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Post by fujiwara on May 8, 2005 21:20:30 GMT -5
A quick question about blade forging: is the curve in a blade the result of uneven cooling caused by the clay, or is the steel formed into a curve then tempered?
Arigatou!
- Fujiwara
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Post by Takeda Sanjuichiro on May 9, 2005 15:29:59 GMT -5
A quick question about blade forging: is the curve in a blade the result of uneven cooling caused by the clay, or is the steel formed into a curve then tempered? Ummm... Both! Depending on the method used in constructing the blade blank (sandwich form, wraped, san-mai etc.)... Depending upon the compisition of the steel (carbon and alloy content) ... Depending upon the thickness of clay, the temperature of the water, the salinity and acidity/alkilinity of said water... All of these have an effect on how much the blade will curve, or not curve upon the transition of autinite to marsenite at the ha, and from austenite to pearlite at the shinogiji. It also depends on the complexity of the hamon and how the clay is applied. In short an experianced smith knows how to gauge his steel an imparts a curve if he feels the hardening process will not give enough... Conversely if he knows it will be insufficent, he will add curvature so it comes out correct in the end. So much for a simple answer. |
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Post by raito on May 9, 2005 22:35:49 GMT -5
Ummm... Neither!  It's not the uneven cooling that causes a curve, it's the difference in structure. That doesn't come from uneven cooling, it comes from uneven heating. That's not to say that you can't cause a curve from uneven cooling -- I've done it (ironically, on a sen, a metal scraper for rough-forming blades), but that's not what happens with a sword blade. The metallurgy behind it is dull unless you're into that sort of thing. I can't think of a single modern smith that curves the blade prior to treating it -- it just isn't necessary. Proper manipulation of the geometry will get you perhaps 80% or so of the curve you want, and the clay the rest. Somehwere out there on the net is a finite element animation of a quench. It shows the blade doing a reverse curve, then curving the way we would expect. I have seen that. It looks really weird. And yes, I've done this, several times. I concluded that a life learning to wield the weapon is what I'm destined for. Making them would take another lifetime. If you want to know more, I'd suggest this book: www.amazon.com/exec/obidos/tg/detail/-/087011798X/qid=1115695483It seems to be the current English primer on the subject. (Just making an Amazon link because it's handy). |
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Post by Takeda Sanjuichiro on May 9, 2005 23:32:07 GMT -5
I have to dissagree with you Raito, mainly on some points of specifics... I'm sorry, I'm a steel geek  The heating is not where hardness it imparted (and by result curvature), it is in the cooling. The steel must be heated to the austenizing point for the carbon and iron to become solvent enough for appreciable change to the structure of the steel (it's phase) to take place. It is the time/temperature curve comming down from that point that controls what the final phase of the steel will be. The pressure/torsion created by two phases of steel residing linearly along the same plane is what controls/causes curvature in Japanese blades. Marstenite is (in compairison) a larger looser grain/crystalization in the steel, it takes up more room than pearlite or bainite. It is this difference that imparts the curve. You are right, there are few modern smiths (though I personally can thing of a half dozen, including Yoshinda Yoshihara) who will impart a curve or reverse curve on certain sunobe to get a certain shape. It is not done in the mainstream since blades tend to have complex hamon these days, and are an even curve for the majority... (torii-zori IIRC, it is late for me) most blades that require 1/2 to 3/4 sori the sunobe can and should be dead straight. However with the early tachi, in koshi-zori form a slight curve was imparted, (and is imparted on swords made to be this way by modern smiths) and this is especially true because on early to mid heian era blades the hardend section of the ha does not always go to the hamachi, but ends up to 2.5 inches up the ha from the habaki!. (to prevent breaking as has been theorized). A point of note, if it is the specific cross sectional shape of the sunobe and the claying process that is the only factor to curvature, why does the same results happen in shinogi-zukuri, kanmuri-otoshi, shobu-zukuri, katashinogi-zukuri, Kiriha-zukuri and hira-zukuri? Additionally then why are sushi knives not curved?, or Japanese plane blades, chisles, etc. They all are of various shapes and high grade ones are made of the same process of steel making. The pattern of clay is importaint, so is the cross-section, the grades of steel, the methods of forging, the temperature of the quench, and the shape of the sunobe. Strangely, suguha, usally between ito and chu, and without any ashi tend to impart the strongest curvature. I'd be happy to go into all the specifics and metalurgical details of why this is and cite specifics if anyone is interested now, if you all can wait, I should have my big arse paper on it done in about 3 more weeks, which I will happily distribute to you all via link. -Takeda Sanjuichiro |
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Post by raito on May 10, 2005 10:25:11 GMT -5
I have to dissagree with you Raito, mainly on some points of specifics... I'm sorry, I'm a steel geek The heating is not where hardness it imparted (and by result curvature), it is in the cooling. The steel must be heated to the austenizing point for the carbon and iron to become solvent enough for appreciable change to the structure of the steel (it's phase) to take place. It is the time/temperature curve comming down from that point that controls what the final phase of the steel will be. The pressure/torsion created by two phases of steel residing linearly along the same plane is what controls/causes curvature in Japanese blades. Exactly my point. By your statement above, the temp at the beginning of the quench is (at last, in part) what determines the final structure. Differential temperatures produce a differential quench. I don't believe that youre' saying that that has no effect. No disagreement there. I don't disagree, except in degree. Perhaps I was being too simplistic there. Maybe better to say that most of the modern smiths don't pre-curve the balde to make it curve (as it will do so already), but to control the curve. But does it? I'd certainly be interested in seeing the differences. If you look at the typical Heian blade, it gets considerably narrower at the tip than the typical Muromachi blade. In part, because they tend to be wider from edge to back. (and most suchi knives do have curved blades, if not backs  . That will be interesting to read. |
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Post by Takeda Sanjuichiro on May 10, 2005 11:22:22 GMT -5
Exactly my point. By your statement above, the temp at the beginning of the quench is (at least, in part) what determines the final structure. Differential temperatures produce a differential quench. I don't believe that youre' saying that that has no effect. Ah, I understand what you were saying a little better now and I do agree with you. If a portion of the steel is never heated to the critical temperature to reach austinite in the first place, it will not be fully solvent when it is quenched to properly form marsenite. So in short, by bringing only the edge up to the austenizing temperature for the steel, you pad your chances for achiving differential hardening. That does make sense, maybe if I had more experiance with a good directional forge like the Japanese smiths use, I'd have understood more on the first go... I'm used to forges that give a more even heating, so I've had to rely on the clay to retard the time/temperature curve instead. I'd love to talk more with you about this in the future -Takeda |
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Post by raito on May 10, 2005 13:13:52 GMT -5
And I understand your statements better, too.
On the occasions that I've had to use enclosed forges for this, I was taught to add ground forging scale to the clay for the back, and ground charcoal to the clay for the edge. The theory is that the charcols burns out ad leaves the clay on the edge more porous, so it heats faster, and upon quenching, leaves the blade more quickly, resuling in a faster quench. The scale does the opposite.
(For those of you who are still with us, this is probably the most civilized conversation you're likely to hear on this topic. ;D)
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Post by fujiwara on May 10, 2005 13:21:08 GMT -5
This has been most enlightening, counsins. Since I'm an engineer, I would be most interested in all the gory metallurgical details. Given the modest appointments of a home shop, how sucessful could one be a forging a proper nihonto? Arigatou!
- Fujiwara
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Post by Takeda Sanjuichiro on May 10, 2005 13:29:27 GMT -5
...I was taught to add ground forging scale to the clay for the back, and ground charcoal to the clay for the edge... I have heard the same thing, but I have not had an opportunity to try it. This upcomming Saturday I will be going to a class on this very subject from a local smith. I'll be sure to share the details with you. It is and dang enjoyable for a change. BTW where are you out of Raito? and are you planning on going to Pennsic? -Takeda |
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Post by raito on May 10, 2005 15:06:56 GMT -5
I live in the Barony of Jararvellir in the Kingdom of Northshield (Madison, WI).
This year, I'll only be going to Pennsic if I win Crown this weekend. The potential Princess doesn't care for Pennsic, and Northshield isn't part of the Middle any more. I will be going to Lilies, though.
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