Damascus steel
2007 Schools Wikipedia Selection. Related subjects: Engineering
Damascus steel, also known as Damascened steel and sometimes watered steel, now commonly refers to two types of steel used in custom knife and sword making, pattern-weld (giving the appearance of original damascus steel) and wootz (true damascus, a steel of legendary sharpness and strength whose method of forging has been lost to time). Both types of Damascened steel show complex patterns on the surface, which are the result of internal structural elements in the steel. These patterns are the result of the unique forging methods used for the creation of Damascened steel; skilled swordsmiths can manipulate the patterns to mimic the complex designs found in the surface of the original, ancient damascus steel. Recent research into the structure and composition of true damascus steel by a Dresden scientist has revealed that the almost mythical sharpness and strength of the steel was a result of carbon nanotubes and carbide nanowires present in the structure of the forged metal--the secret of which forging method was lost around 1800 A.D.
Origin of the term "Damascus"
The origins of the name "Damascus" remains somewhat controversial. Although it would seem obvious that it refers to swords forged in Damascus, there are several equally likely sources of the name. One is the Arabic word damas for water, referring to the surface pattern of moiré ripples which looks like turbulent water and is also seen in some damask weaves of fabric. Another potential source is the swordsmith himself: the author al-Beruni refers to swords made by a man he names Damasqui. Finally another author, al-Kindi, refers to swords made in Damascus as Damascene. This word has often been employed as an epithet in various Eastern European legends (Sabya Damaskinya or Sablja Dimiskija meaning "Damascene sword"), of which perhaps the best known are the Bulgarian and Serbian legends of Prince Marko, a historical figure of the late 14th century in what is now the Republic of Macedonia.
Manufacture
The original Damascus steel swords may have been made in the vicinity of Damascus, Syria, in the period from 900 AD to as late as 1750 AD. Damascus steel is a type of steel alloy that is both hard and flexible, a combination that made it ideal for the building of swords. It is said that when Damascus-made swords were first encountered by Europeans during the Crusades it garnered an almost mythical reputation—a Damascus steel blade was said to be able to cut a piece of silk in half as it fell to the ground, as well as being able to chop through normal blades, or even rock, without losing its sharp edge. Recent metallurgical experiments, based on microscopic studies of preserved Damascus-steel blades, have claimed to reproduce a very similar steel via possible reconstructions of the historical process.
When forming a batch of steel, impurities are added to control the properties of the resulting alloy. In general, notably during the era of Damascus steel, one could produce an alloy that was hard and brittle at one extreme by adding up to 2% carbon, or soft and malleable at the other, with about 0.5% carbon. The problem for a swordsmith is that the best steel should be both hard and malleable—hard to hold an edge once sharpened, but malleable so it would not break when hitting other metal in combat. This was not possible with normal processes.
Metalsmiths in India and Sri Lanka perhaps as early as 300 BC developed a new technique known as wootz steel that produced a high-carbon steel of unusually high purity. Glass was added to a mixture of iron and charcoal and then heated. The glass would act as a flux and bind to other impurities in the mixture, allowing them to rise to the surface and leave a more pure steel when the mixture cooled. Thousands of steel making sites were found in Samanalawewa area in Sri Lanka that made high carbon steel (Juleff, 1996). These steel making furnaces were built facing western monsoon winds and wind turbulance and suction was used to create heat in the furnace. Steel making sites in Sri Lanka have been dated to 300 BC using carbon dating technology. The technique propagated very slowly through the world, reaching modern-day Turkmenistan and Uzbekistan around 900 AD, and then the Middle East around 1000 AD.
This process was further refined in the middle east, either using locally produced steels, or by re-working wootz purchased from India. The exact process remains unknown, but allowed carbides to precipitate out as micro particles arranged in sheets or bands within the body of a blade. The carbides are far harder than the surrounding low carbon steel, allowing the swordsmith to make an edge which would cut hard materials with the precipitated carbides, while the bands of softer steel allowed the sword as a whole to remain tough and flexible.
The banded carbide precipitates appear in the blade as a swirling pattern. By manipulating the ingot of steel in a certain way during forging, various intentional patterns could be induced in the steel. The most common of these was a pattern of lateral bands, often called Mohammed's Ladder, most likely formed by cutting or forging notches into the surface of the ingot, then forging it into the blade shape (this is the method Pendray (below) used to reproduce the pattern). The notches resulted in different degrees of work hardening between top and bottom, and thus controlled the size of the carbide particles in the surface at those areas, and thus the appearance of the bands.
A 2006 study published in Nature determined that some carbon nanotubes are present in Damascus blades, possibly helping to account for their strength.
Loss of the technique
For reasons that are not entirely clear, but possibly because sources of ores containing trace amounts of tungsten and/or vanadium needed for its production were depleted, the process was lost to the middle-eastern metalsmiths around 1750. It has been eagerly sought by many since that time.
It has long been argued that the raw material for Damascus steel swords was imported from India, because India was the only known centre of crucible-fired steels like wootz. However this conclusion became suspect when the furnaces in Turkmenistan were discovered, demonstrating at least that the technique was moving out from India. The wootz may have been manufactured locally in the Damascus area, but so far no remains of the distinctive wootz furnaces have appeared. Verhoeven et al.'s work supports the hypothesis that the wootz used was from India, as several key impurities that appear to give Damascus steel its properties point to particular ores available only in India.
The Russian bulat steel has many similar properties, at least in nature if not in process. Recently various groups have claimed to have recreated steel with properties consistent with true Damascus blades, through experimental archaeology, though even they admit they cannot be certain how it was originally created. Verhoeven et al. (1998) argued that the keys are ores with certain trace elements, controlled thermal cycling after the initial forging, and a grinding process to reveal the final damask pattern. A somewhat different technique was proposed by Wadsworth and Sherby (1980; also 2001).
Attempts at reproduction
From the very start, the superior capabilities of Damascus swords attracted significant attention, and many attempts were made to reproduce either the performance or the appearance of the Damascus blades. Since pattern welding was a widespread technique, and produced surface patterns similar to those found on Damascus blades, many people believed that Damascus blades were made using a pattern welding technique. This belief was challenged in the 1990s when J. D. Verhoeven and A. H. Pendray published an article on their experiments on reproducing the elemental, structural, and visual characteristics of Damascus steel.
Verhoeven and Pendray started with a cake of steel that matched the properties of the original wootz steel from India, which also matched a number of original Damascus swords they had access to. The wootz was in a soft, annealed state, with a large grain structure, and many beads of pure iron carbide which were the result of the hypereutectoid state of the wootz. They had already determined that the grains on the surface of the steel were grains of iron carbide, so their question was how to reproduce the fine iron carbide patterns they saw in the Damascus blades from the large grains in the wootz.
By heating the cake of wootz to just below the critical temperature which would cause the iron carbide to return to solution, it was possible to forge the wootz with hand tools. Repeated forging, working the wootz into a long, thin shape suitable for a knife or sword blade, caused the large iron carbide crystals to fracture and spread out in the pearlite matrix. The resulting steel contains bands of iron carbide in a pearlite matrix, alternating with bands of ferrite and cementite. In this process the steel work hardens, which is what allows the normally soft wootz to be used for knives and swords.
Studies published in 2006 by Peter Paufler of the Technical University of Dresden, Germany, and colleagues, utilizing an electron microscope to study samples of a 17th-century sword, have discovered clear evidence of carbon nanotubes and nanowires, and associated cementite wires. They believe that the nanotubes and the nanowires were formed by the special process of forging and annealing the steel, and could explain the unique mechanical properties of the swords.
Pattern welded "Damascened" steel
For some time, it was believed that Damascus steel was made in a similar fashion to what is known as pattern welding, a sword making technique that was widely used in Europe and Japan. Pattern welding was very common in the ancient world; Viking swords, Japanese katana and Indonesian kris or keris swords were all made using pattern welding techniques.
Pattern welding is a mechanical process that lays up strips of material which are then pounded together, or folded, as in Japanese practice. If the blade is then etched in acid the layering below the surface is revealed, these patterns are similar to that of Damascus steel. For some time this similarity was used to dismiss Damascus as yet another pattern-welded steel, but modern metallurgy demonstrated this to be wrong.
Pattern welded steel is commonly sold today as "Damascus steel", though it appears that the original Damascus steel was not created with that technique. Pattern weld Damascus is made out of several types of steel and iron slices, which are then welded together to form a billet. The patterns vary depending on what the smith does to the billet. The billet is drawn out and folded until the desired number of layers are formed. The end result, if done well, bears a strong resemblance to the surface appearance of a true Damascus blade, though the internal structure is completely dissimilar.
Another material similar to pattern weld is mokume-gane. Mokume is made of the softer metals, like gold, silver, and copper. It is made in much the same way as pattern weld Damascus, and is used for rings, tsubas (the guard on a katana), and knife bolsters. The name mokume-gane means "wood eye", referring to the pattern of the metals, which looks like wood grain. It was first made by the Japanese.
Some old shotgun barrels (usually on double barreled guns) were formed from wires that were wrapped around a mandrel and forged and welded into shape. This leaves a visible wire pattern in the barrel and such are referred to as "Damascus Barrels". Guns made with damascus barrels are significantly weaker than fluid steel barrels, and more prone to corrosion and failure due to the welds along the length of the barrels. Damascus barrel shotguns should be examined by a qualified gunsmith and proof tested before use, to ensure that the barrels are sound before using the shotgun.