Damascus steel () is the high-carbon crucible steel of the blades of historical swords forged using the wootz process in the Near East, characterized by distinctive patterns of banding and mottling reminiscent of flowing water, sometimes in a "ladder" or "rose" pattern. Damascus steel was reputed to be tough, resistant to shattering, and capable of being honed to a sharp, resilient edge. This is not to be confused with damascene, which is a form of metal inlaying.
Originally, it came from India and Sri Lanka, where the steel-making techniques used were first developed. Arabic adopted the word for steel from pre-New Persian pōlād.
The term "Damascus steel" is rooted in the medieval city of Damascus, perhaps as an early example of branding. However, there is now a general agreement that many of the swords, or at least the steel ingots from which they were forged, were imported from elsewhere.
Naming The origin of the name "Damascus steel" is contentious. Islamic scholars al-Kindi (circa 800 CE – 873 CE) and al-Biruni (circa 973 CE – 1048 CE) both wrote about swords and steel made for swords, based on their surface appearance, geographical location of production or forging, or the name of the smith. Each mentions "damascene" or "damascus" swords to some extent.
Drawing from al-Kindi and al-Biruni, there are three potential sources for the term "Damascus" in the context of steel:
The word "damas" is the root word for "watered" in Arabic with "water" being "ma" in Arabic and Damascus blades are often described as exhibiting a water-pattern on their surface, and are often referred to as "watered steel" in multiple languages. Al-Kindi called swords produced and forged in Damascus as Damascene, but these swords were not described as having a pattern in the steel. Al-Biruni mentions a sword-smith called Damasqui who made swords of crucible steel.
The most common explanation is that steel is named after Damascus, the capital city of Syria and one of the largest cities in the ancient Levant. In Damascus, where many of these swords were sold, there is no evidence of local production of crucible steel, though there is evidence of imported steel being forged into swords in Damascus. The name could have been an early form of branding.
"Damascus steel" may either refer to swords made or sold in Damascus directly, or simply those with the distinctive surface patterns on the swords, in the same way that Damask fabrics (also named for Damascus), got their name.
History
Damascus blades were first manufactured in the Near East from ingots of wootz steel that were imported from Southern India (present-day Telangana, Tamil Nadu, Karnataka and Kerala). Al-Kindi states that crucible steel was also made in Khorasan known as Muharrar, in addition to steel that was imported. There was also domestic production of crucible steel outside of India, including Merv (Turkmenistan) and Yazd, Iran.
In addition to being made into blades in India (particularly Golconda) and Sri Lanka, wootz / ukku was exported as ingots to various production centers, including Khorasan, and Isfahan, where the steel was used to produce blades, as well as across the Middle East.
The Arabs introduced the wootz steel to Damascus, where a weapons industry thrived. From the 3rd century to the 17th century, steel ingots were being shipped to the Middle East from South India.
Legends The reputation and history of Damascus steel have given rise to many legends, such as the ability to cut through a bar of iron without harming the edge, and of swords made of the related wootz steel; it was said that they could cut a wisp of silk floss falling across the blade.
The blade that Beowulf used to kill Grendel's mother in the story Beowulf was described in some Modern English translations as "damascened". Although this could also refer to a form of metal decoration known as damascene.
It was previously incorrectly believed that the steel was hardened by thrusting it six times into the back and thighs of an enslaved person. The misconception originated in an article in the November 4, 1894 issue of the Chicago Tribune titled Tempering Damascus Blades. The note asserts that a certain "Prof. von Eulenspiegel" found a scroll "among the ruins of ancient Tyre"; "Eulenspiegel" is the name of a legendary prankster of medieval Germany.
Material and mechanical properties
O. M. Becker, writing on steel used for tool-making, claimed in 1910 that ancient Damascus alloys remained unequaled even in his own time in terms of tempering quality.Becker (1910) p. 5. He mentions, however, that modern electric steel is said to outperform crucible steel, a category which includes Damascus steel.Becker (1910), p. 12. The production process of Damascus steel and the traces of elements such as tungsten, nickel and manganese found in it, which are also used in modern high-speed varieties, made the blades very flexible and very hard at the same time, extraordinary qualities considering their age.Becker (1910), pp. 3-5. In fact, extant examples of patterned crucible steel swords were often tempered in such a way as to retain a bend after being flexed past their elastic limit.
Verhoeven, Peterson, and Baker completed mechanical characterization of a Damascus sword, performing tensile testing as well as hardness testing. They found that the Damascus steel was somewhat comparable to hot-rolled steel bars with 1.0 wt% carbon with regards to mechanical properties. The average yield strength of 740 MPa was higher than the hot-rolled steel yield strength of 550 MPa, and the average tensile strength of 1070 MPa was higher than the hot-rolled steel tensile strength of 965 MPa.
These results are likely due to the finer pearlite spacing in the Damascus steel, refining the microstructure. The elongation and reduction in area were also slightly higher than the averages for hot-rolled steel. Rockwell hardness measurements of the Damascus steel ranged from 62 to 67. These mechanical properties were consistent with those expected for the material's constituent steels, falling between the upper and lower bounds set by the original steels.
Folding Another study investigated the properties of Damascus steel produced from 1075 steel and 15N20 steel, which have approximately equal carbon content, but 15N20 steel notably contains 2 wt% nickel. The 1075 steel is known for high strength, but low toughness, with a pearlitic microstructure, and the 15N20 steel is known for high toughness with a ferritic microstructure. The mechanical properties of the resultant Damascus steel laminate were characterized in samples with 54 folds in production, as well as samples with 250 folds.
Charpy V-notch impact tests showed that the 54-fold samples had an impact toughness of 4.36 J/cm2, while the 250-fold samples had an impact toughness of 5.49 J/cm2. Tensile testing showed that the yield strengths and elongations of both samples were similar, at approximately 475 MPa and 3.2%, respectively. However, the maximum strength of the 54-fold samples was notably lower than that of the 250-fold samples (750 MPa vs. 860 MPa). This study showed that the folding process significantly affects the mechanical properties of the steel, with toughness increasing as the number of folds increases. This effect is likely due to the thinning and refinement of the microstructure, and to achieve optimal properties, the steel should be folded a few hundred times.
Further studies of Damascus steel made from other steels showed similar results, confirming that increasing the number of folds increases impact strength and toughness, and that this effect extends to higher temperatures. They also compare the mechanical properties of the Damascus to the original materials, finding that the properties of the Damascus steel lie between those of the two constituent steels, which is consistent with composite material properties.
Lamination and banding The processing and design of the laminations and bands can also significantly affect mechanical properties. Regardless of tempering temperature and the liquid in which the steel is quenched, the impact strength of Damascus steel, when the impact is perpendicular to the band orientation, is significantly higher than when the impact is parallel to the band orientation.
This is due to the failure and fracture mechanisms in Damascus steel, where cracks propagate fastest along the interfaces between the two constituent steels. When impact is directed parallel to the bands, cracks can propagate easily along the lamination interfaces. When impact is directed perpendicular to the bands, the lamination interfaces are effectively protected, deflecting the cracks and increasing the energy required for cracks to propagate through the material. Band orientation should be chosen to protect against deformation and increase toughness.
Metallurgical process Identification of crucible "Damascus" steel based on metallurgical structures is difficult, as crucible steel cannot be reliably distinguished from other types of steel by just one criterion, so the following distinguishing characteristics of crucible steel must be taken into consideration:
The crucible steel was liquid, leading to a relatively homogeneous steel content with virtually no slag The formation of dendrites is a typical characteristic The segregation of elements into dendritic and interdendritic regions throughout the sample
By these definitions, modern recreations of crucible steel are consistent with historic examples.
Addition of carbon
During the smelting process to obtain wootz steel ingots, woody biomass and leaves are known to have been used as carburizing additives along with certain specific types of iron rich in microalloying elements. These ingots would then be further forged and worked into Damascus steel blades. Research now shows that carbon nanotubes can be derived from plant fibers, suggesting how the nanotubes were formed in the steel. Some experts expect to discover such nanotubes in more relics as they are analyzed more closely.
Wootz was also mentioned to have been made out of a co-fusion process using "shaburqan" (hard steel, likely white cast iron) and "narmahan" (soft steel) by Biruni, both of which were forms of either high- and low-carbon bloomery iron, or low-carbon bloom with cast iron. In such a crucible recipe, no added plant material is necessary to provide the required carbon content, and as such any nanowires of cementite or carbon nanotubes would not have been the result of plant fibers.
Modern research A research team in Germany published a report in 2006 revealing nanowires and carbon nanotubes in a blade forged from Damascus steel, although John Verhoeven of Iowa State University in Ames suggests that the research team that reported nanowires in crucible steel was seeing cementite, which can itself exist as rods, so there might not be any carbon nanotubes in the rod-like structure.
Loss of the technique Production of these patterned swords gradually declined, ceasing by around 1900, with the last account being from 1903 in Sri Lanka documented by Coomaraswamy. Some gunsmiths during the 18th and 19th century used the term "damascus steel" to describe their pattern-welded gun barrels, but they did not use crucible steel. Several modern theories have ventured to explain this decline:
Due to the distance of trade for this steel, a sufficiently lengthy disruption of the trade routes could have ended the production of Damascus steel and eventually led to the loss of the technique. Key trace impurities of carbide formers such as tungsten, vanadium, or manganese within the materials needed for the production of the steel may be absent if this material was acquired from different production regions or smelted from ores lacking these key trace elements.