trader with Central Asia (Transoxiana, Afghanistan, Persia), which was a major exporter of crucible steel. Given the large number of coins from the region found in Viking sites, the trade was large scale. (The Vikings went further than the Khazar Khanate, e.g., raiding in the Caspian Sea, but the bulk of their Asian trade was with the Khazars, AFAIK.) Were the Ulfberhts predominantly Mediterranean, there might be a controversy as to whether the steel was imported from India or Central Asia, but given Viking/Rus trade routes, Central Asia looks good. Controversies as to which Ulfberhts are oldest, whether groups of them are counterfeits of the "genuine" ones, what "Ulfberht" means, etc. - those make sense. Crucible steel from Central Asia looks like the best answer to the "crucible steel" ones. Not certain and thus we might change our mind given more information, but I don't see any reason why it would be controversial. I did not mean to say that scandinavians trading with Asia is a controversial idea, just that it is controversial that these Ulfberhts showing crucible steel structure are the original ones. We don't even know if Ulfberths were coming from the same workshop. Also, there is no evidence even that majority of Ulfberhts spelled +VLFBERH+T are made out of crucible steel. Some yes, very probably, but even that is not 100% sure, but I agree it is likely. I have even seen an italian medieval sword probably made of wootz. If Ulfberths were made in scandinavia, why use latin letters and crosses? Unless these later Ulfberhts are copying the original frankish ones. ;) About Ulfberhts, nothing is certain. :) Williams in his article about this theory also says that europeans did "rather inept attempts to copy it (asian damascus steel) in the West by ‘pattern-welding’". This is completely wrong since pattern welding in Europe started in celtic times and in no period at all patterns similar to wootz steel were made. Earliest roman patterns were definitely not copying the look of asian crucible steel.
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Luka
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Post by Luka on Jan 31, 2015 22:42:59 GMT
For those interested, here is the original article behind all of this. :) www.academia.edu/6426127/Crucible_steel_in_medieval_swords
You'll notice that only 4 swords are proven to be almost certainly made of crucible steel. Not really enough for such a strong statements as his if you ask me. ;) It could be argued that frankish made swords with refined iron or low carbon steel core and higher carbon harder steel edges were safer to use since they were less likely to snap and more popular, and many of these blades were made with Ulfberht inlay. Scandinavians couldn't get enough such blades either with trading or looting, so they started making their own out of crucible steel which was available to them, but since it was not as good functionally because it sometimes snaped and it was easy to overheat it when forging, scandinavians tried to raise the popularity of such blades by copying good old Ulfberht inlay. I'm not saying this is true, but it could be argued. A good argument for that would be that even Arabs prized frankish blades highly and prefered them to the blades available to them in the islamic world (several arab chroniclers state that).
A thread at myarmoury with an interesting discussion: www.myarmoury.com/talk/viewtopic.php?t=8879&highlight=frankish+arab+swords
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Mikeeman
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Post by Mikeeman on Feb 1, 2015 17:04:03 GMT
I feel like I'm gonna have a PhD in Historical Metallurgy after this thread. Seriously, though. Lots of good stuff.
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