Even wootz blades can break

[Jens Nordlunde]

In the book Persian Steel, one of the authors Dr. Brian Gilmore, in the chapter ‘The Development of Iron and Steel Technology’, on page 60 writes about the winter as an enemy to some blades.

Al-Biruni (AD 973-1048) describes two different types of pattern in blades, blades with welded pattern and blades where the pattern is inherent in the steel from which they are made. Al-Biruni says that the Rus (Russians, Vikings or other north European people living in the Novgerod area) makes pattern welded blades (soft steel and hard or steely iron) in contrast to Eastern blades, strongly suggesting that the latter were made from non-welded iron or steel. He also says, that blades made out of crucible steel cannot withstand the cold of the Russian winters, in which they are liable to break, as brittle stress fracture is likely to be a problem with blades made of high-carbon steel (1.5-2.0% carbon), like most of the Eastern blades were.

Does anyone know, how far north blades made out of wootz ingots could be used, in relative safety for not breaking them?

[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......)

[Chris Evans]

Hi,

The failure of swords in very cold climates is a fairly well known phenomena, indeed, as Tom so correctly points out, of all kinds of steel objects.

I have heard of Japanese swords so failing in the very cold winters of Hokaido. Essentially, it us due to the `Brittle transition temperature' (BTT).

The BTT is a temperature region at which the steel begins to lose all ductility and becomes exceedingly brittle. Alloying elements influence the BTT and it is determined by some kind of impact testing, usually by the Charpy or Izod tests, conducted over a range of temperatures. The temperature range at which the steel begins to exhibit brittle behaviour can thus be determined.

The steels from which old swords were made were a pretty mixed lot, especially when it came to alloying elements. As such, their behaviour at low temperatures was unpredictable.

Cheers
Chris

[Gt Obach]

hi
i guess my post may have been a little confusing... it is tough to find a source of error as to why the wootz may have been brittle in the northlands...
- retained austenite is just one possibility..
- grain growth during forging is another.. (if you forge at too high a temp for too long, it will encourage the crystal structure in steel to grow large-- this can make a blade brittle)
-stress in the steel..... if the steel is forged bellow non-magnetic, stress is put into the metal and this can make it brittle
- quenching a blade in an aggressive quenchant can also put lots of stress in the steel... it can lead to cracks.... this may not be apparent till later when the sword is used ....
-inclusions in the steel can also weaken it...

so as you can see..... there are several possibilities to having brittle steel ...... and lot's of it involve the smith and the way it was forged and heat treated

I have read the Persian steel book.....it is very interesting.....in there you will find a part that says some swords were quenched in hemp oil and fat.... or by other means.. there are many ways to heat treat wootz.... it all depends on the structures you want...

i've seen several persian swords with a quench line....where the sword etches darkly on the tempered martensite and very litely on the untempered side.....
-- i know this because this is exactly what happens with my blades... since i prefer to oil quench

I have made some swords of wootz.....and they all worked well.... preformed similarly to 5160 .... which is all I can tell
- I've chopped some of my bowies into 1/4 plate iron... (the are very large bowies.....since i like foot long blades).... and they handled the iron with good effect..... cutting a series of 1/8 inch gooves and no cracks or blade chips..


I haven't noticed any weakness due to pattern... ... sometimes as you hammer an ingot out.... you will get these large cracks... almost like delaminations ..... and my solution to this problem is to grind them out with a 6inch grinder......then forge it flat and keep going......
-however this give you a crazy pattern... since it has cut through some of the sheeting..... yet it will still make a dandy knife
- the prophets ladder can be made by grinding ladders in and forging flat.... and this pattern has shown no problem with cutting

I have a feeling that bulat is a little different....just by looking at the steel I feel that some of those blades are alloyed with different elements... their etch is different...
- how ever I don't think the bulat is weak or cracky..... i believe it can be if you don't roast your ingots before forging them out...
-I've had more problems with crackiness with those kinds of ingots..... and the pattern is much denser

I will try to email Visily and see if he finds his bulat is brittle in the cold..


Greg

I also agree that alloy could affect how it functions in cold

[Jens Nordlunde]

Hi Greg,



You wrote: ‘I have made some swords of wootz.....and they all worked well.... preformed similarly to 5160 .... which is all I can tell’.
What does 5160 mean?

When you have hammered an ingot out, and see there are cracks, can’t you melt it down again and start all over?

Jens

[Gt Obach]

Hi Jens
5160 is a carbon steel which has up to 1%Cr and .6 carbon.... therefore it is a medium carbon steel that deep hardens...... it works excellently for swords and other long blades...

Cracking... the cracks are not the same ones that you find on some ingots ..... these cracks form as you are forging ..... they resemble the delaminations you find occuring with pattern welded blades... .
- you could remelt the whole ingot......but this would cost alot of money.... 30lbs of propane and 40.00 for the crucible for the remelt....... it is better to grind out the crack.... and continue forging..... which has worked for me in the past.....
-- you can never tell which ingot will turn out to be grumpy and disobedient....lol

- in one experiment.....i left the delam and made it into a sword..... it worked fine....just have a big line in the middle of the blade.... it is unsightly

Greg

[Jens Nordlunde]

Hi Greg,

Have a look at the picture. Close to the grip the watering is nice, but then it starts to change - why?

Jens

[tom hyle]

BTW, let me just say that it has never been my impression that great strength, in general, was the reputed high magic of the wootz/bulat, but the magical cutting edge?

[Jens Nordlunde]

Hi Tom,

I am not sure that I agree to this, but I will have to come back to it later, as I don't have any more time at the moment.

Jens

[tom hyle]

Thanks. I don't mean, BTW, to imply that when well made, they are especially weak; just I haven't heard they are extra-strong.

[Gt Obach]

Hi Jens
if you have a sort of blotchy area .....it can sometimes result from the way the blade way polished.... I find to get a decent etch you have to avoid burnishing the metal... this is why I like to use abrasive with a lube to wash away the cuttings...... if you load the abrasive up with metal it will intern burnish the surface and make the etch results inconsistent.
-- it is somewhat the same as polishing a japanese sword.... if you burnish the surface it will be extremely hard to see the hamon....

the blotchy areas can also be a result of overheating.... you can over heat a blade in local areas and it won't pattern as well..... or even loose pattern...... it could also be that there is a local area of decarburization... ?

-- sometimes you can have an incomplete melt..... by this I mean that all the charge ingredients you started out with aren't fully melted but are incased within the ingot...... this is a cruel surprise.... that you will only find out when you finish etching the blade at the end....

-- another critical problem is etching.... if the blade is not totally degreased.... and spotless.... you can have really weird streeks and odd irregularities
if your etch is not nice... then I think you miss the beauty of wootz...

I don't think of it as a super steel..... because it just works as good as my regular steel knives... but where it excels.....is the beautiful patterns.... and this is it's true magic


the above blade looks good..... it maybe that the steel was abit burnished in areas before the etch... (but this is just a guess)

the major blotches look like the blade was pulled out of the acid....and the drops of acid on the underside of the blade weren't wiped away.... so the drops kept etching...... this will give that blackened pattern...

- it doesn't look at all like cracking...... so it is a good blade

Greg

[Jens Nordlunde]

Thank you for your answers, it is most interesting.
Tom, I think that Indian blades famed by al-Biruni and al-Kindi back in the 8th and 10th century must mean something. They knew swords, probably used them too, so they would not fame a blade 'only' for sharpness, there must have been more to it than that, flexibility, hard to break, things like that. There must have been a reason why these blades were more expensive than other blades.

[Jens Nordlunde]

Her comes a recipe for quenching, but before I bring it, I think you should have a small lecture in botany. In the recipe is mentioned ‘Serpent’s mushroom’. As I did not know what it was I tried Google, with no result, then I read further and it said that it was the same as ‘Mountain celery’. That gave a result, 138 to more exact, and it also gave a lot of recipes how to use ‘mountain celery’ in different dishes, this was a surprise to me, as it clearly says that ‘serpent’s mushroom’ is fatal if eaten. Well I thought, it could be, that those dishes were only meant for nasty mothers in law – who knows?

The text below is from ‘Persian Steel’, the chapter ‘The Development of Iron and Steel Technology’, written by Dr. Brian Gilmour.

In the 9th century, al-Kindi wrote that ‘moderation of quenching is an aid to sharpness, for quenching, if intensive, causes the serving of the blade in adversity, in other words, that too sudden quenching, as in cold water, made the blade too brittle.

(Although I would like to put the whole book on the forum, I can’t – you will have to buy it – it is very interesting, and a god investment, I think. Jens). And now to the recipe.

‘Take the mushroom which is known as ‘serpent’s mushroom’, so called because it is fatal if eaten, and which is the same as mountain celery [sic]. It frequently grows especially at the foot of large olive trees or in asses’ dung. Grind it up, collect the juice of Persian alkali and the jujube, and vine lees, sea foam, sal ammoniac, canthardies, the juice of the tender henbane, grind the solid parts to a powder and mix them with the liquid, place them in a bottle stoppered at the top, and bury in manure for 40 days until completely dissolved. Then take felt, soak it for three days in old urine, dry in the shade, and sprinkle the abovementioned liquid upon it. Bring the sabre to red heat in the fire and spray it, using wool, as is done for sabre iron. When it has drunk, cool it, cover it to protect it from dust. It will cut anything, and if a saw is made out of it, it will cut through glass like another will cut through wood; this is a noble tempering.’

This suggests that Tom is more right than I, the sharpness was most important. But he also states that the blade should be right tempered – so I was also right.

[Ann Feuerbach]

FYI...I disagree with Brian's translation...I think al-Kindi meant tempering and not quenching. As far as I understand, true quenching (heating to red heat and then emersion in liquid, produces martensite) was not done for crucible steel. No archaeological evidence for martensite and you would loose the pattern. It is a great book