Ethnographic Arms & Armour - View Single Post

Chris Evans · 21st November 2006, 07:53 AM

Hi Folks,

Rivkin very kindly sent me a copy of that paper that was published in Nature. He is indeed a gentleman and a scholar and my sincerest thanks go to him

I hurriedly read it and the thing that immediately struck me is is the claim that Wootz had superior qualities, without telling us which exact attributes were being talked about. After all, in the context of swords, there are a number of mechanical properties that are considered desirable, most having to do with hardness and toughness. Hardness, is relatively simple, but toughness has many aspects.

The most often mentioned advantage of Wootz is its supposed combination of hardness and ductility resulting from the presence of carbides and nearly pure iron in its microstructure. The simplistic logic appears to be that the hard carbides do the cutting and the soft near pure iron provides the toughness. This paradigm is contrasted by that of conventional quenched & tempered Martensitic steels in which the same homogenous microstructure embodies both attributes.

Whilst true to some extent, I have a lot of trouble in accepting the above line of reasoning as a justification for declaring Wootz to be a superior steel. After all, it is well known that steel obtains its optimal hardness and toughness in the quenched and tempered Martensitic state, though I hasten to add, that work hardened Pearlitic steels, such as piano wire, can also be both surprisingly tough and hard. Whether Wotz swords were ever work hardened to to the same extent as modern piano wire, I have yet to find out.

A theoretical evaluation, from first principles, of Wootz is very difficult because the very large number of variables to be considered and all this has to be done in the context of various sword, the design of which introduces yet more variables.

Based on the papers that I read, most Wootz blades were not Martensic, rather work hardened Pearlitic with additional iron carbide embedded in it, though GT Obach did make the very important observation that partially quenched Martensitic blades, where the edge was expected to do the cutting, as well as fully quenched, were not uncommon. However, here we have to remember that once the carbon content of Martensitic steels exceeds 0.8%, the surplus carbon precipitates out as iron carbide, which can have detrimental effects on toughness, depending on its microstructure and localization. Whilst this effect can be minimized with very careful heat treatment, it is extremely unlikely that the ancients would have had the means or knowledge to achieve this.

So where does this leave us in relation to carbon nanotubes and which properties did these influence? I am at a loss.

Just looking at the evidence that so far I have managed to lay my hands on, it would appear that in centuries past Wootz acquired its formidable reputation more than anything else on account of the fact that it was melted during firing.

Unlike primitive steel, Wootz was free from insoluble inclusions, such as slag, which would float to the surface -The presence of coarse lumps of impurities in primitive steel could greatly weaken it and hence the need to remove these and disperse uniformly what remained - This was done by the process of extensive hammering and folding. But the presence of these impurities could only be minimized, never eliminated, and as such, primitive Martensitic steel always had a question mark against it. Also, during the process of hammering and folding, often the welds were incomplete due to poor technique or bad luck, introducing additional flaws.

To complete this rambling, I should reiterate that the great disadvantage of primitive Martensitic steel, in contrast to Wootz, was its variability due to the then poor understanding of metallurgy, as well as the presence of slag like impurities.

Of course, Wootz was good steel to start out with, but the forging process could very easily ruin it and the end product was not necessarily any better than that made from primitive steel. I think, that by sheer chance, it was possible to make a sword out of primitive Martensitic steel that was every bit as good as those made from Wootz, for in the end, all that was required was a correctly heat treated blade of about 0.8% carbon (optimal) and largely free from slag inclusions; But given the then extant incomplete knowledge of metallurgy and on the balance of probabilities, the odds lay with Wootz to deliver a superior blade.

Cheers
Chris

21st November 2006, 07:53 AM	#165
Chris Evans Member Join Date: Mar 2005 Location: Australia Posts: 664	Hi Folks, Rivkin very kindly sent me a copy of that paper that was published in Nature. He is indeed a gentleman and a scholar and my sincerest thanks go to him I hurriedly read it and the thing that immediately struck me is is the claim that Wootz had superior qualities, without telling us which exact attributes were being talked about. After all, in the context of swords, there are a number of mechanical properties that are considered desirable, most having to do with hardness and toughness. Hardness, is relatively simple, but toughness has many aspects. The most often mentioned advantage of Wootz is its supposed combination of hardness and ductility resulting from the presence of carbides and nearly pure iron in its microstructure. The simplistic logic appears to be that the hard carbides do the cutting and the soft near pure iron provides the toughness. This paradigm is contrasted by that of conventional quenched & tempered Martensitic steels in which the same homogenous microstructure embodies both attributes. Whilst true to some extent, I have a lot of trouble in accepting the above line of reasoning as a justification for declaring Wootz to be a superior steel. After all, it is well known that steel obtains its optimal hardness and toughness in the quenched and tempered Martensitic state, though I hasten to add, that work hardened Pearlitic steels, such as piano wire, can also be both surprisingly tough and hard. Whether Wotz swords were ever work hardened to to the same extent as modern piano wire, I have yet to find out. A theoretical evaluation, from first principles, of Wootz is very difficult because the very large number of variables to be considered and all this has to be done in the context of various sword, the design of which introduces yet more variables. Based on the papers that I read, most Wootz blades were not Martensic, rather work hardened Pearlitic with additional iron carbide embedded in it, though GT Obach did make the very important observation that partially quenched Martensitic blades, where the edge was expected to do the cutting, as well as fully quenched, were not uncommon. However, here we have to remember that once the carbon content of Martensitic steels exceeds 0.8%, the surplus carbon precipitates out as iron carbide, which can have detrimental effects on toughness, depending on its microstructure and localization. Whilst this effect can be minimized with very careful heat treatment, it is extremely unlikely that the ancients would have had the means or knowledge to achieve this. So where does this leave us in relation to carbon nanotubes and which properties did these influence? I am at a loss. Just looking at the evidence that so far I have managed to lay my hands on, it would appear that in centuries past Wootz acquired its formidable reputation more than anything else on account of the fact that it was melted during firing. Unlike primitive steel, Wootz was free from insoluble inclusions, such as slag, which would float to the surface -The presence of coarse lumps of impurities in primitive steel could greatly weaken it and hence the need to remove these and disperse uniformly what remained - This was done by the process of extensive hammering and folding. But the presence of these impurities could only be minimized, never eliminated, and as such, primitive Martensitic steel always had a question mark against it. Also, during the process of hammering and folding, often the welds were incomplete due to poor technique or bad luck, introducing additional flaws. To complete this rambling, I should reiterate that the great disadvantage of primitive Martensitic steel, in contrast to Wootz, was its variability due to the then poor understanding of metallurgy, as well as the presence of slag like impurities. Of course, Wootz was good steel to start out with, but the forging process could very easily ruin it and the end product was not necessarily any better than that made from primitive steel. I think, that by sheer chance, it was possible to make a sword out of primitive Martensitic steel that was every bit as good as those made from Wootz, for in the end, all that was required was a correctly heat treated blade of about 0.8% carbon (optimal) and largely free from slag inclusions; But given the then extant incomplete knowledge of metallurgy and on the balance of probabilities, the odds lay with Wootz to deliver a superior blade. Cheers Chris Last edited by Chris Evans; 21st November 2006 at 08:33 AM.