True Combat Value of Wootz

[Chris Evans]

Hi Ann,

Originally Posted by Ann Feuerbach

Sorry to be a pain, but where in the book do they mention a historical crucible steel blade with martensite? I have had a look and can not find it. Plus is GT Orbach's one from replication or an historical object? I remember doing a survey of all known published historical crucible steel objects, and I do not remember any with martensite, but I could have missed it. .

First I must thank Frank for his correction and the supplementary links.

I found that link late in the night and read it too hastily. The authors were most certainly not by V&P - My mistake, for which I apologize.

In my haste, I did not read the work in full, just did a global search for the words `quench' and `Martensite'. However, it appears to me that the author links the hardening of Wootz with quenching and tempering, but I add, none too clearly for me, especially when we get to Pg 87.

On page 29/90 under the heading of Steel Processing: Reference to Indians smiths quenching swords into banana trees and worse

Pg 86/90: Reference to work by Kochman and colleagues in which a historical blade was examined for microstructure and bits of Martensite were found. The full article can be read here:

http://www.crystalresearch.com/crt/ab40/905_a.pdf

I found it interesting that: a) Martensite was formed in the 1st place, as this usually requires quenching of some sort, b) that there appears to be little Cementite near the very edge and c) the rather obtuse angle of the edge, which suggests something or another.

Pg 87/90: Elaboration on the idea of high carbon Martensite decomposing.

Cheers
Chris

[Ann Feuerbach]

Thanks loads Chris for the link. I did not have a copy of the article.
Ok, let me add some more murkiness to the mud.....

From Samuel's Optical Microscopy of Carbon Steels, 1980, ASM, P 26-28.
"Sorbite....It was subsequently shown that these constituents often were merely fine lammellar pearlite, but unfortunatly the terms were also indiscriminately used to refer to tempered martensite. This duality or origin was in fact recognized in the original ISI definition......." The text goes on in detail (sorbite was named for Sorby if anyone is interested).

From what I gather, there is primary and secondary sorbite: Primary from the eutectoid transformation process (and perhaps very important for pattern discussion) and secondary sorbite which is tempered marteniste.

Now all that said, my brain hurts and I am no more the wise.

[Gt Obach]

Hi Ann

yes.. you are correct and note... that it seems that sorbite... is a confusing term.. ... due to it being used for both tempered martensite and pearlitic sorbite ...

i've read more that a couple times that its an old term that seems to be out of style...lol

I had to reread that study i quoted several times before i realized they were talking about tempered martensite...... the term sorbite had fooled me at first

you see... he mentions sorbite that is produced in the case of these two swords were made according to the Massalski and Barker accounts..... In the Massalski account ... this is definitely an oil quench and that would make martensite ...

if it was pearlitic sorbite... then you wouldn't need an oil quench nor a temper cycle afterwards....... just air cooling


Greg

[Chris Evans]

Hi Folks,

1. I am beginning to think that we are rapidly reaching an impasse because of a lack of what can be considered sufficient studies on enough samples to be representative of Wootz swords - Especially those that were more than just eye candy. Nevertheless, we can state with some confidence the following:

a) In the absence of new knowledge, the quench hardening of hypereutectoid (>0.8%C) Wootz would have presented the ancients with enough problems to render the process quite haphazard - Whilst it is conceivable that some smiths could consistently estimate the lowest Austenitization temperature by the colour of the heated steel, a bit too much heat and some of the carbides re-disolved leading to retained Austenite after quenching (very undesirable);

b) That whilst unquenched hypereutectoid Woots can be work-hardened, the hardness obtainable would have been insufficient to produce swords capable of cutting through armour, or for that matter, knives and tools (say woodworking or stone cutting) with a sufficiently keen/hard edge to be truly functional;

c) Quenching/tempering and the attendant superior qualities thus attainable were sufficiently well known in antiquity, for Indian and Middle Eastern smiths to ignore and be satisfied with the inferior alternatives; And

d) there are too many instances of quenching being mentioned in olden times.

2. Other thoughts on this matter:

Why are we concentrating on hypereutectoid Wootz and exclude hypoeutectoid (<0.8%C) as representative of the kind?

What I am getting at is that there is no real difficulty in obtaining excellent Martensitic steel from hypoeutectoid stock, and tempered Martensite is the preferred microstructure for a sword that cuts by impact.

If the Indians could reliable produce hypoeutectoid crucible steel then the problem of how to obtain truly great hardness&toughness disappears. I imagine that it may have even been possible to arrive at a hypoeutectoid steel by de-carburizing hypereutectoid crucible steel stock. At this point of my deliberations, the only real advantage that I can see for hypereutectoid Wootz, apart from appearance, is a lower melting point which facilitated the crucible reduction process.

Greg could be right, as per his posts elsewhere, that our current day definition of what constitutes Wootz is unreasonably narrow by restricting it to hypereutectoid steel. For example, Vehroheven&Pendray decided that one of the swords they studied was not Woots Damascus because it did not contain the expected carbides. Ands yet, the term Wootz is said to be the Anglicization of the Kannada word for steel (any steel or crucible steel?). Of course they added the appellation `Damascus' to their definition, but then why go looking for mechanical attributes that may have have been the property of swords exclusive to this definition?

I think that it is fairly safe to say that when ancient chroniclers recorded that some swords performed remarkable cutting feats, that they did not class them by their carbon content, rather their origin, and even that very broadly.


Cheers
Chris

[Ann Feuerbach]

Hi Chris,
You are right. I have been arguing that hypoeutectoid crucible steel (producing ferrite/pearlite banding pattern) should not been seen as inferior. I am SURE that both were made in the same workshop, and were in the furnace next to each other, to control a difference between >0.8% and <0.8% would have been difficult to control. I am sure that cast iron was occasionally made as well.

Also, when I did my PhD I found that only 18 blades had been studied, which is why I am trying to increase that "database". How can we base any theories on such a small sample base? Plus, where the sample was take on the blade is also a concern when it comes to microstructures etc.

Just a note to say that I am not against any quenching/tempering of ancient blades, just the lack of evidence, but as mentioned above, could be due to sampling.

[Emanuel]

Hello,

This is a wonderful discussion, thanks to all the metallurgists for the great information!

In "Armes blanches du monde Islamique" by Alain Jacob, I think, I recall an account by a French officer in Napoleon's army who commented on Mamluk sabres. He gave an account of the way Mamluks trained: they would ride at full speed towards a block of wood on which was placed a turban. They would have to slice the turban in half without displacing it off the block, careful not to hit the block of wood as it would break the sword and cause great shame. I don't recall if he characterized the blade as Damascus, but the passage indicates that these blades could hold a magnificent edge, but were extremely brittle. Would such blades exhibit a high austenite content?

Regards,
Emanuel

[tsubame1]

Originally Posted by Manolo

Hello,

This is a wonderful discussion, thanks to all the metallurgists for the great information!

In "Armes blanches du monde Islamique" by Alain Jacob, I think, I recall an account by a French officer in Napoleon's army who commented on Mamluk sabres. He gave an account of the way Mamluks trained: they would ride at full speed towards a block of wood on which was placed a turban. They would have to slice the turban in half without displacing it off the block, careful not to hit the block of wood as it would break the sword and cause great shame. I don't recall if he characterized the blade as Damascus, but the passage indicates that these blades could hold a magnificent edge, but were extremely brittle. Would such blades exhibit a high austenite content?

Regards,
Emanuel

Emanuel, have you realized that hitting a wooden block at that speed would have meant to cut into the block itself making angled leverage on the blade during the very few seconds of gallopping away ? This would break *every* sword or bent a too soft one. Never cut, eh ?

[S.Al-Anizi]

Originally Posted by Manolo

Hello,

This is a wonderful discussion, thanks to all the metallurgists for the great information!

In "Armes blanches du monde Islamique" by Alain Jacob, I think, I recall an account by a French officer in Napoleon's army who commented on Mamluk sabres. He gave an account of the way Mamluks trained: they would ride at full speed towards a block of wood on which was placed a turban. They would have to slice the turban in half without displacing it off the block, careful not to hit the block of wood as it would break the sword and cause great shame. I don't recall if he characterized the blade as Damascus, but the passage indicates that these blades could hold a magnificent edge, but were extremely brittle. Would such blades exhibit a high austenite content?

Regards,
Emanuel

Hi Manolo,

this practice technique is in the furussiya manual, and is the basis of mounted sword use. It advances onto a stage where a mamluk has to cut his way through a series of turbans, not just one, on his left and right. The manual also states that training swords, and I assume, the ones used here are, incredibly sharp and brittle, but are not to be used in real combat.

[Chris Evans]

Hi Manolo,

Originally Posted by Manolo

..... Would such blades exhibit a high austenite content?

Thank you for your appreciative words. I think that both Ann and Greg,as well as the others deserve a special thanks for their extermely valuable contribution. I certainly learned a lot about Wootz from this thread.

Now for your question: It is hard to explain all the ins and outs of the heat treatment of steel within the constrains of a thread like this, but I'll try, albeit at the risk of oversimplification.

Carbon steel at room temperature consists of a mixture of near pure fairly malleable iron, known as Ferrite, and very hard iron carbides, known as Cementite. In this state, steel is moderately soft and can be bent and worked fairly easily.

Hardening by Quenching and tempering:

Steel is heated to a temperature at which its crystal structure changes and becomes as soft and malleable as lead. This structure is called Austenite and it can dissolve all of the carbides that we mentioned above, forming a solid solution of carbon in iron. Here I should mention that solids can dissolve in other solids, not just liquids - Hard to believe, but the process is complex and you'll have to take my word for it.

When heated Austenitic steel is rapidly cooled, as when quenched in water, the carbon cannot come out of solid solution, as it would under slower cooling, and the Austenitic crystal structure changes to one that is very resistant to deformation, on account of the carbon atoms trapped in it.

This new crystal structure is called Martensite and it is very hard and brittle.To render it usable, it is usually tempered by reheating, so as to allow some of the carbon atoms to come out of solid solution and thus reduce both its extreme hardness and brittleness. The carbon that is thus removed from the Martensite forms tiny spheroids of Cementite and results in a structure sometimes known as Sorbite, but more commonly called tempered Martensite. If Martensitic steel is tempered at high temperatures for a very long time it reverts to its original unhardened structure of Ferrite plus Cementite.

OK - Those are the raw basics. Now for the problems.

Plain carbon steel (without additional alloying elements) with less than about 0.4%C cannot be cooled fast enough to transform the Austenite into Martensite, but between 0.4%C and 0.8%C there are no great problems.

However, once the carbon content exceeds 0.8%C, known as the eutectoid composition, then upon quenching the tendency of the Austenite is to stay as it is and not transform into Martensite - Contrary to its usual high temperature `habitat', this Austenite remains as such at room temperature and is known by metallurgists as `retained Austenite', that is retained after the quench.

If we quench hypereutectoid steel (>0.8%C) not all of the steel remains as Austenite. In practice, depending on by how much the 0.8%C is exceeded, we tend to get a mixture of Martensite (hard and brittle) together with retained Austenite. Now remember that as I said at the start, Austenite is very soft and malleable. At the risk of gross oversimplification, now you should think of the retained Austenite as if it wasn't there, because it is so weak. The net result is a Martensitic sword blade with what amounts to all intents and purposes as `strength gaps' all over and inside it. Really disastrous for strength. Of course, the real picture is more complex, but at this level we need not overly concern ourselves with metallurgical minutiae.

In the heat treatment of modern high carbon steels there are strategies to minimize the problem posed by retained Austenite; For example with cutlery high carbon stainless steels such as 440C, any retained Austenite is converted into Martensite by cooling to very low temperatures.

However, the ancients, not understanding what went on inside the steel, would have had only two options (that I can think of):

a) Stick with hypoeutectoid steels (0.4%C-0.8%C), not easy to do as they could not analyze for carbon, nor knew about its critical role; And

b) if having to heat treat higher carbon content steels, they would have had to be extremely careful to quench from the lowest possible temperature at which Austenite forms. This so as to minimize the dissolution of the segregated carbides back into the Austenite and thus raising its carbon content, which would lead to retained Austenite. I imagine that by trial and error this temperature could be judged by the colour of the hot steel, but my guess is that they would have turned out a lot of bad blades.

I hope that this helps. If you would like to obtain more information see the entries in Wikipedia, as it gives a fairly good account.

I also hope also that you can see why the manufacture of a well hardened sword was more often than not a stroke of luck and why such swords had such exalted and legendary status.

Cheers
Chris