Even wootz blades can break

[Gt Obach]

Hi Jens
It puzzles me why some concider wootz brittle in the northern climes... I live in northern ontario where much of the winter is -20 to -30 cel..... and my work knives that I use in the forrest are made of wootz.... none has been brittle ... yet !

but .... you must remember that wootz is a highly alloyed steel !
-these kinds of steels can be a risk to retained austenite: I'll explain further,how this is bad-
- quench procedure: 1) heat blade to non-mag/cherry red- steel becomes austenitic (carbon is in solution)
2) quench blade - this cools the steel quickly enough so as to avoid producing pearlite structure ( and favour producing Martensite.... begining at MS/martensite start)
3) once steel has reached temp for MS.... it can now only produce martensite...
4) it must cool completely to MF/ martensite finish to produce the most martensite and get rid of almost all the austenite
5) if you do not undercool the steel enough... you may have remaining austenite called " retained austenite"
- this is notorious in stainless steels.... this is why you cryoquench these steels, in order to under cool it enough and convert the retained austenite... by reaching MF

6) now you temper your steel..... to produce a tempered martensite....which is not as hard but much tougher..... ( temper cycles can no trip of some austenite to become untempered martensite -- which is brittle--)
7) this is why you should temper 2 to 3 times....to minimize this phoenomena

this is just inna nutshell.... theres more to it...

anyhow......if the steel matrix in the wootz blade has some retained austenite...and its brought into a cold climate.... you could possibly reach MF and produce some untempered martensite in the blade..... which is a brittle structure... (the cure would be another temper cycle)


hope that helps a little...
-have abit of the flu... so i'll proof read it later... :-(
Greg

[Jens Nordlunde]

Hi Greg,

Thanks for your mail. I don't know why the blades were brittle, and the man who wrote it has been dead for about a thousand years, so we can't ask him, but maybe they did not temper the blades enough. One thing is that the Indians and the Persians knew what to do, but maybe they did not know it in Novgerod - although I doubt that they have missed that part.
You really lost me a few times, but Google helped me to understand your mail better - I am still confused, but on a higher level.
In the book Persian Steel there are quotations going back to 8th and 10th century, telling about tempering blades several times, now I better understand why. They also give several recepies on how to make the pattern show.
Do you know the book?

Jens

[Jeff D]

Originally Posted by Jens Nordlunde

Hi Greg,

but maybe they did not temper the blades enough
Jens

Hi Jens,

I personally think this is the answer. If the blade is heated too much the wootz pattern is lost. I suspect a large number of these blades were under tempered for this reason. Remember they were heating it to a certain colour (prethermometer era) Verhoeven et al has shown that this has a large margin of error.

Jeff

[tom hyle]

A large margin of error, perhaps, for acceptable work, but what I've heard is that the best/most proper work is more tightly controlled by the expert hand eye and feel of a truly expert worker, and this is much in line with my experience of craft (my sister is a great caulker; who knew? Don't stalk her; you know me....). I think jens has an excellent point concerning the idea that problems which are told of/occur at the edges of the bulat technology area might be tales arising from distance-distortion of true tales from the heart of the area, or may be true tales arising from some sort of habitual poor working of the steel/distortion of the technology at the edge of its area.
Gt Obach, any comment? Another question for you, if you don't mind: There is a folkloric idea that seems to make sense (?) that bulat is subject to cracks (and thus tempered soft, because the whatever the name crystal cutting inclusions form the magic edge, not the steel matrix, yes?) because the crystal inclusions (I thought they were carbide crystals; can't remember what you said; checking would've been easier than explaining; I am a stupid and lazy man.....), or I suppose the "cavities" in the matrix if you imagined them gone, would provide places for cracks to start, due either to their hardness(?) or to an effect similar to when a crack starts from a sharp scratch or a sharp square tang shoulder, etc.? Please inform us. We have mostly folklore, AFAIK. People are going to be following you and Ann and being like "He threw his shoe at me. No! He threw it at me! Give me that! I have His shoe......" so watch out..................

[Ann Feuerbach]

There are other references also to blades being brittle (see Foster in Bronson, 1986, 25 for a 17th century mention). Since there were so many variations in the production of crucible steel, some were bound to be of lesser quality. Also we do not know if the blades that break are hypereutectic with spherical cementite to make the pattern, or were they hypoeutectic and had a ferrite pearlite banding? I think there is also a mention about how you should not get a blade that has a pattern that goes across the width of the blade. This makes sense because of crack propagation and it could spread across the blade. As far as I remember, crucible steel is never quenched, as this would destroy the pattern. The steel has to be forged below red heat to keep the pattern. Low temperature tempering can be done in oil, or as some references say...in a fat Nubian slave, or in the wind while riding on horseback. Also, as already noted, the matrix of the blade can be very different too, usually pearlite, ferrite or DET (divorced eutectic transformation). No exampes of crucible Damascus steel blades which have been examined and published have tempered martensite. One of the theories of why they are so strong is that if you do have a crack, when it hits the spherical cementite the force is spread and the crack stops. Oh, as far as how far north...we also have unpublished crucible steel blades from Western Siberia, which got there via trade.

[Jens Nordlunde]

Jeff, Tom and Ann,
Thank you for your answers, I think I agree with all of you, when saying like Ann did - not all smiths were at the same level. This may have led al-Burini to think it was the cold weather, rather than bad tempering which made the blades break. I find it most interesting what Ann mentions, about avoiding patterns crossing the blade.
Ann did they really import fat Nubian slaves for the test? I know the Indians imported slaves from Africa - but still.
Greg, I would think that when you have a knife (short blade) it would be less likely to break, than a long blade (sword), especially when you use it as a knife, and not in a fight when the blade is hit by another blade - am I wrong?

Jens

[Rivkin]

I'm sorry to say this, but all treatments of the "wootz question" where far more historical than technology oriented.

May be it's somehow obvious that wootz is brittle due to some basic properties of wootz, but there is no experimental data that proves it - a single phrase here and there, with no description of what really happened (how many blades where purchased, where, and of what exact kind) certainly does not seem to qualify for anything.

Concerning cracks and patterns - I was always interested in reading somewhere, how exactly swords react to the physical contact (and I still hope to see someone producing a beautiful picture of time evolution of stress distribution in various swords). I think that the general picture should be completely linear (it's not like the stress is going to be supersonic in this case ?), and therefore should be really easy to obtain.

In general the stability theory (which is inapplicable in this case ?) directs that the wielding should be performed right in the middle of discontinuities in the structure - for example when you have a bridge, the most dangerous place is near to one of the ends - if, even due to thermal fluctuations, excessive stress builds up there, there can be not enough time to take it away from the bridge.
Please correct me if my memory on stability theory is wrong.

I don't think it's applicable to swords, a lot of them seem to violate this rule -wielding patterns ending right at the edge, "maiden hair" pattern etc..

[tom hyle]

I may not follow you, but many swords, especially some of the finest European swords, are designed to break in certain places, if they break, as the distal taper to a thin tip and a thick soft base; the tip takes up much stress in its easy flex, though it cutting it can be vibratory, and I find slashing or drawing the cut helps, while the (sometimes) soft thick base and soft usually thick tang are greatly absorbant of all other shock/stress. Also, some were desinged with a breaking point in the tang, above (behind, pommelward of) a rivet, so if the tang does break, it's still attached. The geometry, simple or crystaline of this I do not understand, BTW, as I am not the best heavy pommel balancer, neither, but I've read of it, and seen its results, many times.
Broken and damaged pieces are so educational to us, even if we don't repair them. Anyone got a snapped or chipped wootz blade to help us, maybe? Any modern smiths do toughness tests and find conditions/alloys/whatever where the steel is brittle?
Everything is harder and more brittle when cold. I have seen hard steel axes hammers and files chip or snap way "too" easily when very cold. They were all, AFAIK, modern steel, though say early to mid 20th. Folklore of Europe is "the Vikings" the North-Germans, and specifically the Swedes invented the sword that could take the cold by pattern-welding; note we just got an Eastern version of this lore, too(?): However, also, this seems to be the "viking spatha/swert" known to history and archaeology as mostly Frankish(? or Burgundian?) in numbers manufactured, if not in origin/design (hmmmmm; like navajas......)