Damascus steel
|
|
Damascus steel, also known as Damascened steel, is a type of steel alloy that is both strong and malleable, a material that is perfect for the building of swords. The term refers to the metal used by the artisans and swordsmiths of Damascus, Syria. The process for making Damascus steel was used between about 900 and 1600 in the Middle East, and then disappeared for reasons that are not entirely understood. It is said that when it was 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 alloy via possible reconstructions of the (still unknown) historical process.
| Contents |
Development of Damascus steel
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 strong 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 strong and malleable—strong 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 as early as 300 BC (although more likely 200) 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 technique propagated very slowly though the world, reaching modern-day Turkmenistan and Uzbekistan around 900, and then the Middle East around 1000.
This process was further refined, 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 steel, allowing the swordsmith to make an edge centered on one of the carbide bands and thus very strong, while the sword as a whole remained flexible as in normal steels. The banded carbide precipitates appear in the blade as a beautiful swirling patterning, apparently the origin of the term damask.
Loss of the technique
For reasons that are not entirely clear, the process was then lost to the Middle-Eastern metalsmiths around 1600 AD, and has been eagerly sought by many since that time. The Russian bulat steel has many similar properties, at least in nature if not in process. Recently various groups have claimed to have recreated the process, though even they admit they cannot be certain how it was originally created. Verhoeven et. al (1998) believe that the key is controlled thermal cycling (10-20 heating/cooling repetitions between room temperature and about 100C below the austenitizing temperature) after the initial forging; a somewhat different technique was proposed by Wadsworth and Sherby (1980; also 2001).
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 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, the patterns being 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.
It has also long been argued that the raw material for Damascus steel swords was imported from India, because India was the only known center of crucible-fired steels like wootz. However this too proved wrong when the furnaces in Turkmenistan were discovered, demonstrating at least that the technique was moving out from India. There appears to be no reason to suspect that similar metal factories were not built in Damascus, although if this were the case their later disappearance requires explanation. However, if Alfred Pendray's work is correct, several key impurities that appear to give damascus steel its properties point to particular ores available in India.
Another common myth is that Crusaders introduced the term to Europe after meeting it in combat. However several historical studies have demonstrated that the term did not appear in English until the 16th century.
Even the name itself remains somewhat controversial. Although it would seem obvious that it refers to swords built in Damascus, there are several equally likely sources. One is the Arabic word damas for water, referring to the surface pattern that looks like turbulent water. 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.
So, even after 1000 years, Damascus steel remains something of a mystery.
Types of Damascus
The original Damascus was a steel type now called wootz. Until the techniques were rediscovered in the 1980s by Alfred Pendray, it was widely believed that nobody knew exactly how this was made, though a very similar material was made by the Stanford team of Oleg Sherby and Jeff Wadsworth. Pendray's recreation of the traditional process involves putting iron and several other ingredients in a clay crucible and heating them until they meld together. Other recent metallurgical work, both in Russia and the United States, may have created new pathways to this marvelous material.
Pattern welded steel is commonly known today as Damascus, although this is historically incorrect. 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. Japanese katana were made with this method. Also kris or keris swords of Indonesia were made of pattern weld.
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 ancient shotgun barrels (usually on double barreled guns) were formed from forged wires. This leaves a visible wire pattern in the barrel and such are referred to as "Damascus Barrels".
See also
References
- Eric M. Taleff, Bruce L. Bramfitt, Chol K. Syn, Donald R. Lesuer, Jeffrey Wadsworth, and Oleg D. Sherby, "Processing, structure, and properties of a rolled ultrahigh-carbon steel plate exhibiting a damask pattern," Materials Characterization 46 (1), 11-18 (2001).
- J. D. Verhoeven, "A review of microsegregation induced banding phenomena in steels", J. Materials Engineering and Performance 9 (3), 286-296 (2000).
- J. D. Verhoeven, A. H. Pendray, and W. E. Dauksch, "The Key Role of Impurities in Ancient Damascus Steel Blades (http://www.tms.org/pubs/journals/JOM/9809/Verhoeven-9809.html)", JOM 50 (9), 58-64 (1998).
- J. Wadsworth and O. D. Sherby, "On the Bulat — Damascus steel revisited," Prog. Materials Science 68, 25-35 (1980).