urukku -- wootz!

[Yaj]

Inder the pattern welding method is very old, it was widely used in the west by the Celts, vikings etc.The Japanese katana too is a type of forge welding, sandwiching different layers of steel.
The custom knives in the west made by the well known bladesmiths are users as well as collectibles.The pattern welded blades being made in India now are mostly from Rajasthan and are mainly for display.
Regards,
Yaj.

[kanwar76]

The pattern welded blades being made in India now are mostly from Rajasthan and are mainly for display.
Regards,
Yaj.

Aaah so it will be a waste of money if I buy one...

[timmy]

kanwar76:

The second link I cited in the post that kicked off this thread has the answer to your question regarding what causes the signature patterns in Wootz steel blades. From that document:

The hypereutectoid carbon level of these steels plays a key role in producing the characteristic surface pattern, because the pattern results from alignment of the Fe3C particles that form in such steels on cooling.

comment: the word "hypereutectoid" may require some explanation: when a material -- in this case, iron -- is alloyed with some other element -- in this case, carbon -- the melting point of the resulting alloy can be less than the melting point of either iron or carbon, in which case, the alloy is said to be "eutectoid." However, if the alloying element -- in this case, carbon -- is added past a certain concentration (in this case, when the carbon content of the alloy exceeds more than ~ 0.8%), the alloy is said to be "hypereutectoid," or, "over eutectoid."

Verhoeven continues:

The internal microstructure of a wootz Damascus blade possessing a high-quality damascene surface pattern is a unique metallurgical microstructure.8 It consists of bands of small (generally around 6 mm diameter) particles of Fe3C (cementite) clustered along the band centerline. The bands have a characteristic spacing in the 30-70 mm range and are contained in a steel matrix. The structure of the steel matrix varies depending on how the smith heat-treated the blade, but it is generally found to be pearlite. The bands lie parallel to the forging plane of the blades. By manipulating the angle of the blade surface relative to the plane of the bands, the smith can produce a variety of convoluted patterns of intersection of the bands with the blade surface. With polishing and etching, the Fe3C particles cause the bands to appear white and the steel matrix nearly black; thus, the surface pattern is created.

(I believe that the article's quote makes an error: rather than the measurements being in mm, they should be in nm, or nanometers.)

Thus, it is cementite that produces the bands. Cementite is actually iron carbide, a ceramic -- meaning that the bands you see on the true Wootz steel represent ceramic bands in the structure of the steel blade. The visible bands you see on imitations are something else. It is this carbide that makes the blade retain an edge and, to a certain extent, be self-sharpening.

This illustration is a chemistry diagram, but it conveys how the heat treatment alters the appearance by changing how cementite forms in the steel:



However, Verhoeven's explanation supplied more of the story:

The discovery that vanadium is extremely effective in producing Fe3C banding in high-carbon steels17 was aided by the accidental use of Sorel metal as a raw material for making the small ingots. Sorel metal is a high-purity Fe-C alloy, containing 3.9-4.7% C, marketed by Rio Tinto Iron and Titanium America, Chicago. The alloy is produced from a large ilmenite ore deposit at Lac Tio on the north shore of the St. Lawrence River. Analyses of several batches of the Sorel metal has found that it consistently contains a few hundred ppmw of vanadium impurity. Apparently, the impurity is contained in the ilmenite ore. This suggests the possibility that the low levels of vanadium found in the genuine wootz blades of Table III may have resulted from ore deposits in India where the wootz steels were produced.
One of the big mysteries of wootz Damascus steel has been why the art of making these blades was lost. The vanadium levels provide the basis for a theory. Based on our studies, it is clear that to produce the damascene patterns of a museum-quality wootz Damascus blade the smith would have to fulfill at least three requirements. First, the wootz ingot would have to have come from an ore deposit that provided significant levels of certain trace elements, notably, Cr, Mo, Nb, Mn, or V. This idea is consistent with the theory of some authors30 who believe the blades with good patterns were only produced from wootz ingots made in southern India, apparently around Hyderabad. Second, the data of Table IV confirm previous knowledge that wootz Damascus blades with good patterns are characterized by a high phosphorus level.

So here, Verhoeven's research shows that additional trace elements, or impurities in the ore that remained in the steel, were also necessary to obtained the unique appearance noted in a Wootz blade.

However, this only explains the appearance, but not the performance of the Wootz blade. More of the story was related in the 2006 Nature article, which, in turn, reported on the paper I cited in the 4th link in that initial post.

In that paper, Reibold et al recapped the existing knowledge:

Applying optical microscopy to polished blades, Belaiew identified the beautiful watering as
‘milky ways’ of cementite (Fe3C) and concluded that small, round-shaped cementite is embedded in the
ground-mass of damascene steel thus avoiding the typical brittleness of hypereutectoid steels with their needle-form cementite [9]. The spheroidisation seemed to be the consequence of repeated hammering and heating. The cementite veins run closer up to the edge of the blade thus providing good cutting properties. Belaiew supposed that the properties and the distribution of the carbides play a more considerable role than the (martensitic) matrix.

...It is generally agreed that the beautiful patterns arise from the aggregation of carbide particles.

Newer work then is discussed, which formed the background for Reibold's research:

A new view upon the microstructure and the properties of Damascus steel has been opened by the finding of Kochmann et al. [25]. Using high-resolution transmission electron microscopy (HRTEM), they detected a high density of cementite nanowires (diameter 10-20 nm, lengths several hundred nm) in a genuine Damascus sabre. These components of the microstructure at nanometer scale have certainly been overlooked so far because of the resolution needed. Kochmann et al. [25] reported on preliminary results concerning structural data.

Toward the end of the paper, the arrangements and distribution of carbon nanowires are depicted and discussed.

Wikipedia notes, in the "Nanowire" entry, that:

Due to their high Young's moduli, their use in mechanically enhancing composites is being investigated.

This puts the product of those ancient fellows, smelting iron on hillsides in South India and Sri Lanka, right in the middle of cutting edge research and technology. There's really nothing like something new, is there?

[vikram69]

hi have you guys heard about a sword called katana i will be a proud owner in a couple of months

[xl_target]

Yaj covered the Katana in a previous post. Look at the first post on page 2 of this thread.

Metallurgy in India apparently was very advanced at one time. in addition of the items brought up by Timmy's post, there was also the Iron pillar near the Qutb Minar.
Quote from Wikipedia:

Made up of 98% pure wrought iron, it is 7.21m (23 feet 8 inches) high, with 93 cm (36.6 inches) buried below the present floor level,[10] and has a diameter of 41 cm (16 inches) at the bottom which tapers towards the upper end. The pillar was manufactured by forge welding. The temperatures required to form such a pillar by forge welding could only have been achieved by the combustion of coal. The pillar is a testament to the high level of skill achieved by ancient Indian iron smiths in the extraction and processing of iron.

Resistance to corrosion:

It has attracted the attention of both archaeologists and metallurgists, as it has withstood corrosion for over 1600 years in the open air.

http://en.wikipedia.org/wiki/Iron_pillar_of_Delhi

[timmy]

I have been digging through my stuff, trying to clean up my home office (a hopeless task!). I came across this paper from Nature: Carbon nanotubes in an ancient Damascus sabre while going through a stack of papers. This was the thing that got me interested in this business of wootz.

Here is a link to Nature: http://www.nature.com/nature/journal/v4 ... 4286a.html but as you can see, it won't do you much good, since you have to pay to get the article. Since I have access to academic journal databases, I was able to retrieve an electronic copy. The summary says this:

Thermal cycling and cyclic forging cause catalytic elements to segregate gradually into planar arrays parallel to the forging plane. These elements may give rise to the growth of carbon nanotubes, which in turn initiate formation of cementite nanowires and coarse cementite particles. As the nanoscale structure of Damascus steel emerges, a refined interpretation of its remarkable mechanical properties should become possible.

It's actually quite interesting to think of those ancients, forging wootz in furnaces fanned by the monsoon winds, being the pioneers of carbon nanotube technology! So, what's new under the sun today?