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Old 8th January 2009, 01:41 AM   #27
Chris Evans
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Join Date: Mar 2005
Location: Australia
Posts: 565
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Hi Kisak,

Quote:
Originally Posted by kisak
A thought about the heat treating of these hypereutectoid steels. As changing the carbon content in such would only change the amount of carbides, not the composition of the carbides and matrix (well, in theory at least), could it be that the smiths who were good enough with keeping the austenitisation temperature just so where then presented with a steel which might have been more predictable in how it reacted to the heat treatment?

Such could, I guess, result in a slightly higher overall quality amongst the blades which weren't more or less obviously botched.


From a modern perspective and without having done any hands on experimentation myself, it seems to me that Wootz is a variation on the theme of carbided tool steels, many of which have been adapted to cutlery usage. Their heat treatment is not difficult, but this is with modern technology, especially temperature control (pyrometry), all backed with knowledge. The general idea is to heat the steel just sufficiently to austenitize the pearlite and leave the primary carbides undissolved, so that upon quenching a sound microstructure results. With these tool steels the role of the carbides is to provide abrasion resistance. If you would like to read up on this here is a very good work: http://www.feine-klingen.de/PDFs/verhoeven.pdf

Whether any of the ancient smiths knew about this I cannot say, but do find it plausible that every once in a while someone would have got the temperature just right by chance with a very gratifying end result.

Again from a modern perspective, we would not make a sword blade from high carbon (hypereutectoid) steel because of lack of toughness, even if given optimal heat treatment. For one the martensite that forms at the higher carbon contents is very brittle and the cementite (iron carbide) does nothing, save to provide unnecessary abrasion resistance, and undermines toughness further. However in knives the added abrasion resistance is welcome and toughness is much less of a requirement.

Something to keep in mind is that piano wire, which is work hardened (hard drawn) unquenched pearlitic (eutectoid) steel is very tough, surprisingly hard and is used in springs. I mention this because of the possibility of cold work hardened but unquenched Wootz edges being up to the task of cutting very well and at the same time retaining a high level of toughness and springiness.

But there was more to ancient swordmaking than the above simplistic considerations would suggest. Those smiths could come up with composite layering and heat treatments and thereby overcome the inherent limitations of the steels that they worked with. How good were these swords? We don't know as there is not enough published data. Some time ago there was this thread http://www.vikingsword.com/vb/showthread.php?t=3377 and the question posed in the first post remained unanswered.

Cheers
Chris
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