Wootz steel

Wootz steel is a crucible steel characterized by a pattern of bands. These bands are formed by sheets of microscopic carbides within a tempered martensite or pearlite matrix in higher carbon steel, or by ferrite and pearlite banding in lower carbon steels. It was a pioneering steel alloy developed in Southern India (Tamilakam present day Tamil Nadu and Kerala) and Sri Lanka in the 6th century BC and exported globally. It was also known in the ancient world by many different names including ukku, Hindvi steel, Hinduwani steel, Teling steel and seric iron.

History

Wootz steel originated in South India, in Tamilakam present day Tamil Nadu and Kerala, and ancient Sri Lanka.  There are several ancient Tamil, Greek, Chinese and Roman literary references to high carbon Tamil steel. The crucible steel production process started in the 6th century BC, at production sites of Kodumanal in Tamil Nadu, Golconda in Telangana, Karnataka and Sri Lanka and exported globally; the Tamils of the Chola Dynasty producing what was termed the finest steel in the world, i.e., Seric Iron to the Romans, Egyptians, Chinese and Arabs by 500 BC. The steel was exported as cakes of steely iron that came to be known as "Wootz". Wootz steel in India had high amounts of carbon in it.

The Tamilakam method was to heat black magnetite ore in the presence of carbon in a sealed clay crucible inside a charcoal furnace to completely remove slag. An alternative was to smelt the ore first to give wrought iron, then heat and hammer it to remove slag. The carbon source was bamboo and leaves from plants such as Avārai. The Chinese and locals in Sri Lanka adopted the production methods of creating wootz steel from the Chera Tamils by the 5th century BC. In Sri Lanka, this early steel-making method employed a unique wind furnace, driven by the monsoon winds. Production sites from antiquity have emerged, in places such as Anuradhapura, Tissamaharama and Samanalawewa, as well as imported artifacts of ancient iron and steel from Kodumanal. A 200 BC Tamil trade guild in Tissamaharama, in the South East of Sri Lanka, brought with them some of the oldest iron and steel artifacts and production processes to the island from the classical period.

The Arabs introduced the South Indian/Sri Lankan wootz steel to Damascus, where an industry developed for making weapons of this steel. The 12th century Arab traveler Edrisi mentioned the "Hinduwani" or Indian steel as the best in the world. Arab accounts also point to the fame of ‘Teling’ steel, which can be taken to refer to the region of Telangana. The Golconda region of Telangana clearly being the nodal centre for the export of wootz steel to West Asia.

Another sign of its reputation is seen in a Persian phraseto give an "Indian answer", meaning "a cut with an Indian sword". Wootz steel was widely exported and traded throughout ancient Europe and the Arab world, and became particularly famous in the Middle East.

Development of modern metallurgy 

From the 17th century onwards, several European travelers observed the steel manufacturing in South India, at Mysore, Malabar and Golconda. The word "wootz" appears to have originated as a mistranscription of wook, The Tamil language root word for the alloy is urukku. Another theory says that the word is a variation of uchcha or ucha ("superior"). According to one theory, the word ukku is based on the meaning "melt, dissolve"; other Dravidian languages have similar-sounding words for steel. ukku, the word for steel in the Kannada and Telugu languages. When Benjamin Heyne inspected the Indian steel in Ceded Districts and other Kannada-speaking areas, he was informed that the steel was ucha kabbina ("superior iron"), also known as ukku tundu in Mysore.

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 was 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.

In 1790, samples of wootz steel were received by Sir Joseph Banks, president of the British Royal Society, sent by Helenus Scott. These samples were subjected to scientific examination and analysis by several experts.

Specimens of daggers and other weapons were sent by the Rajahs of India to the Great Exhibition in London in 1851 and 1862 International Exhibition. 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.

Characteristics
Wootz is characterized by a pattern caused by bands of clustered  particles made by microsegregation of low levels of carbide-forming elements. The presence of cementite nanowires, and carbon nanotubes has been identified by Peter Paufler of TU Dresden in the microstructure of wootz steel. There is a possibility of an abundance of ultrahard metallic carbides in the steel matrix precipitating out in bands. Wootz swords, especially Damascus blades, were renowned for their sharpness and toughness.

Steel manufactured in Kutch particularly enjoyed a widespread reputation, similar to those manufactured at Glasgow and Sheffield.

The techniques for its making died out around 1700. According to Sir Richard Burton, the British prohibited the trade in 1866.

Reproduction research

Russian metallurgist Pavel Petrovich Anosov (see Bulat steel) was almost able to reproduce ancient Wootz steel with nearly all of its properties and the steel he created was very similar to traditional Wootz. He documented four different methods of producing Wootz steel that exhibited traditional patterns. He died before he could fully document and publish his research. Oleg Sherby and Jeff Wadsworth and Lawrence Livermore National Laboratory have all done research, attempting to create steels with characteristics similar to Wootz, but without success. J.D Verhoeven and Alfred Pendray reconstructed methods of production, proved the role of impurities of ore in the pattern creation, and reproduced Wootz steel with patterns microscopically and visually identical to one of the ancient blade patterns. Reibold et al.'s analyses spoke of the presence of carbon nanotubes enclosing nanowires of cementite, with the trace elements/impurities of vanadium, molybdenum, chromium etc. contributing to their creation, in cycles of heating/cooling/forging. This resulted in a hard high carbon steel that remained malleable

There are other smiths who are now consistently producing Wootz steel blades visually identical to the old patterns.

Wootz was made over nearly a 2,000-year period (the oldest sword samples date to around 200 AD) and the methods of production of ingots, the ingredients, and the methods of forging varied from one area to the next. Some Wootz blades displayed a pattern, while some did not. Heat treating was quite different from forging, and there were many different patterns which were created by the various smiths who spanned from China to Scandinavia.

See also 
 Damascus steel
 Iron pillar of Delhi
 Pattern welding
 Ferrous metallurgy

References

Further reading
 
 
 
 urukku - from the Tamil Lexicon, University of Madras

External links
 
 
 
 Wootz Militaria
 
 
 

Category:Steels
Category:History of India
Category:Indian inventions
Category:History of metallurgy
Category:Economic history of Tamil Nadu
Category:Chera kingdom
Category:Tamilakam

nl:Wootz