Wootz steel is a steel characterized by a pattern of bands or sheets of micro carbides within a tempered martensite or pearlite matrix. It was developed in India around 300 BCE.[1] The word wootz[2] may have been a mistranscription of wook, an anglicised version of urukke the word for steel in Tamil and Malayalam or ukku, the word for steel in Kannada, Telugu and many other southern Indian languages.[3][4]
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According to traditional history wootz steel originated in India before the beginning of the common era.[5] There is archaeological evidence of the manufacturing process in South India from that time.[6][7] Wootz steel was widely exported and traded throughout ancient Europe and the Arab world, and became particularly famous in the Middle East, where it was known as Damascus steel and was later traced to workshops in western India.[8]
In ancient times, thirty pounds of steel was a precious gift, deemed by King Porus worthy of presentation to Alexander the Great. Another sign that Ancient India was celebrated for its steel is seen in a Persian phrase - to give an "Indian answer," meaning "a cut with an Indian sword."[8]
Legends of wootz steel and Damascus swords aroused the curiosity of the European scientific community from the 17th to the 19th Century. The use of high carbon alloys were not known in Europe previously and thus the research into wootz steel played an important role in the development of modern English, French and Russian metallurgy.[9]
The presence of British in India in the 1750s gave a fresh impetus for western research. By 1790, samples of wootz steel were received by Sir Joseph Banks, President of the British Royal society. These samples were subjected to scientific examination and analysis by several experts.[10][11]
Specimens of daggers, and other warlike weapons were sent by the Rajahs of India to the International Exhibition of 1851 and 1862. Though the arms of the swords were beautifully decorated and jeweled, they were most highly prized for the quality of their steel. The swords of the Sikhs were said to bear bending and crumpling, and yet be fine and sharp.[8]
A critical characteristic of wootz steel is the abundance of ultrahard metallic carbides in the steel matrix precipitating out in bands, making wootz steel display a characteristic banding on its surface. Wootz swords, especially Damascus blades, were renowned for their sharpness and toughness.
While other methods may be used today, it is known that wootz was classically made in crucibles, e.g., crucible steel by combining a mixture of wrought iron or iron ore and charcoal with glass, which is then sealed and heated in a furnace. The result is a mixture of impurities mixed with glass as slags, and "buttons" of steel. The buttons (with a typical carbon content of 1.5%) were separated from the slag and forged into ingots. The ingots could be further forged out into blades/tools or welded to other ingots to increase the mass of the steel for larger items.
The ore was beaten with a stone hammer into a bar, then cut into small pieces and placed in crucibles, with green berries and dry wood. Much importance was given to the kind of wood used, as it influenced the kind of steel produced. Steel manufactured in Kutch particularly enjoyed a widespread reputation, similar to those manufactured at Glasgow and Sheffield.[8]
The techniques for its making died out around 1700 after the principal sources of special ores needed for its production were depleted. Those sources contained trace amounts of tungsten and/or vanadium which other sources did not. Oral tradition in India maintains that a small piece of either white or black hematite (or old wootz) had to be included in each melt, and that a minimum of these elements must be present in the steel for the proper segregation of the micro carbides to take place.
Wootz was possibly rediscovered in the mid 19th century by the Russian metallurgist Pavel Petrovich Anosov (see Bulat steel), who refused to reveal the secret of its manufacture other than to write five one-sentence descriptions of different ways in which it could be made.
Master bladesmith Alfred Pendray re-discovered what may be the classic techniques in the early 1980s, as later verified by Dr. John Verhoeven.[12][13]
Another method of wootz production, using modern technology, was developed around 1980 by Dr. Oleg Sherby and Dr. Jeff Wadsworth at Stanford University and Lawrence Livermore National Laboratory. Even though this steel had the characteristic bands of microcarbides, whether or not this could be considered wootz was disputed by Verhoeven since it was not made in a classical manner.
Recently, researcher Peter Paufler from Dresden University of Technology in Germany has discovered evidence of carbon nanotubes in wootz steel,[14] although this is disputed.[15]