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Damascus steel

2007 Schools Wikipedia Selection. Related subjects: Engineering

   Characteristic pattern on damascus steel
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   Characteristic pattern on damascus steel

   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

   Pattern welded "Damascus steel" pocket knife
   Enlarge
   Pattern welded "Damascus steel" pocket knife

   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.

   Retrieved from " http://en.wikipedia.org/wiki/Damascus_steel"
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   with only minor checks and changes (see www.wikipedia.org for details
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